The diffuse ultraviolet background and its relation to neutral hydrogen column density

1989 ◽  
Author(s):  
Brent W. Studer
Keyword(s):  
Column Density ◽  
Neutral Hydrogen ◽  
Hydrogen Column Density

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

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 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.

scholarly journals Using realistic host galaxy metallicities to improve the GRB X-ray equivalent total hydrogen column density and constrain the intergalactic medium density

2020 ◽  
Vol 495 (2) ◽  
pp. 2342-2353
Author(s):  
Tony Dalton ◽  
Simon L Morris
Keyword(s):  
Column Density ◽  
Intergalactic Medium ◽  
Neutral Hydrogen ◽  
Accurate Estimate ◽  
Host Galaxy ◽  
Lower Envelope ◽  
Sample Mean ◽  
X Ray ◽  
Hydrogen Column Density ◽  
Solar Metallicity

ABSTRACT It is known that the GRB equivalent hydrogen column density (NHX) changes with redshift and that, typically, NHX is greater than the GRB host neutral hydrogen column density. We have compiled a large sample of data for GRB NHX and metallicity [X/H]. The main aims of this paper are to generate improved NHX for our sample by using actual metallicities, dust corrected where available for detections, and for the remaining GRB, a more realistic average intrinsic metallicity using a standard adjustment from solar. Then, by approximating the GRB host intrinsic hydrogen column density using the measured neutral column (NHI, IC) adjusted for the ionization fraction, we isolate a more accurate estimate for the intergalactic medium (IGM) contribution. The GRB sample mean metallicity is = −1.17 ± 0.09 rms (or 0.07 ± 0.05 Z/Zsol) from a sample of 36 GRB with a redshift 1.76 ≤ z ≤ 5.91, substantially lower than the assumption of solar metallicity used as standard for many fitted NHX. Lower GRB host mean metallicity results in increased estimated NHX with the correction scaling with redshift as Δlog (NHX cm−2) = (0.59 ± 0.04)log(1 + z) + 0.18 ± 0.02. Of the 128 GRB with data for both NHX and NHI, IC in our sample, only six have NHI, IC &gt; NHX when revised for realistic metallicity, compared to 32 when solar metallicity is assumed. The lower envelope of the revised NHX – NHI, IC, plotted against redshift can be fit by log(NHX – NHI, IC cm−2) = 20.3 + 2.4 log(1 + z). This is taken to be an estimate for the maximum IGM hydrogen column density as a function of redshift. Using this approach, we estimate an upper limit to the hydrogen density at redshift zero (n0) to be consistent with n0 = 0.17 × 10−7cm−3.

scholarly journals Spectral Observations of the Diffuse FUV Background with DUVE (the Diffuse UV Experiment)

1997 ◽  
Vol 166 ◽  
pp. 57-60
Author(s):  
Eric J. Korpela ◽  
Stuart Bowyer
Keyword(s):  
Column Density ◽  
Emission Measure ◽  
Neutral Hydrogen ◽  
Integration Time ◽  
Hydrogen Line ◽  
Plasma Parameters ◽  
Interstellar Plasma ◽  
Hydrogen Column Density ◽  
Upper Limits ◽  
Effective Integration

AbstractWe present results from a search for FUV emission from the diffuse ISM conducted with an orbital FUV spectrometer, DUVE, which was launched in July, 1992. The DUVE spectrometer, which covers the band from 950 Å to 1080 Å with 3.2 Å resolution, observed a region of low neutral hydrogen column density near the south galactic pole for a total effective integration time of 1583 seconds, the only emission line detected was a geocoronal hydrogen line at 1025 Å . We were able to place upper limits to several emission features that provide constraints to interstellar plasma parameters. We were also able to place continuum limits in this band. We use these upper limits to place constraints upon the emission measure vs. temperature distribution of this gas using an isothermal Landini and Fossi model.

scholarly journals Exploring the pattern of the Galactic HI foreground of GRBs with the ATCA

2019 ◽  
Author(s):  
H Dénes ◽  
P A Jones ◽  
L V Tóth ◽  
S Zahorecz ◽  
B-C Koo ◽  
...  
Keyword(s):  
Column Density ◽  
Gamma Ray ◽  
Neutral Hydrogen ◽  
Far Infrared ◽  
Host Galaxy ◽  
Valuable Insight ◽  
Host Galaxies ◽  
Sky Survey ◽  
Hydrogen Column Density ◽  
Density Values

Abstract The afterglow of a gamma ray burst (GRB) can give us valuable insight into the properties of its host galaxy. To correctly interpret the spectra of the afterglow we need to have a good understanding of the foreground interstellar medium (ISM) in our own Galaxy. The common practice to correct for the foreground is to use neutral hydrogen (H i) data from the Leiden/Argentina/Bonn (LAB) survey. However, the poor spatial resolution of the single dish data may have a significant effect on the derived column densities. To investigate this, we present new high-resolution H i observations with the Australia Telescope Compact Array (ATCA) towards 4 GRBs. We combine the interferometric ATCA data with single dish data from the Galactic All Sky Survey (GASS) and derive new Galactic H i column densities towards the GRBs. We use these new foreground column densities to fit the Swift XRT X-ray spectra and calculate new intrinsic hydrogen column density values for the GRB host galaxies. We find that the new ATCA data shows higher Galactic H i column densities compared to the previous single dish data, which results in lower intrinsic column densities for the hosts. We investigate the line of sight optical depth near the GRBs and find that it may not be negligible towards one of the GRBs, which indicates that the intrinsic hydrogen column density of its host galaxy may be even lower. In addition, we compare our results to column densities derived from far-infrared data and find a reasonable agreement with the H i data.

Probing the circumstellar medium of GRB afterglows through absorption-line observations

2007 ◽  
Vol 365 (1854) ◽  
pp. 1247-1253 ◽  
Author(s):  
Hsiao-Wen Chen
Keyword(s):  
Absorption Line ◽  
Radiation Field ◽  
High Velocity ◽  
Column Density ◽  
Gamma Ray ◽  
Neutral Hydrogen ◽  
Gamma Ray Bursts ◽  
Host Galaxies ◽  
Hydrogen Column Density ◽  
Progenitor Stars

A systematic search of Wolf–Rayet wind signatures, as represented by blue-shifted, high-velocity (|Δ v |=1000–5000 km s −1 ) C IV λλ 1548, 1550 absorption doublet has yielded an estimate of 20% for the incidence of these C IV absorbers near the host galaxies of gamma-ray bursts (GRBs). This is consistent with what is observed near classical damped Ly α absorbers that have a comparable neutral hydrogen column density as the GRB host galaxies. A detailed ionization analysis of these absorbers, including the associated low-ionization species, shows that the majority in fact originate in foreground galaxies along the sightline, rather than in the vicinity of the GRB afterglows. Taking into account the enhanced afterglow radiation field, the lack of Wolf–Rayet signatures can be applied to constrain the C/He ratio and the density contrast of the winds in the vicinity of GRB progenitor stars.

scholarly journals Influence of Gravitational Lensing on Estimates of Ω in Neutral Hydrogen

1996 ◽  
Vol 173 ◽  
pp. 97-98
Author(s):  
Matthias Bartelmann ◽  
Abraham Loeb
Keyword(s):  
Observational Data ◽  
Gravitational Lensing ◽  
Column Density ◽  
Spiral Galaxies ◽  
Neutral Hydrogen ◽  
Absorption Lines ◽  
Gravitational Lenses ◽  
High Column

A wealth of observational data supports the commonly held view that damped Lyman-α (Lyα) absorption in QSO spectra is associated with neutral-hydrogen (HI) disks in spiral galaxies. Most of the HI probed by QSO absorption lines is traced by damped Lyα lines because of their high column densities, N > 1020 cm–2. The spiral galaxies hosting the HI disks can act as gravitational lenses on the QSOs. If the HI column density increases towards the center of the disks, as suggested by observations of local galaxies, the magnification bias preferentially selects for high column-density systems. The estimates of HI in damped Lyα systems can then systematically be distorted by gravitational lensing.

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