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FLASH Early Science -- Discovery of an intervening HI 21-cm absorber from an ASKAP survey of the GAMA 23 field | J. R. Allison
; E. M. Sadler
; S. Bellstedt
; L. J. M. Davies
; S. P. Driver
; S. L. Ellison
; M. Huynh
; A. D. Kapinska
; E. K. Mahony
; V. A. Moss
; A. S. G. Robotham
; M. T. Whiting
; S. J. Curran
; J. Darling
; A. W. Hotan
; R. W. Hunstead
; B. S. Koribalski
; C. D. P. Lagos
; M. Pettini
; K. A. Pimbblet
; M. A. Voronkov
; | Date: |
2 Apr 2020 | Abstract: | We present early science results from the First Large Absorption Survey in HI
(FLASH), a spectroscopically blind survey for 21-cm absorption lines in cold
hydrogen HI gas at cosmological distances using the Australian Square Kilometre
Array Pathfinder (ASKAP). We have 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 we
did not obtain any detections of 21-cm absorbers above our reliability
threshold. Assuming a fiducial value for the HI spin temperature of $T_{
m
spin}$ = 100 K and source covering fraction $c_{
m f} = 1$, the total comoving
absorption path length sensitive to all Damped Lyman-$alpha$ Absorbers (DLAs;
$N_{
m HI} geq 2 imes 10^{20}$ cm$^{-2}$) is $Delta{X} = 6.6 pm 0.3$
($Delta{z} = 3.7 pm 0.2$) and super-DLAs ($N_{
m HI} geq 2 imes 10^{21}$
cm$^{-2}$) is $Delta{X} = 111 pm 6$ ($Delta{z} = 63 pm 3$). We estimate
upper limits on the HI column density frequency distribution function that are
consistent with measurements from prior surveys for redshifted optical DLAs,
and nearby 21-cm emission and absorption. By cross matching our sample of radio
sources with optical spectroscopic identifications of galaxies in the GAMA 23
field, we were able to detect 21-cm absorption at $z = 0.3562$ towards NVSS
J224500$-$343030, with a column density of $N_{
m HI} = (1.2 pm 0.1) imes
10^{20} (T_{
m spin}/100~mathrm{K})$ cm$^{-2}$. The absorber is associated
with GAMA J22450.05$-$343031.7, a massive early-type galaxy at an impact
parameter of 17 kpc with respect to the radio source and which may contain a
massive ($M_{
m HI} gtrsim 3 imes 10^{9}$ M$_{odot}$) gas disc. Such
gas-rich early types are rare, but have been detected in the nearby Universe. | Source: | arXiv, 2004.0847 | Services: | Forum | Review | PDF | Favorites |
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