Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
AMUSE-Virgo. II. Down-sizing in Black Hole Accretion
We complete the census of nuclear X-ray activity in 100 early-type Virgogalaxies observed by the Chandra X-ray Telescope as part of theAMUSE-Virgo survey, down to a (3?) limiting luminosity of 3.7× 1038 erg s-1 over 0.5-7 keV. Thestellar mass distribution of the targeted sample, which is mostlycomposed of formally "inactive" galaxies, peaks below 1010 Msun, a regime where the very existence of nuclearsupermassive black holes (SMBHs) is debated. Out of 100 objects, 32 showa nuclear X-ray source, including 6 hybrid nuclei which also host amassive nuclear cluster as visible from archival Hubble Space Telescopeimages. After carefully accounting for contamination from nuclearlow-mass X-ray binaries based on the shape and normalization of theirX-ray luminosity function (XLF), we conclude that between 24% and 34% ofthe galaxies in our sample host an X-ray active SMBH (at the 95%confidence level). This sets a firm lower limit to the black hole (BH)occupation fraction in nearby bulges within a cluster environment. Thedifferential logarithmic XLF of active SMBHs scales with the X-rayluminosity as L X -0.4±0.1 up to1042 erg s-1. At face value, the activefraction—down to our luminosity limit—is found to increasewith host stellar mass. However, taking into account selection effects,we find that the average Eddington-scaled X-ray luminosity scales withBH mass as M BH ^{-0.62^{+0.13}_{-0.12}}, with an intrinsicscatter of 0.46+0.08 -0.06 dex. This findingcan be interpreted as observational evidence for "down-sizing" of BHaccretion in local early types, that is, low-mass BHs shine relativelycloser to their Eddington limit than higher mass objects. As aconsequence, the fraction of active galaxies, defined as those above afixed X-ray Eddington ratio, decreases with increasing BH mass.
| Diffuse Tidal Structures in the Halos of Virgo Ellipticals
We use deep V-band surface photometry of five of the brightestelliptical galaxies in the Virgo Cluster to search for diffuse tidalstreams, shells, and plumes in their outer halos (r>50 kpc). We fitand subtract elliptical isophotal models from the galaxy images toreveal a variety of substructure, with surface brightnesses in the range? V = 26-29 mag arcsec-2. M49 possessesan extended, interleaved shell system reminiscent of the radialaccretion of a satellite companion, while M89's complex system of shellsand plumes suggests a more complicated accretion history involvingeither multiple events or a major merger. M87 has a set of longstreamers as might be expected from stripping of low luminosity dwarfson radial orbits in Virgo. M86 also displays a number of small streamsindicative of stripping of dwarf companions, but these comprise muchless luminosity than those of M87. Only M84 lacks significant tidalfeatures. We quantify the photometric properties of these structures,and discuss their origins in the context of each galaxy's environmentand kinematics within the Virgo Cluster.
| A substantial population of low-mass stars in luminous elliptical galaxies
The stellar initial mass function (IMF) describes the mass distributionof stars at the time of their formation and is of fundamental importancefor many areas of astrophysics. The IMF is reasonably well constrainedin the disk of the Milky Way but we have very little direct informationon the form of the IMF in other galaxies and at earlier cosmic epochs.Here we report observations of the NaI doublet and the Wing-Fordmolecular FeH band in the spectra of elliptical galaxies. These linesare strong in stars with masses less than 0.3Msolar (whereMsolar is the mass of the Sun) and are weak or absent in allother types of stars. We unambiguously detect both signatures,consistent with previous studies that were based on data of lowersignal-to-noise ratio. The direct detection of the light of low-massstars implies that they are very abundant in elliptical galaxies, makingup over 80% of the total number of stars and contributing more than 60%of the total stellar mass. We infer that the IMF in massive star-forminggalaxies in the early Universe produced many more low-mass stars thanthe IMF in the Milky Way disk, and was probably slightly steeper thanthe Salpeter form in the mass range 0.1Msolar to1Msolar.
| The Nuclear X-ray Emission of Nearby Early-type Galaxies
Nuclear hard X-ray luminosities (L X,nuc) for a sample of 112early-type galaxies within a distance of 67 Mpc are used to investigatetheir relationship with the central galactic black hole mass MBH (coming from direct dynamical studies or the MBH-? relation), the inner galactic structure (using theparameters describing its cuspiness), the hot gas content, and the coreradio luminosity. For this sample, L X,nuc ranges from1038 to 1042 erg s–1, and theEddington ratio L X,nuc/L Edd from10–9 to 10–4, with the largest valuesbelonging to four Seyfert galaxies. Together with a trend for LX,nuc to increase on average with the galactic luminosityLB and M BH, there is a wide variation of LX,nuc (and L X,nuc/L Edd), by up to 4orders of magnitude, at any fixed LB > 6 ×109 L B,sun or M BH >107 M sun. This large observed range shouldreflect a large variation of the mass accretion rate \dot{M}_BH, andpossible reasons for this difference are searched for. On thecircumnuclear scale, in a scenario where accretion is (quasi) steady,\dot{M}_BH at fixed LB (or M BH) could vary due todifferences in the fuel production rate from stellar mass return linkedto the inner galactic structure; a trend of L X,nuc withcuspiness is not observed, though, while a tendency for LX,nuc/L Edd to be larger in cuspier galaxies ispresent. In fact, \dot{M}_BH is predicted to vary with cuspiness by afactor exceeding a few only in hot gas-poor galaxies and for largedifferences in the core radius; for a subsample with thesecharacteristics the expected effect seems to be present in the observedL X,nuc values. L X,nuc does not show a dependenceon the age of the stellar population in the central galactic region, forages >3 Gyr; less luminous nuclei, though, are found among theyoungest galaxies or galaxies with a younger stellar component. On theglobal galactic scale, L X,nuc shows a trend with the totalgalactic hot gas cooling rate (L X,ISM): it is detected bothin gas-poor and gas-rich galaxies, and on average increases with L X,ISM, but again with a large scatter. The observed lack of atight relationship between L X,nuc and the circumnuclear andtotal gas content can be explained if accretion is regulated by factorsovercoming the importance of fuel availability, as (1) the gas is heatedby black hole feedback and \dot{M}_BH varies due to an activity cycle,and (2) the mass effectively accreted by the black hole can be largelyreduced with respect to that entering the circumnuclear region, as inradiatively inefficient accretion with winds/outflows. Finally,differently from L X,nuc, the central 5 GHz VLA luminosityshows a clear trend with the inner galactic structure that is similar tothat shown by the total soft X-ray emission; therefore, it is suggestedthat they could both be produced by the hot gas.
| A Relationship Between AGN Jet Power and Radio Power
Using Chandra X-ray and Very Large Array radio data, we investigate thescaling relationship between jet power, P jet, andsynchrotron luminosity, P radio. We expand the samplepresented in Bîrzan et al. to lower radio power by incorporatingmeasurements for 21 giant elliptical galaxies (gEs) to determine if theBîrzan et al. P jet-P radio scalingrelations are continuous in form and scatter from gEs up to brightestcluster galaxies. We find a mean scaling relation of P jet? 5.8 × 1043(Pradio/1040)0.70 ergs–1 which is continuous over ~6-8 decades in Pjet and P radio with a scatter of ? 0.7 dex.Our mean scaling relationship is consistent with the model presented inWillott et al. if the typical fraction of lobe energy in non-radiatingparticles to that in relativistic electrons is gsim100. We identifyseveral gEs whose radio luminosities are unusually large for their jetpowers and have radio sources which extend well beyond the densest partsof their X-ray halos. We suggest that these radio sources are unusuallyluminous because they were unable to entrain appreciable amounts of gas.
| The Supermassive Black Hole in M84 Revisited
The mass of the central black hole in the giant elliptical galaxy M84has previously been measured by two groups using the same observationsof emission-line gas with the Space Telescope Imaging Spectrograph(STIS) on the Hubble Space Telescope, giving strongly discrepantresults: Bower et al. found M BH = (1.5+1.1-0.6) × 109 M sun, whileMaciejewski & Binney estimated M BH = 4 ×108 M sun. In order to resolve this discrepancy,we have performed new measurements of the gas kinematics in M84 from thesame archival data and carried out comprehensive gas-dynamical modelingfor the emission-line disk within ~70 pc from the nucleus. In comparisonwith the two previous studies of M84, our analysis includes a morecomplete treatment of the propagation of emission-line profiles throughthe telescope and STIS optics, as well as inclusion of the effects of anintrinsic velocity dispersion in the emission-line disk. We find that anintrinsic velocity dispersion is needed in order to match the observedline widths, and we calculate gas-dynamical models both with and withouta correction for asymmetric drift. Including the effect of asymmetricdrift improves the model fit to the observed velocity field. Ourbest-fitting model with asymmetric drift gives M BH =(8.5+0.9 -0.8) × 108 Msun (68% confidence). This is a factor of ~2 smaller than themass often adopted in studies of the MBH-?sstarf and M BH-Lrelationships. Our result provides a firmer basis for the inclusion ofM84 in the correlations between black hole mass and host galaxyproperties.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the Data Archive at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555. These observations areassociated with programs GO-7124 and GO-6094.
| X-ray Properties of Young Early-type Galaxies. I. X-ray Luminosity Function of Low-mass X-ray Binaries
We have compared the combined X-ray luminosity function (XLF) oflow-mass X-ray binaries (LMXBs) detected in Chandra observations ofyoung, post-merger elliptical galaxies with that of typical oldelliptical galaxies. We find that the XLF of the "young" sample does notpresent the prominent high-luminosity break at LX > 5× 1038 erg s-1 found in the oldelliptical galaxy XLF. The "young" and "old" XLFs differ with a 3?statistical significance (with a probability less than 0.2% that theyderive from the same underlying parent distribution). Young ellipticalgalaxies host a larger fraction of luminous LMXBs (LX > 5× 1038 erg s-1) than old ellipticalgalaxies and the XLF of the young galaxy sample is intermediate betweenthat of typical old elliptical galaxies and that of star-forminggalaxies. This observational evidence may be related to the lastmajor/minor mergers and the associated star formation.
| Homogeneous UGRIZ Photometry for ACS Virgo Cluster Survey Galaxies: A Non-parametric Analysis from SDSS Imaging
We present photometric and structural parameters for 100 ACS VirgoCluster Survey (ACSVCS) galaxies based on homogeneous, multi-wavelength(ugriz), wide-field SDSS (DR5) imaging. These early-type galaxies, whichtrace out the red sequence in the Virgo Cluster, span a factor of nearly~103 in g-band luminosity. We describe an automated pipelinethat generates background-subtracted mosaic images, masks field sourcesand measures mean shapes, total magnitudes, effective radii, andeffective surface brightnesses using a model-independent approach. Aparametric analysis of the surface brightness profiles is also carriedout to obtain Sérsic-based structural parameters and mean galaxycolors. We compare the galaxy parameters to those in the literature,including those from the ACSVCS, finding good agreement in most cases,although the sizes of the brightest, and most extended, galaxies arefound to be most uncertain and model dependent. Our photometry providesan external measurement of the random errors on total magnitudes fromthe widely used Virgo Cluster Catalog, which we estimate to be?(BT )? 0.13 mag for the brightest galaxies, risingto ? 0.3 mag for galaxies at the faint end of our sample(BT ? 16). The distribution of axial ratios of low-mass("dwarf") galaxies bears a strong resemblance to the one observed forthe higher-mass ("giant") galaxies. The global structural parameters forthe full galaxy sample—profile shape, effective radius, and meansurface brightness—are found to vary smoothly and systematicallyas a function of luminosity, with unmistakable evidence for changes instructural homology along the red sequence. As noted in previousstudies, the ugriz galaxy colors show a nonlinear but smooth variationover a ~7 mag range in absolute magnitude, with an enhanced scatter forthe faintest systems that is likely the signature of their more diversestar formation histories.
| Optical Colors of Intracluster Light in the Virgo Cluster Core
We continue our deep optical imaging survey of the Virgo cluster usingthe CWRU Burrell Schmidt telescope by presenting B-band surfacephotometry of the core of the Virgo cluster in order to study thecluster's intracluster light (ICL). We find ICL features down to? B ?29 mag arcsec–2, confirming theresults of Mihos et al., who saw a vast web of low surface brightnessstreams, arcs, plumes, and diffuse light in the Virgo cluster core usingV-band imaging. By combining these two data sets, we are able to measurethe optical colors of many of the cluster's low surface brightnessfeatures. While much of our imaging area is contaminated by galacticcirrus, the cluster core near the cD galaxy, M87, is unobscured. Wetrace the color profile of M87 out to over 2000'', and find a blueingtrend with radius, continuing out to the largest radii. Moreover, wehave measured the colors of several ICL features which extend beyondM87's outermost reaches and find that they have similar colors to theM87's halo itself, B – V ?0.8. The common colors of thesefeatures suggest that the extended outer envelopes of cD galaxies, suchas M87, may be formed from similar streams, created by tidalinteractions within the cluster, that have since dissolved into a smoothbackground in the cluster potential.
| The ACS Fornax Cluster Survey. VIII. The Luminosity Function of Globular Clusters in Virgo and Fornax Early-type Galaxies and Its Use as a Distance Indicator
We use a highly homogeneous set of data from 132 early-type galaxies inthe Virgo and Fornax clusters in order to study the properties of theglobular cluster luminosity function (GCLF). The globular cluster systemof each galaxy was studied using a maximum likelihood approach to modelthe intrinsic GCLF after accounting for contamination and completenesseffects. The results presented here update our Virgo measurements andconfirm our previous results showing a tight correlation between thedispersion of the GCLF and the absolute magnitude of the parent galaxy.Regarding the use of the GCLF as a standard candle, we have found thatthe relative distance modulus between the Virgo and Fornax clusters issystematically lower than the one derived by other distance estimators,and in particular, it is 0.22 mag lower than the value derived fromsurface brightness fluctuation measurements performed on the same data.From numerical simulations aimed at reproducing the observed dispersionof the value of the turnover magnitude in each galaxy cluster weestimate an intrinsic dispersion on this parameter of 0.21 mag and 0.15mag for Virgo and Fornax, respectively. All in all, our study shows thatthe GCLF properties vary systematically with galaxy mass showing noevidence for a dichotomy between giant and dwarf early-type galaxies.These properties may be influenced by the cluster environment assuggested by cosmological simulations.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute (STScI), which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| Jet-powered Molecular Hydrogen Emission from Radio Galaxies
H2 pure-rotational emission lines are detected from warm(100-1500 K) molecular gas in 17/55 (31% of) radio galaxies at redshiftz < 0.22 observed with the Spitzer IR Spectrograph. The summedH2 0-0 S(0)-S(3) line luminosities are L(H2) = 7× 1038-2 × 1042 ergs-1, yielding warm H2 masses up to 2 ×1010 M sun. These radio galaxies, of both FR radiomorphological types, help to firmly establish the new class ofradio-selected molecular hydrogen emission galaxies (radio MOHEGs).MOHEGs have extremely large H2 to 7.7 ?m polycyclicaromatic hydrocarbon (PAH) emission ratios: L(H2)/L(PAH7.7) =0.04-4, up to a factor 300 greater than the median value for normalstar-forming galaxies. In spite of large H2 masses, MOHEGsappear to be inefficient at forming stars, perhaps because the moleculargas is kinematically unsettled and turbulent. Low-luminosity mid-IRcontinuum emission together with low-ionization emission line spectraindicates low-luminosity active galactic nuclei (AGNs) in all but threeradio MOHEGs. The AGN X-ray emission measured with Chandra is notluminous enough to power the H2 emission from MOHEGs. Nearlyall radio MOHEGs belong to clusters or close pairs, including fourcool-core clusters (Perseus, Hydra, A2052, and A2199). We suggest thatthe H2 in radio MOHEGs is delivered in galaxy collisions orcooling flows, then heated by radio-jet feedback in the form of kineticenergy dissipation by shocks or cosmic rays.
| Detection of a Large-Scale Structure of Intracluster Globular Clusters in the Virgo Cluster
Globular clusters are usually found in galaxies, and they are excellenttracers of dark matter. Long ago it was suggested that intraclusterglobular clusters (IGCs) may exist that are bound to a galaxy clusterrather than to any single galaxy. Here we present a map showing thelarge-scale distribution of globular clusters over the entire Virgocluster. It shows that IGCs are found out to 5 million light years fromthe Virgo center and that they are concentrated in several substructuresthat are much larger than galaxies. These objects might have been mostlystripped off from low-mass dwarf galaxies.
| A Correlation Between Central Supermassive Black Holes and the Globular Cluster Systems of Early-type Galaxies
Elliptical, lenticular, and early-type spiral galaxies show a remarkablytight power-law correlation between the mass M • oftheir central supermassive black hole (SMBH) and the number NGC of globular clusters (GCs): M • = m•/sstarf × N 1.08±0.04GC with m •/sstarf = 1.7 ×105 M sun. Thus, to a good approximation the SMBHmass is the same as the total mass of the GCs. Based on a limited sampleof 13 galaxies, this relation appears to be a better predictor of SMBHmass (rms scatter 0.2 dex) than the M •-? relationbetween SMBH mass and velocity dispersion ?. The small scatterreflects the fact that galaxies with high GC specific frequencySN tend to harbor SMBHs that are more massive than expectedfrom the M •-? relation.
| Spectral Energy Distributions of Weak Active Galactic Nuclei Associated with Low-Ionization Nuclear Emission Regions
We present a compilation of spectral energy distributions (SEDs) of 35weak active galactic nuclei (AGNs) in low-ionization nuclear emissionregions (LINERs) using recent data from the published literature. Wemake use of previously published compilations of data, aftercomplementing and extending them with more recent data. The mainimprovement in the recent data is afforded by high-spatial-resolutionobservations with the Chandra X-Ray Observatory andhigh-spatial-resolution radio observations utilizing a number offacilities. In addition, a considerable number of objects have beenobserved with the Hubble Space Telescope in the near-IR through near-UVbands since the earlier compilations were published. The data includeupper limits resulting from either non-detections or observations at lowspatial resolution that do not isolate the AGN. For the sake ofcompleteness, we also compute and present a number of quantities fromthe data, such as optical-to-X-ray spectral indices(αox), bolometric corrections, bolometric luminosities,Eddington ratios, and the average SED. We anticipate that these datawill be useful for a number of applications. In a companion paper, weuse a subset of these data ourselves to assess the energy budgets ofLINERs.
| An Assessment of the Energy Budgets of Low-Ionization Nuclear Emission Regions
Using the spectral energy distributions (SEDs) of the weak activegalactic nuclei (AGNs) in 35 low-ionization nuclear emission regions(LINERs) presented in a companion paper, we assess whetherphotoionization by the weak AGN can power the emission-line luminositiesmeasured through the large (few-arcsecond) apertures used inground-based spectroscopic surveys. Spectra taken through such aperturesare used to define LINERs as a class and constrain non-stellarphotoionization models for LINERs. Therefore, our energy budget test isa self-consistency check of the idea that the observed emission linesare powered by an AGN. We determine the ionizing luminosities and photonrates by integrating the observed SEDs and by scaling a template SED. Wefind that even if all ionizing photons are absorbed by the line-emittinggas, more than half of the LINERs in this sample suffer from a deficitof ionizing photons. In 1/3 of LINERs the deficit is severe. If only 10%of the ionizing photons are absorbed by the gas, there is an ionizingphoton deficit in 85% of LINERs. We disfavor the possibility thatadditional electromagnetic power, either obscured or emitted in theunobservable far-UV band, is available from the AGN. Therefore, weconsider other power sources such as mechanical heating by compact jetsfrom the AGN and photoionization by either young or old stars.Photoionization by young stars may be important in a small fraction ofcases. Mechanical heating can provide enough power in most cases but itis not clear how this power would be transferred to the emission-linegas. Photoionization by post asymptotic giant branch stars is animportant power source; it provides more ionizing photons than the AGNin more than half of the LINERs and enough ionizing photons to power theemission lines in 1/3 of the LINERs. It appears likely that theemission-line spectra of LINERs obtained from the ground include the sumof emission from different regions where different power sourcesdominate.
| The SAURON project - XVI. On the sources of ionization for the gas in elliptical and lenticular galaxies
Following our study on the incidence, morphology and kinematics of theionized gas in early-type galaxies, we now address the question of whatis powering the observed nebular emission. To constrain the likelysources of gas excitation, we resort to a variety of ancillary data wedraw from complementary information on the gas kinematics, stellarpopulations and galactic potential from the SAURON data, and use theSAURON-specific diagnostic diagram juxtaposing the [OIII]?5007/H? and [NI] ??5197, 5200/H? lineratios. We find a tight correlation between the stellar surfacebrightness and the flux of the H? recombination line across oursample, which points to a diffuse and old stellar source as the maincontributor of ionizing photons in early-type galaxies, withpost-asymptotic giant branch (pAGB) stars being still the best candidatebased on ionizing balance arguments. The role of AGN photoionization isconfined to the central 2-3arcsec of an handful of objects with radio orX-ray cores. OB-stars are the dominant source of photoionization in 10per cent of the SAURON sample, whereas for another 10 per cent theintense and highly ionized emission is powered by the pAGB populationassociated to a recently formed stellar subcomponent. Fast shocks arenot an important source of ionization for the diffuse nebular emissionof early-type galaxies since the required shock velocities can hardly beattained in the potential of our sample galaxies. Finally, in the mostmassive and slowly or non-rotating galaxies in our sample, which canretain a massive X-ray halo, the finding of a spatial correlationbetween the hot and warm phases of the interstellar medium (ISM)suggests that the interaction with the hot ISM provides an additionalsource of ionization besides old ultraviolet-bright stars. This is alsosupported by a distinct pattern towards lower values of the[OIII]/H? ratio. These results lead us to investigate the relativerole of stellar and AGN photoionization in explaining the ionized gasemission observed in early-type galaxies by the Sloan Digital Sky Survey(SDSS). By simulating how our sample galaxies would appear if placed atfurther distance and targeted by the SDSS, we conclude that only in veryfew, if any, of the SDSS galaxies which display modest values for theequivalent width of the [OIII] line (less than ~2.4 Å) andlow-ionization nuclear emission-line region like [OIII]/H? valuesthe nebular emission is truly powered by an AGN.
| Accretion and nuclear activity in Virgo early-type galaxies
We use Chandra observations to estimate the accretion rate of hot gasonto the central supermassive black hole in four giant (of stellar massM_* 1011-1012 Msun) early-typegalaxies located in the Virgo cluster. They are characterized by anextremely low radio luminosity, in the range L ?3×1025-1027 erg s-1Hz-1. We find that, accordingly, accretion in these objectsoccurs at an extremely low rate, 0.2-3.7×10-3M? yr-1, and that they smoothly extend therelation accretion-jet power found for more powerful radio-galaxies.This confirms the dominant role of hot gas and of the galactic coronaein powering radio-loud active galactic nuclei across 4 orders ofmagnitude in luminosity. A suggestive trend between jet power andlocation within the cluster also emerges.Appendix is only available in electronic form at http://www.aanda.org
| Is BL Lacertae an ``orphan'' AGN?. Multiband and spectroscopic constraints on the parent population
Aims: We have analysed optical spectra of BL Lacertae, theprototype of its blazar subclass, to verify the broad H? emissionline detected more than a decade ago and its possible flux variation. Weused the spectroscopic information to investigate the question of the BLLacertae parent population. Methods: Low- and high-resolutionoptical spectra of BL Lacertae were acquired with the DOLORESspectrograph at the 3.58 m telescopio nazionale Galileo (TNG) duringfour nights in 2007-2008, when the source was in a relatively faintstate. In three cases we were able to fit the complex H? spectralrange with multiple line components and to measure both the broadH? and several narrow emission line fluxes. Results: Acritical comparison with previous results suggests that the broadH? flux has increased by about 50% in ten years. This might be dueto an addition of gas in the broad line region (BLR), or to astrengthening of the disc luminosity, but such flux changes are notunusual in Broad Lined active nuclei. We estimated the BL Lacertae blackhole mass by means of its relation with the bulge luminosity, finding4-6 × 108 M?. The virial mass estimatedfrom the spectroscopic data gives instead a value 20-30 times lower. Ananalysis of the disc and BLR properties in different AGNs suggests thatthis discrepancy is due to an underluminosity of the BL Lacertae BLR.Finally, we addressed the problem of the BL Lacertae parent population,comparing its isotropic quantities with those of other AGN classes. Fromthe point of view of the narrow emission line spectrum, the source islocated close to low-excitation radio galaxies. When one also considersits diffuse radio power, an association with FR I radio galaxies isseverely questioned due to the lower radio luminosity (at a given lineluminosity) of BL Lacertae. The narrow line and radio luminosities of BLLacertae instead match those of a sample of miniature radio galaxies,which however do not show a BLR. Yet, if existing, “misaligned BLLacertae” objects should have entered that sample. We also ruleout the possibility that they were excluded because of a QSO opticalappearance. Conclusions: The observational constraints suggestthat BL Lacertae is caught in a short term transient stage, which doesnot leave a detectable evolutionary “trace” in the AGNpopulation. We present a scenario that can account for the observedproperties.Based on observations made with the Italian Telescopio Nazionale Galileooperated on the island of La Palma by the Centro Galileo Galilei of INAF(Istituto Nazionale di Astrofisica) at the Spanish Observatorio delRoque del los Muchachos of the Instituto de Astrofisica de Canarias.
| Soft band X/K luminosity ratios for gas-poor early-type galaxies
Aims: We aim to place upper limits on the combined X-ray emissionfrom the population of steady nuclear-burning white dwarfs in galaxies.In the framework of the single-degenerate scenario, these systems, knownas supersoft sources, are believed to be likely progenitors of Type Iasupernovae. Methods: From the Chandra archive, we selected normalearly-type galaxies with the point source detection sensitivity betterthan 1037 erg s-1 in order to minimize thecontribution of unresolved low-mass X-ray binaries. The galaxies,contaminated by emission from ionized ISM, were identified based on theanalysis of radial surface brightness profiles and energy spectra. Thesample was complemented by the bulge of M 31 and the data for the solarneighborhood. To cover a broad range of ages, we also included NGC 3377and NGC 3585 which represent the young end of the age distribution forelliptical galaxies. Our final sample includes eight gas-poor galaxiesfor which we determine LX/LK ratios in the 0.3-0.7keV energy band. This choice of the energy band was optimized to detectsoft emission from thermonuclear-burning on the surface of an accretingwhite dwarf. In computing the LX we included both unresolvedemission and soft resolved sources with the color temperature ofkTbb ? 200 eV. Results: We find that the X/Kluminosity ratios are in a rather narrow range of (1.7-3.2) ×1027 erg s-1 LK,?. The data showno obvious trends with mass, age, or metallicity of the host galaxy,although a weak anti-correlation with the Galactic NH appears to exist.It is much flatter than predicted for a blackbody emission spectrum withtemperature of ~ 50-75 eV, suggesting that sources with such softspectra contribute significantly less than a half to the observed X/Kratios. However, the correlation of the X/K ratios with NH has asignificant scatter and in the strict statistical sense cannot beadequately described by a superposition of a power law and a blackbodycomponents with reasonable parameters, thus precluding quantitativeconstraints on the contribution from soft sources.
| The SAURON project - XV. Modes of star formation in early-type galaxies and the evolution of the red sequence
We combine SAURON integral field data of a representative sample oflocal early-type, red sequence galaxies with Spitzer/Infrared ArrayCamera imaging in order to investigate the presence of trace starformation in these systems. With the Spitzer data, we identify galaxieshosting low-level star formation, as traced by polycyclic aromatichydrocarbon emission, with measured star formation rates that comparewell to those estimated from other tracers. This star formation proceedsaccording to established scaling relations with molecular gas content,in surface density regimes characteristic of disc galaxies andcircumnuclear starbursts. We find that star formation in early-typegalaxies happens exclusively in fast-rotating systems and occurs in twodistinct modes. In the first, star formation is a diffuse process,corresponding to widespread young stellar populations and high moleculargas content. The equal presence of co- and counter-rotating componentsin these systems strongly implies an external origin for thestar-forming gas, and we argue that these star formation events may bethe final stages of (mostly minor) mergers that build up the bulges ofred sequence lenticulars. In the second mode of star formation, theprocess is concentrated into well-defined disc or ring morphologies,outside of which the host galaxies exhibit uniformly evolved stellarpopulations. This implies that these star formation events representrejuvenations within previously quiescent stellar systems. Evidence forearlier star formation events similar to these in all fast-rotatingearly-type galaxies suggests that this mode of star formation may becommon to all such galaxies, with a duty cycle of roughly 1/10, andlikely contributes to the embedded, corotating inner stellar discsubiquitous in this population.
| FIR colours and SEDs of nearby galaxies observed with Herschel
We present infrared colours (in the 25-500 ?m spectral range) and UVto radio continuum spectral energy distributions of a sample of 51nearby galaxies observed with SPIRE on Herschel. The observed sampleincludes all morphological classes, from quiescent ellipticals to activestarbursts. Active galaxies have warmer colour temperatures than normalspirals. In ellipticals hosting a radio galaxy, the far-infrared (FIR)emission is dominated by the synchrotron nuclear emission. The colourtemperature of the cold dust is higher in quiescent E-S0a than instar-forming systems probably because of the different nature of theirdust heating sources (evolved stellar populations, X-ray, fastelectrons) and dust grain properties. In contrast to the colourtemperature of the warm dust, the f350/f500 index sensitive to the colddust decreases with star formation and increases with metallicity,suggesting an overabundance of cold dust or an emissivity parameter? < 2 in low metallicity, active systems.Herschel is an ESA space observatory with science instruments providedby Principal Investigator consortia. It is open for proposals forobserving time from the worldwide astronomical community.
| The Type Ia Supernova Rate in Radio and Infrared Galaxies from the Canada-France-Hawaii Telescope Supernova Legacy Survey
We have combined the large SN Ia database of the Canada-France-HawaiiTelescope Supernova Legacy Survey and catalogs of galaxies withphotometric redshifts, Very Large Array 1.4 GHz radio sources, andSpitzer infrared sources. We present eight SNe Ia in early-type hostgalaxies which have counterparts in the radio and infrared sourcecatalogs. We find the SN Ia rate in subsets of radio and infraredearly-type galaxies is ~1-5 times the rate in all early-type galaxies,and that any enhancement is always lsim2σ. Rates in these subsetsare consistent with predictions of the two-component "A+B" SN Ia ratemodel. Since infrared properties of radio SN Ia hosts indicatedust-obscured star formation, we incorporate infrared star formationrates into the "A+B" model. We also show the properties of SNe Ia inradio and infrared galaxies suggest the hosts contain dust and support acontinuum of delay time distributions (DTDs) for SNe Ia, although otherDTDs cannot be ruled out based on our data.
| A simplified model of ADAF with the jet driven by the large-scale magnetic field
We propose a simplified model of outflow/jet driven by theBlandford-Payne (BP) process from advection-dominated accretionflows (ADAF) and derive the expressions of the BP power and diskluminosity based on the conservation laws of mass, angular momentum andenergy. We fit the 2-10 keV luminosity and kinetic power of 15active galactic nucleus (AGNs) of sub-Eddington luminosity. It is foundthat there exists an anti-correlation between the accretion rate and theadvection parameter, which could be used to explain the correlationbetween Eddington-scaled kinetic power and bolometric luminosity of the15 samples. In addition, the Ledlow-Owen relation for FR I/IIdichotomy is re-expressed in a parameter space consisting of logarithmof dimensionless accretion rate versus that of the BH mass. It turns outthat the FR I/II dichotomy is determined mainly by the dimensionlessaccretion rate, being insensitive to the BH mass. And the dividingaccretion rate is less than the critical accretion rate for ADAFs,suggesting that FR I sources are all in the ADAF state.
| The Herschel Virgo Cluster Survey. III. A constraint on dust grain lifetime in early-type galaxies
Passive early-type galaxies (ETGs) provide an ideal laboratory forstudying the interplay between dust formation around evolved stars andits subsequent destruction in a hot gas. Using Spitzer-IRS and Herscheldata we compare the dust production rate in the envelopes of evolved AGBstars with a constraint on the total dust mass. Early-type galaxieswhich appear to be truly passively evolving are not detected byHerschel. We thus derive a distance independent upper limit to the dustgrain survival time in the hostile environment of ETGs of<46±25 Myr for amorphous silicate grains. This implies thatETGs which are detected at far-infrared wavelengths have acquired a cooldusty medium via interaction. Given likely time-scales for ram-pressurestripping, this also implies that only galaxies with dust in a cool(atomic) medium can release dust into the intra-cluster medium.Herschel is an ESA space observatory with science instruments providedby European-led Principal Investigator consortia and with importantparticipation from NASA.
| Nearby early-type galaxies with ionized gas. IV. Origin and powering mechanism of the ionized gas
Aims: A significant fraction of early-type galaxies (ETGs)exhibit emission lines in their optical spectra. We attempt to identifythe producing the emission mechanism and the ionized gas in ETGs, andits connection with the host galaxy evolution. Methods: Weanalyzed intermediate-resolution optical spectra of 65 ETGs, mostlylocated in low density environments and exhibiting spectros-copicdiagnostic lines of ISM from which we had previously derived stellarpopulation properties. To extract the emission lines from the galaxyspectra, we developed a new fitting procedure that accurately subtractsthe underlying stellar continuum, and accounts for the uncertaintiescaused by the age-metallicity degeneracy. Results: Opticalemission lines are detected in 89% of the sample. The incidence andstrength of emission correlate with neither the E/S0 classification, northe fast/slow rotator classification. By means of the classical[OIII]/H? versus [NII]/H? diagnostic diagram, the nucleargalaxy activity is classified such that 72% of the galaxies withemission are LINERs, 9% are Seyferts, 12% are composite/transitionobjects, and 7% are non-classified. Seyferts have youngluminostiy-weighted ages (?5 Gyr), and appear, on average,significantly younger than LINERs and composites. Excluding the Seyfertsfrom our sample, we find that the spread in the ([OIII], H?, or[NII]) emission strength increases with the galaxy central velocitydispersion ?_c. Furthermore, the [NII]/H? ratio tends toincrease with ?_c. The [NII]/H? ratio decreases withincreasing galactocentric distance, indicative of either a decrease inthe nebular metallicity, or a progressive “softening” of theionizing spectrum. The average nebular oxygen abundance is slightly lessthan solar, and a comparison with the results obtained in Paper III fromLick indices shows that it is ?0.2 dex lower than that of stars. Conclusions: The nuclear (r < re/16) emission can beattributed to photoionization by PAGB stars alone only for ?22% ofthe LINER/composite sample. On the other hand, we cannot exclude animportant role of PAGB star photoionization at larger radii. For themajor fraction of the sample, the nuclear emission is consistent withexcitation caused by either a low-accretion rate AGN or fast shocks(200-500 km s-1) in a relatively gas poor environment (n? 100 cm-3), or both. The derived [SII]6717/6731 ratiosare consistent with the low gas densities required by the shock models.The derived nebular metallicities are indicative of either an externalorigin of the gas, or an overestimate of the oxygen yields by SN models.Based on observations obtained at the European Southern Observatory, LaSilla, Chile.Appendix and Tables 2 and 3 are only available inelectronic form at http://www.aanda.org
| The central dark matter content of early-type galaxies: scaling relations and connections with star formation histories
We examine correlations between masses, sizes and star formationhistories for a large sample of low-redshift early-type galaxies, usinga simple suite of dynamical and stellar population models. We confirm ananticorrelation between the size and stellar age and go on to survey fortrends with the central content of dark matter (DM). An average relationbetween the central DM density and galaxy size of ~ R-2eff provides thefirst clear indication of cuspy DM haloes in these galaxies - akin tostandard ? cold dark matter haloes that have undergone adiabaticcontraction. The DM density scales with galaxy mass as expected,deviating from suggestions of a universal halo profile for dwarf andlate-type galaxies.We introduce a new fundamental constraint on galaxy formation by findingthat the central DM fraction decreases with stellar age. This result isonly partially explained by the size-age dependencies, and the residualtrend is in the opposite direction to basic DM halo expectations.Therefore, we suggest that there may be a connection between age andhalo contraction and that galaxies forming earlier had stronger baryonicfeedback, which expanded their haloes, or lumpier baryonic accretion,which avoided halo contraction. An alternative explanation is a lighterinitial mass function for older stellar populations.
| The effect of dust extinction on the observed properties of galaxies in the near-infrared
Galaxies behind the Milky Way suffer size reduction and dimming due totheir obscuration by dust in the disc of our Galaxy. The degree ofobscuration is wavelength dependent. It decreases towards longerwavelengths. Compared to the optical, the near-infrared (NIR)Ks-band extinction is only ~10 per cent that of the B band.This makes NIR surveys well suited for galaxy surveys close to theGalactic plane, where extinction is severe.While Galactic obscuration is less prominent in the NIR, it is notnegligible. In this paper, we derive empirical relations to correctisophotal radii and magnitudes of galaxies observed in the NIR forforeground absorption. We simulate extinction in the J, H andKs bands on 64 (unobscured) galaxies from the Two Micron AllSky Survey Large Galaxy Atlas. We propose two methods for the extinctioncorrection, the first is optimized to provide the most accuratecorrection and the second provides a convenient statistical correctionthat works adequately in lower extinction regions. The optimizedcorrection utilizes the galaxy surface brightness, either the disccentral surface brightness, ?0, or the combined disc plusbulge central surface brightness, elliptical and disc/spiral Hubbletypes. A detailed comparison between the different methods and theiraccuracy is provided.
| An optical spectroscopic survey of the 3CR sample of radio galaxies with z < 0.3 . II. Spectroscopic classes and accretion modes in radio-loud AGN
In a previous paper we presented a homogeneous and 92% complete opticalspectral dataset of the 3CR radio sources with redshift <0.3. Here weuse the emission line measurements to explore the spectroscopicproperties of the sample. The 3CR sources show a bimodal distribution ofexcitation index, a new spectroscopic indicator that measures therelative intensity of low and high excitation lines. This unveils thepresence of two main sub-populations of radio-loud AGN to which we referto, following previous studies, as high and low excitation galaxies (HEGand LEG, respectively). In addition to the two main classes, we find onesource with a spectrum typical of star forming galaxies, and 3 objectsof extremely low level of excitation. All broad-line objects are HEGfrom the point of view of their narrow emission line ratios and all HEGare FR II radio-galaxies with log L178 [erg s-1]⪆ 32.8. Conversely LEG cover the whole range of radio powerencompassed by this 3CR subsample (30.7 ⪉ log L178 ⪉35.4) and they are of both FR I and FR II type. The brightest LEG areall FR II. HEG and LEG obey to two (quasi) linear correlations betweenthe optical line and extended radio luminosities, with HEG beingbrighter than LEG in the [O III] line by a factor of ~10. HEG and LEGare offset also in a plane that compares the black hole mass and theionizing nuclear luminosity. However, although HEG are associated withhigher nuclear luminosities, we find LEG among the brightest radiosources of the sample and with a clear FR II morphology,indistinguishable from those seen in HEG. This suggests that LEG are notsimply objects with a lower level of accretion. We speculate that thedifferences between LEG and HEG are related to a different mode ofaccretion: LEG are powered by hot gas, while HEG require the presence ofcold accreting material. The high temperature of the accreting gas inLEG accounts for the lack of “cold” structures (i.e.molecular torus and broad line region), for the reduced radiative outputof the accretion disk, and for the lower gas excitation.Based on observations made with the Italian Telescopio Nazionale Galileooperated on the island of La Palma by the Centro Galileo Galilei of INAF(Istituto Nazionale di Astrofisica) at the Spanish Observatorio delRoque del los Muchachos of the Instituto de Astrofísica deCanarias.
| TANGO I: Interstellar medium in nearby radio galaxies. Molecular gas
Context. Powerful radio-AGN are hosted by massive elliptical galaxiesthat are usually very poor in molecular gas. Nevertheless, gas is neededat their very center to feed the nuclear activity. Aims: We studythe molecular gas properties (i.e., mass, kinematics, distribution,origin) of these objects, and compare them with results for other knownsamples. Methods: At the IRAM-30m telescope, we performed asurvey of the CO(1-0) and CO(2-1) emission from the most powerful radiogalaxies of the Local Universe, selected only on the basis of theirradio continuum fluxes. Results: The main result of our survey isthat the molecular gas content of these galaxies is very low compared tospiral or FIR-selected galaxies. The median value of the molecular gasmass, including detections and upper limits, is 2.2 ×108 M?. When separated into FR-I and FR-IItypes, a difference in their H2 masses is found. The medianvalue of FR-I galaxies is about 1.9 × 108M? and higher for FR-II galaxies, at about 4.5 ×108 M?. Which is probably entirely because ofa Malmquist bias. Our results contrast with those of previous surveys,whose targets were mainly selected by means of their FIR emission,implying that we measure higher observed masses of molecular gas.Moreover, the shape of CO spectra suggest that a central molecular gasdisk exists in 30% of these radio galaxies, a lower rate than in otheractive galaxy samples. Conclusions: We find a low level ofmolecular gas in our sample of radio-selected AGNs, indicating thatgalaxies do not need much molecular gas to host an AGN. The presence ofa molecular gas disk in some galaxies and the wide range of moleculargas masses may be indicative of different origins for the gas, which wecan not exclude at present (e.g., minor/major mergers, stellar massloss, or accretion).Appendices and Figure 15 are only available in electronic form at http://www.aanda.org
| Polytropic dark haloes of elliptical galaxies
The kinematics of stars and planetary nebulae in early-type galaxiesprovide vital clues to the enigmatic physics of their dark matterhaloes. We fit published data for 14 such galaxies using a spherical,self-gravitating model with two components: (i) a Sérsic stellarprofile fixed according to photometric parameters, and (ii) a polytropicdark matter halo that conforms consistently to the shared gravitationalpotential. The polytropic equation of state can describe extendedtheories of dark matter involving self-interaction, non-extensivethermostatistics or boson condensation (in a classical limit). In suchmodels, the flat-cored mass profiles widely observed in disc galaxiesare due to innate dark physics, regardless of any baryonic agitation.One of the natural parameters of this scenario is the number ofeffective thermal degrees of freedom of dark matter (Fd)which is proportional to the dark heat capacity. By default, we assume acosmic ratio of baryonic and dark mass. Non-Sérsic kinematicideosyncrasies and possible non-sphericity thwart fitting in some cases.In all 14 galaxies, the fit with a polytropic dark halo improves or atleast gives similar fits to the velocity dispersion profile, compared toa stars-only model. The good halo fits usually prefer Fdvalues from six to eight. This range complements the recently inferredlimit of 7 < Fd < 10, derived from constraints ongalaxy cluster core radii and black hole masses. However, a degeneracyremains: radial orbital anisotropy or a depleted dark mass fractioncould shift our models' preference towards lower Fd; whereasa loss of baryons would favour higher Fd.
| Not Available
Not Available
| The Unusual X-Ray Morphology of NGC 4636 Revealed by Deep Chandra Observations: Cavities and Shocks Created by Past Active Galactic Nucleus Outbursts
We present Chandra ACIS-I and ACIS-S observations (~200 ks in total) ofthe X-ray luminous elliptical galaxy NGC 4636, located in the outskirtsof the Virgo cluster. A soft band (0.5-2 keV) image shows the presenceof a bright core in the center surrounded by an extended X-ray coronaand two pronounced quasi-symmetric, 8 kpc long, arm-like features. Eachof these features defines the rim of an ellipsoidal bubble. Anadditional bubble-like feature, whose northern rim is located ~2 kpcsouth of the northeastern arm, is detected as well. We present surfacebrightness and temperature profiles across the rims of the bubbles,showing that their edges are sharp and characterized by temperaturejumps of about 20%-25%. Through a comparison of the observed profileswith theoretical shock models, we demonstrate that a scenario where thebubbles were produced by shocks, probably driven by energy depositedoff-center by jets, is the most viable explanation to the X-raymorphology observed in the central part of NGC 4636. As a confirmationto this scenario, radio jets extending toward the bubbles and a centralweak X-ray and radio source are detected and are most likely the signsof active galactic nuclei activity which was more intense in the past. Abright dense core of ~1 kpc radius is observed at the center of NGC4636. A sharp decline in surface brightness from the core to the ambientgas is observed and is not accompanied by a variation in the temperatureand thus could not be in thermal pressure equilibrium. However, thebright core could be a long-lived feature if the radio jets are actingas a balancing factor to thermal pressure or if the bright core isproduced by steep abundance gradients.
| Spitzer Observations of Passive and Star-Forming Early-Type Galaxies: An Infrared Color–Color Sequence
We describe the infrared properties of a large sample of early-typegalaxies, comparing data from the Spitzer archive with Ks-band emissionfrom the Two Micron All Sky Survey. While most representations of thisdata result in correlations with large scatter, we find a remarkablytight relation among colors formed by ratios of luminosities inSpitzer-Multiband Imaging Photometer bands (24, 70, and 160 μm) andthe Ks band. Remarkably, this correlation among E and S0 galaxiesfollows that of nearby normal galaxies of all morphological types. Inparticular, the tight infrared color-color correlation for S0 galaxiesalone follows that of the entire Hubble sequence of normal galaxies,roughly in order of galaxy type from ellipticals to spirals toirregulars. The specific star formation rate (SFR) of S0 galaxiesestimated from the 24 μm luminosity increases with decreasing K-bandluminosity (or stellar mass) from essentially zero, as with most massiveellipticals, to rates typical of irregular galaxies. Moreover, theluminosities of the many infrared-luminous S0 galaxies can significantlyexceed those of the most luminous (presumably post-merger) E galaxies.SFRs in the most infrared-luminous S0 galaxies approach 1-10 solarmasses per year. Consistently, with this picture we find that while mostearly-type galaxies populate an infrared red sequence, about 24% of theobjects (mostly S0s) are in an infrared blue cloud together withlate-type galaxies. For those early-type galaxies also observed at radiofrequencies, we find that the far-infrared luminosities correlate withthe mass of neutral and molecular hydrogen, but the scatter is large.This scatter suggests that the star formation may be intermittent orthat similar S0 galaxies with cold gaseous disks of nearly equal masscan have varying radial column density distributions that alter thelocal and global SFRs.
| The Combined NVSS-FIRST Galaxies (CoNFIG) sample - II. Comparison of space densities in the Fanaroff-Riley dichotomy
This paper focuses on a comparison of the space densities ofFanaroff-Riley type I (FRI) and FRII sources at different epochs, with aparticular focus on FRI sources.First, we present the concluding steps in constructing the CombinedNVSS-FIRST Galaxies (CoNFIG) catalogue, including new Very Large Arrayobservations, optical identifications and redshift estimates. The finalcatalogue consists of 859 sources over four samples (CoNFIG-1, -2, -3and -4 with flux density limits of S1.4GHz = 1.3, 0.8, 0.2and 0.05Jy, respectively). It is 95.7 per cent complete in radiomorphology classification and 74.3 per cent of the sources have redshiftdata.Combining CoNFIG with complementary samples, the distribution andevolution of FRI and FRII sources are investigated. We find that FRIsources undergo mild evolution and that, at the same radio luminosity,FRI and FRII sources show similar space density enhancements in variousredshift ranges, possibly implying a common evolution.
| A Very Large Array Radio Survey of Early-Type Galaxies in the Virgo Cluster
We present the results of an 8.4 GHz Very Large Array radio survey ofearly-type galaxies extracted from the sample selected byCôté and collaborators for the Advanced Camera for SurveysVirgo Cluster Survey. The aim of this survey is to investigate theorigin of radio emission in early-type galaxies and its link with thehost properties in an unexplored territory toward the lowest levels ofboth radio and optical luminosities. Radio images, available for all 63galaxies with B T < 14.4, show the presence of a compactradio source in 12 objects, with fluxes spanning from 0.13 mJy to 2700mJy. The remaining 51 galaxies, undetected at a flux limit of ~0.1 mJy,have radio luminosities L lsim 4 × 1018 WHz–1. The fraction of radio-detected galaxies are astrong function of stellar mass, in agreement with previous results:none of the 30 galaxies with M sstarf < 1.7 ×1010 M sun is detected, while 8 of the 11 mostmassive galaxies have radio cores. There appears to be no simplerelation between the presence of a stellar nucleus and radio emission.In fact, we find radio sources associated with two nucleated galaxies,but the majority of nucleated objects are not a radio emitter above ourdetection threshold. A multiwavelength analysis of the active galacticnucleus (AGN) emission, combining radio and X-ray data, confirms thelink between optical surface brightness profile and radio loudness inthe sense that the bright core galaxies are associated with radio-loudAGNs, while non-core galaxies host radio-quiet AGNs. Not allradio-detected galaxies have an X-ray nuclear counterpart (and viceversa). A complete census of AGNs (and supermassive black holes, SMBHs)thus requires observations, at least, in both bands. Nonetheless, thereare massive galaxies in the sample, expected to host a large SMBH (MBH ~ 108 M sun), whose nuclear emissioneludes detection despite their proximity and the depth and the spatialresolution of the available observations. Most likely this is due to anextremely low level of accretion onto the central SMBH.
| VLA Imaging of Virgo Spirals in Atomic Gas (VIVA). I. The Atlas and the H I Properties
We present the results of a new VLA H I Imaging survey of Virgogalaxies, the VLA Imaging survey of Virgo galaxies in Atomic gas (VIVA).The survey includes high-resolution H I data of 53 carefully selectedlate type galaxies (48 spirals and five irregular systems). The goal isto study environmental effects on H I gas properties of cluster galaxiesto understand which physical mechanisms affect galaxy evolution indifferent density regions, and to establish how far out the impact ofthe cluster reaches. As a dynamically young cluster, Virgo containsexamples of galaxies experiencing a variety of environmental effects.Its nearness allows us to study each galaxy in great detail. We haveselected Virgo galaxies with a range of star formation properties in lowto high density regions (at projected distances from M87, d87 = 0.3-3.3 Mpc). Contrary to previous studies, more thanhalf of the galaxies in the sample (~60%) are fainter than 12 mag inBT . Overall, the selected galaxies represent the late typeVirgo galaxies (S0/a to Sd/Irr) down to mp lsim 14.6 fairlywell in morphological type, systemic velocity, subcluster membership, HI mass, and deficiency. The H I observations were done in C short (CS)configuration of the VLA radio telescope, with a typical spatialresolution of 15'' and a column density sensitivity of ≈3-5 ×1019 cm–2 in 3σ per 10 kms–1 channel. The survey was supplemented with data ofcomparable quality from the NRAO archive, taken in CS or Cconfiguration. In this paper, we present H I channel maps, totalintensity maps, velocity fields, velocity dispersions, global/radialprofiles, position-velocity diagrams and overlays of H I/1.4 GHzcontinuum maps on the optical images. We also present H I propertiessuch as total flux (S H I ), H I mass (M H I ),linewidths (W 20 and W 50), velocity (V H I), deficiency (def H I ), and size (D effH I and D iso H I ), and describe theH I morphology and kinematics of individual galaxies in detail. Thesurvey has revealed details of H I features that were never seen before.In this paper, we briefly discuss differences in typical H I morphologyfor galaxies in regions of different galaxy densities. We confirm thatgalaxies near the cluster core (d 87 lsim 0.5 Mpc) have H Idisks that are smaller compared to their stellar disks (D H I/D 25 < 0.5). Most of these galaxies in the corealso show gas displaced from the disk, which is either currently beingstripped or falling back after a stripping event. At intermediatedistances (d 87 ~ 1 Mpc) from the center, we find aremarkable number of galaxies with long one-sided H I tails pointingaway from M87. In a previous letter, we argue that these galaxies arerecent arrivals, falling into the Virgo core for the first time. In theoutskirts, we find many gas-rich galaxies, with gas disks extending farbeyond their optical disks. Interestingly, we also find some galaxieswith H I disks that are smaller compared to their stellar disks at largeclustercentric distances.
| Radio and spectroscopic properties of miniature radio galaxies: revealing the bulk of the radio-loud AGN population
We explore radio and spectroscopic properties of a sample of 14miniature radio galaxies, i.e. early-type core galaxies hostingradio-loud AGN of extremely low radio power, 1027-29 ergs-1 Hz-1 at 1.4 GHz. Miniature radio galaxiessmoothly extend the relationships found for the more powerful FR I radiogalaxies between emission line, optical and radio nuclear luminositiesto lower levels. However, they have a deficit of a factor of ~100 inextended radio emission with respect to that of the classical example of3CR/FR I. This is not due to their low luminosity, since we found radiogalaxies of higher radio core power, similar to those of 3CR/FR I,showing the same behavior, i.e. lacking significant extended radioemission. Such sources form the bulk of the population of radio-loud AGNin the Sloan Digital Sky Survey. At a given level of nuclear emission,one can find radio sources with an extremely wide range, a factor of⪆100, of radio power. We argue that the prevalence of sources withluminous extended radio structures in flux limited samples is due to aselection bias, since the inclusion of such objects is highly favored.The most studied catalogues of radio galaxies are thus composed by theminority of radio-loud AGN that meet the physical conditions required toform extended radio sources, while the bulk of the population isvirtually unexplored.Based on observations made with the Italian Telescopio Nazionale Galileooperated on the island of La Palma by the Centro Galileo Galilei of INAF(Istituto Nazionale di Astrofisica) at the Spanish Observatorio delRoque del los Muchachos of the Instituto de Astrofisica de Canarias.
| The First Generation of Virgo Cluster Dwarf Elliptical Galaxies?
In the light of the question whether most early-type dwarf (dE) galaxiesin clusters formed through infall and transformation of late-typeprogenitors, we search for an imprint of such an infall history in theoldest, most centrally concentrated dE subclass of the Virgo cluster:the nucleated dEs that show no signatures of disks or central residualstar formation. We select dEs in a (projected) region around the centralelliptical galaxies, and subdivide them by their line-of-sight velocityinto fast-moving and slow-moving ones. These subsamples turn out to havesignificantly different shapes: while the fast dEs are relatively flatobjects, the slow dEs are nearly round. Likewise, when subdividing thecentral dEs by their projected axial ratio into flat and round ones,their distributions of line-of-sight velocities differ significantly:the flat dEs have a broad, possibly two-peaked distribution, whereas theround dEs show a narrow single peak. We conclude that the round dEsprobably are on circularized orbits, while the flat dEs are still onmore eccentric or radial orbits typical for an infalling population. Inthis picture, the round dEs would have resided in the cluster alreadyfor a long time, or would even be a cluster-born species, explainingtheir nearly circular orbits. They would thus be the first generation ofVirgo cluster dEs. Their shape could be caused by dynamical heatingthrough repeated tidal interactions. Further investigations throughstellar population measurements and studies of simulated galaxy clusterswould be desirable to obtain definite conclusions on their origin.
| The Fundamental Plane of Accretion onto Black Holes with Dynamical Masses
Black hole accretion and jet production are areas of intensive study inastrophysics. Recent work has found a relation between radio luminosity,X-ray luminosity, and black hole mass. With the assumption that radioand X-ray luminosities are suitable proxies for jet power and accretionpower, respectively, a broad fundamental connection between accretionand jet production is implied. In an effort to refine these links andenhance their power, we have explored the above relations exclusivelyamong black holes with direct, dynamical mass-measurements. Thisapproach not only eliminates systematic errors incurred through the useof secondary mass measurements, but also effectively restricts the rangeof distances considered to a volume-limited sample. Further, we haveexclusively used archival data from the Chandra X-ray Observatory tobest isolate nuclear sources. We find log LR = (4.80 ±0.24) + (0.78 ± 0.27)log M BH + (0.67 ±0.12)log LX , in broad agreement with prior efforts. Owing tothe nature of our sample, the plane can be turned into an effective masspredictor. When the full sample is considered, masses are predicted lessaccurately than with the well-known M-σ relation. If obscuredactive galactic nuclei are excluded, the plane is potentially a betterpredictor than other scaling measures.
| X-ray Isophotes in a Rapidly Rotating Elliptical Galaxy: Evidence of Inflowing Gas
We describe two-dimensional gasdynamical computations of the X-rayemitting gas in the rotating elliptical galaxy NGC 4649 that indicate aninflow of ~1 M sun yr–1 at every radius.Such a large instantaneous inflow cannot have persisted over a Hubbletime. The central constant-entropy temperature peak recently observed inthe innermost 150 pc is explained by compressive heating as gas flowstoward the central massive black hole. Since the cooling time of thisgas is only a few million years, NGC 4649 provides the most acutelyconcentrated known example of the cooling flow problem in which thetime-integrated apparent mass that has flowed into the galactic coreexceeds the total mass observed there. This paradox can be resolved byintermittent outflows of energy or mass driven by accretion energyreleased near the black hole. Inflowing gas is also required atintermediate kpc radii to explain the ellipticity of X-ray isophotes dueto spin-up by mass ejected by stars that rotate with the galaxy and toexplain local density and temperature profiles. We provide evidence thatmany luminous elliptical galaxies undergo similar inflow spin-up. Asmall turbulent viscosity is required in NGC 4649 to avoid forming largeX-ray luminous disks that are not observed, but the turbulent pressureis small and does not interfere with mass determinations that assumehydrostatic equilibrium.
| A Spitzer Unbiased Ultradeep Spectroscopic Survey
We carried out an unbiased, spectroscopic survey using thelow-resolution module of the infrared spectrograph (IRS) onboard Spitzertargeting two 2.6 square arcminute regions in the GOODS-North field. TheIRS was used in a spectral mapping mode with 5 hr of effectiveintegration time per pixel. One region was covered between 14 and 21μm and the other between 20 and 35 μm. We extracted spectra for 45sources. About 84% of the sources have reported detections by GOODS at24 μm, with a median f ν(24 μm) ~ 100 μJy. Allbut one source are detected in all four IRAC bands, 3.6 to 8 μm. Weuse a new cross-correlation technique to measure redshifts and estimateIRS spectral types; this was successful for ~60% of the spectra.Fourteen sources show significant polycyclic aromatic hydrocarbonemission, four mostly SiO absorption, eight present mixed spectralsignatures (low PAH and/or SiO) and two show a single line in emission.For the remaining 17, no spectral features were detected. Redshiftsrange from z ~ 0.2 to z ~ 2.2, with a median of 1. IR luminosities areroughly estimated from 24 μm flux densities, and have median valuesof 2.2 × 1011 L sun and 7.5 ×1011 L sun at z ~ 1 and z ~ 2, respectively. Thissample has fewer active galactic nuclei than previous faint samplesobserved with the IRS, which we attribute to the fainter luminositiesreached here.
| Globular cluster system erosion in elliptical galaxies
Context: We analyse data of 8 elliptical galaxies to study thedifference between the radial distributions of their globular clustersystems (GCSs) and their galactic stellar component. In all galaxiesstudied, the GCS density profile is significantly flatter towards thegalactic centre than that of the stars. Aims: A flatter profileof the radial distribution of the GCS with respect to that of thegalactic stellar component is a difference with astrophysical relevance.A quantitative comparative analysis of the profiles may provide insightinto both galaxy and globular cluster formation and evolution. If thedifference is caused by erosion of the GCS, the missing GCs in thegalactic central region may have merged around the galactic centre andformed, or at least increased in mass, the galactic nucleus.Observational support to this are the correlations between the galaxyintegrated absolute magnitude and the number of globular clusters lostand that between the central massive black hole mass and the total massof globular clusters lost. Methods: We fitted both the stellarand globular cluster system radial profiles of a set of galaxiesobserved at high resolution. We found that the GCS profile is lesssharply peaked at the galactic centre than the stellar one. Assumingthat this difference is caused by GCS evolution, starting from a radialdistribution initially indistinguishable from that of stars, we canevaluate by a simple normalization procedure the number (and mass) ofGCs that have “disappeared”. Results: The number ofmissing globular clusters is significant, ranging from 21% to 71% oftheir initial population abundance in the eight galaxies examined. Thecorresponding mass lost to the central galactic region is (for everygalaxy of the sample) in the 2.77 × 10^7-1.58 ×109 M_ȯ interval. All the transported mass towards thecentral galactic regions have had probably an important effect on theinnermost galactic zone, including its violent transient activity (AGN)and local massive black hole formation and growth.
| An X-ray view of 82 LINERs with Chandra and XMM-Newton data
We present the results of a homogeneous X-ray analysis for 82 nearbylow-ionisation, narrow emission-line regions (LINERs) selected from thecatalogue of Carrillo et al. (1999, Rev. Mex. Astron. Astrofis., 35,187). All sources have available Chandra (68 sources) and/or XMM-Newton(55 sources) observations. This is the largest sample of LINERs withX-ray spectral data (60 out of the 82 objects), and it significantlyimproves our previous analysis based on Chandra data for 51 LINERs(Gonzalez-Martin et al. 2006b, A&A, 460, 45). It both increases thesample size and adds XMM-Newton data. New models permit the inclusion ofdouble absorbers in the spectral fits. Nuclear X-ray morphology isinferred from the compactness of detected nuclear sources in the hardband (4.5-8.0 keV). Sixty per cent of the sample shows a compact nuclearsource and are classified as active galactic nucleus (AGN) candidates.The spectral analysis indicates that best fits involve a compositemodel: 1) absorbed primary continuum and 2) soft spectrum below 2 keVdescribed by an absorbed scatterer and/or a thermal component. Theresulting median spectral parameters and their standard deviations are<Γ> = 2.11 ± 0.52, < kT> = 0.54 ± 0.30keV, < log(NH1) > } = 21.32 {± 0.71 and < log(NH2)> }= 21.93 {± 1.36. We complement our X-ray results with an analysisof HST optical images and literature data on emission lines, radiocompactness, and stellar population. After adding all thesemultiwavelength data, we conclude that evidence supports the AGN natureof their nuclear engine for 80% of the sample (66 out of 82 objects).Tables 1 to 15, and Appendices are only available in electronic form athttp://www.aanda.org
| Strategies for spectroscopy on extremely large telescopes - III. Remapping switched fibre systems
We explore the use of remapping techniques to improve the efficiency ofhighly multiplexed fibre systems for astronomical spectroscopy. This isparticularly important for the implementation of diverse fieldspectroscopy (DFS) using highly multiplexed monolithic fibre systems(MFS). DFS allows arbitrary distributions of target regions to beaddressed to optimize observing efficiency when observing complex,clumpy structures such as protoclusters which will be increasinglyaccessible to extremely large telescopes. We show how the adoption ofvarious types of remapping between the input and output of an MFS canallow contiguous regions of spatial elements to be selected using onlysimple switch arrays. Finally, we show how this compares in efficiencywith integral-field and multi-object spectroscopy by simulations usingartificial and real catalogues of objects. With the adoption of thesemapping strategies, DFS outperforms other techniques when addressing arange of realistic target distributions. These techniques are alsoapplicable to biomedical science and were in fact inspired by it.
| The Herschel Reference Survey
The Herschel Reference Survey is a Herschel guaranteed time key projectand will be a benchmark study of dust in the nearby universe. The surveywill complement a number of other Herschel key projects including largecosmological surveys that trace dust in the distant universe. We willuse Herschel to produce images of a statistically-complete sample of 323galaxies at 250, 350, and 500 ?m. The sample is volume-limited,containing sources with distances between 15 and 25 Mpc and flux limitsin the band to minimize the selection effects associated with dust andwith young high-mass stars and to introduce a selection in stellar mass.The sample spans the whole range of morphological types (ellipticals tolate-type spirals) and environments (from the field to the center of theVirgo Cluster) and as such will be useful for other purposes than ourown. We plan to use the survey to investigate (i) the dust content ofgalaxies as a function of Hubble type, stellar mass, and environment;(ii) the connection between the dust content and composition and theother phases of the interstellar medium; and (iii) the origin andevolution of dust in galaxies. In this article, we describe the goals ofthe survey, the details of the sample and some of the auxiliaryobserving programs that we have started to collect complementary data.We also use the available multifrequency data to carry out an analysisof the statistical properties of the sample.
| The anticorrelation between the hard X-ray photon index and the Eddington ratio in low-luminosity active galactic nuclei
We find a significant anticorrelation between the hard X-ray photonindex Γ and the Eddington ratio Lbol/LEddfor a sample of low-ionization nuclear emission-line regions and localSeyfert galaxies, compiled from literature with Chandra or XMM-Newtonobservations. This result is in contrast with the positive correlationfound in luminous active galactic nuclei (AGN), while it is similar tothat of X-ray binaries (XRBs) in the low/hard state. Our result isqualitatively consistent with the spectra produced fromadvection-dominated accretion flows (ADAFs). It implies that the X-rayemission of low-luminosity active galactic nuclei (LLAGN) may originatefrom the Comptonization process in ADAF, and the accretion process inLLAGN may be similar to that of XRBs in the low/hard state, which isdifferent from that in luminous AGN.
| The SAURON project - XIII. SAURON-GALEX study of early-type galaxies: the ultraviolet colour-magnitude relations and Fundamental Planes
We present Galaxy Evolution Explorer far-ultraviolet (FUV) andnear-ultraviolet (NUV) imaging of 34 nearby early-type galaxies from theSAURON representative sample of 48 E/S0 galaxies, all of which haveground-based optical imaging from the MDM Observatory. The surfacebrightness profiles of nine galaxies (~26 per cent) show regions withblue UV-optical colours suggesting RSF. Five of these (~15 per cent)show blue integrated UV-optical colours that set them aside in the NUVintegrated colour-magnitude relation. These are objects with eitherexceptionally intense and localized NUV fluxes or blue UV-opticalcolours throughout. They also have other properties confirming they havehad RSF, in particular Hβ absorption higher than expected for aquiescent population and a higher CO detection rate. This suggests thatresidual star formation is more common in early-type galaxies than weare used to believe. NUV blue galaxies are generally drawn from thelower stellar velocity dispersion (σe <200kms-1) and thus lower dynamical mass part of the sample.We have also constructed the first UV Fundamental Planes and show thatNUV blue galaxies bias the slopes and increase the scatters. If they areeliminated, the fits get closer to expectations from the virial theorem.Although our analysis is based on a limited sample, it seems that adominant fraction of the tilt and scatter of the UV Fundamental Planesis due to the presence of young stars in preferentially low-massearly-type galaxies. Interestingly, the UV-optical radial colourprofiles reveal a variety of behaviours, with many galaxies showingsigns of RSF, a central UV-upturn phenomenon, smooth but large-scale ageand metallicity gradients and in many cases a combination of these. Inaddition, FUV-NUV and FUV-V colours even bluer than those normallyassociated with UV-upturn galaxies are observed at the centre of somequiescent galaxies. Four out of the five UV-upturn galaxies are slowrotators. These objects should thus pose interesting challenges tostellar evolutionary models of the UV upturn.
| The SAURON Project - XIV. No escape from Vesc: a global and local parameter in early-type galaxy evolution
We present the results of an investigation of the local escape velocity(Vesc) - line strength index relationship for 48 early-typegalaxies from the SAURON sample, the first such study based on a largesample of galaxies with both detailed integral field observations andextensive dynamical modelling. Values of Vesc are computedusing multi-Gaussian expansion (MGE) photometric fitting andaxisymmetric, anisotropic Jeans' dynamical modelling simultaneously onHubble Space Telescope and ground-based images. We determine linestrengths and escape velocities at multiple radii within each galaxy,allowing an investigation of the correlation within individual galaxiesas well as amongst galaxies. We find a tight correlation betweenVesc and the line-strength indices. For Mgb, we find thatthis correlation exists not only between different galaxies but alsoinside individual galaxies - it is both a local and global correlation.The Mgb-Vesc relation has the form: log(Mgb/4Å) = (0.32+/- 0.03) log(Vesc/500km s-1) - (0.031 +/- 0.007)with an rms scatter σ = 0.033. The relation within individualgalaxies has the same slope and offset as the global relation to a goodlevel of agreement, though there is significant intrinsic scatter in thelocal gradients. We transform our line strength index measurements tothe single stellar population (SSP) equivalent ages (t), metallicity([Z/H]) and enhancement ([α/Fe]) and carry out a principalcomponent analysis of our SSP and Vesc data. We find that inthis four-dimensional parameter space the galaxies in our sample are toa good approximation confined to a plane, given by log (Vesc/500 kms -1) = 0.85 [Z/H] + 0.43 log (t/Gyr) -0.29. It is surprising that a combination of age and metallicity isconserved; this may indicate a `conspiracy' between age and metallicityor a weakness in the SSP models. How the connection between stellarpopulations and the gravitational potential, both locally and globally,is preserved as galaxies assemble hierarchically may provide animportant constraint on modelling.
| Every BCG with a Strong Radio Agn has an X-Ray Cool Core: Is the Cool Core-Noncool Core Dichotomy Too Simple?
The radio active galactic nucleus (AGN) feedback in X-ray cool cores hasbeen proposed as a crucial ingredient in the evolution of baryonicstructures. However, it has long been known that strong radio AGNs alsoexist in "noncool core" clusters, which brings up the question whetheran X-ray cool core is always required for the radio feedback. In thiswork, we present a systematic analysis of brightest cluster galaxies(BCGs) and strong radio AGNs in 152 groups and clusters from the Chandraarchive. All 69 BCGs with radio AGN more luminous than 2 ×1023 W Hz-1 at 1.4 GHz are found to haveX-ray cool cores. BCG cool cores can be divided into two classes: thelarge cool core (LCC) class and the corona class. Small coronae, easilyoverlooked at z > 0.1, can trigger strong heating episodes in groupsand clusters, long before LCCs are formed. Strong radio outburststriggered by coronae may destroy embryonic LCCs and thus provide anothermechanism to prevent the formation of LCCs. However, it is unclearwhether coronae are decoupled from the radio feedback cycles as theyhave to be largely immune to strong radio outbursts. Our sample studyalso shows the absence of groups with a luminous cool core while hostinga strong radio AGN, which is not observed in clusters. This points to agreater impact of radio heating on low-mass systems than clusters. Few L1.4 GHz > 1024 W Hz-1 radioAGNs (~16%) host an L 0.5-10 keV > 1042 ergs-1 X-ray AGN, while above these thresholds, all X-rayAGNs in BCGs are also radio AGNs. As examples of the corona class, wealso present detailed analyses of a BCG corona associated with a strongradio AGN (ESO 137-006 in A3627) and one of the faintest coronae known(NGC 4709 in the Centaurus cluster). Our results suggest that thetraditional cool core/noncool core dichotomy is too simple. A betteralternative is the cool core distribution function, with the enclosedX-ray luminosity or gas mass.
| Fitting Liner Nuclei within the Active Galactic Nucleus Family: A Matter of Obscuration?
In this paper, we study the nuclear obscuration of galaxies hosting lowionization narrow emission regions (LINERs) based on their X-ray andoptical emission. They show column densities at soft energies (0.5-2keV) mostly related to the diffuse emission around the active galacticnucleus (AGN), showing a correlation with the optical extinction. Columndensities at hard energies (2-10 keV) seem to be much higher than whatwould be expected from the optical extinction. They might be associatedwith the inner regions of the AGN, buried at optical wavelengths. Themain result of this paper is that around 50% of our LINER sample showssignatures of Compton-thickness according to the most common tracers:the X-ray spectral index, {F_{X}(2\--10\;keV)/F([\mbox{O}\,\mathsc{iii}])} ratio, and FeKα equivalent width (EW). However, the EWsof the Compton-thick LINERs are significantly lower than in theCompton-thick Seyferts (sime200 eV against >=500 eV), suggesting thatthe 2-10 keV emission is dominated by electron scattering of theotherwise invisible AGN, or by emission from shocked gas associated withstar formation rather than by reflection from the inner wall of thetorus. However, no clear relation seems to exist between galaxies withoptical dust lanes and X-ray classified Compton-thick objects. This maysuggest that Compton-thick sources should be related to absorbingmaterial located at the very inner regions of the AGN, maybe in theputative dusty torus. Larger black hole masses and lower Eddingtonratios than Seyfert galaxies have been found. This effect can be betterattributed to LINER nuclei being hosted by earlier morphological typesthan Seyfert nuclei. However, it has to be noted that, once a propercorrection to the X-ray luminosity is applied, LINERs show Eddingtonratios overlapping those of type 2 Seyferts. We speculate with apossible scenario for LINER nuclei: an inner obscuring matter similar tothat of type 2 Seyfert, and an external obscuring matter responsible forthe optical extinction. Compton-thick sources appear to be more commonamong LINERs than Seyferts.
| A Hertzsprung-Russell-like Diagram for Galaxies: The M • Versus M Gσ2 Relation
We show that the relation between the mass of supermassive black holeslocated in the center of the host galaxies and the kinetic energy ofrandom motions of the corresponding bulges is a useful tool to study theevolution of galaxies. In the form \log_{10}(M_{\bullet })=b+m\log_{10}(M_G\sigma^2/c^2), the best-fitting results for a sample of 64galaxies of various morphological types are the slope m = 0.80 ±0.03 and the normalization b = 4.53 ± 0.13. We note that, inanalogy with the Hertzsprung-Russell diagram for stars, eachmorphological type of galaxy generally occupies a different area in theM •-(M Gσ2)/c 2plane. In particular, we find elliptical galaxies in the upper part ofthe line of best fit, the lenticular galaxies in the middle part, andthe late-type galaxies in the lower part, the mass of the central blackhole giving an estimate of the age, whereas the kinetic energy of thestellar bulges is directly connected with the temperature of eachgalactic system. Finally, the values of the linear correlationcoefficient, the intrinsic scatter, and the χ2 obtainedby using the M •-M Gσ2relation are better than the corresponding ones obtained from the M•-σ or the M •-M Grelation.
| Hydrostatic Gas Constraints on Supermassive Black Hole Masses: Implications for Hydrostatic Equilibrium and Dynamical Modeling in a Sample of Early-type Galaxies
We present new mass measurements for the supermassive black holes(SMBHs) in the centers of three early-type galaxies. The gas pressure inthe surrounding, hot interstellar medium (ISM) is measured throughspatially resolved spectroscopy with the Chandra X-ray Observatory,allowing the SMBH mass (M BH) to be inferred directly underthe hydrostatic approximation. This technique does not requirecalibration against other SMBH measurement methods and its accuracydepends only on the ISM being close to hydrostatic, which is supportedby the smooth X-ray isophotes of the galaxies. Combined with resultsfrom our recent study of the elliptical galaxy NGC 4649, this brings thenumber of galaxies with SMBHs measured in this way to four. Of these,three already have mass determinations from the kinematics of either thestars or a central gas disk, and hence join only a handful of galaxieswith M BH measured by more than one technique. We find goodagreement between the different methods, providing support for theassumptions implicit in both the hydrostatic and the dynamical models.The stellar mass-to-light ratios for each galaxy inferred by ourtechnique are in agreement with the predictions of stellar populationsynthesis models assuming a Kroupa initial mass function (IMF). Thisconcurrence implies that no more than ~10%-20% of the ISM pressure isnonthermal, unless there is a conspiracy between the shape of the IMFand nonthermal pressure. Finally, we compute Bondi accretion rates({\dot{M}_{bondi}}), finding that the two galaxies with the highest{\dot{M}_{bondi}} exhibit little evidence of X-ray cavities, suggestingthat the correlation with the active galactic nuclei jet power takestime to be established.
| The Bologna complete sample of nearby radio sources. II. Phase referenced observations of faint nuclear sources
Aims. To study statistical properties of different classes of sources,it is necessary to observe a sample that is free of selection effects.To do this, we initiated a project to observe a complete sample of radiogalaxies selected from the B2 Catalogue of Radio Sources and the ThirdCambridge Revised Catalogue (3CR), with no selection constraint on thenuclear properties. We named this sample “the Bologna CompleteSample” (BCS). Methods: We present new VLBI observations at 5 and1.6 GHz for 33 sources drawn from a sample not biased towardorientation. By combining these data with those in the literature,information on the parsec-scale morphology is available for a total of76 of 94 radio sources with a range in radio power and kiloparsec-scalemorphologies. Results: The fraction of two-sided sources atmilliarcsecond resolution is high (30%), compared to the fraction foundin VLBI surveys selected at centimeter wavelengths, as expected from thepredictions of unified models. The parsec-scale jets are generally foundto be straight and to line up with the kiloparsec-scale jets. A fewpeculiar sources are discussed in detail.Tables 1-4 are only available in electronic form at http://www.aanda.org
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
Каталоги и обозначения:
|
