Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDynamical Models of Elliptical Galaxies in z=0.5 Clusters: II. Mass-to-Light Ratio Evolution without Fundamental Plane Assumptions
65
0
0.0
(
0
)
Added by
Roeland van der Marel
Publication date
2006
fields
Physics
and research's language is
English
Authors
Roeland P. van der Marel
Ask ChatGPT about the research
No Arabic abstract
We study M/L evolution of early-type galaxies using dynamical modeling of resolved internal kinematics. This makes fewer assumptions than Fundamental Plane (FP) studies and provides a powerful new approach for studying galaxy evolution. We focus on the sample of 25 galaxies in clusters at z=0.5 modeled in Paper I. For comparison we compile and homogenize M/L literature data for 60 nearby galaxies that were modeled in comparable detail. The nearby sample obeys log(M/L)_B = Z + S log(sigma_eff/[200 km/s]), with Z = 0.896 +/- 0.010, S = 0.992 +/- 0.054, and sigma_eff the effective velocity dispersion. The z=0.5 sample follows a similar relation but with lower zeropoint. The implied M/L evolution is Delta log(M/L) / Delta z = -0.457 +/- 0.046(random) +/- 0.078(systematic), consistent with passive evolution following high-redshift formation. This agrees with the FP results for this sample by van Dokkum & van der Marel. This confirms that FP evolution tracks M/L evolution, which is an important verification of the assumptions that underly FP studies. However, while we find more FP evolution for galaxies of low sigma_eff (or low mass), the dynamical M/L evolution instead shows little trend with sigma_eff. We argue that this difference can be plausibly attributed to a combination of two effects: (a) evolution in structural galaxy properties other than M/L; and (b) the neglect of rotational support in studies of FP evolution. The results leave the question open whether the low-mass galaxies in the sample have younger population ages than the high-mass galaxies. This highlights the general importance in the study of population ages for complementing dynamical measurements with broad-band colors or spectroscopic population diagnostics.
rate research
Read More
We present spatially resolved stellar rotation velocity and velocity dispersion profiles form Keck/LRIS absorption-line spectra for 25 galaxies, mostly visually classified ellipticals, in three clusters at z=0.5. We interpret the kinematical data and HST photometry using oblate axisymmetric two-integral f(E,Lz) dynamical models based on the Jeans equations. This yields good fits, provided that the seeing and observational characteristics are carefully modeled. The fits yield for each galaxy the dynamical M/L and a measure of the galaxy rotation rate. Paper II addresses the implied M/L evolution. Here we study the rotation-rate evolution by comparison to a sample of local elliptical galaxies of similar present-day luminosity. The brightest galaxies in the sample all rotate too slowly to account for their flattening, as is also observed at z=0. But the average rotation rate is higher at z=0.5 than locally. This may be due to a higher fraction of misclassified S0 galaxies (although this effect is insufficient to explain the observed strong evolution of the cluster S0 fraction with redshift). Alternatively, dry mergers between early-type galaxies may have decreased the average rotation rate over time. It is unclear whether such mergers are numerous enough in clusters to explain the observed trend quantitatively. Disk-disk mergers may affect the comparison through the so-called progenitor bias, but this cannot explain the direction of the observed rotation-rate evolution. Additional samples are needed to constrain possible environmental dependencies and cosmic variance in galaxy rotation rates. Either way, studies of the internal stellar dynamics of distant galaxies provide a valuable new approach for exploring galaxy evolution.
In this paper, we present an analysis of the dynamics and segregation of galaxies in rich clusters from z~0.32 to z~0.48 taken from the CFHT Optical PDCS (COP) survey and from the CNOC survey (Carlberg et al. 1997). Our results from the COP survey are based upon the recent observational work of Adami et al. (2000) and Holden et al. (2000) and use new spectroscopic and photometric data on six clusters selected from the Palomar Distant Cluster Survey (PDCS; Postman et al. 1996). We have compared the COP and CNOC samples to the ESO Nearby Abell Cluster Survey (ENACS: z~0.07). Our sample shows that the z<0.4 clusters have the same velocity dispersion versus magnitude, morphological type and radius relationships as nearby Abell clusters. The z~0.48 clusters exhibit, however, departures from these relations. Furthermore, there appears to be a higher fraction of late-type (or bluer, e.g. Butcher and Oemler, 1984) galaxies in the distant clusters compared to the nearby ones. The classical scenario in which massive galaxies virialize before they evolve from late into early type explain our observations. In such a scenario, the clusters of our sample began to form before a redshift of ~0.8 and the late-type galaxy population had a continuous infall into the clusters.
We present a study focusing on the nature of compact groups through the study of their elliptical galaxies. We determine velocity dispersions ($sigma$) for 18 18 bright elliptical galaxies located in the core of Hickson compact groups and a control sample of 12 bright bona fide ellipticals located in the field or very loose groups. Several tests are carried out to avoid sources of systematic effects in $sigma$ measurements. We use these velocity dispersions to compare the position of 11 compact group galaxies in the Fundamental Plane to that of a large and homogeneous sample of elliptical galaxies (Burstein et al. 1987). We find that little or no significant difference exists, as far as the Fundamental Plane is concerned, between ellipticals in compact groups and their counterparts in other environments.
We present spectroscopic observations obtained at the {it Large Binocular Telescope} in the field of the cluster XLSSJ0223-0436 at $z=1.22$. We confirm 12 spheroids cluster members and determine stellar velocity dispersion for 7 of them. We combine these data with those in the literature for clusters RXJ0848+4453 at $z=1.27$ (8 galaxies) and XMMJ2235-2557 at $z=1.39$ (7 galaxies) to determine the Fundamental Plane of cluster spheroids. We find that the FP at $zsim1.3$ is offset and { rotated ($sim3sigma$)} with respect to the local FP. The offset corresponds to a mean evolution $Delta$rm{log}(M$_{dyn}$/L$_B$)=(-0.5$pm$0.1)$z$. High-redshift galaxies follow a steeper mass-dependent M$_{dyn}$/L$_B$-M$_{dyn}$ relation than local ones. Assuming $Delta$ log$(M_{dyn}/L_B)$=$Delta$ log$(M^*/L_B)$, higher-mass galaxies (log(M$_{dyn}$/M$_odot$)$geq$11.5) have a higher-formation redshift ($z_fgeq$6.5) than lower-mass ones ($z_fleq$2 for log(M$_{dyn}$/M$_odot$$leq$10)), with a median $z_fsimeq2.5$ for the whole sample. Also, galaxies with higher stellar mass density host stellar populations formed earlier than those in lower density galaxies. At fixed IMF, M$_{dyn}$/M$^*$ varies systematically with mass and mass density. It follows that the evolution of the stellar populations (M$^*/L_B$) accounts for the observed evolution of M$_{dyn}/L_B$ for M$_{dyn}$$>10^{11}$ M$_odot$ galaxies, while accounts for $sim$85% of the evolution at M$_{dyn}$$<10^{11}$ M$_odot$. We find no evidence in favour of structural evolution of individual galaxies, while we find evidences that spheroids later added to the population account for the observed discrepancy at masses $<10^{11}$ M$_odot$. [Abridged]
We present preliminary results of an extensive study of the fundamental properties of dwarf elliptical galaxies (dEs) in the Coma cluster. Our study will combine HST surface photometry with ground-based UBRIJK photometry and optical spectroscopy. The combined data set will be used to investigate the intrinsic correlations among global parameters in cluster dEs, including the Fundamental Plane, the color-magnitude relation, the Faber-Jackson and Kormendy relation, and velocity dispersion versus line strength indices. These empirical correlations have provided important constraints to theoretical models of galaxy formation and evolution for normal elliptical galaxies. Although dEs are the most abundant galaxy population in clusters their properties remain, however, largely unknown. Our study aims to provide an essential reference for testing current theories on the formation and evolution of dEs in clusters, and understanding their relation to more massive elliptical galaxies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
