[show abstract][hide abstract] ABSTRACT: We present the initial highlights of the HOBYS key program, which are based on Herschel images of the Rosette molecular complex and maps of the RCW120 H ii region. Using both SPIRE at 250/350/500 μm and PACS at 70/160 μm or 100/160 μm, the HOBYS survey provides an unbiased and complete census of intermediate- to high-mass young stellar objects, some of which are not detected by Spitzer. Key core properties, such as bolometric luminosity and mass (as derived from spectral energy distributions), are used to constrain their evolutionary stages. We identify a handful of high-mass prestellar cores and show that their lifetimes could be shorter in the Rosette molecular complex than in nearby low-mass star-forming regions. We also quantify the impact of expanding H ii regions on the star formation process acting in both Rosette and RCW 120. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Figures 4 and 5 are only available in electronic form at http://www.aanda.org
[show abstract][hide abstract] ABSTRACT: Context. By means of different physical mechanisms, the expansion of H ii regions can promote the formation of new stars of all masses. RCW 120 is a nearby Galactic H ii region where triggered star formation occurs. This region is well-studied - there being a wealth of existing data - and is nearby. However, it is surrounded by dense regions for which far infrared data is essential to obtain an unbiased view of the star formation process and in particular to establish whether very young protostars are present. Aims: We attempt to identify all young stellar objects (YSOs), especially those previously undetected at shorter wavelengths, to derive their physical properties and obtain insight into the star formation history in this region. Methods: We use Herschel-PACS and -SPIRE images to determine the distribution of YSOs observed in the field. We use a spectral energy distribution fitting tool to derive the YSOs physical properties. Results: Herschel-PACS and -SPIRE images confirm the existence of a young source and allow us to determine its nature as a high-mass (8-10 M&sun;) Class 0 object (whose emission is dominated by a massive envelope Menv ~= 103 M&sun;) towards the massive condensation 1 observed at (sub)-millimeter wavelengths. This source was not detected at 24 mum and only barely seen in the MISPGAL 70 mum data. Several other red sources are detected at Herschel wavelengths and coincide with the peaks of the millimeter condensations. SED fitting results for the brightest Herschel sources indicate that, apart from the massive Class 0 that forms in condensation 1, low mass (0.8-4 M&sun;) stars are forming around RCW 120 with ages younger than 5 × 104 years. This indicates that YSOs observed on the borders of RCW 120 are younger than its ionizing star, which has an age of about 2.5 Myr. Conclusions: Herschel images allow us to detect new YSOs that are too young and embedded to be detected at shorter wavelengths (25 of the 49 Herschel sources are new detections). This offers a new and more complete view of the star formation in this region. PACS and SPIRE fluxes were obtained for the brightest YSOs and allow us to strongly constrain both their spectral energy distribution and their physical properties through SED fitting. A more accurate determination of their properties allows us, for the first time, to discuss the star formation history in this region by comparing similar sources at different evolutionary stages. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Astronomy and Astrophysics 01/2010; · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Context. RCW 120 is a well-studied, nearby Galactic H ii region with ongoing star formation in its surroundings. Previous work has shown that it displays a bubble morphology at mid-infrared wavelengths, and has a massive layer of collected neutral material seen at sub-mm wavelengths. Given the well-defined photo-dissociation region (PDR) boundary and collected layer, it is an excellent laboratory to study the ``collect and collapse'' process of triggered star formation. Using Herschel Space Observatory data at 100, 160, 250, 350, and 500 mum, in combination with Spitzer and APEX-LABOCA data, we can for the first time map the entire spectral energy distribution of an H ii region at high angular resolution. Aims: We seek a better understanding of RCW 120 and its local environment by analysing its dust temperature distribution. Additionally, we wish to understand how the dust emissivity index, beta, is related to the dust temperature. Methods: We determine dust temperatures in selected regions of the RCW 120 field by fitting their spectral energy distribution (SED), derived using aperture photometry. Additionally, we fit the SED extracted from a grid of positions to create a temperature map. Results: We find a gradient in dust temperature, ranging from ⪆30 K in the interior of RCW 120, to ~20 K for the material collected in the PDR, to ~10 K toward local infrared dark clouds and cold filaments. There is an additional, hotter (~100 K) component to the dust emission that we do not investigate here. Our results suggest that RCW 120 is in the process of destroying the PDR delineating its bubble morphology. The leaked radiation from its interior may influence the creation of the next generation of stars. We find support for an anti-correlation between the fitted temperature and beta, in rough agreement with what has been found previously. The extended wavelength coverage of the Herschel data greatly increases the reliability of this result. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.