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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?

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?
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?

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 o and 20 ≤ star formation rate (SFR) ≤ 680 M o 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 o. 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.

galaxies: evolution, galaxies: high-redshift, galaxies: interactions, galaxies: ISM, galaxies: star formation
2041-8205
1-6
Puglisi, A.
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Daddi, E.
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Liu, D.
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Bournaud, F.
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Silverman, J. D.
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Circosta, C.
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Calabrò, A.
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Aravena, M.
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Cibinel, A.
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Dannerbauer, H.
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Delvecchio, I.
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Elbaz, D.
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Gao, Y.
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Gobat, R.
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Jin, S.
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Floc'H, E. Le
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Magdis, G. E.
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Mancini, C.
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Riechers, D. A.
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Rodighiero, G.
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Sargent, M.
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Valentino, F.
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Zanisi, L.
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Puglisi, A.
c4da7e1b-14d1-4ab1-98f5-654529162ee4
Daddi, E.
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Liu, D.
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Bournaud, F.
c0cdb312-34cd-4081-9772-c780f76ab207
Silverman, J. D.
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Circosta, C.
7e3da034-3374-4eff-8676-42b2e6eba7fe
Calabrò, A.
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Aravena, M.
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Cibinel, A.
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Dannerbauer, H.
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Delvecchio, I.
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Elbaz, D.
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Gao, Y.
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Gobat, R.
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Jin, S.
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Floc'H, E. Le
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Magdis, G. E.
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Mancini, C.
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Riechers, D. A.
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Rodighiero, G.
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Sargent, M.
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Valentino, F.
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Zanisi, L.
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Puglisi, A., Daddi, E., Liu, D., Bournaud, F., Silverman, J. D., Circosta, C., Calabrò, A., Aravena, M., Cibinel, A., Dannerbauer, H., Delvecchio, I., 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. and Zanisi, L. (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 Letters, 877 (2), 1-6, [L23]. (doi:10.3847/2041-8213/ab1f92).

Record type: Article

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 o and 20 ≤ star formation rate (SFR) ≤ 680 M o 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 o. 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.

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More information

Accepted/In Press date: 7 May 2019
e-pub ahead of print date: 29 May 2019
Keywords: galaxies: evolution, galaxies: high-redshift, galaxies: interactions, galaxies: ISM, galaxies: star formation

Identifiers

Local EPrints ID: 433857
URI: http://eprints.soton.ac.uk/id/eprint/433857
ISSN: 2041-8205
PURE UUID: 26cccb0a-9f4e-40d5-a32f-a73d56863f6f

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Date deposited: 04 Sep 2019 16:30
Last modified: 03 Feb 2021 17:38

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Contributors

Author: A. Puglisi
Author: E. Daddi
Author: D. Liu
Author: F. Bournaud
Author: J. D. Silverman
Author: C. Circosta
Author: A. Calabrò
Author: M. Aravena
Author: A. Cibinel
Author: H. Dannerbauer
Author: I. Delvecchio
Author: D. Elbaz
Author: Y. Gao
Author: R. Gobat
Author: S. Jin
Author: E. Le Floc'H
Author: G. E. Magdis
Author: C. Mancini
Author: D. A. Riechers
Author: G. Rodighiero
Author: M. Sargent
Author: F. Valentino
Author: L. Zanisi

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