Molecular environs and triggered star formation around the large Galactic infrared bubble N 24

Abstract

A multi-wavelength analysis of the large Galactic infrared bubble N 24 is has been presented in this paper in order to investigate the molecular and star formation environment around expanding H ii regions. Using archival data from Herschel and ATLASGAL, the distribution and physical properties of the dust over the entire bubble are studied. Twenty three dense clumps are identified using the Clumpfind2d algorithm with sizes and masses in the range 0.65-1.73 pc and 600-16300 M , respectively. To analyse the molecular environment in N 24, observations of NH 3 (1,1) and (2,2) were carried out using the Nanshan 26-m radio telescope. Analysis of the kinetic temperature and gravitational stability of these clumps suggests gravitational collapse in several of them. The mass-size distributions of the clumps and the presence of massive young protostars indicate that the shell of N 24 is a region of ongoing massive star formation. The compatibility of the dynamical and fragmentation time-scales and the overabundance of YSOs and clumps on the rim suggest that the "collect and collapse" mechanism is in play at the boundary of the bubble, but the existence of the IRDC at the edge of bubble indicates that "radiation-driven implosion" mechanism may also have played a role there.

New Insights into the H ii Region G18.88–0.49: Hub–Filament System and Accreting Filaments

“…They proposed that the H ii regions G18.88−0.49 and G18.937−0.434 were triggered by the expansion of the W39 H ii region. This interpretation was also supported by Li et al (2019). However, it is an extremely difficult task to distinguish which stars are triggered and which ones formed spontaneously, and one should be cautious in interpreting observations in favour of triggered star formation (Dale et al 2015).…”

“…This figure reveals a wide-open bubble and an extended H ii region in the direction of W39 (radial velocity (V lsr ) range = (60, 70) km s −1 ; distance ∼4.7 kpc; see Kerton et al 2013). Kerton et al (2013) found a local minimum in the radio emission that allowed them to propose the position of the exciting star(s) of the W39 H ii region, which is indicated in Figure 1a (see also Li et al 2019). Figure 1a shows the positions of 52 APEX Telescope Large Area Survey of the Galaxy (AT-LASGAL; Schuller et al 2009) clumps at 870 µm from Urquhart et al (2018).…”

“…Kerton et al (2013) reported an age difference between the W39 H ii region (age ∼1.5 Myr) and the compact H ii regions (i.e., G18.88−0.49 and G18.937−0.434; age ∼10 5 years). On the basis of the observed morphology of W39 and the age difference argument, they suggested a triggered star formation scenario in W39 (see also Li et al 2019). They proposed that the H ii regions G18.88−0.49 and G18.937−0.434 were triggered by the expansion of the W39 H ii region.…”

“…Kerton et al (2013) reported that the H ii region G18.88−0.49 is excited by a young Otype star (age ∼10 5 years). Li et al (2019) studied the physical environment of W39 (including G18.88−0.49) using Herschel continuum images at 70-500 µm and the NH 3 line data. To examine the near-infrared and midinfrared (MIR) view, Figure 1b shows a three colorcomposite image of G18.88−0.49 with Spitzer 24 µm in red, 8.0 µm in green, and 3.6 µm in blue (see a dotted-dashed box in Figure 1a).…”

Characterization of dense Planck clumps observed with Herschel and SCUBA-2

“…In addition, there is evidence that larger mass reservoirs are required for SF in energetic environments such as the Galactic center (Trujillo-Gomez et al 2019). Regions with second-generation SF, such as the edges of bubbles, are also likely to have higher column and volume density than the general ISM (Thompson et al 2012;Liu et al 2012Liu et al , 2016Li et al 2019b), leading to an increased occurrence of SF in these regions (Kendrew et al 2012;Palmeirim et al 2017). Changing environments make it necessary to study the interplay of these forces under different conditions.…”