Tracing the History of Star Formation and Accretion with a Deep Spitzer/Radio Survey

Details Tracing the History of Star Formation and Accretion with a Deep Spitzer/Radio Survey Tracing the History of Star Formation and Accretion with a Deep Spitzer/Radio Survey

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50162r&link_type=abstract

Spitzer Proposal ID #50162

Physics

Scientific paper

At the faint flux densities reached by the deepest radio surveys (<50uJy at 1.4GHz), thousands of sources are detected per square degree. Population models predict that most of the faintest radio sources should be star-forming galaxies (SFGs). Hence the deepest radio surveys offer an excellent method to examine star-formation out to z>2; a method that is free from many of the assumptions (e.g. dust attenuation) typically made when measuring star formation rates. However, a significant minority of the faint radio population is accretion powered (i.e. by AGN), and such objects must first be removed from the SFG sample before we can e.g. measure the cosmic star formation rate density. Determining the power source behind the faintest radio sources is difficult due to their typically low luminosities at optical/NIR wavelengths. We have explored a range of measures such as radio morphology, radio spectral index and radio-to-24um flux density ratio to determine the power source (AGN or SFG) for faint radio sources detected in our VLA/GMRT/MERLIN/Spitzer survey field. We find that the radio-to-24um flux density ratio discriminator is particularly effective at separating AGN and SFRG powered radio sources, but unfortunately our current 24um MIPS data are not sufficiently deep to allow secure classification of radio sources below ~100uJy - the flux range where SFGs are expected to become the dominant radio population. Therefore we request further deep MIPS observations of our field in order to apply the radio-to-24um discrimination method to our entire radio sample. With this Spitzer data we will be able to make an independent measure of the cosmic star-formation rate density, and determine the radio luminosity function of starforming galaxies to z~2.

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