The stellar mass, star formation rate and dark matter halo properties of LAEs at z ∼ 2

Creators: Kusakabe, Haruka; Shimasaku, Kazuhiro; Ouchi, Masami; Nakajima, Kimihiko; Goto, Ryosuke; Hashimoto, Takuya; Konno, Akira; Harikane, Yuichi; Silverman, John D.; Capak, Peter L.

Abstract

We present average stellar population properties and dark matter halo masses of z ∼ 2 Lyα emitters (LAEs) from spectral energy distribution fitting and clustering analysis, respectively, using ≃ 1250 objects (NB387 ≤ 25.5) in four separate fields of ≃ 1 deg^2 in total. With an average stellar mass of 10.2 ± 1.8 × 10^8 M⊙ and star formation rate of 3.4 ± 0.4 M⊙ yr^(−1), the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be 4.0^(+5.1)_(−2.9)×10^(10) M⊙ with an effective bias of 1.22^(+0.16)_(−0.18, which is lower than that of z ∼ 2 LAEs (1.8 ± 0.3) obtained by a previous study based on a three times smaller survey area, with a probability of 96%. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low H I gas mass, this result appears to be consistent with the observations of a high Lyα escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press–Schechter formalism predicts that at z = 0 our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their star formation rates are largely suppressed after z ∼ 2 as some previous studies have reported for the LMC itself.

Additional Information

© The Author(s) 2018. Published by Oxford University Press on behalf of the Astronomical Society of Japan. Received: 28 July 2017; Accepted: 22 November 2017; Published: 13 January 2018. We thank the anonymous referee for his/her helpful comments and suggestions. We are grateful to Lihwai Lin and Li-Ting Hsu for kindly providing us with J, H, and Ks images of the HDFN field and data in Lin et al. (2012) plotted in figures 8, 9, and 10. We are also grateful to Yoshiaki Ono for giving insightful comments and suggestions on SED fitting. We would like to show our appreciation to Takashi Hamana for helpful comments on cosmic variance and computer programs of the covariance of dark matter angular correlation function and the EPS model. We would like to express our gratitude to David Sobral, Naveen A. Reddy, Giulia Rodighiero, and Shogo Ishikawa for kindly providing their data plotted in figures 5a, 7, 8, and 9, respectively. We would like to thank Alex Hagen, James E. Rhoads, Jorryt Matthee, and Peter S. Behroozi for useful comments on their results. We also would like to thank Akio K. Inoue, Cai-Na Hao, Hidenobu Yajima, Ikkoh Shimizu, Ken Mawatari, Kotaro Kohno, Kyoung-Soo Lee, Tsutomu T. Takeuchi, Mana Niida and Yuki Yoshimura for insightful discussion. We acknowledge Ryota Kawamata, Taku Okamura, and Kazushi Irikura for constructive discussions at weekly meetings. This work is based on observations taken by the Subaru Telescope which is operated by the National Astronomical Observatory of Japan. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under ESO programme ID 179.A-2005 and on data products produced by TERAPIX and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. This research made use of IRAF, which is distributed by NOAO, which is operated by AURA under a cooperative agreement with the National Science Foundation and of Python packages for Astronomy: Astropy (Astropy Collaboration et al. 2013), Colossus, CosmoloPy and PyRAF, which is produced by the Space Telescope Science Institute, which is operated by AURA for NASA. H.K acknowledges support from the JSPS through the JSPS Research Fellowship for Young Scientists. This work is supported in part by KAKENHI (16K05286) Grant-in-Aid for Scientific Research (C) through the JSPS.

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