TY - JOUR
T1 - MMT spectroscopy of Lyman-alpha at z ≃ 7
T2 - Evidence for accelerated reionization around massive galaxies
AU - Endsley, Ryan
AU - Stark, Daniel P.
AU - Charlot, Stéphane
AU - Chevallard, Jacopo
AU - Robertson, Brant
AU - Bouwens, Rychard J.
AU - Stefanon, Mauro
N1 - Publisher Copyright:
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
PY - 2021/4/1
Y1 - 2021/4/1
N2 - Reionization-era galaxies tend to exhibit weak Ly α emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this picture, with strong Ly α emission now known in four of the most massive z = 7-9 galaxies in the CANDELS fields, all of which also exhibit intense [O iii]+H β emission (EW > 800 Å). To better understand why Ly α is anomalously strong in a subset of massive z ≃ 7-9 galaxies, we have initiated an MMT/Binospec survey targeting a larger sample (N = 22) of similarly luminous (≃1-6 L$^{\ast }_{\mathrm{UV}}$) z ≃7 galaxies selected over very wide-area fields (∼3 deg2). We confidently (>7σ) detect Ly α in 78 per cent (7/9) of galaxies with strong [O iii]+H β emission (EW > 800 Å) as opposed to only 8 per cent (1/12) of galaxies with more moderate (EW = 200-800 Å) [O iii]+H β. We argue that the higher Ly α EWs of the strong [O iii]+H β population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs (≳30 Gyr-1). We also find evidence that Ly α transmission from massive galaxies declines less rapidly over 6 < z < 7 than in low-mass lensed systems. In particular, our data suggest no strong evolution in Ly α transmission, consistent with a picture wherein massive z ≃ 7 galaxies often reside in large ionized regions. We detect three closely separated (R = 1.7 physical Mpc) z ≃ 7 Ly α emitters in our sample, conceivably tracing a large ionized structure that is consistent with this picture. We detect tentative evidence for an overdensity in this region, implying a large ionizing photon budget in the surrounding volume.
AB - Reionization-era galaxies tend to exhibit weak Ly α emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this picture, with strong Ly α emission now known in four of the most massive z = 7-9 galaxies in the CANDELS fields, all of which also exhibit intense [O iii]+H β emission (EW > 800 Å). To better understand why Ly α is anomalously strong in a subset of massive z ≃ 7-9 galaxies, we have initiated an MMT/Binospec survey targeting a larger sample (N = 22) of similarly luminous (≃1-6 L$^{\ast }_{\mathrm{UV}}$) z ≃7 galaxies selected over very wide-area fields (∼3 deg2). We confidently (>7σ) detect Ly α in 78 per cent (7/9) of galaxies with strong [O iii]+H β emission (EW > 800 Å) as opposed to only 8 per cent (1/12) of galaxies with more moderate (EW = 200-800 Å) [O iii]+H β. We argue that the higher Ly α EWs of the strong [O iii]+H β population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs (≳30 Gyr-1). We also find evidence that Ly α transmission from massive galaxies declines less rapidly over 6 < z < 7 than in low-mass lensed systems. In particular, our data suggest no strong evolution in Ly α transmission, consistent with a picture wherein massive z ≃ 7 galaxies often reside in large ionized regions. We detect three closely separated (R = 1.7 physical Mpc) z ≃ 7 Ly α emitters in our sample, conceivably tracing a large ionized structure that is consistent with this picture. We detect tentative evidence for an overdensity in this region, implying a large ionizing photon budget in the surrounding volume.
KW - dark ages, reionization, first stars
KW - galaxies: evolution
KW - galaxies: high-redshift
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U2 - 10.1093/mnras/stab432
DO - 10.1093/mnras/stab432
M3 - Article
AN - SCOPUS:85105143876
VL - 502
SP - 6044
EP - 6063
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 4
ER -