* Astronomy

Title: A bright-rimmed cloud sculpted by the H ii region Sh2-48
Authors: M. E. Ortega, S. Paron, E. Giacani, M. Rubio, G. Dubner

To characterise a bright-rimmed cloud embedded in the HII region Sh2-48 searching for evidence of triggered star formation. We carried out observations towards a region of 2'x2' centred at RA=18h 22m 11.39s, dec.=-14deg 35m 24.81s (J2000) using the Atacama Submillimeter Telescope Experiment (ASTE; Chile) in the 12CO J=3-2,13CO J=3-2, HCO+ J=4-3, and CS J=7-6 lines with an angular resolution of about 22". We also present radio continuum observations at 5 GHz carried out with the Jansky Very Large Array (JVLA; EEUU) interferometer with a synthetised beam of 7"x5". The analysis of our molecular observations reveals the presence of a relatively dense clump with n(H_2)~3x10^3 cm^-3, located in projection onto the interior of the HII region Sh2-48. The emission distribution of the four observed molecular transitions has, at VLSR~38 kms^-1, morphological anti-correlation with the bright-rimmed cloud as seen in the optical emission. From the new radio continuum observations we identify a thin layer of ionised gas located at the border of the clump which is facing to the ionising star. The ionised gas has an electron density of about 73 cm^-3 which supports the hypothesis that the clump is being photoionised by the nearby star, BD-14 5014. From the evaluation of the pressure balance between the ionised and molecular gas, we conclude that the clump would be in a pre-pressure balance state with the shocks being driven into the surface layer. Two YSO candidates (class I), are placed slightly beyond the bright rim suggesting that their formation could have been triggered via the radiation-driven implosion process.

Read more (3409kb, PDF)