THE MAJOR AND MINOR GALAXY MERGER RATES AT z < 1.5

By J. Lotz, P. Jonsson, Thomas J. Cox, Darren Croton, Joel R. Primack, R. Somerville, Kyle R. Stewart. 2011

297 citations recorded by the source corpus.

Calculating the galaxy merger rate requires both a census of galaxies identified as merger candidates and a cosmologically averaged “observability” timescale 〈Tobs(z)〉 for identifying galaxy mergers. While many have counted galaxy mergers using a variety of techniques, 〈Tobs(z)〉 for these techniques have been poorly constrained. We address this problem by calibrating three merger rate estimators with a suite of hydrodynamic merger simulations and three galaxy formation models. We estimate 〈Tobs(z)〉 for (1) close galaxy pairs with a range of projected separations, (2) the morphology indicator G − M20, and (3) the morphology indicator asymmetry A. Then, we apply these timescales to the observed merger fractions at z < 1.5 from the recent literature. When our physically motivated timescales are adopted, the observed galaxy merger rates become largely consistent. The remaining differences between the galaxy merger rates are explained by the differences in the ranges of the mass ratio measured by different techniques and differing parent galaxy selection. The major merger rate per unit comoving volume for samples selected with constant number density evolves much more strongly with redshift (∝(1 + z)+3.0 ± 1.1) than samples selected with constant stellar mass or passively evolving luminosity (∝(1 + z)+0.1 ± 0.4). We calculate the minor merger rate (1:4 <Msat/Mprimary ≲ 1:10) by subtracting the major merger rate from close pairs from the “total” merger rate determined by G − M20. The implied minor merger rate is ∼3 times the major merger rate at z ∼ 0.7 and shows little evolution with redshift.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/da6818315c3ea55569b8766ecf68f62be2cd997d

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In Astronomy and Astrophysics

1. L. Hernquist
2. P. Hopkins
3. R. Dav'e
4. R. Somerville
5. P. V. van Dokkum
6. C. Conroy
7. Volker Springel
8. A. Dekel

In Instrumentation

1. L. Hernquist
2. P. Hopkins
3. P. V. van Dokkum
4. R. Dav'e
5. C. Conroy
6. R. Somerville
7. A. Dekel
8. Volker Springel

Citations in the corpus

• PRIMUS: CONSTRAINTS ON STAR FORMATION QUENCHING AND GALAXY MERGING, AND THE EVOLUTION OF THE STELLAR MASS FUNCTION FROM z = 0–1 (2013, background): “We emphasize that our measurement complements, but is only implicitly related to measurements of the major and minor merger rate (see, e.g., Lotz et al. 2011, and references therein).”
• The mean star formation rate of X-ray selected active galaxies and its evolution from z~2.5: results from PEP-Herschel (2012, background): “Part of the reason for this uncertainty is that the structural identification of b na- fide mergers is not entirely straightforward (Lotz et al. 2011, and references therein).”
• THE SFR–M* RELATION AND EMPIRICAL STAR FORMATION HISTORIES FROM ZFOURGE AT 0.5 < z < 4 (2015, background): “However this would require between 25−65% of these galaxies to merge with a more massive galaxy per Gyr, which substantially exceeds current estimates of galaxy merger rates (e.g. Lotz et al. 2011; Williams et al. 2011; Leja et al. 2015).”
• Galaxy morphology and star formation in the Illustris Simulation at z = 0 (2015, methodology): “We measure non-parametric morphologies by using code originally developed for idealized merger simulations (Lotz et al. 2008a, 2010a,b) and also applied to galaxy surveys (Lotz et al. 2004, 2008b, 2011).”
• Constraining the galaxy–halo connection over the last 13.3 Gyr: star formation histories, galaxy mergers and structural properties (2017, methodology): “We also adjusted galaxy merger rates by using the cosmologically averaged observability timescales from Lotz et al. (2011).”
• CAN MINOR MERGING ACCOUNT FOR THE SIZE GROWTH OF QUIESCENT GALAXIES? NEW RESULTS FROM THE CANDELS SURVEY (2011, background): “For a recent review, we refer to Lotz et al. (2011).”
• Massive Black Hole Binary Mergers in Dynamical Galactic Environments (2016, background): “Massive Black Holes (MBH) occupy at least the majority of massive galaxies (e.g. Soltan 1982; Kormendy & Richstone 1995; Magorrian et al. 1998) which are also known to merge with each other as part of their typical lifecycles (e.g. Lacey & Cole 1993; Lotz et al. 2011; Rodriguez-Gomez et al. 2015).”
• Galaxy and Mass Assembly (GAMA): ugriz galaxy luminosity functions (2011, background): “…the mechanism that causes this transition will be the subject of future work, but it appears unlikely that mergers play a dominant role at these moderate redshifts, given the low merger fraction (∼ 5 per cent or less) observed at low redshift by e.g. Conselice et al. (2009) and Lotz et al. (2011).”
• 3D-HST: A WIDE-FIELD GRISM SPECTROSCOPIC SURVEY WITH THE HUBBLE SPACE TELESCOPE (2012, methodology): “Within the 3D-HST sample, the pair fraction can be measured as a function of mass and redshift, and the fractions can be turned into a merger rate using models (e.g., Kitzbichler & White 2008; Lotz et al. 2011; Williams et al. 2011).”
• CANDELS: THE PROGENITORS OF COMPACT QUIESCENT GALAXIES AT z ∼ 2 (2012, background): “Considering pair fractions of roughly 10% (Williams et al. 2011), merger time scales of 1 Gyr (Lotz et al. 2011) and a density of massive galaxies of .”
• The ALPINE-ALMA [CII] survey (2020, background): “…major and minor, are observed at all epochs (e.g., Conselice 2014), with a major merger rate increasing from the local universe to z ∼ 2 (e.g., Lotz et al. 2011; LópezSanjuan et al. 2013; Mantha et al. 2018), and possibly flattening to z ∼ 4−5 (e.g., Tasca et al. 2014; Ventou et al. 2017),…”
• THE DEPENDENCE OF QUENCHING UPON THE INNER STRUCTURE OF GALAXIES AT 0.5 ⩽ z < 0.8 IN THE DEEP2/AEGIS SURVEY (2012, background): “Lotz et al. (2011) addressed the issue of disparate observational merger rates;they found that the major reason for these differences is the assumed timescale in which a merger is observable.”
• Inferring the star formation histories of massive quiescent galaxies with bagpipes: evidence for multiple quenching mechanisms (2017, background): “…feedback is one process which has the capability to cause extremely rapid quenching, and, if triggered by major-merger events, would also be expected to be much more common at high redshift, as the rate of major mergers is known to be a strong function of redshift (e.g. Lotz et al. 2011).”
• How do minor mergers promote inside-out growth of ellipticals, transforming the size, density profile and dark matter fraction? (2012, background): “…(Malin & Carter 1983; Schweizer & Seitzer 1992; Tran et al. 2005; van Dokkum 2005; Bell et al. 006a,b; Faber 2007; McIntosh et al. 2008; Whitaker & van Dokkum 2008; Robaina et al. 2010; Duc 2011; Lotz et al. 2011; Trujillo et al. 2011; Weinzirl et al. 2011; Tal et al. 2012; López-Sanjuan 2012).”
• The origin of discs and spheroids in simulated galaxies (2011, background): “However, questions might remain open, as the estimation of merger times from observations is non-trivial (Lotz et al. 2011).”
• The Kilo-Degree Survey (2012, background): “For example, various observational constraints on the influence of galaxy mergers on the evolution of the galaxy population at redshifts higher than ∼ 0.5 differ up to an order of magnitude (see e.g. [17]).”
• A LINK BETWEEN STAR FORMATION QUENCHING AND INNER STELLAR MASS DENSITY IN SLOAN DIGITAL SKY SURVEY CENTRAL GALAXIES (2013, background): “This picture neglects major mergers, but they are expected to be rare at low redshifts (Lotz et al. 2011) and an insignificant contribution to the overall mass growth (Moustakas et al. 2013).”