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?
Date Issued
2019
Author(s)
•
Daddi, E.
•
Liu, D.
•
Bournaud, F.
•
Silverman, J. D.
•
Circosta, C.
•
Calabrò, A.
•
Aravena, M.
•
Cibinel, A.
•
Dannerbauer, H.
•
•
Elbaz, D.
•
Gao, Y.
•
Gobat, R.
•
Jin, S.
•
Floc’h, E. Le
•
Magdis, G. E.
•
Mancini, C.
•
Riechers, D. A.
•
Rodighiero, G.
•
Sargent, M.
•
Valentino, F.
•
Zanisi, L.
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.
Volume
877
Issue
2
Start page
L23
Issn Identifier
2041-8205
Ads BibCode
2019ApJ...877L..23P
Rights
open.access
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