Big Three Dragons: A z = 7.15 Lyman-break galaxy detected in [O iii] 88 μm, [C ii] 158 μm, and dust continuum with ALMA

Abstract

We present new ALMA observations and physical properties of a Lyman Break Galaxy at z = 7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, M UV ≈ −22.4, and has been spectroscopically identified in Lyα with a small rest-frame equivalent width of ≈ 4Å. Previous HST image has shown that the target is comprised of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [Oiii] 88 µm, [Cii] 158 µm, and their underlying dust continuum emission. In the whole system of B14-65666, the [Oiii] and [Cii] lines have consistent redshifts of 7.1520 ± 0.0003, and the [Oiii] luminosity, (34.4 ± 4.1) × 10 8 L ⊙ , is about three times higher than the [Cii] luminosity, (11.0 ± 1.4) × 10 8 L ⊙ . With our two continuum flux densities, the dust temperature is constrained to be T d ≈ 50 − 60 K under the assumption of the dust emissivity index of β d = 2.0 − 1.5, leading to a large total infrared luminosity of L TIR ≈ 1 × 10 12 L ⊙ . Owing to our high spatial resolution data, we show that the [Oiii] and [Cii] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by ≈ 200 km s −1 . We also find these two clumps have comparable UV, infrared, [Oiii], and [Cii] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major-merger. The merger interpretation is also supported by the large specific star-formation rate (defined as the star-formation rate per unit stellar mass), sSFR = 260 +119 −57 Gyr −1 , inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [Oiii]-to-[Cii] luminosity ratio.

Direct Measurement of the [C i] Luminosity to Molecular Gas Mass Conversion Factor in High-redshift Star-forming Galaxies

“…This work provides the first direct calibration of the conversion between the [C i] line luminosity L [CI](1−0) to the total molecular gas mass for high-redshift galaxies. This calibration is also specifically sensitive to the metal-poor regime that is difficult to survey at low redshifts, but is now increasingly being probed by sub-mm observations of low-mass galaxies that dominate the high-redshift galaxy population (Hashimoto et al 2019). The remarkable consistency between the scaling relations derived here for the absorption-selected galaxies, compared to that observed for molecular clouds in the Milky Way and local galaxies, validates this technique and suggests that the properties of molecular clouds are ubiquitous both in the local and high-redshift universe.…”

A lack of evolution in the very bright end of the galaxy luminosity function from z ≃ 8 to 10

“…Tamura et al 2019;Bowler et al 2018;Laporte et al 2017), the derived dust masses in these sources are reduced compared to low-redshift observations, because of the higher assumed dust temperature (e.g. Hashimoto et al 2019). In addition to the effect of reduced dust at the highest redshifts, there is reason to believe that the underlying MF of galaxies during this epoch is shallower than observed in the local Universe.…”

An ALMA Multiline Survey of the Interstellar Medium of the Redshift 7.5 Quasar Host Galaxy J1342+0928

“…Given the high ionization energy required to produce O ++ emission, it originates exclusively in an ionized medium around early-type stars or in the presence of active galactic nuclei (AGNs). This line shows a promising future for high-redshift galaxy observations (see also Hashimoto et al 2019). Singly ionized nitrogen gives rise to two emission lines , which can provide additional ionization diagnostics (see, e.g., Herrera-Camus et al 2016), especially when used in conjunction with other lines.…”