THE PAIR FRACTION OF MASSIVE GALAXIES AT 0 {<=} z {<=} 3
- Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen (Denmark)
- Max-Planck-Institut fuer Extraterrestrische Physik, Garching bei Muenchen (Germany)
Using a mass-selected (M{sub *} {>=} 10{sup 11} M{sub Sun }) sample of 198 galaxies at 0 {<=} z {<=} 3.0 with Hubble Space Telescope/NICMOS H{sub 160}-band images from the COSMOS survey, we find evidence for the evolution of the pair fraction above z {approx} 2, an epoch in which massive galaxies are believed to undergo significant structural and mass evolution. We observe that the pair fraction of massive galaxies is 0.15 {+-} 0.08 at 1.7 {<=}z {<=} 3.0, where galaxy pairs are defined as massive galaxies having a companion of flux ratio from 1:1 to 1:4 within a projected separation of 30 kpc. This is slightly lower but still consistent with the pair fraction measured previously in other studies, and the merger fraction predicted in halo-occupation modeling. The redshift evolution of the pair fraction is described by a power law F(z) = (0.07 {+-} 0.04) Multiplication-Sign (1 + z){sup 0.6{+-}0.5}. The merger rate is consistent with no redshift evolution; however it is difficult to constrain due to the limited sample size and the high uncertainties in the merging timescale. Based on the merger rate calculation, we estimate that a massive galaxy undergoes on average 1.1 {+-} 0.5 major mergers from z = 3 to 0. The observed merger fraction is sufficient to explain the number density evolution of massive galaxies, but insufficient to explain the size evolution. This is a hint that mechanism(s) other than major merging may be required to increase the sizes of the massive, compact quiescent galaxies from z {approx} 2 to 0.
- OSTI ID:
- 22004292
- Journal Information:
- Astrophysical Journal, Vol. 744, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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