Related papers: Variable Interstellar Absorption toward the Halo S…
We have investigated the time scale for formation of molecular clouds by examining the conversion of HI to H2 using a time-dependent model. H2 formation on dust grains and cosmic ray and photo destruction are included in one-dimensional…
We present high-resolution HI 21 cm observations with the Karl G. Jansky Very Large Array (VLA) for three HI rich galaxies in absorption against radio quasars. Our sample contains six sightlines with impact parameters from 2.6 to 32.4 kpc.…
We present high-resolution echelle observations of SN 2011dh, which exploded in the nearby, nearly face-on spiral galaxy M51. Our data, acquired on three nights when the supernova was near maximum brightness, reveal multiple absorption…
We report Far Ultraviolet Spectroscopic Explorer (FUSE) observations of interstellar O VI absorption in the halo of the Milky Way towards 12 early-type stars in the Large Magellanic Cloud (LMC) and 11 in the Small Magellanic Cloud (SMC).…
We present a novel absorption line survey using 54 blue horizontal branch stars (BHBs) in the Milky Way halo as background sources for detecting gas flows at the disk-halo interface. Distance measurements to high-latitude ($b$ > 60{\deg})…
A Near-infrared (1.18-1.35 micron) high-resolution spectrum of the gravitationally-lensed QSO APM 08279+5255 was obtained with the IRCS mounted on the Subaru Telescope using the AO system. We detected strong NaI D 5891,5897 doublet…
The vertical distribution of cold neutral hydrogen (HI) clouds is a constraint on models of the structure, dynamics, and hydrostatic balance of the interstellar medium. In 1978, Crovisier pioneered a method to infer the vertical…
We combine HI 21cm observations of the Milky Way, M31, and the local galaxy population with QSO absorption-line measurements to geometrically model the three-dimensional distribution of infalling neutral gas clouds (HVCs) in the extended…
We present new high resolution (R>50,000) absorption measurements of the NaI doublet (5889 - 5895A) along 482 nearby sight-lines, in addition to 807 new measurements of the CaII K (3933A) absorption line. We have combined these new data…
We analyze high-resolution UV spectra of the Mg II h and k lines for 18 members of the Hyades Cluster to study inhomogeneity along these proximate lines of sight. The observations were taken by the Space Telescope Imaging Spectrograph…
We have recently used the Hubble Space Telescope to study a pair of high velocity clouds in the direction of Mrk 509 that have unusual ionization properties. They exhibit strong CIV absorption with little or no low ion absorption or HI 21cm…
We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of interstellar molecular hydrogen (H_2) in two Galactic high-velocity clouds (HVCs). Molecular hydrogen absorption is detected in the Magellanic Stream (abundance ~0.3…
We present recent results on highly ionized gas in Galactic High-Velocity Clouds (HVCs), originally surveyed in OVI (Sembach et al. 2003). In a new FUSE/HST survey of SiII/III/IV (Shull et al. 2009) toward 37 AGN, we detected SiIII (lambda…
Context. The earliest phases of high-mass star formation are poorly understood. Aims. Our goal is to determine the physical conditions and kinematic structure of massive star-forming cloud clumps. Methods. We analyze H$_2$O 557 GHz line…
We report results from a FUSE survey of interstellar molecular hydrogen (H2) in the Galactic disk toward 139 O-type and early B-type stars at Galactic latitudes $|b| < 10^{\circ}$, with updated photometric and parallax distances. The H2…
We perform a systematic study of physical properties and distribution of neutral and ionised gas in the halo of the Milky Way (MW). Beside the large neutral intermediate- and high-velocity cloud (IVC, HVC) complexes there exists a…
We present Hubble Space Telescope Imaging Spectrograph (HST/STIS) and Far Ultraviolet Spectroscopic Explorer (FUSE) observations of high ion interstellar absorption along the sight line to HD 116852. At a distance of 4.8 kpc, HD 116852 is…
We have detected absorption lines from the High Velocity Cloud Complex WB in the spectrum of the star HE1048+0231. This detection sets an upper distance limit to the cloud of 8.8^{+2.3}_{-1.3} kpc. Non-detection (at >4 sigma confidence) in…
The ionization rate of interstellar material by cosmic rays has been a major source of controversy, with different estimates varying by three orders of magnitude. Observational constraints of this rate have all depended on analyzing the…
There is a robust polyatomic chemistry in diffuse, partially-molecular interstellar gas that is readily accessible in absorption at radio/mm/sub-mm wavelengths. Accurate column densities are derived owing to the weak internal excitation, so…