The Extreme Star Formation Activity of Arp 299 Revealed by Spitzer IRS Spectral Mapping
Abstract
We present Spitzer/IRS spectral mapping observations of the luminous infrared galaxy Arp 299 (IC 694 + NGC 3690) covering the central ~45'' ~ 9 kpc. The integrated mid-IR spectrum of Arp 299 is similar to that of local starbursts despite its strongly interacting nature and high-IR luminosity, L IR ~ 6 × 1011 L sun. This is explained because the star formation (probed by, e.g., high [Ne III]15.56 μm/[Ne II]12.81 μm line ratios) is spread across at least 6-8 kpc. Moreover, a large fraction of this star formation is taking place in young regions of moderate mid-IR optical depths such as the C+C' complex in the overlap region between the two galaxies and in H II regions in the disks of the galaxies. It is only source A, the nuclear region of IC 694, which shows the typical mid-IR characteristics of ultraluminous infrared galaxies (ULIRGs; L IR > 1012 L sun), that is, very compact (less than 1 kpc) and dust-enshrouded star formation resulting in a deep silicate feature and moderate equivalent widths of the polycyclic aromatic hydrocarbons. The nuclear region of NGC 3690, known as source B1, hosts a low-luminosity active galactic nucleus (AGN) and is surrounded by regions of star formation. Although the high-excitation [Ne V]14.32 μm line typical of AGN is not detected in B1, its upper limit is consistent with the value expected from the X-ray luminosity. The AGN emission is detected in the form of a strong hot-dust component that accounts for 80%-90% of the 6 μm luminosity of B1. The similarity between the Arp 299 integrated mid-IR spectrum and those of high-z ULIRGs suggests that Arp 299 may represent a local example, albeit with lower IR luminosity and possibly higher metallicity, of the star formation processes occurring at high-z.
Based on observations obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407.- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2009
- DOI:
- 10.1088/0004-637X/697/1/660
- arXiv:
- arXiv:0903.1495
- Bibcode:
- 2009ApJ...697..660A
- Keywords:
-
- galaxies: evolution;
- galaxies: individual: Arp299;
- galaxies: nuclei;
- galaxies: Seyfert;
- galaxies: structure;
- infrared: galaxies;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted in ApJ