TY - JOUR
T1 - THE RELATION between [O III]/Hβ and SPECIFIC STAR FORMATION RATE in GALAXIES at z ∼ 2
AU - Dickey, Claire Mackay
AU - Van Dokkum, Pieter G.
AU - Oesch, Pascal A.
AU - Whitaker, Katherine E.
AU - Momcheva, Ivelina G.
AU - Nelson, Erica J.
AU - Leja, Joel
AU - Brammer, Gabriel B.
AU - Franx, Marijn
AU - Skelton, Rosalind E.
N1 - Funding Information:
This work is based on observations taken by the 3D-HST Treasury Program (GO 12177 and 12328) with the NASA/ ESA HST, which is operated by the Associations of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. C.M.D. thanks B.S. for support and many useful discussions. K.E.W. gratefully acknowledges support by NASA through Hubble Fellowship grant #HF2-51368.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS 5-26555.
Publisher Copyright:
© 2016. The American Astronomical Society. All rights reserved.
PY - 2016/9/1
Y1 - 2016/9/1
N2 - Recent surveys have identified a seemingly ubiquitous population of galaxies with elevated [O III]/Hβ emission line ratios at z > 1, although the nature of this phenomenon continues to be debated. The [O III]/Hβ line ratio is of interest because it is a main component of the standard diagnostic tools used to differentiate between active galactic nuclei and star-forming galaxies as well as the gas-phase metallicity indicators O23 and R23. Here, we investigate the primary driver of increased [O III]/Hβ ratios by median-stacking rest-frame optical spectra for a sample of star-forming galaxies in the 3D-HST survey in the redshift range z ∼ 1.4-2.2. Using N = 4220 star-forming galaxies, we stack the data in bins of mass and specific star formation rates (sSFRs), respectively. After accounting for stellar Balmer absorption, we measure [O III]λ5007 Å/Hβ down to M ∼ 109.2 M⊙ and sSFR ∼ 10-9.6 yr-1, greater than an order of magnitude lower than previous work at similar redshifts. We find an offset of 0.59 ± 0.05 dex between the median ratios at z ∼ 2 and z ∼ 0 at fixed stellar mass, in agreement with existing studies. However, with respect to sSFR, the z ∼ 2 stacks all lie within 1σ of the median SDSS ratios, with an average offset of only -0.06 ± 0.05. We find that the excitation properties of galaxies are tightly correlated with their sSFR at both z ∼ 2 and z ∼ 0, with a relation that appears to be roughly constant over the last 10 Gyr of cosmic time.
AB - Recent surveys have identified a seemingly ubiquitous population of galaxies with elevated [O III]/Hβ emission line ratios at z > 1, although the nature of this phenomenon continues to be debated. The [O III]/Hβ line ratio is of interest because it is a main component of the standard diagnostic tools used to differentiate between active galactic nuclei and star-forming galaxies as well as the gas-phase metallicity indicators O23 and R23. Here, we investigate the primary driver of increased [O III]/Hβ ratios by median-stacking rest-frame optical spectra for a sample of star-forming galaxies in the 3D-HST survey in the redshift range z ∼ 1.4-2.2. Using N = 4220 star-forming galaxies, we stack the data in bins of mass and specific star formation rates (sSFRs), respectively. After accounting for stellar Balmer absorption, we measure [O III]λ5007 Å/Hβ down to M ∼ 109.2 M⊙ and sSFR ∼ 10-9.6 yr-1, greater than an order of magnitude lower than previous work at similar redshifts. We find an offset of 0.59 ± 0.05 dex between the median ratios at z ∼ 2 and z ∼ 0 at fixed stellar mass, in agreement with existing studies. However, with respect to sSFR, the z ∼ 2 stacks all lie within 1σ of the median SDSS ratios, with an average offset of only -0.06 ± 0.05. We find that the excitation properties of galaxies are tightly correlated with their sSFR at both z ∼ 2 and z ∼ 0, with a relation that appears to be roughly constant over the last 10 Gyr of cosmic time.
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U2 - 10.3847/2041-8205/828/1/L11
DO - 10.3847/2041-8205/828/1/L11
M3 - Article
AN - SCOPUS:84987879935
SN - 2041-8205
VL - 828
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 1
M1 - L11
ER -