Volume 652, number 1: Close Galaxy Counts as a Probe of Hierarchical Structure Formation
16th Nov 2006, 17:54 GMT
The standard ΛCDM model predicts that the major merger rate of galaxy-size dark matter halos rises rapidly with redshift. The average number of close companions per galaxy, N c , is often used to infer the galaxy merger rate; however, recent observational studies suggest that N c evolves very little with redshift. Here we use a “hybrid” N-body simulation plus analytic substructure model to predict N c directly. We identify dark matter subhalos with galaxies and show that the observed lack of close-pair count evolution arises because the high merger rate per halo at early times is counteracted by a decrease in the number of halos massive enough to host a galaxy pair. We compare our results to data compiled from the DEEP2, SSRS2, and UZC redshift surveys. Observed pair counts match our predictions if we assume a monotonic mapping between galaxy luminosity and the maximum circular velocity that each subhalo had when it was first accreted onto its host halo. This suggests that satellite galaxies are significantly more resilient to mass loss than are dissipationless dark matter subhalos. We argue that while N c does not provide a direct measure of the halo merger rate, it offers a powerful means to constrain both the halo occupation distribution and the spatial distribution of galaxies within halos. Interpreted in this way, close-pair counts provide a useful test of galaxy formation processes on ∼10–100 kpc scales.
Latest news from ApJ Latest Issue:
- Volume 652, number 1: The Oxygen Abundance Calibrations and N/O Abundance Ratios of ~40,000 SDSS Star-forming Galaxies
- Volume 652, number 1: The Hard X-Ray 20-40 keV AGN Luminosity Function
- Volume 652, number 1: Smoothing Algorithms and High-Order Singularities in Gravitational Lensing
- Volume 652, number 1: Mass Determination and Detection of the Onset of Chromospheric Activity for the Substellar Object in EF Eridani
- Volume 652, number 1: X-Ray Absorption and an X-Ray Jet in the Radio-loud Broad Absorption-line Quasar PG 1004+130
- Volume 652, number 1: From Galaxy-Galaxy Lensing to Cosmological Parameters
- Volume 652, number 1: A Physical Model for Active Galactic Nuclei with Double-peaked Broad Emission Lines
- Volume 652, number 1: On the Migration of Protogiant Solid Cores
- Volume 652, number 1: Spitzer Observations of the Orion OB1 Association: Second-Generation Dust Disks at 5-10 Myr
- Volume 652, number 1: Helium-rich Thermonuclear Bursts and the Distance to the Accretion-powered Millisecond Pulsar SAX J1808.4-3658