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Circumnuclear Structure and Black Hole Fueling: Hubble Space Telescope NICMOS Imaging of 250 Active and Normal Galaxies
Why are the nuclei of some galaxies more active than others? If mostgalaxies harbor a central massive black hole, the main difference isprobably in how well it is fueled by its surroundings. We investigatethe hypothesis that such a difference can be seen in the detailedcircumnuclear morphologies of galaxies using several quantitativelydefined features, including bars, isophotal twists, boxy and diskyisophotes, and strong nonaxisymmetric features in unsharp-masked images.These diagnostics are applied to 250 high-resolution images of galaxycenters obtained in the near-infrared with NICMOS on the Hubble SpaceTelescope. To guard against the influence of possible biases andselection effects, we have carefully matched samples of Seyfert 1,Seyfert 2, LINER, starburst, and normal galaxies in their basicproperties, taking particular care to ensure that each was observed witha similar average scale (10-15 pc pixel-1). Severalmorphological differences among our five different spectroscopicclassifications emerge from the analysis. The H II/starburst galaxiesshow the strongest deviations from smooth elliptical isophotes, whilethe normal galaxies and LINERs have the least disturbed morphology. TheSeyfert 2s have significantly more twisted isophotes than any othercategory, and the early-type Seyfert 2s are significantly more disturbedthan the early-type Seyfert 1s. The morphological differences betweenSeyfert 1s and Seyfert 2s suggest that more is at work than simply theviewing angle of the central engine. They may correspond to differentevolutionary stages.
| The Near-Infrared Ca II Triplet-σ Relation for Bulges of Spiral Galaxies
We present measurements of the near-infrared Ca II triplet (CaT, CaT*),Paschen (PaT), and magnesium (Mg I) indices for a well-studied sample of19 bulges of early to intermediate spiral galaxies. We find that boththe CaT* and CaT indices decrease with central velocity dispersionσ with small scatter. This dependence is similar to that recentlyfound by Cenarro for elliptical galaxies, implying a uniformCaT*-σ relation that applies to galaxies from ellipticals tointermediate-type spirals. The decrease of CaT and CaT* with σcontrasts with the well-known increase of another α-element index,Mg2, with σ. We discuss the role of Ca underabundance([Ca/Fe]<0) and initial mass function variations in the onset of theobserved relations.
| Minor axis kinematics of 19 S0-Sbc bulges
We present minor axis kinematic profiles for a well-studied sample of 19early- to intermediate-type disk galaxies. We introduce, for the firsttime, the use of single-burst stellar population (SSP) models to obtainstellar velocities, velocity dispersions and higher order Gauss-Hermitemoments (h3, h4) from galaxy spectra in thenear-infrared Ca II triplet region. SSP models, which employs thesynthetic spectra of \citet{vazdekis03}, provide a means to address thetemplate-mismatch problem, and are shown to provide as good or betterfits as traditional stellar templates. We anticipate the technique to beof particular use for high-redshift galaxy kinematics. We give themeasurement of a recently defined CaT* index\citep{cenarro01}, and describe the global properties of the bulgekinematics as derived from the kinematic profiles. We detectsmall-amplitude minor-axis rotation, generally due to inner isophotaltwists as a result of slightly triaxial bulges or misaligned innerdisks; such inner features do not show peculiar colors or distinctCaT* index values. Velocity dispersion profiles, which extendwell into the disk region, show a wide range of slopes. Flattened bulgestend to have shallower velocity dispersion profiles. The inferredsimilarity of bulge and disk radial velocity dispersions supports theinterpretation of these bulges as thickened disks.Appendix B is only available in electronic form athttp://www.edpsciences.org
| Bulges on the Fundamental Plane of early-type galaxies
In an ongoing effort to study the formation and evolution of galacticbulges, we have investigated the position of 19 bulges of type S0-Sbc onthe Fundamental Plane (FP). We find that bulges, in both B and K band,lie close to but slightly below the FP defined by ellipticals and S0s,i.e. are slightly brighter. There are hints that bulges of latermorphological type are situated below the other bulges in our sample.The FP results are consistent with the picture, obtained from our recentanalysis of HST colours, that bulges are old, except for the Sbcgalaxies. The fact that bulges lie so close to the FP of ellipticals andS0s implies that their formation epoch must have been similar to, atmost about 2.5 Gyr earlier than, cluster Es and S0s, and that thesurrounding disc does not significantly affect their structure.
| A catalogue and analysis of local galaxy ages and metallicities
We have assembled a catalogue of relative ages, metallicities andabundance ratios for about 150 local galaxies in field, group andcluster environments. The galaxies span morphological types from cD andellipticals, to late-type spirals. Ages and metallicities were estimatedfrom high-quality published spectral line indices using Worthey &Ottaviani (1997) single stellar population evolutionary models. Theidentification of galaxy age as a fourth parameter in the fundamentalplane (Forbes, Ponman & Brown 1998) is confirmed by our largersample of ages. We investigate trends between age and metallicity, andwith other physical parameters of the galaxies, such as ellipticity,luminosity and kinematic anisotropy. We demonstrate the existence of agalaxy age-metallicity relation similar to that seen for local galacticdisc stars, whereby young galaxies have high metallicity, while oldgalaxies span a large range in metallicities. We also investigate theinfluence of environment and morphology on the galaxy age andmetallicity, especially the predictions made by semi-analytichierarchical clustering models (HCM). We confirm that non-clusterellipticals are indeed younger on average than cluster ellipticals aspredicted by the HCM models. However we also find a trend for the moreluminous galaxies to have a higher [Mg/Fe] ratio than the lowerluminosity galaxies, which is opposite to the expectation from HCMmodels.
| Correlations among Global Photometric Properties of Disk Galaxies
Using a two-dimensional galaxy image decomposition technique, we extractglobal bulge and disk parameters for a complete sample of early-typedisk galaxies in the near-infrared K band. We find significantcorrelation of the bulge parameter n with the central bulge surfacebrightness μb(0) and with effective radiusre. Using bivariate analysis techniques, we findthat logn, logre, and μb(0) are distributed ina plane with small scatter. We do not find a strong correlation of nwith bulge-to-disk luminosity ratio, contrary to earlier reports. Forthese early-type disk galaxies, re and the diskscale length rd are well correlated, but withlarge scatter. We examine the implications of our results for variousbulge formation scenarios in disk galaxies.
| Galactic bulges from Hubble Space Telescope NICMOS observations: ages and dust
We present optical and near-infrared colour maps of the central regionsof bulges of S0 and spiral galaxies obtained with WFPC2 and NICMOS onthe Hubble Space Telescope (HST). By combined use of HST andground-based data, the colour information spans a region from a few tensof pc to a few kpc. In almost all galaxies, the colour profiles in thecentral 100-200pc become more rapidly redder. We attribute the highcentral colour indices to a central concentration of dust. We infer anaverage extinction at the centre of AV=0.6-1.0mag. Severalobjects show central dust rings or discs at subkpc scales similar tothose found by others in giant ellipticals. For galactic bulges of typesS0 to Sb, the tightness of the B-I versus I-H relation suggests that theage spread among bulges of early-type galaxies is small, at most 2Gyr.Colours at 1Reff, where we expect extinction to benegligible, are similar to those of elliptical galaxies in the Comacluster, suggesting that these bulges formed at the same time as thebright galaxies in Coma. Furthermore, the galaxy ages are found to beindependent of their environment. As it is likely that Coma was formedat redshift z>3, our bulges, which are in groups and in the field,must also have been formed at this epoch. Bulges of early-type spiralscannot be formed by secular evolution of bars at recent epochs, becausesuch bulges would be much younger. There are three galaxies of type Sbcand later; their bulges are younger and could perhaps arise from secularevolution of transient bars. Our results are in good agreement withsemi-analytic predictions, which also predict that bulges, in clustersand in the field, are as old as giant ellipticals in clusters.
| 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.
| Near-infrared surface photometry of bulges and disks of spiral galaxies. The data
We present optical and near-infrared (NIR) surface brightness and colourprofiles, in bands ranging from U to K, for the disk and bulgecomponents of a complete sample of 30 nearby S0 to Sbc galaxies withinclinations larger than 50 deg. We describe in detail the observationsand the determination of colour parameters. Calibrated monochromatic andreal-colour images are presented, as well as colour index maps. Thisdata set, tailored for the study of the population characteristics ofgalaxy bulges, provides useful information on the colours of inner disksas well. In related papers, we have used them to quantify colourgradients in bulges, and age differentials between bulge and inner disk.
| Ages of Galaxies Bulges and Disks From Optical and Near-Infrared Colors
We compare optical and near-infrared colors of disks and bulges in adiameter-limited sample of inclined, bright, nearby, early-type spirals.Color profiles along wedge apertures at 15^deg^ from the major axis andon the minor axis on the side of the galaxy opposite to the dust laneare used to assign nominal colors for the inner disks (at 2 scalelength) and for the bulges (~0.5r_eff_), respectively. We estimate thatthe effects of dust reddening and the cross-talk between the colors ofthe two components is negligible. We find that color differences(bulge-disk) are very small: {DELTA}(U-R) = 0.126+/-0.165,{DELTA}(R-K)=0078+/-0.165. Disks tend to be bluer by an amount threetimes smaller than that reported by Bothun & Gregg [ApJ,350,73(1990)] for S0s. Color variations from galaxy to galaxy are muchlarger than color differences between disk and bulge in each galaxy.Probably, the underlying old population of disks and bulges is much moresimilar than the population paradigm would lead us to believe. Impliedage differences, assuming identical metallicities, are less than 30%.
| The Shape of the Luminosity Profiles of Bulges of Spiral Galaxies
Using a 2D generalization of Kent's model-independent decompositionmethod, we extract the K-band light profiles of the bulges of a sampleof field galaxies with morphological types ranging from S0 to Sbc. Wethen examine the shape of the bulge profiles, by means of fitting aseeing-convolved power law of the form μ(r) is proportional tor^1/n^, where the exponent n is allowed to vary. The best-fittingexponent n is found to vary systematically from values around 1(exponential) to 6 from late- to early- type bulges; the profiles tendto fall off more steeply in the outer parts for the later types. Thesame trend is seen as a function of bulge to disc ratio. Application ofthe method to artificial data proves that this result is not caused bydisc-light contamination. There are also indications that n becomeslarger with increasing total luminosity and radius of the bulge. Asimilar relation has recently been found for elliptical galaxies. Thesmooth trend of n with morphological type shows that the formation of orinteraction with the disc has affected the density distribution of thebulge.
| Arm structure in normal spiral galaxies, 1: Multivariate data for 492 galaxies
Multivariate data have been collected as part of an effort to develop anew classification system for spiral galaxies, one which is notnecessarily based on subjective morphological properties. A sample of492 moderately bright northern Sa and Sc spirals was chosen for futurestatistical analysis. New observations were made at 20 and 21 cm; thelatter data are described in detail here. Infrared Astronomy Satellite(IRAS) fluxes were obtained from archival data. Finally, new estimatesof arm pattern radomness and of local environmental harshness werecompiled for most sample objects.
| Galaxy structures in the Hercules region
216 redshifts have been obtained in a region of 981 sq deg south of theHercules supercluster. 172 of these redshifts are of galaxies withmpg less than or equal to 15.1, 110 of which had no previousvelocity measurement. 44 new redshifts are of galaxies fainter thanmpg = 15.1. With these new data we have been able to define asample in a vast region (approximately 1700 sq deg) around Herculeslimited to mpg less than or equal to 15.1 with a velocitycompleteness of 81.5%. 189 galaxies have been morphologically classifiedso that all galaxies in the sample with known velocity now also haveknown morphology. The magnitude limited sample, including 556 galaxies,is then used to identify and describe galaxy structures in the region.We find that the overdense volume is small, that its overall appearanceis that of a coral branch floating in a sea of nothing and that earlyand late type galaxies defined different structures.
| Colors and color gradients in bulges of galaxies
We have obtained surface photometry in U, B, R, and I for a completeoptically selected sample of 45 early-type spiral galaxies, toinvestigate the colors and color gradients of spiral bulges. Colorprofiles in U-R, B-R, U-B, and R-I have been determined in wedgesopening on the semiminor axes. Based on several criteria, like thesmoothness of the color profiles, the absence of dust lanes, and thecentral colors, we have defined a subsample of 18 objects whose colorsare largely unaffected by dust. We believe such colors are suitable forinferring properties of the stellar populations of bulges. We find thatthe colors of bulges are predominantly bluer than those of ellipticals.This result holds even when bulges are compared to ellipticals of thesame luminosity, and indicates that bulges are younger and/or more metalpoor than old elliptical galaxies. Most bulges do not reach solarmetallicities. Bulges show predominantly negative color gradients (blueroutward). For bright bulges (MBulgeR is less than-20.0), the magnitude of the gradient increases with bulge luminosity.For fainter bulges, gradients scatter around large negative values. Thebehavior of color gradients as a function of bulge luminosity suggestsdifferent formation mechanisms for faint and bright spheroids. Forbright bulges, the scaling of gradients with luminosity suggests aformation process involving dissipation. The similarity with ellipticalssuggests that the formation of the disk did not affect the stellarpopulations of the bulge in a major way. For small bulges (MRis greater than -20), the existence of pronounced color gradientssuggests a different formation mechanism. For these objects, thepresence of the disk may have severely affected the radial populationdistribution in the bulge.
| Axial ratios of edge-on spirals
A diameter-limited sample of 888 normal Sa-Sc galaxies was compiled fromthe Uppsala General Catalog. New micrometer measures of the axial ratiosR of the disk components of 262 edge-on spirals in this sample were madeon copies of blue Palomar Sky Survey plates and calibrated againstphotometric standards. The distribution of isophotal axial ratios forthe whole sample was analyzed to give information on the true axialratios R0 of spiral disks. The mean value of logR0 is 0.95 +/- 0.03 and the dispersion about this mean is0.12 +/- 0.04. A similar mean value (0.90) was obtained from avolume-limited sub-sample of 348 spirals. The dispersion in logR0 is partly due to a dependence of R0 onmorphological type, and the mean value of log R0 for eachtype was estimated. Inclinations of 342 edge-on (R is greater than about3) spirals were determined from their isophotal axial ratios and types.No significant dependence of R0 on luminosity at each typewas found.
| Velocity calibration of the Las Campanas redshift survey
The Center for Astrophysics redshift survey is being extended bySchectman et al. (1983) to the south galactic cap. Their initial resultsprovide independent estimates of both emission Ve velocities and theabsorption line Vc velocities, such that (Ve-Vc) = 54 + or - 13 km/s. HI line observations of 40 of the sample are presented here, to provide asecure velocity scale calibration. The Vc velocities are found to have a32 + or - 9 km/s zero-point error.
| Redshifts for 115 galaxies near the equator
New redshifts for 115 bright galaxies located near the celestial equatorare reported. The spectra were observed with a blue-sensitivephoton-counting Reticon on the 100-in. DuPont telescope, and theredshifts were derived using the data-analysis system developed for theCfA Redshift Survey. Comparisons with other measured redshifts suggestthat these data are similar in quality to the redshifts measured at Mt.Hopkins for the CfA Redshift Survey; the velocity zero point is good to10 or 15 km/s, with a typical error of 35 km/s for the individualmeasurements.
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