A New, Large-scale Map of Interstellar Reddening Derived from H i Emission

Lenz, Daniel; Hensley, Brandon; Doré, O.

doi:10.3847/1538-4357/aa84af

Cited by 129 publications

(202 citation statements)

References 70 publications

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“…Liszt (2014a,b) compared N H I and E(B − V), resulting in N H (cm −2 )/E(B − V) = 8.3 × 10 21 cm −2 mag −1 for |b| ≥ 20 • and 0.015 ≤ E(B − V) ≤ 0.075. Similar results have also been found by Lenz et al (2017) in low N H I (< 4 × 10 20 cm −2 ) regions, and by Nguyen et al (2018) along purely atomic sightlines (8.8 × 10 21 and (9.4 ± 1.6) × 10 21 cm −2 mag −1 , respectively). γ-ray observations from Fermi show the ratio decreases from atomic clouds to dense molecular clouds by a factor of ∼0.6 (Remy et al 2018).…”

Section: Hco + As a Molecular Gas Tracersupporting

confidence: 86%

Revealing the CO X-factor in Dark Molecular Gas through Sensitive ALMA Absorption Observations

Luo

Tang³

et al. 2020

ApJL

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Carbon-bearing molecules, particularly CO, have been widely used as tracers of molecular gas in the interstellar medium (ISM). In this work, we aim to study the properties of molecules in diffuse, cold environments, where CO tends to be under-abundant and/or sub-thermally excited. We performed one of the most sensitive (down to τ CO rms ∼ 0.002 and τ HCO + rms ∼ 0.0008) sub-millimeter molecular absorption line observations towards 13 continuum sources with the ALMA. CO absorption was detected in diffuse ISM down to A v < 0.32 mag and HCO + was down to A v < 0.2 mag, where atomic gas and dark molecular gas (DMG) starts to dominate. Multiple transitions measured in absorption toward 3C454.3 allow for a direct determination of excitation temperatures T ex of 4.1 K and 2.7 K, for CO and for HCO + , respectively, which are close to the cosmic microwave background (CMB) and provide explanation for their being undercounted in emission surveys. A stronger linear correlation was found between N HCO + and N H2 (Pearson correlation coefficient P ∼ 0.93) than that of N CO and N H2 (P ∼ 0.33), suggesting HCO + being a better tracer of H 2 than CO in diffuse gas. The derived CO-to-H 2 conversion factor (the CO X-factor) of (14 ± 3) × 10 20 cm −2 (K km s −1 ) −1 is approximately 6 times larger than the average value found in the Milky Way.

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Section: Hco + As a Molecular Gas Tracersupporting

confidence: 86%

Revealing the CO X-factor in Dark Molecular Gas through Sensitive ALMA Absorption Observations

Luo

Tang³

et al. 2020

ApJL

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“…Although this relationship breaks down at higher column densities where molecular gas can constitute a significant fraction of the hydrogen column, N HI is a reliable tracer of the total dust column for low-column lines of sight. Recent analysis of the HI4PI data found that N HI and the dust reddening E(B − V ) are well-fit by a linear relationship for N HI < 4 × 10 20 cm −2 with a scatter of ∼ 10% (Lenz et al 2017).…”

Section: Observational Basismentioning

confidence: 99%

“…In general we expect contamination from these extragalactic objects to decrease the correlation between our H i-based maps and the Planck data, as the component-separated 353 GHz maps in principle trace only Galactic dust. This is particularly true in the case of HVCs, which are H i rich but dust deficient (Wakker & Boulanger 1986;Planck Collaboration XXIV 2011;Lenz et al 2017). We have purposefully restricted the velocity range of the H i gas that we consider in this work to −93.9 < v < 96.7 km s −1 in order to avoid the bulk of this high-velocity emission.…”

Section: Comparison Of Integrated Quantities As a Function Of H I Velmentioning

confidence: 99%

Mapping the Magnetic Interstellar Medium in Three Dimensions over the Full Sky with Neutral Hydrogen

Clark¹,

Hensley²

2019

ApJ

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149

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Recent analyses of 21-cm neutral hydrogen (H i) emission have demonstrated that H i gas is organized into linear filamentary structures that are preferentially aligned with the local magnetic field, and that the coherence of these structures in velocity space traces line-of-sight magnetic field tangling. On this basis, we introduce a paradigm for modeling the properties of magnetized, dusty regions of the interstellar medium, using the orientation of H i structure at different velocities to map "magnetically coherent" regions of space. We construct three-dimensional (position-position-velocity) Stokes parameter maps using H i4PI full-sky spectroscopic H i data. We compare these maps, integrated over the velocity dimension, to Planck maps of the polarized dust emission at 353 GHz. Without any free parameters governing the relation between H i intensity and dust emission, we find that our Q and U maps are highly correlated (r > 0.75) with the 353 GHz Q and U maps of polarized dust emission observed by Planck and reproduce many of its large-scale features. The E/B ratio of the dust emission maps agrees well with the H i-derived maps at large angular scales ( 120), supporting the interpretation that this asymmetry arises from the coupling of linear density structures to the Galactic magnetic field. We demonstrate that our 3D Stokes parameter maps constrain the 3D structure of the Galactic interstellar medium and the orientation of the interstellar magnetic field.

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“…In this work, we employ the N H i map 4 derived from the HI4PI data by Lenz et al (2017), which filters out all H I emission having radial velocity |v LSR | > 90 km s −1 . Such high velocity gas was found to have little correlation with dust reddening (Lenz et al 2017), and so the filtered map provides a better predictor of the dust column. Additionally, this velocity-filtered map is free from extragalactic contamination down to very low levels (Chiang & Ménard 2019).…”

Section: H I Mapmentioning

confidence: 99%

An Imprint of the Galactic Magnetic Field in the Diffuse Unpolarized Dust Emission

Hensley

Zhang

Bock

2019

ApJ

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It is well known that aligned, aspherical dust grains emit polarized radiation and that the degree of polarization depends on the angle ψ between the interstellar magnetic field and the line of sight. However, anisotropy of the dust absorption cross sections also modulates the total intensity of the radiation as the viewing geometry changes. We report a detection of this effect in the high Galactic latitude Planck data, finding that the 353 GHz dust intensity per N H i is smaller when the Galactic magnetic field is mostly in the plane of the sky and larger when the field is mostly along the line of sight. These variations are of opposite sign and roughly equal magnitude as the changes in polarized intensity per N H i with ψ, as predicted. In principle, the variation in intensity can be used in conjunction with the dust polarization angle to constrain the full 3D orientation of the Galactic magnetic field.

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A New, Large-scale Map of Interstellar Reddening Derived from H i Emission

Cited by 129 publications

References 70 publications

Revealing the CO X-factor in Dark Molecular Gas through Sensitive ALMA Absorption Observations

Revealing the CO X-factor in Dark Molecular Gas through Sensitive ALMA Absorption Observations

Mapping the Magnetic Interstellar Medium in Three Dimensions over the Full Sky with Neutral Hydrogen

An Imprint of the Galactic Magnetic Field in the Diffuse Unpolarized Dust Emission

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