Imaginary picture of GRB. Image credit: [NASA/SkyWorks Digital]
Gamma-Ray Bursts (GRBs) theories predict that GRBs happen in low metallicity environments. In general, metallicity environments of GRBs are investigated with rest-frame optical observations. However the rest-frame optical observations are difficult for a dusty population of GRB host galaxies which increases at redshift ~1-2 or higher. A discovery of a new “dust-extinction free” parameter has been awaited for many years.
I, for the first time, detected a [CII]158um emission line from a GRB host galaxy at redshift~2 (Fig. 1). The luminosity ratio of [CII]158um emission and far-infrared (FIR) continuum is very low, so-called the “[CII] deficit”, compared with that of other star-forming galaxies at the same redshift. I found a new “dust-extinction free” parameter to characterize GRB host galaxy. Model calculations predict that the [CII] deficit is controlled by metallicity, ultra-violet radiation field, initial mass function, and gas densiy.
![Fig. 1: (Left) [CII]158um emission line of a GRB host galaxy at redshift~2, first detected with ALMA. Red curve is the best-fit Gaussian function of the emission line. Dashed lines are +- 1 sigma uncertainties. The continuum is subtracted. (Right) [CII]158um map integrated over +-125 km s^-1. The continuum is subtracted. The GRB host position is at the center of the image. Ellipse indicates a beam size.](/~tetsuya/publication/journal-article4/figure2-min_hu3ed90bdfdd9671e322487e686bcf00b7_160434_bfd31a9534028dba98dce4f935f91f5d.png)
This project is based on the following publication.
Tetsuya Hashimoto, Bunyo Hatsukade, Tomotsugu Goto, Seong Jin Kim, Kouji Ohta, Tohru Nagao, Albert K. H. Kong, Kouichiro Nakanishi, and Jirong Mao, 'Star-formation rates of two GRB host galaxies at z~2 and a [C II] deficit observed with ALMA' , Monthly Notices of the Royal Astronomical Society, (2019).
