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The properties of submm galaxies in hierarchical models

Swinbank, A. M. and Lacey, C. G. and Smail, Ian and Baugh, C. M. and Frenk, C. S. and Blain, A. W. and Chapman, S. C. and Coppin, K. E. K. and Ivison, R. J. and González, J. E. and Hainline, L. J. (2008) The properties of submm galaxies in hierarchical models. Monthly Notices of the Royal Astronomical Society, 391 (1). pp. 420-434. ISSN 0035-8711.

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We use the combined GALFORM semi-analytical model of galaxy formation and GRASIL spectrophotometric code to investigate the properties of galaxies selected via their submillimetre (submm) emission. The fiducial model we use has previously been shown to fit the properties of local Ultra-Luminous Infrared Galaxies, as well as the number counts of faint submm galaxies. Here, we test the model in more detail by comparing the SEDs and stellar, dynamical, gas and halo masses of submm galaxies against observational data. We precisely mimic the submm and radio selection function of the observations and show that the predicted far-infrared properties of model galaxies with S-850 > 5 mJy and S-1.4 > 30 μJy are in good agreement with observations. Although the dust emission model does not assume a single dust temperature, the far-infrared SEDs are well described by single component modified blackbody spectrum with characteristic temperature 32 +/- 5 K, in good agreement with observations. We also find evidence that the observations may have uncovered evolution in the far-infrared-radio relation in ULIRGs out to z similar to 2. We show that the predicted redshift distribution of submm galaxies provides a reasonable fit to the observational data with a median redshift z = 2.0. The radio-selected subset of submm galaxies are predicted to make up approximately 75 per cent of the population and peak at z = 1.7, in a reasonable agreement with the observed radio detected fraction and redshift distribution. However, the predicted K band and mid-infrared (3-8 μm) flux densities of the submm galaxies [and Lyman-Break Galaxies (LBGs)] are up to a factor of 10x fainter than observed. We show that including the stellar thermally pulsating asymptotic giant branch phase in the stellar population models does not make up for this deficit. This discrepancy may indicate that the stellar masses of the submm galaxies in the model are too low: M-star similar to 10^(10) M☉, while observations suggest more massive systems, M* greater than or similar to 10^(11) M☉. However, if the predicted K- and 3-8-μm extinctions in the model could be dramatically reduced, then this would reduce, but not eliminate, this discrepancy. Finally, we discuss the potential modifications to the models which may improve the fit to the observational data, as well as the new observational tests which will be made possible with the arrival of new facilities, such as Submillimetre Common-User Bolometer Array2.

Item Type:Article
Related URLs:
URLURL TypeDescription
Swinbank, A. M.0000-0003-1192-5837
Lacey, C. G.0000-0001-9016-5332
Smail, Ian0000-0003-3037-257X
Baugh, C. M.0000-0002-9935-9755
Frenk, C. S.0000-0002-2338-716X
Blain, A. W.0000-0001-7489-5167
Ivison, R. J.0000-0001-5118-1313
Additional Information:© 2008 The Authors. Journal compilation © 2008 RAS. Accepted 2008 September 1. Received 2008 July 25; in original form 2008 June 20. We would like to thank the anonymous referee for providing a number of suggestions which significantly improved the content and clarity of this paper. We thank Claudia Maraston for providing us with stellar population models with a top-heavy IMF and Laura Hainline and Thomas Greve for providing us with the IRAC and MAMBO photometry of SMGs prior to their publication. We thank John Helly and Liang Gao for calculating the merger rates and clustering lengths of haloes from the Millennium Simulation. We also gratefully acknowledge Dave Alexander, Richard Bower, Reinhard Genzel and Linda Tacconi for valuable discussions. AMS acknowledges an STFC fellowship. IRS and CMB acknowledge the Royal Society. This work was also supported by the STFC rolling grant for extragalactic astronomy and cosmology at Durham.
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
Subject Keywords:galaxies: evolution; galaxies: formation; galaxies: high-redshift; submillimetre
Issue or Number:1
Record Number:CaltechAUTHORS:SWImnras08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13249
Deposited By: Tony Diaz
Deposited On:05 Feb 2009 05:56
Last Modified:11 Dec 2020 23:16

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