Star formation associated with a large-scale infrared bubble^⋆

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
e-mail: xujl@bao.ac.cn
² NAOC-TU Joint Center for Astrophysics, Lhasa 850000, PR China
³ Purple Mountain Observatory, Qinghai Station, 817000, Delingha, PR China
⁴ Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008, PR China

Received: 7 April 2014
Accepted: 16 July 2014

Abstract

Aims. To investigate how a large-scale infrared bubble centered at l = 53.9° and b = 0.2° forms, and to study if star formation is taking place at the periphery of the bubble, we performed a multiwavelength study.

Methods. Using the data from the Galactic Ring Survey (GRS) and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), we performed a study of a large-scale infrared bubble with a size of about 16 pc at a distance of 2.0 kpc. We present the ¹²CO J = 1−0, ¹³CO J = 1−0, and C¹⁸O J = 1−0 observations of HII region G53.54-0.01 (Sh2-82) obtained at the Purple Mountain Observation (PMO) 13.7 m radio telescope to investigate the detailed distribution of associated molecular material. In addition, we also used radiorecombination line and VLA data. To select young stellar objects (YSOs) consistent with this region, we used the GLIMPSE I catalog.

Results. The large-scale infrared bubble shows a half-shell morphology at 8 μm. The H II regions of G53.54-0.01, G53.64+0.24, and G54.09-0.06 are situated on the bubble. Comparing the radio recombination line velocities and associated ¹³CO J = 1−0 components of the three H II regions, we found that the 8 μm emission associated with H II region G53.54-0.01 should belong to the foreground emission, and only overlap with the large-scale infrared bubble in the line of sight. Three extended green objects (EGOs, the candidate massive young stellar objects), as well as three H II regions and two small-scale bubbles are found located in the G54.09-0.06 complex, indicating an active massive star-forming region. Emission from C¹⁸O at J = 1−0 presents four cloud clumps on the northeastern border of H II region G53.54-0.01. By comparing the spectral profiles of ¹²CO J = 1−0, ¹³CO J = 1−0, and C¹⁸O J = 1−0 at the peak position of each clump, we found the collected gas in the three clumps, except for the clump coinciding with a massive YSO (IRAS 19282+1814). Using the evolutive model of the H II region, we derived that the age of H II region G53.54-0.01 is 1.5 × 10⁶ yr. The significant enhancement of several Class I and Class II YSOs around G53.54-0.01 indicates the presence of some recently formed stars, which may be triggered by this H II region through the collect-and-collapse process.