The rate of major galaxy-galaxy merging is theoretically predicted to steadily increase with redshift during the peak epoch of massive galaxy development (1 ≤ z ≤ 3). We use close-pair statistics to objectively study the incidence of massive galaxies (stellar M1 > 2 × 1010M⊙) hosting major companions (1 ≤ M1/M2 ≤ 4; i.e. < 4:1) at six epochs spanning 0 < z < 3. We select companions from a nearly complete, mass-limited (≥5 × 109M⊙) sample of 23 696 galaxies in the five Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey fields and the Sloan Digital Sky Survey. Using 5-50 kpc projected separation and close redshift proximity criteria, we find that the major companion fraction fmc(z) based on stellar mass-ratio (MR) selection increases from 6 per cent (z ~ 0) to 16 per cent (z ~ 0.8), then turns over at z ~ 1 and decreases to 7 per cent (z ~ 3). Instead, if we use a major F160W flux-ratio (FR) selection, we find that fmc(z) increases steadily until z = 3 owing to increasing contamination from minor (MR > 4:1) companions at z > 1. We show that these evolutionary trends are statistically robust to changes in companion proximity. We find disagreements between published results are resolved when selection criteria are closely matched. If we compute merger rates using constant fraction-to-rate conversion factors (Cmerg,pair = 0.6 and Tobs,pair = 0.65 Gyr), we find that MR rates disagree with theoretical predictions at z > 1.5. Instead, if we use an evolving Tobs,pair(z) ∝ (1 + z)-2 from Snyder et al., our MR-based rates agree with theory at 0 < z < 3. Our analysis underscores the need for detailed calibration of Cmerg,pair and Tobs,pair as a function of redshift, mass, and companion selection criteria to better constrain the empirical major merger history.
Bibliographical noteFunding Information:
This work is dedicated in memory of K. N. V. S. Kishore Babu, a dear friend who inspired KBM to pursue Astrophysics. We are grateful to Peter Behroozi, Mark Brodwin, Philip Hopkins, Kartheik Iyer, Allison Kirkpatrick, Viraj Pandya, Vicente Rodriguez-Gomez, Brett Salmon, and Raymond Simons for helpful comments and discussions during different manifestations of this work. Special thanks to Daniel Shanaberger for carefully reading the manuscript, thanks to Gillen Brown, Cody Ciaschi, Bandon Decker, Benjamin Floyd, Ripon Saha, and Madalyn Weston for their valuable inputs during the University of Missouri Kansas City (UMKC) Galaxy Evolution Group discussions. DHM and KBM acknowledge support from the Missouri Consortium of National Aeronautics and Space Administration (NASA)’s National Space Grant College and Fellowship Program, and funding from the University of Missouri Research Board. RSS acknowledges support from the Downsbrough family, and from the Simons Foundation. SL acknowledges support from the National Research Foundation of Korea grant, no. 2017R1A3A3001362, funded by the Korea government. This work is based on observations taken by the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for Program number HST-GO-12060 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. This publication makes use of the SDSS. Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the US Department of Energy, the NASA, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. This publication also made use of NASA’s Astrophysics Data System Bibliographic Services, TOPCAT (Tools for OPerations on Catalogues And Tables, Taylor 2005), the core PYTHON package for the astronomy community (Astropy 1.2.1; Astropy Collaboration et al. 2013).
© 2017 The Author(s).
- Galaxies: evolution
- Galaxies: high-redshift
- Galaxies: interactions
- Galaxies: statistics