TY - JOUR
T1 - Rest-frame optical emission lines in z ∼ 3.5 Lyman-break-selected galaxies
T2 - the ubiquity of unusually high [OIII]/Hβ ratios at 2 Gyr
AU - Holden, B. P.
AU - Oesch, P. A.
AU - González, V. G.
AU - Illingworth, G. D.
AU - Labbé, I.
AU - Bouwens, R.
AU - Franx, M.
AU - Van Dokkum, P.
AU - Spitler, L.
PY - 2016/3/20
Y1 - 2016/3/20
N2 - We present K-band spectra of rest-frame optical emission lines for 24 star-forming galaxies at z ∼ 3.2-3.7 using MOSFIRE on the Keck I telescope. Strong rest-frame optical [OIII] and Hβ emission lines were detected in 18 Lyman break galaxies (LBGs). The median flux ratio of [OIII]λ5007 to Hβ is 5.1+0.5-0.5. This is a factor of 5-10 times higher than in local galaxies with similar stellar masses. None of our sources are detected in deep X-ray stacks, ruling out significant contamination by active galactic nuclei. Combining our sample with a variety of LBGs from the literature, including 49 galaxies selected in a very similar manner, we find a high median ratio of [OIII]/Hβ = 4.8+0.8-1.7. This high ratio seems to be a ubiquitous feature of z ∼ 3-4 LBGs, very different from typical local star-forming galaxies at similar stellar masses. The only comparable systems at z ∼ 0 are those with similarly high specific star formation rates (SSFRs), though ∼5 times lower stellar masses. High SSFRs may result in a higher ionization parameter, higher electron density, or harder ionizing radiation, which, combined different elemental abundances, result in a much higher [OIII]/Hβ line ratio. This implies a strong relation between a global property of a galaxy, the SSFR, and the local conditions of ISM in star-forming regions.
AB - We present K-band spectra of rest-frame optical emission lines for 24 star-forming galaxies at z ∼ 3.2-3.7 using MOSFIRE on the Keck I telescope. Strong rest-frame optical [OIII] and Hβ emission lines were detected in 18 Lyman break galaxies (LBGs). The median flux ratio of [OIII]λ5007 to Hβ is 5.1+0.5-0.5. This is a factor of 5-10 times higher than in local galaxies with similar stellar masses. None of our sources are detected in deep X-ray stacks, ruling out significant contamination by active galactic nuclei. Combining our sample with a variety of LBGs from the literature, including 49 galaxies selected in a very similar manner, we find a high median ratio of [OIII]/Hβ = 4.8+0.8-1.7. This high ratio seems to be a ubiquitous feature of z ∼ 3-4 LBGs, very different from typical local star-forming galaxies at similar stellar masses. The only comparable systems at z ∼ 0 are those with similarly high specific star formation rates (SSFRs), though ∼5 times lower stellar masses. High SSFRs may result in a higher ionization parameter, higher electron density, or harder ionizing radiation, which, combined different elemental abundances, result in a much higher [OIII]/Hβ line ratio. This implies a strong relation between a global property of a galaxy, the SSFR, and the local conditions of ISM in star-forming regions.
KW - galaxies: evolution
KW - galaxies: high-redshift
KW - galaxies: star formation
KW - techniques: spectroscopic
UR - http://www.scopus.com/inward/record.url?scp=84961645027&partnerID=8YFLogxK
U2 - 10.3847/0004-637X/820/1/73
DO - 10.3847/0004-637X/820/1/73
M3 - Article
AN - SCOPUS:84961645027
VL - 820
SP - 1
EP - 13
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 73
ER -