Gary A. Mamon

The Structure of Compact Groups of Galaxies

Compact groups are small close isolated associations of galaxies, High space densities (≤104/Mpc3) and short crossing times (~0.1 H−1) make them particularly susceptible to dynamical evolution. Several well known groups contain galaxies with very discrepant redshifts, casting doubt upon the physical reality of compact groups in general or on the cosmological redshift hypothesis. The small population of these groups, typically less than ten galaxies, makes the interpretation of the structure and dynamics of an individual group difficult at best. It is often more informative to investigate the statistical properties of a homogeneous sample of groups. Galaxies in such groups are generally too faint to appear in standard galaxy catalogs, however, so they cannot be found by automated techniques used to study loose groups (Turner and Gott, 1976, Geller, this volume). For this reason a survey was undertaken of the Palomar Observatory Sky Survey (POSS) prints for groups satisfying three selection criteria of population, isolation, and mean surface brightness. The resulting catalog of 100 groups (Hickson, 1982) forms our study sample.

AGN feedback in dwarf galaxies

Dwarf galaxy anomalies, such as their abundance and cusp-core problems, remain a prime challenge in our understanding of galaxy formation. The inclusion of baryonic physics could potentially solve these issues, but the efficiency of stellar feedback is still controversial. We analytically explore the possibility of feedback from Active Galactic Nuclei (AGN) in dwarf galaxies and compare AGN and supernova (SN) feedback. We assume the presence of an intermediate mass black hole within low mass galaxies and standard scaling relations between the relevant physical quantities. We model the propagation and properties of the outflow and explore the critical condition for global gas ejection. Performing the same calculation for SNe, we compare the ability of AGN and SNe to drive gas out of galaxies. We find that a critical halo mass exists below which AGN feedback can remove gas from the host halo and that the critical halo mass for AGN is greater than the equivalent for SNe in a significant part of the parameter space, suggesting that AGN could provide an alternative and more successful source of negative feedback than SNe, even in the most massive dwarf galaxies.

A finer view of the conditional galaxy luminosity function and magnitude-gap statistics

The gap between first and second ranked galaxy magnitudes in groups is often considered a tracer of their merger histories, which in turn may affect galaxy properties, and also serves to test galaxy luminosity functions (LFs). We remeasure the conditional luminosity function (CLF) of the Main Galaxy Sample of the SDSS in an appropriately cleaned subsample of groups from the Yang catalog. We find that, at low group masses, our best-fit CLF have steeper satellite high ends, yet higher ratios of characteristic satellite to central luminosities in comparison with the CLF of Yang et al. (2008). The observed fractions of groups with large and small magnitude gaps as well as the Tremaine & Richstone (1977) statistics, are not compatible with either a single Schechter LF or with a Schechter-like satellite plus lognormal central LF. These gap statistics, which naturally depend on the size of the subsamples, and also on the maximum projected radius,

Kinematic Modelling of NGC 3379

R_{rm max}

M/L and velocity anisotropy from observations of spherical galaxies, or must M87 have a massive black hole?

, for defining the 2nd brightest galaxy, can only be reproduced with two-component CLFs if we allow small gap groups to preferentially have two central galaxies, as expected when groups merge. Finally, we find that the trend of higher gap for higher group velocity dispersion,

Optimization of source extraction & galaxy luminosity function of the cluster of galaxies Abell 85

sigma_{rm v}

Erratum: Anisotropic q-Gaussian 3D velocity distributions in ΛCDM haloes

, at given richness, discovered by Hearin et al. (2013), is strongly reduced when we consider

How well does the Friends-of-Friends algorithm recover group properties from distance- and luminosity-limited galaxy catalogs?

sigma_{rm v}

Anisotropic q-Gaussian 3D velocity distributions inCDM halos

in bins of richness, and virtually disappears when we use group mass instead of

6dF galaxy survey final redshift release (6dFGS) (Jones+, 2009)

sigma_{rm v}