L. Infante

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.

A census of star-forming galaxies in the z ∼ 9-10 universe based on hst+spitzer observations over 19 clash clusters: Three candidate z ∼ 9-10 galaxies and improved constraints on the star formation rate density at z

We utilise a two-color Lyman-Break selection criterion to search for z � 9-10 galaxies over the first 19 clusters in the CLASH program. Key to this search are deep observations over our clusters in five near-IR passbands to 1.6µm, allowing us good constraints on the position of the Lyman break to z � 10. A systematic search yields three z � 9-10 candidates in total above a 6� detection limit. While we have already reported the most robust of these candidates, MACS1149-JD, in a previous publication, two additional z � 9 candidates are also revealed in our expanded search. The new candidates have H160-band AB magnitudes of �26.2-26.9 and are located behind MACSJ1115.9+0129 and MACSJ1720.3+3536. The observed H160 Spitzer/IRAC colors for the sources are sufficiently blue to strongly favor redshifts of z � 9 for these sources. A careful assessment of various sources of contamination suggests .1 contaminants for our z � 9-10 selection. To determine the implications of these search results for the LF and SFR density at z � 9, we introduce a new differential approach to deriving these quantities in lensing fields. Our procedure is to derive the evolution by comparing the number of z � 9-10 galaxy candidates found in CLASH with the number of galaxies in a slightly lower redshift sample (after correcting for the differences in selection volumes), here taken to be z � 8. This procedure takes advantage of the fact that the relative selection volumes available for the z � 8 and z � 9-10 selections behind lensing clusters are not greatly dependent on the details of the gravitational lensing models. We find that the normalization of the UV LF at z � 9 is just 0.22 +0.30 −0.15 × that at z � 8, �2 +31× lower than what we would infer extrapolating z � 4-8 LF results. These results therefore suggest a more rapid evolution in the UV LF at z > 8 than seen at lower redshifts (although the current evidence here is weak). Compared to similar evolutionary findings from the HUDF, our result is much more insensitive to large-scale structure uncertainties, given our many independent sightlines on the high-redshift universe. Subject headings: galaxies: evolution — galaxies: high-redshift

FAINT GALAXIES IN DEEP ADVANCED CAMERA FOR SURVEYS OBSERVATIONS

We present the analysis of the faint galaxy population in the Advanced Camera for Surveys (ACS) Early Release Observation fields VV 29 (UGC 10214) and NGC 4676. Here we attempt to thoroughly consider all aspects relevant for faint galaxy counting and photometry, developing methods which are based on public software and that are easily reproducible by other astronomers. Using simulations we determine the best SExtractor parameters for the detection of faint galaxies in deep HST observations, paying special attention to the issue of deblending, which significantly affects the normalization and shape of the number count distribution. We confirm, as claimed by Bernstein, Freedman and Madore (2002), that Kron-like magnitudes, such as the ones generated by SExtractor, can miss more than half of the light of faint galaxies, what dramatically affects the slope of the number counts. We present catalogs for the VV 29 and NGC 4676 fields with photometry in the g,V and I bands. We also show that combining the bayesian software BPZ with superb ACS data and new spectral templates enables us to estimate reliable photometric redshifts for a significant fraction of galaxies with as few as three filters. After correcting for selection effects, we measure slopes of 0.32+- 0.01 for 22 25.5 can be well approximated in all our filters by a passive luminosity evolution model based on the COMBO-17 luminosity function (\alpha=-1.5), with a strong merging rate following the prescription of Glazebrook et al. (1994), \phi^*\propto (1+Qz), with Q=4.We present the analysis of the faint galaxy population in the Advanced Camera for Surveys (ACS) Early Release Observation fields VV 29 (UGC 10214) and NGC 4676. These observations cover a total area of 26.3 arcmin 2 and have depths close to that of the Hubble Deep Fields in the deepest part of the VV 29 image, with 10 � detection limits for point sources of 27.8, 27.6, and 27.2 AB magnitudes in the g F475W , VF606W ,a ndIF814W bands, respectively. Measuring the faint galaxy number count distribution is a difficult task, with different groups arriving at widely varying results even on the same data set. Here we attempt to thoroughly consider all aspects relevant for faint galaxy counting and photometry, developing methods that are based on public software and that are easily reproducible by other astronomers. Using simulations we determine the best SExtractor parameters for the detection of faint galaxies in deep Hubble Space Telescope observations, paying special attention to the issue of deblending, which significantly affects the normalization and shape of the number count distribution. We confirm, as claimed by Bernstein, Freedman, & Madore, that Kron-like magnitudes, such as the ones generated by SExtractor, can miss more than half of the light offaint galaxies, what dramatically affects the slope of the number counts. We show how to correct for this effect, which depends sensitively not only on the characteristics of the observations, but also on the choice of SExtractor parameters. We present catalogs for the VV 29 and NGC 4676 fields with photometry in the F475W, F606W, and F814W bands. We also show that combining the Bayesian software BPZ with superb ACS data and new spectral templates enables us to estimate reliable photometric redshifts for a significant fraction of galaxies with as few as three filters. After correcting for selection effects, we measure slopes of 0:32 � 0:01for 22 25:5 can be well approximated in all our filters by a passive luminosity evolution model based on the COMBO-17 luminosity function (� ¼� 1:5), with a strong merging rate following the prescription of

Hubble Space Telescope ACS Coronagraphic Imaging of the Circumstellar Disk around HD 141569A

Multicolor coronagraphic images of the circumstellar disk around HD 141569A have been obtained with the Hubble Space Telescope Advanced Camera for Surveys. The B, V, and I images show that the disks previously described multiple-ring structure is actually a continuous distribution of dust with a tightly wound spiral structure. Extending from the disk are two, more open spiral arms, one of which appears to reach the nearby binary star HD 141569BC. Diffuse dust is seen up to 1200 AU from HD 141569A. Although planets may exist in the inner region of the disk, tidal interaction with HD 141569BC seems more likely to be the cause of these phenomena. The disk appears redder than the star (B-V = 0.21 and V-I = 0.25), and its color is spatially uniform. A scattering asymmetry factor of g = 0.25–0.35 is derived. The azimuthal density distribution is asymmetric, varying by a factor of ~3 at some radii.

The globular cluster system of NGC 1399 *,**,*** V. dynamics of the cluster system out to 80 kpc

Globular clusters (GCs) are tracers of the gravitational potential of their host galaxies. Moreover, their kinematic properties may provide clues for understanding the formation of GC systems and their host galaxies. We use the largest set of GC velocities obtained so far of any elliptical galaxy to revise and extend the previous investigations (Richtler et al. 2004) of the dynamics of NGC 1399, the central dominant galaxy of the nearby Fornax cluster of galaxies. The GC velocities are used to study the kinematics, their relation with population properties, and the dark matter halo of NGC 1399. We have obtained 477 new medium-resolution spectra (of these, 292 are spectra from 265 individual GCs, 241 of which are not in the previous data set). with the VLT FORS 2 and Gemini South GMOS multi-object spectrographs. We revise velocities for the old spectra and measure velocities for the new spectra, using the same templates to obtain an homogeneously treated data set. Our entire sample now comprises velocities for almost 700 GCs with projected galactocentric radii between 6 and 100 kpc. In addition, we use velocities of GCs at larger distances published elsewhere. Combining the kinematic data with wide-field photometric Washington data, we study the kinematics of the metal-poor and metal-rich subpopulations. We discuss in detail the velocity dispersions of subsamples and perform spherical Jeans modelling. The most important results are: the red GCs resemble the stellar field population of NGC 1399 in the region of overlap. The blue GCs behave kinematically more erratic. Both subpopulations are kinematically distinct and do not show a smooth transition. It is not possible to find a common dark halo which reproduces simultaneously the properties of both red and blue GCs. Some velocities of blue GCs are only to be explained by orbits with very large apogalactic distances, thus indicating a contamination with GCs which belong to the entire Fornax cluster rather than to NGC 1399. Also, stripped GCs from nearby elliptical galaxies, particularly NGC 1404, may contaminate the blue sample. We argue in favour of a scenario in which the majority of the blue cluster population has been accreted during the assembly of the Fornax cluster. The red cluster population shares the dynamical history of the galaxy itself. Therefore we recommend to use a dark halo based on the red GCs alone. The dark halo which fits best is marginally less massive than the halo quoted previously. The comparison with X-ray analyses is satisfactory in the inner regions, but without showing evidence for a transition from a galaxy to a cluster halo, as suggested by X-ray work.

Evidence for ubiquitous high-equivalent-width nebular emission in z ∼ 7 galaxies : toward a clean measurement of the specific star-formation rate using a sample of bright, magnified galaxies

Growing observational evidence indicates that nebular line emission has a significant impact on the rest-frame optical fluxes of z ~ 5-7 galaxies. This line emission makes z ~ 5-7 galaxies appear more massive, with lower specific star-formation rates (sSFRs). However, corrections for this line emission have been difficult to perform reliably because of huge uncertainties on the strength of such emission at z ≳ 5.5. In this paper, we present the most direct observational evidence thus far for ubiquitous high-equivalent-width (EW) [O III] + Hβ line emission in Lyman-break galaxies at z ~ 7, and we present a strategy for an improved measurement of the sSFR at z ~ 7. We accomplish this through the selection of bright galaxies in the narrow redshift window z ~ 6.6-7.0 where the Spitzer/Infrared Array Camera (IRAC) 4.5 μm flux provides a clean measurement of the stellar continuum light, in contrast with the 3.6 μm flux, which is contaminated by the prominent [O III] + Hβ lines. To ensure a high signal-to-noise ratio for our IRAC flux measurements, we consider only the brightest (H_(160) < 26 mag) magnified galaxies we have identified behind galaxy clusters. It is remarkable that the mean rest-frame optical color for our bright seven-source sample is very blue, [3.6]-[4.5] = –0.9 ± 0.3. Such blue colors cannot be explained by the stellar continuum light and require that the rest-frame EW of [O III] + Hβ is greater than 637 A for the average source. The four bluest sources from our seven-source sample require an even more extreme EW of 1582 A. We can also set a robust lower limit of ≳ 4 Gyr^(–1) on the sSFR of our sample based on the mean spectral energy distribution.

Discovery of a Very Bright Strongly Lensed Galaxy Candidate at z ≈ 7.6*

Using Hubble Space Telescope (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 ( -->z = 0.18). The galaxy candidate, which we refer to as A1689-zD1, shows a strong -->z850 − J110 break of at least 2.2 mag and is completely undetected ( J110 − H160 and -->H160 − [ 4.5 μ m ] 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 ( -->χ2ν = 1.1). Attempts to reproduce these properties with a model galaxy at -->z χ2ν ≥ 25). A1689-zD1 has an observed (lensed) magnitude of 24.7 AB (8 σ) in the NICMOS H160 band and is ~1.3 mag brighter than the brightest known z850-dropout galaxy. When corrected for the cluster magnification of ~9.3 at -->z ~ 7.6, the candidate has an intrinsic magnitude of -->H160 = 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) × 109 M☉, stellar ages 45-320 Myr, star formation rates 7.6 M☉ yr−1, and low reddening with -->AV ≤ 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.

CLASH: The CONCENTRATION-MASS RELATION of GALAXY CLUSTERS

We present a new determination of the concentration–mass (c–M) relation for galaxy clusters based on our comprehensive lensing analysis of 19 X-ray selected galaxy clusters from the Cluster Lensing and Supernova Survey with Hubble (CLASH). Our sample spans a redshift range between 0.19 and 0.89. We combine weak-lensing constraints from the Hubble Space Telescope (HST) and from ground-based wide-field data with strong lensing constraints from HST. The results are reconstructions of the surface-mass density for all CLASH clusters on multi-scale grids. Our derivation of Navarro–Frenk–White parameters yields virial masses between 0.53 × 10^(15) M_⊙ h and 1.76 × 10^(15) M_⊙ h and the halo concentrations are distributed around c_(200c) ∼ 3.7 with a 1σ significant negative slope with cluster mass. We find an excellent 4% agreement in the median ratio of our measured concentrations for each cluster and the respective expectation from numerical simulations after accounting for the CLASH selection function based on X-ray morphology. The simulations are analyzed in two dimensions to account for possible biases in the lensing reconstructions due to projection effects. The theoretical c–M relation from our X-ray selected set of simulated clusters and the c–M relation derived directly from the CLASH data agree at the 90% confidence level.

HUBBLE SPACE TELESCOPE ADVANCED CAMERA FOR SURVEYS CORONAGRAPHIC IMAGING OF THE AU MICROSCOPII DEBRIS DISK

We present Hubble Space Telescope Advanced Camera for Surveys multicolor coronagraphic images of the recently discovered edge-on debris disk around the nearby (� 10 pc) M dwarf AU Microscopii. The disk is seen between r ¼ 0B75 and 15 00 (7.5–150 AU) from the star. It has a thin midplane with a projected FWHM thickness of 2.5–3.5 AU within r < 50 AU of the star that increases to 6.5–9 AU at r � 75 AU. The disk’s radial brightness profile is generally flat forr < 15 AU, then decreases gradually (I / r � 1:8 )o ut tor � 43 AU, beyond which it falls rapidly (I / r � 4:7 ). Within 50 AU the midplane is straight and aligned with the star, and beyond that it deviates by � 3 � , resulting in a bowed appearance that was also seen in ground-based images. Three-dimensional modeling of the disk shows that the inner region (r < 50 AU) is inclined to the line of sight by less than 1 � and the outer disk by � 3 � . The inclination of the outer disk and moderate forward scattering (g � 0:4) can explain the apparentbow. The intrinsic, deprojected FWHM thickness is 1.5–10 AU, increasing with radius. The models indicate that the disk is clear of dust within � 12 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 with 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.

Spectroscopic Metallicities for Fornax Ultracompact Dwarf Galaxies, Globular Clusters, and Nucleated Dwarf Elliptical Galaxies*

Various formation channels for the puzzling ultra-compact dwarf galaxies (UCDs) have been proposed in the last few years. To better judge on some of the competing scenarios, we present spectroscopic [Fe/H] estimates for a sample of 26 compact objects in the central region of the Fornax cluster, covering the magnitude range of UCDs and bright globular clusters. We find a break in the metallicity distribution of compact objects at M_V ~ -11 mag (~3*10^6 M_sun): for M_V -11 mag. This metallicity break is accompanied by a change in the size-luminosity relation for compact objects, as deduced from HST-imaging: for M_V -11 mag, r_h is almost luminosity-independent. We therefore assume a limiting absolute magnitude of M_V=-11 mag between UCDs and globular clusters. The mean metallicity of five Fornax dE,N nuclei included in our study is about 0.8 dex lower than that of the UCDs, at 4.5 sigma significance. Because of this large metallicity discrepancy we disfavor the hypothesis that most of the Fornax UCDs are the remnant nuclei of tidally stripped dE,Ns. Our metallicity estimates for UCDs are closer to but slightly below those derived for young massive clusters (YMCs) of comparable masses. We therefore favor a scenario where most UCDs in Fornax are successors of merged YMCs produced in the course of violent galaxy-galaxy mergers. It is noted that in contrast to that, the properties of Virgo UCDs are more consistent with the stripping scenario, suggesting that different UCD formation channels may dominate in either cluster.Various formation channels for the puzzling ultracompact dwarf galaxies (UCDs) have been proposed in the last few years. To better judge some of the competing scenarios, we present spectroscopic [Fe/H] estimates for a sample of 26 compact objects in the central region of the Fornax Cluster, covering the magnitude range of UCDs and bright globular clusters (18 mag -11 mag. This metallicity break is accompanied by a change in the size-luminosity relation for compact objects, as deduced from Hubble Space Telescope imaging: for MV -11 mag, rh is almost luminosity-independent. In our study we therefore assume a limiting absolute magnitude of MV = -11 mag between UCDs and globular clusters. The mean metallicity of five Fornax nucleated dwarf elliptical galaxy (dE,N) nuclei included in our study is about 0.8 dex lower than that of the UCDs, a difference significant at the 4.5 σ level. This difference is marginally higher than expected from a comparison of their (V - I) colors, indicating that UCDs are younger than or at most coeval to dE,N nuclei. Because of the large metallicity discrepancy between UCDs and nuclei, we disfavor the hypothesis that most of the Fornax UCDs are the remnant nuclei of tidally stripped dE,Ns. Our metallicity estimates for UCDs are closer to but slightly below those derived for young massive clusters (YMCs) of comparable masses. We therefore favor a scenario in which most UCDs in Fornax are successors of merged YMCs produced in the course of violent galaxy-galaxy mergers. It is noted that, in contrast, the properties of Virgo UCDs are more consistent with the stripping scenario, suggesting that different UCD formation channels may dominate in either cluster.