Related papers: 21-cm absorbers at intermediate redshifts
We present the results of three separate searches for HI 21-cm absorption in a total of twelve damped Lyman-alpha absorption systems (DLAs) and sub-DLAs over the redshift range z = 0.86-3.37. We find no absorption in the five systems for…
In this paper we investigate the possible reasons why HI 21-cm absorption in damped Lyman-alpha systems (DLAs) has only been detected at low redshift... We suggest that the lack of 21-cm absorption detections at high redshift arises from…
Intervening HI 21-cm absorption systems at z > 1.0 are very rare and only 4 confirmed detections have been reported in the literature. Despite their scarcity, they provide interesting and unique insights into the physical conditions in the…
We present deep GMRT 21cm absorption spectra of 10 damped Lyman-$\alpha$ systems (DLAs), of which 8 are at redshifts $z \ga 1.3$. HI absorption was detected in only one DLA, the $z = 0.5318$ absorber toward PKS 1629+12, which has been…
As part of a larger program to identify low redshift radio analogues of the damped Lyman-alpha (DLA) absorbers seen in the spectra of high redshift quasars, Westerbork Synthesis Radio Telescope (WSRT) observations have discovered two new HI…
To search for low-redshift damped Lyman-alpha (DLA) and sub-DLA quasar absorbers, we have conducted a 21cm absorption survey of radio-loud quasars at small impact parameters to foreground galaxies selected from the Sloan Digital Sky Survey…
We report results from a deep search for redshifted HI 21cm absorption from eight damped Lyman-$\alpha$ absorbers (DLAs) detected in our earlier optical survey for DLAs towards radio-loud quasars. HI 21cm absorption was detected from the $z…
We investigate the practice of assigning high spin temperatures to damped Lyman-alpha absorption systems (DLAs) not detected in HI 21-cm absorption. In particular, Kanekar & Chengaulr (2003) have attributed the mix of 21-cm detections and…
We present the results of a survey for 21-cm absorption in four never previously searched damped Lyman-alpha absorption systems (DLAs) with the Westerbork Synthesis Radio Telescope. We add our results to other recent studies in order to…
(Abridged) We present the results of a systematic GBT and GMRT survey for 21-cm absorption in a sample of 10 DLAs at 2<z_abs<3.4. Analysis of L-band VLBA images of the background QSOs are also presented. We detect 21-cm absorption in only…
Quasar damped Ly-alpha (DLA) absorption line systems with redshifts z<1.65 are used to trace neutral gas over approximately 70 per cent of the most recent history of the Universe. However, such systems fall in the UV and are rarely found in…
We report the GMRT detection of HI 21cm absorption from the $z \sim 3.39$ damped Lyman-$\alpha$ absorber (DLA) towards PKS 0201+113, the highest redshift at which 21cm absorption has been detected in a DLA. The absorption is spread over…
We report Giant Metrewave Radio Telescope (GMRT) 21cm observations of two confirmed and one candidate low redshift damped Lyman-alpha systems (DLAS). HI absorption was detected in the two confirmed systems, at z=0.2378 and z=0.5247, with…
We report a deep search for redshifted HI 21 cm emission from three damped and sub-damped Lyman-$\alpha$ absorbers (DLAs) at $z \approx 0.1$ with the Green Bank Telescope (GBT). No evidence for a redshifted HI 21 cm emission signal was…
We report {\it HST} COS spectroscopy of 10 quasars with foreground star-forming galaxies at 0.02$<$$z$$<$ 0.14 within impact parameters of $\sim$1-7 kpc. We detect damped/sub-damped Ly$\alpha$ absorption in 100$\%$ of cases where no…
We present Giant Metrewave Radio Telescope HI 21cm absorption observations, of candidate and confirmed damped Lyman-$\alpha$ systems (DLAS). The derived spin temperatures (T_s) are in all cases $\sim 1000$ K or higher. We have also collated…
We study the nature of damped Lya absorption (DLA) systems at z<=1 using a sample of 11 DLA galaxies, for which accurate redshift measurements are available. We demonstrate that the precision of photometric redshifts is sufficient for…
We report results on the incidence and cosmological mass density of damped Lyman-alpha (DLA) systems at redshifts less that 1.65. We used HST and an efficient non-traditional (but unbiased) survey technique to discover DLA systems at…
We report the detection of redshifted HI~21cm absorption in the $z \sim 2.347$ damped Lyman-$\alpha$ absorber (DLA) towards PKS B0438-436, with the Green Bank Telescope. This is the second-highest redshift at which 21cm absorption has been…
Damped Lyman-$\alpha$ absorbers (DLAs) with molecular hydrogen have been probed in detail through both spectroscopic observations and numerical modelling. However, such H$_2$ absorbers are quite sparse at very high redshifts. We identify…