Modelling the Spectral Energy Distribution of compact luminous infrared galaxies: Constraints from high frequency radio data
Abstract
We have performed 23 GHz VLA observations of 7 compact, luminous infrared galaxies, selected as showing evidence of starburst activity. New and published multi-frequency data are combined to obtain the spectral energy distributions of all 7 galaxies from the near-infrared to the radio (at 1.4 GHz). These SEDs are compared with new models, for dust enshrouded galaxies, which account for both starburst and AGN components.
In all 7 galaxies the starburst provides the dominant contribution to the infrared luminosity; in 4 sources no contribution from an AGN is required. Although AGN may contribute up to 50 percent of the total far-infrared emission, the starbursts always dominate in the radio. The SEDs of most of our sources are best fit with a very high optical depth of ∼50 at 1 μm. The scatter in the far-infrared/radio correlation, found among luminous IRAS sources, is due mainly to the different evolutionary status of their starburst components. The short time-scale of the star formation process amplifies the delay between the far-infrared and radio emission. This becomes more evident at low radio frequencies (below about 1 GHz) where synchrotron radiation is the dominant process. In the far-infrared (at wavelengths shorter than 100 μm) an additional source of scatter is provided by AGN, when present. AGN may be detected in the near-infrared by the absence of the knee, typical of stellar photospheres. However, near-infrared data alone cannot constrain the level at which AGN contribute because the interpretation of their observed properties, in this wave-band, depends strongly on model parameters.- Publication:
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Astronomy and Astrophysics
- Pub Date:
- July 2004
- DOI:
- 10.1051/0004-6361:20035679
- arXiv:
- arXiv:astro-ph/0403581
- Bibcode:
- 2004A&A...421..115P
- Keywords:
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- ISM: dust;
- extinction;
- galaxies: stellar content;
- infrared: galaxies;
- radio continuum: galaxies;
- Astrophysics
- E-Print:
- 14 pages, accepted for publication in Astronomy and Astrophysics