2008 (IPP)

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Towards a robust estimate of the merger rate evolution using near-IR photometry
(2008-04-01) Rawat, A.; Kembhavi, A.K.
We use a combination of deep, high angular resolution imaging data from the CDFS (HST/ACS GOODS survey) and ground based near-IR Ks 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)3.43±0.49 for optically selected pairs, and ∝ (1 + z)2.18±0.18 for pairs selected in the near-IR. Our result is unlikely to be aﬀected by luminosity evolution which is relatively modest when using restframe J band selection. The apparently more rapid evolution that we ﬁnd in the visible is likely caused by biases relating to incompleteness and spatial resolution aﬀecting the ground based near IR photometry, underestimating pair counts at higher redshifts in the near-IR. The major merger rate was ∼5.6 times higher at z ∼ 1.2 than at the current epoch. Overall 41%×(0.5Gyr/τ ) of all galaxies with MJ ≤ −19.5 have undergone a major merger in the last ∼ 8Gyr, 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.