Towards a robust estimate of the merger rate evolution using near-IR photometry

Abstract

We use a combination of deep, high angular resolution imaging data from the HST/ACS GOODS survey and ground based near-IR K_s images to derive the evolution of the galaxy major merger rate in the redshift range 0.2 ≤ z ≤ 1.2. We select galaxies on the sole basis of their J-band rest-frame, absolute magnitude, which is a good tracer of the stellar mass. We find steep evolution with redshift, with the merger rate ∝ (1+z)^2.44±0.39 for optically selected pairs, and ∝ (1+z)^2.07±0.74 for pairs selected in the near-IR. Our result is unlikely affected by luminosity evolution which is relatively modest when using a rest-frame J band selection. The major merger rate evolves by a factor ~5 from the current epoch to 1.6×10⁻³ Mpc⁻³ Gyr⁻¹ at z ~ 1.2, suggesting that 58%×(0.5 Gyr/τ) of all galaxies with M_J ≤ −19.5 have undergone a major merger in the last ~ 8 Gyr (where τ is the merger timescale). Interestingly, we find no effect on the derived major merger rate due to the presence of the large scale structure at z = 0.735 in the CDFS. We do find some evidence for increased star formation due to possible interactions between members of a pair using Spitzer MIPS 24μm fluxes to estimate the SFR.