The effect of gas fraction on the morphology and time-scales of disc galaxy mergers

By J. Lotz, P. Jonsson, Thomas J. Cox, Joel R. Primack. 2009

149 citations recorded by the source corpus.

The majority of galaxy mergers are expected to be minor mergers. The observational signatures of minor mergers are not well understood; thus, there exist few constraints on the minor merger rate. This paper seeks to address this gap in our understanding by determining if and when minor mergers exhibit disturbed morphologies and how they differ from the morphology of major mergers. We simulate a series of unequal-mass moderate gas-fraction disc galaxy mergers. With the resulting g-band images, we determine how the time-scale for identifying galaxy mergers via projected separation and quantitative morphology (the Gini coefficient G, asymmetry A and the second-order moment of the brightest 20 per cent of the light M 20 ) depends on the merger mass ratio, relative orientations and orbital parameters. We find that G-M 20 is as sensitive to 9:1 baryonic mass ratio mergers as 1:1 mergers, with observability time-scales of ∼0.2-0.4 Gyr. In contrast, asymmetry finds mergers with baryonic mass ratios between 4:1 and 1:1 (assuming local disc galaxy gas fractions). Asymmetry time-scales for moderate gas-fraction major disc mergers are ∼0.2-0.4 Gyr and less than 0.06 Gyr for moderate gas-fraction minor mergers. The relative orientations and orbits have little effect on the time-scales for morphological disturbances. Observational studies of close pairs often select major mergers by choosing paired galaxies with similar luminosities and/or stellar masses. Therefore, the various ways of finding galaxy mergers (G-M 20 , A, close pairs) are sensitive to galaxy mergers of different mass ratios. By comparing the frequency of mergers selected by different techniques, one may place empirical constraints on the major and minor galaxy merger rates.

Subfields: Astronomy and Astrophysics, Computer Vision and Pattern Recognition

View Paper: https://www.semanticscholar.org/paper/fbe34a4d24d1032c1f235d48edf95db5e785788c

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Citations in the corpus

THE MAJOR AND MINOR GALAXY MERGER RATES AT z < 1.5 (2011, methodology): “This is consistent with the results from galaxy merger simulations, which predict that G −M20 identifies merging systems for only a short period while double nuclei are evident (Lotz et al. 2008; Lotz et al. 2010a, b).”
Galaxy pairs in the Sloan Digital Sky Survey – II. The effect of environment on interactions (2010, result): “Our study has selected close pairs of galaxies as sites of possible mergers and is complimentary to studies which select interac ing galaxies based on visible asymmetries (e.g. Lotz et al. 2010).”
MERGERS IN ΛCDM: UNCERTAINTIES IN THEORETICAL PREDICTIONS AND INTERPRETATIONS OF THE MERGER RATE (2010, background): “This makes the merger time within ∼ 20− 50kpc shorter by a factor≈ 2, relative to that estimated without baryonic galaxies (see e.g. Lotz et al. 2008a, 2010b,a), and can even lead to the merger and/or destruction of the baryonic galaxiesbeforethe subhalo (their bound dark matter) is significantly…”
OVERVIEW OF THE SDSS-IV MaNGA SURVEY: MAPPING NEARBY GALAXIES AT APACHE POINT OBSERVATORY (2014, methodology): “Through comparisons with suites of hydrodynamical merger simulations (e.g., Lotz et al. 2010a,b), new statistical metrics can be devised that will help diagnose the merger phase (i.e., first approach, second passage, final coalescence) and the mass ratio of the interacting galaxies.”
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).”
MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER? (2009, methodology): “The difference in the latter owes to the dependence of observable timescale on gas fraction as calibrated in Lotz et al. (2009a) (here we adopt a median appropriate for the median gas fractions of the model galaxies), and from the dependence on merger mass ratio as calibrated in Lotz et al. (2009b)…”
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).”
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).”
Morphologies of z ∼ 0.7 AGN host galaxies in CANDELS: no trend of merger incidence with AGN luminosity (2014, background): “Theoretical models generally predict a delay of about 100 Myr between coalescence and the peak quasar activity (see e.g. Di Matteo et al. 2005; Hopkins et al. 2008), which is a time-scale on which merger signatures should stay very apparent (Lotz et al. 2010a,b).”
ON SIZES, KINEMATICS, M/L GRADIENTS, AND LIGHT PROFILES OF MASSIVE COMPACT GALAXIES AT z ∼ 2 (2010, background): “The timescales of a morphological merger signature depend on mass ratio (Lotz et al. 2010a) and gas fraction (Lotz et al. 2010b) of the merger.”