Stephane Courteau

Homogeneous Velocity-Distance Data for Peculiar Velocity Analysis. III. The Mark III Catalog of Galaxy Peculiar Velocities

This is the third in a series of papers in which we assemble and analyze a homogeneous catalog of peculiar velocity data. In Papers I and II, we described the Tully-Fisher (TF) redshift-distance samples that constitute the bulk of the catalog and our methodology for obtaining mutually consistent TF calibrations for these samples. In this paper, we supply further technical details of the treatment of the data and present a subset of the catalog in tabular form. The full catalog, known as the Mark III Catalog of Galaxy Peculiar Velocities, is available in accessible on-line databases, as described herein. The electronic catalog incorporates not only the TF samples discussed in Papers I and II but also elliptical galaxy Dn-σ samples originally presented elsewhere. The relative zero pointing of the elliptical and spiral data sets is discussed here. The basic elements of the Mark III Catalog are the observables for each object (redshift, magnitude, velocity width, etc.) and inferred distances derived from the TF or Dn-σ relations. Distances obtained from both the forward and inverse TF relations are tabulated for the spirals. Malmquist bias-corrected distances are computed for each catalog object using density fields obtained from the IRAS 1.2 Jy redshift survey. Distances for both individual objects and groups are provided. A variety of auxiliary data, including distances and local densities predicted from the IRAS redshift survey reconstruction method, are tabulated as well. We study the distributions of TF residuals for three of our samples and conclude that they are well approximated as Gaussian. However, for the Mathewson et al. sample we demonstrate a significant decrease in TF scatter with increasing velocity width. We test for, but find no evidence of, a correlation between TF residuals and galaxy morphology. Finally, we derive transformations that map the apparent magnitude and velocity width data for each spiral sample onto a common system. This permits the application of analysis methods that assume that a unique TF relation describes the entire sample.

A Revised Model for the Formation of Disk Galaxies: Low Spin and Dark Halo Expansion

We use observed rotation velocity-luminosity (VL) and size-luminosity (RL) relations to single out a specific scenario for disk galaxy formation in the ΛCDM cosmology. Our model involves four independent lognormal random variables: dark halo concentration c, disk spin λgal, disk mass fraction mgal, and stellar mass-to-light ratio I. A simultaneous match of the VL and RL zero points with adiabatic contraction requires low-c halos, but this model has V2.2 ~ 1.8Vvir (where V2.2 and Vvir are the circular velocity at 2.2 disk scale lengths and the virial radius, respectively), which will be unable to match the luminosity function (LF). Similarly models without adiabatic contraction but standard c also predict high values of V2.2/Vvir. Models in which disk formation induces an expansion rather than the commonly assumed contraction of the dark matter halos have V2.2 ~ 1.2Vvir, which allows a simultaneous fit of the LF. This may result from nonspherical, clumpy gas accretion, where dynamical friction transfers energy from the gas to the dark matter. This model requires low λgal and mgal values, contrary to naive expectations. However, the low λgal is consistent with the notion that disk galaxies predominantly survive in halos with a quiet merger history, while a low mgal is also indicated by galaxy-galaxy lensing. The smaller than expected scatter in the RL relation and the lack of correlation between the residuals of the VL and RL relations, respectively, imply that the scatter in λgal and in c needs to be smaller than predicted for ΛCDM halos, again consistent with the idea that disk galaxies preferentially reside in halos with a quiet merger history.

Evidence for Secular Evolution in Late-Type Spirals

We combine deep optical and IR photometry for 326 spiral galaxies from two recent galaxy samples and report that the surface brightness profiles of late-type spirals are best fitted by two exponentials. Moreover, the ratio of bulge and disk scale lengths takes on a restricted range of values and is uncorrelated with Hubble type. This suggests a scale-free Hubble sequence for late-type spirals. Careful numerical simulations ensure that our results are not affected by seeing or resolution effects. Many of these galaxies show spiral structure continuing into the central regions with a previously undetected small bar and slowly changing colors between the inner disk and the bulge. We invoke secular dynamical evolution and interpret the nature of disk central regions in the context of gas inflow via angular momentum transfer and viscous transport. In this scenario, galaxy morphologies in late-type spirals are not imprinted at birth but are the result of evolution.

Scaling Relations of Spiral Galaxies

We construct a large data set of global structural parameters for 1300 field and cluster spiral galaxies and explore the joint distribution of luminosity L, optical rotation velocity V, and disk size R at I and 2MASS K bands. The I- and K-band velocity-luminosity (VL) relations have log slopes of 0.29 and 0.27, respectively, with σ_(ln)(VL) ~ 0.13, and show a small dependence on color and morphological type in the sense that redder, earlier type disk galaxies rotate faster than bluer, later type disk galaxies for most luminosities. The VL relation at I and K bands is independent of surface brightness, size, and light concentration. The log slope of the I- and K-band size-luminosity (RL) relations is a strong function of morphology and varies from 0.25 to 0.5, with a mean of 0.32 for all Hubble types. At most luminosities, early-type disk galaxies have shorter scale lengths than later type ones. The average dispersion σ_(ln)(RL) decreases from 0.33 at I band to 0.29 at K, likely due to the 2MASS selection bias against lower surface brightness galaxies. The VL and RL residuals are largely uncorrelated with each other with a correlation coefficient r = -0.16 and Δ log V|L/Δ log R|L = -0.07 ± 0.01; the RV - RL residuals show a weak positive correlation with r = 0.53. These correlations suggest that scatter in luminosity is not a significant source of the scatter in the VL and RL relations. We discuss in two Appendices various pitfalls of standard analytical derivations of galaxy scaling relations, including the Tully-Fisher relation with different slopes. Our galaxy database is available at http://www.astro.queensu.ca/~courteau/data/VRL2007.dat.

Old stellar populations .4. Empirical fitting functions for features in the Spectra of G and K stars

Empirical fitting functions are presented that model the behavior of 11 strong atomic and molecular features in the spectra of Galactic G and K stars. The functions express the strength of spectral features as a function of V - K, surface gravity, and metallicity. The gravity calibration rests on stars in Galactic globular and open clusters, for which gravities have been derived by fitting to stellar evolutionary isochrones. The range of application of the fitting functions is set by the calibrating stars. There is good metallicity coverage from [Fe/H] = -0.75 to +0.50 dex, and cluster ages span 3.15 x 10^9 yr. However, the range in age is large only near solar metallicity, and the gravity partial derivatives may therefore be uncertain at metallicities much higher or lower than this value. In addition, the fitting functions build in whatever abundance ratio trajectories of elements relative to iron are present in local Galactic stars; these might differ from the element ratios present in external galaxies. In general, the behavior of the fitting functions matches expectations as to how these spectral features should behave as a function of basic stellar atmospheric parameters. The exception is CN (4150 A), for which we find strong evidence for rapid onset of giant-branch mixing of CNO products to the stellar surface, setting in at V - K = 2.10. This confirms other recent studies of this index. The paper also presents new Lick line strength data on 112 field dwarfs and 92 cluster stars, plus colors, metallicities, and surface gravities for all Lick G and K stars published previously. The fitting functions are inverted to produce new output gravity and metallicity estimates for these stars and new average metallicities for all clusters, with errors of ±0.15 dex in [Fe/H] and ±0.23 dex in log g per star.

The Solar Motion Relative to the Local Group

New data on the membership of the Local Group (LG) are used, in conjunction with new and improved radial velocity data, to refine the derivation of the motion of the Sun relative to the LG. The Sun is found to be moving with a velocity of V = 306 ± 18 km s-1 toward an apex at l = 99° ± 5° and b = -4° ± 4°. This finding agrees very well with previous analyses, but we discuss the possibility of a bias if the phase-space distribution of LG galaxies is bimodal. The LG radial velocity dispersion is 61 ± 8 km s-1. We use various mass estimators to compute the mass of the LG and the Andromeda subgroup. We find MLG = (2.3 ± 0.6) × 1012 M⊙, from which M/LV = 44 ± 12 (in solar units). For an assumed LG age of 14 ± 2 Gyr, the radius of an idealized LG zero-velocity surface is r0 = 1.18 ± 0.15 Mpc. The LG is found to have 35 likely members. Only three of these have (uncertain) distances 1.0 Mpc from the LG barycenter. Barring new discoveries of low surface brightness dwarfs, this suggests that the LG is more compact and more isolated from its surroundings than previously believed.

THE LUMINOSITY PROFILE AND STRUCTURAL PARAMETERS OF THE ANDROMEDA GALAXY

We have constructed an extended composite luminosity profile for the Andromeda galaxy, M31, and have decomposed it into three basic luminous structural components: a bulge, a disk, and a halo. The dust-free Spitzer/Infrared Array Camera (IRAC) imaging and extended spatial coverage of ground-based optical imaging and deep star counts allow us to map M31s structure from its center to 22 kpc along the major axis. We apply, and address the limitations of, different decomposition methods for the one-dimensional luminosity profiles and two-dimensional images. These methods include nonlinear least-squares and Bayesian Monte Carlo Markov chain analyses. The basic photometric model for M31 has a Sbulge with shape index n � 2.2 ± .3 and effective radius Re = 1.0 ± 0.2 kpc, and a dust-free exponential disk of scale length Rd = 5.3 ± .5 kpc; the parameter errors reflect the range between different decomposition methods. Despite model covariances, the convergence of solutions based on different methods and current data suggests a stable set of structural parameters. The ellipticities (� = 1 − b/a) of the bulge and the disk from the IRAC image are 0.37 ± 0.03 and 0.73 ± 0.03, respectively. The bulge parameter n is rather insensitive to bandpass effects and its value (2.2) suggests a first rapid formation via mergers followed by secular growth from the disk. The M31 halo has a two-dimensional power-law index �− 2.5 ± 0. 2( or−3.5 in three-dimensional), comparable to that of the Milky Way. We find that the M31 bulge light is mostly dominant over the range Rmin 1.2 kpc. The disk takes over in the range 1.2 kpc Rmin 9 kpc, whereas the halo dominates at Rmin 9 kpc. The stellar nucleus, bulge, disk, and halo components each contribute roughly 0.05%, 23%, 73%, and 4% of the total light of M31 out to 200 kpc along the minor axis. Nominal errors for the structural parameters of the M31 bulge, disk, and halo amount to 20%. If M31 and the Milky Way are at all typical, faint stellar halos should be routinely detected in galaxy surveys reaching below μi � 27 mag arcsec −2 . We stress that our results rely on this photometric analysis alone. Structural parameters may change when other fundamental constraints, such as those provided by abundance gradients and stellar kinematics, are considered simultaneously.

The GHOSTS Survey. I. Hubble Space Telescope Advanced Camera for Surveys data

We present an overview of the GHOSTS survey, the largest study to date of the resolved stellar populations in the outskirts of disk galaxies. The sample consists of 14 disk galaxies within 17 Mpc, whose outer disks and halos are imaged with the Hubble Space Telescope Advanced Camera for Surveys (ACS). In the first paper of this series, we describe the sample, explore the benefits of using resolved stellar populations, and discuss our ACS F606W and F814W photometry. We use artificial star tests to assess completeness and use overlapping regions to estimate photometric uncertainties. The median depth of the survey at 50% completeness is 2.7?mag below the tip of the red giant branch (TRGB). We comprehensively explore and parameterize contamination from unresolved background galaxies and foreground stars using archival fields of high-redshift ACS observations. Left uncorrected, these would account for 100.65 ? F814W ? 19.0 detections per mag per arcsec2. We therefore identify several selection criteria that typically remove 95% of the contaminants. Even with these culls, background galaxies are a significant limitation to the surface brightness detection limit which, for this survey, is typically V ~ 30?mag?arcsec?2. The resulting photometric catalogs are publicly available and contain some 3.1 million stars across 76 ACS fields, predominantly of low extinction. The uniform magnitudes of TRGB stars in these fields enable galaxy distance estimates with 2%-7% accuracy.

The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey. I. Star-Forming Molecular Gas in Virgo Cluster Spiral Galaxies

We present large-area maps of the CO J = 3-2 emission obtained at the James Clerk Maxwell Telescope for four spiral galaxies in the Virgo Cluster. We combine these data with published CO J = 1-0, 24 μm, and Hα images to measure the CO line ratios, molecular gas masses, and instantaneous gas depletion times. For three galaxies in our sample (NGC 4254, NGC 4321, and NGC 4569), we obtain molecular gas masses of 7 × 108 – 3 × 109 M ☉ and disk-averaged instantaneous gas depletion times of 1.1-1.7 Gyr. We argue that the CO J = 3-2 line is a better tracer of the dense star-forming molecular gas than the CO J = 1-0 line, as it shows a better correlation with the star formation rate surface density both within and between galaxies. NGC 4254 appears to have a larger star formation efficiency (smaller gas depletion time), perhaps because it is on its first passage through the Virgo Cluster. NGC 4569 shows a large-scale gradient in the gas properties traced by the CO J = 3-2/J = 1-0 line ratio, which suggests that its interaction with the intracluster medium is affecting the dense star-forming portion of the interstellar medium directly. The fourth galaxy in our sample, NGC 4579, has weak CO J = 3-2 emission despite having bright 24 μm emission; however, much of the central luminosity in this galaxy may be due to the presence of a central active galactic nucleus.

A Library of Integrated Spectra of Galactic Globular Clusters

We present a new library of integrated spectra of 40 Galactic globular clusters, obtained with the Blanco 4 m telescope and the R-C spectrograph at the Cerro Tololo Inter-American Observatory. The spectra cover the range ~3350-6430 A with ~3.1 A (FWHM) resolution. The spectroscopic observations and data reduction were designed to integrate the full projected area within the cluster core radii in order to properly sample the light from stars in all relevant evolutionary stages. The S/N values of the flux-calibrated spectra range from 50 to 240 A-1 at 4000 A and from 125 to 500 A-1 at 5000 A. The selected targets span a wide range of cluster parameters, including metallicity, horizontal-branch morphology, Galactic coordinates, Galactocentric distance, and concentration. The total sample is thus fairly representative of the entire Galactic globular cluster population and should be valuable for comparison with similar integrated spectra of unresolved stellar populations in remote systems. For most of the library clusters, our spectra can be coupled with deep color-magnitude diagrams and reliable metal abundances from the literature to enable the calibration of stellar population synthesis models. In this paper we present a detailed account of the observations and data reduction. The spectral library is publicly available in electronic format from the National Optical Astronomical Observatory Web site.