No abstract

We report data for I-band surface brightness Ñuctuation (SBF) magnitudes, (V [I) colors, and distance moduli for 300 galaxies. The survey contains E, S0, and early-type spiral galaxies in the proportions of 49 : 42 : 9 and is essentially complete for E galaxies to Hubble velocities of 2000 km s~1, with a substantial sampling of E galaxies out to 4000 km s~1. The median error in distance modulus is 0.22 mag. We also present two new results from the survey. (1) We compare the mean peculiar Ñow velocity (bulk Ñow) implied by our distances with predictions of typical cold dark matter transfer functions as a function of scale, and we Ðnd very good agreement with cold, dark matter cosmologies if the transfer function scale parameter ! and the power spectrum normalization are related by Derived p 8 p 8 !~0.5 B 2^0.5. directly from velocities, this result is independent of the distribution of galaxies or models for biasing. This modest bulk Ñow contradicts reports of large-scale, large-amplitude Ñows in the D200 Mpc diameter volume surrounding our survey volume. (2) We present a distance-independent measure of absolute galaxy luminosity, and show how it correlates with galaxy properties such as color and velocity dis-N persion, demonstrating its utility for measuring galaxy distances through large and unknown extinction.

We present the photometric calibration of the Advanced Camera for Surveys (ACS). The ACS was installed in the Hubble Space Telescope (HST) in 2002 March. It comprises three cameras: the Wide Field Channel (WFC), optimized for deep near-IR survey imaging programs; the High Resolution Channel (HRC), a high-resolution imager that fully samples the HST point-spread function (PSF) in the visible; and the Solar Blind Channel (SBC), a far-UV imager. A significant amount of data has been collected to characterize the on-orbit performance of the three channels. We give here an overview of the performance and calibration of the two CCD cameras (WFC and HRC) and a description of the best techniques for reducing ACS CCD data. The overall performance is as expected from prelaunch testing of the camera. Surprises were a better-thanpredicted sensitivity in the visible and near-IR for both the WFC and HRC and an unpredicted dip in the HRC UV response at ∼3200 A ˚. On-orbit observations of spectrophotometric standard stars have been used to revise the prelaunch estimate of the instrument response curves to best match predicted and observed count rates. Synthetic photometry has been used to determine zero points for all filters in three magnitude systems and to derive interstellar extinction values for the ACS photometric systems. Due to the CCD internal scattering of longwavelength photons, the width of the PSF increases significantly in the near-IR, and the aperture correction for photometry with near-IR filters depends on the spectral energy distribution of the source. We provide a detailed recipe to correct for the latter effect. Transformations between the ACS photometric systems and the UBVRI and WFPC2 systems are presented. In general, two sets of transformations are available: one based on the observation of two star clusters; the other on synthetic photometry. We discuss the accuracy of these transformations and their sensitivity to details of the spectra being transformed. Initial signs of detector degradation due to the HST radiative environment are already visible. We discuss the impact on the data in terms of dark rate increase, charge transfer inefficiency, and "hot" pixel population.

We present a detailed analysis of the morphology, isophotal parameters and surface brightness profiles for 100 early-type members of the Virgo Cluster, from dwarfs (M B = −15.1 mag) to giants (M B = −21.8 mag). Each galaxy has been imaged in two filters, closely resembling the Sloan g and z passbands, using the Advanced Camera for Surveys on board the Hubble Space Telescope. Dust and complex morphological structures are common. Dust is detected in as many as 18, preferentially bright, galaxies. The incidence rate in the 26 galaxies brighter than B T = 12.15 mag, which form a magnitude limited sample, is 42%. The amount and distribution of dust show no obvious correlations with galaxy morphology; dust features range from faint wisps and patches on tens of parsec scales, to regular, highly organized kpc-scale dust disks. Blue star clusters are interspersed within the larger, clumpier dust disks, while thin, dynamically cold stellar disks are seen in association with the smaller, uniform nuclear dust disks. Kiloparsec-scale stellar disks, bars, and nuclear stellar disks are seen in 60% of galaxies with intermediate luminosity (−20 M B −17). In at least one case (VCC 1938 = NGC 4638), the large-scale stellar disk has a sharp inner edge, possibly produced when disk instabilities led to the formation of a (now dissolved) bar. This process might indeed be seen unfolding in one galaxy, VCC 1537 (=NGC 4528). A spiral structure might be present in VCC 1199, an elliptical companion of M49. In dwarf galaxies, spiral structures are confirmed in VCC 856 and detected for the first time in VCC 1695. Surface brightness profiles, ellipticities, major axis position angles, and isophotal shapes are derived typically within 8 kpc from the center for the brightest galaxies, and 1.5 kpc for the faintest systems, with a resolution (FWHM) of 7 pc. For all but 10 of the galaxies, the surface brightness profiles are well described by a Sérsic model with index n which increases steadily from the fainter to the brightest galaxies. In agreement with previous claims, the inner profiles (typically within 100 pc of the center) of eight of the 10 brightest galaxies, to which we will refer as "core" galaxies, are lower than expected based on an extrapolation of the outer Sérsic model, and are better described by a single power-law function. Core galaxies are clearly distinct in having fainter central surface brightness, µ 0 , and shallower logarithmic slope of the inner surface brightness profile, γ, than expected based on the extrapolation of the trend followed by the rest of the sample, for which both µ 0 and γ increase steadily with galaxy magnitude. Large-scale, global properties also set core galaxies apart: the effective radius in particular is found to be almost one order of magnitude larger than for only slightly less luminous non-core galaxies. Contrary to previous claims, we find no evidence in support of a strong bimodal behavior of the inner profile slope, γ; in particular the γ distribution for galaxies which do not show evidence of m...

We present the color distributions of globular cluster (GC) systems for 100 Virgo cluster earlytype galaxies observed in the ACS Virgo Cluster Survey, the deepest and most homogeneous survey of this kind to date. While the color distributions of individual GC systems can show significant variations from one another, their general properties are consistent with continuous trends across galaxy luminosity, color, and stellar mass. On average, galaxies at all luminosities in our study (−22 < M B < −15) appear to have bimodal or asymmetric GC color distributions. Almost all galaxies possess a component of metal-poor GCs, with the average fraction of metal-rich GCs ranging from 15 to 60%. The colors of both subpopulations correlate with host galaxy luminosity and color, with the red GCs having a steeper slope. The steeper correlation seen in the mean color of the entire GC system is driven by the increasing fraction of metal-rich GCs for more luminous galaxies.To convert color to metallicity, we also introduce a preliminary (g-z)-[Fe/H] relation calibrated to Galactic, M49 and M87 GCs. This relation is nonlinear with a steeper slope for [Fe/H] −0.8. As a result, the metallicities of the metal-poor and metal-rich GCs vary similarly with respect to galaxy luminosity and stellar mass, with relations of [Fe/H] MP ∝ L 0.16±0.04 ∝ M 0.17±0.04 ⋆ and [Fe/H] MR ∝ L 0.26±0.03 ∝ M 0.22±0.03 ⋆, respectively. Although these relations are shallower than the mass-metallicity relation predicted by wind models and observed for dwarf galaxies, they are very similar to the mass-metallicity relation for star forming galaxies in the same mass range. The offset between the two GC populations varies slowly (∝ M 0.05 ⋆ ) and is approximately 1 dex across three orders of magnitude in mass, suggesting a nearly universal amount of enrichment between the formation of the two populations of GCs. We also find that although the metal-rich GCs show a larger dispersion in color, it is the metal-poor GCs that have an equal or larger dispersion in metallicity. The similarity in the M ⋆ -[Fe/H] relations for the two populations, implies that the conditions of GC formation for metal-poor and metal-rich GCs could not have been too different. Like the color-magnitude relation, these relations derived from globular clusters present stringent constraints on the formation and evolution of early-type galaxies.

The ACS Virgo Cluster Survey consists of HST ACS imaging for 100 early-type galaxies in the Virgo Cluster, observed in the F475W (%SDSS g) and F850LP (%SDSS z) filters. We derive distances for 84 of these galaxies using the method of surface brightness fluctuations (SBFs), present the SBF distance catalog, and use this database to examine the three-dimensional distribution of early-type galaxies in the Virgo Cluster. The SBF distance moduli have a mean (random) measurement error of 0.07 mag (0.5 Mpc), or roughly 3 times better than previous SBF measurements for Virgo Cluster galaxies. Five galaxies lie at a distance of d % 23 Mpc and are members of the W 0 cloud. The remaining 79 galaxies have a narrow distribution around our adopted distance of hdi ¼ 16:5 AE 0:1 (random mean error) AE1.1 Mpc (systematic). The rms distance scatter of this sample is (d ) ¼ 0:6 AE 0:1 Mpc, with little or no dependence on morphological type or luminosity class (i.e., 0:7 AE 0:1 and 0:5 AE 0:1 Mpc for the giants and dwarfs, respectively). The back-to-front depth of the cluster measured from our sample of early-type galaxies is 2:4 AE 0:4 Mpc (i.e., AE 2 of the intrinsic distance distribution). The M87 (cluster A) and M49 (cluster B) subclusters are found to lie at distances of 16:7 AE 0:2 and 16:4 AE 0:2 Mpc, respectively. There may be a third subcluster associated with M86. A weak correlation between velocity and line-of-sight distance may be a faint echo of the cluster velocity distribution not having yet completely virialized. In three dimensions, Virgo's early-type galaxies appear to define a slightly triaxial distribution, with axis ratios of (1: 0.7 : 0.5). The principal axis of the best-fit ellipsoid is inclined $20 Y 40 from the line of sight, while the galaxies belonging to the W 0 cloud lie on an axis inclined by $10 Y15 .

We present (g 475 −z 850 ) color and z 850 -band surface brightness fluctuations (SBF) measurements for 43 earlytype galaxies in the Fornax cluster imaged with the Hubble Space Telescope Advanced Camera for Surveys. These are combined with our earlier measurements for Virgo cluster galaxies to derive a revised, nonlinear calibration of the z 850 -band SBF absolute magnitude M z as a function of (g 475 −z 850 ) color, valid for the AB color range 0.8 < (g 475 −z 850 ) < 1.6. In all, we tabulate recalibrated SBF distances for 134 galaxies in Virgo, Fornax, the Virgo W ′ group, and NGC 4697 in the Virgo Southern Extension. The calibration procedure yields a highly precise relative distance modulus for Fornax with respect to Virgo of ∆(m− M) FV = 0.42 ± 0.03 mag, or a distance ratio d F /d V = 1.214±0.017. The resulting Fornax distance modulus is (m−M) For = 31.51±0.03±0.15 mag, corresponding to d F = 20.0 ± 0.3 ± 1.4 Mpc, where the second set of error bars reflects the total systematic uncertainty from our assumed Virgo distance of 16.5 Mpc. The rms distance scatter for the early-type Fornax cluster galaxies is σ d = 0.49 +0.11 −0.15 Mpc, or a total line-of-sight depth of 2.0 +0.4 −0.6 Mpc, consistent with its compact appearance on the sky. This translates to a depth scatter smaller than the intrinsic, or "cosmic," scatter σ cos in the SBF calibration, unlike the case for the larger Virgo cluster. As a result, we are able to place the first tight constraints on the value of σ cos . We find σ cos = 0.06 ± 0.01 mag, with a firm upper limit of σ cos < 0.08 mag, for the subsample of galaxies with (g 475 −z 850 ) > 1.02, but it is about twice as large for bluer galaxies. We also present an alternative SBF calibration based on the 'fluctuation count' parameter N = m − m tot , a proxy for galaxy mass. This gives a consistent relative distance but with larger intrinsic scatter, and we adopt the result from the calibration on (g 475 −z 850 ) because of its basis in stellar population properties alone. Finally, we find no evidence for systematic trends of the galaxy distances with position or velocity (e.g., no current infall); the Fornax cluster appears both compact and well virialized.

We have detected 506 i-dropouts (z ∼ 6 galaxies) in deep, wide-area HST ACS fields: HUDF, enhanced GOODS, and HUDF-Parallel ACS fields (HUDF-Ps). The contamination levels are 8% (i.e., 92% are at z ∼ 6). With these samples, we present the most comprehensive, quantitative analyses of z ∼ 6 galaxies yet and provide optimal measures of the U V luminosity function (LF) and luminosity density at z ∼ 6, and their evolution to z ∼ 3. We redetermine the size and color evolution from z ∼ 6 to z ∼ 3. Field-to-field variations (cosmic variance), completeness, flux, and contamination corrections are modelled systematically and quantitatively. After corrections, we derive a rest-frame continuum UV (∼ 1350Å) LF at z ∼ 6 that extends to M 1350,AB ∼ −17.5 (0.04L * z=3 ). There is strong evidence for evolution of the LF between z ∼ 6 and z ∼ 3, most likely through a brightening (0.6 ± 0.2 mag) of M * (at 99.7% confidence) though the degree depends upon the faint-end slope. As expected from hierarchical models, the most luminous galaxies are deficient at z ∼ 6. Density evolution (φ * ) is ruled out at >99.99% confidence. Despite large changes in the LF, the luminosity density at z ∼ 6 is similar (0.82 ± 0.21×) to that at z ∼ 3. Changes in the mean UV color of galaxies from z ∼ 6 to z ∼ 3 suggest an evolution in dust content, indicating the true evolution is substantially larger: at z ∼ 6 the star formation rate density is just ∼ 30% of the z ∼ 3 value. Our UV luminosity function is consistent with z ∼ 6 galaxies providing the necessary UV flux to reionize the universe.