Parametric modelling of the 3.6um to 8um colour distributions of galaxies in the SWIRE Survey

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dc.creatorDavoodi, Payam
dc.creatorOliver, Seb
dc.creatorPolletta, Maria del Carmen
dc.creatorRowan-Robinson, Michael
dc.creatorSavage, Richard S.
dc.creatorWaddington, Ian
dc.creatorFarrah, Duncan
dc.creatorBabbedge, Tom
dc.creatorLonsdale, Carol
dc.creatorEvans, Tracey
dc.creatorFang, Fan
dc.creatorGonzalez-Solares, Eduardo
dc.creatorJarrett, Tom
dc.creatorShupe, David L.
dc.creatorSiana, Brian
dc.creatorSmith, Harding E.
dc.creatorSurace, Jason
dc.creatorXu, C. Kevin
dc.date2006-04-20
dc.date.accessioned2026-07-07T11:25:31Z
dc.date.available2026-07-07T11:25:31Z
dc.descriptionWe fit a parametric model comprising a mixture of multi-dimensional Gaussian functions to the 3.6 to 8um colour and optical photo-z distribution of galaxy populations in the ELAIS-N1 and Lockman Fields of SWIRE. For 16,698 sources in ELAIS-N1 we find our data are best modelled (in the sense of the Bayesian Information Criterion) by the sum of four Gaussian distributions or modes (C_a, C_b, C_c and C_d). We compare the fit of our empirical model with predictions from existing semi-analytic and phenomological models. We infer that our empirical model provides a better description of the mid-infrared colour distribution of the SWIRE survey than these existing models. This colour distribution test is thus a powerful model discriminator and complementary to comparisons of number counts. We use our model to provide a galaxy classification scheme and explore the nature of the galaxies in the different modes of the model. C_a consists of dusty star-forming systems such as ULIRG's. Low redshift late-type spirals are found in C_b, where PAH emission dominates at 8um. C_c consists of dusty starburst systems at intermediate redshifts. Low redshift early-type spirals and ellipticals dominate C_d. We thus find a greater variety of galaxy types than one can with optical photometry alone. Finally we develop a new technique to identify unusual objects, and find a selection of outliers with very red IRAC colours. These objects are not detected in the optical, but have very strong detections in the mid-infrared. These sources are modelled as dust-enshrouded, strongly obscured AGN, where the high mid-infrared emission may either be attributed to dust heated by the AGN or substantial star-formation. These sources have z_ph ~ 2-4, making them incredibly infrared luminous, with a L_IR ~ 10^(12.6-14.1) L_sun.
dc.description44 pages, 10 figures, 6 tables. Accepted for publication in the Astronomical Journal
dc.identifierhttps://arxiv.org/abs/astro-ph/0604429
dc.identifierhttp://arxiv.org/abs/astro-ph/0604429
dc.identifierAstron.J.132:1818-1833,2006
dc.identifierdoi:10.1086/506385
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/195530
dc.subjectAstrophysics
dc.titleParametric modelling of the 3.6um to 8um colour distributions of galaxies in the SWIRE Survey
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