JWST catches the assembly of a z ∼ 5 ultra-low-mass galaxy

Author:

Asada Yoshihisa12,Sawicki Marcin1,Desprez Guillaume1,Abraham Roberto3,Bradač Maruša4,Brammer Gabriel5,Harshan Anishya4ORCID,Iyer Kartheik67,Martis Nicholas S18ORCID,Mowla Lamiya6,Muzzin Adam9,Noirot Gaël1,Ravindranath Swara10,Sarrouh Ghassan T E9,Strait Victoria511,Willott Chris J8,Zabl Johannes1ORCID

Affiliation:

1. Department of Astronomy & Physics and Institute for Computational Astrophysics , Saint Mary’s University, 923 Robie Street, Halifax NS B3H 3C3, Canada

2. Department of Astronomy, Kyoto University , Sakyo-ku, Kyoto 606-8502, Japan

3. David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, Ontario M5S 3H4, Canada

4. University of Ljubljana, Department of Mathematics and Physics , Jadranska ulica 19, SI-1000 Ljubljana, Slovenia

5. Niels Bohr Institute, University of Copenhagen , Jagtvej 128, DK-2200 Copenhagen N, Denmark

6. Dunlap Institute for Astronomy and Astrophysics , 50 St. George Street, Toronto, Ontario M5S 3H4, Canada

7. Columbia Astrophysics Laboratory, Columbia University , 550 West 120th Street, New York, NY 10027, USA

8. National Research Council of Canada, Herzberg Astronomy & Astrophysics Research Centre , 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada

9. Department of Physics and Astronomy, York University , 4700 Keele St. Toronto, Ontario M3J 1P3, Canada

10. Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA

11. Cosmic Dawn Center (DAWN) , Denmark

Abstract

ABSTRACT Using CANUCS imaging we found an apparent major merger of two $z$ ∼ 5 ultra-low-mass galaxies (M⋆∼107M⊙ each) that are doubly imaged and magnified ∼12–15× by the lensing cluster MACS 0417. Both galaxies are experiencing young (∼100 Myr), synchronised bursts of star formation with log (sSFR/Gyr−1) ∼1.3–1.4, yet SFRs of just ∼0.2M⊙ yr−1. They have sub-solar (Z ∼ 0.2Z⊙) gas-phase metallicities and are connected by an even more metal-poor star-forming bridge. The galaxy that forms from the merger will have a mass of at least M⋆∼2 × 107 M⊙, at least half of it formed during the interaction-induced starburst. More than half of the ionizing photons produced by the system (before and during the merger) will have been produced during the burst. This system provides the first detailed look at a merger involving two high-$z$ ultra-low-mass galaxies of the type believed to be responsible for reionizing the Universe. It suggests that such galaxies can grow via a combination of mass obtained through major mergers, merger-triggered starbursts, and long-term in-situ star formation. If such high-$z$ mergers are common, then merger-triggered starbursts could be significant contributors to the ionizing photon budget of the Universe.

Funder

Natural Sciences and Engineering Research Council of Canada

ARRS

NASA

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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