27th of April 2020 |
---|
ASKAP FLASH detection of neutral hydrogen absorption |
by Allison et al. |
Allison et al. have presented early science results from the First Large
Absorption Survey in H I (FLASH), a survey for 21-cm absorption lines in
cold hydrogen (HI) gas at cosmological distances using the Australian
Square Kilometre Array Pathfinder (ASKAP).
FLASH is probing how the neutral interstellar medium in galaxies has
evolved over the history of the Universe.
The team searched for HI absorption towards 1253 radio sources in the GAMA
23 field, covering redshifts between z = 0.34 and 0.79 over a sky area of
approximately 50 square degrees. In a purely blind search no
detections of 21-cm absorbers were made above the reliability threshold.
However, by cross matching their sample of radio
sources with optical spectroscopic identifications of galaxies in the GAMA
23 field, they were able to detect 21-cm absorption at z = 0.3562 towards
the galaxy NVSS J224500−343030.
The absorber is associated with GAMA
J22450.05−343031.7, a massive early-type galaxy.
The image above shows an ASKAP-12 mosaic of the 900 MHz radio continuum in the GAMA 23 field as a grey scale image. (The Galaxy And Mass Assembly survey is a detailed multi-wavelength survey in five survey fields, with the GAMA 23 field centred on a Right Ascension of 23h.) The small circles indicate the 1253 radio sources which were examined for HI 21-cm absorption. The colour scale denotes the median RMS noise per 18.5 kHz channel as a fraction of the continuum; darker circles indicate higher sensitivity to 21-cm absorption. The small black square indicates the position of NVSS J224500−343030, towards which HI 21-cm absorption was detected. The larger black boundary denotes the extent of the GAMA 23 field. More details are given in the paper, to be published in Monthly Notices of the Royal Astronomical Society. |