The GALFA-H i Survey Data Release 2

Peek, J. E. G.; Babler, B.; Zheng, Yong; Clark, Susan; Douglas, K. A.; Korpela, E. J.; Putman, Mary E.; Stanimirović, Snežana; Gibson, Steven J.; Heiles, Carl

doi:10.3847/1538-4365/aa91d3

Cited by 110 publications

(100 citation statements)

References 77 publications

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“…Equation 2 is correct under the assumption that the H i emission is optically thin, which is not valid for all sightlines in these data, but is generally a good approximation at high Galactic latitudes (Murray et al 2018). We also use the publicly available H i intensity and RHT output of ∆v = 3.7 km s −1 GALFA-H i channel maps from -36.4 km s −1 to +37.2 km s −1 described in Peek et al (2018), and convert to Galactic coordinates. Maps constructed from GALFA-H i data not only use independent 21-cm observations that are higher resolution than H i4PI, but also a different velocity range and binning scheme.…”

Section: Neutral Hydrogenmentioning

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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154

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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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Section: Neutral Hydrogenmentioning

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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154

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“…This calls for methods that can extract the information of each HI phase from fully sampled 21 cm emission data only. Huge efforts have been made to map the 21 cm emission of the Galactic HI (recent examples are Taylor et al 2003;Kalberla et al 2005;Stil et al 2006;McClure-Griffiths et al 2009;Winkel et al 2016;Peek et al 2018) and a large amount of data is now available. The information about the multiphase and multi-scale nature of the HI contained in these large hyperspectral data cubes has remained elusive due to the difficulty to separate the emission from the different phases on each line of sight.…”

Section: Introductionmentioning

confidence: 99%

ROHSA: Regularized Optimization for Hyper-Spectral Analysis

Marchal

Miville-Deschênes

Orieux

et al. 2019

A&A

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Context. Extracting the multiphase structure of the neutral interstellar medium (ISM) is key to understand the star formation in galaxies. The radiative condensation of the diffuse warm neutral medium producing a thermally unstable lukewarm medium and a dense cold medium is closely related to the initial step which leads the atomic-to-molecular (HI-to-H 2 ) transition and the formation of molecular clouds. Up to now the mapping of these phases out of 21 cm emission hyper-spectral cubes has remained elusive mostly due to the velocity blending of individual cold structures present on a given line of sight. As a result, most of the current knowledge about the HI phases rests on a small number of absorption measurements on lines of sight crossing radio sources. Aims. The goal of this work was to develop a new algorithm to perform separation of diffuse sources in hyper-spectral data. Specifically the algorithm was designed in order to address the velocity blending problem by taking advantage of the spatial coherence of the individual sources. The main scientific driver of this effort was to extract the multiphase structure of the HI from 21 cm line emission only, providing a mean to map each phase separately, but the algorithm developed here should be generic enough to extract diffuse structures in any hyper-spectral cube. Methods. We developed a new Gaussian decomposition algorithm named ROHSA (Regularized Optimization for Hyper-Spectral Analysis) based on a multi-resolution process from coarse to fine grid. ROHSA uses a regularized non-linear least-square criterion to take into account simultaneously the spatial coherence of the emission and the multiphase nature of the gas. In order to obtain a solution with spatially smooth parameters, the optimization is performed on the whole data cube at once. The performances of ROHSA were tested on a synthetic observation computed from numerical simulations of thermally bi-stable turbulence. An application on a 21 cm observation of a high Galactic latitude region from the GHIGLS survey is presented. Results. The evaluation of ROHSA on synthetic 21 cm observations shows that it is able to recover the multiphase nature of the HI. For each phase, the power spectra of the column density and centroid velocity are well recovered. More generally that test reveals that a Gaussian decomposition of HI emission is able to recover physically meaningful information about the underlying three-dimensional fields (density, velocity and temperature). The application on a real 21 cm observation of a high Galactic latitude field produces a picture of the multiphase HI, with isolated, filamentary and narrow (σ ∼ 1 − 2 km s −1 ) structures and wider (σ ∼ 4 − 10 km s −1 ), diffuse and space filling components. The test-case field used here contains significant intermediate-velocity clouds that were well mapped out by the algorithm. As ROHSA is designed to extract spatially coherent components, it performs well at projecting out the noise. Conclusions. In this paper we are introducing ROHSA a new a...

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“…-Locations of all 79 background radio continuum sources considered in this study, overlaid on the map of HI column density N * HI from the Arecibo GALFA-HI survey (DR2;Peek et al 2018). The N * HI range is (1-80) × 10 20 cm −2 .…”

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confidence: 99%

Exploring the Properties of Warm and Cold Atomic Hydrogen in the Taurus and Gemini Regions

Nguyen

Dawson

Lee

et al. 2019

ApJ

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We report Arecibo 21 cm absorption-emission observations to characterise the physical properties of neutral hydrogen (HI) in the proximity of five giant molecular clouds (GMCs): Taurus, California, Rosette, Mon OB1, NGC 2264. Strong HI absorption was detected toward all 79 background continuum sources in the ∼60×20 square degree region. Gaussian decompositions were performed to estimate temperatures, optical depths and column densities of the cold and warm neutral medium (CNM and WNM). The properties of individual CNM components are similar to those previously observed along random Galactic sightlines and in the vicinity of molecular clouds, suggesting a universality of cold HI properties. The CNM spin temperature (T s ) histogram peaks at ∼50 K. The turbulent Mach numbers of CNM components vary widely, with a typical value of ∼4, indicating that their motions are supersonic. About 60% of the total HI gas is WNM, and nearly 40% of the WNM lies in thermally unstable regime 500-5000 K. The observed CNM fraction is higher around GMCs than in diffuse regions, and increases with increasing column density (N HI ) to a maximum of ∼75%. On average, the optically thin approximation (N * HI ) underestimates the total column density by ∼21%, but we find large regional differences in the relationship between N HI and the required correction factor, f =N HI /N * HI . We examine two different methods (linear fit of f vs log 10 (N * HI ) and uniform T s ) to correct for opacity effects using emission data from the GALFA-HI survey. We prefer the uniform T s method, since the linear relationship does not produce convincing fits for all subregions.

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The GALFA-H i Survey Data Release 2

Cited by 110 publications

References 77 publications

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

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

ROHSA: Regularized Optimization for Hyper-Spectral Analysis

Exploring the Properties of Warm and Cold Atomic Hydrogen in the Taurus and Gemini Regions

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