Star formation in a diffuse high-altitude cloud?

Abstract

Context. A recent discovery of two stellar clusters associated with the diffuse high-latitude cloud HRK 81.4-77.8 has important implications for star formation in the Galactic halo. Aims. We derive a plausible distance estimate to HRK 81.4-77.8 primarily from its gaseous properties. Methods. We spatially correlate state-of-the-art HI, far-infrared and soft X-ray data to analyze the diffuse gas in the cloud. The absorption of the soft X-ray emission from the Galactic halo by HRK 81.4-77.8 is used to constrain the distance to the cloud. Results. HRK 81.4-77.8 is most likely located at an altitude of about 400 pc within the disk-halo interface of the Milky Way Galaxy. The HI data discloses a disbalance in density and pressure between the warm and cold gaseous phases. Apparently, the cold gas is compressed by the warm medium. This disbalance might trigger the formation of molecular gas high above the Galactic plane on pc to sub-pc scales.

SCOPE: SCUBA-2 Continuum Observations of Pre-protostellar Evolution – survey description and compact source catalogue

“…Some clouds at higher latitudes show signs of star formation (e.g. McGehee 2008;Malinen et al 2014;Kerp, Lenz & Röhser 2016). Hence, high-latitude clouds could be contributing to Galactic star formation, both at present and in the future by providing source material for fresh star formation.…”

HI4PI: a full-sky H i survey based on EBHIS and GASS

“…In the past it has been used to study the MW halo (Ford et al 2008;Winkel et al 2011;Ben Bekhti et al 2012;Venzmer et al 2012;Hernandez et al 2013;Moss et al 2013;For et al 2014;Röhser et al 2014;Hammer et al 2015;Lenz et al 2016;Kerp et al 2016b) and the disk-halo interaction (Ford et al 2010;McClureGriffiths et al 2010;Lenz et al 2015;Röhser et al 2016a). Likewise the MW disk material itself can be explored in much greater detail than previously feasible (e.g., Haud 2013; , also revealing spectacular Galactic super-shells (McClure-Griffiths et al 2006;Moss et al 2012).…”

Probing galaxy evolution through Hi 21-cm emission and absorption: current status and prospects with square kilometre array

“…Over the last two decades, much progress has been made in observations of Hi gas in the milky way (MW) and nearby galaxies. Several galactic all-sky low-resolution surveys, such as the Effelsberg-Bonn Hi survey (EBHIS; Kerp et al 2011), the galactic allsky survey (GASS; McClure-Griffiths et al 2009), the galactic Arecibo L-band feed array Hi survey (GALFA-HI; Peek et al 2011), and the Hi 4π survey (HI4PI; HI4PI Collaboration et al 2016) were used to unravel the volume density distribution of the gaseous disk up to its borders, to study the MW halo (Ford et al 2008;Winkel et al 2011;Moss et al 2013;Hammer et al 2015;Kerp et al 2016;Lenz et al 2016) and the diskhalo interaction (Ford et al 2010;McClure-Griffiths et al 2010;Lenz et al 2015;Röhser et al 2016). The high resolution galactic plane surveys, such as the Canadian galactic plane survey (CGPS; Taylor et al 2003), the southern galactic plane survey (SGPS; McClure-Griffiths et al 2005), the VLA galactic plane survey (VGPS; Stil et al 2006) and the Hi, OH, recombination line survey of the milky way (THOR; Beuther et al 2016) have been instrumental in the study of the multiphase structure of Hi gas (e.g., Strasser et al 2007;Dickey et al 2009) and in the discovery of galactic shells and filaments that give clear evidence of the injection of energy into the ISM by supernova explosions (e.g., Dawson et al 2011).…”