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Nebular Emission Line Ratios in z ≃ 2–3 Star-forming Galaxies with KBSS-MOSFIRE: Exploring the Impact of Ionization, Excitation, and Nitrogen-to-Oxygen Ratio

Strom, Allison L. and Steidel, Charles C. and Rudie, Gwen C. and Trainor, Ryan F. and Pettini, Max and Reddy, Naveen A. (2017) Nebular Emission Line Ratios in z ≃ 2–3 Star-forming Galaxies with KBSS-MOSFIRE: Exploring the Impact of Ionization, Excitation, and Nitrogen-to-Oxygen Ratio. Astrophysical Journal, 836 (2). Art. No. 164. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20170221-162631848

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Abstract

We present a detailed study of the rest-optical (3600–7000 Å) nebular spectra of ~380 star-forming galaxies at z ≃ 2–3, obtained with Keck/Multi-object Spectrometer for Infrared Exploration (MOSFIRE) as part of the Keck Baryonic Structure Survey (KBSS). The KBSS-MOSFIRE sample is representative of star-forming galaxies at these redshifts, with stellar masses M_* = M^9 – M^(11.5) M_⊙ and star formation rates SFR = 3–1000 M_⊙ yr^(-1). We focus on robust measurements of many strong diagnostic emission lines for individual galaxies: [O II]λλ3727, 3729, [Ne III]λ3869, Hβ, [O III]λλ 4960, 5008, [N II]λλ 6549, 6585, Hα, and [S II]λλ6718, 6732. Comparisons with observations of typical local galaxies from the Sloan Digital Sky Survey and between subsamples of KBSS-MOSFIRE show that high-redshift galaxies exhibit a number of significant differences in addition to the well-known offset in log([O III]λ5008/Hβ) and log([N II]λ6585/Hα). We argue that the primary difference between H II regions in z ~ 2.3 galaxies and those at z ~ 0 is an enhancement in the degree of nebular excitation, as measured by [O III]/Hβ and R23 ≡ log [([O III]λλ4960, 5008+[O II]λλ3727, 3729)/Hβ]. At the same time, KBSS-MOSFIRE galaxies are ~10 times more massive than z ~ 0 galaxies with similar ionizing spectra and have higher N/O (likely accompanied by higher O/H) at fixed excitation. These results indicate the presence of harder ionizing radiation fields at fixed N/O and O/H relative to typical z ~ 0 galaxies, consistent with Fe-poor stellar population models that include massive binaries, and highlight a population of massive, high-specific star formation rate galaxies at high redshift with systematically different star formation histories than galaxies of similar stellar mass today.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/836/2/164DOIArticle
http://iopscience.iop.org/article/10.3847/1538-4357/836/2/164PublisherArticle
https://arxiv.org/abs/1608.02587arXivDiscussion Paper
ORCID:
AuthorORCID
Strom, Allison L.0000-0001-6369-1636
Steidel, Charles C.0000-0002-4834-7260
Rudie, Gwen C.0000-0002-8459-5413
Trainor, Ryan F.0000-0002-6967-7322
Pettini, Max0000-0002-5139-4359
Reddy, Naveen A.0000-0001-9687-4973
Additional Information:© 2017 The American Astronomical Society. Received 2016 August 2; accepted 2017 January 16; published 2017 February 17. We are grateful to the referee for the thoughtful and constructive feedback provided during the review process. We also thank the organizers and attendees of the Carnegie Symposium in honor of Leonard Searle, “Understanding Nebular Emission in High-redshift Galaxies,” held at the Carnegie Observatories in Pasadena, for many interesting conversations that contributed to the work presented here. This work has been supported in part by a US National Science Foundation (NSF) Graduate Research Fellowship (ALS), by the NSF through grants AST-0908805 and AST-1313472 (CCS, ALS, RFT, GCR), and by an Alfred P. Sloan Research Fellowship (NAR). Finally, the authors wish to recognize and acknowledge the significant cultural role and reverence that the summit of Maunakea has within the indigenous Hawaiian community. We are privileged to have the opportunity to conduct observations from this mountain.
Group:Astronomy Department
Funders:
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
NSFAST-0908805
NSFAST-1313472
Alfred P. Sloan FoundationUNSPECIFIED
Subject Keywords:Cosmology: observations; galaxies: evolution; galaxies: high-redshift; galaxies: ISM; H ii regions; ISM: abundances
Issue or Number:2
Record Number:CaltechAUTHORS:20170221-162631848
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170221-162631848
Official Citation:Allison L. Strom et al 2017 ApJ 836 164
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74443
Collection:CaltechAUTHORS
Deposited By: Melissa Ray
Deposited On:22 Feb 2017 19:52
Last Modified:04 Dec 2019 23:07

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