Recovering Interstellar Gas Properties with Hi Spectral Lines: A Comparison between Synthetic Spectra and 21-SPONGE

Murray, Claire E.; Stanimirović, Snežana; Kim, Chang-Goo; Ostriker, Eve C.; Lindner, Robert R.; Heiles, Carl; Dickey, John M.; Babler, B.

doi:10.3847/1538-4357/aa5d12

Cited by 33 publications

(43 citation statements)

References 45 publications

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“…Each spectrum can be decomposed into a set of Gaussian basis functions, yielding a compressed description of the data (e.g., Haud 2000). This approach has been adopted by many previous works for studying the properties of different ISM phases (e.g., Roy et al 2013;Lindner et al 2015;Murray et al 2017;Kalberla & Haud 2018;Marchal et al 2019;Riener et al 2019), as well as detecting different classes of clouds (e.g., Haud 2008Haud , 2010. D. Lenz (2020, in preparation) created a Gaussian decomposition of this data set that is publicly available.…”

Section: Data and Gaussian Decompositionmentioning

confidence: 99%

Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Panopoulou

Lenz

2020

ApJ

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Characterizing the structure of the Galactic interstellar medium (ISM) in three dimensions is of high importance for accurate modeling of dust emission as a foreground to the cosmic microwave background (CMB). At high Galactic latitude, where the total dust content is low, accurate maps of the 3D structure of the ISM are lacking. We develop a method to quantify the complexity of the distribution of dust along the line of sight with the use of H I line emission. The method relies on a Gaussian decomposition of the H I spectra to disentangle the emission from overlapping components in velocity. We use this information to create maps of the number of clouds along the line of sight. We apply the method to (a) the high Galactic latitude sky and (b) the region targeted by the BICEP/Keck experiment. In the north Galactic cap we find on average three clouds per 0.2 square degree pixel, while in the south the number falls to 2.5. The statistics of the number of clouds are affected by intermediate-velocity clouds (IVCs), primarily in the north. IVCs produce detectable features in the dust emission measured by Planck. We investigate the complexity of H I spectra in the BICEP/Keck region and find evidence for the existence of multiple components along the line of sight. The data (doi: 10.7910/DVN/8DA5LH) and software are made publicly available and can be used to inform CMB foreground modeling and 3D dust mapping.Unified Astronomy Thesaurus concepts: Interstellar medium (847); Neutral hydrogen clouds (1099); Interstellar atomic gas (833)

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Section: Data and Gaussian Decompositionmentioning

confidence: 99%

Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Panopoulou

Lenz

2020

ApJ

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“…The τ spectra can be described as the sum of Gaussian components (e.g. Heiles & Troland 2003a;Murray et al 2017). To decompose the absorption spectra into Gaussian components we use the Autonomous Gaussian Decomposition algorithm (AGD; GaussPy) from Lindner et al (2015).…”

Section: Gaussian Decompositionmentioning

confidence: 99%

“…Because of the location of the R-C cloud, in the Galactic plane and in front of the GC, these data are especially susceptible. Murray et al (2017) investigated the recovery rate of the AGD algorithm on simulated H i spectra. They found that AGD has a very good recovery rate for simple LOS, e.g.…”

Section: Sources Of Uncertainty and Errorsmentioning

confidence: 99%

Calibrating the HISA temperature: Measuring the temperature of the Riegel–Crutcher cloud

Dénes

McClure-Griffiths

Dickey

et al. 2018

Monthly Notices of the Royal Astronomical Society

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H i self absorption (HISA) clouds are clumps of cold neutral hydrogen (H i) visible in front of warm background gas, which makes them ideal places to study the properties of the cold atomic component of the interstellar medium (ISM). The Riegel-Crutcher (R-C) cloud is the most striking HISA feature in the Galaxy. It is one of the closest HISA clouds to us and is located in the direction of the Galactic Centre, which provides a bright background. High-resolution interferometric measurements have revealed the filamentary structure of this cloud, however it is difficult to accurately determine the temperature and the density of the gas without optical depth measurements. In this paper we present new H i absorption observations with the Australia Telescope Compact Array (ATCA) against 46 continuum sources behind the Riegel-Crutcher cloud to directly measure the optical depth of the cloud. We decompose the complex H i absorption spectra into Gaussian components using an automated machine learning algorithm. We find 300 Gaussian components, from which 67 are associated with the R-C cloud (0 < v LSR < 10 km s −1 , FWHM < 10 km s −1 ). Combining the new H i absorption data with H i emission data from previous surveys we calculate the spin temperature and find it to be between 20 and 80 K. Our measurements uncover a temperature gradient across the cloud with spin temperatures decreasing towards positive Galactic latitudes. We also find three new OH absorption lines associated with the cloud, which support the presence of molecular gas.

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“…On smaller scales, simulations have been used to study the link between H and molecular clouds in the outer Galaxy (Douglas et al 2010), the effect of outflows on the H content of galaxies (Davé et al 2013), the observable properties and physical conditions of the Galactic interstellar H (Kim et al 2014;Murray et al 2017;Fukui et al 2018), H surface density profiles (Bahé et al 2016;Stevens et al 2019b), and the origin of spiral arms in H far beyond the optical radius of a galaxy (Khoperskov & Bertin 2016). Other studies used the H content of simulated galaxies to study gas kinematics (El-Badry et al 2018), dwarf galaxy rotation curves (Oman et al 2019), and damped Lyman-alpha absorbers (Garratt-Smithson et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Drivers of asymmetry in synthetic H I emission-line profiles of galaxies in the EAGLE simulation

Manuwal,

Ludlow,

Stevens

et al. 2021

Preprint

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We study the shapes of spatially integrated H emission line profiles of galaxies in the simulation using three separate measures of the profile's asymmetry. We show that the subset of galaxies whose gas fractions and stellar masses are consistent with those in the xGASS survey also have similar H line asymmetries. Central galaxies with symmetric H line profiles typically correspond to rotationally supported H and stellar disks, but those with asymmetric line profiles may or may not correspond to dispersion-dominated systems. Galaxies with symmetric H emission lines are, on average, more gas rich than those with asymmetric lines, and also exhibit systematic differences in their specific star formation rates, suggesting that turbulence generated by stellar or AGN feedback may be one factor contributing to H line asymmetry. The line asymmetry also correlates strongly with the dynamical state of a galaxy's host dark matter halo: older, more relaxed haloes host more-symmetric galaxies than those hosted by unrelaxed ones. At fixed halo mass, asymmetric centrals tend to be surrounded by a larger number of massive subhaloes than their symmetric counterparts, and also experience higher rates of gas accretion and outflow. At fixed stellar mass, central galaxies have, on average, more symmetric H emission lines than satellites; for the latter, ram pressure and tidal stripping are significant sources of asymmetry.

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Recovering Interstellar Gas Properties with Hi Spectral Lines: A Comparison between Synthetic Spectra and 21-SPONGE

Cited by 33 publications

References 45 publications

Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Calibrating the HISA temperature: Measuring the temperature of the Riegel–Crutcher cloud

Drivers of asymmetry in synthetic H I emission-line profiles of galaxies in the EAGLE simulation

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