Major Merging History in CANDELS. I. Evolution of the Incidence of Massive Galaxy-Galaxy Pairs from z=3 to z~0

18 Dec 2017  ·  Mantha Kameswara Bharadwaj, McIntosh Daniel H., Brennan Ryan, Ferguson Henry C., Kodra Dritan, Newman Jeffrey A., Rafelski Marc, Somerville Rachel S., Conselice Christopher J., Cook Joshua S., Hathi Nimish P., Koo David C., Lotz Jennifer M., Simmons Brooke D., Straughn Amber N., Synder Gregory F., Wuyts Stijn, Bell Eric F., Dekel Avishai, Kartaltepe Jeyhan, Kocevski Dale D., Koekemoer Anton M., Lee Seong-Kook, Lucas Ray A., Pacifici Camilla, Peth Michael A., Barro Guillermo, Dahlen Tomas, Finkelstein Steven L., Fontana Adriano, Galametz Audrey, Grogin Norman A., Guo Yicheng, Mobasher Bahram, Nayyeri Hooshang, Perez-Gonzalez Pablo G., Pforr Janine, Santini Paola, Stefanon Mauro, Wiklind Tommy ·

The rate of major galaxy-galaxy merging is theoretically predicted to steadily increase with redshift during the peak epoch of massive galaxy development ($1{\leq}z{\leq}3$). We use close-pair statistics to objectively study the incidence of massive galaxies (stellar $M_{1}{\geq}2{\times}10^{10}M_{\odot}$) hosting major companions ($1{\leq}M_{1}/M_{2}{\leq}4$; i.e., $<$4:1) at six epochs spanning $0{<}z{<}3$... We select companions from a nearly complete, mass-limited ($\geq5{\times}10^{9}M_{\odot}$) sample of 23,696 galaxies in the five CANDELS fields and the SDSS. Using $5-50$ kpc projected separation and close redshift proximity criteria, we find that the major companion fraction $f_{\mathrm{mc}}(z)$ based on stellar mass-ratio (MR) selection increases from 6% ($z{\sim}0$) to 16% ($z{\sim}0.8$), then turns over at $z{\sim}1$ and decreases to 7% ($z{\sim}3$). Instead, if we use a major F160W flux ratio (FR) selection, we find that $f_{\mathrm{mc}}(z)$ 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 ($C_{\mathrm{merg,pair}}{=}0.6$ and $T_{\mathrm{obs,pair}}{=}0.65\mathrm{Gyr}$), we find that MR rates disagree with theoretical predictions at $z{>}1.5$. Instead, if we use an evolving $T_{\mathrm{obs,pair}}(z){\propto}(1+z)^{-2}$ from Snyder et al., our MR-based rates agree with theory at $0{<}z{<}3$. Our analysis underscores the need for detailed calibration of $C_{\mathrm{merg,pair}}$ and $T_{\mathrm{obs,pair}}$ as a function of redshift, mass and companion selection criteria to better constrain the empirical major merger history. read more

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Astrophysics of Galaxies