3 research outputs found
THE LOCAL GALAXY DENSITY AND THE BULGE-TO-DISK RATIO OF DISK GALAXIES
Relying on samples of disk galaxies for which a detailed photometric
bulge/disk decomposition has been provided in the literature, we examine the
dependence of the bulge-to-disk luminosity ratio (B/D) on the blue absolute
luminosity and on the environmental density. In our statistical analysis of
various B/D data sets we pay particular attention to disentangling the role
played by the galaxy morphology--galaxy density relation. Besides, we focus our
attention on nearby () galaxies, for which we can provide a
three-dimensional characterization of the local galaxy density. We find that
the observed tendency of galaxies to have greater B/D with increasing galaxy
density simply reflects the average decline of B/D towards later morphological
types together with the morphology--density relation. This relation tends to
give rise also to a greater proportion of bright bulges in denser regions,
because the decrease of B/D towards later types is mostly due to a dimming of
the bulge rather than to a brightening of the disk. But when we remove the
effect induced by the morphology--density relation, we detect no clear evidence
of a dependence of B/D on galaxy density. Furthermore, B/D turns out to be
substantially unrelated to the blue absolute magnitude of the galaxy. We
briefly discuss to what extent our results (partially) disagree with previous
claims.Comment: LATEX file, 19 pages, figures available on reques
Observational Mass-to-Light Ratio of Galaxy Systems: from Poor Groups to Rich Clusters
We study the mass-to-light ratio of galaxy systems from poor groups to rich
clusters, and present for the first time a large database for useful
comparisons with theoretical predictions. We extend a previous work, where B_j
band luminosities and optical virial masses were analyzed for a sample of 89
clusters. Here we also consider a sample of 52 more clusters, 36 poor clusters,
7 rich groups, and two catalogs, of about 500 groups each, recently identified
in the Nearby Optical Galaxy sample by using two different algorithms. We
obtain the blue luminosity and virial mass for all systems considered. We
devote a large effort to establishing the homogeneity of the resulting values,
as well as to considering comparable physical regions, i.e. those included
within the virial radius. By analyzing a fiducial, combined sample of 294
systems we find that the mass increases faster than the luminosity: the linear
fit gives M\propto L_B^{1.34 \pm 0.03}, with a tendency for a steeper increase
in the low--mass range. In agreement with the previous work, our present
results are superior owing to the much higher statistical significance and the
wider dynamical range covered (about 10^{12}-10^{15} M_solar). We present a
comparison between our results and the theoretical predictions on the relation
between M/L_B and halo mass, obtained by combining cosmological numerical
simulations and semianalytic modeling of galaxy formation.Comment: 25 pages, 12 eps figures, accepted for publication in Ap
The local galaxy density and the bulge-to-disk ratio of disk galaxies
Consiglio Nazionale delle Ricerche (CNR). Biblioteca Centrale / CNR - Consiglio Nazionale delle RichercheSIGLEITItal