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Optical and infrared diagnostics of SDSS galaxies in the SWIRE survey

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journal contribution
posted on 2023-06-12, 06:35 authored by P Davoodi, F Pozzi, Seb OliverSeb Oliver, M Polletta, A Afonso-Luis, D Farrah, E Hatziminaoglou, G Rodighiero, S Berta, I Waddington, C Lonsdale, M Rowan-Robinson, D L Shupe, T Evans, F Fang, H E Smith, J Surace
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 (SWIRE) Legacy Survey and the Sloan Digital Sky Survey (SDSS). We discuss the optical and infrared colours of our sample and analyse in detail the contribution of dusty star-forming galaxies and active galactic nuclei (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-disc ratio. The (g-r) colour is found to be sensitive to the bulge-to-disc ratio for disc-dominated galaxies, whereas the log(L24/L3.6) colour is more sensitive for bulge-dominated systems. We identify ~18 per cent (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 correspond to ~13 per cent of the total number density of our sample. In addition, these systems contribute ~13 per cent of the total optical luminosity density, and 28 per cent of the total infrared luminosity density of our SWIRE/SDSS sample. These objects may reduce the need for ‘dry mergers’.

History

Publication status

  • Published

File Version

  • Published version

Journal

Monthly Notices of the Royal Astronomical Society

ISSN

0035-8711

Publisher

Oxford University Press

Issue

3

Volume

371

Page range

1113-1124

Pages

12

Department affiliated with

  • Physics and Astronomy Publications

Notes

We identified a significant population of actively star-forming galaxies in the infrared that are apparently passive in the optical. Davoodi, my DPhil student, worked under my close guidance. The choice of this topic, subsequent direction, and interpretation was largely mine. Technical work came from Davoodi and Pozzi.

Full text available

  • Yes

Peer reviewed?

  • Yes

Legacy Posted Date

2012-02-06

First Open Access (FOA) Date

2016-03-22

First Compliant Deposit (FCD) Date

2016-11-16

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