Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Relation between Morphology and Dynamics of Poor Groups of Galaxies
480
0
0.0
(
0
)
Added by
Manolis Plionis Dr.
Publication date
2009
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We investigate the relation between the projected morphology (b/a) and the velocity dispersion (sigma_v) of groups of galaxies using two recently compiled group catalogs, one based on the 2MASS redshift survey and the other on the SDSS Data Release 5 galaxy catalog. We find that the sigma_v of groups is strongly correlated with the group projected b/a and size, with elongated and larger groups having a lower sigma_v. Such a correlation could be attributed to the dynamical evolution of groups, with groups in the initial stages of formation, having small sigma_v, a large size and an elongated shape that reflects the anisotropic accretion of galaxies along filamentary structures. The same sort of correlations, however, could also be reproduced in prolate-like groups, if the net galaxy motion is preferentially along the group elongation, since then the groups oriented close to the line of sight will appear more spherical, will have a small projected size and large sigma_v, while groups oriented close to the sky-plane will appear larger in projection, more elongated, and will have smaller sigma_v. We perform tests that relate only to the dynamical evolution of groups (eg., calculating the fraction of early type galaxies in groups) and indeed we find a strong positive (negative) correlation between the group sigma_v (projected major axis) with the fraction of early type galaxies. We conclude that (a) the observed dependencies of the group sigma_v on the group projected size and b/a, should be attributed mostly to the dynamical state of groups and (b) groups in the local universe do not constitute a family of objects in dynamical equilibrium, but rather a family of cosmic structures that are presently at various stages of their virialization process.
rate research
Read More
We confirm the detection of 3 groups in the Lynx supercluster, at z~1.3, and give their redshifts and masses. We study the properties of the group galaxies as compared to the central clusters, RXJ0849+4452 and RXJ0848+4453, selecting 89 galaxies in the clusters and 74 galaxies in the groups. We morphologically classify galaxies by visual inspection, noting that our early-type galaxy (ETG) sample would have been contaminated at the 30% -40% level by simple automated classification methods (e.g. based on Sersic index). In luminosity selected samples, both clusters and groups show high fractions of Sa galaxies. The ETG fractions never rise above ~50% in the clusters, which is low compared to the fractions observed in clusters at z~1. However, ETG plus Sa fractions are similar to those observed for ETGs in clusters at z~1. Bulge-dominated galaxies visually classified as Sas might also be ETGs with tidal features or merger remnants. They are mainly red and passive, and span a large range in luminosity. Their star formation seems to have been quenched before experiencing a morphological transformation. Because their fraction is smaller at lower redshifts, they might be the spiral population that evolves into ETGs. For mass-selected samples, the ETG fraction show no significant evolution with respect to local clusters, suggesting that morphological transformations occur at lower masses and densities. The ETG mass-size relation shows evolution towards smaller sizes at higher redshift in both clusters and groups, while the late-type mass-size relation matches that observed locally. The group ETG red sequence shows lower zero points and larger scatters than in clusters, both expected to be an indication of a younger galaxy population. The estimated age difference is small when compared to the difference in age at different galaxy masses.
We apply a stellar population synthesis code to the spectra of a large sample of SDSS galaxies to classify these according to their activity (using emission-line diagnostic diagrams), environment (using catalogues of isolated and cluster galaxies), and using parameters that correlate with their morphology.
We derive the stellar-to-halo mass relation (SHMR), namely $f_starpropto M_star/M_{rm h}$ versus $M_star$ and $M_{rm h}$, for early-type galaxies from their near-IR luminosities (for $M_star$) and the position-velocity distributions of their globular cluster systems (for $M_{rm h}$). Our individual estimates of $M_{rm h}$ are based on fitting a dynamical model with a distribution function expressed in terms of action-angle variables and imposing a prior on $M_{rm h}$ from the concentration-mass relation in the standard $Lambda$CDM cosmology. We find that the SHMR for early-type galaxies declines with mass beyond a peak at $M_starsim 5times 10^{10}M_odot$ and $M_{rm h}sim 10^{12}M_odot$ (near the mass of the Milky Way). This result is consistent with the standard SHMR derived by abundance matching for the general population of galaxies, and with previous, less robust derivations of the SHMR for early types. However, it contrasts sharply with the monotonically rising SHMR for late types derived from extended HI rotation curves and the same $Lambda$CDM prior on $M_{rm h}$ as we adopt for early types. The SHMR for massive galaxies varies more or less continuously, from rising to falling, with decreasing disc fraction and decreasing Hubble type. We also show that the different SHMRs for late and early types are consistent with the similar scaling relations between their stellar velocities and masses (Tully-Fisher and Faber-Jackson relations). Differences in the relations between the stellar and halo virial velocities account for the similarity of the scaling relations. We argue that all these empirical findings are natural consequences of a picture in which galactic discs are built mainly by smooth and gradual inflow, regulated by feedback from young stars, while galactic spheroids are built by a cooperation between merging, black-hole fuelling, and feedback from AGNs.
Satellite galaxies in rich clusters are subject to numerous physical processes that can significantly influence their evolution. However, the typical L* satellite galaxy resides in much lower mass galaxy groups, where the processes capable of altering their evolution are generally weaker and have had less time to operate. To investigate the extent to which satellite and central galaxy evolution differs, we separately model the stellar mass - halo mass (M* -Mh) relation for these two populations over the redshift interval 0 < z < 1. This relation for central galaxies is constrained by the galaxy stellar mass function while the relation for satellite galaxies is constrained against recent measurements of the galaxy two-point correlation function (2PCF). At z ~ 0 the satellites, on average, have ~10% larger stellar masses at fixed peak subhalo mass compared to central galaxies of the same halo mass. This is required in order to reproduce the observed stellar mass-dependent 2PCF and satellite fractions. At low masses our model slightly under-predicts the correlation function at ~1 Mpc scales. At z ~ 1 the satellite and central galaxy M*-Mh relations are consistent within the errors, and the model provides an excellent fit to the clustering data. At present, the errors on the clustering data at z ~ 2 are too large to constrain the satellite model. A simple model in which satellite and central galaxies share the same M*-Mh relation is able to reproduce the extant z ~ 2 clustering data. We speculate that the striking similarity between the satellite and central galaxy M*-Mh relations since z ~ 2 arises because the central galaxy relation evolves very weakly with time and because the stellar mass of the typical satellite galaxy has not changed significantly since it was accreted. [Abridged]
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
