Massive Young Stellar Objects in the Large Magellanic Cloud: water masers and ESO-VLT 3-4 micron spectroscopy

Abstract

We investigate the conditions of star formation in the Large Magellanic Cloud. We have conducted a survey for water maser emission arising from massive young stellar objects in the 30 Doradus region (N 157) and several other H II regions in the Large Magellanic Cloud (N 105A, N 113 and N 160A). We have identified a new maser source in 30 Dor at the systemic velocity of the LMC. We have obtained 3-4 micron spectra, with the ESO Very Large Telescope, of two candidate young stellar objects. N 105A IRS1 shows H recombination line emission and its Spectral Energy Distribution (SED) and mid-infrared colours are consistent with a massive young star ionising the molecular cloud. N 157B IRS1 is identified as an embedded young object, based on its SED and a tentative detection of water ice. The data on these four H II regions are combined with mid-infrared archival images from the Spitzer Space Telescope to study the location and nature of the embedded massive young stellar objects and signatures of stellar feedback. Our analysis of 30 Dor, N 113 and N 160A confirms the picture that the feedback from the massive O and B-type stars, which creates the H II regions, also triggers further star formation on the interfaces of the ionised gas and the surrounding molecular cloud. Although in the dense cloud N 105A star formation seems to occur without evidence of massive star feedback, the general conditions in the LMC seem favourable for sequential star formation as a result of feedback. In an appendix we present water maser observations of the galactic red giants R Doradus and W Hydrae.