Oral Presentation
JWST catches the mass assembly of z~5 ultra-low-mass galaxies
Presenter: Yoshihisa Asada (Kyoto Univ.)
The majority of ionizing photons produced at high redshift are thought to originate from galaxies with very low masses and luminosities significantly below L*. We will present an early result from the JWST GTO program CANUCS (CAnadian NIRISS Unbiased Cluster Survey) that identifies an apparent major merger of two z~5 such ultra-low-mass galaxies (Mstars ~ 10^7 Msun each) which are doubly imaged and magnified by ~12-15x by the massive lensing cluster MACS0417. Using our deep and high-resolution JWST/NIRCam observations, we found that the two galaxies are experiencing recent (~100 Myr), synchronized bursts of star formation likely triggered by the galaxy-galaxy encounter. The galaxies have sub-solar gas-phase metallicities (Z~0.2Zsun) and are connected by an even more metal-poor bridge-like structure. The galaxy that forms from the merger will have a stellar mass of at least ~2x10^7 Msun, at least half of it formed during the interaction-induced SF burst. Similarly, more than half of the ionizing photons produced by the system (before and during the merger) will have been produced during the SF burst. This system shows the power of JWST combined with gravitational lensing to study distant galaxies and provides the first detailed insights into a merger involving two high-z ultra-low-mass SF galaxies. It suggests that such merger-triggered bursts of star formation could be a major channel of galaxy growth and ionizing photon production in high-z low-mass galaxies of the kind thought to be responsible for reionizing the Universe.
asiaa.sinica.edu.tw