Illuminating the past 8 billion years of cold gas towards two gravitationally lensed quasars

Abstract

Using the Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder (ASKAP BETA), we have carried out the first $z=0-1$ survey for HI and OH absorption towards the gravitationally lensed quasars PKSB1830$-$211 and MGJ0414$+$0534. Although we detected all previously reported intervening systems towards PKSB1830$-$211, in the case of MGJ0414+0534 three systems were not found, indicating that the original identifications may have been confused with radio frequency interference. Given the sensitivity of our data, we find that our detection yield is consistent with the expected frequency of intervening HI systems estimated from previous surveys for 21-cm emission in nearby galaxies and $z\sim 3$ damped Lyman $\alpha$ absorbers. We find spectral variability in the $z=0.886$ face-on spiral galaxy towards PKSB1830$-$211, from observations undertaken with the Westerbork Synthesis Radio Telescope in 1997/1998 and ASKAP BETA in 2014/2015. The HI equivalent width varies by a few per cent over approximately yearly time-scales. This long-term spectral variability is correlated between the north-east and south-west images of the core, and with the total flux density of the source, implying that it is observationally coupled to intrinsic changes in the quasar. The absence of any detectable variability in the ratio of HI associated with the two core images is in stark contrast to the behaviour previously seen in the molecular lines. We therefore infer that coherent opaque HI structures in this galaxy are larger than the parsec-scale molecular clouds found at mm-wavelengths.

19 pages, 11 figures, published in MNRAS

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• A successful search for intervening 21 cm HI absorption in galaxies at 0.4 < z <1.0 with the Australian Square Kilometre Array Pathfinder (ASKAP)
• Connecting X-ray absorption and 21cm neutral hydrogen absorption in obscured radio AGN
• A study of submillimeter methanol absorption toward PKS1830-211: Excitation, invariance of the proton-electron mass ratio, and systematics
• All good things come in threes: the third image of the lensed quasar PKS1830-211
• A pilot search for extragalactic OH absorption with FAST
• A statistical measurement of the HI spin temperature in DLAs at cosmological distances
• FLASH Pilot Survey: Detections of associated 21 cm HI absorption in GAMA galaxies at 0.42 < z <1.00
• Intervening or associated? Machine learning classification of redshifted H I 21-cm absorption
• The potential of tracing the star formation history with HI 21-cm in intervening absorption systems
• Discovery of Hydrogen Radio Recombination Lines at z=0.89 towards PKS 1830-211
• On the scarcity of redshifted OH and millimetre-band molecular absorption