Ammonia observations of bright-rimmed clouds: establishing a sample of triggered protostars

Abstract

We observed 42 molecular condensations within previously identified bright‐rimmed clouds in the ammonia rotational inversion lines NH3(1,1), (2,2), (3,3) and (4,4) using the Green Bank Telescope in Green Bank, West Virginia. Using the relative peaks of the ammonia lines and their hyperfine satellites we have determined important parameters of these clouds, including rotational temperatures and column densities. These observations confirm the presence of dense gas towards IRAS point sources detected at submillimetre wavelengths. Derived physical properties allow us to refine the sample of bright‐rimmed clouds into those likely to be sites of star formation, triggered via the process of radiatively driven implosion. An investigation of the physical properties of our sources shows that triggered sources are host to greater turbulent velocity dispersions, likely indicative of shock motions within the cloud material. These may be attributed to the passage of triggered shocks or simply the association of outflow activity with the sources. In all, we have refined the Sugitani, Fukui and Ogura catalogue to 15 clouds which are clearly star‐forming and influenced by external photoionization‐induced shocks. These sources may be said, with high confidence, to represent the best examples of triggering within bright‐rimmed clouds.

Thermal balance and comparison of gas and dust properties of dense clumps in the Hi-GAL survey

“…Independent estimations of Tdust and Tkin have been presented by different groups in the past. Comparisons of kinetic temperatures from ammonia and dust temperatures from SED fitting of continuum emission with submm to mid-IR bands using SCUBA and IRAS fluxes, find a general agreement between both temperatures toward massive star forming regions, though the large dispersion of the estimated values and the small sample of sources (e.g., Hill et al 2010;Morgan et al 2010). Comparison of dust temperatures obtained from SED fitting with Herschel /Hi-GAL maps exhibits a better agreement with respect to the NH3 gas temperature measurements on small samples of dense clumps as shown, for example, by Guzmán et al (2015) who compared dust temperatures obtained from Hi-GAL images toward 150 ATLAS-GAL sources, and Giannetti et al (2013) who targeted 39 sources previously mapped in 1.2 mm continuum emission.…”

“…It is expected that in dense regions (n > 10 4 cm −3 ) the gas and dust temperatures are coupled (e.g., Goldsmith & Langer 1978;Goldsmith 2001;Crimier et al 2010). Nevertheless, observational work addressing the dust-gas temperature coupling relies on a small sample of objects (e.g., Giannetti et al 2013;Merello et al 2015), or is done in particular regions or set of sources without considering different environments (e.g., Morgan et al 2010).…”

Magnetic fields in multiple bright-rimmed clouds in different directions of H ii region IC 1396

“…The line width of 13 CO(2-1) towards BRC 39 as 1.7 km s −1 (due to unavailability of CO data) has been adopted from Weikard et al (1996). The volume densities toward these clouds are calculated using the hydrogen column density information from Morgan et al (2010) which is found to be 16 × 10 21 cm −2 towards BRC 39. For other two clouds IC 1396A and BRC 38, we considered the average column density as ∼ 10 22 cm −2 (based on the values given for all other BRCs in Morgan et al (2010)).…”

“…The volume densities toward these clouds are calculated using the hydrogen column density information from Morgan et al (2010) which is found to be 16 × 10 21 cm −2 towards BRC 39. For other two clouds IC 1396A and BRC 38, we considered the average column density as ∼ 10 22 cm −2 (based on the values given for all other BRCs in Morgan et al (2010)). This value is found similar to the column densities obtained by CO(1-0) and C 18 O(1-0) observations (Soam et al in prep., Neha et al in prep.…”

High-resolution Near-infrared Observations of a Small Cluster Associated with a Bright-rimmed Cloud in W5

“…Sugitani et al (1991) and Sugitani & Ogura (1994) cataloged 89 BRCs associated with IRAS point sources as candidate sites for induced star formation, and they classified them into three morphological types of BRCs (type "A"; moderately curved rims, "B"; tightly curved rims, and "C"; cometary rims). These catalogs have stimulated many observations (e.g., Morgan et al 2004Morgan et al , 2009Morgan et al , 2010Urquhart et al 2009;Nakano et al 2012;Fukuda et al 2013;Panwar et al 2014;Kusune et al 2015). As one such example, Morgan et al (2008) carried out 450 µm and 850 µm imaging of BRCs in a systematic way using SCUBA on JCMT, and suggested that the bright rim types of B and C represent true "trig-gered" star formation.…”