The relation between optical extinction and hydrogen column density in the Galaxy

Güver, T.; Özel, Feryal

doi:10.1111/j.1365-2966.2009.15598.x

Cited by 549 publications

(256 citation statements)

References 53 publications

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“…This is about an order of magnitude lower than the hydrogen column density inferred from the ∼100 magnitudes of visual extinction corresponding to the silicate absorption feature, adopting a ratio of N(h) = 2.2×10 21 A(v) cm −2 (e.g. Guver & Ozel 2009). However, although the core is very compact at both IR and radio wavelengths, the underlying emission sampled by the silicate absorption may well have a different spatial extent to the radio continuum, and so we should perhaps not expect close agreement.…”

Section: The Obscured Nucleus Of Ngc 4418mentioning

confidence: 67%

The silicate absorption profile in the interstellar medium towards the heavily obscured nucleus of NGC 4418

Roche

Alonso‐Herrero

González‐Martín³

2015

Monthly Notices of the Royal Astronomical Society

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The 9.7-µm silicate absorption profile in the interstellar medium provides important information on the physical and chemical composition of interstellar dust grains. Measurements in the Milky Way have shown that the profile in the diffuse interstellar medium is very similar to the amorphous silicate profiles found in circumstellar dust shells around late M stars, and narrower than the silicate profile in denser star-forming regions. Here, we investigate the silicate absorption profile towards the very heavily obscured nucleus of NGC 4418, the galaxy with the deepest known silicate absorption feature, and compare it to the profiles seen in the Milky Way. Comparison between the 8-13 µm spectrum obtained with TReCS on Gemini and the larger aperture spectrum obtained from the Spitzer archive indicates that the former isolates the nuclear emission, while Spitzer detects low surface brightness circumnuclear diffuse emission in addition. The silicate absorption profile towards the nucleus is very similar to that in the diffuse ISM in the Milky Way with no evidence of spectral structure from crystalline silicates or silicon carbide grains.

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Section: The Obscured Nucleus Of Ngc 4418mentioning

confidence: 67%

The silicate absorption profile in the interstellar medium towards the heavily obscured nucleus of NGC 4418

Roche

Alonso‐Herrero

González‐Martín³

2015

Monthly Notices of the Royal Astronomical Society

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“…Most studies in the Galaxy have therefore not probed the ISM of the Milky Way in either a complete or unbiased way. These studies have consistently found a dust-to-gas ratio at a level of N H /A V ∼ 2 × 10 21 cm −2 mag −1 (Bohlin et al 1978;Whittet 1981;Diplas & Savage 1994;Ryter 1996;Reina & Tarenghi 1973;Gorenstein 1975;Ryter et al 1975;Predehl & Schmitt 1995;Vuong et al 2003;Güver & Özel 2009;Rachford et al 2009). The statistical errors quoted for some studies have been as small as a few 10 19 cm −2 mag −1 , however the variation from study to study is closer to a few parts in 10 20 cm −2 mag −1 .…”

Section: Introductionmentioning

confidence: 85%

The Galactic dust-to-metals ratio and metallicity using gamma-ray bursts

Watson

2011

A&A

112

108

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The metallicity and dust-to-metals ratio of the Galaxy are fundamental parameters in understanding the interstellar medium (ISM). Currently, there is still some uncertainty surrounding these parameters. In this paper, the dust-to-metals ratio in the Galaxy is determined using the photoelectric absorption of the soft X-ray afterglows of a large sample of several hundred gamma-ray bursts (GRBs) to determine the metal column density in combination with Galactic dust maps to determine the line-of-sight dust extinction through the Galaxy in the direction of the GRB. GRB afterglows often have large extragalactic soft X-ray absorptions and therefore the GRB sample's upper-bound will define the Galactic dust-to-metals relation. Using a two-dimensional two-sample Kolmogorov-Smirnoff test, we determine this upper-bound and so derive the dust-to-metals ratio of the Galaxy. We find N H = 2.2 +0.3 −0.4 × 10 21 cm −2 A V asassuming solar, Anders & Grevesse (1989, Geochim. Cosmochim. Acta, 53, 197), metallicity. This result is consistent with previous findings using bright X-ray sources in the Galaxy. Using the same technique but substituting the H i maps from the Leiden-ArgentineBonn survey for the dust maps, allows us to place a limit on the metallicity in the Galaxy. We find a metallicity consistent with the Anders & Grevesse (1989) solar values often used in X-ray fitting. Based on this and previous studies, we suggest that the metallicity of a typical ISM sightline through the Galaxy is ∼0.25 dex higher than the current best estimate of the solar metallicity. We further show that the dust-to-gas ratio seems to be correlated with the total gas column density, and that this may be due to the metallicity gradient observed toward the Galactic centre. Based on the non-constant nature of the dust-to-gas ratio, we propose that the dust column density, at N H = 2.2 × 10 21 cm −2 A V , represents a better proxy for the soft X-ray absorption column density than H i maps.

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“…We then proceeded to de-redden the magnitudes by choosing a value for the neutral hydrogen absorption column of N 1.4 0.2 10 cm Patruno et al 2009a). We used the relation (Güver & Özel 2009):…”

Section: Space-borne Uv/optical Observationsmentioning

confidence: 99%

The Reflares and Outburst Evolution in the Accreting Millisecond Pulsar Sax J1808.4–3658: A Disk Truncated Near Co-Rotation?

Patruno

Maitra

Curran

et al. 2016

ApJ

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The accreting millisecond X-ray pulsar SAX J1808.4-3658 shows peculiar low luminosity states known as "reflares" after the end of the main outburst. During this phase the X-ray luminosity of the source varies by up to three orders of magnitude in less than 1-2 days. The lowest X-ray luminosity observed reaches a value of 10 erg s 32 1 -, only a factor of a few brighter than its typical quiescent level. We investigate the 2008 and 2005 reflaring state of SAX J1808.4-3658 to determine whether there is any evidence for a change in the accretion flow with respect to the main outburst. We perform a multiwavelength photometric and spectral study of the 2005 and 2008 reflares with data collected during an observational campaign covering the near-infrared, optical, ultra-violet and X-ray band. We find that the NIR/optical/UV emission, expected to come from the outer accretion disk, shows variations in luminosity over an order of magnitude. The corresponding X-ray luminosity variations are instead much deeper, spanning about 2-3 orders of magnitude. The X-ray spectral state observed during the reflares does not change substantially with X-ray luminosity, indicating a rather stable configuration of the accretion flow. We investigate the most likely configuration of the innermost regions of the accretion flow and we infer an accretion disk truncated at or near the co-rotation radius. We interpret these findings as due to either a strong outflow (due to a propeller effect) or a trapped disk (with limited/no outflow) in the inner regions of the accretion flow.

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The relation between optical extinction and hydrogen column density in the Galaxy

Cited by 549 publications

References 53 publications

The silicate absorption profile in the interstellar medium towards the heavily obscured nucleus of NGC 4418

The silicate absorption profile in the interstellar medium towards the heavily obscured nucleus of NGC 4418

The Galactic dust-to-metals ratio and metallicity using gamma-ray bursts

The Reflares and Outburst Evolution in the Accreting Millisecond Pulsar Sax J1808.4–3658: A Disk Truncated Near Co-Rotation?

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