Correlation of HI shells and CO clumps in the outer Milky Way

Ehlerová, S.; Palouš, J.

doi:10.1051/0004-6361/201526870

Cited by 11 publications

(10 citation statements)

References 26 publications

(37 reference statements)

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“…Assuming that the R-C cloud was formed by the Local Bubble pushing out and piling up the H i in a sheet-like structure, which we observe as an H i self-absorption cloud, makes it a plausible site for triggered molecular cloud formation similar to the edges of other supershells (e.g. Fukui & Kawamura 2010;Dawson et al 2011;Ehlerová & Palouš 2016;Dawson 2013 and references within). 4 https://www.cfa.harvard.edu/rtdc/CO/CompositeSurveys/ (Crutcher 1973) and the pink crosses show our OH line detections, the green triangles show the CRRL lines from (Roshi & Kantharia 2011).…”

Section: Discussionmentioning

confidence: 76%

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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Section: Discussionmentioning

confidence: 76%

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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“…Bagetakos et al (2011) established a spatial correlation between HI shells and super-bubbles created by the activity of massive stars in stellar clusters. Ehlerová & Palouš (2016) studied spatial correlation between HI shells and CO in the outer parts of the Milky Way. They found an increased occurrence of CO clouds in the walls of the HI shells.…”

Section: Discussionmentioning

confidence: 99%

Gas kinematics in high-mass star-forming regions from the Perseus spiral arm

2017

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We present results of a survey of 14 star-forming regions from the Perseus spiral arm in CS (2-1) and 13 CO (1-0) lines with the Onsala Space Observatory 20 m telescope. Maps of 10 sources in both lines were obtained. For the remaining sources a map in just one line or a single-point spectrum were obtained. On the basis of newly obtained and published observational data we consider the relation between velocities of the "quasi-thermal" CS (2-1) line and 6.7 GHz methanol maser line in 24 high-mass star-forming regions in the Perseus arm. We show that, surprisingly, velocity ranges of 6.7 GHz methanol maser emission are predominantly red-shifted with respect to corresponding CS (2-1) line velocity ranges in the Perseus arm. We suggest that the predominance of the "red-shifted masers" in the Perseus arm could be related to the alignment of gas flows caused by the large-scale motions in the Galaxy. Large-scale galactic shock related to the spiral structure is supposed to affect the local kinematics of the star-forming regions. Part of the Perseus arm, between galactic longitudes from 85 • to 124 • , does not contain blue-shifted masers at all. Radial velocities of the sources are the greatest in this particular part of the arm, so the velocity difference is clearly pronounced. 13 CO (1-0) and CS (2-1) velocity maps of G183.35-0.58 show gas velocity difference between the center and the periphery of the molecular clump up to 1.2 km s −1 . Similar situation is likely to occur in G85.40-0.00. This can correspond to the case when the large-scale shock wave entrains the outer parts of a molecular clump in motion while the dense central clump is less affected by the shock.

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“…The idea that the condensed gas in large-scale shocks fragments and causes the formation of molecular clouds is supported by observations of excess dense gas or young stars around superbubbles with respect to the field (Walborn & Parker 1992;Oey & Smedley 1998;Oey et al 2005;Dawson et al 2011bDawson et al ,a, 2013Ehlerová & Palouš 2016).…”

Section: Introductionmentioning

confidence: 97%

The role of magnetic fields in the structure and interaction of supershells

Ntormousi

Dawson

Hennebelle

et al. 2017

A&A

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Context. Large-scale shocks formed by clustered feedback of young OB stars are considered an important source of mechanical energy for the interstellar medium (ISM) and a trigger of molecular cloud formation. Their interaction sites are locations where kinetic energy and magnetic fields are redistributed between ISM phases. Aims. In this work we address two questions, both involving the role of galactic magnetic fields in the dynamics of supershells and their interactions. On the one hand, we study the effect of the magnetic field on the expansion and fragmentation of supershells and, on the other hand, we look for the signatures of supershell collisions on dense structures and on the kinetic and magnetic energy distribution of the ISM. Methods. We performed a series of high-resolution, three-dimensional simulations of colliding supershells. The shocks are created by time-dependent feedback and evolve in a diffuse turbulent environment that is either unmagnetized or has different initial magnetic field configurations. Results. In the hydrodynamical situation, the expansion law of the superbubbles is consistent with the radius-time relation R ∝ t 3/5 that is theoretically predicted for wind-blown bubbles. The supershells fragment over their entire surface into small dense clumps that carry more than half of the total kinetic energy in the volume. However, this is not the case when a magnetic field is introduced, either in the direction of the collision or perpendicular to the collision. In both situations, the shell surfaces are more stable to dynamical instabilities. When the magnetic field opposes the collision, the expansion law of the supershells also becomes significantly flatter than in the hydrodynamical case. Although a two-phase medium arises in all cases, in the magnetohydrodynamical (MHD) simulations the cold phase is limited to lower densities and the cold clumps are located further away from the shocks with respect to the hydrodynamical simulations. Conclusions. For the parameters we explored, self-gravity has no effect on either the superbubble expansion or the shock fragmentation. In contrast, a magnetic field, whether mostly parallel or mostly perpendicular to the collision axis, causes a deceleration of the shocks, deforms them significantly, and largely suppresses the formation of the dense gas on their surface. The result is a multi-phase medium in which the cold clumps are not spatially correlated with the supershells.

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Correlation of HI shells and CO clumps in the outer Milky Way

Cited by 11 publications

References 26 publications

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

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

Gas kinematics in high-mass star-forming regions from the Perseus spiral arm

The role of magnetic fields in the structure and interaction of supershells

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