Abstract
Abstract
We present a Keck/MOSFIRE rest-optical composite spectrum of 16 typical gravitationally lensed star-forming dwarf galaxies at 1.7 ≲ z ≲ 2.6 (z
mean = 2.30), all chosen independent of emission-line strength. These galaxies have a median stellar mass of
log
(
M
*
/
M
⊙
)
med
=
8.29
−
0.43
+
0.51
and a median star formation rate of
S
F
R
H
α
m
e
d
=
2.25
−
1.26
+
2.15
M
⊙
y
r
−
1
. We measure the faint electron-temperature-sensitive [O iii] λ4363 emission line at 2.5σ (4.1σ) significance when considering a bootstrapped (statistical-only) uncertainty spectrum. This yields a direct-method oxygen abundance of
12
+
log
(
O
/
H
)
direct
=
7.88
−
0.22
+
0.25
(
0.15
−
0.06
+
0.12
Z
⊙
). We investigate the applicability at high z of locally calibrated oxygen-based strong-line metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strong-line ratio. At fixed M
*, our composite is well represented by the z ∼ 2.3 direct-method stellar mass—gas-phase metallicity relation (MZR) of Sanders et al. When comparing to predicted MZRs from the IllustrisTNG and FIRE simulations, having recalculated our stellar masses with more realistic nonparametric star formation histories
(
log
(
M
*
/
M
⊙
)
med
=
8.92
−
0.22
+
0.31
)
, we find excellent agreement with the FIRE MZR. Our composite is consistent with no metallicity evolution, at fixed M
* and SFR, of the locally defined fundamental metallicity relation. We measure the doublet ratio [O ii] λ3729/[O ii] λ3726 = 1.56 ± 0.32 (1.51 ± 0.12) and a corresponding electron density of
n
e
=
1
−
0
+
215
cm
−
3
(
n
e
=
1
−
0
+
74
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 z ∼ 2.
Funder
National Science Foundation
Publisher
American Astronomical Society
Subject
Space and Planetary Science,Astronomy and Astrophysics
Cited by
2 articles.
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