Merging Galaxies with Multiple Nuclei from HST ULIRGs Snapshot Survey

Abstract

Abstract.We perform photometric measurements on a large HST snapshot imaging survey sample of 97 ultraluminous infrared galaxies (ULIRGs). We classify all the sources into three categories with multiple, double and single nucleus/nuclei, mainly based on a quantitative criterion of I-band luminosity. The resultant fractions of multiple, double and single nucleus/nuclei ULIRGs are 18%, 39% and 43%, respectively. This supports the multiple merger scenario as a possible origin of ULIRGs, in addition to the commonly-accepted pair merger model. Further statistical studies indicate that the fraction of AGN increases from multiple (18%) to double (39%) and then to single (43%) nucleus/nuclei ULIRGs. For the single nucleus category, there is a high luminosity tail in the luminosity distribution, which corresponds to a Seyfert l/QSO excess. This supports the statement that active galactic nuclei tend to appear at final merging stage. For multiple and double mergers, we also find a considerably high fraction of very close nucleus pairs (e.g., 2/3 for those separated by less than 5 kpc). This strengthens the conclusion that systems at late merging phase preferentially host ULIRGs.

Galaxy Zoo: multimergers and the Millennium Simulation

“…In this paper, we introduce a new test for galaxy-evolution models that has, until now, been too difficult to find observationally: the fraction and properties of galaxies in (near simultaneous) multi-mergers (mergers of three or more galaxies of similar mass). Several individual multi-merger systems have been studied (Cui et al 2001;Amram et al 2007;Rines, Finn & Vikhlinin 2007) and a few numerical simulations of multi-mergers carried out (Weil & Herquist 1996;Bekki 2001;Renaud, Appleton & Xu 2010) but no practical method has been obtained till now that might locate multimergers in a near complete manner.…”