NGC 3503 and its molecular environment

¹ Instituto Argentino de Radioastronomia, CONICET, CCT-La Plata, CC 5, 1894 Villa Elisa, Argentina
e-mail: duronea@iar.unlp.edu.ar
² Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina

Received: 26 August 2011
Accepted: 14 November 2011

Abstract

Aims. We present a study of the molecular gas and interstellar dust distribution in the environs of the Hii  region NGC 3503 associated with the open cluster Pis 17 with the aim of investigating the spatial distribution of the molecular gas linked to the nebula and achieving a better understanding of the interaction of the nebula and Pis 17 with their molecular environment.

Methods. We based our study on ¹²CO(1−0) observations of a region of  ~0$\stackrel{\mathrm{°}}{.}$6 in size obtained with the 4-m NANTEN telescope, unpublished radio continuum data at 4800 and 8640 MHz obtained with the ATCA telescope, radio continuum data at 843 MHz obtained from SUMSS, and available IRAS, MSX, IRAC-GLIMPSE, and MIPSGAL images.

Results. We found a molecular cloud (Component 1) having a mean velocity of –24.7 km s^-1 ,compatible with the velocity of the ionized gas, which is associated with the nebula and its surroundings. Adopting a distance of 2.9  ±  0.4 kpc, the total molecular mass yields (7.6  ±  2.1)  ×  10³M_⊙ and density yields 400  ±  240 cm^-3.

The radio continuum data confirm the existence of an electron density gradient in NGC 3503. The IR emission shows a PDR bordering the higher density regions of the nebula. The spatial distribution of the CO emission shows that the nebula coincides with a molecular clump, and the strongest CO emission peak is located close to the higher electron density region. The more negative velocities of the molecular gas (about –27 km s^-1), are coincident with NGC 3503. Candidate young stellar objects (YSOs) were detected toward the Hii region, suggesting that embedded star formation may be occurring in the neighborhood of the nebula. The clear electron density gradient, along with the spatial distribution of the molecular gas and PAHs in the region indicates that NGC 3503 is a blister-type Hii  region that has probably undergone a champagne phase.