283 research outputs found
The Local Galaxy Density and the Arm Class of Spiral Galaxies
We have examined the effect of the environmental density on the arm
classification of an extensive sample of spiral galaxies included in the Nearby
Galaxy Catalog (Tully, 1988a). We have also explored the dependence of the arm
class of a galaxy on other factors, such as its blue absolute magnitude and its
disk-to-total mass ratio, inferred in the literature either from the gradient
of a good galaxy rotation curve or from a photometric mass decomposition
method. We have found that the arm class is strongly related to the absolute
magnitude in the mid-type spirals (in the sense that grand design galaxies are,
on average, more luminous than flocculent objects), whilst this relation is
considerably weaker in the early and late types. In general the influence of
the local density on the arm structure appears to be much weaker than that of
the absolute magnitude. The local density acts essentially in strengthening the
arm class--absolute magnitude relation for the mid types, whereas no
environmental density effects are observed in the early and late types. Using
the most recent estimates of the disk-to-total mass ratio, we do not confirm
this ratio to be a significant factor which affects the arm class;
nevertheless, owing to poor statistics and large uncertanties, the issue
remains open. Neither a local density effect nor an unambiguous bar effect on
the disk-to-total mass ratio is detectable; the latter finding may challenge
some theoretical viewpoints on the formation of bar structures.Comment: 15 pages, Latex, SISSA 102/93/A openbib.sty and 4 POSTSCRIPT figures
appende
The Mass Function of Nearby Galaxy Clusters
We present the distribution of virial masses for nearby galaxy clusters, as
obtained from a data-set of 75 clusters, each having at least 20 galaxy members
with measured redshifts within 1 Abell radius. After having accounted for
problems of incompleteness of the data-set, we fitted a power-law to the
cluster mass distribution.Comment: 10 pages (2 figures not included, available upon request), LATEX,
Ref.SISSA 54/93/
Groups of galaxies in the local supercluster: some hypotheses on the evolutionary stage
Journal ArticleWe present a method capable of determining the evolutionary stage of bound, isolated systems of galaxies. In particular, we apply it to a sample of groups, belonging to the Local Supercluster, taken from the Geller and Huchra's (1983) catalogue. We find that most of them are still in the phase of collapse and not yet virialized. Their evolutionary stages are distributed around that of the Virgo cluster, which lies in a central position in the region considered. Moreover, the knowledge of the evolutionary stage of a system permits the determination of its mass even when it is not in virial equilibrium. The median M/L ratio of the groups in our sample proves to be in the range (550-700) hMo/L0(B) (H0 =/h1OO kms -1 Mpc-1)
Structures in Galaxy Clusters
The analysis of the presence of substructures in 16 well-sampled clusters of
galaxies suggests a stimulating hypothesis: Clusters could be classified as
unimodal or bimodal, on the basis of to the sub-clump distribution in the {\em
3-D} space of positions and velocities. The dynamic study of these clusters
shows that their fundamental characteristics, in particular the virial masses,
are not severely biased by the presence of subclustering if the system
considered is bound.Comment: (16 pages in LATEX, 4 tables in LATEX are at the end of the file, the
figures not included are available upon request), REF SISSA 158/93/
Study od a Slice at +9 to +15 degrees of Declination: I. The Neutral Hydrogen Content of Galaxies in Loose Groups
We examine the H1 content of spiral galaxies in groups by using a catalog of
loose groups of galaxies identified in a magnitude limited sample m < 15.7
spanning the range 8 h to 18 h in right ascension and +9 to +15 in declination.
The redshift completeness of the galaxy sample is ~95%. No significant effect
of H1 depletion is found, although there may be a hint that the earliest type
spirals are slightly deficient.Comment: 10 pages, Latex, 3 tables, 5 figures, to appear in the Astronomical
Journa
- …