Related papers: A Bare Molecular Cloud at z~0.45
Hundreds of high-velocity atomic gas clouds exist above and below the Galactic Centre, with some containing a molecular component. However, the origin of these clouds in the Milky Way's wind is unclear. This paper presents new…
We use archival UV absorption-line data from HST/STIS to statistically analyse the absorption characteristics of the high-velocity clouds (HVCs) in the Galactic halo towards more than 40 extragalactic background sources. We determine…
We discuss physical conditions in Galactic neutral hydrogen based on deep, high velocity resolution interferometric HI 21 cm absorption spectroscopy towards 33 compact extra-galactic radio sources. The HI 21 cm optical depth spectra have…
Ionized carbon is the main gas-phase reservoir of carbon in the neutral diffuse interstellar medium and its 158 micron fine structure transition [CII] is the most important cooling line of the diffuse interstellar medium (ISM). We combine…
We have observed the $^{12}$CO J=2-1, J=3-2, and $^{13}$CO J=2-1 lines in a sample of seven giant molecular clouds in the Local Group spiral galaxy M33. The $^{12}$CO/$^{13}$CO J=2-1 line ratio is constant across the entire sample, while…
Our understanding of how molecular clouds form in the interstellar medium (ISM) would be greatly helped if we had a reliable observational tracer of the gas flows responsible for forming the clouds. Fine structure emission from singly…
Aims: We present observations from the Interface Region Imaging Spectrograph (IRIS) of absorption features from a multitude of cool atomic and molecular lines within the profiles of Si IV transition region lines. Many of these spectral…
We explore the distribution of cool (~$10^4$K) gas around galaxies and its dependence on galaxy properties. By cross-correlating about 50,000 MgII absorbers with millions of sources from the SDSS (optical), WISE (IR), and GALEX (UV) surveys…
We present a simple model that explains the origin of warm diffuse gas seen primarily as highly ionized absorption line systems in the spectra of background sources. We predict the observed column densities of several highly ionized…
HI 21 cm observations with the NRAO 140 Foot telescope have revealed a giant HI cloud (G28.17+0.05) in the Galactic plane that has unusual properties. The cloud is 150 pc in diameter, is at a distance of 5 kpc, and contains as much as…
The majority of hydrogen in the interstellar medium (ISM) is in atomic form. The transition from atoms to molecules and, in particular, the formation of the H$_2$ molecule, is a key step in cosmic structure formation en route to stars.…
An independent analysis of the molecular hydrogen absorption system at z = 2.059 in the spectrum of the quasar J2123-0050 is presented. The H_2 system consists of two components (A and B) with column densities log N^A(H_2) = 17.94+/-0.01…
We performed a detailed study of the extended cool gas, traced by MgII absorption [$W_r(2796)\geq0.3$~{\AA}], surrounding 14 narrow-line active galactic nuclei (AGNs) at 0.12<z<0.22 using background quasar sight-lines. The background…
CO$_2$ is an important, stable, and abundant molecule in the Universe, but it is very difficult to detect because it has no observable pure rotational transitions. The unique sensitivity and resolution of the James Webb Space Telescope…
We present a detailed study of HI and metals for 110 MgII absorption systems discovered at 1.98 <= z <= 5.33 in the infrared spectra of high redshift QSOs. Using new measurements of rest-frame UV lines from optical spectra of the same…
The Magellanic Stream, a tidal tail of diffuse gas falling onto the Milky Way, formed by interactions between the Small and Large Magellanic Clouds, is primarily composed of neutral atomic hydrogen (HI). The deficiency of dust and the…
We present the detection and analysis of a weak low-ionization absorber at $z = 0.12122$ along the blazar sightline PG~$1424+240$, using spectroscopic data from both $HST$/COS and STIS. The absorber is a weak Mg II analogue, with incidence…
We present a wide grid of models for the structure and transmission properties of warm absorbers in active galactic nuclei (AGN). Contrary to commonly used constant density models, our absorbing cloud is assumed to be under constant total…
We report the detection of a peculiar molecular cloud, CO 0.02-0.02, lying about 5' Galactic-east from the center of the Galaxy. (12)CO images taken with NRO 45 m telescope showed that it is relatively compact (about 3x4 pc^2) as well as…
The abundance of H2 in molecular clouds, relative to the commonly used tracer CO, has only been measured toward a few embedded stars, which may be surrounded by atypical gas. We present observations of near-infrared absorption by H2, CO,…