Galaxy Pairwise Velocity Distributions on Nonlinear Scales

Abstract

view Abstract Citations (43) References (66) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galaxy Pairwise Velocity Distributions on Nonlinear Scales Diaferio, Antonaldo ; Geller, Margaret J. Abstract The redshift-space correlation function ξ_s_ for projected galaxy separations <~ 1 h^-1^ Mpc can be expressed as the convolution of the real-space correlation function with the galaxy pairwise velocity distribution function (PVDF). An exponential PVDF yields the best fit to the ξ_s_ measured from galaxy samples of different redshift surveys. We show that this exponential PVDF is not merely a fitting function but arises from well-defined gravitational processes. Two ingredients conspire to yield a PVDF with a nearly exponential shape: (1) the number density n(σ) of systems with velocity dispersion σ and (2) the unrelaxed dynamical state of most galaxy systems. The former ingredient determines the exponential tail, and the latter determines the central peak of the PVDF. We examine a third issue: the transfer of orbital kinetic energy to galaxy internal degrees of freedom. Although this effect is of secondary importance for the PVDF exponential shape, it is detectable in galaxy groups, which indicates that galaxy merging is an ongoing process in the present universe. We compare the ξ_s_ measured on nonlinear scales from galaxy samples of the Center for Astrophysics redshift surveys with different models of the PVDF convolved with the measured real-space correlation function. This preliminary comparison indicates that the agreement between model and observations depends strongly on both the underlying cosmological model and the internal dynamics of galaxy systems. Neither parameter dominates. Moreover, the agreement depends sensitively on the accuracy of the galaxy position and velocity measurements. We expect that ξ_s_ will pose further constraints on the model of the universe and will improve the knowledge of the dynamics of galaxy systems on very small scales if we improve (1) the galaxy coordinate determination and (2) the measurement of relative velocities of galaxies with small projected separation. In fact, the redshift-space correlation function ξ_s_ depends sensitively on the internal pairwise velocity distribution of individual galaxy systems for projected pair separations <~ 0.5 h^-1^ Mpc and relative velocities π <~ 300 km s^-1^. Publication: The Astrophysical Journal Pub Date: August 1996 DOI: 10.1086/177582 arXiv: arXiv:astro-ph/9602086 Bibcode: 1996ApJ...467...19D Keywords: COSMOLOGY: THEORY; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: INTERACTIONS; GALAXIES: KINEMATICS AND DYNAMICS; Astrophysics E-Print: 28 pages, TeX, to appear in The Astrophysical Journal full text sources arXiv | ADS | data products NED (1)