Related papers: The thermally-unstable warm neutral medium: key fo…

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…

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…

The Warm-Hot Intergalactic Medium (WHIM) arises from shock-heated gas collapsing in large-scale filaments and probably harbours a substantial fraction of the baryons in the local Universe. Absorption-line measurements in the ultraviolet…

Today, the majority of the cosmic baryons in the Universe are not observed directly, leading to an issue of "missing baryons" at low redshift. Cosmological hydrodynamical simulations have indicated that a significant portion of them will be…

The neutral component of the interstellar medium is segregated into the cold neutral medium (CNM) and warm neutral medium (WNM) as a result of thermal instability. It was found that a plane-parallel CNM-WNM evaporation interface, across…

We present an analysis of the HI absorption in a sample of 101 flux-selected radio AGN (S_1.4 GHz > 50 mJy) observed with the Westerbork Synthesis Radio Telescope (WSRT). HI absorption is detected in 32 galaxies, showing a broad variety of…

We compare observations of HI from the Very Large Array (VLA) and the Arecibo Observatory and observations of HCO$^+$ from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Northern Extended Millimeter Array (NOEMA) in the…

We present a physically-based absorption-line model for the spectroscopic study of the intergalactic medium (IGM). This model adopts results from Cloudy simulations and theoretical calculations by Gnat and Sternberg (2007) to examine the…

We present the results of a pilot survey for neutral hydrogen (HI) 21 cm absorption in the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFALFA) Survey. This project is a wide-area "blind" search for HI absorption in the local universe,…

I report the detection of HI 21cm absorption in two high column density damped Lyman-$\alpha$ absorbers (DLAs) at $z \approx 2$ using new wide-band $250-500$ MHz receivers onboard the Giant Metrewave Radio Telescope. The integrated HI 21cm…

A high latitude HI 21 cm-line absorption survey toward extragalactic sources was recently completed using the Giant Meterwave Radio Telescope (GMRT). A total of 104 sources with mod(b) > 15 deg. and with a 21 cm flux density greater than 1…

The main goal of this analysis is to present a new method to estimate the physical properties of diffuse cloud of atomic hydrogen observed at high Galactic latitude. This method, based on a comparison of the observations with fractional…

We explore the possibility of detecting HI 21cm absorption by the neutral intergalactic medium (IGM) toward very high redshift radio sources. The epoch considered is between the time when the first ionizing sources form and when the bulk of…

I report detections of four new HI 21-cm absorbers associated with sources at intermediate redshifts, 0.7 < z < 1.0. The sources are part of a sample of 11 radio-loud galaxies, all at 0.7 < z < 1.0, that were searched for associated HI…

Resolving the phase structure of neutral hydrogen (HI) is crucial for understanding the life cycle of the interstellar medium (ISM). However, accurate measurements of HI temperature and density are limited by the availability of background…

We present Giant Metrewave Radio Telescope and Very Large Array observations of HI 21-cm absorption in ten z<=0.2 galaxy mergers that host strong radio sources. Seven of these mergers show strong absorption [with N(HI) ~10^{21-22} cm^{-2},…

We have searched for HI 21-cm absorption in 11 strong MgII systems ($W_{\rm r}$(MgII $\lambda 2796$) $\ge 1$ \AA) at $0.3<z<0.5$ using the Giant Metrewave Radio Telescope. We have detected HI 21-cm absorption in two of these. From the…

We present the early science results from a blind search of the extragalactic HI 21-cm absorption lines at z $\leqslant$ 0.09 with the drift-scan observation of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We carried…

We use three-dimensional numerical hydrodynamic simulations of the turbulent, multiphase atomic interstellar medium (ISM) to construct and analyze synthetic HI 21 cm emission and absorption lines. Our analysis provides detailed tests of 21…

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…