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The hot, warm and cold gas in Arp 227 - an evolving poor group
Arp 227 represents a prototypical example of an interacting mixed pairof galaxies located in a low-density environment. We investigate the gasproperties of the pair in the X-ray, Hα, HI and CO bands. We alsodetect two additional members of the group in HI which indicates thatthe pair constitutes the dominant members of a loose group.The HI distribution shows a tail of gas that connects the spiral member,NGC 470, to the lenticular, NGC 474, showing that the two main membersare currently undergoing interaction. The Hα emission reveals thepresence of secondary components at the centre of NGC 470, superposed onthe main component tracing the rotation of the galaxy. This latter mapsa nearly unperturbed velocity field. The dominant, nearly unperturbedtrend of the kinematics is confirmed by CO observations, althoughrestricted to the centre of the galaxy. The X-ray luminosity of NGC 470is comparable with that of a `normal' spiral galaxy. NGC 474 on theother hand is very gas-poor and has not been detected in Hα. ItsX-ray luminosity is consistent with the low end of the expected emissionfrom discrete sources.Arp 227 as a loose group shows several signatures of galaxy-galaxyinteraction. Our observations suggest the presence of signatures ofinteraction in the overall kinematics of the spiral companion. Theongoing interaction is clearly visible only in the outer HI halo of NGC470. While the large shell system of NGC 474 could be associated with anaccretion event, the secondary components in the Hα profile in thecentre of NGC 470 could be due to the interaction with the companion.The low X-ray luminosity of NGC 470 seems to be a characteristic ofdynamically young systems. All the above evidence suggest that Arp 227is an evolving group in the early phase of its evolution and that itsdrivers are the accretion of faint galaxies and the ongoing large-scaleinteraction between NGC 470 and 474.
| The Two-dimensional XMM-Newton Group Survey: z < 0.012 Groups
We present the results of the two-dimensional XMM-Newton Group Survey(2dXGS), an archival study of nearby galaxy groups. In this paper weconsider 11 nearby systems (z<0.012) in Mulchaey et al., which span abroad range in X-ray luminosity from 1040 to 1043ergs s-1. We measure the iron abundance and temperaturedistribution in these systems and derive pressure and entropy maps. Wefind statistically significant evidence for structure in the entropy andpressure of the gas component of seven groups on the 10%-20% level. TheXMM-Newton data for the three groups with best statistics also suggestpatchy metallicity distributions within the central 20-50 kpc of thebrightest group galaxy, probed with 2-10 kpc resolution. This providesinsights into the processes associated with thermalization of thestellar mass loss. Analysis of the global properties of the groupsreveals a subclass of X-ray-faint groups, which are characterized byboth higher entropy and lower pressure. We suggest that the mergerhistory of the central elliptical is responsible for both the source andthe observed thermodynamical properties of the hot gas of theX-ray-faint groups.
| Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters
We present new (B, I) photometry for the globular cluster systems ineight brightest cluster galaxies (BCGs), obtained with the ACS/WFCcamera on the Hubble Space Telescope. In the very rich cluster systemsthat reside within these giant galaxies, we find that all have stronglybimodal color distributions that are clearly resolved by themetallicity-sensitive (B-I) index. Furthermore, the mean colors andinternal color range of the blue subpopulation are remarkably similarfrom one galaxy to the next, to well within the +/-0.02-0.03 maguncertainties in the foreground reddenings and photometric zero points.By contrast, the mean color and internal color range for the redsubpopulation differ from one galaxy to the next by twice as much as theblue population. All the BCGs show population gradients, with muchhigher relative numbers of red clusters within 5 kpc of their centers,consistent with their having formed at later times than the blue,metal-poor population. A striking new feature of the color distributionsemerging from our data is that for the brightest clusters(MI<-10.5) the color distribution becomes broad and lessobviously bimodal. This effect was first noticed by Ostrov et al. andDirsch et al. for the Fornax giant NGC 1399; our data suggest that itmay be a characteristic of many BCGs and perhaps other large galaxies.Our data indicate that the blue (metal-poor) clusters brighter thanMI~=-10 become progressively redder with increasingluminosity, following a mass/metallicity scaling relationZ~M0.55. A basically similar relation has been found for M87by Strader et al. (2005). We argue that these GCS characteristics areconsistent with a hierarchical-merging galaxy formation picture in whichthe metal-poor clusters formed in protogalactic clouds or densestarburst complexes with gas masses in the range107-1010 Msolar, but where the moremassive clusters on average formed in bigger clouds with deeperpotential wells where more preenrichment could occur.
| A radio census of nuclear activity in nearby galaxies
In order to determine the incidence of black hole accretion-drivennuclear activity in nearby galaxies, as manifested by their radioemission, we have carried out a high-resolution Multi-ElementRadio-Linked Interferometer Network (MERLIN) survey of LINERs andcomposite LINER/Hii galaxies from a complete magnitude-limited sample ofbright nearby galaxies (Palomar sample) with unknown arcsecond-scaleradio properties. There are fifteen radio detections, of which three arenew subarcsecond-scale radio core detections, all being candidate AGN.The detected galaxies supplement the already known low-luminosity AGN -low-luminosity Seyferts, LINERs and composite LINER/Hii galaxies - inthe Palomar sample. Combining all radio-detected Seyferts, LINERs andcomposite LINER/Hii galaxies (LTS sources), we obtain an overall radiodetection rate of 54% (22% of all bright nearby galaxies) and weestimate that at least ~50% (~20% of all bright nearby galaxies) aretrue AGN. The radio powers of the LTS galaxies allow the construction ofa local radio luminosity function. By comparing the luminosity functionwith those of selected moderate-redshift AGN, selected from the 2dF/NVSSsurvey, we find that LTS sources naturally extend the RLF of powerfulAGN down to powers of about 10 times that of Sgr A*.
| 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.
| The host galaxy/AGN connection in nearby early-type galaxies. Is there a miniature radio-galaxy in every "core" galaxy?
This is the second of a series of three papers exploring the connectionbetween the multiwavelength properties of AGN in nearby early-typegalaxies and the characteristics of their hosts. We selected two sampleswith 5 GHz VLA radio flux measurements down to 1 mJy, reaching levels ofradio luminosity as low as 1036 erg s-1. In PaperI we presented a study of the surface brightness profiles for the 65objects with available archival HST images out of the 116 radio-detectedgalaxies. We classified early-type galaxies into "core" and "power-law"galaxies, discriminating on the basis of the slope of their nuclearbrightness profiles, following the Nukers scheme. Here we focus on the29 core galaxies (hereafter CoreG). We used HST and Chandra data toisolate their optical and X-ray nuclear emission. The CoreG invariablyhost radio-loud nuclei, with an average radio-loudness parameter of LogR = L5 {GHz} / LB 3.6. The optical and X-raynuclear luminosities correlate with the radio-core power, smoothlyextending the analogous correlations already found for low luminosityradio-galaxies (LLRG) toward even lower power, by a factor of 1000, covering a combined range of 6 orders of magnitude. This supportsthe interpretation of a common non-thermal origin of the nuclearemission also for CoreG. The luminosities of the nuclear sources, mostlikely dominated by jet emission, set firm upper limits, as low asL/L_Edd 10-9 in both the optical and X-ray band, on anyemission from the accretion process. The similarity of CoreG and LLRGwhen considering the distributions host galaxies luminosities and blackhole masses, as well as of the surface brightness profiles, indicatesthat they are drawn from the same population of early-type galaxies.LLRG represent only the tip of the iceberg associated with (relatively)high activity levels, with CoreG forming the bulk of the population. Wedo not find any relationship between radio-power and black hole mass. Aminimum black hole mass of M_BH = 108 Mȯ isapparently associated with the radio-loud nuclei in both CoreG and LLRG,but this effect must be tested on a sample of less luminous galaxies,likely to host smaller black holes. In the unifying model for BL Lacsand radio-galaxies, CoreG likely represent the counterparts of the largepopulation of low luminosity BL Lac now emerging from the surveys at lowradio flux limits. This suggests the presence of relativistic jets alsoin these quasi-quiescent early-type "core" galaxies.
| 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.
| 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.
| 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.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| Detection of Radial Surface Brightness Fluctuations and Color Gradients in Elliptical Galaxies with the Advanced Camera for Surveys
We study surface brightness fluctuations (SBFs) in a sample of eightelliptical galaxies using the Advanced Camera for Surveys (ACS) WideField Channel (WFC) data drawn from the Hubble Space Telescope archive.SBF magnitudes in the F814W bandpass and galaxy colors from F814W,F435W, and F606W images, when available, are presented. Galaxy surfacebrightness profiles are determined as well. We present the firstSBF-broadband color calibration for the ACS WFC F814W bandpass and(relative) distance moduli estimates for seven of our galaxies. Wedetect and study in detail the SBF variations within individual galaxiesas a probe of possible changes in the underlying stellar populations.Inspecting both the SBF and color gradients in comparison to modelpredictions, we argue that SBFs and SBF gradients can in principle beused for unraveling the different evolutionary paths taken by galaxies,although a more comprehensive study of this issue would be required. Weconfirm that the radial variation of galaxy stellar populationproperties is mainly connected to the presence of radial chemicalabundance gradients, with the outer galaxy regions being more metal-poorthan the inner ones.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555. These observations areassociated with programs 9427, 9293, and 9399.
| Star Formation Histories of Nearby Elliptical Galaxies. I. Volume-Limited Sample
This work presents high signal-to-noise ratio spectroscopic observationsof a representative sample of nearby elliptical galaxies. Theseobservations provide a strong test of models for the formation ofelliptical galaxies and their star formation histories. Combining thesedata with the González data set, a volume-limited sample of 45galaxies has been defined. Results are in agreement with previousstudies: the existence of the metallicity hyperplane and the Z-plane ofTrager and coworkers is confirmed, and the distribution is clearly dueto physical variations in stellar population parameters and notmeasurement uncertainty. Trends between stellar population parametersand galaxy structural parameters suggest that angular momentum maydetermine the chemical abundance of a galaxy at a given mass.
| The Centers of Early-Type Galaxies with Hubble Space Telescope. V. New WFPC2 Photometry
We present observations of 77 early-type galaxies imaged with the PC1CCD of the Hubble Space Telescope (HST) WFPC2. ``Nuker-law'' parametricfits to the surface brightness profiles are used to classify the centralstructure into ``core'' or ``power-law'' forms. Core galaxies aretypically rounder than power-law galaxies. Nearly all power-law galaxieswith central ellipticities ɛ>=0.3 have stellar disks,implying that disks are present in power-law galaxies withɛ<0.3 but are not visible because of unfavorable geometry. Afew low-luminosity flattened core galaxies also have disks; these may betransition forms from power-law galaxies to more luminous core galaxies,which lack disks. Several core galaxies have strong isophote twistsinterior to their break radii, although power-law galaxies have interiortwists of similar physical significance when the photometricperturbations implied by the twists are evaluated. Central colorgradients are typically consistent with the envelope gradients; coregalaxies have somewhat weaker color gradients than power-law galaxies.Nuclei are found in 29% of the core galaxies and 60% of the power-lawgalaxies. Nuclei are typically bluer than the surrounding galaxy. Whilesome nuclei are associated with active galactic nuclei (AGNs), just asmany are not; conversely, not all galaxies known to have a low-level AGNexhibit detectable nuclei in the broadband filters. NGC 4073 and 4382are found to have central minima in their intrinsic starlightdistributions; NGC 4382 resembles the double nucleus of M31. In general,the peak brightness location is coincident with the photocenter of thecore to a typical physical scale of <1 pc. Five galaxies, however,have centers significantly displaced from their surrounding cores; thesemay be unresolved asymmetric double nuclei. Finally, as noted byprevious authors, central dust is visible in about half of the galaxies.The presence and strength of dust correlates with nuclear emission;thus, dust may outline gas that is falling into the central black hole.The prevalence of dust and its morphology suggest that dust clouds form,settle to the center, and disappear repeatedly on ~108 yrtimescales. We discuss the hypothesis that cores are created by thedecay of a massive black hole binary formed in a merger. Apart fromtheir brightness profiles, there are no strong differences between coregalaxies and power-law galaxies that demand this scenario; however, therounder shapes of core, their lack of disks, and their reduced colorgradients may be consistent with it.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS 5-26555. These observations are associated withGO and GTO proposals 5236, 5446, 5454, 5512, 5943, 5990, 5999, 6099,6386, 6554, 6587, 6633, 7468, 8683, and 9107.
| Near infra-red and optical colour gradients in E-type galaxies. Inferences on dust content
Colour gradients are considered for a sample of circa 50 E-type galaxiesin the Local Supercluster. The new data includes isophotal colourprofiles in J-H, J-K, V-J and V-K, measured using 2MASS frames mostlyfrom the Large Galaxies Atlas, V frames from previous work and Vprofiles from the literature. This is supplemented by U-B, B-V, B-R, V-Icolour gradients obtained anew from published photometric data. Colourgradients in E galaxies show remarkably large variations from object toobject and do not correlate with other properties. Metallicity gradientsare the primary cause as shown before. Age gradients with oppositeeffects are possibly needed to explain objects with small colourgradients. Some empirical evidence of such age effects has been foundfor a subset of objects with morphological peculiarities and youngerstars mixed. Dust has only modest effects on colour gradients, as shownby the fact that objects with zero IRAS 100 μ flux have the sameaverage values of the gradients, except in V-J and V-K, as those withnon zero flux (cf. Table 7). This last subsample however exhibits poorbut definite correlations between IRAS flux and gradients, which mightbe caused by the presence of a few relatively dusty galaxies in thesample. Given the absence of a correlation between any gradients andgalaxy velocity dispersion (and hence mass), the observations do notagree with the predictions of the monolithic scenario for the formationof E galaxies. Simulated datasets of “dummy” objectsmimicking the hierarchical scenario have been obtained, and used to testa technique for estimating the dust content of E-galaxies from thecomparison of the V-K (or V-J) colour gradients with the U-B (or B-V)ones: the contents of diffuse dust, gauged in terms of published models,are obtained for a dozen objects.
| The host galaxy/AGN connection in nearby early-type galaxies. Sample selection and hosts brightness profiles
This is the first of a series of three papers exploring the connectionbetween the multiwavelength properties of AGNs in nearby early-typegalaxies and the characteristics of their hosts. We selected twosamples, both with high resolution 5 GHz VLA observations available andproviding measurements down to 1 mJy level, reaching radio-luminositiesas low as 1019 W Hz-1. We focus on the 116radio-detected galaxies as to boost the fraction of AGN with respect toa purely optically selected sample. Here we present the analysis of theoptical brightness profiles based on archival HST images, available for65 objects. We separate early-type galaxies on the basis of the slope oftheir nuclear brightness profiles, into core and power-law galaxiesfollowing the Nuker's scheme, rather than on the traditionalmorphological classification (i.e. into E and S0 galaxies). Our sampleof AGN candidates is indistinguishable, when their brightness profilesare concerned, from galaxies of similar optical luminosity but hostingweaker (or no) radio-sources. We confirm previous findings thatrelatively bright radio-sources (Lr > 1021.5 WHz-1) are uniquely associated to core galaxies. However,below this threshold in radio-luminosity core and power-law galaxiescoexist and they do not show any apparent difference in theirradio-properties. Not surprisingly, since our sample is deliberatelybiased to favour the inclusion of active galaxies, we found a higherfraction of optically nucleated galaxies. Addressing the multiwavelengthproperties of these nuclei will be the aim of the two forthcomingpapers.
| Radio sources in low-luminosity active galactic nuclei. IV. Radio luminosity function, importance of jet power, and radio properties of the complete Palomar sample
We present the completed results of a high resolution radio imagingsurvey of all ( 200) low-luminosity active galactic nuclei (LLAGNs) andAGNs in the Palomar Spectroscopic Sample of all ( 488) bright northerngalaxies. The high incidences of pc-scale radio nuclei, with impliedbrightness temperatures ≳107 K, and sub-parsec jetsargue for accreting black holes in ≳50% of all LINERs andlow-luminosity Seyferts; there is no evidence against all LLAGNs beingmini-AGNs. The detected parsec-scale radio nuclei are preferentiallyfound in massive ellipticals and in type 1 nuclei (i.e. nuclei withbroad Hα emission). The radio luminosity function (RLF) of PalomarSample LLAGNs and AGNs extends three orders of magnitude below, and iscontinuous with, that of “classical” AGNs. We find marginalevidence for a low-luminosity turnover in the RLF; nevertheless LLAGNsare responsible for a significant fraction of present day massaccretion. Adopting a model of a relativistic jet from Falcke &Biermann, we show that the accretion power output in LLAGNs is dominatedby the kinetic power in the observed jets rather than the radiatedbolometric luminosity. The Palomar LLAGNs and AGNs follow the samescaling between jet kinetic power and narrow line region (NLR)luminosity as the parsec to kilo-parsec jets in powerful radio galaxies.Eddington ratios {l_Edd} (=L_Emitted/L_Eddington) of≤10-1{-}10-5 are implied in jet models of theradio emission. We find evidence that, in analogy to Galactic black holecandidates, LINERs are in a “low/hard” state (gas poornuclei, low Eddington ratio, ability to launch collimated jets) whilelow-luminosity Seyferts are in a “high” state (gas richnuclei, higher Eddington ratio, less likely to launch collimated jets).In addition to dominating the radiated bolometric luminosity of thenucleus, the radio jets are energetically more significant thansupernovae in the host galaxies, and are potentially able to depositsufficient energy into the innermost parsecs to significantly slow thegas supply to the accretion disk.
| A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies
We examine the properties of central dust in nearby quiescent and activeearly-type galaxies. The active galaxies are low-power radio galaxieswith Fanaroff & Riley type I or I/II radio jets. We focus on (a) thecomparison of the dust distributions in the active and quiescent galaxysamples; and (b) the relation between the radio jet and dustorientations. Our main observational conclusions are: (i) in line withprevious studies, the dust detection rate is higher in radio-jetgalaxies than in non radio-jet galaxies; (ii) radio galaxies contain ahigher fraction of regular dust “ellipses” compared toquiescent galaxies which contain more often irregular dustdistributions; (iii) the morphology, size and orientation of dustellipses and lanes in quiescent early-types and active early-types withkpc-scale radio jets is very similar; (iv) dust ellipses are alignedwith the major axis of the galaxy, dust lanes do not show a preferredalignment except for large (>kpc) dust lanes which are aligned withthe minor axis of the galaxy; and (v) as projected on the sky, jets donot show a preferred orientation relative to the galaxy major axis (andhence dust ellipses), but jets are preferentially perpendicular to dustlanes. We show that the dust ellipses are consistent with being nearlycircular thin disks viewed at random viewing angles. The lanes arelikely warped dust structures, which may be in the process of settlingdown to become regular disks or are being perturbed by anon-gravitational force. We use the observed dust-jet orientations toconstrain the three-dimensional angle θDJ between jetand dust. For dust-lane galaxies, the jet is approximately perpendicularto the dust structure, while for dust-ellipse galaxies there is a muchwider distribution of θDJ. We discuss two scenariosthat could explain the dust/jet/galaxy orientation dichotomy. If lanesare indeed settling, then the jet orientation apparently is roughlyaligned with the angular momentum of the dust before it settles. Iflanes are perturbed by a jet-related force, it appears that it causesthe dust to move out of its equilibrium plane in the galaxy into a planewhich is perpendicular to the jet.
| Peculiarities and populations in elliptical galaxies. II. Visual-near IR colours as population indices
As a complement to the data collected and discussed in Paper I of thisseries, 2MASS near-IR images have been used, in connection withavailable V light aperture photometry, to derive the colours V-J, V-K,J-H and J-K within the effective aperture A_e: nearly the same completesample of 110 E-type galaxies is treated. In Paper I these wereclassified, based on morphological criteria, into the ``peculiar'' (orPec) and ``normal'' (or Nop) subsamples. For the Nop subsample, thederived colour indices are tightly related to the galaxy masses, asmeasured by the central velocity dispersion σ0,although with rather small slopes as regards J-H and J-K. For the Pecsubsample, the V-J and V-K colours behave as UBV and line-indices: partof the objects show blue residuals from the appropriatecolour-σ0 regression, which is evidence of a youngerpopulation mixed with the ``normal'' one traced by the Nop regressions;the other shows no deviations from the Nop subsample. The distinctionamong Pec objects between the YP family (NGC 2865 type), and the NP one(NGC 3923 type), is statistically supported, and generally confirmed inspecific cases.Based in part on observations collected at the Observatoire deHaute-Provence.Table 4 is only available in electonic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/819
| The Group Evolution Multiwavelength Study (GEMS): bimodal luminosity functions in galaxy groups
We present B- and R-band luminosity functions (LFs) for a sample of 25nearby groups of galaxies. We find that the LFs of the groups with lowX-ray luminosity (LX < 1041.7 ergs-1) are significantly different from those of the X-raybrighter groups, showing a prominent dip around MB=-18. Whileboth categories show lack of late-type galaxies in their centralregions, X-ray dim groups also show a more marked concentration ofoptical luminosity towards the centre. A toy simulation shows that inthe low velocity dispersion environment, as in the X-ray dim group,dynamical friction would facilitate more rapid merging, thus depletingintermediate-luminosity galaxies to form a few giant central galaxies,resulting in the prominent dip seen in our LFs. We suggest that X-raydim (or low velocity dispersion) groups are the present sites of rapiddynamical evolution rather than their X-ray bright counterparts, and maybe the modern precursors of fossil groups. We predict that these groupsof low velocity dispersion would harbour younger stellar populationsthan groups or clusters with higher velocity dispersion.
| Nuclear activity and the dynamics of elliptical galaxies
This Letter looks for any correlation between the internal dynamics ofelliptical galaxies and the relatively mild nuclear activity found inmany such systems. We show that there is such a relation in the sensethat the active ellipticals tend to be significantly less rotationallysupported than their inactive cousins. The correlation can partly berelated to the galaxies' luminosities: the brightest galaxies tend to bemore active and less rotationally supported. However, even at lowerluminosities the active and inactive galaxies seem to havesystematically different dynamics. This variation suggests that thereare significant large-scale structural differences between active andinactive elliptical galaxies, and hence that the existence of both typesof system cannot just be the result of random sporadic nuclear activity.
| The GEMS project: X-ray analysis and statistical properties of the group sample
The Group Evolution Multiwavelength Study (GEMS) involves amultiwavelength study of a sample of 60 galaxy groups, chosen to span awide range of group properties. Substantial ROSAT Position SensitiveProportional Counter (PSPC) observations, available for all of thesegroups, are used to characterize the state of the intergalactic mediumin each. We present the results of a uniform analysis of these ROSATdata and a statistical investigation of the relationship between X-rayand optical properties across the sample. Our analysis improves inseveral respects on previous work: (i) we distinguish between systems inwhich the hot gas is a group-scale medium and those in which it appearsto be just a hot halo associated with a central galaxy; (ii) weextrapolate X-ray luminosities to a fixed overdensity radius(r500) using fitted surface brightness models, in order toavoid biases arising from the fact that cooler systems are detectable tosmaller radii, and (iii) optical properties have been rederived in auniform manner from the NASA Extragalactic Database, rather than relyingon the data in the disparate collection of group catalogues from whichour systems are drawn.The steepening of the LX-TX relation in the groupregime reported previously is not seen in our sample, which fits well onto the cluster trend, albeit with large non-statistical scatter. Anumber of biases affect the fitting of regression lines under thesecircumstances, and until the impact of these has been thoroughlyinvestigated it seems best to regard the slope of the groupLX-TX relation as being poorly determined. Asignificant problem in comparing the properties of groups and clustersis the derivation of system radii, to allow different systems to becompared within regions having the same overdensity. We find evidencethat group velocity dispersion (σv) provides a veryunreliable measure of system mass (and hence radius), with a number ofgroups having remarkably low values of σv, given thatthey appear from their X-ray properties to be collapsed systems. Weconfirm that the surface brightness profiles of groups are significantlyflatter than those of clusters - the maximum value of theβfit parameter for our sample is 0.58, lower than thetypical value of 0.67 seen in clusters - however, we find no significanttendency within our sample for cooler groups to show flatter profiles.This result is inconsistent with simple universal pre-heating models.The morphology of the galaxies in the GEMS groups is correlated to theirX-ray properties in a number of ways: we confirm the very strongrelationship between X-ray emission and a dominant early-type centralgalaxy, which has been noted since the early X-ray studies of groups,and also find that spiral fraction is correlated with the temperature ofthe hot gas and hence the depth of the gravitational potential. A classof spiral-rich groups with little or no X-ray emission probablycorresponds to groups that have not yet fully collapsed.
| XMM-Newton and Chandra observations of three X-ray-faint early-type galaxies
We present XMM-Newton observations of three X-ray-underluminouselliptical galaxies, NGC 3585, 4494 and 5322. All three galaxies haverelatively large optical luminosities (logLB= 10.35-10.67Lsolar) but have X-ray luminosities consistent with emissionfrom discrete sources only. In conjunction with a Chandra observation ofNGC 3585, we analyse the XMM-Newton data and show that the threegalaxies are dominated by discrete source emission, but do possess someX-ray-emitting gas. The gas is at relatively low temperatures, kT~=0.25-0.44 keV. All three galaxies show evidence of recent dynamicaldisturbance and formation through mergers, including kinematicallydistinct cores, young stellar ages and embedded stellar discs. Thisleads us to conclude that the galaxies formed relatively recently andhave yet to build up large X-ray haloes. They are likely to be in adevelopmental phase where the X-ray gas has a very low density, makingit undetectable outside the galaxy core. However, if the gas is aproduct of stellar mass loss, as seems most probable, we would expect toobserve supersolar metal abundances. While abundance is not wellconstrained by the data, we find best-fitting abundances <0.1Zsolar for single-temperature models, and it seems unlikelythat we could underestimate the metallicity by such a large factor.
| Scaling relations in early-type galaxies belonging to groups
We present a photometric analysis of a large sample of early-typegalaxies in 16 nearby groups, imaged with the Wide-Field Camera on theIsaac Newton Telescope. Using a two-dimensional surface brightnessdecomposition routine, we fit Sersic (r1/n) and exponentialmodels to their bulge and disc components, respectively. Dividing thegalaxies into three subsamples according to the X-ray luminosities oftheir parent groups, we compare their photometric properties. Galaxiesin X-ray luminous groups tend to be larger and more luminous than thosein groups with undetected or low X-ray luminosities, but no significantdifferences in n are seen. Both normal and dwarf elliptical galaxies inthe central regions of groups are found to have cuspier profiles thantheir counterparts in group outskirts.Structural differences between dwarf and normal elliptical galaxies areapparent in terms of an offset between their `photometric planes' in thespace of n, re and μ0. Dwarf ellipticals arefound to populate a surface, with remarkably low scatter, in this spacewith significant curvature, somewhat similar to the surfaces of constantentropy proposed by Màrquez et al. Normal ellipticals are offsetfrom this distribution in a direction of higher specific entropy. Thismay indicate that the two populations are distinguished by the action ofgalaxy merging on larger galaxies.
| Cold Dust in Early-Type Galaxies. I. Observations
We describe far-infrared observations of early-type galaxies selectedfrom the Infrared Space Observatory (ISO) archive. This ratherinhomogeneous sample includes 39 giant elliptical galaxies and 14 S0 (orlater) galaxies. These galaxies were observed with the array photometerPHOT on-board the ISO satellite using a variety of different observingmodes-sparse maps, mini-maps, oversampled maps, and singlepointings-each of which requires different and often rather elaboratephotometric reduction procedures. The ISO background data agree wellwith the COBE-DIRBE results to which we have renormalized ourcalibrations. As a further check, the ISO fluxes from galaxies at 60 and100 μm agree very well with those previously observed with IRAS atthese wavelengths. The spatial resolution of ISO is several timesgreater than that of IRAS, and the ISO observations extend out to 200μm, which views a significantly greater mass of colder dust notassessable to IRAS. Most of the galaxies are essentially point sourcesat ISO resolution, but a few are clearly extended at FIR wavelengthswith image sizes that increase with FIR wavelength. The integratedfar-infrared luminosities do not correlate with optical luminosities,suggesting that the dust may have an external, merger-related origin. Ingeneral, the far-infrared spectral energy distributions can be modeledwith dust at two temperatures, ~43 and ~20 K, which probably representlimits of a continuous range of temperatures. The colder dust componentdominates the total mass of dust, 106-107Msolar, which is typically more than 10 times larger than thedust masses previously estimated for the same galaxies using IRASobservations. For S0 galaxies we find that the optically normalizedfar-infrared luminosity LFIR/LB correlatesstrongly with the mid-infrared luminosityL15μm/LB, but that correlation is weaker forelliptical galaxies.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, theNetherlands, and United Kingdom) and with the participation of ISAS andNASA.
| A Chandra View of the Normal S0 Galaxy NGC 1332. II. Solar Abundances in the Hot Gas and Implications for Supernova Enrichment
Using a new Chandra ACIS-S3 observation of the normal, isolated,moderate-LX lenticular galaxy NGC 1332, we resolve theemission into ~75 point sources and a significant diffuse component. Wepresent a detailed analysis of the spectral properties of the diffuseemission, constraining both the temperature profile and the metalabundances in the hot gas. The characteristics of the point-sourcepopulation and the spatial properties of the diffuse emission arediscussed in two companion papers. The diffuse component comprises hotgas with an ~isothermal temperature profile (~0.5 keV) and emission fromunresolved point sources. In contrast with the cool cores of many groupsand clusters, we find a small central temperature peak. We obtainemission-weighted abundance constraints within 20 kpc for several keyelements: Fe, O, Ne, Mg, and Si. The measured iron abundance(ZFe=1.1 in solar units; >0.53 at 99% confidence) stronglyexcludes the very subsolar values often historically reported forearly-type galaxies. This continues, in a lower LX system, atrend in recent observations of bright galaxies and groups. Theabundance ratios, with respect to Fe, of the other elements were alsofound to be ~solar, with the exception of ZO/ZFe,which was significantly lower (<0.4), as seen in several brightgalaxies, groups, and clusters. Such a low O abundance is not predictedby simple models of ISM enrichment by Type Ia and Type II supernovae(SNe) and may indicate a significant contribution from primordialhypernovae. Revisiting Chandra observations of themoderate-LX, isolated elliptical galaxy NGC 720, we obtainsimilar abundance constraints(ZFe=0.71+0.40-0.21, 90% confidence;ZO/ZFe=0.23+/-0.21). Adopting standard SNe Ia andSNe II metal yield models, our abundance ratio constraints imply that73%+/-5% and 85%+/-6% of the Fe enrichment in NGC 1332 and NGC 720,respectively, arises from SNe Ia. Although these results are sensitiveto the considerable systematic uncertainty in the SNe yields, they arein good agreement with observations of more massive systems. These twocases of moderate-LX early-type galaxies reveal a consistentpattern of metal enrichment from cluster scales to moderateLX/LB galaxies.
| Companions to Isolated Elliptical Galaxies: Revisiting the Bothun-Sullivan Sample
We investigate the number of physical companion galaxies for a sample ofrelatively isolated elliptical galaxies. The NASA/IPAC ExtragalacticDatabase (NED) has been used to reinvestigate the incidence of satellitegalaxies for a sample of 34 elliptical galaxies, first investigated byBothun & Sullivan using a visual inspection of Palomar Sky Surveyprints out to a projected search radius of 75 kpc. We have repeatedtheir original investigation using data cataloged in NED. Nine of theseelliptical galaxies appear to be members of galaxy clusters; theremaining sample of 25 galaxies reveals an average of +1.0+/-0.5apparent companions per galaxy within a projected search radius of 75kpc, in excess of two equal-area comparison regions displaced by 150-300kpc. This is significantly larger than the +0.12+/-0.42companions/galaxy found by Bothun & Sullivan for the identicalsample. Making use of published radial velocities, mostly availablesince the completion of the Bothun-Sullivan study, identifies thephysical companions and gives a somewhat lower estimate of +0.4companions per elliptical galaxy. This is still 3 times larger than theoriginal statistical study, but given the incomplete and heterogeneousnature of the survey redshifts in NED, it still yields a firm lowerlimit on the number (and identity) of physical companions. An expansionof the search radius out to 300 kpc, again restricted to sampling onlythose objects with known redshifts in NED, gives another lower limit of4.5 physical companions per galaxy. (Excluding five elliptical galaxiesin the Fornax Cluster, this average drops to 3.5 companions perelliptical.) These physical companions are individually identified andlisted, and the ensemble-averaged radial density distribution of theseassociated galaxies is presented. For the ensemble, the radial densitydistribution is found to have a falloff consistent withρ~R-0.5 out to approximately 150 kpc. For non-FornaxCluster companions the falloff continues out to the 300 kpc limit of thesurvey. The velocity dispersion of these companions is found to reach amaximum of 350 km s-1 at around 120 kpc, after which theyfall at a rate consistent with Keplerian falloff. This falloff may thenindicate the detection of a cut-off in the mass-density distribution inthe elliptical galaxies' dark matter halo at ~100 kpc.
| A New Nonparametric Approach to Galaxy Morphological Classification
We present two new nonparametric methods for quantifying galaxymorphology: the relative distribution of the galaxy pixel flux values(the Gini coefficient or G) and the second-order moment of the brightest20% of the galaxy's flux (M20). We test the robustness of Gand M20 to decreasing signal-to-noise ratio (S/N) and spatialresolution and find that both measures are reliable to within 10% forimages with average S/N per pixel greater than 2 and resolutions betterthan 1000 and 500 pc, respectively. We have measured G andM20, as well as concentration (C), asymmetry (A), andclumpiness (S) in the rest-frame near-ultraviolet/optical wavelengthsfor 148 bright local ``normal'' Hubble-type galaxies (E-Sd) galaxies, 22dwarf irregulars, and 73 0.05
| Peculiarities and populations in elliptical galaxies. I. An old question revisited
Morphological peculiarities, as defined from isophote asymmetries andnumber of detected shells, jets or similar features, have been estimatedin a sample of 117 E classified galaxies, and qualified by an ad hocΣ2 index. The overall frequency of ``peculiar'' objects(Pec subsample) is 32.5%. It decreases with the cosmic density of theenvironment, being minimal for the Virgo cluster, the densestenvironment in the sampled volume. This environmental effect is strongerfor galaxies with relatively large Σ2.The Pec subsample objects are compared with ``normal'' objects (Nopsubsample) as regards their basic properties. Firstly, theysystematically deviate from the Fundamental Plane and the Faber-Jacksonrelation derived for the Nop subsample, being too bright for their mass.Secondly, the dust content of galaxies, as estimated from IRAS fluxes,are similar in both subsamples. Third, the same is true of the frequencyof Kinematically Distinct cores (KDC), suggesting that KDC andmorphological peculiarities do not result from the same events in thehistory of E-galaxies.Using the Nop sample alone, we obtain very tight reference relationsbetween stellar population indicators (U-B, B-V, B-R, V-I,Mg2, Hβ, , Mgb) and the central velocitydispersion σ0. The discussion of the residuals of theserelations allows us to classify the Pec galaxies in two families i.e.the YP or NGC 2865 family, and the NP or NGC 3923 one. Galaxies in thefirst group show consistent evidence for a younger stellar populationmixed with the old one, in agreement with classical results (Schweizeret al. \cite{Schweizer1990}; Schweizer & Seitzer\cite{Schweizer1992}). The second group, however, has ``normal``, orreddish, populations. It is remarkable that a fraction (circa 40%) ofmorphologically perturbed objects do not display any signature of ayoung population, either because the event responsible for thepecularity is too ancient, or because it did not produce significantstar formation (or eventually that the young sub-population has highmetallicity).A preliminary attempt is made to interpret the populations of Pecobjects by combining a young Single Stellar Population with a Nopgalaxy, with only limited success, perhaps largely due to uncertaintiesin the SSP indices used.Based in part on observations collected at the Observatoire deHaute-Provence.Figures \ref{fig1}-\ref{fig3} are only available in electronic form athttp://www.edpsciences.orgTable 10 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/423/833
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