Ultraluminous starbursts in major mergers

Abstract

We use numerical simulation to investigate the triggering of starbursts in merging disk galaxies. The properties of the merger-driven starbursts are sensitive to the structure of the progenitor galaxies; speci cally, to the amount of material in a dense central bulge. Galaxies without bulges develop bars shortly after their rst close passage, driving signi cant gas in ow and subsequent starbursts in the centers of the galaxies. These starbursts signi cantly deplete the star-forming gas, so that only relatively weak starbursts arise during the nal merger. By contrast, models of galaxies with central bulges show that a bulge acts to stabilize the galaxies against in ow and starbursts until the galaxies actually merge. At this time, strong dissipation leads to the formation of a massive central gas mass and an ensuing star formation rate two orders of magnitude greater than that in our isolated disk models. These starbursts are very short in duration, typically 50 Myr, suggesting that the rarity of ultraluminous infrared galaxies is a result of their being in a very short evolutionary phase, rather than special and rare formation conditions. The fact that these mergers display many of the properties of ultraluminous infrared galaxies { tidal features, double nuclei, massive compact gas concentrations, and extreme levels of starburst activity { suggests that merger-driven starbursts can explain the emission from many ultraluminous infrared galaxies without an active nucleus.

B2 0648+27: A radio galaxy in a major merger

“…Hibbard & van Gorkom 1996;Wilson 1996;Mihos & Hernquist 1994;Morganti et al 1997) This is presented in Fig. 6.…”

SDSS-IV MaNGA-resolved Star Formation and Molecular Gas Properties of Green Valley Galaxies: A First Look with ALMA and MaNGA

“…Recent IFU observations demonstrate that many nearby spiral galaxies show negative gradients in stellar ages and metallicities, supporting this inside-out picture (González Delgado et al 2014;Sánchez-Blázquez et al 2014;Li et al 2015;Belfiore et al 2017;Goddard et al 2017). On the other hand, if "nurture" dominates galaxy evolution, external processes such as ram-pressure stripping (Gunn & Gott 1972), high speed galaxy encounters (Moore et al 1996), galaxy mergers (Mihos & Hernquist 1994), and "strangulation" (Larson et al 1980;Balogh et al 2000;Peng et al 2015) are responsible for quenching. In this picture, star formation quenching is likely to occur globally or in the outer regions of galaxies first due to the lack of continuous supply for the cold gas reservoir.…”

Evidence of ongoing AGN-driven feedback in a quiescent post-starburst E+A galaxy

“…This can trigger an active galactic nucleus (AGN) that lasts as long as the gas supply from the galaxy is sufficient to maintain its activity (Mihos & Hernquist 1994;Bekki, Shioya & Couch 2001;Springel et al 2005;Springel, Di Matteo & Hernquist 2005b;Hopkins et al 2006). Various processes can quench the massive, ongoing, SF in such systems (negative feedback).…”