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The Kyoto tridimensional spectrograph II
The Kyoto tridimensional spectrograph II is a multimode spectrograph. Itis so far the only spectrograph with Fabry Perot and/or integral fieldspectrograph (IFS) modes that is mounted on the Subaru Telescope. Itspixel/lenslet sampling matches Subaru’s excellent image quality.This compact spectrograph is also used at the UH 88-inch telescope.Possible merits of lenslet IFS’s are discussed.
| Gemini/GMOS spectra of globular clusters in the Virgo giant elliptical NGC 4649
NGC 4649 (M60) is one of a handful of giant Virgo ellipticals. We haveobtained Gemini/GMOS (Gemini North Multi-Object Spectrograph) spectrafor 38 globular clusters (GCs) associated with this galaxy. Applying themulti-index χ2 minimization technique of Proctor andSansom with the single stellar population models of Thomas, Maraston andKorn, we derive ages, metallicities and α-element abundanceratios. We find several young (2-3 Gyr old) supersolar metallicity GCs,while the majority are old (>10 Gyr), spanning a range ofmetallicities from solar to [Z/H]=-2. At least two of these young GCsare at large projected radii of 17-20 kpc. The galaxy itself shows noobvious signs of a recent starburst, interaction or merger. A trend ofdecreasing α-element ratio with increasing metallicity is found.
| Gemini/GMOS spectra of globular clusters in the Leo group elliptical NGC 3379
The Leo group elliptical NGC 3379 is one of the few normal ellipticalgalaxies close enough to make possible observations of resolved stellarpopulations, deep globular cluster (GC) photometry and highsignal-to-noise ratio GC spectra. We have obtained Gemini/GMOS spectrafor 22 GCs associated with NGC 3379. We derive ages, metallicities andα-element abundance ratios from simple stellar population modelsusing the recent multi-index χ2 minimization method ofProctor & Sansom. All of these GCs are found to be consistent withold ages, i.e. >~10Gyr, with a wide range of metallicities. This iscomparable to the ages and metallicities that Gregg et al. found acouple of years ago for resolved stellar populations in the outerregions of this elliptical. A trend of decreasing α-elementabundance ratio with increasing metallicity is indicated.The projected velocity dispersion of the GC system is consistent withbeing constant with radius. Non-parametric, isotropic models require asignificant increase in the mass-to-light ratio at large radii. Thisresult is in contrast to that of Romanowsky et al., who recently found adecrease in the velocity dispersion profile as determined from planetarynebulae (PN). Our constant dispersion requires a normal-sized dark halo,although without anisotropic models we cannot rigorously determine thedark halo mass.A two-sided χ2 test over all radii gives a 2σdifference between the mass profile derived from our GCs compared to thePN-derived mass model of Romanowsky et al. However, if we restrict ouranalysis to radii beyond one effective radius and test if the GCvelocity dispersion is consistently higher, we determine a > 3σdifference between the mass models, and hence we favour the conclusionthat NGC 3379 does indeed have dark matter at large radii in its halo.
| A data-driven Bayesian approach for finding young stellar populations in early-type galaxies from their ultraviolet-optical spectra
Efficient predictive models and data analysis techniques for theanalysis of photometric and spectroscopic observations of galaxies arenot only desirable, but also required, in view of the overwhelmingquantities of data becoming available. We present the results of a novelapplication of Bayesian latent variable modelling techniques, where wehave formulated a data-driven algorithm that allows one to explore thestellar populations of a large sample of galaxies from their spectra,without the application of detailed physical models. Our only assumptionis that the galaxy spectrum can be expressed as a linear superpositionof a small number of independent factors, each a spectrum of a stellarsubpopulation that cannot be individually observed. A probabilisticlatent variable architecture that explicitly encodes this assumption isthen formulated, and a rigorous Bayesian methodology is employed forsolving the inverse modelling problem from the available data. Apowerful aspect of this method is that it formulates a density model ofthe spectra, based on which we can handle observational errors. Further,we can recover missing data both from the original set of spectra whichmight have incomplete spectral coverage of each galaxy, or frompreviously unseen spectra of the same kind.We apply this method to a sample of 21 ultraviolet-optical spectra ofwell-studied early-type galaxies, for which we also derive detailedphysical models of star formation history (i.e. age, metallicity andrelative mass fraction of the component stellar populations). We alsoapply it to synthetic spectra made up of two stellar populations,spanning a large range of parameters. We apply four different datamodels, starting from a formulation of principal component analysis(PCA), which has been widely used. We explore alternative factor models,relaxing the physically unrealistic assumption of Gaussian factors, aswell as constraining the possibility of negative flux values that areallowed in PCA, and show that other models perform equally well orbetter, while yielding more physically acceptable results. Inparticular, the more physically motivated assumptions of our rectifiedfactor analysis enable it to perform better than PCA, and to recoverphysically meaningful results.We find that our data-driven Bayesian modelling allows us to identifythose early-type galaxies that contain a significant stellar populationthat is <~1-Gyr old. This experiment also concludes that our sampleof early-type spectra showed no evidence of more than two major stellarpopulations differing significantly in age and metallicity. This methodwill help us to search for such young populations in a large ensemble ofspectra of early-type galaxies, without fitting detailed models, andthereby to study the underlying physical processes governing theformation and evolution of early-type galaxies, particularly thoseleading to the suppression of star formation in dense environments. Inparticular, this method would be a very useful tool for automaticallydiscovering various interesting subclasses of galaxies, for example,post-starburst or E+A galaxies.
| Variability Study of Seyfert 2 Galaxies with XMM-Newton
We present the results of timing analysis of XMM-Newton observations ofSeyfert 2 galaxies in order to search for differences in the meanproperties of Seyfert 1 galaxies and Seyfert 2 galaxies. We selected 13Seyfert 2 galaxies from the XMM-Newton archive that have hard X-raycomponents in their spectra and calculated the excess variance(σ2rms) in the 2-10 keV band. We found thatsix Seyfert 2 galaxies (3C 98, IRAS 05189-2524, MCG -5-23-16, NGC 6300,UGC 4203, and PKS 1814-637) have buried luminous nuclei and that thenuclei have timing properties similar to those of Seyfert 1 nuclei. Thisindicates that these galaxies are candidates for having buried Seyfert 1nuclei as expected by the unified Seyfert model. The first five galaxiesshow significant time variability. The amplitude of the time variabilityof IRAS 05189-2524 is similar to that of narrow-line Seyfert 1 galaxies.In contrast, the amplitude of variability of the seven other galaxies isquite small, much smaller than that of Seyfert 1 galaxies with similarX-ray luminosity. The lack of short time variability in these objects isexplained by the dominance of the reflection component in three galaxies(Mrk 3, Mrk 463, and NGC 7582), and by the presence of very massiveblack holes and an inferred low accretion rate in the other threegalaxies (NGC 1052, NGC 4507, and NGC 7172). For Mrk 348, thesignificant time variability that is expected based on the estimate ofthe central black hole mass was not detected.
| Spatially Resolved Narrow-Line Region Kinematics in Active Galactic Nuclei
We have analyzed Hubble Space Telescope spectroscopy of 24 nearby activegalactic nuclei (AGNs) to investigate spatially resolved gas kinematicsin the narrow-line region (NLR). These observations effectively isolatethe nuclear line profiles on less than 100 pc scales and are used toinvestigate the origin of the substantial scatter between the widths ofstrong NLR lines and the stellar velocity dispersion σ*of the host galaxy, a quantity that relates with substantially lessscatter to the mass of the central, supermassive black hole and moregenerally characterize variations in the NLR velocity field with radius.We find that line widths measured with STIS at a range of spatial scalessystematically underestimate both σ* and the line widthmeasured from ground-based observations, although they do havecomparably large scatter to the relation between ground-based NLR linewidth and σ*. There are no obvious trends in theresiduals when compared with a range of host galaxy and nuclearproperties. The widths and asymmetries of [O III] λ5007 and [SII] λλ6716, 6731 as a function of radius exhibit a widerange of behavior. Some of the most common phenomena are substantialwidth increases from the STIS to the large-scale, ground-based apertureand almost no change in line profile between the unresolved nuclearspectrum and ground-based measurements. We identify asymmetries in asurprisingly large fraction of low-ionization [S II] line profiles andseveral examples of substantial red asymmetries in both [O III] and [SII]. These results underscore the complexity of the circumnuclearmaterial that constitutes the NLR and suggest that the scatter in theNLR width and σ* correlation cannot be substantiallyreduced with a simple set of empirical relations.
| X-ray and radio emission in the nuclei of radio galaxies and the disk-jet connection
It appears that relativistic jets are produced by accreting black holes.We might therefore expect that events observed in jets, such as theappearance of bright radio knots moving at apparent superluminal speeds,originate as disturbances in the central engine. This is observed in anumber of compact X-ray binary systems in our Galaxy, manifested aschanges in the X-ray emission state followed by superluminal ejections.The author and collaborators have detected somewhat similar events inthe radio galaxies 3C 120 (type Fanaroff-Riley I) and 3C 111 (FR II).The data both confirm the disk-jet connection in accreting supermassiveblack holes and provide constraints on the structure of the jet betweenthe central engine and the millimeter-wave core.
| Neutral hydrogen in radio galaxies: Results from nearby, importance for far away
The study of neutral hydrogen emission and absorption in radio galaxiesis giving new and important insights on a variety of phenomena observedin these objects. Such observations are helping to understand the originof the host galaxy, the effects of the interaction between the radio jetand the ISM, the presence of fast gaseous outflows as well asjet-induced star formation. Recent results obtained on these phenomenaare summarized in this review. Although the {H I observationsconcentrate on nearby radio galaxies, the results also have relevancefor the high-z objects as all these phenomena are important, and likelyeven more common, in high-redshift radio sources.
| A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei
Seyfert galaxies commonly host compact jets spanning 10-100 pc scales,but larger structures are resolved out in long-baseline aperturesynthesis surveys. Previous, targeted studies showed thatkiloparsec-scale radio structures (KSRs) may be a common feature ofSeyfert and LINER galaxies, and the origin of KSRs may be starbursts oractive galactic nuclei (AGNs). We report a new Very Large Array surveyof a complete sample of Seyfert and LINER galaxies. Out of all of thesurveyed radio-quiet sources, we find that 44% (19 out of 43) showextended radio structures at least 1 kpc in total extent that do notmatch the morphology of the disk or its associated star-forming regions.The detection rate is a lower limit owing to the combined effects ofprojection and resolution. The infrared colors of the KSR host galaxiesare unremarkable compared to other Seyfert galaxies, and the large-scaleoutflows orient randomly with respect to the host galaxy axes. The KSRSeyfert galaxies instead stand out by deviating significantly from thefar-infrared-radio correlation for star-forming galaxies, with tendencytoward radio excess, and they are more likely to have a relativelyluminous, compact radio source in the nucleus; these results argue thatKSRs are powered by the AGNs rather than starbursts. The high detectionrate indicates that Seyfert galaxies generate radio outflows over asignificant fraction of their lifetime, which is much longer than thedynamical timescale of an AGN-powered jet but is comparable instead tothe buoyancy timescale. The likely explanation is that the KSRsoriginate from jet plasma that has been decelerated by interaction withthe nuclear interstellar medium (ISM). Based on a simple ram pressureargument, the kinetic power of the jet on kiloparsec scales is about 3orders of magnitude weaker than the power of the jet on 10-100 pcscales. This result is consistent with the interaction model, in whichcase virtually all of the jet power must be lost to the ISM within theinner kiloparsec.
| Star Formation Histories of Nearby Elliptical Galaxies. II. Merger Remnant Sample
This work presents high signal-to-noise spectroscopic observations of asample of six suspected merger remnants, selected primarily on the basisof H I tidal debris detections. Single stellar population analysis ofthese galaxies indicates that their ages, metallicities, andα-enhancement ratios are consistent with those of a representativesample of nearby elliptical galaxies. The expected stellar population ofa recent merger remnant, a young age combined with low [α/Fe], isnot seen in any H I-selected galaxy. However, one galaxy (NGC 2534) isfound to deviate from the Z-plane in the sense expected for a mergerremnant. Another galaxy (NGC 7332), selected by other criteria, bestmatches the merger remnant expectations.
| MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. II. First-Epoch 15 GHz Circular Polarization Results
We report first-epoch circular polarization results for 133 activegalactic nuclei in the MOJAVE program to monitor the structure andpolarization of a flux-limited sample of extragalactic radio jets withthe VLBA at 15 GHz. We found strong circular polarization (>=0.3%) inapproximately 15% of our sample. The circular polarization was usuallyassociated with jet cores; however, we did find a few strong jetcomponents to be circularly polarized. The levels of circularpolarization were typically in the range of 0.3%-0.5% of the localStokes I value. We found no strong correlations between fractionalcircular polarization of jet cores and source type, redshift, EGRETdetections, linear polarization, or other observed parsec-scale jetproperties. There were differences between the circular-to-linearpolarization ratios of two nearby galaxies versus more distant quasarsand BL Lac objects. We suggest this is because the more distant sourceshave either (1) less depolarization of their linear polarization, and/or(2) poorer effective linear resolution, and therefore, their VLBA coresapparently contain a larger amount of linearly polarized jet emission.The jet of 3C 84 shows a complex circular polarization structure,similar to observations by Homan & Wardle 5 years earlier; however,much of the circular polarization seems to have moved, consistent with aproper motion of 0.06c. The jet of 3C 273 also has several circularlypolarized components, and we find that their fractional circularpolarization decreases with distance from the core.
| Extragalactic H_2O masers and X-ray absorbing column densities
Having conducted a search for the λ 1.3 cm (22 GHz) water vaporline towards galaxies with nuclear activity, large nuclear columndensities or high infrared luminosities, we present H2O spectra for NGC2273, UGC 5101, and NGC 3393 with isotropic luminosities of 7, 1500, and400 Lȯ. The H2O maser in UGC 5101 is by far the mostluminous yet found in an ultraluminous infrared galaxy. NGC 3393 revealsthe classic spectrum of a "disk maser", represented by three distinctgroups of Doppler components. As in all other known cases except NGC4258, the rotation velocity of the putative masing disk is well below1000 km s-1. Based on the literature and archive data, X-rayabsorbing column densities are compiled for the 64 galaxies withreported maser sources beyond the Magellanic Clouds. For NGC 2782 andNGC 5728, we present Chandra archive data that indicate the presence ofan active galactic nucleus in both galaxies. Modeling the hard nuclearX-ray emission, NGC 2782 is best fit by a high energy reflectionspectrum with NH 1024 cm-2. ForNGC 5728, partial absorption with a power law spectrum indicatesNH 8 × 1023 cm-2. Thecorrelation between absorbing column and H2O emission is analyzed. Thereis a striking difference between kilo- and megamasers with megamasersbeing associated with higher column densities. All kilomasers (L_H_2O< 10 Lȯ) except NGC 2273 and NGC 5194 areCompton-thin, i.e. their absorbing columns are <1024cm-2. Among the H{2}O megamasers, 50% arise fromCompton-thick and 85% from heavily obscured (>1023cm-2) active galactic nuclei. These values are not larger butconsistent with those from samples of Seyfert 2 galaxies not selected onthe basis of maser emission. The similarity in column densities can beexplained by small deviations in position between maser spots andnuclear X-ray source and a high degree of clumpiness in thecircumnuclear interstellar medium.
| Peculiarities and populations in elliptical galaxies. III. Dating the last star formation event
Using 6 colours and 4 Lick line-indices we derive two-component modelsof the populations of ellipticals, involving a "primary" and a"juvenile" population. The first component is defined by the regressionsof indices against the central velocity dispersion found in Papers I andII for the {Nop} sample of non-peculiar objects. The second one isapproximated by an SSP, and the modeling derives its age A, metallicityZ and fractional V-luminosity q_V, the fractional mass qMbeing found therefrom. The model is designed for "blueish" peculiargalaxies, i.e. the {Pec} sample and NGC 2865 family in the terminologyof Paper I. The morphological peculiarities and the population anomalyare then believed to involve the same event, i.e. a merger plusstarburst. It is possible to improve the models in a few cases byintroducing diffuse dust (as suggested by far IR data), and/or by takinginto account the fact that Lick- and colour indices do not relate toidentical galaxy volumes. In most of the cases, the mass ratio of youngstars qM seems too small for the product of a recent majormerger: the events under consideration might be minor mergers bringing"the final touch" to the build-up of the structure of the E-type object.The same modeling has been successfully applied to blueish galaxies ofthe {Nop} sample, without morphological peculiarities however, tosupport the occurence of a distinct perturbing event. A few reddishobjects of the {Pec} sample (NGC 3923 family) and of the {Nop} sampleare also modeled, in terms of an excess of high metallicity stars, ordiffuse dust, or both, but the results are inconclusive.
| Continuum emission in NGC 1068 and NGC 3147: indications for a turnover in the core spectra
We present new interferometric observations of the continuum emission atmm wavelengths in the Seyfert galaxies NGC 1068 and NGC 3147. Three mmcontinuum peaks are detected in NGC 1068, one centered on the core, oneassociated with the jet and the third one with the counter-jet. This isthe first significant detection of the radio jet and counter-jet at mmwavelengths in NGC 1068. While the fluxes of the jet components agreewith a steep spectral index extrapolated from cm-wavelengths, the corefluxes indicate a turnover of the inverted cm- into a steep mm-spectrumat roughly ~50 GHz which is most likely caused by electron-scatteredsynchrotron emission. As in NGC 1068, the spectrum of the pointlikecontinuum source in NGC 3147 also shows a turnover between cm andmm-wavelengths at ~25 GHz resulting from synchrotron self-absorptiondifferent to NGC 1068. This strongly resembles the spectrum of Sgr A*,the weakly active nucleus of our own galaxy, and M 81*, a link betweenSgr A* and Seyfert galaxies in terms of activity sequence, which maydisplay a similar turnover.
| A hard X-ray view of giga-hertz peaked spectrum radio galaxies
We present the first broadband X-ray observations of four Giga-HertzPeaked Spectrum (GPS) radio galaxies at redshift 1 performed byChandra and XMM-Newton. These observations more than double the numberof members of this class with measured spectra in hard (E > 2 keV)X-rays. All sources were detected. Their radio-to-X-ray spectral energydistributions are similar, except for PKS 0941-080, which is X-rayunder-luminous by about two orders of magnitude. The comparison betweenthe full sample of GPS galaxies with measurements in hard X-rays and acontrol sample of radio galaxies rules out intrinsic X-ray weakness ascausing a lower detection rate of GPS sources in X-ray surveys. Four outof seven GPS galaxies exhibit high X-ray column densities, whereas forthe remaining three this measurement is hampered by the poor spectralstatistics. Bearing in mind the low number statistics in both the GPSand the control sample, the average column density measured in GPSgalaxies is larger than in FR I or Broad Line Region FR II radiogalaxies, but consistent with that measured in High-Excitation FR IIgalaxies. This leads to a location the absorbing gas in an obscuring"torus", which prevents us from observing the nuclear region alonglines-of-sight perpendicular to the radio axis. This interpretation issupported by the discovery of rapid (timescale ~ 103 s) X-rayvariability in the GPS galaxy COINSJ0029+3456, and by an almostorder-of-magnitude difference between the HI column density measured inradio and X-rays in PKS 0500+019.
| Constraints on evolutionary properties of GHz Peaked Spectrum galaxies
We have used the available samples of Gigahertz Peaked Spectrum (GPS)galaxies to investigate their evolution properties in the framework ofthe "youth" scenario. Care was taken to properly allow for the differentselection criteria used to define the samples. We find that the observedredshift and peak frequency distributions can be satisfactorilyaccounted for in terms of simple luminosity evolution of individualsources, along the lines discussed by Fanti et al. (1995, A&A, 302,317) and Begelman (1996, in Proc. Cygnus A, Study of Radio Galaxy; 1999,in Proc. of KNAW Colloq.), although the derived parameter values havelarge uncertainties due to ambiguities in the selection of GPS sourcesand to the incompleteness of redshift measurements. However the simplestself-similar model, whereby the evolution is controlled only by theradial profile of the density of the ambient medium is not good enoughand one additional parameter needs to be introduced. The fit requires adecrease of the emitted power and of the peak luminosity with source ageor with decreasing peak frequency, at variance with the Snellen et al.(2000, MNRAS, 319, 445) model. On the other hand, our analysis confirmsthe rather flat slope of the luminosity function, found by Snellen etal. (2000) who also report indications of a high luminosity break, notrequired by the data sets we have used. Our results suggest that the GPSgalaxies are the precursors of extended radio sources with luminositiesbelow the break of the luminosity function. No cosmological evolution ofthe GPS galaxy population is required by presently available data.
| High-frequency radio observations of the Kühr sample and the epoch-dependent luminosity function of flat-spectrum quasars
We discuss our ATCA 18.5 and 22 GHz flux density measurements ofSouthern extragalactic sources in the complete 5 GHz sample of Kühret al. (1981, A&AS, 45, 367). The high frequency (5-18.5 GHz)spectral indices of steep-spectrum sources for which we have 18.5 GHzdata (66% of the complete sample) are systematically steeper than thelow frequency (2.7-5 GHz) ones, with median α^52.7 =0.76, median α18.55 = 1.18(Sν∝ ν-α), and median steepeningΔα = 0.32, and there is evidence of an anti-correlation ofΔα18.55 with luminosity. Thecompleteness of 18.5 GHz data is much higher (89%) for flat-spectrumsources (mostly quasars), which also exhibit a spectral steepening:median α^52.7=-0.14, medianα18.55=0.16 (Sν∝ν-α), and median Δα = 0.19. Takingadvantage of the almost complete redshift information on flat-spectrumquasars, we have estimated their 5 GHz luminosity function in severalredshift bins. The results confirm that their radio luminosity densitypeaks at z_peak ≃ 2.5 but do not provide evidence for deviationsfrom pure luminosity evolution as hinted at by other data sets. Acomparison of our 22 GHz flux densities with WMAP K-band data forflat-spectrum sources suggests that WMAP flux densities may be low by amedian factor of ≃1.2. The extrapolations of 5 GHz counts andluminosity functions of flat-spectrum radio quasars using the observeddistribution of the 5-18.5 GHz spectral indices match those deriveddirectly from WMAP data, indicating that the high frequency WMAP surveydoes not detect any large population of FSRQs with anomalous spectra.
| Nearby early-type galaxies with ionized gas. II. Line-strength indices for 18 additional galaxies
We previously presented a data-set of line-strength indices for 50early-type galaxies in the nearby Universe. The galaxy sample is biasedtoward galaxies showing emission lines, located in environmentscorresponding to a broad range of local galaxy densities, althoughpredominantly in low density environments. The present addendum enlargesthe above data-set of line-strength indices by analyzing 18 additionalearly-type galaxies (three galaxies, NGC 3607, NGC 5077 and NGC 5898were presented in the previous set). We measured 25 line-strengthindices, defined by the Lick IDS "standard" system (Trager et al. 1998,ApJS, 116, 1; Worthey & Ottaviani 1997, ApJS, 111, 377), for 7luminosity weighted apertures and 4 gradients of each galaxy. Thisaddendum presents the line-strength data-set and compares it with theavailable data in the literature.
| Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black holeresearch, as seen from a purely observational standpoint. Since theearly ‘90s, rapid technological advances, most notably the launchof the Hubble Space Telescope, the commissioning of the VLBA andimprovements in near-infrared speckle imaging techniques, have not onlygiven us incontrovertible proof of the existence of supermassive blackholes, but have unveiled fundamental connections between the mass of thecentral singularity and the global properties of the host galaxy. It isthanks to these observations that we are now, for the first time, in aposition to understand the origin, evolution and cosmic relevance ofthese fascinating objects.
| Water-Vapor Maser Survey for Active Galactic Nuclei: A Megamaser in NGC 6926
We made a survey of water-vapor maser emission for 93 AGNs with theNobeyama 45-m and Mopra 22-m telescopes from 1999 to 2002. A megamaserwas detected in a Seyfert 2 galaxy, NGC 6926, at a distance of 80Mpc, in2002 June. [Greenhill et al. (2003a) have also reported a detection ofthe megamaser at the close date.] The peak flux density was 110mJy, andthe total isotropic luminosity was 340 Lȯ. The masershows triply peaked spectrum, suggesting an edge-on disk. A narrow-linefeature of the maser components at VLSR = 6001 kms-1 was strongly variable with a time scale of a few tens ofdays, and the variation should be of intrinsic origin. We also showed apossibility of variability of water-vapor maser emission of a megamaserpreviously detected in a Seyfert/ultraluminous FIR galaxy, NGC 6240.
| Orientation and size of the `Z' in X-shaped radio galaxies
Some X-shaped radio galaxies show a Z-symmetric morphology in the lessluminous secondary lobes. Within the scenario of a merger between twogalaxies, each hosting a supermassive black hole in its centre, thisstructure has been explained before. As the smaller galaxy spiralstowards the common centre, it releases gas to the interstellar medium ofthe larger active galaxy. The ram pressure of this streaming gas willbend the lobes of the pre-merger jet into a Z-shape. After the blackholes have merged, the jet propagates in a new direction that is alignedwith the angular momentum of the binary black hole. In this paper wedeproject the pre- and post-merger jets. Taking into account theexpected angles between the jet pairs and with the assumption that theirdirections are uncorrelated, we show that one of three possibleorientations of the jets with respect to the line of sight is morelikely than the others. This actually depends on the distance where thebending occurs. Another result of our deprojection is that the streaminggas bends the jet into a Z-shape in a range between about 30 and 100 kpcdistance to the centre of the primary galaxy. We confirm this finding bycomparing our predictions for the properties of the rotational velocityfield and its radius with observations and numerical simulations ofmerging galaxies. Thus, our results support the merger scenario asexplanation for X- and Z-shaped radio galaxies with the jet pointingalong the former axis of orbital angular momentum of the binary.
| The X-ray emission properties and the dichotomy in the central stellar cusp shapes of early-type galaxies
The Hubble Space Telescope has revealed a dichotomy in the centralsurface brightness profiles of early-type galaxies, which havesubsequently been grouped into two families: core, boxy, anisotropicsystems; and cuspy (`power-law'), discy, rotating ones. Here weinvestigate whether a dichotomy is also present in the X-ray propertiesof the two families. We consider both their total soft emission(LSX,tot), which is a measure of the galactic hot gascontent, and their nuclear hard emission (LHX,nuc), mostlycoming from Chandra observations, which is a measure of the nuclearactivity. At any optical luminosity, the highest LSX,totvalues are reached by core galaxies; this is explained by their beingthe central dominant galaxies of groups, subclusters or clusters, inmany of the logLSX,tot (ergs-1) >~ 41.5 cases.The highest LHX,nuc values, similar to those of classicalactive galactic nuclei (AGNs), in this sample are hosted only by core orintermediate galaxies; at low luminosity AGN levels, LHX,nucis independent of the central stellar profile shape. The presence ofoptical nuclei (also found by HST) is unrelated to the level ofLHX,nuc, even though the highest LHX,nuc are allassociated with optical nuclei. The implications of these findings forgalaxy evolution and accretion modalities at the present epoch arediscussed.
| Dark matter in early-type galaxies: dynamical modelling of IC 1459, IC 3370, NGC 3379 and NGC 4105
We analyse long-slit spectra of four early-type galaxies which extendfrom ~1 to 3 effective radii: IC 1459; IC 3370; NGC 3379 and NGC 4105.We have extracted the full line-of-sight velocity distribution (in thecase of NGC 3379 we also used data from the literature), which we modelusing the two-integral approach. Using two-integral modelling, we findno strong evidence for dark haloes, but the fits suggest thatthree-integral modelling is necessary. We also find that the inferredconstant mass-to-light ratio in all the four cases is typical forearly-type galaxies. Finally, we also discuss the constraints on themass-to-light ratio, which can be obtained using X-ray haloes in thecase of IC 1459, NGC 3379 and NGC 4105, and compare the estimated valueswith the predictions from the dynamical modelling.
| The XMM-Newton Needles in the Haystack Survey: the local X-ray luminosity function of `normal' galaxies
In this paper we estimate the local (z < 0.22) X-ray luminosityfunction of `normal' galaxies derived from the XMM-Newton Needles in theHaystack Survey. This is an on-going project that aims to identifyX-ray-selected normal galaxies (i.e. non-AGN dominated) in the localUniverse. We are using a total of 70 XMM-Newton fields covering an areaof 11 deg2 which overlap with the Sloan Digital Sky SurveyData Release 2. Normal galaxies are selected on the basis of theirresolved optical light profile, their low X-ray-to-optical flux ratio[log(fx/fo) < - 2] and soft X-ray colours. Wefind a total of 28 candidate normal galaxies to the 0.5-8keV band fluxlimit of ~2 × 10-15ergcm-2s-1.Optical spectra are available for most sources in our sample (82 percent). These provide additional evidence that our sources are bona fidenormal galaxies with X-ray emission coming from diffuse hot gas emissionand/or X-ray binaries rather than a supermassive black hole. 16 of ourgalaxies have narrow emission lines or a late-type spectral energydistribution (SED) while the remaining 12 present only absorption linesor an early-type SED. Combining our XMM-Newton sample with 18 local (z< 0.22) galaxies from the Chandra Deep Field North and South surveys,we construct the local X-ray luminosity function of normal galaxies.This can be represented with a Schechter form with a break atL*~ 3+1.4-1.0×1041ergs-1 and a slope of α~ 1.78 +/- 0.12.Using this luminosity function and assuming pure luminosity evolution ofthe form ~(1 +z)3.3 we estimate a contribution to the X-raybackground from normal galaxies of ~10-20 per cent (0.5-8keV). Finally,we derive, for the first time, the luminosity functions for early- andlate-type systems separately.
| Group, field and isolated early-type galaxies - II. Global trends from nuclear data
We have derived ages, metallicities and enhanced-element ratios[α/Fe] for a sample of 83 early-type galaxies essentially ingroups, the field or isolated objects. The stellar-population propertiesderived for each galaxy correspond to the nuclear re/8aperture extraction. The median age found for Es is 5.8+/-0.6 Gyr andthe average metallicity is +0.37+/-0.03 dex. For S0s, the median age is3.0+/-0.6 Gyr and [Z/H]= 0.53+/-0.04 dex. We compare the distribution ofour galaxies in the Hβ-[MgFe] diagram with Fornax galaxies. Ourelliptical galaxies are 3-4 Gyr younger than Es in the Fornax cluster.We find that the galaxies lie in a plane defined by [Z/H]= 0.99logσ0- 0.46 log(age) - 1.60, or in linear terms Z~σ0× (age) -0.5. More massive (largerσ0) and older galaxies present, on average, large[α/Fe] values, and therefore must have undergone shorterstar-formation time-scales. Comparing group against field/isolatedgalaxies, it is not clear that environment plays an important role indetermining their stellar-population history. In particular, ourisolated galaxies show ages differing by more than 8 Gyr. Finally weexplore our large spectral coverage to derive log(O/H) metallicity fromthe Hα and NIIλ6584 and compare it with model-dependent[Z/H]. We find that the O/H abundances are similar for all galaxies, andwe can interpret it as if most chemical evolution has already finishedin these galaxies.
| Evolutionary history of the elliptical galaxy NGC 1052
We have obtained Keck spectra for 16 globular clusters (GCs) associatedwith the merger remnant elliptical NGC 1052, as well as a long-slitspectrum of the galaxy. We derive ages, metallicities and abundanceratios from simple stellar population models using the recentlypublished methods of Proctor & Sansom, applied to extragalactic GCsfor the first time. A number of GCs indicate the presence of strong bluehorizontal branches that are not fully accounted for in the currentstellar population models. We find all of the GCs to be ~13 Gyr oldaccording to simple stellar populations, with a large range ofmetallicities. From the galaxy spectrum we find NGC 1052 to have aluminosity-weighted central age of ~2 Gyr and metallicity of[Fe/H]~+0.6. No strong gradients in either age or metallicity were foundto the maximum radius measured (0.3re~= 1 kpc). However, wedo find a strong radial gradient in α-element abundance, whichreaches a very high central value. The young central starburst age isconsistent with the age inferred from the HI tidal tails and infallinggas of ~1 Gyr. Thus, although NGC 1052 shows substantial evidence for arecent merger and an associated starburst, it appears that the mergerdid not induce the formation of new GCs, perhaps suggesting that littlerecent star formation occurred. This interpretation is consistent with`frosting' models for early-type galaxy formation.
| X-ray bright optically inactive galaxies in XMM-Newton/Sloan Digital Sky Survey fields: more diluted than absorbed?
We explore the properties of X-ray bright optically inactive galaxies(XBONGs) detected in the 0.5-8 keV spectral band in 20 public XMM-Newtonfields overlapping with the Sloan Digital Sky Survey (SDSS). Weconstrain our sample to optically extended systems withlogfX/fopt > -2 that have spectroscopicidentifications available from the SDSS (r < 19.2 mag). The resultingsample contains 12 objects with LX(0.5-8 keV) = 5 ×1041-2 × 1044 erg s-1 in theredshift range 0.06 < z < 0.45. The X-ray emission in four casesis extended, suggesting the presence of hot gas associated with acluster or group of galaxies. The X-ray spectral fits show that twoadditional sources are best fit with a thermal component emission (kT~ 1keV). Three sources are most likely associated with active galacticnuclei (AGNs): their X-ray spectrum is described by a steep photon indexΓ~ 1.9 typical of unobscured AGNs, while they are very luminous inX-rays [LX(0.5-8 keV) ~ 1043-1044 ergs-1]. Finally, three more sources could be associated witheither normal galaxies or unobscured low-luminosity AGNs (LX< 1042 erg s-1). We find no evidence forsignificant X-ray absorbing columns in any of our XBONGs. The abovesuggest that XBONGs, selected in the total 0.5-8 keV band, comprise amixed bag of objects primarily including normal elliptical galaxies andtype 1 AGNs whose optical nuclear spectrum is probably diluted by thestrong stellar continuum. Nevertheless, as our sample is notstatistically complete we cannot exclude the possibility that a fractionof optically fainter XBONGs may be associated with heavily obscuredAGNs.
| Mass-to-light ratio gradients in early-type galaxy haloes
Owing to the fact that the near future should see a rapidly expandingset of probes of the halo masses of individual early-type galaxies, weintroduce a convenient parameter for characterizing the halo masses fromboth observational and theoretical results:∇lΥ, the logarithmic radial gradient of themass-to-light ratio. Using halo density profiles from Λ-cold darkmatter (CDM) simulations, we derive predictions for this gradient forvarious galaxy luminosities and star formation efficienciesɛSF. As a pilot study, we assemble the available∇lΥ data from kinematics in early-type galaxies- representing the first unbiased study of halo masses in a wide rangeof early-type galaxy luminosities - and find a correlation betweenluminosity and ∇lΥ, such that the brightestgalaxies appear the most dark-matter dominated. We find that thegradients in most of the brightest galaxies may fit in well with theΛCDM predictions, but that there is also a population of faintergalaxies whose gradients are so low as to imply an unreasonably highstar formation efficiency ɛSF > 1. This difficultyis eased if dark haloes are not assumed to have the standard ΛCDMprofiles, but lower central concentrations.
| Evidence for radio-source heating of groups
We report evidence that the gas properties of X-ray groups containingradio galaxies differ from those of radio-quiet groups. For awell-studied sample of ROSAT-observed groups, we found that more thanhalf of the elliptical-dominated groups can be considered `radio-loud',and that radio-loud groups are likely to be hotter at a given X-rayluminosity than radio-quiet groups. We tested three different models forthe origin of the effect and conclude that radio-source heating is themost likely explanation. We found several examples of groups where thereis strong evidence from Chandra or XMM-Newton images for interactionsbetween the radio source and the group gas. A variety of radio-sourceheating processes are important, including shock-heating by youngsources and gentler heating by larger sources. The heating effects canbe longer-lasting than the radio emission. We show that the sample ofX-ray groups used in our study is not significantly biased in thefraction of radio-loud groups that it contains. This allows us toconclude that the energy per particle that low-power radio galaxies caninject over the group lifetime is comparable to the requirements ofstructure formation models.
| Group, field and isolated early-type galaxies - I. Observations and nuclear data
This is the first paper of a series on the investigation of stellarpopulation properties and galaxy evolution of an observationallyhomogeneous sample of early-type galaxies in groups, field and isolatedgalaxies.Here we present high signal-to-noise ratio (S/N) long-slit spectroscopyof 86 nearby elliptical and S0 galaxies. Eight of them are isolated,selected according to a rigorous criterion, which guarantees a genuinelow-density subsample. The present survey has the advantage of coveringa larger wavelength range than normally found in the literature, whichincludes [OIII]λ5007 and Hα, both lines important foremission correction. Among the 86 galaxies with S/N >= 15 (perresolution element, for re/8 central aperture), 57 have theirHβ-index corrected for emission (the average correction is 0.190Åin Hβ) and 42 galaxies reveal [OIII]λ5007 emission,of which 16 also show obvious Hα emission. Most of the galaxies inthe sample do not show obvious signs of disturbances nor tidal featuresin the morphologies, although 11 belong to the Arp catalogue of peculiargalaxies; only three of them (NGC 750, 751 and 3226) seem to be stronglyinteracting. We present the measurement of 25 central line-strengthindices calibrated to the Lick/IDS system. Kinematic information isobtained for the sample. We analyse the line-strength index versusvelocity dispersion relations for our sample of mainly low-densityenvironment galaxies, and compare the slope of the relations withcluster galaxies from the literature. Our main findings are that theindex-σ0 relations presented for low-density regionsare not significantly different from those of cluster E/S0s. The slopeof the index-σ0 relations does not seem to change forearly-type galaxies of different environmental densities, but thescatter of the relations seems larger for group, field and isolatedgalaxies than for cluster galaxies.
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