The fraction of stellar mass contained in globular clusters (GCs), also measured by number as the specific frequency, is a fundamental quantity that reflects both a galaxy's early star formation and its entire merging history. We present specific frequencies, luminosities, and mass fractions for the globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster Survey. This catalog represents the largest homogeneous catalog of GC number and mass fractions across a wide range of galaxy luminosity (−22 < M B < −15). We find that 1) GC mass fractions can be high in both giants and dwarfs, but are universally low in galaxies with intermediate luminosities (−20 < M B < −17).2) The fraction of red GCs increases with galaxy luminosity, but stays constant or decreases for galaxies brighter than M z = −22. As a result, although specific frequencies for blue and red GCs are both higher in massive galaxies, the behavior of specific frequency across galaxy mass is dominated by the blue GCs.3) The GC fractions of low-mass galaxies exhibit a dependence on environment, where dwarf galaxies closer to the cluster center have higher GC fractions. Nearly all dwarfs with high GC fractions are within 1 Mpc of the cD galaxy M87, presenting the first strong evidence that GC formation in dwarf galaxies is biased toward dense environments. 4) GC formation in central dwarfs is biased because their stars form earliest and most intensely. Comparisons to early-type dwarf galaxies in the Millennium Simulation show that central dwarfs are likely to have older stellar populations and form more of their stars at higher star formation rates (SFRs) and star formation rate surface densities. In addition, the SFR surface density in simulated dwarfs peaks before the total SFR, naturally producing GC populations that are older and more metal-poor than the field stars. 5) Dwarfs within ∼ 40 kpc of the giant ellipticals M87 and M49 are red for their luminosities and have few or no GCs, suggesting that they have been tidally stripped and have contributed their GCs to the halos of their giant neighbors. The central dwarfs with high GC mass fractions are thus likely to be the survivors most similar to the protogalaxies that assembled the rich M87 globular cluster system.
We present a study of the stellar populations of galaxies in the cluster RX J0152.7À1357 at a redshift of 0.83. The study is based on new high signal-to-noise ratio spectroscopy of 29 cluster members covering the wavelength range 5000-10000 8, as well as r 0 i 0 z 0 photometry of the cluster. We use scaling relations between the central velocity dispersions of the galaxies and their luminosities, Balmer line strengths, and various metal line strengths to parameterize the differences between the members of RX J0152.7À1357 and our low-redshift comparison sample. The luminosities of the RX J0152.7À1357 galaxies and the strengths of the higher order Balmer lines H and H (for non-emission-line galaxies) appear to be in agreement with pure passive evolution of the stellar populations with a formation redshift z form % 4. However, the strengths of the D4000 indices and the metal indices do not support this interpretation. Compared with our low-redshift comparison sample, the metal indices (C4668, Fe4383, CN3883, G4300, and CN 2 ) show that at least half of the non-emission-line galaxies in RX J0152.7À1357 have an -element abundance ratio =Fe ½ of 0.2 dex higher, and about half of the galaxies have significantly lower metal content. X-ray data have previously shown that RX J0152.7À1357 is in the process of merging from two subclumps. We find that differences in stellar populations of the galaxies are associated with the location of the galaxies relative to the X-ray emission. The galaxies with weak C4668 and G4300, as well as galaxies for which weak [O ii] emission indicates a very recent star formation episode involving about 1% of the mass, are located in areas of low X-ray luminosity, on the outskirts of the two subclumps. It is possible that these galaxies are experiencing the effect of the cluster merger as (short) episodes of star formation, while the galaxies in the cores of the subclumps are unaffected by the merger. The spectroscopy of the RX J0152.7À1357 galaxies shows for the first time galaxies in a rich cluster at intermediate redshift that cannot evolve passively into the present-day galaxy population in rich clusters. Additional physical processes may be at work, and we speculate that merging with infalling (disk) galaxies in which stars have formed over an extended period might produce the required reduction in =Fe ½ . However, the merging could not be accompanied by star formation involving a substantial mass fraction. We note that our conclusions, in part, rely on stellar population models for which the predictions of the indices in the rest-frame blue have not yet been tested extensively.
The Deep Extragalactic Evolutionary Probe (DEEP) is a series of spectroscopic surveys of faint galaxies, targeted at understanding the properties and clustering of galaxies at redshifts z ∼ 1. We present the redshift catalog of the DEEP 1 Groth Strip pilot phase of this project, a Keck/LRIS survey of faint galaxies in the Groth Survey Strip imaged with HST WFPC2. The redshift catalog and data, including reduced spectra, are made publicly available through a Web-accessible database. The catalog contains 658 secure galaxy redshifts with a median z = 0.65. The distribution of these galaxies shows large-scale structure walls to z ∼ 1. We find a bimodal distribution in the galaxy color-magnitude diagram which persists to the same distance. A similar color division has been seen locally by the SDSS survey and to z ∼ 1 by the COMBO-17 survey. The HST imaging allows us to measure structural properties of the galaxies, and we find that the color division corresponds generally to a structural division. Most red galaxies, ∼ 75%, are centrally concentrated, with a red bulge or spheroidal stellar component, 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). Comparison to a local sample drawn from the RC3 suggests that 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 beyond z > 1.2 that have been found in deep K-selected surveys. We measure the color evolution of both red and blue galaxies by comparing our U − B colors to those from the RC3. 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. Larger, more carefully defined samples with better colors are needed to improve this measurement. Reconciling evolution in color, luminosity, mass, morphology, and star-formation rates will be an active topic of future research.
We present a proper-motion, CCD photometric study of stars in the distant halo globular cluster Palomar 13. The absolute proper motion of Pal 13 with respect to the background galaxies, derived from moderate-scale photographic plates separated by a 40 year baseline, is (k a cos d , k d ) \ (2.30, 0.27) (0.26, 0.25) mas yr~1. The resultant total space velocity (315 km s~1) implies that Pal 13 is in the inner part of its orbit near perigalacticon. Orbital integration reveals that the cluster possesses an inclined, very eccentric, retrograde orbit. These data conÐrm that Pal 13 is a paradigm "" young halo ÏÏ globular cluster. The derived proper motions for cluster stars are used to produce membership probabilities and a cleaned CCD UBV catalog for Pal 13. With this data set we have made small revisions to Pal 13Ïs distance, metallicity, position, and light proÐle. The membership of four previously reported RR Lyrae variables and a disproportionately large group of blue straggler stars is conÐrmed. As expected, the blue stragglers are centrally concentrated. The small size of this cluster, combined with the shape of its light proÐle, which shows a clear departure from a classical King function beyond the tidal radius, suggests that Pal 13 is in the Ðnal throes of destruction. This could explain the large blue straggler speciÐc frequency, as destructive processes would preferentially strip less massive stars.
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