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We have compiled a sample of early-type cluster galaxies from 0 < z < 1.3 and measured the evolution of their ellipticity distributions. Our sample contains 487 galaxies in 17 z>0.3 clusters with high quality space-based imaging and a comparable sample of 210 galaxies in 10 clusters at z<0.05. We select early-type galaxies (elliptical and S0 galaxies) that fall within the cluster R_{200}, and which lie on the red-sequence in the magnitude range -19.3 > M_B > -21, after correcting for luminosity evolution. Our ellipticity measurements are made in a consistent manner over our whole sample. We perform extensive simulations to quantify the systematic and statistical errors, and find that it is crucial to use PSF-corrected model fits. We find that neither the median ellipticity, nor the shape of the ellipticity distribution of cluster early-type galaxies evolves with redshift from z ~ 0 to z > 1. These results are strongly suggestive of an unchanging overall bulge-to-disk ratio distribution for cluster early-type galaxies over the last ~8Gyr. This result contrasts with that from visual classifications which show that the fraction of morphologically-selected disk-dominated early-type galaxies, or S0s, is significantly lower at z>0.4 than at z~0. Taking the ellipticity measurements and assuming, as in all previous studies, that the intrinsic ellipticity distribution of both elliptical and S0 galaxies remains constant, then we conclude from the lack of evolution in the observed early-type ellipticity distribution that the relative fractions of ellipticals and S0s do not evolve from z~1 to z=0 for a red-sequence selected samples of galaxies in the cores of clusters of galaxies., Comment: 21 pages, 15 color figures, revised to match final ApJ version. Corrected discussion of Andreon et al 1996 from previous version

We present extensive early photometric (ultraviolet through near-infrared) and spectroscopic (optical and near-infrared) data on supernova (SN) 2008D as well as X-ray data analysis on the associated Swift/X-ray transient (XRT) 080109. Our data span a time range of 5 hours before the detection of the X-ray transient to 150 days after its detection, and detailed analysis allowed us to derive constraints on the nature of the SN and its progenitor; throughout we draw comparisons with results presented in the literature and find several key aspects that differ. We show that the X-ray spectrum of XRT 080109 can be fit equally well by an absorbed power law or a superposition of about equal parts of both power law and blackbody. Our data first established that SN 2008D is a spectroscopically normal SN Ib (i.e., showing conspicuous He lines), and show that SN 2008D had a relatively long rise time of 18 days and a modest optical peak luminosity. The early-time light curves of the SN are dominated by a cooling stellar envelope (for \Delta t~0.1- 4 day, most pronounced in the blue bands) followed by 56^Ni decay. We construct a reliable measurement of the bolometric output for this stripped-envelope SN, and, combined with estimates of E_K and M_ej from the literature, estimate the stellar radius R_star of its probable Wolf-Rayet progenitor. According to the model of Waxman et al. and of Chevalier & Fransson, we derive R_star^{W07}= 1.2+/-0.7 R_sun and R_star^{CF08}= 12+/-7 R_sun, respectively; the latter being more in line with typical WN stars. Spectra obtained at 3 and 4 months after maximum light show double-peaked oxygen lines that we associate with departures from spherical symmetry, as has been suggested for the inner ejecta of a number of SN Ib cores., Comment: Accepted to ApJ, v3 contains more data than v2 and more references, conclusions not significantly changed, 28 pages in emulateapj, 17 figures

Using HST and Spitzer IRAC imaging, we report the discovery of a very bright strongly lensed Lyman break galaxy (LBG) candidate at z~7.6 in the field of the massive galaxy cluster Abell 1689. The galaxy candidate, which we refer to as A1689-zD1, shows a strong z-J break of at least 2.2 mag and is completely undetected (<1 sigma) in HST/ACS g, r, i, and z-band data. These properties, combined with the very blue J-H and H-[4.5] colors, are exactly the properties of an z~7.6 LBG and can only be reasonably fit by a star-forming galaxy at z=7.6 +/- 0.4. Attempts to reproduce these properties with a model galaxy at z<4 yield particularly poor fits. A1689-zD1 has an observed (lensed) magnitude of 24.7 AB (8 sigma) in the NICMOS H band and is ~1.3 mag brighter than the brightest-known z-dropout galaxy. When corrected for the cluster magnification of 9.3 at z~7.6, the candidate has an intrinsic magnitude of H=27.1 AB, or about an L* galaxy at z~7.6. The source-plane deprojection shows that the star formation is occurring in compact knots of size ~<300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1.6-3.9) x 10^9 M_sun, stellar ages 45-320 Myr, star-formation rates ~<7.6 M_sun/yr, and low reddening with A_V <= 0.3. These properties are generally similar to those of LBGs found at z~5-6. The inferred stellar ages suggest a formation redshift of z~8-10 (t~<0.63 Gyr). A1689-zD1 is the brightest observed, highly reliable z>7.0 galaxy candidate found to date., Comment: Accepted for publication in the Astrophysical Journal, 8 pages, 8 figures, updated to match version in press

We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies at 2

The Sloan Digital Sky Survey (SDSS) and photometric/spectroscopic surveys in the GOODS-South field (the Chandra Deep Field-South, CDFS) are used to construct volume-limited, stellar mass-selected samples of galaxies at redshifts 02.5. The fraction of E+S0 galaxies is 43+/-3%$ at z~0.03 and 48+/-7% at z~0.8, i.e., it has not changed significantly since z~0.8. When combined with recent results for cluster galaxies in the same redshift range, we find that the morphology-density relation for galaxies more massive than 0.5M* has remained constant since at least z~0.8. This implies that galaxies evolve in mass, morphology and density such that the morphology-density relation does not change. In particular, the decline of star formation activity and the accompanying increase in the stellar mass density of red galaxies since z~1 must happen without large changes in the early-type galaxy fraction in a given environment., Comment: 16 pages, 13 figures, 2 tables. Updated to match journal version. Will appear in ApJ (vol. 670, p. 206)

We examined the morphology-density relations for galaxy samples selected by luminosity and by mass in each of five massive X-ray clusters from z=0.023 to 0.83 for 674 spectroscopically-confirmed members. Rest-frame optical colors and visual morphologies were obtained primarily from Hubble Space Telescope images. Morphology-density relations (MDR) are derived in each cluster from a complete, luminosity-selected sample of 452 galaxies with a magnitude limit M_V < M^{*}_{V} + 1. The change in the early-type fraction with redshift matches previous work for massive clusters of galaxies. We performed a similar analysis, deriving MDRs for complete, mass-selected samples of 441 galaxies with a mass-limit of 10^{10.6} M_{\sun}. Our mass limit includes faint objects, the equivalent of =~1 mag below L^{*} for the red cluster galaxies, and encompasses =~70% of the stellar mass in cluster galaxies. The MDRs in the mass-selected sample at densities of Sigma > 50 galaxies Mpc^{-2} are similar to those in the luminosity-selected sample but show larger early-type fractions. However, the trend with redshift in the fraction of elliptical and S0 galaxies with masses > 10^{10.6} M_{\sun} differs significantly between the mass- and luminosity-selected samples. The clear trend seen in the early-type fraction from z=0 to z=~ 0.8 is not found in mass-selected samples. The early-type galaxy fraction changes much less, and is consistent with being constant at 92% +/- 4% at \Sigma> 500 galaxies Mpc^{-2} and 83 +/- 3% at 50 < \Sigma < 500 galaxies Mpc^{-2}. This suggests that galaxies of mass lower than > 10^{10.6} M_{\sun} play a significant role in the evolution of the early-type fraction in luminosity-selected samples. (Abstract abridged), Comment: 18 pages in emulate ApJ format, with 10 color figures, Accepted to ApJ. Version updated to reflect published version, includes new references and a correction to table 3

We measure the obscured star formation in z~1 early-type galaxies. This constrains the influence of star formation on their optical/near-IR colors, which, we found, are redder than predicted by the model by Bruzual & Charlot (2003). From deep ACS imaging we construct a sample of 95 morphologically selected early-type galaxies in the HDF-N and CDF-S with spectroscopic redshifts in the range 0.852 sigma detections (~25 muJy} is 17(-4,+9)%. Of the 15 galaxies with significant detections at least six have an AGN. Stacking the MIPS images of the galaxies without significant detections and adding the detected galaxies without AGN we find an upper limit on the mean star formation rate (SFR) of 5.2+/-3.0 Msol yr^-1, and on the mean specific SFR of 4.6+/-2.2 * 10^-11 yr^-1. Under the assumption that the average SFR will decline at the same rate as the cosmic average, the in situ growth in stellar mass of the early-type galaxy population is less than 14+/-7% between z=1 and the present. We show that the typically low IR luminosity and SFR imply that the effect of obscured star formation (or AGN) on their rest-frame optical/near-IR SEDs is negligible for ~90% of the galaxies in our sample. Hence, their optical/near-IR colors are most likely dominated by evolved stellar populations. This implies that the colors predicted by the Bruzual & Charlot (2003) model for stellar populations with ages similar to those of z~1 early-type galaxies (~1-3 Gyr) are most likely too blue, and that stellar masses of evolved, high-redshift galaxies can be overestimated by up to a factor of ~2., Comment: Accepted for publication in ApJ, 8 pages, 4 figures, 1 table

We present a comprehensive mass reconstruction of the rich galaxy cluster Cl 0024+17 at z~0.4 from ACS data, unifying both strong- and weak-lensing constraints. The weak-lensing signal from a dense distribution of background galaxies (~120 per square arcmin) across the cluster enables the derivation of a high-resolution parameter-free mass map. The strongly-lensed objects tightly constrain the mass structure of the cluster inner region on an absolute scale, breaking the mass-sheet degeneracy. The mass reconstruction of Cl 0024+17 obtained in such a way is remarkable. It reveals a ringlike dark matter substructure at r~75" surrounding a soft, dense core at r~50". We interpret this peculiar sub-structure as the result of a high-speed line-of-sight collision of two massive clusters 1-2 Gyr ago. Such an event is also indicated by the cluster velocity distribution. Our numerical simulation with purely collisionless particles demonstrates that such density ripples can arise by radially expanding, decelerating particles that originally comprised the pre-collision cores. Cl 0024+17 can be likened to the bullet cluster 1E0657-56, but viewed $along$ the collision axis at a much later epoch. In addition, we show that the long-standing mass discrepancy for Cl 0024+17 between X-ray and lensing can be resolved by treating the cluster X-ray emission as coming from a superposition of two X-ray systems. The cluster's unusual X-ray surface brightness profile that requires a two isothermal sphere description supports this hypothesis., Comment: To appear in the June 1 issue of The Astrophysical Journal

We present results of the HST Advanced Camera for Surveys spectroscopic ground-based redshift survey in the field of A1689. We measure 98 redshifts, increasing the number of spectroscopically confirmed objects by sixfold. We present two spectra from this catalog of the Sextet Arcs, images which arise from a strongly-lensed Lyman Break Galaxy (LBG) at a redshift of z=3.038. Gravitational lensing by the cluster magnifies its flux by a factor of ~16 and produces six separate images with a total r-band magnitude of r_625=21.7. The two spectra, each of which represents emission from different regions of the LBG, show H I and interstellar metal absorption lines at the systemic redshift. Significant variations are seen in Ly-alpha profile across a single galaxy, ranging from strong absorption to a combination of emission plus absorption. A spectrum of a third image close to the brightest arc shows Ly-alpha emission at the same redshift as the LBG, arising from either another spatially distinct region of the galaxy, or from a companion galaxy close to the LBG. Taken as a group, the Ly-alpha equivalent width in these three spectra decreases with increasing equivalent width of the strongest interstellar absorption lines. We discuss how these variations can be used to understand the physical conditions in the LBG. Intrinsically, this LBG is faint, ~0.1L*, and forming stars at a modest rate, ~4 solar masses per year. We also detect absorption line systems toward the Sextet Arcs at z=2.873 and z=2.534. The latter system is seen across two of our spectra., Comment: Accepted for publication in ApJ

We present ACS/HST coronagraphic observations of HD 100546, a B9.5 star, 103 pc away from the sun, taken in the F435W, F606W, and F814W bands. Scattered light is detected up to 14'' from the star. The observations are consistent with the presence of an extended flattened nebula with the same inclination as the inner disk. The well-known ``spiral arms'' are clearly observed and they trail the rotating disk material. Weaker arms never before reported are also seen. The inter-arm space becomes brighter, but the structures become more neutral in color at longer wavelengths, which is not consistent with models that assume that they are due to the effects of a warped disk. Along the major disk axis, the colors of the scattered-light relative to the star are \Delta (F435W-F606W) ~ 0.0--0.2 mags and \Delta (F435W-F814W)~0.5--1 mags. To explain these colors, we explore the role of asymmetric scattering, reddening, and large minimum sizes on ISM-like grains. We conclude each of these hypotheses by itself cannot explain the colors. The disk colors are similar to those derived for Kuiper Belt objects, suggesting that the same processes responsible for their colors may be at work here. We argue that we are observing only the geometrically thick, optically thin envelope of the disk, while the optically thick disk responsible for the far-IR emission is undetected. The observed spiral arms are then structures on this envelope. The colors indicate that the extended nebulosity is not a remnant of the infalling envelope but reprocessed disk material., Comment: Accepted to ApJ

We present complimentary techniques to find emission-line targets and measure their properties in a semi-automated fashion from grism observations obtained with the Advanced Camera for Surveys aboard the Hubble Space Telescope. The first technique is to find all likely sources in a direct image, extract their spectra and search them for emission lines. The second method is to look for emission-line sources as compact structures in an unsharp masked version of the grism image. Using these methods we identify 46 emission-line targets in the Hubble Deep Field North using a modest (3 orbit) expenditure of HST observing time. Grism spectroscopy is a powerful tool for efficiently identifying interesting low luminosity, moderate redshift emission-line field galaxies. The sources found here have a median i band flux 1.5 mag fainter than the spectroscopic redshift catalog of Cohen et al. They have redshift z <= 1.42, high equivalent widths (typically EW > 100{\AA}), and are usually less luminous than the characteristic luminosity at the same redshift. The chief obstacle in interpreting the results is line identification, since the majority of sources have a single emission line and the spectral resolution is low. Photometric redshifts are useful for providing a first guess redshift. However, even at the depth of the state-of-the-art data used here, photometric errors can result in uncertainties in line identifications, especially for sources with i > ~24.5 ABmag. Reliable line identification for the faintest emission-line galaxies requires additional ground-based spectroscopy for confirmation. Of particular concern are the faint high EW [OII] emitters which could represent a strongly evolving galaxy population if the possibility that they are mis-identified lower redshift interlopers can be ruled out. (Slightly abridged), Comment: AJ accepted. 27 pages, 4 tables, 11 figures. Uses emulateapj.cls

We present results from an extensive spectroscopic survey, carried out with VLT FORS, and from an extensive multiwavelength imaging data set from the HST Advanced Camera for Surveys and ground based facilities, of the cluster of galaxies RDCS J1252.9-2927. We have spectroscopically confirmed 38 cluster members in the redshift range 1.22 < z < 1.25. A cluster median redshift of z=1.237 and a rest-frame velocity dispersion of 747^{+74}_{-84} km/s are obtained. Using the 38 confirmed redshifts, we were able to resolve, for the first time at z > 1, kinematic structure. The velocity distribution, which is not Gaussian at the 95% confidence level, is consistent with two groups that are also responsible for the projected east-west elongation of the cluster. The groups are composed of 26 and 12 galaxies with velocity dispersions of 486^{+47}_{-85} km/s and 426^{+57}_{-105} km/s, respectively. The elongation is also seen in the intracluster gas and the dark matter distribution. This leads us to conclude that RDCS J1252.9-2927 has not yet reached a final virial state. We extend the analysis of the color-magnitude diagram of spectroscopic members to more than 1 Mpc from the cluster center. The scatter and slope of non-[OII]-emitting cluster members in the near-IR red sequence is similar to that seen in clusters at lower redshift. Furthermore, most of the galaxies with luminosities greater than ~ K_s*+1.5 do not show any [OII], indicating that these more luminous, redder galaxies have stopped forming stars earlier than the fainter, bluer galaxies. Our observations provide detailed dynamical and spectrophotometric information on galaxies in this exceptional high-redshift cluster, delivering an in-depth view of structure formation at this epoch only 5 Gyr after the Big Bang., Comment: 29 pages. 16 figures. ApJ accepted. Tables 2,3 and 5, figure 1 and the full figure 5 will be available in the paper and electronic editions from ApJ. v2: minor corrections to the abstract and text to match the Journal's version

We report on deep spectroscopy using LRIS on Keck I and FORS2 on the VLT of a sample of 22 candidate z~6 Lyman Break galaxies (LBGs) selected by the i-z> 1.3 dropout criterion. Redshifts could be measured for eight objects. These redshifts are all in the range z = 5.5 - 6.1, confirming the efficiency of the i-z color selection technique. Six of the confirmed galaxies show Ly-alpha emission. Assuming that the 14 objects without redshifts are z~6 LBGs, but lack detectable Ly-alpha emission lines, we infer that the fraction of Ly-alpha emitting LBGs with Ly-alpha equivalent widths greater than 20 Angstroms among z~6 LBGs is ~30%, similar to that found at z~3. Every Ly-alpha emitting object in our sample is compact with r <= 0.14". Furthermore, all the Ly-alpha emitting objects in our sample are more compact than average relative to the observed size-magnitude relation of a large i-dropout sample (332 candidate z~6 objects). We can reject the hypothesis that the Ly-alpha emitting population is a subset of the rest of the z~6 LBG population at >97% confidence. We speculate the small sizes of Ly-alpha emitting LBGs are due to these objects being less massive than other LBGs at z~6., Comment: 24 pages in emulate ApJ, 17 color figures (some resized to fit submission limits), and 3 tables. Accepted for publication in the Astrophysical Journal

We present a deep image of the radio galaxy MRC 1138-262 taken with the Hubble Space Telescope (HST) at a redshift of z = 2.2. The galaxy is known to have properties of a cD galaxy progenitor and be surrounded by a 3 Mpc-sized structure, identified with a protocluster. The morphology shown on the new deep HST/ACS image is reminiscent of a spider's web. More than 10 individual clumpy features are observed, apparently star-forming satellite galaxies in the process of merging with the progenitor of a dominant cluster galaxy 11 Gyr ago. There is an extended emission component, implying that star formation was occurring over a 50 times 40 kpc region at a rate of more than 100 M_sun/yr. A striking feature of the newly named ``Spiderweb galaxy'' is the presence of several faint linear galaxies within the merging structure. The dense environments and fast galaxy motions at the centres of protoclusters may stimulate the formation of these structures, which dominate the faint resolved galaxy populations in the Hubble Ultra Deep Field. The new image provides a unique testbed for simulations of forming dominant cluster galaxies., Comment: 5 pages, 2 figures (reduced to grayscale); ApJ Letters

Using Spitzer IRAC mid-infrared imaging from the Great Observatories Origins Deep Survey, we study z_850-dropout sources in the Hubble Ultra Deep Field. After carefully removing contaminating flux from foreground sources, we clearly detect two z_850-dropouts at 3.6 micron and 4.5 micron, while two others are marginally detected. The mid-infrared fluxes strongly support their interpretation as galaxies at z~7, seen when the Universe was only 750 Myr old. The IRAC observations allow us for the first time to constrain the rest-frame optical colors, stellar masses, and ages of the highest redshift galaxies. Fitting stellar population models to the spectral energy distributions, we find photometric redshifts in the range 6.7-7.4, rest-frame colors U-V=0.2-0.4, V-band luminosities L_V=0.6-3 x 10^10 L_sun, stellar masses 1-10 x 10^9 M_sun, stellar ages 50-200 Myr, star formation rates up to ~25 M_sun/yr, and low reddening A_V<0.4. Overall, the z=7 galaxies appear substantially less massive and evolved than Lyman break galaxies or Distant Red Galaxies at z=2-3, but fairly similar to recently identified systems at z=5-6. The stellar mass density inferred from our z=7 sample is rho* = 1.6^{+1.6}_{-0.8} x 10^6 M_sun Mpc^-3 (to 0.3 L*(z=3)), in apparent agreement with recent cosmological hydrodynamic simulations, but we note that incompleteness and sample variance may introduce larger uncertainties. The ages of the two most massive galaxies suggest they formed at z>8, during the era of cosmic reionization, but the star formation rate density derived from their stellar masses and ages is not nearly sufficient to reionize the universe. The simplest explanation for this deficiency is that lower-mass galaxies beyond our detection limit reionized the universe., Comment: 4 pages, 3 figures, emulateapj, Accepted for publication in ApJ Letters

We analyse the cluster color-magnitude relation (CMR) for early-type galaxies in two of the richer clusters in the z ~ 0.9 supercluster system to derive average ages and formation redshifts for the early-type galaxy population. Both clusters were observed with the Advanced Camera for Surveys aboard the {\it Hubble Space Telescope} through the F606W and F814W filters, which brackets the rest-frame 4000 \AA break at the cluster redshifts of z\sim 0.9. We fit the zeropoint and slope of the red cluster sequence, and model the scatter about this relation to estimate average galaxy ages and formation redshifts. We find intrinsic scatters of 0.038-0.053 mag in ($V_{606}-I_{814}$) for the E and E+S0 populations, corresponding to average ages of 3.5-3.7 Gyr and formation redshifts z_{f}=2.4-2.6. We find at least one significant difference between the Cl1604+4304 and Cl1604+4321 early-type CMRs. Cl1604+4321, the less X-ray luminous and massive of the two, lacks bright L^* ellipticals. We combine the galaxy samples to fit a composite CMR down to 0.15L^*, and find that the slope of the combined cluster CMR is significantly steeper than for RX J0152.7-1357 but consistent with MS 1054-03, both at similar redshift. The slope of the Cl1604 CMR at the bright end (L > 0.5L^*) is flatter and consistent with the CMR slopes found for other high redshift clusters. We find evidence for increasing scatter with increasing magnitude along the early-type CMR, consistent with a 'downsizing' scenario, indicating younger mean ages with decreasing galaxy mass., Comment: replaced to fix bizarre shift in vertical centering, ApJ accepted

We examine the distribution of stellar masses of galaxies in MS 1054-03 and RX J0152.7-1357, two X-ray selected clusters of galaxies at z=0.83. Our stellar mass estimates, from spectral energy distribution fitting, reproduce the dynamical masses as measured from velocity dispersions and half-light radii with a scatter of 0.2 dex in the mass for early-type galaxies. When we restrict our sample of members to high stellar masses, > 1e11.1 Msun (M* in the Schechter mass function for cluster galaxies), we find that the fraction of early-type galaxies is 79 +/- 6% at z=0.83 and 87 +/- 6% at z=0.023 for the Coma cluster, consistent with no evolution. Previous work with luminosity-selected samples finds that the early-type fraction in rich clusters declines from =~80% at z=0 to =~60% at z=0.8. The observed evolution in the early-type fraction from luminosity-selected samples must predominately occur among sub-M* galaxies. As M* for field and group galaxies, especially late-types, is below M* for clusters galaxies, infall could explain most of the recent early-type fraction growth. Future surveys could determine the morphological distributions of lower mass systems which will confirm or refute this explanation., Comment: 5 pages in emulate ApJ format with three color figures. Accepted for publication in ApJ Letters, v642n2. Updated to correct grammatical and typographic errors found by the journal

We study the photometric and structural properties of spectroscopically confirmed members in the two massive X-ray--selected z=0.83 galaxy clusters MS1054-03 and RXJ0152-1357 using three-band mosaic imaging with the Hubble Space Telescope Advanced Camera for Surveys. The samples include 105 and 140 members of MS1054-03 and RXJ0152-1357, respectively, with ACS F775W magnitude < 24.0. We develop a promising new structural classification method, based on a combination of the best-fit Sersic indices and the normalized root-mean-square residuals from the fits; the resulting classes agree well with the visual ones, but are less affected by galaxy orientation. We examine the color--magnitude relations in detail and find that the color residuals correlate with the local mass density measured from our weak lensing maps; we identify a threshold density of $\Sigma \approx 0.1$, in units of the critical density, above which the star formation appears to cease. For RXJ0152-1357, we also find a trend in the color residuals with velocity, resulting from an offset of about 980 km/s in the mean redshifts of the early- and late-type galaxies. Analysis of the color--color diagrams indicates that a range of star formation time-scales are needed to reproduce the loci of the galaxy colors. We also identify some cluster galaxies whose colors can only be explained by large amounts, $A_V \approx 1$ mag, of internal dust extinction. [Abstract shortened], Comment: 30 pages, emulateapj format; 23 figures, many in color. Accepted by ApJ; scheduled for the 10 June 2006 issue. Some figures degraded; for a higher resolution version, see: http://astro.wsu.edu/blakeslee/z1clusters/

(Abridged.) We present F435W (B), F606W (Broad V), and F814W (Broad I) coronagraphic images of the debris disk around Beta Pictoris obtained with HST's Advanced Camera for Surveys. We confirm that the previously reported warp in the inner disk is a distinct secondary disk inclined by ~5 deg from the main disk. The main disk's northeast extension is linear from 80 to 250 AU, but the southwest extension is distinctly bowed with an amplitude of ~1 AU over the same region. Both extensions of the secondary disk appear linear, but not collinear, from 80 to 150 AU. Within ~120 AU of the star, the main disk is ~50% thinner than previously reported. The surface-brightness profiles along the spine of the main disk are fitted with four distinct radial power laws between 40 and 250 AU, while those of the secondary disk between 80 and 150 AU are fitted with single power laws. These discrepancies suggest that the two disks have different grain compositions or size distributions. The F606W/F435W and F814W/F435W flux ratios of the composite disk are nonuniform and asymmetric about both projected axes of the disk. Within ~120 AU, the m_F435W-m_F606W and m_F435W-m_F814W colors along the spine of the main disk are ~10% and ~20% redder, respectively, than those of Beta Pic. These colors increasingly redden beyond ~120 AU, becoming 25% and 40% redder, respectively, than the star at 250 AU. We compare the observed red colors within ~120 AU with the simulated colors of non-icy grains having a radial number density ~r^-3 and different compositions, porosities, and minimum grain sizes. The observed colors are consistent with those of compact or moderately porous grains of astronomical silicate and/or graphite with sizes >0.15-0.20 um, but the colors are inconsistent with the blue colors expected from grains with porosities >90%., Comment: 38 pages (including 21 figures and 4 tables) in EmulateApJ format, accepted for publication in The Astronomical Journal. Full-resolution figures and fully processed FITS images (with error maps) are available at http://acs.pha.jhu.edu/~dag/betapic Version 2: Added 4 references and some clarifying text. Basic facts and conclusions are unchanged

The color-magnitude relation has been determined for the RDCS J0910+5422 cluster of galaxies at redshift z = 1.106. Cluster members were selected from HST ACS images, combined with ground--based near--IR imaging and optical spectroscopy. The observed early--type color--magnitude relation (CMR) in (i_775 -z_850) versus z_850 shows intrinsic scatters in color of 0.042 +/- 0.010 mag and 0.044 +/- 0.020 mag for ellipticals and S0s, respectively. From the scatter about the CMR, a mean luminosity--weighted age t > 3.3 Gyr (z > 3) is derived for the elliptical galaxies. Strikingly, the S0 galaxies in RDCS J0910+5422 are systematically bluer in (i_775 - z_850) by 0.07 +/- 0.02 mag, with respect to the ellipticals. The ellipticity distribution as a function of color indicates that the face-on S0s in this particular cluster have likely been classified as elliptical. Thus, if anything, the offset in color between the elliptical and S0 populations may be even more significant. The color offset between S0 and E corresponds to an age difference of ~1 Gyr, for a single-burst solar metallicity model. A solar metallicity model with an exponential decay in star formation will reproduce the offset for an age of 3.5 Gyr, i.e. the S0s have evolved gradually from star forming progenitors. The early--type population in this cluster appears to be still forming. The blue early-type disk galaxies in RDCS J0910+5422 likely represent the direct progenitors of the more evolved S0s that follow the same red sequence as ellipticals in other clusters. Thirteen red galaxy pairs are observed and the galaxies associated in pairs constitute ~40% of the CMR galaxies in this cluster., Comment: ApJ, in press

(Abridged) We present a HST/ACS weak-lensing study of RX J0849+4452 and RX J0848+4453, the two most distant (at z=1.26 and z=1.27, respectively) clusters yet measured with weak-lensing. The two clusters are separated by ~4' from each other and appear to form a supercluster in the Lynx field. Using our deep ACS F775W and F850LP imaging, we detected weak-lensing signals around both clusters at ~4 sigma levels. The mass distribution indicated by the reconstruction map is in good spatial agreement with the cluster galaxies. From the SIS fitting, we determined that RX J0849+4452 and RX J0848+4453 have similar projected masses of ~2.0x10^14 solar mass and ~2.1x10^14 solar mass, respectively, within a 0.5 Mpc (~60") aperture radius., Comment: Accepted to ApJ. Full resolution version can be downloaded at http://acs.pha.jhu.edu/~mkjee/lynx.pdf

We present deep HST/ACS observations in g,r,i,z towards the z=4.1 radio galaxy TN J1338-1942 and its overdensity of >30 spectroscopically confirmed Lya emitters (LAEs). We select 66 g-band dropouts to z=27, 6 of which are also a LAE. Although our color-color selection results in a relatively broad redshift range centered on z=4.1, the field of TN J1338-1942 is richer than the average field at the >5 sigma significance, based on a comparison with GOODS. The angular distribution is filamentary with about half of the objects clustered near the radio galaxy, and a small, excess signal (2 sigma) in the projected pair counts at separations of <10" is interpreted as being due to physical pairs. The LAEs are young (a few x 10^7 yr), small ( = 0.13") galaxies, and we derive a mean stellar mass of ~10^8-9 Msun based on a stacked K-band image. We determine star formation rates, sizes, morphologies, and color-magnitude relations of the g-dropouts and find no evidence for a difference between galaxies near TN J1338-1942 and in the field. We conclude that environmental trends as observed in clusters at much lower redshift are either not yet present, or are washed out by the relatively broad selection in redshift. The large galaxy overdensity, its corresponding mass overdensity and the sub-clustering at the approximate redshift of TN J1338-1942 suggest the assemblage of a >10^14 Msun structure, confirming that it is possible to find and study cluster progenitors in the linear regime at z>4., Comment: Accepted for publication in ApJ (33 pages, 19 figures, emulateapj). v3 includes updated methods, discussion and referencing

Using the deep multi-wavelength MUSYC, GOODS, and FIRES surveys we construct a stellar mass-limited sample of galaxies at 210^11 Solar masses distributed over four independent fields with a total area of almost 400 sq arcmin. The mean number density of massive galaxies in this redshift range is (2.2+-0.6) x 10^-4 Mpc^-3. We present median values and 25th and 75th percentiles for the distributions of observed R mags, observed J-K colors, and rest-frame UV continuum slopes, M/L(V) ratios, and U-V colors. The galaxies show a large range in all these properties. The ``median galaxy'' is faint in the observer's optical (R=25.9), red in the observed near-IR (J-K=2.48), has a rest-frame UV spectrum which is relatively flat (beta=-0.4), and rest-frame optical colors resembling those of nearby spiral galaxies (U-V=0.62). We determine which galaxies would be selected as Lyman break galaxies (LBGs) or Distant Red Galaxies (DRGs, having J-K>2.3) in this mass-limited sample. By number DRGs make up 69% of the sample and LBGs 20%, with a small amount of overlap. By mass DRGs make up 77% and LBGs 17%. Neither technique provides a representative sample of massive galaxies at 2

A five square arcminute region around the luminous radio-loud quasar SDSS J0836+0054 (z=5.8) hosts a wealth of associated galaxies, characterized by very red (1.3 < i_775 - z_{850} < 2.0) color. The surface density of these z~5.8 candidates is approximately six times higher than the number expected from deep ACS fields. This is one of the highest galaxy overdensities at high redshifts, which may develop into a group or cluster. We also find evidence for a substructure associated with one of the candidates. It has two very faint companion objects within two arcseconds, which are likely to merge. The finding supports the results of a recent simulation that luminous quasars at high redshifts lie on the most prominent dark-matter filaments and are surrounded by many fainter galaxies. The quasar activity from these regions may signal the buildup of a massive system., Comment: Four figures. The Astrophysical Journal: in press

We measure the evolution of the rest-frame K-band Fundamental Plane from z=1 to the present by using IRAC imaging of a sample of early-type galaxies in the Chandra Deep Field-South at z~1 with accurately measured dynamical masses. We find that $M/L_K$ evolves as $\Delta\ln{(M/L_K)}=(-1.18\pm0.10)z$, which is slower than in the B-band ($\Delta\ln{(M/L_B)}=(-1.46\pm0.09)z$). In the B-band the evolution has been demonstrated to be strongly mass dependent. In the K-band we find a weaker trend: galaxies more massive than $M=2\times10^{11}M_{\odot}$ evolve as $\Delta\ln{(M/L_K)}=(-1.01\pm0.16)z$; less massive galaxies evolve as $\Delta\ln{(M/L_K)}=(-1.27\pm0.11)z$. As expected from stellar population models the evolution in $M/L_K$ is slower than the evolution in $M/L_B$. However, when we make a quantitative comparison, we find that the single burst Bruzual-Charlot models do not fit the results well, unless large dust opacities are allowed at z=1. Models with a flat IMF fit better, Maraston models with a different treatment of AGB stars fit best. These results show that the interpretation of rest-frame near-IR photometry is severely hampered by model uncertainties and therefore that the determination of galaxy masses from rest-frame near-IR photometry may be harder than was thought before., Comment: 5 pages, 3 figures, Accepted for publication in ApJL

We present deep near-infrared Js, H, and Ks band imaging of a field around MS1054-03, a massive cluster at z=0.83. The observations were carried out with ISAAC at the ESO VLT as part of the Faint InfraRed Extragalactic Survey (FIRES). The total integration time amounts to 25.9h in Js, 24.4h in H, and 26.5h in Ks, divided nearly equally between four pointings covering 5.5'x5.3'. The 3-sigma total limiting AB magnitudes for point sources from the shallowest to deepest pointing are Js=26.0-26.2, H=25.5-25.8, and Ks=25.3-25.7. The effective spatial resolution of the coadded images has FWHM=0.48", 0.46", and 0.52" in Js, H, and Ks. We complemented the ISAAC data with deep optical imaging using existing HST WFPC2 mosaics in the F606W and F814W filters and new U, B and V band data from VLT FORS1. We constructed a Ks-band limited multicolour source catalogue to Ks(total,AB)=25 (about 5-sigma for point sources). The catalogue contains 1858 objects, of which 1663 have eight-band photometry. We describe the observations, data reduction, source detection and photometric measurements method. We present the number counts, colour distributions, and photometric redshifts z_ph of the catalogue sources. We find that our counts at the faint end 22=0.078. The MS1054-03 field observations complement our HDF-South data set with nearly five times larger area at about 0.7 brighter magnitudes. [ABRIDGED], Comment: Accepted for publication in the Astronomical Journal. 32 pages, 14 b/w figures, 1 color figure

We present a comparison of late-type galaxies (Sa and later) in intermediate redshift clusters and the field using ACS imaging of four cluster fields: CL0152-1357, CL1056-0337 (MS1054), CL1604+4304, and CL1604+4321. Concentration, asymmetry, and clumpiness parameters are calculated for each galaxy in blue (F606W or F625W) and red (F775W or F814W) filters. Galaxy half-light radii, disk scale lengths, color gradients, and overall color are compared. We find marginally significant differences in the asymmetry distributions of spiral and irregular galaxies in the X-ray luminous and X-ray faint clusters. The massive clusters contain fewer galaxies with large asymmetries. The physical sizes of the cluster and field populations are similar; no significant differences are found in half-light radii or disk scale lengths. The most significant difference is in rest-frame $U-B$ color. Late-type cluster galaxies are significantly redder, $\sim 0.3$ magnitudes at rest-frame $U-B$, than their field counterparts. Moreover, the intermediate-redshift cluster galaxies tend to have blue inward color gradients, in contrast to the field galaxies, but similar to late-type galaxies in low redshift clusters. These blue inward color gradients are likely to be the result of enhanced nuclear star formation rates relative to the outer disk. Based on the significant rest-frame color difference, we conclude that late-type cluster members at $z\sim0.9$ are not a pristine infalling field population; some difference in past and/or current star formation history is already present. This points to high redshift ``groups'', or filaments with densities similar to present-day groups, as the sites where the first major effects of environment are imprinted., Comment: updated title

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 modelled systematically and quantitatively. After corrections, we derive a rest-frame continuum UV (~1350 A) 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 (phi*) is ruled out at >99.99% confidence. Despite large changes in the LF, the luminosity density at z~6 is similar (0.82+/-0.21x) 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., Comment: 36 pages, 22 figures, 24 tables, accepted for publication in the Astrophysical Journal. Very minor changes made to exactly match version in press

We present HST/ACS observations of the most distant radio galaxy known, TN J0924-2201 at z=5.2. This radio galaxy has 6 spectroscopically confirmed Lya emitting companion galaxies, and appears to lie within an overdense region. The radio galaxy is marginally resolved in i_775 and z_850 showing continuum emission aligned with the radio axis, similar to what is observed for lower redshift radio galaxies. Both the half-light radius and the UV star formation rate are comparable to the typical values found for Lyman break galaxies at z~4-5. The Lya emitters are sub-L* galaxies, with deduced star formation rates of 1-10 Msun/yr. One of the Lya emitters is only detected in Lya. Based on the star formation rate of ~3 Msun/yr calculated from Lya, the lack of continuum emission could be explained if the galaxy is younger than ~2 Myr and is producing its first stars. Observations in V_606, i_775, and z_850 were used to identify additional Lyman break galaxies associated with this structure. In addition to the radio galaxy, there are 22 V-break (z~5) galaxies with z_850<26.5 (5sigma), two of which are also in the spectroscopic sample. We compare the surface density of 2/arcmin^2 to that of similarly selected V-dropouts extracted from GOODS and the UDF Parallel fields. We find evidence for an overdensity to very high confidence (>99%), based on a counts-in-cells analysis applied to the control field. The excess is suggestive of the V-break objects being associated with a forming cluster around the radio galaxy., Comment: 39 pages (15 figures). Accepted to ApJ. Full resolution version available at http://acs.pha.jhu.edu/science/papers/

We present a study of the submillimeter (submm) emission of Distant Red Galaxies (DRGs). The DRGs are selected by the criterion (J-K)>2.3, and are generally massive galaxies at redshifts higher than 2, with red rest-frame optical colors. Using a deep SCUBA submm image of a field centred on the cluster MS1054-03, we obtain a statistical detection of the DRGs at redshift z=2-3.5, with an average 850um flux density of 1.11+-0.28mJy. The detection implies an average star formation rate (SFR) of 127+-34 M_sun/yr (lensing corrected), assuming that the far-infrared (FIR) spectral energy distribution (SED) is well-described by a modified blackbody. The SFR derived from the submm agrees well with SFRs derived from SED fitting of optical-near-infrared data and average X-ray emission. Constant Star Formation models imply ages of 2Gyr, extinction A_V=2.4 mag, which is consistent with the FIR to rest-frame optical luminosity ratio of ~15. DRGs are older and have lower SFRs relative to optical luminosity than (ultra-)luminous infrared galaxies, although their FIR luminosities are similar. The DRGs at 24) at 1

Hubble Space Telescope Advanced Camera for Surveys images of the young binary GG Tauri and its circumbinary disk in V and I bandpasses were obtained in 2002 and are the most detailed of this system to date. The confirm features previously seen in the disk including: a "gap" apparently caused by shadowing from circumstellar material; an asymmetrical distribution of light about the line of sight on the near edge of the disk; enhanced brightness along the near edge of the disk due to forward scattering; and a compact reflection nebula near the secondary star. New features are seen in the ACS images: two short filaments along the disk; localized but strong variations in disk intensity ("gaplets"); and a "spur" or filament extending from the reflection nebulosity near the secondary. The back side of the disk is detected in the V band for the first time. The disk appears redder than the combined light from the stars, which may be explained by a varied distribution of grain sizes. The brightness asymmetries along the disk suggest that it is asymmetrically illuminated by the stars due to extinction by nonuniform circumstellar material or the illuminated surface of the disk is warped by tidal effects (or perhaps both). Localized, time-dependent brightness variations in the disk are also seen., Comment: 28 pages, 7 figures, accepted for publication in the Astronomical Journal

We present Hubble Space Telescope/Advanced Camera for Surveys (ACS) weak-lensing and Chandra X-ray analyses of MS 1054-0321 at z=0.83, the most distant and X-ray luminous cluster in the Einstein Extended Medium-Sensitivity Survey (EMSS). The high-resolution mass reconstruction through ACS weak-lensing reveals the complicated dark matter substructure in unprecedented detail, characterized by the three dominant mass clumps with the four or more minor satellite groups within the current ACS field. The direct comparison of the mass map with the Chandra X-ray image shows that the eastern weak-lensing substructure is not present in the X-ray image and, more interestingly, the two X-ray peaks are displaced away from the hypothesized merging direction with respect to the corresponding central and western mass clumps, possibly because of ram pressure. In addition, as observed in our previous weak-lensing study of another high-redshift cluster CL 0152-1357 at z=0.84, the two dark matter clumps of MS 1054-0321 seem to be offset from the galaxy counterparts. We examine the significance of these offsets and discuss a possible scenario, wherein the dark matter clumps might be moving ahead of the cluster galaxies. The non-parametric weak-lensing mass modeling gives a projected mass of M(r<1 Mpc)=(1.02+-0.15)x 10^{15} solar mass, where the uncertainty reflects both the statistical error and the cosmic shear effects. Our temperature measurement of T=8.9_{-0.8}^{+1.0} keV utilizing the newest available low-energy quantum efficiency degradation prescription for the Chandra instrument, together with the isothermal beta description of the cluster (r_c=16"+-15" and beta=0.78+-0.08), yields a projected mass of M(r<1 Mpc)=(1.2+-0.2) x 10^{15} solar mass, consistent with the weak-lensing result., Comment: Accepted for publication in apj. Full-resolution version can be downloaded from http://acs.pha.jhu.edu/~mkjee/ms1054.pdf

We present the photometric calibration of the HST Advanced Camera for Surveys (ACS). We give here an overview of the performance and calibration of the 2 CCD cameras, the Wide Field Channel (WFC) and the High Resolution Channel (HRC), and a description of the best techniques for reducing ACS CCD data. On-orbit observations of spectrophotometric standard stars have been used to revise the pre-launch estimate of the instrument response curves to best match predicted and observed count rates. Synthetic photometry has been used to determine zeropoints for all filters in 3 magnitude systems and to derive interstellar extinction values for the ACS photometric systems. Due to the CCD internal scattering of long wavelength 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 encircled energy curves and 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: 1 based on the observation of 2 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., Comment: 101 pages, 29 figures, 31 tables; PASP accepted

We have obtained a high S/N (22.3 hr integration) UV continuum VLT FORS2 spectrum of an extremely bright (z_850 = 24.3) z = 5.515 +/- 0.003 starforming galaxy (BD38) in the field of the z = 1.24 cluster RDCS 1252.9-2927. This object shows substantial continuum (0.41 +/- 0.02 \muJy at \lambda1300) and low-ionization interstellar absorption features typical of LBGs at lower redshift (z ~ 3); this is the highest redshift LBG confirmed via metal absorption spectral features. The equivalent widths of the absorption features are similar to z ~ 3 strong Ly\alpha absorbers. No noticeable Ly\alpha emission was detected (F <= 1.4 * 10^-18 ergs cm^-2 s^-1, 3\sigma). The half-light radius of this object is 1.6 kpc (0\farcs25) and the star formation rate derived from the rest-frame UV luminosity is SFR_UV = 38 h^-2_0.7 M_sun yr^-1 (142 h^-2_0.7 M_sun yr^-1 corrected for dust extinction). In terms of recent determinations of the z ~ 6 UV luminosity function, this object appears to be 6L*. The Spitzer IRAC fluxes for this object are 23.3 and 23.2 AB mag (corrected for 0.3 mag of cluster lensing) in the 3.6\mu and 4.5\mu channels, respectively, implying a mass of 1-6 * 10^10 M_sun from population synthesis models. This galaxy is brighter than any confirmed z ~ 6 i-dropout to date in the z_850 band, and both the 3.6\mu and 4.5\mu channels, and is the most massive starbursting galaxy known at z > 5. -- Abstract Abridged, Comment: Accepted to ApJ Letters. 4 pages in emulate ApJ format, 3 color figures, 1 with lower resolution. Full resolution file available at http://physics.ucsc.edu/~cdow/bd38/bd38.pdf

We present deep optical imaging of the z=4.1 radio galaxy TN J1338--1942 obtained using the ACS on-board HST. The radio galaxy is known to reside within a large galaxy overdensity (both in physical extent and density contrast). There is good evidence that this `protocluster' region is the progenitor of a present-day rich galaxy cluster. TN J1338 is the dominant galaxy in the protocluster, in terms of size and luminosity and therefore seems destined to evolve into the brightest cluster galaxy. The high spatial-resolution ACS images reveal several kpc-scale features within and around the radio galaxy. The continuum light is aligned with the radio axis and is resolved into two clumps in the i-band and z-band bands. These components have luminosities ~10^9 L_sun and sizes of a few kpc. The estimated star-formation rate for the whole radio galaxy is ~200 M_sun/yr. A simple model in which the jet has triggered star-formation in these continuum knots is consistent with the available data. An unusual feature is seen in Lyman-alpha emission. A wedge-shaped extension emanates from the radio galaxy perpendicularly to the radio axis. This `wedge' naturally connects to the surrounding, asymmetric, large-scale (~100 kpc) Lyman-alpha halo. We posit that the wedge is a starburst-driven superwind, associated with the first major epoch of formation of the brightest cluster galaxy. The shock and wedge are examples of feedback processes due to both AGN and star-formation in the earliest stages of massive galaxy formation., Comment: 41 pages, 12 figures. Accepted to ApJ

We study the dynamical origin of the structures observed in the scattered-light images of the resolved debris disk around HD 141569A. We explore the roles of radiation pressure from the central star, gas drag from the gas disk, and the tidal forces from two nearby stars in creating and maintaining these structures. We use a simple one-dimensional axisymmetric model to show that the presence of the gas helps confine the dust and that a broad ring of dust is produced if a central hole exists in the disk. This model also suggests that the disk is in a transient, excited dynamical state, as the observed dust creation rate applied over the age of the star is inconsistent with submillimeter mass measurements. We model in two dimensions the effects of a fly-by encounter between the disk and a binary star in a prograde, parabolic, coplanar orbit. We track the spatial distribution of the disk's gas, planetesimals, and dust. We conclude that the surface density distribution reflects the planetesimal distribution for a wide range of parameters. Our most viable model features a disk of initial radius 400 AU, a gas mass of 50 M_earth, and beta = 4 and suggests that the system is being observed within 4000 yr of the fly-by periastron. The model reproduces some features of HD 141569A's disk, such as a broad single ring and large spiral arms, but it does not reproduce the observed multiple spiral rings or disk asymmetries nor the observed clearing in the inner disk. For the latter, we consider the effect of a 5 M_Jup planet in an eccentric orbit on the planetesimal distribution of HD 141569A., Comment: Accepted to ApJ

We take advantage of the Hubble Ultra Deep Field (UDF) data to study the restframe optical and ultra violet (UV) morphologies of the novel population of Distant Red Galaxies (DRGs). Six galaxies with J-Ks > 2.3 are found to Ks=21.5, five of which have photometric redshifts z_phot > 2, corresponding to a surface density of 0.9/arcmin^2. The surface brightness distributions of the z_phot > 2 galaxies are better represented by exponential disks than R^{1/4}-laws. Two of the z_phot > 2 galaxies are extended, while three have compact morphologies. The restframe optical morphology of the z_phot > 2 galaxies is quite different from the restframe UV morphology: all the galaxies have red central components which dominate in the NICMOS H_{160}-band images, and distinct off-center blue features which show up in (and often dominate) the ACS images. The mean measured effective radius of the z_phot > 2 galaxies is =1.9+/-1.4 kpc, similar (within the errors) to the mean size of LBGs at similar redshifts. All the DRGs are resolved in the ACS images, while four are resolved in the NICMOS images. Two of the z_phot > 2 galaxies are bright X-ray sources and hence host AGN. The diverse restframe optical and UV morphological properties of DRGs derived here suggest that they have complex stellar populations, consisting of both evolved populations that dominate the mass and the restframe optical light, and younger populations, which show up as patches of star formation in the restframe UV light; in many ways resembling the properties of normal local galaxies. This interpretation is supported by fits to the broadband SEDs, which for all five z_phot > 2 are best represented by models with extended star formation histories and substantial amounts of dust., Comment: Accepted for publication in APJL

We investigate the evolution in the distribution of surface brightness, as a function of size, for elliptical and S0 galaxies in the two clusters RDCS J1252.9-2927, z=1.237 and RX J0152.7-1357, z=0.837. We use multi-color imaging with the Advanced Camera for Surveys on the Hubble Space Telescope to determine these sizes and surface brightnesses. Using three different estimates of the surface brightnesses, we find that we reliably estimate the surface brightness for the galaxies in our sample with a scatter of < 0.2 mag and with systematic shifts of \lesssim 0.05 mag. We construct samples of galaxies with early-type morphologies in both clusters. For each cluster, we use a magnitude limit in a band which closely corresponds to the rest-frame B, to magnitude limit of M_B = -18.8 at z=0, and select only those galaxies within the color-magnitude sequence of the cluster or by using our spectroscopic redshifts. We measure evolution in the rest-frame B surface brightness, and find -1.41 \+/- 0.14 mag from the Coma cluster of galaxies for RDCS J1252.9-2927 and -0.90 \+/- 0.12 mag of evolution for RX J0152.7-1357, or an average evolution of (-1.13 \+/- 0.15) z mag. Our statistical errors are dominated by the observed scatter in the size-surface brightness relation, sigma = 0.42 \+/- 0.05 mag for RX J0152.7-1357 and sigma = 0.76 \+/- 0.10 mag for RDCS J1252.9-2927. We find no statistically significant evolution in this scatter, though an increase in the scatter could be expected. Overall, the pace of luminosity evolution we measure agrees with that of the Fundamental Plane of early-type galaxies, implying that the majority of massive early-type galaxies observed at z =~ 1 formed at high redshifts., Comment: Accepted in ApJ, 16 pages in emulateapj format with 15 eps figures, 6 in color

We present an analysis of the Fundamental Plane for a sample of 27 field early-type galaxies in the redshift range 0.62 x 10^11 Msol$, we find no significant difference between the evolution of field and cluster galaxies: $Delta ln (M/L_B) = -1.20+/-0.18z for field galaxies and $Delta ln (M/L_B) = -1.12+/-0.06z$ for cluster galaxies. The relation between the measured M/L evolution and mass is partially due to selection effects. However, even when taking selection effects into account, we still find a relation between M/L evolution and mass, which is most likely caused by a lower mean age and a larger intrinsic scatter for low mass galaxies. Results from lensing early-type galaxies, which are mass-selected, show a very similar trend with mass. This, combined with our findings, provides evidence for down-sizing. Previous studies of the rate of evolution of field early-type galaxies found a large range of mutually exclusive values. We show that these differences are largely caused by the differences between fitting methods. (Abridged), Comment: figures 3 and 4 available at http://www.strw.leidenuniv.nl/~vdwel/private/FPpaper/

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 on board the Hubble Space Telescope. Simulations and independent comparisons of ourvisually derived morphologies indicate that ACS allows one to distinguish between E, S0, and spiral morphologies down to zmag = 24, corresponding to L/L* = 0.21 and 0.30 at z = 0.83 and z = 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, f_E+SO, with increasing density proceeds less rapidly at z ~ 1 than it does at z ~ 0. At z ~ 1 and density <= 500 galaxies/Mpc^2, we find = 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 >= 40 galaxies/Mpc^2 and appears to be primarily due to a deficit of S0 galaxies and an excess of Spiral+Irr galaxies relative to the local galaxy population. The Elliptical fraction - density relation exhibits no significant evolution between z = 1 and z = 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., Comment: 30 pages, 18 figures. Accepted for publication in ApJ. Full resolution versions of figs 2,3,6,8 are available at http://www.stsci.edu/~postman/mdr_figures

We present a weak lensing analysis of one of the most distant massive galaxy cluster known, RDCS 1252.9-2927 at z=1.24, using deep images from the Advanced Camera for Survey (ACS) on board the Hubble Space Telescope (HST). By taking advantage of the depth and of the angular resolution of the ACS images, we detect for the first time at z>1 a clear weak lensing signal in both the i (F775W) and z (F850LP) filters. We measure a 5-\sigma signal in the i band and a 3-\sigma signal in the shallower z band image. The two radial mass profiles are found to be in very good agreement with each other, and provide a measurement of the total mass of the cluster inside a 1Mpc radius of M(<1Mpc) = (8.0 +/- 1.3) x 10^14 M_\odot in the current cosmological concordance model h =0.70, \Omega_m=0.3, \Omega_\Lambda=0.7, assuming a redshift distribution of background galaxies as inferred from the Hubble Deep Fields surveys. A weak lensing signal is detected out to the boundary of our field (3' radius, corresponding to 1.5Mpc at the cluster redshift). We detect a small offset between the centroid of the weak lensing mass map and the brightest cluster galaxy, and we discuss the possible origin of this discrepancy. The cumulative weak lensing radial mass profile is found to be in good agreement with the X-ray mass estimate based on Chandr and XMM-Newton observations, at least out to R_500=0.5Mpc., Comment: 38 pages, ApJ in press. Full resolution images available at http://www.eso.org/~prosati/RDCS1252/Lombardi_etal_accepted.pdf

Using deep HST ACS imaging and VLT FORS2 spectra, we determined the velocity dispersions, effective radii and surface brightnesses for four early-type galaxies in the $z=1.237$ cluster \cl. All four galaxies are massive, $> 10^{11} M_{\sun}$. These four galaxies, combined with three from \lynx at $z=1.276$, establish the Fundamental Plane of massive early-type cluster galaxies at $\bar{z}=1.25$. The offset of the Fundamental Plane shows that the luminosity evolution in rest-frame $B$ is $\Delta \ln M/L_B = (-0.98 \pm 0.06) z$ for galaxies with $M > 10^{11.5} M_{\sun}$. To reproduce the observed mass-to-light ratio ($M/L$) evolution, we determine the characteristic age of the stars in these $M > 10^{11.5} M_{\sun}$ galaxies to be $3.0^{+0.3}_{-0.3}$ Gyrs, {\em i.e.} $z_{*}=3.4^{+0.5}_{-0.4}$. Including selection effects caused by morphological bias (the ``progenitor bias''), we estimate an age of $2.1^{+0.2}_{-0.2}$ Gyrs, or $z_{*} = 2.3^{+0.2}_{-0.2}$ for the elliptical galaxy population. Massive cluster early-type galaxies appear to have a large fraction of stars that formed early in the history of the universe. However, there is a large scatter in the derived $M/L$ values, which is confirmed by the spread in the galaxies' colors. Two lower mass galaxies in our $\bar{z}=1.25$ sample have much lower $M/L$ values, implying significant star-formation close to the epoch of observation. Thus, even in the centers of massive clusters, there appears to have been significant star formation in some massive, $M \simeq 10^{11} M_{\sun}$, galaxies at $z\simeq 1.5$., Comment: 5 pages in emulate ApJ, 1 bw and 4 color figures, accepted to ApJL

We combine imaging data from the Advanced Camera for Surveys (ACS) with VLT/FORS optical spectroscopy to study the properties of star-forming galaxies in the z=0.837 cluster CL0152-1357. We have morphological information for 24 star-forming cluster galaxies, which range in morphology from late-type and irregular to compact early-type galaxies. We find that while most star-forming galaxies have $r_{625}-i_{775}$ colors bluer than 1.0, eight are in the red cluster sequence. Among the star-forming cluster population we find five compact early-type galaxies which have properties consistent with their identification as progenitors of dwarf elliptical galaxies. The spatial distribution of the star-forming cluster members is nonuniform. We find none within $R\sim 500$ Mpc of the cluster center, which is highly suggestive of an intracluster medium interaction. We derive star formation rates from [OII] $\lambda\lambda 3727$ line fluxes, and use these to compare the global star formation rate of CL0152-1357 to other clusters at low and intermediate redshifts. We find a tentative correlation between integrated star formation rates and $T_{X}$, in the sense that hotter clusters have lower integrated star formation rates. Additional data from clusters with low X-ray temperatures is needed to confirm this trend. We do not find a significant correlation with redshift, suggesting that evolution is either weak or absent between z=0.2-0.8., Comment: ApJ accepted

We present new measurements of the galaxy luminosity function (LF) and its dependence on local galaxy density, color, morphology, and clustocentric radius for the massive z=0.83 cluster MS1054-0321. Our analyses are based on imaging performed with the ACS onboard the HST in the F606W, F775W and F850LP passbands and extensive spectroscopic data obtained with the Keck LRIS. Our main results are based on a spectroscopically selected sample of 143 cluster members with morphological classifications derived from the ACS observations. Our three primary findings are (1) the faint-end slope of the LF is steepest in the bluest filter, (2) the LF in the inner part of the cluster (or highest density regions) has a flatter faint-end slope, and (3) the fraction of early-type galaxies is higher at the bright end of the LF, and gradually decreases toward fainter magnitudes. These characteristics are consistent with those in local galaxy clusters, indicating that, at least in massive clusters, the common characteristics of cluster LFs are established at z=0.83. We also find a 2sigma deficit of intrinsically faint, red galaxies (i-z>0.5, Mi>-19) in this cluster. This trend may suggest that faint, red galaxies (which are common in z<0.1 rich clusters) have not yet been created in this cluster at z=0.83. The giant-to-dwarf ratio in MS1054-0321 starts to increase inwards of the virial radius or when Sigma>30 Mpc^-2, coinciding with the environment where the galaxy star formation rate and the morphology-density relation start to appear. (abridged), Comment: ApJ in press, references updated

We present resolved scattered-light images of the debris disk around HD 107146, a G2 star 28.5 pc from the Sun. This is the first debris disk to be resolved in scattered light around a solar-type star. We observed it with the HST/ACS coronagraph, using a 1.8'' occulting spot and the F606W (broad V) and F814W (broad I) filters. Within 2'' from the star, the image is dominated by PSF subtraction residuals. Outside this limit, the disk looks featureless except for a northeast-southwest brightness asymmetry that we attribute to forward scattering. The disk has scattered-light fractional luminosities of $(L_{Sca}/L_*)_{F606W}=6.8 \pm 0.8 \times 10^{-5}$ and $(L_{Sca}/L_*)_{F814W}=10 \pm 1 \times 10^{-5}$ and it is detected up to 6.5'' away from the star. To map the surface density of the disk, we deproject it by $25^\circ \pm 5^\circ$, divide by the dust scattering phase ($g_{F606W} = 0.3 \pm 0.1$, $g_{F814W} = 0.2 \pm 0.1$) and correct for the geometric dilution of starlight. Within the errors, the surface density has the same shape in each bandpass, and it appears to be a broad (85 AU) ring with most of the opacity concentrated at 130 AU. The ratio of the relative luminosity in F814W to that in F606W has the constant value of $1.3\pm0.3$, with the error dominated by uncertainties in the value of $g$ in each filter. An examination of far infrared and submillimeter measurements suggests the presence of small grains. The colors and the derived values of $g$ are consistent with the presence of dust particles smaller than the radiation pressure limit. The dust generated by the creation of a small planet or the scattering and circularization of a large one, are possible scenarios that may explain the shape of the surface density profile., Comment: To appear in ApJ Letters Figure 3 in the original version had the wrong vertical scale. In this version it has been replaced by the correct one

We present $V$ and $I$ continuum images and H$\alpha$+[N II] maps of nine early-type galaxies observed with the Wide Field Channel of the Advanced Camera for Surveys on the Hubble Space Telescope. Dust and ionized gas are detected in all galaxies. The optical nebulae are primarily concentrated on the nuclei and extend out to radii of a few hundred parsecs, in compact clumps, filaments, or disks. Two galaxies, NGC 6166 and NGC 6338, also possess diffuse, ionized filaments on kiloparsec scales. The ionized gas is entirely contained within the nuclear disks of ESO 208-G021, NGC 3078, and NGC 7720. In the radio-loud galaxy NGC 6166, emission-line filaments are detected along the radio lobes, possibly as a result of shock ionization. A wide range of ionized gas masses, $M_g\approx7\times10^2-3\times10^6$ $M_\odot$, are calculated from the observed fluxes. Even in this small sample, the orientation of the ionized material correlates well with the major or minor axis of the galaxies, consistent with an external origin for the dust and gas., Comment: Accepted for publication in the Astronomical Journal, to appear Dec 4, 2004. 14 pages, 4 figures

The Deep Extragalactic Evolutionary Probe (DEEP) is a series of spectroscopic surveys of faint galaxies, targeted at the properties and clustering of galaxies at redshifts z ~ 1. We present the redshift catalog of the DEEP 1 GSS pilot phase of this project, a Keck/LRIS survey in the HST/WFPC2 Groth Survey Strip. The redshift catalog and data, including reduced spectra, are publicly available through a Web-accessible database. The catalog contains 658 secure galaxy redshifts with a median z=0.65, and shows large-scale structure walls to z = 1. We find a bimodal distribution in the galaxy color-magnitude diagram which persists to z = 1. A similar color division has been seen locally by the SDSS and to z ~ 1 by COMBO-17. For red galaxies, we find a reddening of only 0.11 mag from z ~ 0.8 to now, about half the color evolution measured by COMBO-17. We measure structural properties of the galaxies from the HST imaging, and find that the color division corresponds generally to a structural division. Most red galaxies, ~ 75%, are centrally concentrated, with a red bulge or spheroid, while blue galaxies usually have exponential profiles. However, there are two subclasses of red galaxies that are not bulge-dominated: edge-on disks and a second category which we term diffuse red galaxies (DIFRGs). The distant edge-on disks are similar in appearance and frequency to those at low redshift, but analogs of DIFRGs are rare among local red galaxies. DIFRGs have significant emission lines, indicating that they are reddened mainly by dust rather than age. The DIFRGs in our sample are all at z>0.64, suggesting that DIFRGs are more prevalent at high redshifts; they may be related to the dusty or irregular extremely red objects (EROs) beyond z>1.2 that have been found in deep K-selected surveys. (abridged), Comment: ApJ in press. 24 pages, 17 figures (12 color). The DEEP public database is available at http://saci.ucolick.org/

We present {\it Hubble Space Telescope} Advanced Camera for Surveys multicolor coronagraphic images of the recently discovered edge-on debris disk around the nearby ($\sim10$ pc) M dwarf AU Microscopii. The disk is seen between $r = $0\farcs 75 -- 15'' (7.5 -- 150 AU) from the star. It has a thin midplane with a projected full-width-at-half-maximum (FWHM) thickness of 2.5 -- 3.5 AU within $r < 50$ AU of the star that increases to 6.5 -- 9 AU at $r \sim 75$ AU. The disk's radial brightness profile is generally flat for $r < 15$ AU, then decreases gradually ($I \propto r^{-1.8}$) out to $r \approx 43$ AU, beyond which it falls rapidly ($I \propto r^{-4.7}$). Within 50 AU the midplane is straight and aligned with the star, and beyond that it deviates by $\sim3^{\circ}$, resulting in a bowed appearance that was also seen in ground-based images. Three-dimensional modelling of the disk shows that the inner region ($r < 50$ AU) is inclined to the line-of-sight by $<1^{\circ}$ and the outer disk by $\sim3^{\circ}$. The inclination of the outer disk and moderate forward scattering ($g \approx 0.4$) can explain the apparent bow. The intrinsic, deprojected FWHM thickness is 1.5 -- 10 AU, increasing with radius. The models indicate that the disk is clear of dust within $\sim12$ AU of the star, in general agreement with the previous prediction of 17 AU based on the infrared spectral energy distribution. The disk is blue, being 60% brighter at $B$ than $I$ relative to the star. One possible explanation for this is that there is a surplus of very small grains compared to other imaged debris disks that have more neutral or red colors. This may be due to the low radiation pressure exerted by the late-type star. Observations at two epochs show that an extended source seen along the midplane is a background galaxy., Comment: 11 figures

We present a weak lensing analysis of the X-ray luminous cluster CL 0152-1357 at z~0.84 using HST/ACS observations. The unparalleled resolution and sensitivity of ACS enable us to measure weakly distorted, faint background galaxies to the extent that the number density reaches ~175 arcmin^-2. The PSF of ACS has a complicated shape that also varies across the field. We construct a PSF model for ACS from an extensive investigation of 47 Tuc stars in a modestly crowded region. We show that this model PSF excellently describes the PSF variation pattern in the cluster observation when a slight adjustment of ellipticity is applied. The high number density of source galaxies and the accurate removal of the PSF effect through moment-based deconvolution allow us to restore the dark matter distribution of the cluster in great detail. The direct comparison of the mass map with the X-ray morphology from Chandra observations shows that the two peaks of intracluster medium traced by X-ray emission are lagging behind the corresponding dark matter clumps, indicative of an on-going merger. The overall mass profile of the cluster can be well described by an NFW profile with a scale radius of r_s =309+-45 kpc and a concentration parameter of c=3.7+-0.5. The mass estimates from the lensing analysis are consistent with those from X-ray and Sunyaev-Zeldovich analyses. The predicted velocity dispersion is also in good agreement with the spectroscopic measurement from VLT observations. In the adopted WMAP cosmology, the total projected mass and the mass-to-light ratio within 1 Mpc are estimated to be 4.92+-0.44 10^14 solar mass and 95+-8 solar mass/solar luminosity, respectively., Comment: Accepted for publication in Astrophysical Journal. 58 pages, 26 figures. Figures have been degraded to meet size limit; a higher resolution version available at http://acs.pha.jhu.edu/~mkjee/ms_cl0152.pdf

Combined HST, X-ray, and ground-based optical studies show that clusters of galaxies are largely "in place" by $z \sim 1$, an epoch when the Universe was less than half its present age. High resolution images show that elliptical, S0, and spiral galaxies are present in clusters at redshifts up to $z \sim 1.3$. Analysis of the CMDs suggest that the cluster ellipticals formed their stars several Gyr earlier, near redshift 3. The morphology--density relation is well established at $z\sim1$, with star-forming spirals and irregulars residing mostly in the outer parts of the clusters and E/S0s concentrated in dense clumps. The intracluster medium has already reached the metallicity of present-day clusters. The distributions of the hot gas and early-type galaxies are similar in $z\sim1$ clusters, indicating both have largely virialized in the deepest potentials wells. In spite of the many similarities between $z\sim1$ and present-day clusters, there are significant differences. The morphologies revealed by the hot gas, and particularly the early-type galaxies, are elongated rather than spherical. We appear to be observing the clusters at an epoch when the sub-clusters and groups are still assembling into a single regular cluster. Support for this picture comes from CL0152 where the gas appears to be lagging behind the luminous and dark mass in two merging sub-components. Moreover, the luminosity difference between the first and second brightest cluster galaxies at $z\sim1$ is smaller than in 93% of present-day Abell clusters, which suggests that considerable luminosity evolution through merging has occurred since that epoch. Evolution is also seen in the bolometric X-ray luminosity function., Comment: 18 pages, 12 figures, to appear in Penetrating Bars through Masks of Cosmic Dust: the Hubble Tuing Fork Strikes a New Note, eds. D.L. Block, K.C. Freeman, I. Puerari & R. Groess. Figures degraded to meet astroph size limit; a version with higher resolution figures may be downloaded from: http://acs.pha.jhu.edu/~jpb/z1clusters/ford_clusters.pdf