TY - JOUR

T1 - Balmer Break Galaxy Candidates at z ˜ 6

T2 - A Potential View on the Star Formation Activity at z ≳ 14

AU - Mawatari, Ken

AU - Inoue, Akio K.

AU - Hashimoto, Takuya

AU - Silverman, John

AU - Kajisawa, Masaru

AU - Yamanaka, Satoshi

AU - Yamada, Toru

AU - Davidzon, Iary

AU - Capak, Peter

AU - Lin, Lihwai

AU - Hsieh, Bau-Ching

AU - Taniguchi, Yoshiaki

AU - Tanaka, Masayuki

AU - Ono, Yoshiaki

AU - Harikane, Yuichi

AU - Sugahara, Yuma

AU - Fujimoto, Seiji

AU - Nagao, Tohru

PY - 2020/2/1

Y1 - 2020/2/1

N2 - We search for galaxies with a strong Balmer break (Balmer break galaxies; BBGs) at z ˜ 6 over a 0.41 deg2 effective area in the COSMOS field. Based on rich imaging data, including data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), three candidates are identified by their extremely red K–[3.6] colors, as well as by nondetection in the X-ray, optical, far-infrared, and radio bands. The nondetection in the deep ALMA observations suggests that they are not dusty galaxies but BBGs at z ˜ 6, although contamination from active galactic nuclei at z ˜ 0 cannot be completely ruled out for the moment. Our spectral energy distribution analyses reveal that the BBG candidates at z ˜ 6 have stellar masses of ≈5 × 1010 M⊙ dominated by old stellar populations with ages of ≳ 700 Myr. Assuming that all three candidates are real BBGs at z ˜ 6, we estimate the stellar mass density to be ${2.4}_{-1.3}^{+2.3}\times {10}^{4}\,{M}_{\odot }$ Mpc‑3. This is consistent with an extrapolation from the lower-redshift measurements. The onset of star formation in the three BBG candidates is expected to be several hundred million yr before the observed epoch of z ˜ 6. We estimate the star formation rate density (SFRD) contributed by progenitors of the BBGs to be 2.4–12 × 10‑5 M⊙ yr‑1 Mpc‑3 at z > 14 (99.7% confidence range). Our result suggests a smooth evolution of the SFRD beyond z = 8.

AB - We search for galaxies with a strong Balmer break (Balmer break galaxies; BBGs) at z ˜ 6 over a 0.41 deg2 effective area in the COSMOS field. Based on rich imaging data, including data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), three candidates are identified by their extremely red K–[3.6] colors, as well as by nondetection in the X-ray, optical, far-infrared, and radio bands. The nondetection in the deep ALMA observations suggests that they are not dusty galaxies but BBGs at z ˜ 6, although contamination from active galactic nuclei at z ˜ 0 cannot be completely ruled out for the moment. Our spectral energy distribution analyses reveal that the BBG candidates at z ˜ 6 have stellar masses of ≈5 × 1010 M⊙ dominated by old stellar populations with ages of ≳ 700 Myr. Assuming that all three candidates are real BBGs at z ˜ 6, we estimate the stellar mass density to be ${2.4}_{-1.3}^{+2.3}\times {10}^{4}\,{M}_{\odot }$ Mpc‑3. This is consistent with an extrapolation from the lower-redshift measurements. The onset of star formation in the three BBG candidates is expected to be several hundred million yr before the observed epoch of z ˜ 6. We estimate the star formation rate density (SFRD) contributed by progenitors of the BBGs to be 2.4–12 × 10‑5 M⊙ yr‑1 Mpc‑3 at z > 14 (99.7% confidence range). Our result suggests a smooth evolution of the SFRD beyond z = 8.

U2 - 10.3847/1538-4357/ab6596

DO - 10.3847/1538-4357/ab6596

M3 - Journal article

VL - 889

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 137

ER -