Far infrared and radio emission in dusty starburst galaxies

Free access article

Issue		A&A Volume 392, Number 2, September III 2002


Page(s)		377 - 391
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20020960

A&A 392, 377-391 (2002)
DOI: 10.1051/0004-6361:20020960

Far infrared and radio emission in dusty starburst galaxies

A. Bressan^{1, 2}, L. Silva³ and G. L. Granato^{1, 2}

¹ INAF, Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
² SISSA, Strada Costiera, 34131 Trieste, Italy
³ INAF, Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34131 Trieste, Italy

(Received 11 January 2002 / Accepted 31 May 2002)

Abstract
We revisit the nature of the far infrared (FIR)/radio correlation by means of the most recent models of star forming galaxies, focusing in particular on the case of obscured starbursts. We model the IR emission with our population synthesis code, GRASIL (Silva et al. 1998). For the radio emission, we revisit the simple model of Condon & Yin (1990). We find that a tight FIR/radio correlation is natural when the synchrotron mechanism dominates over the inverse Compton, and the electron cooling time is shorter than the fading time of the supernova (SN) rate. Observations indicate that both these conditions are met in star forming galaxies, from normal spirals to obscured starbursts. However, since the radio non-thermal (NT) emission is delayed, deviations are expected both in the early phases of a starburst, when the radio thermal component dominates, and in the post-starburst phase, when the bulk of the NT component originates from less massive stars. We show that this delay allows the analysis of obscured starbursts with a time resolution of a few tens of Myrs, unreachable with other star formation (SF) indicators. We suggest a strategy to complement the analysis of the deviations from the FIR/radio correlation with the radio slope ( q-radio slope diagram) to obtain characteristic parameters of the burst, e.g. its intensity, age and fading time scale. The analysis of a sample of compact ULIRGs shows that they are intense but transient starbursts, to which one should not apply usual SF indicators devised for constant SF rates. We also discuss the possibility of using the q-radio slope diagram to assess the presence of obscured AGN. A firm prediction of the models is an apparent radio excess during the post-starburst phase, which seems to be typical of a class of star forming galaxies in rich cluster cores. Finally we discuss how deviations from the correlation, due to the evolutionary status of the starburst, affect the technique of photometric redshift determination widely used for high- z sources.

Key words: ISM: dust, extinction -- galaxies: stellar content -- infrared: galaxies -- radio continuum: galaxies

Offprint request: A. Bressan, bressan@pd.astro.it

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.