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

Abstract

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.

Supernovae and their host galaxies – II. The relative frequencies of supernovae types in spirals

“…During the relatively short time-scale of the merging stage (∼ 0.5 Gyr), as predicted by numerical simulations (e.g. Di Matteo et al 2005;Lotz et al 2008), the spiral, gas-rich galaxies do not have enough time to produce many Type Ia SNe (lifetime > 0.5 Gyr), but can intensively produce CC SNe, assuming short lifetimes for the CC SNe progenitors (lifetime < 0.1 Gyr). Moreover, the positions of CC SNe in our merging hosts mostly coincide with circumnuclear regions and only in few cases with bright H II regions, which is in agreement with the previously found central excess of CC SNe in extremely disturbed or merging galaxies (e.g.…”

“…These levels of disturbance are arranged in an approximate chronological order, according to the different stages of interaction, and have their own time-scales and levels of star formation (e.g. Lotz et al 2008). Table 13 presents the values of the NIa/NCC and N Ibc /NII ratios as a function of disturbance level, and Fig.…”

“…Di Matteo et al 2005;Lotz et al 2008). The post-merging/remnant galaxies have enough time to produce many Type Ia SNe, but not enough high-mass star formation to produce sufficient number of CC SNe.…”

The accretion histories of brightest cluster galaxies from their stellar population gradients

“…The simulations of Naab et al (2014), predict that angular momentum mostly depends on the gas content of the galaxies involved in the interaction, suggesting that the slow or fast rotation could be a temporary state. Jimmy et al (2013), also find through photometric analysis (G − M20; Lotz et al 2008) that 40 per cent of the galaxies in the sample have undergone a minor merger within the last 0.2 Gyr.…”

“…They measured the effective radius by fitting a 2D de Vaucouleurs profile. They also analysed the presence of recent mergers using the Gini, and M20 coefficients (Lotz et al 2008). This method studies the distribution of light looking for irregularities that could indicate morphological signatures of mergers.…”