Star formation triggered by H II regions in our Galaxy

Abstract

Context. It has been shown that by means of different physical mechanisms the expansion of H ii regions can trigger the formation of new stars of all masses. This process may be important to the formation of massive stars but has never been quantified in the Galaxy. Aims. We use Herschel-PACS and -SPIRE images from the Herschel infrared survey of the Galactic plane, Hi-GAL, to perform this study. Methods. We combine the Spitzer-GLIMPSE and -MIPSGAL, radio-continuum and submillimeter surveys such as ATLASGAL with Hi-GAL to study young stellar objects (YSOs) observed towards Galactic H ii regions. We select a representative H ii region, N49, located in the field centered on l = 30 • observed as part of the Hi-GAL science demonstration phase, to demonstrate the importance Hi-GAL will have to this field of research. Results. Hi-GAL PACS and SPIRE images reveal a new population of embedded young stars, coincident with bright ATLASGAL condensations. The Hi-GAL images also allow us, for the first time, to constrain the physical properties of the newly formed stars by means of fits to their spectral energy distribution. Massive young stellar objects are observed at the borders of the N49 region and represent second generation massive stars whose formation has been triggered by the expansion of the ionized region. Conclusions. The first Hi-GAL images obtained using PACS and SPIRE have demonstrated the capability to investigate star formation triggered by H ii regions. With radio, submillimeter, and shorter wavelength infrared data from other surveys, the Hi-GAL images reveal young massive star-forming clumps surrounding the perimeter of the N49 H ii generated bubble. Hi-GAL enables us to detect a population of young stars at different evolutionary stages, cold condensations only being detected in the SPIRE wavelength range. The far IR coverage of Hi-GAL strongly constrains the physical properties of the YSOs. The large and unbiased spatial coverage of this survey offers us a unique opportunity to lead, for the first time, a global study of star formation triggered by H ii regions in our Galaxy.

Herschelfar-infrared observations of the Carina Nebula complex

“…However, advancing ionization fronts and expanding superbubbles can also compress nearby clouds and thereby trigger the formation of new generations of stars (e.g., Reach et al 2004;Cannon et al 2005;Oey et al 2005;Preibisch & Zinnecker 2007;Deharveng et al 2009;Zavagno et al 2010;Brand et al 2011). The interaction of the massive stars with the surrounding clouds and the balance between cloud destruction and triggered star formation determine the characteristics and the final outcome of the star formation process (see Dale et al 2007;Dale & Bonnell 2008;Bate 2009;Gritschneder et al 2010, for numerical studies).…”

HerschelSPIRE-FTS observations of RCW 120

“…The stellar content of these condensations is described in detail in Zavagno et al (2007) and in Deharveng et al (2009). The properties of the point sources observed in this region with Herschel PACS and SPIRE are described in Zavagno et al (2010a). An off position (OFF) was obtained to serve as a reference.…”

“…This region contains a massive Class 0 source revealed with Herschel (Zavagno et al 2010a) and a chain of young, lower mass stars ). -C2: this condensation contains a bright Class I source and is, as C1, also located on the southern (and densest) border of the PDR.…”

“…This phenomenon has been studied in detail over the past ten years (Deharveng et al 2003;Zavagno et al 2007Zavagno et al , 2010aPomarès et al 2009;Paron et al 2011;Davies et al 2012). All these studies concentrate on specific Galactic H ii regions where young stellar objects (YSOs) are observed on their borders.…”

Molecular clumps and star formation associated with the infrared dust bubble N131

“…A few individual bubbles have been studied well, such as N22 (Ji et al 2012), N49 (Watson et al 2008;Deharveng et al 2010;Zavagno et al 2010), N65 (Petriella et al 2010), N68 (Zhang & Wang 2012b), and S51 (Zhang & Wang 2012a). There are many models and observations to explain the dusty windblown bubbles, such as bubble N49 of Everett & Churchwell (2010).…”