arXiv subjects

A. Cavaliere

Publications and source records attributed to A. Cavaliere.

58 records · Page 4Linked to original sources

arXiv1997

The Luminosity-Temperature Relation for Groups and Clusters of Galaxies

We model the effects of shocks on the diffuse, X-ray emitting baryons in clusters of galaxies. Shocks separate the infalling from the inner gas nearly at equilibrium, and dominate the compression and the density gradients of the latter in the dark-matter potential of the cluster. We find that, independently of the detailed shape of the potential, the density gradient is steeper and the compression factor larger for the richer clusters. We show, considering the different merging histories, that in the hierarchical cosmogony the above effects lead, in X-rays, to a luminosity-temperature relation L \propto T^5 at the scale of groups which flattens down to L \propto T^{3} for rich clusters in accord with the observations, and then saturates toward L \propto T^2 for higher temperatures. From the merging histories we also compute statistical fluctuations of the L-T correlation.

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arXiv1996

Faint Blue Galaxies and Merging: the Evolution of the Luminosity Function

We probe to what extent not only the counts of the faint blue galaxies and their redshift distribution but also their z-resolved luminosity functions can be explained in terms of binary merging (aggregations). We present a dynamical theory of such interactions. On this basis we find that ``minimal aggregations'' taking place within large scale structures and triggering starbusts yield rates and timing such as to explain the observations of the local, flat luminosity function and of its progressive rising and steepening for redshifts out to $z\approx 1$. Correspondingly, we predictfaint blue counts still rising up to $m_B\sim 28 -29$, redshift distributions shifting toward larger z with increasing $m_B$; in addition, we predict an upturn of the faint end of the luminosity function more pronounced in clusters than in the field. We propose that our picture provides the differential dynamics missing in the canonical hierarchical theories. This reconciles with the observations the steep luminosity functions predicted at high z by such theories.

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arXiv1996

Small groups of Galaxies as Cosmological Clocks

We study the formation and evolution of small groups of galaxies using new Monte Carlo simulations. These are directly based on the random walk approach to the statistics of condensations collapsing by gravitational instability, and the results are consistent with the Press and Schechter formula. We stress how observational features of groups, such as galaxy membership, depend on the global dynamics of the Universe. This is because the amount of aggregations between infalling galaxies is governed by the ratio of the group age to the time scale for dynamical friction. This ratio strongly depends on cosmology. Thus in low-density models, even if flat, collapse of group sized perturbations followed by fast mergers, would often originate a single massive remnant. This is contrast to observed associations as compact groups of galaxies.

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arXiv1994

The Cosmological Mass Distribution from Cayley Trees with Disorder

We present a new approach to the statistics of the cosmic density field and to the mass distribution of high-contrast structures, based on the formalism of Cayley trees. Our approach includes in one random process both fluctuations and interactions of the density perturbations. We connect tree-related quantities, like the partition function or its generating function, to the mass distribution. The Press \& Schechter mass function and the Smoluchowski kinetic equation are naturally recovered as two limiting cases corresponding to independent Gaussian fluctuations, and to aggregation of high-contrast condensations, respectively. Numerical realizations of the complete random process on the tree yield an excess of large-mass objects relative to the Press \& Schechter function. When interactions are fully effective, a power-law distribution with logarithmic slope -2 is generated.

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