The HRS GTO program to study the neutral hydrogen column density and D/H ratio in the local interstellar medium

1986 ◽  
Vol 6 (2) ◽  
pp. 91-94
Author(s):  
J.L. Linsky, ◽  
W.B. Landsman ◽  
B.D. Savage ◽  
S.R. Heap ◽  
A.M. Smith ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Column Density ◽  
Neutral Hydrogen ◽  
Local Interstellar Medium ◽  
Hydrogen Column Density

High-resolution Na I Observations of the Local Interstellar Medium

1991 ◽  
Vol 9 (1) ◽  
pp. 122-123
Author(s):  
Barry Y. Welsh ◽  
Peter W. Vedder ◽  
John V. Vallerga
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
Column Density ◽  
Velocity Structure ◽  
Extreme Ultraviolet ◽  
Sodium Absorption ◽  
Local Interstellar Medium ◽  
Neutral Gas ◽  
Hydrogen Column Density ◽  
Early Type Stars

AbstractWe present high-resolution absorption measurements (R ~ 150 000) of the interstellar Na I D-lines at 5890 Å observed towards 46 early-type stars. The distance to these stars ranges from 20–200 pc, allowing a probe of the local interstellar medium (LISM). The velocity structure, velocity dispersions and column densities of the various cloud components have been derived using an absorption line-fitting analysis. Sodium column densities have been determined for 23 of the 46 target stars. No sodium absorption was detected towards any of the stars with distances < 43 pc. Such null results imply a corresponding hydrogen column density limit, N(H), of ~ 2.5 × 1018cm−2 in many directions in the LISM. For three exceptionally vacant lines of sight (to β CMa, 36 Lyn and η Hya) this limit of low hydrogen column density can be placed out to a much further distance of > 150 pc.We have plotted the distribution of sodium column density in the LISM for a total of 118 stars in the form of three galactic maps. These maps qualitatively show that the present picture of the LISM, in which the first 50 pc is essentially free of dense clumps of neutral gas, is correct. Our map of sodium columns for stars with distances > 100 pc shows that the region within the galactic quadrant defined by 200° < l < 270° shows a conspicuous absence of any significant concentration of neutral gas. This region will be a prime direction of study for forthcoming soft X-ray and extreme ultraviolet satellite experiments.

scholarly journals Spectroscopic Observations of the Far Ultraviolet Background

1990 ◽  
Vol 139 ◽  
pp. 223-224
Author(s):  
Christopher Martin ◽  
Mark Hurwitz ◽  
Stuart Bowyer
Keyword(s):  
Column Density ◽  
Neutral Hydrogen ◽  
Spectroscopic Observations ◽  
Hydrogen Column Density ◽  
Dust Component ◽  
Far Ultraviolet

We report on results from the Berkeley Ultraviolet Experiment (UVX), which performed 15 ± 2 Å resolution spectroscopy of the diffuse far ultraviolet background in eight directions. We have used the spectrum obtained in the direction of low H I column density to derive constraints on any extragalactic background. We find evidence that a hitherto unidentified dust component is present that accounts for most of the background in directions of low neutral hydrogen column density.

scholarly journals OH absorption in the first quadrant of the Milky Way as seen by THOR

2018 ◽  
Vol 618 ◽  
pp. A159 ◽  
Author(s):  
M. R. Rugel ◽  
H. Beuther ◽  
S. Bihr ◽  
Y. Wang ◽  
J. Ott ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Column Density ◽  
Milky Way ◽  
Hydrogen Gas ◽  
Molecular Gas ◽  
Very Large Array ◽  
Spatially Resolved ◽  
Large Program ◽  
Hydrogen Column Density ◽  
Starting Point

Context. The hydroxyl radical (OH) is present in the diffuse molecular and partially atomic phases of the interstellar medium (ISM), but its abundance relative to hydrogen is not clear. Aims. We aim to evaluate the abundance of OH with respect to molecular hydrogen using OH absorption against cm-continuum sources over the first Galactic quadrant. Methods. This OH study is part of the H I/OH/Recombination line survey of the inner Milky Way (THOR). THOR is a Karl G. Jansky Very Large Array (VLA) large program of atomic, molecular and ionized gas in the range 15° ≤ l ≤ 67° and |b|≤ 1°. It is the highest-resolution unbiased OH absorption survey to date towards this region. We combine the optical depths derived from these observations with literature 13CO(1–0) and H I observations to determine the OH abundance. Results. We detect absorption in the 1665 and 1667 MHz transitions, that is, the “main” hyperfine structure lines, for continuum sources stronger than Fcont ≥ 0.1 Jy beam−1. OH absorption is found against approximately 15% of these continuum sources with increasing fractions for stronger sources. Most of the absorption occurs in molecular clouds that are associated with Galactic H II regions. We find OH and 13CO gas to have similar kinematic properties. The data indicate that the OH abundance decreases with increasing hydrogen column density. The derived OH abundance with respect to the total hydrogen nuclei column density (atomic and molecular phase) is in agreement with a constant abundance for AV < 10−20. Towards the lowest column densities, we find sources that exhibit OH absorption but no 13CO emission, indicating that OH is a well suited tracer of the low column density molecular gas. We also present spatially resolved OH absorption towards the prominent extended H II-region W43. Conclusions. The unbiased nature of the THOR survey opens a new window onto the gas properties of the interstellar medium. The characterization of the OH abundance over a large range of hydrogen gas column densities contributes to the understanding of OH as a molecular gas tracer and provides a starting point for future investigations.

scholarly journals The Interstellar and Circumstellar Environment of White Dwarfs

1997 ◽  
Vol 166 ◽  
pp. 69-74
Author(s):  
M.A. Barstow ◽  
P.D. Dobbie ◽  
J.B. Holberg
Keyword(s):  
Interstellar Medium ◽  
White Dwarfs ◽  
Column Density ◽  
Line Of Sight ◽  
Local Distribution ◽  
Local Interstellar Medium ◽  
Weighted Mean ◽  
Ionization Fraction ◽  
Absorbing Material ◽  
Circumstellar Environment

AbstractWe have studied the EUV spectra of 13 DA white dwarfs, observed by the EUVE satellite, paying attention to the possible sources of absorbing material along the lines-of-sight in both the local interstellar medium and in the photospheres of the stars themselves. The range of interstellar column densities seen are consistent with our previous understanding of the local distribution of material. Absorption from interstellar He II is found in the direction of five stars, allowing us to measure directly the He ionization fraction and estimate, indirectly, that of H. The weighted mean ionization fractions along these lines-of-sight are 0.27 ± 0.04 and 0.35 ± 0.1 respectively. Where He II is directly detected, the observed ionization fractions are not correlated with direction or with the volume/column density of material along the line-of-sight. Furthermore, the limits on the amount of He II established in all other directions completely encompass the range of observed values. Indeed, all the data can be consistent with more or less constant He and H ionization fractions throughout the local ISM. However, observation of very hot DA stars, indicating higher He II columns, might contradict this picture if the material is not photospheric or circumstellar.

scholarly journals The X-shooter GRB afterglow legacy sample (XS-GRB)

2019 ◽  
Vol 623 ◽  
pp. A92 ◽  
Author(s):  
J. Selsing ◽  
D. Malesani ◽  
P. Goldoni ◽  
J. P. U. Fynbo ◽  
T. Krühler ◽  
...  
Keyword(s):  
Selection Criteria ◽  
Column Density ◽  
Neutral Hydrogen ◽  
Cosmic Time ◽  
Late Time ◽  
Host Galaxies ◽  
X Ray ◽  
Hydrogen Column Density ◽  
X Ray Absorption

In this work we present spectra of all γ-ray burst (GRB) afterglows that have been promptly observed with the X-shooter spectrograph until 31/03/2017. In total, we have obtained spectroscopic observations of 103 individual GRBs observed within 48 hours of the GRB trigger. Redshifts have been measured for 97 per cent of these, covering a redshift range from 0.059 to 7.84. Based on a set of observational selection criteria that minimise biases with regards to intrinsic properties of the GRBs, the follow-up effort has been focused on producing a homogeneously selected sample of 93 afterglow spectra for GRBs discovered by the Swift satellite. We here provide a public release of all the reduced spectra, including continuum estimates and telluric absorption corrections. For completeness, we also provide reductions for the 18 late-time observations of the underlying host galaxies. We provide an assessment of the degree of completeness with respect to the parent GRB population, in terms of the X-ray properties of the bursts in the sample and find that the sample presented here is representative of the full Swift sample. We have constrained the fraction of dark bursts to be <28 per cent and confirm previous results that higher optical darkness is correlated with increased X-ray absorption. For the 42 bursts for which it is possible, we have provided a measurement of the neutral hydrogen column density, increasing the total number of published HI column density measurements by ∼33 per cent. This dataset provides a unique resource to study the ISM across cosmic time, from the local progenitor surroundings to the intervening Universe.

scholarly journals Environmental Effects on Properties of Type 2 QSOs

2009 ◽  
Vol 5 (S267) ◽  
pp. 106-106
Author(s):  
Lin-wen Chen ◽  
Li-Ting Hsu
Keyword(s):  
Column Density ◽  
Neutral Hydrogen ◽  
Photometric Redshifts ◽  
X Ray ◽  
Sky Survey ◽  
Hydrogen Column Density ◽  
Population Figure ◽  
Two Populations ◽  
Projected Distance

Type 2 QSOs (QSO2s) are intrinsically luminous QSOs embedded in dusty environments. In this work, we study the radio, optical, and soft X-ray properties of 887 optically selected [O III]-based QSO2s (Reyes et al. 2008) at z<0.83 to investigate the connection between QSO2s and their environments. We use SDSS data to measure the luminosity-limited galaxy counts in a volume centered on each QSO2 and defined by Δ z<0.1 (based on photometric redshifts) and within a projected distance of 1.5 Mpc of the QSO2 (δ1.5Mpc). We used ROSAT All Sky Survey (RASS) data to estimate the X-ray excess. Hsu & Chen (2010), after correcting for Galactic absorption, obtain a lower limit for the intrinsic neutral hydrogen column density (NH) toward each of the QSO2s. About 50% of these sources have NH > 1022 cm−2. We take this value as a threshold to subdivide QSO2s into high- and low-NH groups, and compare their environments. The distributions δ1.5Mpc of the two populations show that, in regions of higher galaxy density, QSO2s are dominated by the high-NH population (Figure 1), suggesting a closer connection between more obscured QSO2s and surrounding galaxies.

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