John P. Blakeslee

The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances*

We report data for I-band surface brightness fluctuation (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 flow velocity (bulk flow) implied by our distances with predictions of typical cold dark matter transfer functions as a function of scale, and we find very good agreement with cold, dark matter cosmologies if the transfer function scale parameter Γ and the power spectrum normalization σ8 are related by σ8Γ-0.5 ≈ 2 ± 0.5. Derived directly from velocities, this result is independent of the distribution of galaxies or models for biasing. This modest bulk flow contradicts reports of large-scale, large-amplitude flows in the ~200 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 dispersion, demonstrating its utility for measuring galaxy distances through large and unknown extinction.

The Photometric Performance and Calibration of the Hubble Space Telescope Advanced Camera for Surveys

ABSTRACT 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‐than‐predicted 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 stand...

The ACS Virgo Cluster Survey. VI. Isophotal Analysis and the Structure of Early-Type Galaxies*

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 (MB = -15.1 mag) to giants (MB = -21.8 mag), imaged in the 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 42% of galaxies brighter than BT = 12.15 mag, while kiloparsec-scale stellar disk, bars, and nuclear stellar disks are seen in 60% of galaxies with intermediate luminosity. Isophotal parameters are derived typically within 8 kpc from the center for the brightest galaxies, and 1.5 kpc for the faintest systems, with a resolution of 7 pc. For most galaxies, the surface brightness profiles are well described by a Sersic model with index n that increases steadily with the galaxy luminosity; only for 8 of the 10 brightest galaxies are the inner profiles (typically within 100 pc of the center) lower than expected based on an extrapolation of the outer Sersic model, and are better described by a single power-law function. Contrary to previous claims, we find no evidence in support of a strong bimodal behavior of the logarithmic slope of the inner surface brightness profile, γ; in particular the γ distribution for galaxies that do not show evidence of multiple morphological components is unimodal across the entire magnitude range spanned by the ACSVCS galaxies. Although the brightest galaxies have shallow inner profiles, the shallowest profiles are found in faint dwarf systems. The widely adopted separation of early-type galaxies between core and power-law types is questioned based on the present study.

The unusual afterglow of the γ-ray burst of 26 March 1998 as evidence for a supernova connection

Cosmic γ-ray bursts have now been firmly established as one of the most powerful phenomena in the Universe, releasing almost the rest-mass energy of a neutron star within the space of a few seconds (ref. 1). The two most popular models to explain γ-ray bursts are the coalescence of two compact objects such as neutron stars or black holes, or the catastrophic collapse of a massive star in a very energetic supernova-like explosion. Here we show that, about three weeks after the γ-ray burst of 26 March 1998, the transient optical source associated with the burst brightened to about 60 times the expected flux, based upon an extrapolation of the initial light curve. Moreover, the spectrum changed dramatically, with the colour becoming extremely red. We argue that the new source is an underlying supernova. If our hypothesis is true then this provides evidence linking cosmologically located γ-ray bursts with deaths of massive stars.Palomar Observatory 105-24, Caltech, Pasadena, CA 91125, USA National Radio Astronomy Observatory, P. O. Box O, Socorro, NM 87801, USA Department of Astronomy, University of California, Berkeley, CA 94720-3411 USA National Optical Astronomy Observatories, 950 N. Cherry, Ave. Tucson, AZ 85719, USA Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, 7000 East Avenue, P. O. Box 808, L-413, Livermore, CA 94551-9900, USA Center for Particle Astrophysics, University of California, Berkeley, CA 94720 USA Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA European Southern Observatory, D-85748 Garching, Germany Istituto di Astrofisica Spaziale, CNR, via Fosso del Cavaliere, Roma I-00133, Italy

The Morphology-Density Relation in z ~ 1 Clusters

We measure the morphology-density relation (MDR) and morphology-radius relation (MRR) for galaxies in seven z ~ 1 clusters that have been observed with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. Simulations and independent comparisons of our visually derived morphologies indicate that ACS allows one to distinguish between E, S0, and spiral morphologies down to z850 = 24, corresponding to L/L* = 0.21 and 0.30 at z = 0.83 and 1.24, respectively. We adopt density and radius estimation methods that match those used at lower redshift in order to study the evolution of the MDR and MRR. We detect a change in the MDR between 0.8 < z < 1.2 and that observed at z ~ 0, consistent with recent work; specifically, the growth in the bulge-dominated galaxy fraction, fE+S0, with increasing density proceeds less rapidly at z ~ 1 than it does at z ~ 0. At z ~ 1 and Σ ≥ 500 galaxies Mpc-2, we find fE+S0 = 0.72 ± 0.10. At z ~ 0, an E+S0 population fraction of this magnitude occurs at densities about 5 times smaller. The evolution in the MDR is confined to densities Σ 40 galaxies Mpc-2 and appears to be primarily due to a deficit of S0 galaxies and an excess of Sp+Irr galaxies relative to the local galaxy population. The fE-density relation exhibits no significant evolution between z = 1 and 0. We find mild evidence to suggest that the MDR is dependent on the bolometric X-ray luminosity of the intracluster medium. Implications for the evolution of the disk galaxy population in dense regions are discussed in the context of these observations.

Galaxies at z ~ 6: The UV Luminosity Function and Luminosity Density from 506 HUDF, HUDF Parallel ACS Field, and GOODS i-Dropouts* **

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 UV 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 modeled systematically and quantitatively. After corrections, we derive a rest-frame continuum UV (~1350 ?) LF at z ~ 6 that extends to M1350,AB ~ -17.5 (0.04L). 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), although the degree depends on the faint-end slope. As expected from hierarchical models, the most luminous galaxies are deficient at z ~ 6. Density evolution (*) is ruled out at >99.99% confidence. Despite large changes in the LF, the luminosity density at z ~ 6 is similar to (0.82 ? 0.21 times) 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 that the true evolution is substantially larger: at z ~ 6 the star formation rate density is just ~30% of the z ~ 3 value. Our UV LF is consistent with z ~ 6 galaxies providing the necessary UV flux to reionize the universe.

The acs virgo cluster survey. IX. The color distributions of globular cluster systems in early-type galaxies

We present the color distributions of globular cluster (GC) systems for 100 early-type galaxies observed in the ACS Virgo Cluster Survey, the deepest and most homogeneous survey of this kind to date. On average, galaxies at all luminosities in our study (-22 < MB < -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% and increasing with luminosity. The colors of both subpopulations correlate with host galaxy luminosity and color, with the red GCs having a steeper slope. To convert color to metallicity, we 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 ∝ L0.16±0.04 ∝ M and [Fe/H]MR ∝ L0.26±0.03 ∝ M, 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 relation observed for star-forming galaxies in the same mass range. The offset between the two GC populations is approximately 1 dex across 3 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 Surface Brightness Fluctuation Survey of Galaxy Distances. II. Local and Large-Scale Flows* **

We present results from the Surface Brightness Fluctuation (SBF) Survey for the distances to 300 early-type galaxies, of which approximately half are ellipticals. A modest change in the zero point of the SBF relation, derived by using Cepheid distances to spirals with SBF measurements, yields a Hubble constant H0 = 77 ? 4 ? 7?km?s-1 Mpc-1, somewhat larger than the HST Key Project result. We discuss how this difference arises from a different choice of zero point, a larger sample of galaxies, and a different model for large-scale flows. Our result is 4% larger than found in a recent comparison of the SBF Survey peculiar velocities with predictions derived from the galaxy density field measured by redshift surveys (Blakeslee et al. 1999b). The zero point of the SBF relation is the largest source of uncertainty, and our value for H0 is subject to all the systematic uncertainties of the Key Project zero point, including a 5% decrease if a metallicity correction for the Cepheids is adopted. To analyze local and large-scale flows?departures from smooth Hubble flow?we use a parametric model for the distribution function of mean velocity and velocity dispersion at each point in space. These models include a uniform thermal velocity dispersion and spherical attractors whose position, amplitude, and radial shape are free to vary. Our modeling procedure performs a maximum likelihood fit of the model to the observations. Our models rule out a uniform Hubble flow as an acceptable fit to the data. Inclusion of two attractors, one of which having a best-fit location coincident with the Virgo cluster and the other having a fit location slightly beyond the Centaurus clusters (which we refer to by convention as the Great Attractor), reduces ?2/N from 2.1 to 1.1. The fits to these attractors both have radial profiles such that v ? r-1 (i.e., isothermal) over a range of overdensity between about 10 and 1, but fall off more steeply at larger radius. The best-fit value for the small-scale, cosmic thermal velocity is 180 ? 14 km?s-1. The quality of the fit can be further improved by the addition of a quadrupole correction to the Hubble flow. The dipole velocity offset from the CMB frame for the volume we survey (amplitude ~150?km?s-1) and the quadrupole may be genuine (though weak) manifestations of more distant density fluctuations, but we find evidence that they are more likely due to the inadequacy of spherical models to describe the density profile of the attractors. The residual dipole we find is comparable to the systematic error in these simple, parametrized models; in other words, our survey volume of R < 3000?km?s-1 is, in a mass averaged sense, essentially at rest with respect to the CMB. This contradicts claims of large amplitude flows in much larger volumes that include our sample. Our best-fitting model, which uses attenuated power-law mass distributions for the two attractors, has enclosed mass overdensities at the Local Group of 7 ? 1014 M? for the Virgo Attractor and 9 ? 1015 M? for the Great Attractor. Without recourse to information about the overdensities of these attractors with respect to the cosmic mean we cannot provide a good constraint on ?M, but our data do give us accurate measurements in terms of ?, the overdensities of the enclosed masses with respect to the background: ? ? = 0.33 for the Virgo Attractor and ? ? = 0.27 for the Great Attractor.

Early-Type Galaxies in the Sloan Digital Sky Survey. III. The Fundamental Plane

A magnitude-limited sample of nearly 9000 early-type galaxies in the redshift range 0.01 ≤ z ≤ 0.3 was selected from the Sloan Digital Sky Survey (SDSS) using morphological and spectral criteria. The fundamental plane relation in this sample is Ro ∝ σ1.49±0.05I in the r* band. It is approximately the same in the g*, i*, and z* bands. Relative to the population at the median redshift in the sample, galaxies at lower and higher redshifts have evolved only a little. If the fundamental plane is used to quantify this evolution, then the apparent magnitude limit can masquerade as evolution; once this selection effect has been accounted for, the evolution is consistent with that of a passively evolving population that formed the bulk of its stars about 9 Gyr ago. One of the principal advantages of the SDSS sample over previous samples is that the galaxies in it lie in environments ranging from isolation in the field to the dense cores of clusters. The fundamental plane shows that galaxies in dense regions are slightly different from galaxies in less dense regions.

The ACS Virgo Cluster Survey. X. Half-Light Radii of Globular Clusters in Early-Type Galaxies: Environmental Dependencies and a Standard Ruler for Distance Estimation

We have measured half-light radii, rh, for thousands of globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured half-light radii on both the properties of the GCs themselves and their host galaxies reveals that, in analogy with GCs in the Galaxy but in a milder fashion, the average half-light radius increases with increasing galactocentric distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average half-light radius decreases with the host galaxy color. We also show that there is no evidence for a variation of rh with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average rh depends on the color of GCs, with red GCs being ~17% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed by Jordan. We discuss these findings in light of two simple pictures for the origin of the rh of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies on galaxy color, galactocentric radius, and underlying surface brightness, we show that the average GC half-light radii rh can be successfully used as a standard ruler for distance estimation. We outline the methodology, provide a calibration for its use, and discuss the prospects for this distance estimator with future observing facilities. We find rh = 2.7 ± 0.35 pc for GCs with (g - z) = 1.2 mag in a galaxy with color (g - z)gal = 1.5 mag and at an underlying surface z-band brightness of μz = 21 mag arcsec-2. Using this technique, we place an upper limit of 3.4 Mpc on the 1 σ line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the rh distribution for our sample galaxies and provide an analytic expression that successfully describes this distribution.