The Direct-Method Oxygen Abundance of Typical Dwarf Galaxies at Cosmic High-Noon. (arXiv:2208.05976v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Gburek_T/0/1/0/all/0/1">Timothy Gburek</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Siana_B/0/1/0/all/0/1">Brian Siana</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Alavi_A/0/1/0/all/0/1">Anahita Alavi</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Emami_N/0/1/0/all/0/1">Najmeh Emami</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Richard_J/0/1/0/all/0/1">Johan Richard</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Freeman_W/0/1/0/all/0/1">William R. Freeman</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Stark_D/0/1/0/all/0/1">Daniel P. Stark</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Snapp_Kolas_C/0/1/0/all/0/1">Christopher Snapp-Kolas</a> (1) ((1) University of California-Riverside, (2) IPAC-Caltech, (3) University of Minnesota-Twin Cities, (4) CRAL-Lyon, (5) Steward Observatory-University of Arizona)
We present a Keck/MOSFIRE, rest-optical, composite spectrum of 16 typical,
gravitationally-lensed, star-forming, dwarf galaxies at $1.7 lesssim z
lesssim 2.6$ ($z_{rm{mean}}=2.30$), all chosen independent of emission-line
strength. These galaxies have a median stellar mass of
log($M_ast$/$rm{M_odot}$)$_{rm{med}}$ = 8.29 and a median star formation
rate of $rm{SFR_{Halpha}^{med} = 2.25 M_odot yr^{-1}}$. We measure the
faint, electron-temperature-sensitive, [O III] $lambda$4363 emission line at
$2.5sigma$ ($4.1sigma$) significance when considering a bootstrapped
(statistical-only) uncertainty spectrum. This yields a direct-method oxygen
abundance of $12+log(rm{O/H})_{rm{direct}}=7.87^{+0.24}_{-0.22}$
($0.15^{+0.11}_{-0.06} rm{Z_odot}$). We investigate the applicability at
high-$z$ of locally-calibrated, oxygen-based, strong-line metallicity
relations, finding that the local reference calibrations of arXiv:1805.0822(4)
best reproduce ($lesssim 0.15$ dex) our composite metallicity at fixed
strong-line ratio. At fixed $M_ast$, our composite is well-represented by the
$z sim 2.3$ direct-method stellar mass$,-,$gas-phase metallicity relation
(MZR) of arXiv:1907.0001(3). When comparing to predicted MZRs from the
IllustrisTNG and FIRE simulations, we find excellent agreement with the FIRE
MZR. Our composite is consistent with no metallicity evolution, at fixed
$M_ast$ and SFR, of the locally-defined fundamental metallicity relation. We
measure the doublet ratio [O II] $lambda$3729/[O II] $lambda3726 = 1.56 pm
0.32$ ($1.51 pm 0.12$) and a corresponding electron density of $n_e =
1^{+152}_{-0} rm{cm^{-3}}$ ($n_e = 1^{+49}_{-0} rm{cm^{-3}}$) when
considering the bootstrapped (statistical-only) error spectrum. This result
suggests that lower-mass galaxies have lower densities than higher-mass
galaxies at at $z sim 2$.
We present a Keck/MOSFIRE, rest-optical, composite spectrum of 16 typical,
gravitationally-lensed, star-forming, dwarf galaxies at $1.7 lesssim z
lesssim 2.6$ ($z_{rm{mean}}=2.30$), all chosen independent of emission-line
strength. These galaxies have a median stellar mass of
log($M_ast$/$rm{M_odot}$)$_{rm{med}}$ = 8.29 and a median star formation
rate of $rm{SFR_{Halpha}^{med} = 2.25 M_odot yr^{-1}}$. We measure the
faint, electron-temperature-sensitive, [O III] $lambda$4363 emission line at
$2.5sigma$ ($4.1sigma$) significance when considering a bootstrapped
(statistical-only) uncertainty spectrum. This yields a direct-method oxygen
abundance of $12+log(rm{O/H})_{rm{direct}}=7.87^{+0.24}_{-0.22}$
($0.15^{+0.11}_{-0.06} rm{Z_odot}$). We investigate the applicability at
high-$z$ of locally-calibrated, oxygen-based, strong-line metallicity
relations, finding that the local reference calibrations of arXiv:1805.0822(4)
best reproduce ($lesssim 0.15$ dex) our composite metallicity at fixed
strong-line ratio. At fixed $M_ast$, our composite is well-represented by the
$z sim 2.3$ direct-method stellar mass$,-,$gas-phase metallicity relation
(MZR) of arXiv:1907.0001(3). When comparing to predicted MZRs from the
IllustrisTNG and FIRE simulations, we find excellent agreement with the FIRE
MZR. Our composite is consistent with no metallicity evolution, at fixed
$M_ast$ and SFR, of the locally-defined fundamental metallicity relation. We
measure the doublet ratio [O II] $lambda$3729/[O II] $lambda3726 = 1.56 pm
0.32$ ($1.51 pm 0.12$) and a corresponding electron density of $n_e =
1^{+152}_{-0} rm{cm^{-3}}$ ($n_e = 1^{+49}_{-0} rm{cm^{-3}}$) when
considering the bootstrapped (statistical-only) error spectrum. This result
suggests that lower-mass galaxies have lower densities than higher-mass
galaxies at at $z sim 2$.
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