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Modelling ISO galaxy counts with luminosity and merger rate evolution

Roche, N. and Eales, Stephen Anthony 1999. Modelling ISO galaxy counts with luminosity and merger rate evolution. Monthly Notices of the Royal Astronomical Society 307 (1) , pp. 111-121. 10.1046/j.1365-8711.1999.02630.x

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We model galaxy evolution in the 6.75- and 15-μm passbands of the ISO satellite, by combining models of galaxy evolution at optical wavelengths (which are consistent with the optical galaxy counts) with observed spectral energy distributions in the infrared. Our model is consistent with the local 12-μm galaxy luminosity function (from IRAS), including the bright end if we place a small fraction (∼3.5 per cent at z=0) of the model's spiral galaxies in interacting pairs with mid-infrared luminosities enhanced by major starbursts. Source counts from deep ISO surveys in the 6.75- and 15-μm passbands significantly exceed non-evolving predictions. We find the number counts, redshift distributions and the wide range of mid-infrared/optical flux ratios of the detected galaxies to be reasonably consistent with our evolving model. Our models suggest that the steep number count of 6.75-μm sources can be explained primarily by the evolving E/S0 galaxies. About one-third of 6.75-μm sources do appear to be E/S0s or early-type spirals, but starburst galaxies at 0.6<z<1.1 are more prominent in this passband than we expected. In the 15-μm passband the main contributors appear to be evolving, star-forming spirals and starbursting galaxy mergers, as in our model. Visibly interacting galaxies form ∼31 per cent of the 15-μm detections to 200 μJy, and have high mid-infrared/optical flux ratios consistent with our models for major starbursts with high dust extinction (up to ∼1.8 mag in the rest-frame blue band). The numbers and high mean redshift (0.68±0.08) of merging/interacting galaxies detected in these ISO surveys are only consistent with the local mid-infrared luminosity function if the merger-triggered starbursts undergo significant luminosity evolution, of ∼(1+z)2 to z∼1, in addition to the ∼(1+z)2 number evolution reflecting the increase with redshift in the fraction of merging/interacting galaxies (as estimated from optical surveys).

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Uncontrolled Keywords: methods: miscellaneous; galaxies: evolution; infrared: galaxies
Publisher: Oxford Journals
ISSN: 0035-8711
Last Modified: 04 Jun 2017 04:59

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