Optical and Infrared Diagnostics of SDSS galaxies in the SWIRE Survey

Oliver, S., Davoodi, P., Pozzi, F., Polletta, M., Afonso-Luis, A., Farrah, D., Hatziminaoglou, E., Rodighiero, G., Berta, S., Waddington, I., Lonsdale, C., Rowan-Robinson, M., Shupe, D.L., Evans, T., Fang, F., Smith, H.E. and Surace, J. (2006) Optical and Infrared Diagnostics of SDSS galaxies in the SWIRE Survey. Monthly Notices of the Royal Astronomical Society, 371 (3). pp. 1113-1124. ISSN 0035-8711

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We present the rest-frame optical and infrared colours of a complete sample of 1114 z<0.3 galaxies from the Spitzer Wide-area InfraRed Extragalactic Legacy Survey (SWIRE) and the Sloan Digital Sky Survey (SDSS). We discuss the optical and in frared colours of our sample and analyse in detail the contribution of dusty star forming galaxies and AGN to optically selected red sequence galaxies. We propose that the optical (g-r) colour and infrared log(L24/L3.6) colour of galaxies in our sample are determined primarily by a bulge-to-disk ratio. The (g-r) colour is found to be sensitive to the bulge-to-disk ratio for disk-dominated galaxies, whereas the log(L24/L3.6) colour is more sensitive for bulge-dominated systems. We identify 18% (195 sources) of our sample as having red optical colours and infrared excess. Typically, the infrared luminosities of these galaxies are found to be at the high end of star-forming galaxies with blue optical colours. Using emission line diagnostic diagrams, 78 are found to have an AGN contribution, and 117 are identified as star-forming systems. The red (g-r) colour of the star-forming galaxies could be explained by extinction. However, their high optical luminosities cannot. We conclude that they have a significant bulge component. The number densities of optically red star-forming galaxies are found to corre- spond to 13% of the total number density of our sample. In addition, these systems contribute 13% of the total optical luminosity density, and 28% of the total infrared luminosity density of our SWIRE/SDSS sample. These objects may reduce the need for “dry-mergers”.

Item Type: Article
Additional Information: The definitive version is available at www.blackwell-synergy.com
Keywords: galaxies: evolution – galaxies: formation – infrared: galaxies – galaxies: elliptical and lenticular, cD
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QC Physics
Depositing User: Gemma Farrell
Date Deposited: 14 Mar 2008
Last Modified: 07 Mar 2017 07:04
URI: http://sro.sussex.ac.uk/id/eprint/1709
Google Scholar:25 Citations

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