20,855 research outputs found
Properties of Very Luminous Galaxies
Recent analysis of the SSRS2 data based on cell-counts and two-point
correlation function has shown that very luminous galaxies are much more
strongly clustered than fainter galaxies. In fact, the amplitude of the
correlation function of very luminous galaxies () asymptotically
approaches that of clusters. In this paper we investigate the
properties of the most luminous galaxies, with blue absolute magnitude . We find that: 1) the population mix is comparable to that in other ranges
of absolute magnitudes; 2) only a small fraction are located in bona fide
clusters; 3) the bright galaxy-cluster cross-correlation function is
significantly higher on large scales than that measured for fainter galaxies;
4) the correlation length of galaxies brighter than \MB ,
expressed as a function of the mean interparticle distance, appears to follow
the universal dimensionless correlation function found for clusters and radio
galaxies; 5) a large fraction of the bright galaxies are in interacting pairs,
others show evidence for tidal distortions, while some appear to be surrounded
by faint satellite galaxies. We conclude that very luminous optical galaxies
differ from the normal population of galaxies both in the clustering and other
respects. We speculate that this population is highly biased tracers of mass,
being associated to dark halos with masses more comparable to clusters than
typical loose groups.Comment: 29 pages (6 figures) + 2 tables; paper with all figures and images
available at http://boas5.bo.astro.it/~cappi/papers.html; The Astronomical
Journal, in pres
Labels for non-individuals
Quasi-set theory is a first order theory without identity, which allows us to
cope with non-individuals in a sense. A weaker equivalence relation called
``indistinguishability'' is an extension of identity in the sense that if
is identical to then and are indistinguishable, although the
reciprocal is not always valid. The interesting point is that quasi-set theory
provides us a useful mathematical background for dealing with collections of
indistinguishable elementary quantum particles. In the present paper, however,
we show that even in quasi-set theory it is possible to label objects that are
considered as non-individuals. We intend to prove that individuality has
nothing to do with any labelling process at all, as suggested by some authors.
We discuss the physical interpretation of our results.Comment: 11 pages, no figure
The Power Spectrum of Galaxies in the Nearby Universe
We compute the power spectrum of galaxy density fluctuations in a recently
completed redshift survey of optically-selected galaxies in the southern
hemisphere (SSRS2). The amplitude and shape of the SSRS2 power spectrum are
consistent with results of the Center for Astrophysics redshift survey of the
northern hemisphere (CfA2), including the abrupt change of slope on a scale of
30-50Mpc/h; these results are reproducible for independent volumes of space and
variations are consistent with the errors estimated from mock surveys. Taken
together, the SSRS2 and CfA2 form a complete sample of 14,383 galaxies which
covers one-third of the sky. The power spectrum of this larger sample continues
to rise on scales up to ~ 200Mpc/h, with weak evidence for flattening on the
largest scales. The SSRS2+CfA2 power spectrum and the power spectrum
constraints implied by COBE are well-matched by an Omega*h ~ 0.2,
Omega+lambda_0=1 CDM model with minimal biasing of optically-selected galaxies.Comment: Accepted for publication in The Astrophysical Journal Letters, Sept.
23, 1994. 10 pages uuencoded compressed postscript, including two figures.
JHU-9410200
- …