The MOSDEF survey: a new view of a remarkable z = 1.89 merger

Jordan N. Runco, Alice E. Shapley, Mariska Kriek, Michele Cappellari, Michael W. Topping, Ryan L. Sanders, Vasily I. Kokorev, Sedona H. Price, Naveen A. Reddy, Alison L. Coil, Bahram Mobasher, Brian Siana, Tom Zick, Georgios E. Magdis, Gabriel Brammer, James Aird

Research output: Contribution to journalArticlepeer-review


We present a detailed study of a galaxy merger taking place at z = 1.89 in the GOODS-S field. Here, we analyse Keck/MOSFIRE spectroscopic observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey along with multiwavelength photometry assembled by the 3D-HST survey. The combined data set is modelled to infer the past star formation histories (SFHs) of both merging galaxies. They are found to be massive, with log10(M∗/M⊙) > 11, with a close mass ratio satisfying the typical major-merger definition. Additionally, in the context of delayed-τ models, GOODS-S 43114, and GOODS-S 43683 have similar SFHs and low star formation rates (log10(SFR(SED)/M⊙ yr-1) < 1.0) compared to their past averages. The best-fitting model SEDs show elevated H δA values for both galaxies, indicating that their stellar spectra are dominated by A-type stars, and that star formation peaked ∼0.5-1 Gyr ago and has recently declined. Additionally, based on SED fitting both merging galaxies turned on and shut off star formation within a few hundred Myr of each other, suggesting that their bursts of star formation may be linked. Combining the SFHs and H δA results with recent galaxy merger simulations, we infer that these galaxies have recently completed their first pericentric passage and are moving apart. Finally, the relatively low second velocity moment of GOODS-S 43114, given its stellar mass suggests a disc-like structure. However, including the geometry of the galaxy in the modelling does not completely resolve the discrepancy between the dynamical and stellar masses. Future work is needed to resolve this inconsistency in mass.

Original languageEnglish
Pages (from-to)4405-4416
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Dec 1 2022

Bibliographical note

Funding Information:
This study is based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration, and was made possible by the generous financial support of the W.M. Keck Foundation. We acknowledge support from NSF AAG grants AST1312780, 1312547, 1312764, 1313171, 2009313, 2009085, 2009278, grant AR-13907 from the Space Telescope Science Institute, and grant NNX16AF54G from the NASA ADAP programme. We also acknowledge a NASA contract supporting the 'WFIRST Extragalactic Potential Observations (EXPO) Science Investigation Team' (15-WFIRST15-0004), administered by GSFC. Support for this work was also provided through the NASA Hubble Fellowship grant # HST - HF2-51469.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. We thank the 3D-HST collaboration, who provided spectroscopic and photometric catalogues used to select MOSDEF targets and to derive stellar population parameters. We acknowledge useful conversations with Ian Smail that benefited this work. This research made use of ASTROPY, 9 a community-developed core PYTHON package for Astronomy (Astropy Collaboration 2013, 2018 ). Finally, we wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests.

Publisher Copyright:
© 2022 The Author(s).


  • galaxies: evolution
  • galaxies: high-redshift
  • galaxies: interactions

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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