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Are radio galaxies and quiescent galaxies different? Results from the analysis of HST brightness profiles
We present a study of the optical brightness profiles of early typegalaxies, using a number of samples of radio galaxies and opticallyselected elliptical galaxies. For the radio galaxy samples - B2 ofFanaroff-Riley type I and 3C of Fanaroff-Riley type II - we determined anumber of parameters that describe a "Nuker-law" profile, which werecompared with those already known for the optically selected objects. Wefind that radio active galaxies are always of the "core" type (i.e. aninner Nuker law slope γ < 0.3). However, there are core-typegalaxies which harbor no significant radio source and which areindistinguishable from the radio active galaxies. We do not find anyradio detected galaxy with a power law profile (γ > 0.5). Thisdifference is not due to any effect with absolute magnitude, since in aregion of overlap in magnitude the dichotomy between radio active andradio quiescent galaxies remains. We speculate that core-type objectsrepresent the galaxies that have been, are, or may become, radio activeat some stage in their lives; active and non-active core-type galaxiesare therefore identical in all respects except their eventualradio-activity: on HST scales we do not find any relationship betweenboxiness and radio-activity. There is a fundamental plane, defined bythe parameters of the core (break radius rb and breakbrightness μ_b), which is seen in the strong correlation betweenrb and μ_b. The break radius is also linearly proportionalto the optical Luminosity in the I band. Moreover, for the few galaxieswith an independently measured black hole mass, the break radius turnsout to be tightly correlated with MBH. The black hole masscorrelates even better with the combination of fundamental planeparameters rb and μ_b, which represents the centralvelocity dispersion.
| Star formation history in early-type galaxies - I. The line absorption indices diagnostics
To unravel the formation mechanism and the evolutionary history ofelliptical galaxies (EGs) is one of the goals of modern astrophysics. Ina simplified picture of the issue, the question to be answered iswhether they have formed by hierarchical merging of pre-existingsubstructures (maybe disc galaxies) made of stars and gas, with eachmerging event probably accompanied by strong star formation, orconversely, whether they originated from the early aggregation of lumpsof gas turned into stars in the remote past via a burst-like episodeever since followed by quiescence so as to mimic a sort of monolithicprocess. Even if the two alternatives seem to oppose each other,actually they may both contribute to shaping the final properties of EGsas seen today. Are there distinct signatures of the underlying dominantprocess in the observational data? To this aim we have examined the lineabsorption indices on the Lick system of the normal, field EGs of Tragerand the interacting EGs (pair- and shell-objects) of Longhetti et al.The data show that both normal, field and interacting galaxies have thesame scattered but smooth distribution in the Hβ versus [MgFe]plane even if the interacting ones show a more pronounced tail towardhigh Hβ values. This may suggest that a common physical cause is atthe origin of their distribution. There are two straightforwardinterpretations of increasing complexity. (i) EGs span true large rangesof ages and metallicities. A young age is the signature of theaggregation mechanism, each event accompanied by metal enrichment. Thissimple scheme cannot, however, explain other spectro-photometricproperties of EGs and has to be discarded. (ii) The bulk population ofstars is old but subsequent episodes of star formation scatter the EGsin the diagnostic planes. However, this scheme would predict anoutstanding clump at low Hβ values, contrary to what is observed.The model can be cured by supposing that the primary star formationactivity lasted for a significant fraction of the Hubble time (5<=T<= 13 Gyr) accompanied by global metal enrichment. The`younger' galaxies are more metal-rich. The later burst of starformation should be small otherwise too many high-Hβ objects wouldbe observed. Therefore, the distribution of normal, pair- andshell-galaxies in the Hβ versus [MgFe] plane is due to global metalenrichment. Even though the above schemes provide a formal explanation,they seem to be too demanding because of the many ad hoc ingredientsthat have to be introduced. Furthermore, they neglect theobservationally grounded hint that the stellar content of EGs is likelyto be enhanced in α-elements with [α/Fe] ranging from 0.1 to0.4 dex. Here we propose a new scheme, in which the bulk dispersion ofgalaxies in the Hβ versus [MgFe] plane is caused by a differentmean degree of enhancement. In this model, neither the large age rangesnor the universal enrichment law for the old component are required andthe observed distribution along Hβ is naturally recovered.Furthermore, later bursts of stellar activity are a rare event,involving only those galaxies with very high Hβ (roughly >2.5).Finally, simulations of the scatter in broad-band colours of EGs seem toconfirm that the bulk stars have formed in the remote past, and thatmergers and companion star formation in a recent past are not likely,unless the intensity of the secondary activity is very small.
| Revised Rates of Stellar Disruption in Galactic Nuclei
We compute rates of tidal disruption of stars by supermassive blackholes in galactic nuclei, using downwardly revised black hole massesfrom the MBH-σ relation. In galaxies with steep nucleardensity profiles, which dominate the overall event rate, the disruptionfrequency varies inversely with assumed black hole mass. We compute atotal rate for nondwarf galaxies of ~10-5 yr-1Mpc-3, about a factor of 10 higher than in earlier studies.Disruption rates are predicted to be highest in nucleated dwarfgalaxies, assuming that such galaxies contain black holes. Monitoring ofa rich galaxy cluster for a few years could rule out the existence ofintermediate-mass black holes in dwarf galaxies.
| Lensing and the Centers of Distant Early-Type Galaxies
Gravitational lensing provides a unique probe of the inner 10-1000 pc ofdistant galaxies (z~0.2-1). Theoretical studies have predicted that eachstrong lens system should have a faint image near the center of the lensgalaxy, which should, in principle, be visible in radio lenses but hasnever been detected. We study the predicted ``core'' images using modelsderived from the stellar distributions in nearby early-type galaxies. Wefind that realistic lens galaxies produce a remarkably wide range ofcore images, with magnifications spanning some 6 orders of magnitude.More concentrated galaxies produce fainter core images, although notwith any model-independent relation between the galaxy properties andthe core images. Some real galaxies have diffuse cores that should yieldbright core images (magnification μcore>~0.1), but morecommon are galaxies that yield faint core images(μcore<~0.001). Thus, stellar mass distributions aloneare probably concentrated enough to explain the lack of observed coreimages. Observational sensitivity may need to improve by an order ofmagnitude before detections of core images become common. Two-imagelenses should tend to have brighter core images than four-image lenses,so they will be the better targets for finding core images andexploiting these tools for studying the central mass distributions ofdistant galaxies.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| Evolution of massive binary black holes
Since many or most galaxies have central massive black holes (BHs),mergers of galaxies can form massive binary black holes (BBHs). In thispaper we study the evolution of massive BBHs in realistic galaxy models,using a generalization of techniques used to study tidal disruptionrates around massive BHs. The evolution of BBHs depends on BH mass ratioand host galaxy type. BBHs with very low mass ratios (say, <~0.001)are hardly ever formed by mergers of galaxies, because the dynamicalfriction time-scale is too long for the smaller BH to sink into thegalactic centre within a Hubble time. BBHs with moderate mass ratios aremost likely to form and survive in spherical or nearly sphericalgalaxies and in high-luminosity or high-dispersion galaxies; they aremost likely to have merged in low-dispersion galaxies (line-of-sightvelocity dispersion <~90kms-1 ) or in highly flattened ortriaxial galaxies. The semimajor axes and orbital periods of survivingBBHs are generally in the range 10-3 -10pc and10-105 yr they are also larger in high-dispersion galaxiesthan in low-dispersion galaxies, larger in nearly spherical galaxiesthan in highly flattened or triaxial galaxies, and larger for BBHs withequal masses than for BBHs with unequal masses. The orbital velocitiesof surviving BBHs are generally in the range 102-104 kms-1 . The methods of detecting survivingBBHs are also discussed. If no evidence of BBHs is found in AGNs, thismay be either because gas plays a major role in BBH orbital decay orbecause nuclear activity switches on soon after a galaxy merger, andends before the smaller BH has had time to spiral to the centre of thegalaxy.
| A NICMOS Survey of Early-Type Galaxy Centers: The Relation Between Core Properties, Gas and Dust Content, and Environment
We present a NICMOS 1.6 μm imaging isophotal study of 27 early-typegalaxies. Core galaxies have reduced ellipticity and boxiness near andwithin their core or break radius. This supports a core formationmechanism that mixes or scatters stars such as scattering caused by abinary black hole. We find the same trends between central surfacebrightness and luminosities as the WPFC studies. We find no correlationbetween core properties and dust mass or X-ray luminosity, suggestingthat processes determining the current gas content (e.g., such as minormergers and cooling flows) are unrelated to processes occurring duringcore formation. Core galaxies exist in a variety of environments rangingfrom poor groups to large clusters. A combined sample suggests thatgalaxy groups may harbor more luminous power-law galaxies than clusterssuch as Virgo and Fornax. Based on observations with the NASA/ESA HubbleSpace Telescope obtained at the Space Telescope Science Institute, whichis operated by the Association of University for Research in Astronomy,Inc. (AURA), under NASA contract NAS5-26555.
| Kinematical data on early-type galaxies. V.
We present kinematical data for a sample of 26 galaxies. Rotation curvesand velocity-dispersion profiles are determined for all objects. This isour fifth paper in a series devoted to the presentation of data onelliptical and S0 galaxies, derived from long-slit absorptionspectroscopy; the series now gathers 119 galaxies with homogeneous data.Based on observations collected at the Observatoire de Haute-Provence.Tables 2 and 3 are presented in electronic form only; Tables 1 through 3are available from the CDS, Strasbourg, via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| A catalogue of Mg_2 indices of galaxies and globular clusters
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| Ellipticals with Kinematically Distinct Cores: V-I Color Images with WFPC2
We have analyzed Hubble Space Telescope WFPC2 F555W and F814W (i.e., Vand I) images for 15 elliptical galaxies with kinematically distinctcores. For each of them, we have derived surface brightness andisophotal parameter profiles in the two bands, color maps, and radialprofiles in V - I. Most galaxies show patchy dust absorption close totheir nuclei. However, there are generally no indications ofhomogeneous, diffuse dust components close to the nuclei. The nuclearcolors in the unobscured regions are most likely representative of thecentral stellar populations. We have detected photometric evidence forfaint stellar disks, on scales of a few tens to a few arcseconds, inseven galaxies, namely NGC 1427, 1439, 1700, 4365, 4406, 4494, and 5322.In NGC 1700, the isophotes are slightly boxy at the scale of thecounterrotating component and disky at larger radii. We find nodifference in V - I color greater than 0.02 mag between these disks andthe surrounding galactic regions. Hence, the stellar populations in thekinematically distinct cores are not strongly deviant from thepopulation of the main body. Specifically, there is no evidence for adominating population of blue, very metal weak stars as predicted bysome of the formation scenarios. This argues against models in whichsmall galaxies fall in and survive in the nuclei, unless supermassiveblack holes are present. These would likely disrupt the accreted smallsystems. For one galaxy, NGC 4365, the innermost region is bluer thanthe surrounding regions. This area extends to ~15 pc and contains aluminosity of ~2.5 x 106 Lȯ. If interpreted as a stellar populationeffect, an age difference of ~3--4 Gyr, or an [Fe/H] variation of about0.2 dex, is derived. The nuclear intensity profiles show a largevariety: some galaxies have steep cusp profiles, while others haveshallow cusps and a "break radius." The nuclear cusps of galaxies withkinematically distinct cores follow the same trends as the nuclei ofnormal galaxies. We have not been able to identify a unique, qualifyingfeature in the WFPC2 images that distinguishes the galaxies withkinematically distinct cores from the kinematically normal cores. It ispossible that statistical differences exist: possibly, the kinematicallydistinct cores have a higher fraction of nuclear disks. The similarityof both types of cores puts strong constraints on the formationscenarios. Simulations of galaxy mergers, with the inclusion of starformation and nuclear black holes, are needed to resolve the question ofhow these structures may have formed. Spectra with high spatialresolution are needed to study the nuclear structure of the distinctcomponent in detail.
| The Centers of Early-Type Galaxies with HST. IV. Central Parameter Relations.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1771F&db_key=AST
| The Centers of Early-Type Galaxies With HST. III. Non-Parametric Recovery of Stellar Luminosity Distribution
We have non-parametrically determined the luminosity density profilesand their logarithmic slopes for 42 early-type galaxies observed withHST. Assuming that the isodensity contours are spheroidal, then theluminosity density is uniquely determined from the surface brightnessdata through the Abel equation. For nearly all the galaxies in oursample, the logarithmic slope of the luminosity density (S = d log v/dlog r) measured at 0.1" (the innermost reliable measurement with theuncorrected HST) is significantly different from zero; i.e., mostelliptical galaxies have cusps. There are only two galaxies for which ananalytic core (S approaches 0) cannot be excluded. The distribution oflogarithmic slopes at 0.1" appears to be bimodal, confirming theconclusion of Lauer et al. [AJ, 110,2622(1995)] that early-type galaxiescan be divided into two types based on their surface brightnessprofiles; i.e., those with cuspy cores and those whose steep power-lawprofiles continue essentially unchanged in to the resolution limit. Thepeaks in the slope distribution occur at S = -0.8 and - 1.9. More thanhalf of the galaxies have slopes steeper than - 1.0. Taken together withthe recent theoretical work of Merritt and Fridman, these resultssuggest that many (and maybe most) elliptical galaxies are either nearlyaxisymmetric or spherical near the center, or slowly evolve due to theinfluence of stochastic orbits.
| The Centers of Early-Type Galaxies With HST. II. Empirical Models and Structural Parameters
We present a set of structural parameters for the central parts of 57early-type galaxies observed with the Planetary Camera of the HubbleSpace Telescope. These parameters are based on a new empirical law thatsuccessfully characterizes the centers of early-type galaxies. Thisempirical law assumes that the surface brightness profile is acombination of two power laws with different slopes γ and βfor the inner and outer regions. Conventional structural parameters suchas core radius and central surface brightness are replaced by breakradius r_b_, where the transition between power-law slopes takes place,and surface brightness μ_b_ at that radius. An additional parameterα describes the sharpness of the break. The structural parametersare derived using a X^2^ minimization process applied to the meansurface brightness profiles. The resulting model profiles generally givevery good agreement to the observed profiles out to the radius of ~10"imaged by the Planetary Camera. Exceptions include galaxies which departfrom pure power laws at large radius, those with strong nuclearcomponents, and galaxies partly obscured by dust. The uncertainties inthe derived parameters are estimated using Monte Carlo simulations whichtest the stability of solutions in the face of photon noise and theeffects of the deconvolution process. The covariance of the structuralparameters is examined by computing contours of constant X^2^ inmulti-dimensional parameter space.
| The fundamental plane of early-type galaxies: stellar populations and mass-to-light ratio.
We analyse the residuals to the fundamental plane (FP) of ellipticalgalaxies as a function of stellar-population indicators; these are basedon the line-strength parameter Mg_2_ and on UBVRI broad-band colors, andare partly derived from new observations. The effect of the stellarpopulations accounts for approximately half the observed variation ofthe mass-to-light ratio responsible for the FP tilt. The residual tiltcan be explained by the contribution of two additional effects: thedependence of the rotational support, and possibly that of the spatialstructure, on the luminosity. We conclude to a constancy of thedynamical-to-stellar mass ratio. This probably extends to globularclusters as well, but the dominant factor would be here the luminositydependence of the structure rather than that of the stellar population.This result also implies a constancy of the fraction of dark matter overall the scalelength covered by stellar systems. Our compilation ofinternal stellar kinematics of galaxies is appended.
| A Catalog of Stellar Velocity Dispersions. II. 1994 Update
A catalog of central velocity dispersion measurements is presented,current through 1993 September. The catalog includes 2474 measurementsof 1563 galaxies. A standard set of 86 galaxies is defined, consistingof galaxies with at least three reliable, concordant measurements. It issuggested that future studies observe some of these standard galaxies sothat different studies can be normalized to a consistent system. Allmeasurements are reduced to a normalized system using these standards.
| The Centers of Early-Type Galaxies with HST.I.An Observational Survey
We have obtained V-band images of 45 nearby elliptical galaxies andbulges using the original Planetary Camera of the Hubble SpaceTelescope. The majority of the sample is at distances of 10-20 Mpc. Thisrepresents a substantial increase in the number of galaxies that havebeen studied at a resolution of a few parsecs. At this resolution, manygalaxies reveal previously unknown central disks, dust clouds, andnuclear components. We find that galaxies have two types of brightnessprofiles. The first type consists of galaxies that have cores. Thesegalaxies have brightness profiles that "break" from steep outer powerlaws to shallow inner cusps. The core class includes many galaxies thathad cores apparently resolved from the ground. The second type consistsof galaxies that have profiles that continue into the resolution limitas steep power laws, showing no evidence of cores of any sort. We thusfind that all galaxies studied so far have singular brightness profilesin the sense that I(r) ~ r^-γ^ as r - 0.1", with 0 < γ< 0.3 at the few parsec scale for galaxies with cores, and γ ~1 for power-law galaxies. No galaxies in our sample have a centralregion that is constant in surface brightness. This implies that thestellar density in these systems is still increasing steeply at the HSTresolution limit. Many galaxies reach stellar mass densities of ~5 x10^4^ M_sun_ pc^-3^ at the resolution limit, appearing similar in formto M32 at radii of a few parsecs. The core and power-law profile classescorrespond to the Jaffe et al. (AJ, 108, 1567 (1994)] Type I and IIprofiles; however, we disagree with their suggestion that the presenceof a central stellar disk is closely related to, or even determines,profile type. Power-law galaxies are seen at all ellipticities, and themajority of them show no evidence for central disks.
| Spectroscopy and photometry of elliptical galaxies. III - UBV aperture photometry, CCD photometry, and magnitude-related parameters
Photoelectric aperture photometry of nearly 2000 individual observationsof 449 elliptical galaxies combined with published measurements usingthe self-consistent UVB color catalog developed by Burstein et al.(1987) are presented. The data are placed on a standard magnitude andcolor system, and 'total' magnitudes and effective diameters are derivedby comparison with the standard elliptical magnitude growth curve. Agraphical representation of the standard growth curve and the residualsfrom it for each galaxy are given, and a new diameter measurement Dn ispresented which can be measured reliably for elliptical galaxies andserves as an accurate distance indicator when combined with centralvelocity dispersion. Individual magnitudes, surface brightnesses,effective diameters, and values of Dn are summarized for each galaxy incatalog form.
| Spectroscopy and photometry of elliptical galaxies. II - The spectroscopic parameters
Radial velocities, velocity dispersions, and Mg line-strength indicesare measured for 469 elliptical galaxies using four telescope/detectorconfigurations. The data have been put on a common scale; the scatter ofrepeat measurements indicates an uncertainty of + or - 10 percent and +or - 0.01 mag for single determinations of sigma and Mg2, respectively.A correction for the change in linear aperture size as a function ofdistance has been derived, and mean corrected values of sigma and Mg2are adopted. The galaxies have been assigned to groups by combining thepresent velocities with those in the redshift catalog of Huchra et al.(1983) and using the algorithm of Huchra and Geller (1982).
| New galaxies with high surface brightness in the Nilson system
Using Arkelian's criteria (1974, 1975), data for 47 new High SurfaceBrightness Galaxies (HSBG) in the system of the Uppsala GeneralCatalogue of Galaxies are presented. Of the 193 Arkelian galaxies listedin the catalog, 46 were also found to be HSBGs in the Nilson system(1973). The present list contains 19 Zwicky (1971) compact galaxies (40percent), two of which are listed as HSBGs by Nilson.
| Radio observations of galaxies of the Byurakan classification at 102 MHz
Interplanetary-scintillation observations at 102 MHz have been made of131 galaxies of the Biurakan classification (1975). It is found thatgalaxies with more pronounced nuclei have higher activity in the radiorange and that scintillating components (with angular dimensions about0.1 arcsec) are more frequently found in them. The scintillatingcomponents have steep spectra.
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