A High-Velocity Cloud Impact Forming a Supershell in the Milky Way

Park, Geumsook; Koo, Bon‐Chul; Kang, Ji-hyun; Gibson, Steven J.; Peek, J. E. G.; Douglas, K. A.; Korpela, E. J.; Heiles, Carl

doi:10.3847/2041-8205/827/2/l27

Cited by 15 publications

(21 citation statements)

References 36 publications

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“…This would therefore require in the order of hundreds of Type ii supernovae to drive this shell, which is rather unlikely, especially as there is no strong X-ray source at the centre of the shell, which would be expected in the presence of hundreds of expected supernova remnants. A more suitable explanation might be the passage of a high velocity cloud (HVC) through the Galactic disk, like the one observed by Park et al (2016) causing the Galactic shell GS040.2+00.6-70 in the northern hemisphere. Furthermore, HVCs are known to punch holes through galactic discs (e.g.…”

Section: The Galactic Supershell Gsh 242-03+37mentioning

confidence: 99%

A new search for star forming regions in the southern outer Galaxy

König

Urquhart

Wyrowski

et al. 2021

A&A

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Context. Star formation in the outer Galaxy is thought to be different from that in the inner Galaxy, as it is subject to different environmental parameters such as metallicity, interstellar radiation field, or mass surface density, which all change with galactocentric radius. Extending our star formation knowledge, from the inner to the outer Galaxy, helps us to understand the influences of the change of the environment on star formation throughout the Milky Way. Aims. We aim to obtain a more detailed view on the structure of the outer Galaxy, determining physical properties for a large number of star forming clumps and understanding star formation outside the solar circle. As one of the largest expanding Galactic super-shells is present in the observed region, a unique opportunity is taken here to investigate the influence of such an expanding structure on star formation as well. Methods. We used pointed 12CO(2–1) observations conducted with the APEX telescope to determine the velocity components towards 830 dust clumps identified from 250 μm Herschel/Hi-GAL SPIRE emission maps in the outer Galaxy between 225° < ℓ < 260°. We determined kinematic distances from the velocity components, in order to analyze the structure of the outer Galaxy and to estimate physical properties such as dust temperatures, bolometric luminosities, clump masses, and H2 column densities for 611 clumps. For this, we determined the dust spectral energy density distributions from archival mid-infrared to submillimeter (submm) emission maps. Results. We find the identified CO clouds to be strongly correlated with the highest column density parts of the H I emission distribution, spanning a web of bridges, spurs, and blobs of star forming regions between the larger complexes, unveiling the complex three-dimensional structure of the outer Galaxy in unprecedented detail. Using the physical properties of the clumps, we find an upper limit of 6% (40 sources) capable of forming high-mass stars. This is supported by the fact that only two methanol Class II masers, or 34 known or candidate H II regions, are found in the whole survey area, indicating an even lower fraction that are able to form high-mass stars in the outer Galaxy. We fail to find any correlation of the physical parameters of the identified (potential) star forming regions with the expanding supershell, indicating that although the shell organizes the interstellar material into clumps, the properties of the latter are unaffected. Conclusions. Using the APEX telescope in combination with publicly available Hi-GAL, MSX, and Wise continuum emission maps, we were able to investigate the structure and properties of a region of the Milky Way in unprecedented detail.

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Section: The Galactic Supershell Gsh 242-03+37mentioning

confidence: 99%

A new search for star forming regions in the southern outer Galaxy

König

Urquhart

Wyrowski

et al. 2021

A&A

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“…Kereš & Hernquist 2009) suggest that clouds with masses 3 × 10 5 M should survive the fall through the inner halo of the Galaxy. Recently, Park et al (2016) associated an HVC with a supershell of HI in the outskirts of the Galactic disc.…”

Section: A Plunging Halo Object?mentioning

confidence: 99%

La Freccia Rossa: an IR-dark cloud hosting the Milky Way intermediate-mass black hole candidate

Ravi

Vedantham

Phinney

2018

Monthly Notices of the Royal Astronomical Society: Letters

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The dynamics of the high-velocity compact molecular cloud CO-0.40-0.22 have been interpreted as evidence for a ∼10 5 M black hole within 60 pc of Sgr A *. Recently, Oka et al. have identified a compact millimetre-continuum source, CO-0.40-0.22 * , with this candidate black hole. Here we present a collation of radio and infrared data at this location. Australia Telescope Compact Array constraints on the radio spectrum, and the detection of a mid-infrared counterpart, are in tension with an Sgr A *-like model for CO-0.40-0.22 * despite the comparable bolometric to the Eddington luminosity ratios under the intermediate-mass black hole interpretation. A protostellar-disc scenario is, however, tenable. CO-0.40-0.22(*) is positionally coincident with an arrowhead-shaped infrared-dark cloud (which we call the Freccia Rossa). If the V LSR ≈ 70 km s −1 systemic velocity of CO-0.40-0.22 is common to the entire Freccia Rossa system, we hypothesize that it is the remnant of a high-velocity cloud that has plunged into the Milky Way from the Galactic halo.

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“…Large-scale gravitational instabilities due to the combined action of gas and stars (Jog & Solomon 1984;Elmegreen 2011;Shadmehri & Khajenabi 2012;Marchuk 2018;Marchuk & Sotnikova 2018) can also drive turbulence in galactic disks. Other internal mechanisms of the galaxy that can perturb the self-similar nature of the gas and shape its spatial structure include stellar spiral density waves (e.g., Lin & Shy 1966;Guibert 1974;Adler & Westpfahl 1996;Tosaki et al 2007;Khoperskov & Bertin 2015;Wang et al 2015), the Parker instability (e.g., Parker 1967;Franco et al 2002;Hanasz & Lesch 2003;Rodrigues et al 2016;Mouschovias et al 2009;Heintz et al 2020), and the impact of high-velocity clouds on the galactic disk (e.g., Santillan et al 1999;Boomsma et al 2008;Heitsch & Putman 2009;Park et al 2016). External mechanisms can also impart energy and momentum to the gas on galactic scales.…”

Section: Introductionmentioning

confidence: 99%

The structure and characteristic scales of the H I gas in galactic disks

Dib

Braine

Maheswar

et al. 2021

A&A

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The spatial distribution of the H I gas in galactic disks holds important clues about the physical processes that shape the structure and dynamics of the interstellar medium (ISM). The structure of the ISM could be affected by a variety of perturbations internal and external to the galaxy, and the unique signature of each of these perturbations could be visible in the structure of interstellar gas. In this work, we quantify the structure of the H I gas in a sample of 33 nearby galaxies taken from the HI Nearby Galaxy Survey (THINGS) using the delta-variance (Δ-variance) spectrum. The THINGS galaxies display a large diversity in their spectra, but there are a number of recurrent features. In many galaxies, we observe a bump in the spectrum on scales of a few to several hundred parsec. We find the characteristic scales associated with the bump to be correlated with the galactic star formation rate (SFR) for values of the SFR ≳0.5 M⊙ yr−1 and also with the median size of the H I shells detected in these galaxies. We interpret this characteristic scale as being associated with the effects of feedback from supernova explosions. On larger scales, we observe in most galaxies two self-similar, scale-free regimes. The first regime, on intermediate scales (≲0.5R25), is shallow, and the power law that describes this regime has an exponent in the range [0.1–1] with a mean value of 0.55 that is compatible with the density field that is generated by supersonic turbulence in the cold phase of the H I gas. The second power law is steeper, with a range of exponents between 0.5 and 2.3 and a mean value of ≈1.5. These values are associated with subsonic to transonic turbulence, which is characteristic of the warm phase of the H I gas. The spatial scale at which the transition between the two self-similar regimes occurs is found to be ≈0.5R25, which is very similar to the size of the molecular disk in the THINGS galaxies. Overall, our results suggest that on scales ≲0.5R25, the structure of the ISM is affected by the effects of supernova explosions. On larger scales (≳0.5R25), stellar feedback has no significant impact, and the structure of the ISM is determined by large-scale processes that govern the dynamics of the gas in the warm neutral medium, such as the flaring of the H I disk at large galactocentric radii and the effects of ram pressure stripping.

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A High-Velocity Cloud Impact Forming a Supershell in the Milky Way

Cited by 15 publications

References 36 publications

A new search for star forming regions in the southern outer Galaxy

A new search for star forming regions in the southern outer Galaxy

La Freccia Rossa: an IR-dark cloud hosting the Milky Way intermediate-mass black hole candidate

The structure and characteristic scales of the H I gas in galactic disks

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A High-Velocity Cloud Impact Forming a Supershell in the Milky Way

Cited by 15 publications

References 36 publications

A new search for star forming regions in the southern outer Galaxy

A new search for star forming regions in the southern outer Galaxy

La Freccia Rossa: an IR-dark cloud hosting the Milky Way intermediate-mass black hole candidate

The structure and characteristic scales of the H I gas in galactic disks

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Resources

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The structure and characteristic scales of the H I gas in galactic disks