Dust and gas in luminous proto-cluster galaxies at z=4.05: the case for different cosmic dust evolution in normal and starburst galaxies

Tan, Q, Daddi, E, Magdis, G, Pannella, M, Sargent, M, Riechers, D, Béthermin, M, Bournaud, F, Carilli, C, da Cunha, E, Dannerbauer, H, Dickinson, M, Elbaz, D, Gao, Y, Hodge, J, Owen, F and Walter, F (2014) Dust and gas in luminous proto-cluster galaxies at z=4.05: the case for different cosmic dust evolution in normal and starburst galaxies. Astronomy and Astrophysics, 569. ISSN 0004-6361

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We measure the dust and gas content of the three sub-millimeter galaxies (SMGs) in the GN20 proto-cluster at z=4.05 using new IRAM Plateau de Bure interferometer (PdBI) CO(4-3) and 1.2-3.3mm continuum observations. All these three SMGs are heavily dust obscured, with UV-based star formation rate (SFR) estimates significantly smaller than the ones derived from the bolometric IR, consistent with the spatial offsets revealed by HST and CO imaging. Based also on evaluations of the specific SFR, CO-to-H2 conversion factor and gas depletion timescale, we classify all the three galaxies as starbursts (SBs), although with a lower confidence for GN20.2b that might be a later stage merging event. We place our measurements in the context of the evolutionary properties of main sequence (MS) and SB galaxies. ULIRGs have 3-5 times larger L′CO/Mdust and Mdust/M⋆ ratios than z=0 MS galaxies, but by z∼2 the difference appears to be blurred, probably due to differential metallicity evolution. SB galaxies appear to slowly evolve in their L′CO/Mdust and Mdust/M⋆ ratios all the way to z>6 (consistent with rapid enrichment of SB events), while MS galaxies rapidly increase in Mdust/M⋆ from z=0 to 2 (due to gas fraction increase, compensated by a decrease of metallicities). While no IR/submm continuum detection is available for indisputably normal massive galaxies at z>2.5, we show that if metallicity indeed decrease rapidly for these systems at z>3 as claimed in the literature, we should expect a strong decrease of their Mdust/M⋆, consistent with recent PdBI and ALMA upper limits. We conclude that the Mdust/M⋆ ratio could be a powerful tool for distinguishing starbursts from normal galaxies at z>4.

Item Type: Article
Keywords: Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy
Depositing User: Mark Sargent
Date Deposited: 08 Jan 2015 10:41
Last Modified: 07 Mar 2017 08:15
URI: http://sro.sussex.ac.uk/id/eprint/48775

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