TY - JOUR
T1 - The MOSDEF Survey
T2 - Metallicity Dependence of PAH Emission at High Redshift and Implications for 24 μm Inferred IR Luminosities and Star Formation Rates at z ∼ 2
AU - Shivaei, Irene
AU - Reddy, Naveen A.
AU - Shapley, Alice E.
AU - Siana, Brian
AU - Kriek, Mariska
AU - Mobasher, Bahram
AU - Coil, Alison L.
AU - Freeman, William R.
AU - Sanders, Ryan L.
AU - Price, Sedona H.
AU - Azadi, Mojegan
AU - Zick, Tom
N1 - Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved.
PY - 2017/3/10
Y1 - 2017/3/10
N2 - We present results on the variation of 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission in galaxies spanning a wide range in metallicity at z ∼ 2. For this analysis, we use rest-frame optical spectra of 476 galaxies at 1.37 ≤ z ≤ 2.61 from the MOSFIRE Deep Evolution Field (MOSDEF) survey to infer metallicities and ionization states. Spitzer/MIPS 24 μm and Herschel/PACS 100 and 160 μm observations are used to derive rest-frame 7.7 μm luminosities (L7.7) and total IR luminosities (LIR), respectively. We find significant trends between the ratio of L7.7 to LIR (and to dust-corrected star formation rate [SFR]) and both metallicity and [O iii]/[O ii] (O32) emission line ratio. The latter is an empirical proxy for the ionization parameter. These trends indicate a paucity of PAH emission in low-metallicity environments with harder and more intense radiation fields. Additionally L7.7, is significantly lower in the youngest quartile of our sample (ages of ≲500 Myr) compared to older galaxies, which may be a result of the delayed production of PAHs by AGB stars. The relative strength of L7.7 to LIR is also lower by a factor of ∼2 for galaxies with masses M∗ ∼ 109.6-10.0, compared to the more massive ones. We demonstrate that commonly used conversions of (or 24 μm flux density, f 24) to underestimate the IR luminosity by more than a factor of 2 at . We adopt a mass-dependent conversion of to with = 0.09 and 0.22 for M∗ ≤ 1010 and > 1010M⊙, respectively. Based on the new scaling, the SFR-M ∗ relation has a shallower slope than previously derived. Our results also suggest a higher IR luminosity density at z ∼ 2 than previously measured, corresponding to a ∼30% increase in the SFR density.
AB - We present results on the variation of 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission in galaxies spanning a wide range in metallicity at z ∼ 2. For this analysis, we use rest-frame optical spectra of 476 galaxies at 1.37 ≤ z ≤ 2.61 from the MOSFIRE Deep Evolution Field (MOSDEF) survey to infer metallicities and ionization states. Spitzer/MIPS 24 μm and Herschel/PACS 100 and 160 μm observations are used to derive rest-frame 7.7 μm luminosities (L7.7) and total IR luminosities (LIR), respectively. We find significant trends between the ratio of L7.7 to LIR (and to dust-corrected star formation rate [SFR]) and both metallicity and [O iii]/[O ii] (O32) emission line ratio. The latter is an empirical proxy for the ionization parameter. These trends indicate a paucity of PAH emission in low-metallicity environments with harder and more intense radiation fields. Additionally L7.7, is significantly lower in the youngest quartile of our sample (ages of ≲500 Myr) compared to older galaxies, which may be a result of the delayed production of PAHs by AGB stars. The relative strength of L7.7 to LIR is also lower by a factor of ∼2 for galaxies with masses M∗ ∼ 109.6-10.0, compared to the more massive ones. We demonstrate that commonly used conversions of (or 24 μm flux density, f 24) to underestimate the IR luminosity by more than a factor of 2 at . We adopt a mass-dependent conversion of to with = 0.09 and 0.22 for M∗ ≤ 1010 and > 1010M⊙, respectively. Based on the new scaling, the SFR-M ∗ relation has a shallower slope than previously derived. Our results also suggest a higher IR luminosity density at z ∼ 2 than previously measured, corresponding to a ∼30% increase in the SFR density.
KW - ISM: molecules
KW - galaxies: ISM
KW - galaxies: general
KW - galaxies: high-redshift
KW - galaxies: star formation
KW - infrared: galaxies
UR - http://www.scopus.com/inward/record.url?scp=85015929760&partnerID=8YFLogxK
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U2 - 10.3847/1538-4357/aa619c
DO - 10.3847/1538-4357/aa619c
M3 - Article
AN - SCOPUS:85015929760
SN - 0004-637X
VL - 837
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 157
ER -