The main sequence at z ∼ 1.3 contains a sizable fraction of galaxies with compact star formation sizes: a new population of early post-starbursts?

Puglisi, A, Daddi, E, Liu, D, Bournaud, F, Silverman, J D, Circosta, C, Calbrò, A, Aravena, M, Cibinel, Anna, Dannernauer, H, Delvecchio, I, Elbaz, D, Gao, Y, Gobat, R, Jin, S, Le Floc'h, E, Magdis, G E, Mancini, C, Riechers, D A, Rodighiero, G and Sargent, Mark (2019) The main sequence at z ∼ 1.3 contains a sizable fraction of galaxies with compact star formation sizes: a new population of early post-starbursts? Astrophysical Journal, 877 (L23). pp. 1-6. ISSN 0004-637X

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Abstract

Atacama Large Millimeter/submillimeter Array (ALMA) measurements for 93 Herschel-selected galaxies at 1.1 ≤ z ≤ 1.7 in COSMOS reveal a sizable (>29%) population with compact star formation (SF) sizes, lying on average >×3.6 below the optical stellar mass (M ⋆)─size relation of disks. This sample widely spans the star-forming main sequence (MS), having 108 ≤ M ⋆ ≤ 1011.5 M ☉ and 20 ≤ star formation rate (SFR) ≤ 680 M ☉ yr−1. The 32 size measurements and 61 upper limits are measured on ALMA images that combine observations of CO(5─4), CO(4─3), CO(2─1), and λ obs ∼ 1.1─1.3 mm continuum, all tracing the star-forming molecular gas. These compact galaxies have instead normally extended K band sizes, suggesting strong specific SFR gradients. Compact galaxies comprise the 50 ± 18% of MS galaxies at M ⋆ > 1011 M ☉. This is not expected in standard bimodal scenarios, where MS galaxies are mostly steadily growing extended disks. We suggest that compact MS objects are early post-starburst galaxies in which the merger-driven boost of SF has subsided. They retain their compact SF size until either further gas accretion restores premerger galaxy-wide SF, or until becoming quenched. The fraction of merger-affected SF inside the MS seems thus larger than anticipated and might reach ∼50% at the highest M ⋆. The presence of large galaxies above the MS demonstrates an overall poor correlation between galaxy SF size and specific SFR.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Research Centres and Groups: Astronomy Centre
Subjects: Q Science > QB Astronomy
Depositing User: Mark Sargent
Date Deposited: 17 Jun 2019 15:35
Last Modified: 01 Jul 2019 12:30
URI: http://sro.sussex.ac.uk/id/eprint/84345

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