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, MUV ≈ −22.4, and has been spectroscopically identified in Lyα with a small rest-frame equivalent width of ≈ 4 Å. 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) × 108 L☉, is about three times higher than the [Cii] luminosity, (11.0 ± 1.4) × 108 L☉. With our two continuum flux densities, the dust temperature is constrained to be Td ≈ 50 − 60 K under the assumption of the dust emissivity index of βd = 2.0 − 1.5, leading to a large total infrared luminosity of LTIR ≈ 1 × 1012 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.
|Publication status||Published - 2018 Jun 1|
- Galaxies: formation
- Galaxies: high-redshift
- Galaxies: ISM
ASJC Scopus subject areas