Galaxy merger morphologies and time-scales from simulations of equal-mass gas-rich disc mergers

By J. Lotz, P. Jonsson, Thomas J. Cox, Joel R. Primack, National Optical Astronomy Observatory, U. California, Santa Cruz, H. C. F. Astrophysics. 2008

330 citations recorded by the source corpus.

A key obstacle to understanding the galaxy merger rate and its role in galaxy evolution is the difficulty in constraining the merger properties and time-scales from instantaneous snapshots of the real Universe. The most common way to identify galaxy mergers is by morphology, yet current theoretical calculations of the time-scales for galaxy disturbances are quite crude. We present a morphological analysis of a large suite of gadgetN-body/hydrodynamical equal-mass gas-rich disc galaxy mergers which have been processed through the Monte Carlo radiative transfer code sunrise. With the resulting images, we examine the dependence of quantitative morphology (G, M20, C, A) in the SDSS g band on merger stage, dust, viewing angle, orbital parameters, gas properties, supernova feedback and total mass. We find that mergers appear most disturbed in G−M20 and asymmetry at the first pass and at the final coalescence of their nuclei, but can have normal quantitative morphologies at other merger stages. The merger observability time-scales depend on the method used to identify the merger as well as the gas fraction, pericentric distance and relative orientation of the merging galaxies. Enhanced star formation peaks after and lasts significantly longer than strong morphological disturbances. Despite their massive bulges, the majority of merger remnants appear disc-like and dusty in g-band light because of the presence of a low-mass star-forming disc.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/bbba41638b2c0813ac84806d2bb9596cd129a3ea

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A physical model for z∼ 2 dust-obscured galaxies (2009, background): “…one can precisely mimic local and high-redshift observational selection functions, and directly relate observed trends to physical conditions in the model galaxies (e.g. Jonsson 2006; Jonsson et al. 2006; Lotz et al. 2008; Younger et al. 2009b; Narayanan et al. 2010; Jonsson, Groves & Cox 2010).”
Galaxy morphology and star formation in the Illustris Simulation at z = 0 (2015, methodology): “Although rare, galaxy mergers can play an important role in massive galaxies (e.g., Bell et al. 2006; Lotz et al. 2008b, 2011).”
MERGERS IN ΛCDM: UNCERTAINTIES IN THEORETICAL PREDICTIONS AND INTERPRETATIONS OF THE MERGER RATE (2010, methodology): “Lotz et al. (2008a) specifically cibrate these timescales for the same projected separation and velocity selection from a detailed study of a large suite of hydrodynamic merger simulations (including a range of galaxy masses, orbital parameters, gas fractions and star formation rates) using mock…”
THE MAJOR AND MINOR GALAXY MERGER RATES AT z < 1.5 (2011, methodology): “…by adopting an evolving luminosity selection based on a passive luminosity evolution (PLE) model in which galaxies of a fixed stellar mass are fainter at lower redshift due to passive aging of their stellar populations (e.g. Lotz et al. 2008, Lin et al. 2008, de Ravel et al. 2009, Shi et al. 2009).”
Galaxy pairs in the Sloan Digital Sky Survey – V. Tracing changes in star formation rate and metallicity out to separations of 80 kpc (2012, background): “There is some suggestion from simulations that tidal features are visible for both a shorter period of time than the SFR burst, and at earlier times than the SFR enhancement (Lotz et al. 2008).”
THE BULK OF THE BLACK HOLE GROWTH SINCE z ∼ 1 OCCURS IN A SECULAR UNIVERSE: NO MAJOR MERGER–AGN CONNECTION (2010, methodology): “For example, simulations of major mergers by Lotz et al. (2008) quantified that the strong signatures could still be detected 0.7 Gyr after the merger, by degrading their snapshots to the resolution of HST z ∼ 1 imaging.”
Galaxy formation theory (2010, methodology): “Sunrise has been applied to studies of luminous infrared galaxies (Younger et al. 2009), quantit tive morphology of merger remnants (Lotz et al. 2008), physical models to infer star formation rates from molecular indicators (Narayanan et al. 2010) and tests of our ability to recover physical…”
THE GREATER IMPACT OF MERGERS ON THE GROWTH OF MASSIVE GALAXIES: IMPLICATIONS FOR MASS ASSEMBLY AND EVOLUTION SINCE z ≃ 1 (2009, background): “This may reflect the influence of nonuniform star formation, minor mergers, and even flybys on galaxy morphology as discussed with respect to Figure 3 (also see Lotz et al. 2008a).”
The structures of distant galaxies – III. The merger history of over 20 000 massive galaxies at z < 1.2 (2008, methodology): “We compare our derived merger fractions to previously published merger fractions from Lotz et al. (2008a) and pair studies from Kartaltepe et al. (2007), Lin et al. (2008) and de Ravel et al. (2008).”
The Redshift Evolution of Wet, Dry, and Mixed Galaxy Mergers from Close Galaxy Pairs in the DEEP2 Galaxy Redshift Survey (2008, methodology): “…1995; Neuschaefer et al. 1997; Patton et al. 1997; Carlberg et al. 2000; Le Fèvre et al. 2000; Patton et al. 2002; Conselice et al. 2003; Bundy et al. 2004; Lin et al. 2004; Cassata et al. 2005; Conselice 2006; Bell et al. 2006b; Lotz et al. 2008; Kampczyk et al. 2007; Kartaltepe et al. 2007).”
The Evolution of Galaxy Structure Over Cosmic Time (2014, methodology): “Lotz et al. (2008, 2010a) find that the asymmetry time-scales for gas-rich major mergers are 0.2-0.4 Gyr, and 0.06 Gyr for minor mergers (Lotz et al. 2010a).”
CONSTRAINTS ON THE ASSEMBLY AND DYNAMICS OF GALAXIES. I. DETAILED REST-FRAME OPTICAL MORPHOLOGIES ON KILOPARSEC SCALE OF z ∼ 2 STAR-FORMING GALAXIES (2010, background): “There are several inherent difficulties in studies based on morphologies, including bandshifting, intrinsically complex structure, and uncertainties in the timescales over which key merger signatures are observable (e.g., Toft et al. 2007; Elmegreen et al. 2007, 2009; Lotz et al. 2008, 2010a,b).”
Galaxy pairs in the Sloan Digital Sky Survey – IX. Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer (2014, background): “This discrepancy may be due in part to the low surface brightness of tidal features and the time during the interaction at which they are expected to be visible (e.g. Lotz et al. 2008).”
THE DEPENDENCE OF QUENCHING UPON THE INNER STRUCTURE OF GALAXIES AT 0.5 ⩽ z < 0.8 IN THE DEEP2/AEGIS SURVEY (2012, methodology): “We selected all nonstellar objects with SExtractor CLASS_STAR< 0.9 and I < 25.0 that did not lie within 50 pixels of a tile edge for our automated morphology analysis, covering an effective areaof 710.9 arcmin2 in the ACS images (see Lotz et al. 2008a, for more details).”
The effects of gas on morphological transformation in mergers: implications for bulge and disc demographics (2009, background): “…in a shorter time than the duration of the merger itself, and correcting for the expected duty cycles/lifetimes of these events, a large fraction of these low-mass galaxies should have experienced a violent event in the last ∼10 Gyr (Hopkins et al. 2007; Lotz et al. 2008a; Conselice et al. 2009).”
HYDRODYNAMICS OF HIGH-REDSHIFT GALAXY COLLISIONS: FROM GAS-RICH DISKS TO DISPERSION-DOMINATED MERGERS AND COMPACT SPHEROIDS (2010, background): “First, determinations of the merger rate from highredshift surveys are usually based on irregular structures or disturbed kinematics (e.g., Conselice et al. 2003; Lotz et al. 2006, 2008; Overzier et al. 2010; Jogee et al. 2009; López-Sanjuan et al. 2009; Puech 2010).”
THE PERSISTENCE OF COOL GALACTIC WINDS IN HIGH STELLAR MASS GALAXIES BETWEEN z ∼ 1.4 AND ∼1 (2009, background): “The lines separating different morphological types shown in the figure are taken from Lotz et al. (2008), who found that these divisions are appropriate for galaxies at 0.2 < z < 1.2.”
Forming a large disc galaxy from a z < 1 major merger (2008, neutral): “…have numerical simulations been able to directly compare the observable quantities of the outputs with real data (Jonsson 2006; Chakrabarti et al. 2007; Covington et al. 2008; Lotz et al. 2008; Rocha et al. 2008), rather than simply predicting the mass distribution of the simulated stellar systems.”
The effect of mass ratio on the morphology and time-scales of disc galaxy mergers: Effect of mass ratio on merger morphology (2009, methodology): “We continue the work first presented in Lotz et al. 2008b, hereafter Paper 1.”
The optical morphologies of galaxies in the IllustrisTNG simulation: a comparison to Pan-STARRS observations (2018, methodology): “…and subsequent analysis of synthetic images from hydrodynamic simulations is quickly becoming a powerful tool to connect galaxy formation theory with observations (e.g. Lotz et al. 2008a; Jonsson et al. 2010; Snyder et al. 2015a,b; Bignone et al. 2017; Bottrell et al. 2017a; Trayford et al. 2017).”