We present an analysis of stellar populations and evolutionary history of galaxies in three similarly rich galaxy clusters MS0451.6-0305 (z = 0.54), RXJ0152.7-1357 (z = 0.83), and RXJ1226.9+3332 (z = 0.89). Our analysis is based on high signal-to-noise ground-based optical spectroscopy and Hubble Space Telescope imaging for a total of 17-34 members in each cluster. Using the dynamical masses together with the effective radii and the velocity dispersions we find no indication of evolution of sizes or velocity dispersions with redshift at a given galaxy mass. We establish the Fundamental Plane (FP) and scaling relations between absorption line indices and velocity dispersions. We confirm that the FP is steeper at z ≈ 0.86 compared to the low redshift FP, indicating that under the assumption of passive evolution the formation redshift, z form , depends on the galaxy velocity dispersion (or alternatively mass). At a velocity dispersion of σ = 125 km s −1 (Mass = 10 10.55 M ⊙ ) we find z form = 1.24 ± 0.05, while at σ = 225 km s −1 (Mass = 10 11.36 M ⊙ ) the formation redshift is z form = 1.95 +0.3 −0.2 , for a Salpeter initial mass function. The three clusters follow similar scaling relations between absorption line indices and velocity dispersions as those found for low redshift galaxies. The zero point offsets for the Balmer lines depend on cluster redshifts. However, the offsets indicate a slower evolution, and therefore higher formation redshift, than the zero point differences found from the FP, if interpreting the data using a passive evolution model. Specifically, the strength of the higher order Balmer lines Hδ and Hγ implies z form > 2.8. The scaling relations for the metal indices in general show small and in some cases insignificant zero point offsets, favoring high formation redshifts for a passive evolution model. Based on the absorption line indices and recent stellar population models from Thomas et al. we find that MS0451.6-0305 has a mean metallicity [M/H] approximately 0.2 dex below that of the other clusters and our low redshift sample. We confirm our previous result that RXJ0152.7-1357 has a mean abundance ratio [α/Fe] approximately 0.3 dex higher than that of the other clusters. The differences in [M/H] and [α/Fe] between the high-redshift clusters and the low redshift sample are inconsistent with a passive evolution scenario for early-type cluster galaxies over the redshift interval studied. Low-level star formation may be able to bring the metallicity of MS0451.6-0305 in agreement with the low redshift sample, while we speculate whether galaxy mergers can lead to sufficiently large changes in the abundance ratios for the RXJ0152.7-1357 galaxies to allow them to reach the low redshift sample values in the time available.

We have followed up on the results of a 65 square degree CFHT/MegaCam imaging survey of the nearby M81 Group searching for faint and ultra-faint dwarf galaxies. The original survey turned up 22 faint candidate dwarf members. Based on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as dwarf galaxy members of the group. Distances and stellar population characteristics are discussed for each. To a completeness limit of M r = −10, we find a galaxy luminosity function slope of −1.27 ± 0.04 for the M81 group. In this region, there are now 36 M81 group members known, including 4 blue compact dwarfs, 8 other late types including the interacting giants M81, NGC 3077, and M82, 19 early type dwarfs, and at least 5 potential tidal dwarf galaxies. We find that the dSph galaxies in M81 appear to lie in a flattened distribution, similar to that found for the Milky Way and M31. One of the newly discovered dSph galaxies has properties similar to the ultra-faint dwarfs being found in the Local Group with a size R e ∼ 100 pc and total magnitude estimates M r = −6.8 and M I ∼ −9.1.

An order of magnitude more dwarf galaxies are expected to inhabit the Local Group, based on currently accepted galaxy formation models, than have been observed. This discrepancy has been noted in environments ranging from the field to rich clusters. However, no complete census of dwarf galaxies exists in any environment. The discovery of the smallest and faintest dwarfs is hampered by the limitations in detecting such faint and low surface brightness galaxies. An even greater difficulty is establishing distances to or group/cluster membership for such faint galaxies. The M81 Group provides an almost unique opportunity for establishing membership for galaxies in a low density region complete to magnitudes as faint as M r = −10. With a distance modulus of 27.8, the tip of the red giant branch just resolves in ground-based surveys. We have surveyed a 65 square degree region around M81 with CFHT/MegaCam. From these images we have detected 22 new dwarf galaxy candidates. Photometric, morphological, and structural properties are presented for the candidates. The group luminosity function has a faint end slope characterized by the parameter α = −1.27 ± 0.06. We discuss implications of this dwarf galaxy population for cosmological models.

Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. Measuring these populations is difficult, but important for understanding the assembly of the most massive galaxies. The Coma cluster of galaxies is one of the nearest truly massive galaxy clusters, and is host to a correspondingly large system of globular clusters (GCs). We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs (IGCs) that fills the Coma cluster core and is not associated with individual galaxies. The GC surface density profile around the central massive elliptical galaxy, NGC 4874, is dominated at large radii by a population of IGCs that extend to the limit of our data (R < 520 kpc). We estimate that there are 47000 ± 1600 (random) +4000 −5000 (systematic) IGCs out to this radius, and that they make up ∼ 70% of the central GC system, making this the largest GC system in the nearby Universe. Even including the GC systems of other cluster galaxies, the IGCs still make up ∼ 30-45% of the GCs in the cluster core. Observational limits from previous studies of the intracluster light (ICL) suggest that the IGC population has a high specific frequency. If the IGC population has a specific frequency similar to high-S N dwarf galaxies, then the ICL has a mean surface brightness of µ V ≈ 27 mag arcsec −2 and a total stellar mass of roughly 10 12 M ⊙ within the cluster core. The ICL makes up approximately half of the stellar luminosity and one-third of the stellar mass of the central (NGC4874+ICL) system. The color distribution of the IGC population is bimodal, with blue, metal-poor GCs outnumbering red, metal-rich GCs by a ratio of 4:1. The inner GCs associated with NGC 4874 also have a bimodal distribution in color, but with a redder metal-poor population. The fraction of red IGCs (20%), and the red color of those GCs, implies that IGCs can originate from the halos of relatively massive, L * galaxies, and not solely from the disruption of dwarf galaxies.

We present the fundamental plane (FP) for 38 early-type galaxies in the two rich galaxy clusters RX J0152.7Ϫ1357 ( ) and RX J1226.9ϩ3332 ( ), reaching a limiting magnitude of in z p 0.83 z p 0.89 M p Ϫ19.8B the rest frame of the clusters. While the zero-point offset of the FP for these high-redshift clusters relative to our low-redshift sample is consistent with passive evolution with a formation redshift of , the FP for z ≈ 3.2 form the high-redshift clusters is not only shifted as expected for a mass-independent but rotated relative to the z form low-redshift sample. Expressed as a relation between the galaxy masses and the mass-to-light ratios, the FP is significantly steeper for the high-redshift clusters than for our low-redshift sample. We interpret this as a mass dependency of the star formation history, as has been suggested by other recent studies. The low-mass galaxies ( ) have experienced star formation as recently as (1.5 Gyr prior to their look-back time), while 10.3 10 M z ≈ 1.35, galaxies with masses larger than had their last major star formation episode at .11.310 M z 1 4.5 , Subject headings: galaxies: clusters: individual (RX J0152.7Ϫ1357, RX J1226.9ϩ3332) -galaxies: evolution -galaxies: stellar contentThe fundamental plane (FP) for elliptical (E) and lenticular (S0) galaxies is a key scaling relation, which relates the effective radii, the mean surface brightnesses, and the velocity dispersions in a relation that is linear in logarithmic space (e.g., Dressler et al. 1987;Djorgovski & Davis 1987;Jørgensen et al. 1996. The FP can be interpreted as a relation between the galaxy masses and their mass-to-light ratios ( ). For low-redshift cluster galaxies, the FP has very M/L low internal scatter (e.g., JFK1996). It is therefore a powerful tool for studying the evolution of the as a function of M/L redshift (e.g., Jørgensen et al. 1999;Kelson et al. 2000;van de Ven et al. 2003;Gebhardt et al. 2003;Wuyts et al. 2004;Treu et al. 2005;Ziegler et al. 2005). These authors all find that the FP at is consistent with the passive evoz p 0.2-1.0 lution of the stellar populations of the galaxies, generally with a formation redshift . Most previous studies of the FP z 1 2 form at cover fairly small samples of galaxies in each z p 0.2-1.0 cluster and are limited to a narrow range in luminosities, and therefore masses, making it very difficult to detect possible differences in the FP slope. A few recent studies indicated a steepening of the FP slope for galaxies (di Serego Ali- little for the two choices of profiles. In the following we use the parameters from -fits for consistency with our low-red-1/4 r shift comparison data. None of the main conclusions of this Letter would change had we chosen to use the Sérsic fits. Masses of the galaxies are derived as .Our Coma Cluster sample serves as the low-redshift reference sample (Jørgensen 1999). We have obtained new B-band photometry of this sample with the McDonald Observatory 0.8 m telescope and the Primary Focus Camera (Claver 1995). The data were r...