Balmer Break Galaxy Candidates at z ∼ 6: A Potential View on the Star Formation Activity at z ≳ 14

Creators: Mawatari, Ken; Inoue, Akio K.; Hashimoto, Takuya; Silverman, John; Kajisawa, Masaru; Yamanaka, Satoshi; Yamada, Toru; Davidzon, Iary; Capak, Peter; Lin, Lihwai; Hsieh, Bau-Ching; Taniguchi, Yoshiaki; Tanaka, Masayuki; Ono, Yoshiaki; Harikane, Yuichi; Sugahara, Yuma; Fujimoto, Seiji; Nagao, Tohru

Abstract

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) x {10⁴ M_⊙ 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.

Additional Information

© 2020. The American Astronomical Society. Received 2019 June 28; revised 2019 December 20; accepted 2019 December 23; published 2020 February 3. K.M. and A.K.I. acknowledge financial support from the Japan Society for the Promotion of Science (JSPS) through KAKENHI grant Nos. 26287034 and 17H01114, and grant No. 2016-01. T.H. was supported by Leading Initiative for Excellent Young Researchers, MEXT, Japan. Y.T. is supported by JSPS through KAKENHI grant No. 16H02166. We thank M. Sawicki for discussions regarding the SED fit algorithm, M. Akiyama for discussions regarding the AGN solutions, A. Goulding for discussions in the HSC data analysis, N. Scoville for interpretation of the SED fit results, and C. H. Lee for the English corrections. We also thank I. Smail and C. C. Chen for letting us know about the detections of the previously reported BBG candidate (Mawatari et al. 2016) by SCUBA-2 and ALMA. We would like to thank Editage (www.editage.com) for English language editing. We appreciate the observatories where the data used in this work were taken. The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. The UltraVISTA survey is based on data products from observations made with the ESO Telescopes at the La Silla Paranal Observatory under ESO program ID 179.A-2005 and on data products produced by TERAPIX and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. This paper makes use of the following ALMA data: ADS/JAO.ALMA #2017.1.01259.S. ALMA is a partnership of the ESO (representing its member states), NSF (USA), and NINS (Japan), together with the NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by the ESO, AUI/NRAO, and NAOJ. The HST data used in this work were obtained through the data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. The Hyper Suprime-Cam (HSC) collaboration includes the astronomical communities of Japan and Taiwan and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of Tokyo, the High Energy Accelerator Research Organization (KEK), the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan (ASIAA), and Princeton University. Funding was contributed by the FIRST program from the Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), the Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University. This paper used software developed for the Large Synoptic Survey Telescope. We thank the LSST Project for making their code available as free software at http://dm.lsst.org. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg, and the Max Planck Institute for Extraterrestrial Physics, Garching, the Johns Hopkins University, Durham University, the University of Edinburgh, Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), and the Los Alamos National Laboratory. The HSC-SSP data were collected at the Subaru Telescope and retrieved from the HSC data archive system, which is operated by the Subaru Telescope and Astronomy Data Center at the National Astronomical Observatory of Japan. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. The SCUBA-2 is on the James Clerk Maxwell Telescope, which is operated by the East Asian Observatory on behalf of the National Astronomical Observatory of Japan, Academia Sinica Institute of Astronomy and Astrophysics, the Korea Astronomy and Space Science Institute, the National Astronomical Observatories of China, and the Chinese Academy of Sciences (grant No. XDB09000000), with additional funding support from the Science and Technology Facilities Council of the United Kingdom and participating universities in the United Kingdom and Canada. The VLA is a part of the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The XMM-Newton satellite is an ESA science mission with instruments and contributions directly funded by the ESA Member States and NASA. The scientific results reported in this article are based in part on observations made by the Chandra X-ray Observatory. Facilities: Spitzer(IPAC) - Spitzer Space Telescope satellite, VISTA(ESO) - , Subaru(NAOJ) - Subaru Telescope, HST(STIS) - Hubble Space Telescope satellite, Herschel(ESA) - European Space Agency's Herschel space observatory, JCMT(EAO) - James Clerk Maxwell Telescope, VLA(NRAO) - Very Large Array, XMM-Newton(ESA) - , Chandra(NASA) - . Software: SExtractor (Bertin & Arnouts 1996), IRAF (Tody 1986, 1993), PANHIT (http://www.icrr.u-tokyo.ac.jp/~mawatari/PANHIT/PANHIT.html).

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