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The MOSDEF Survey: Untangling the Emission-line Properties of z ∼ 2.3 Star-forming Galaxies

Runco, Jordan N. and Shapley, Alice E. and Sanders, Ryan L. and Topping, Michael W. and Kriek, Mariska and Reddy, Naveen A. and Coil, Alison L. and Mobasher, Bahram and Siana, Brian and Freeman, William R. and Shivaei, Irene and Azadi, Mojegan and Price, Sedona H. and Leung, Gene C. K. and Fetherolf, Tara and de Groot, Laura and Zick, Tom and Fornasini, Francesca M. and Barro, Guillermo (2020) The MOSDEF Survey: Untangling the Emission-line Properties of z ∼ 2.3 Star-forming Galaxies. . (Unpublished)

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We analyze the rest-optical emission-line spectra of z∼2.3 star-forming galaxies in the complete MOSFIRE Deep Evolution Field (MOSDEF) survey. In investigating the origin of the well-known offset between the sequences of high-redshift and local galaxies in the [O III]5008/Hβ vs. [N II]6585/Hα ("[N II] BPT") diagram, we define two populations of z∼2.3 MOSDEF galaxies. These include the "high" population that is offset towards higher [O III]5008/Hβ and/or [N II]6585/Hα with respect to the local SDSS sequence and the "low" population that overlaps the SDSS sequence. These two groups are also segregated within the [O III]5008/Hβ vs. [S II]6718,6733/Hα and the [O III]4960,5008/[O II]3727,3730 (O32) vs. ([O III]4960,5008+[O II]3727,3730)/Hβ (R23) diagram, which suggests qualitatively that star-forming regions in the more offset galaxies are characterized by harder ionizing spectra at fixed nebular oxygen abundance. We also investigate many galaxy properties of the split sample and find that the "high" sample is on average smaller in size and less massive, but has higher specific star-formation rate and star-formation-rate surface density values and is slightly younger compared to the "low" population. From Cloudy+BPASS photoionization models, we estimate that the "high" population has a lower stellar metallicity (i.e., harder ionizing spectrum) but slightly higher nebular metallicity and higher ionization parameter compared to the "low" population. While the "high" population is more α-enhanced (i.e., higher α/Fe) than the "low" population, both samples are significantly more α-enhanced compared to local star-forming galaxies with similar rest-optical line ratios. These differences must be accounted for in all high-redshift star-forming galaxies -- not only those "offset" from local excitation sequences.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Shapley, Alice E.0000-0003-3509-4855
Kriek, Mariska0000-0002-7613-9872
Reddy, Naveen A.0000-0001-9687-4973
Siana, Brian0000-0002-4935-9511
Freeman, William R.0000-0003-3559-5270
Price, Sedona H.0000-0002-0108-4176
Barro, Guillermo0000-0001-6813-875X
Additional Information:© 2020 The Authors. 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, and 1313171, grant AR-13907 from the Space Telescope Science Institute, and grant NNX16AF54G from the NASA ADAP program.We also acknowledge a NASA contract supporting the “WFIRST Extragalactic Potential Observations (EXPO) Science Investigation Team” (15-WFIRST15-0004), administered by GSFC. We thank the 3D-HST collaboration, who provided us with spectroscopic and photometric catalogs used to select MOSDEF targets and derive stellar population parameters. We acknowledge the First Carnegie Symposium in Honor of Leonard Searle for useful information and discussions that benefited this work. This research made use of Astropy,14 a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013, 2018). We finally wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:galaxies: evolution — galaxies: high-redshift – galaxies: ISM
Record Number:CaltechAUTHORS:20200901-070525641
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105188
Deposited By: Tony Diaz
Deposited On:08 Sep 2020 19:32
Last Modified:08 Sep 2020 19:32

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