Colloquium on Sep. 24, 2020

Properties of galaxies at z = 6 - 9 revealed by ALMA

Speaker: Takuya Hashimoto (Tsukuba University)

Venue: Video Conference

Time: 15:00 PM, Thursday, Sep. 24, 2020

Abstract:

Understanding properties of galaxies in the epoch of reionization (EoR) is a frontier in the modern astronomy. With the advent of ALMA, it has become possible to detect far-infrared fine structure lines (e.g. [CII] 158 micron and [OIII] 88 micron) and dust continuum emission in star-forming galaxies in the EoR. Among these lines, our team is focusing on [OIII] 88 micron observations in high-z galaxies. After the first detection of [OIII] in the epoch of reionization (EoR) in 2016 from our team (z = 7.21; Inoue et al. 2016, Science 352, 1559), there are now more than ten [OIII] detections at z > 6 up to z = 9.1  (e.g. Hashimoto et al. 2018, Nature 557, 392; Tamura et al. 2019, ApJ, 874, 27). Interestingly, high-z galaxies typically have very high [OIII]-to-[CII] luminosity ratio ranging from 3 to 12 or higher, demonstrating [OIII] is a powerful tracer at high-z. The high luminosity ratios may imply that high-z galaxies have low gas-phase metallicity and/or high ionization states (e.g. Harikane et al. 2020, ApJ, 896, 93). These ALMA observations also allow us to detect / place upper limits on dust continuum emission. Some z ~ 7 - 8 galaxies have dust continuum data at multiple wavelengths, allowing us to constrain the (luminosity-weighted) dust temperature. We show that a z = 8.3 galaxy seems to have high dust temperature compared with the local Universe, probably due to strong UV radiation from massive and young stars (Bakx et al. 2020, MNRAS, 493, 4294). In addition to these ISM properties, we also show our detailed SED fitting results at z ~ 7 - 9 taking ALMA data into account, which demonstrate early star forming activity at z > 10.

Report PPT:   SWIFAR_Takuya Hashimoto.pdf