Herschelobservations of the Galactic H ii region RCW 79

Abstract

Context. Triggered star formation around H ii regions could be an important process. The Galactic H ii region RCW 79 is a prototypical object for triggered high-mass star formation. Aims. We aim to obtain a census of the young stellar population observed at the edges of the H ii region and to determine the properties of the young sources in order to characterize the star formation processes that take place at the edges of this ionized region. Methods. We take advantage of Herschel data from the surveys HOBYS, "Evolution of Interstellar Dust", and Hi-Gal to extract compact sources. We use the algorithm getsources. We complement the Herschel data with archival 2MASS, Spitzer, and WISE data to determine the physical parameters of the sources (e.g., envelope mass, dust temperature, and luminosity) by fitting the spectral energy distribution. Results. We created the dust temperature and column density maps along with the column density probability distribution function (PDF) for the entire RCW 79 region. We obtained a sample of 50 compact sources in this region, 96% of which are situated in the ionization-compressed layer of cold and dense gas that is characterized by the column density PDF with a double-peaked lognormal distribution. The 50 sources have sizes of ∼ 0.1 − 0.4 pc with a typical value of ∼ 0.2 pc, temperatures of ∼ 11 − 26 K, envelope masses of ∼ 6 − 760 M , densities of ∼ 0.1 − 44 × 10 5 cm −3 , and luminosities of ∼ 19 − 12712 L . The sources are classified into 16 class 0, 19 intermediate, and 15 class I objects. Their distribution follows the evolutionary tracks in the diagram of bolometric luminosity versus envelope mass (L bol − Menv) well. A mass threshold of 140 M , determined from the L bol − Menv diagram, yields 12 candidate massive dense cores that may form high-mass stars. The core formation efficiency (CFE) for the 8 massive condensations shows an increasing trend of the CFE with density. This suggests that the denser the condensation, the higher the fraction of its mass transformation into dense cores, as previously observed in other high-mass star-forming regions.

Oversized Gas Clumps in an Extremely Metal-poor Molecular Cloud Revealed by ALMA’s Parsec-scale Maps

“…In order to evaluate whether gas clumps at low metallicity show some systematic differences from those at the solar metallicity, we compared clumps in DDO 70 to those in the Milky Way. We measured the clump sizes in the Milky Way using maps of gas mass surface densities of four massive star-forming regions including Cygnus X (Cao et al 2019), NGC 6344 (Russeil et al 2013), RCW 79 (Liu et al 2017) and NGC 7538 (Fallscheer et al 2013) at distances of 1.4, 1.75, 4.3 and 2.7 kpc, respec- Figure 7. Maps of dust clumps with Σ limit gas =700 M /pc 2 in four massive star formation regions of the Milky Way.…”

Radio and infrared study of southern H II regions G346.056−0.021 and G346.077−0.056

“…The possible reason for the higher mass estimate in our work could be the lower dust temperature (21 K) and different dust opacity assumed. One also cannot exclude the effect of flux loss associated with ground based observations (Liu et al 2017). …”

Infrared dust bubble CS51 and its interaction with the surrounding interstellar medium

“…The possible reasons for this could be the different κν and dust temperature values used by these authors and/or the large sizes of the clumps retrieved from the column density map. One also cannot exclude the effect of flux loss associated with ground based observations (Liu et al 2017a). …”

“…The second lognormal form suggesting compression from ionized gas would likely account for the condition required for triggered star formation. The high column density region shows signature of a power-law tail, which is generally attributed to on-going star formation (Schneider et al 2015(Schneider et al , 2012Liu et al 2017a;Schneider et al 2013;Russeil et al 2013). Insufficient data points and low signal-to-noise ratio prevents us from fitting a powerlaw and attempting a more quantitative comparison with the above studies.…”

“…Catalogs of infrared (IR) bubbles (Churchwell et al 2006(Churchwell et al , 2007Simpson et al 2012) show that these features are ubiquitous in our Galaxy. The last few years have seen a plethora of papers on the nature of these bubbles and also on the formation of a new generation of stars in their adjacent shells or bright rimmed clumps (Urquhart et al 2007;Deharveng et al 2010;Dewangan et al 2012;Liu et al 2012;Dewangan & Ojha 2013;Hou & Gao 2014;Ranjan Das et al 2016;Baug et al 2016;Hattori et al 2016;Liu et al 2016Liu et al , 2017a. An interesting statistical study by Thompson et al (2012) shows that the surface density of young stellar objects (YSOs) peak towards the projected angular radius of the bubbles.…”