The Nuclear Interstellar Medium of Ultraluminous Infrared Galaxies
Abstract
We present sub-arcsecond resolution spectroscopic imaging of the prototypical ultraluminous infrared galaxies Arp 220 and NGC 6240 in the near-infrared H2 v = 1-0 S(1) line, combined with near-IR long slit spectroscopy and broad-band imaging from 1 to 10 microns. A crucial result is that in both of these objects the H2 emission peaks between the remnant stellar nuclei. We interpret this result as merging of the dissipative gas components (as a result of hydrodynamical processes) before the stellar components merge (as a result of dynamical friction). We show that the H2 emission is plausibly generated by ubiquitous cloud-cloud shocks in the very dense nuclear interstellar medium. We demonstrate how the H2 emission line flux provides a measure for the rate of inflow of molecular gas towards the centres of these systems. The inflow rate is sufficient to fuel the intense star formation in these nuclei. Alternatively, one may speculate that if star formation is inhibited by the large shear in the nuclear regions (as indicated by very high linewidths), a massive black hole may form in the nuclear concentration.
- Publication:
-
Galaxy Interactions at Low and High Redshift
- Pub Date:
- 1999
- Bibcode:
- 1999IAUS..186..303V