THE GREATER IMPACT OF MERGERS ON THE GROWTH OF MASSIVE GALAXIES: IMPLICATIONS FOR MASS ASSEMBLY AND EVOLUTION SINCE z ≃ 1

By K. Bundy, M. Fukugita, Richard S. Ellis, Thomas Targett, S. Belli, T. Kodama. 2009

187 citations recorded by the source corpus.

Using deep infrared observations conducted with the MOIRCS imager on the Subaru Telescope in the northern GOODS field combined with public surveys in GOODS-S, we investigate the dependence on stellar mass, M*, and galaxy type of the close pair fraction (5 h−1 kpc < rsep < 20 h−1 kpc) and implied merger rate. In terms of combined depth and survey area, our publicly available mass-limited sample represents a significant improvement over earlier infrared surveys used for this purpose. In common with some recent studies, we find that the fraction of paired systems that could result in major mergers is low (∼4%) and does not increase significantly with redshift to z ≈ 1.2, with ∝(1 + z)1.6±1.6. Our key finding is that massive galaxies with M*>1011 M☉ are more likely to host merging companions than less massive systems (M* ∼ 1010M☉). We find evidence for a higher pair fraction for red, spheroidal hosts compared to blue, late-type systems, in line with expectations based on clustering at small scales. The so-called “dry” mergers between early-type galaxies devoid of star formation (SF) represent nearly 50% of close pairs with M*>3 × 1010 M☉ at z ∼ 0.5, but less than 30% at z ∼ 1. This result can be explained by the increasing abundance of red, early-type galaxies at these masses. We compare the volumetric merger rate of galaxies with different masses to mass-dependent trends in galaxy evolution. Our results reaffirm the conclusion of Bundy et al. that major mergers do not fully account for the formation of spheroidal galaxies since z ∼ 1. In terms of mass assembly, major mergers contribute little to galaxy growth below M* ∼ 3 × 1010 M☉ but play a more significant role among galaxies with M* ≳ 1011M☉ ∼ 30% of which have undergone mostly dry mergers over the observed redshift range. Overall, the relatively rapid and recent coalescence of high-mass galaxies mirrors the expected hierarchical growth of halos and is consistent with recent model predictions, even if the top–down suppression of SF and morphological evolution (i.e., “downsizing”) involves additional physical processes.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/625c51490b605a27fc55eb77aadf18f73891f211

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In Astronomy and Astrophysics

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Citations in the corpus

• Galaxy clustering in the CFHTLS-Wide: the changing relationship between galaxies and haloes since z ~ 1.2 (2011, result): “Since a redshift evolution of the merging rate would change the occupation function, we therefore conclude that our measurements imply a constant merging rate since z ∼ 1, which confirms the constant (albeit minor) role of merging for intermediate-mass galaxies (e.g., Bundy et al. 2009).”
• THE BULK OF THE BLACK HOLE GROWTH SINCE z ∼ 1 OCCURS IN A SECULAR UNIVERSE: NO MAJOR MERGER–AGN CONNECTION (2010, background): “…since (1) the S/N determines the visibility of the merger signatures, and (2) while the stellar masses might differ slightly (factors of ∼2 at the same distance and brightness), the mass dependence on the merger rate is not strong, with only a modest increase for higher masses (Bundy et al. 2009).”
• GAS-PHASE OXYGEN GRADIENTS IN STRONGLY INTERACTING GALAXIES. I. EARLY-STAGE INTERACTIONS (2010, background): “These major mergers have likely played an important role in the production and growth of massive, red galaxies since z ∼ 1 (e.g., Bundy et al. 2009; Robaina et al. 2010).”
• Dissecting the size evolution of elliptical galaxies since z∼ 1: puffing-up versus minor-merging scenarios (2011, result): “This evolution is not strong enough to be compatible with the low number of major mergers observed at least since z ∼ 1 (Bundy et al. 2009; de Ravel et al. 2009; Wild et al. 2009; López-Sanjuan et al. 2010), as well as with recent numerical simulations (Khochfar & Silk 2009).”
• THE MAJOR AND MINOR GALAXY MERGER RATES AT z < 1.5 (2011, methodology): “Photometric redshifts are often used as a proxy for spectroscopic velocity separations (e.g. Kartaltepe et al. 2007, Bundy et al. 2009).”
• FORMATION OF MASSIVE GALAXIES AT HIGH REDSHIFT: COLD STREAMS, CLUMPY DISKS, AND COMPACT SPHEROIDS (2009, background): “The cosmological major-merger rate seems insufficient for the purpose (e.g., Jogee 2008; Dekel et al. 2009; Bundy et al. 2009).”
• Galaxy Zoo: the properties of merging galaxies in the nearby Universe – local environments, colours, masses, star formation rates and AGN activity (2009, result): “The more tentative conclusion that this is especially true of ellipticals (by ∼ 2dex) would corroborate the findings of Bundy et al. (2009).8”
• Expected properties of the first gravitational wave signal detected with pulsar timing arrays (2015, background): “We consider four studies of the evolution of the galaxy pair fraction (Bundy et al. 2009; de Ravel et al. 2009; López-Sanjuan et al. 2012; Xu et al. 2012).”
• The Horizon-AGN Simulation: Morphological Diversity of Galaxies ,Promoted by AGN Feedback (2016, background): “…of galaxies in interaction is higher for more massive galaxies and the accompanying burst of star formation is lower with decreasing redshift (Bundy et al. 2009), even though it remains moderate even at the peak epoch of star formation (z ∼ 2) with a factor two enhancement compared to…”
• THE RISE AND FALL OF PASSIVE DISK GALAXIES: MORPHOLOGICAL EVOLUTION ALONG THE RED SEQUENCE REVEALED BY COSMOS (2009, background): “…recent efforts to compare the formation rate of spheroidals to the merger rate have focused only on rarer, major mergers, assuming perhaps incorrectly that single mergers of gas-rich disks are the only channel for spheroidal formation (e.g., Bundy et al. 2007; Genel et al. 2008; Bundy et al. 2009).”
• CAN MINOR MERGING ACCOUNT FOR THE SIZE GROWTH OF QUIESCENT GALAXIES? NEW RESULTS FROM THE CANDELS SURVEY (2011, methodology): “Bundy et al. (2009) selected major pairs at z < 1.4 having K-band flux ratios µK > 0.25.”
• MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER? (2009, methodology): “This should not be surprising, given the agreement with observed merger fractions demonstrated in § 4.2 above; Hopkins et al. (2007a, 2008b), Bundy et al. (2009), and Bell et al. (2006a) have demonstrated that observed major merger fractions are sufficient, within a factor∼ 2, to account for the…”
• THE DEPENDENCE OF QUENCHING UPON THE INNER STRUCTURE OF GALAXIES AT 0.5 ⩽ z < 0.8 IN THE DEEP2/AEGIS SURVEY (2012, result): “Studies that have measured the galaxy merger rate often present different results (e.g., Bell et al. 2006; Conselice 2006; Lin et al. 2008; Lotz et al. 2008b; Bundy et al. 2009; Xu et al. 2011; Bluck et al. 2011).”
• MINOR MERGERS AND THE SIZE EVOLUTION OF ELLIPTICAL GALAXIES (2009, background): “…of dark matter simulations (see e.g. Genel et al. 2008b; Fakhouri & Ma 2008; Genel et al. 2008a) as well as recent observations (see e.g. Bundy et al. 2009) on the mass assembly mechanisms of early-type galaxies and their dark matter halos demonstrate the significance of minor mergers.”
• Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium (2012, background): “…for the existence of ‘realistic’ discs today (Robertson & Bullock 2008; Hopkins et al. 2009e; Stewart et al. 2009), and there appear to be a growing number of observed discs that have undergone recent mergers (Bundy et al. 2009, 2010; Hammer et al. 2009a,b; Puech et al. 2009; Yang et al. 2009).”
• The effects of gas on morphological transformation in mergers: implications for bulge and disc demographics (2009, background): “…there may be some mass dependence in observed merger fractions, it is weak: a factor ∼2 increase with mass from ∼109–1011 M (Zheng, Coil & Zehavi 2007; Conselice, Rajgor & Myers 2008; Patton & Atfield 2008; Bridge et al. 2009; Bundy et al. 2009; Domingue et al. 2009; López-Sanjuan et al. 2009).”
• Systematic investigation of the expected gravitational wave signal from supermassive black hole binaries in the pulsar timing band (2012, background): “We consider four studies of the evolution of the galaxy pair fraction (Bundy et al. 2009; de Ravel et al. 2009; López-Sanjuan et al. 2012; Xu et al. 2012).”
• NEW CONSTRAINTS ON THE EVOLUTION OF THE STELLAR-TO-DARK MATTER CONNECTION: A COMBINED ANALYSIS OF GALAXY–GALAXY LENSING, CLUSTERING, AND STELLAR MASS FUNCTIONS FROM z = 0.2 to z = 1 (2011, background): “The steep rise of M tot∗ /Mh must therefore reflect the greater importance of star formation at masses below Mh ∼ 1012 M over assembly from galaxy mergers (Bundy et al. 2009).”