A Direct Measurement of Major Galaxy Mergers at z ≲ 3

By Christopher J. Conselice, M. Bershady, Mark Dickinson, C. Papovich. 2003

409 citations recorded by the source corpus.

This paper presents direct evidence for hierarchical galaxy assembly out to redshifts z ∼ 3. We identify major mergers using the model-independent CAS (concentration, asymmetry, clumpiness) physical morphological system on galaxies detected, and photometrically selected, in the WFPC2 and NICMOS Hubble Deep Field North. We specifically use the asymmetric distributions of rest-frame optical light measured through the asymmetry parameter (A) to determine the fraction of galaxies undergoing major mergers as a function of redshift (z), stellar mass (M*), and absolute magnitude (MB). We find that the fraction of galaxies consistent with undergoing a major merger increases with redshift for all galaxies, but most significantly, at 5–10 σ confidence, for the most luminous and massive systems. The highest merger fractions we find are 40%–50% for galaxies with MB < -21, or M* > 1010 M⊙ at z > 2.5, e.g., objects identified as Lyman-break galaxies. Using these results, we model the merger fraction evolution in the form fm(A, M*, MB, z) = f0 × (1 + z). We find mA values ∼4–6 for the most luminous and massive galaxies, while lower mass and less luminous galaxies have smaller mA values. We use these merger fractions, combined with merger timescales calculated from N-body simulations, to derive galaxy merger rates to z ∼ 3. We also use stellar masses of HDF-N galaxies to determine the mass accretion rate of field galaxies involved in major mergers. We find an average stellar mass accretion rate of G ∼ 4 × 108 M⊙ Gyr-1 per galaxy at z ∼ 1 for galaxies with stellar masses M* > 109 M⊙. This accretion rate changes with redshift as G = 1.6 × 108(1 + z)0.99±0.32 M⊙ Gyr-1 per galaxy. We also find that the fraction of stellar mass density in galaxies involved in major mergers increases with redshift, with a peak mass fraction ∼0.5 for the brightest, MB < -21, and most massive, M* > 1010 M⊙, systems near z ∼ 2.5. By comparing merger fractions predicted in cold dark matter semianalytic models with our results we find a reasonably good agreement for the largest and brightest systems, although we find more low-mass galaxy mergers at lower redshifts than what these models predict.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Computer Vision and Pattern Recognition

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Citations in the corpus

Galaxy merger morphologies and time-scales from simulations of equal-mass gas-rich disc mergers (2008, methodology): “Most current morphological measurements of the evolution of the galaxy merger rate are done in the rest-frame B or SDSS g (e.g. Conselice et al. 2003, Lotz et al. 2008).”
The Recent and Continuing Assembly of Field Elliptical Galaxies by Red Mergers (2005, background): “…as a free parameter; observational constraints on the evolution of the merger rate may not be quite consistent (see, e.g., Patton et al. 2002; Conselice et al. 2003; Lin et al. 2004), and no studies have specifically considered the evolution of the pair fraction among galaxies on the red…”
DETAILED DECOMPOSITION OF GALAXY IMAGES. II. BEYOND AXISYMMETRIC MODELS (2009, methodology): “The application of non-parametric analysis has mostly been to quantify galaxy mergers (e.g., Conselice et al. 2003; Lotz et al. 2008).”
The Rest-Frame Far-Ultraviolet Morphologies of Star-Forming Galaxies at z ~ 1.5 and 4 (2006, background): “Conselice et al. (2003) found a 50% merger fraction for MB < 21 galaxies at z 2–3 based on a sample of 10 objects in the HDF-N.”
THE SINS SURVEY OF z ∼ 2 GALAXY KINEMATICS: PROPERTIES OF THE GIANT STAR-FORMING CLUMPS (2010, background): “These clumpy, asymmetric structures often resemble z ∼ 0 mergers (Conselice et al. 2003; Lotz et al. 2004).”
The DEEP2 Galaxy Redshift Survey: Evolution of Close Galaxy Pairs and Major-Merger Rates up to z ~ 1.2 (2004, background): “This value is about 1 order of magnitude lower than the average merger rate for galaxies with MB ≤ −19 derived by Conselice et al. (2003).”
Evidence for Quasar Activity Triggered by Galaxy Mergers in HST Observations of Dust-reddened Quasars (2007, methodology): “Conselice et al. (2003) adopts a ratio between the radii containing certain percentages of the total light.”
Red Galaxy Growth and the Halo Occupation Distribution (2008, background): “There are thousands of examples of merging galaxies in the literature, spanning a broad range of galaxy types, mass, and redshift (e.g., Arp & Madore 1987; Toomre & Toomre 1972; Conselice et al. 2003; van Dokkum 2005; Rines et al. 2007; McIntosh et al. 2007; Lotz et al. 2008).”
THE MAJOR AND MINOR GALAXY MERGER RATES AT z < 1.5 (2011, background): “Early studies of small deep HST fields by Abraham et al. (1996) and Conselice et al. (2003, 2005) showed strong evolution in the fraction of asymmetric galaxies at 0 < z < 3 with stellar masses > 1010M⊙.”
THE GREATER IMPACT OF MERGERS ON THE GROWTH OF MASSIVE GALAXIES: IMPLICATIONS FOR MASS ASSEMBLY AND EVOLUTION SINCE z ≃ 1 (2009, background): “1, the merger rate has been estimated based on the occurrence of morphologically disturbed systems (e.g., Conselice et al. 2003; Lotz et al. 2008b) and the frequency of optical pairs, either defined with respect to their relative velocity difference (e.g., Patton et al. 2002; Lin et al. 2004, 2008;…”
Galaxy growth in the concordance ΛCDM cosmology (2007, neutral): “(Bell et al. 2006; Carlberg et al. 2000; Patton et al. 2002; Conselice et al. 2003; Bundy et al. 2004; Lin et al. 2004).”
CANDELS: THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY (2011, positive): “Galaxy interactions, disturbances, and mergers will be identified directly in the CANDELS images using both visual and quantitative methods such as CAS (Conselice et al. 2003) and Gini/M20 (Lotz et al. 2004).”
AGN Host Galaxies at z ~ 0.4-1.3: Bulge-dominated and Lacking Merger-AGN Connection (2005, background): “The decliningC with host magnitude is interpreted as an evolutionary effect; galaxies at higher redshift (and thus generally fainter) are intrinsically less concentrated (Conselice et al. 2003).”
THE HUBBLE SPACE TELESCOPE WIDE FIELD CAMERA 3 EARLY RELEASE SCIENCE DATA: PANCHROMATIC FAINT OBJECT COUNTS FOR 0.2–2 μm WAVELENGTH (2010, background): “The origin of the Hubble sequence is not yet fully understood (e.g., Driver et al. 1998), but is likely related to the balance between major mergers versus minor accretion events and steady infall (i.e., Conselice et al. 2003; Hopkins et al. 2010; Peng et al. 2010).”
Galaxy Zoo: the fraction of merging galaxies in the SDSS and their morphologies (2009, background): “To date though, such studies have concentrated mostly on merger rates (Carlberg et al. 2000; Le Fevre et al. 2000; Patton et al. 2002; Conselice et al. 2003; Bundy et al. 2005; Bell et al. 2006; Conselice, Rajgor & Myers 2008; Lin et al. 2008; Lotz et al. 2008a; Hsieh. et al. 2008, Patton et al.…”
Early and Rapid Merging as a Formation Mechanism of Massive Galaxies: Empirical Constraints (2005, methodology): “This is the simulation where the analysis mode matches the method used to derive the merger fractions in the Hubble Deep Fields.”
The Luminosity, Stellar Mass, and Number Density Evolution of Field Galaxies of Known Morphology from z = 0.5 to 3 (2004, methodology): “This is analogous to the color-asymmetry relationship and its outlier method of identifying major mergers (Conselice et al. 2000a; Conselice et al. 2000b; Conselice 2003; Conselice et al. 2003a).”
The Physical Nature of Rest-UV Galaxy Morphology during the Peak Epoch of Galaxy Formation (2006, positive): “13 kpc at the redshift of our sample, similar to previous analyses (Conselice et al. 2003a, LPM04, Lotz et al. 2006) whose selection radii Figure 2 (continued) range up to about 10 kpc. Based on visual analysis of ACS and ground-based color maps, this appears to be the optimal choice of distance…”