JWST catches the assembly of a $z\sim 5$ ultra-low-mass galaxy

Abstract

Using CANUCS imaging we found an apparent major merger of two $z\sim 5$ ultra-low-mass galaxies ($M_{\star }\sim 10^7{M}_{\odot }$ each) that are doubly imaged and magnified $\sim$12-15$\times$ by the lensing cluster MACS 0417. Both galaxies are experiencing young ($\sim$100 Myr), synchronised bursts of star formation with $\log (sSFR/Gy{\mathrm{r}}^{-1})\sim$1.3-1.4, yet SFRs of just $\sim 0.2M_{\odot }{\mathrm{yr}}^{-1}$. They have sub-solar ($Z\sim 0.2Z_{\odot }$) 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 $M_{\star }\sim 2\times 10^7{M}_{\odot }$, 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.

arXiv comment6 pages, 2 figures, and 1 table; accepted for publication in MNRAS Letter

References in corpus (22)

• Galactic Stellar and Substellar Initial Mass Function
• The Dust Content and Opacity of Actively Star-Forming Galaxies
• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign
• Reionization after Planck: The Derived Growth of the Cosmic Ionizing Emissivity now matches the Growth of the Galaxy UV Luminosity Density
• Rest-frame ultraviolet-to-optical spectral characteristics of extremely metal-poor and metal-free galaxies
• "Big Three Dragons": a z = 7.15 Lyman BreakGalaxy Detected in [OIII] 88 $\mu$m, [CII] 158 $\mu$m, and Dust Continuum with ALMA
• The Lyman-Continuum Photon Production Efficiency xi_{ion} of z~4-5 Galaxies from IRAC-based Halpha Measurements: Implications for the Escape Fraction and Cosmic Reionization
• MMT/MMIRS spectroscopy of $z=1.3-2.4$ extreme [OIII] emitters: Implications for galaxies in the reionization-era
• Non-parametric Star Formation History Reconstruction with Gaussian Processes I: Counting Major Episodes of Star Formation
• The production and escape of Lyman-Continuum radiation from star-forming galaxies at z~2 and their redshift evolution
• Reconstruction of Galaxy Star Formation Histories through SED Fitting: The Dense Basis Approach
• The triggering of starbursts in low-mass galaxies
• The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- II. Wide Field Slitless Spectroscopy
• EMPRESS. V. Metallicity Diagnostics of Galaxies over 12+log(O/H)=~6.9-8.9 Established by a Local Galaxy Census: Preparing for JWST Spectroscopy
• The Recent Burstiness of Star Formation in Galaxies at z~4.5 from H$\alpha$ Measurements
• Filamentary Infall of Cold Gas and Escape of Lyman Alpha and Hydrogen Ionizing Radiation from an Interacting High-Redshift Galaxy
• The ALPINE-ALMA [CII] survey: The contribution of major mergers to the galaxy mass assembly at z~5
• RELICS: Strong Lensing Analysis of MACS J0417.5-1154 and Predictions for Observing the Magnified High-Redshift Universe with JWST
• The Lives of High Redshift Mergers
• The time-scales of major mergers from simulations of isolated binary galaxy collisions
• Ionizing radiation from AGNs at z>3.3 with the Subaru Hyper Suprime-Cam Survey and the CFHT Large Area U-band Deep Survey (CLAUDS)

Cited by in corpus (11)

• Deciphering Lyman-$\alpha$ Emission Deep into the Epoch of Reionisation
• A First Look at Spatially Resolved Balmer Decrements at $1.0<z<2.4$ from JWST NIRISS Slitless Spectroscopy
• SPICE: the connection between cosmic reionisation and stellar feedback in the first galaxies
• Dead or Alive? How Bursty Star Formation and Patchy Dust Can Cause Temporary Quiescence in High Redshift Galaxies
• CANUCS: Constraining the MACS J0416.1-2403 Strong Lensing Model with JWST NIRISS, NIRSpec and NIRCam
• Detailed Study of Stars and Gas in a z = 8.3 Massive Merger with Extreme Dust Conditions
• Possible environmental quenching in an interacting little red dot pair at $z\sim 7$
• Unveiling the Cosmic Gems Arc at $z\sim 10$ with JWST NIRCam
• The COSMOS-Web Lens Survey (COWLS) III: forecasts versus data
• JWST's PEARLS: A z=6 quasar in a train-wreck galaxy merger system
• Gamma Analytical Modeling Evolution (GAME) I: The physical implications of deriving the stellar mass functions from z=0 to z=8