The MOSDEF Survey: A Comprehensive Analysis of the Rest-optical Emission-line Properties of $zsim 2.3$ Star-forming Galaxies. (arXiv:2008.04924v2 [astro-ph.GA] UPDATED)

The MOSDEF Survey: A Comprehensive Analysis of the Rest-optical Emission-line Properties of $zsim 2.3$ Star-forming Galaxies. (arXiv:2008.04924v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Runco_J/0/1/0/all/0/1">Jordan N. Runco</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shapley_A/0/1/0/all/0/1">Alice E. Shapley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanders_R/0/1/0/all/0/1">Ryan L. Sanders</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Topping_M/0/1/0/all/0/1">Michael W. Topping</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kriek_M/0/1/0/all/0/1">Mariska Kriek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reddy_N/0/1/0/all/0/1">Naveen A. Reddy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Coil_A/0/1/0/all/0/1">Alison L. Coil</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mobasher_B/0/1/0/all/0/1">Bahram Mobasher</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Siana_B/0/1/0/all/0/1">Brian Siana</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Freeman_W/0/1/0/all/0/1">William R. Freeman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shivaei_I/0/1/0/all/0/1">Irene Shivaei</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Azadi_M/0/1/0/all/0/1">Mojegan Azadi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Price_S/0/1/0/all/0/1">Sedona H. Price</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Leung_G/0/1/0/all/0/1">Gene C. K. Leung</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fetherolf_T/0/1/0/all/0/1">Tara Fetherolf</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Groot_L/0/1/0/all/0/1">Laura de Groot</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zick_T/0/1/0/all/0/1">Tom Zick</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fornasini_F/0/1/0/all/0/1">Francesca M. Fornasini</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barro_G/0/1/0/all/0/1">Guillermo Barro</a>

We analyze the rest-optical emission-line spectra of $zsim2.3$ 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/H$beta$ vs. [N
II]6585/H$alpha$ (“[N II] BPT”) diagram, we define two populations of
$zsim2.3$ MOSDEF galaxies. These include the “high” population that is offset
towards higher [O III]5008/H$beta$ and/or [N II]6585/H$alpha$ 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/H$beta$
vs. [S II]6718,6733/H$alpha$ and the [O III]4960,5008/[O II]3727,3730
(O$_{32}$) vs. ([O III]4960,5008+[O II]3727,3730)/H$beta$ (R$_{23}$) 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 $alpha$-enhanced (i.e.,
higher $alpha$/Fe) than the “low” population, both samples are significantly
more $alpha$-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.

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