610-MHz observations of galaxy evolution

Details 610-MHz observations of galaxy evolution 610-MHz observations of galaxy evolution

Jun 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt.........3g&link_type=abstract

PhD Thesis, University of Cambridge, 2009

Computer Science

1

Scientific paper

The infrared / radio correlation is a tight relationship between the infrared and radio luminosities of star-forming galaxies, which is typically explained by relating both emission processes to the star formation rate. The infrared luminosity is dominated by dust-reprocessed stellar emission, and the radio luminosity dominated by synchrotron emission from electrons produced within supernova remnants, and accelerated within the galactic magnetic field. Any evolution in the correlation with redshift would imply a variation in one or more of these processes over time.
Four new deep 610-MHz radio surveys are presented, created with the Giant Metrewave Radio Telescope (GMRT). These surveys target regions which have been observed with the Spitzer Space Telescope in either the Spitzer extragalactic First Look Survey (xFLS), or the Spitzer Wide-area Infrared Extragalactic survey (SWIRE). Observation and data reduction techniques are described, and two problems with the GMRT are identified and corrected before the production of mosaics and source catalogues for each field. The 610-MHz differential source counts are calculated, and shown to be consistent with a flat- and steep-spectrum AGN population dominating at mJy flux densities, and a star-forming galaxy population dominating at sub-mJy flux densities and undergoing pure luminosity evolution between 0A sample of 235 galaxies at up to z˜1 with optical, infrared and radio detections and spectroscopic redshifts is created within the xFLS field. Observed flux densities are k-corrected in order to calculate rest-frame infrared and radio luminosities, using the known spectral energy distribution of each galaxy. A linear relationship is found between infrared and radio luminosity, and the k-corrected far-infrared / radio flux density ratio shown to be invariant with redshift out to z˜1. This is followed by a study in the SWIRE fields of 510 galaxies out to z=2, using photometric redshifts in order to expand the redshift range of the sample. No significant variation is found in the relationship between radio luminosity and star formation rate over this redshift range. A statistical study of galaxies which are below the radio detection threshold is then presented, using the technique of `stacking'. No variation is found in the strength of the infrared / radio correlation in galaxies with 24-μm flux density between 150 μJy and 2 mJy, or with 70 micron flux density between 10 and 100 mJy.
Finally, a study is presented of eight sources which have 1.4-GHz flux >1 mJy, but are undetected in the infrared. These Infrared-Faint Radio Sources' are compact (<20 kpc), and their optical, infrared and radio detections or upper limits are compared with the spectral energy distributions of well-studied local radio galaxies. They can be modelled successfully by considering them to be high-redshift (z≳4) Fanaroff-Riley Type II radio galaxies.

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