Hundreds of new cluster candidates in the VISTA Variables in the Vía Láctea survey DR1 ^⋆

¹ Departamento de Física y AstronomíaUniversidad de la Serena, Av. Juan Cisternas 1200 Norte, La Serena, Chile
e-mail: rbarba@userena.cl
² Departamento de Ciencias Físicas, Universidad Andres Bello, 220 República, Santiago, Chile
³ Vatican Observatory, 00120 Vatican City State, Italy
⁴ European Southern Observatory, 3107 Vitacura, Santiago, Chile
⁵ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544-1001, USA
⁶ The Milky Way Millennium Nucleus, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
⁷ Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK
⁸ Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, UK
⁹ Space Telescope Science Institute, MD 21117, USA
¹⁰ Universidade Federal de Sergipe, Departamento de Física, Av. Marechal Rondon s/n, 49100-000 São Cristóvão, SE, Brazil

Received: 22 April 2014
Accepted: 12 January 2015

Abstract

Context. VISTA variables in the Vía Láctea is an ESO Public survey dedicated to scanning the bulge and an adjacent portion of the Galactic disk in the fourth quadrant using the VISTA telescope and its near-infrared camera VIRCAM. One of the leading goals of the VVV survey is to contribute to knowledge of the star cluster population of the Milky Way.

Aims. To improve the census of Galactic star clusters, we performed a systematic and careful scan of the JHK_s images of the Galactic plane section of the VVV survey.

Methods. Our detection procedure is based on a combination of stellar density maps and visual inspection of promising features in the J-, H-, and K_S-band images. The material examined are VVV JHK_S color-composite images corresponding to Data Release 1 of VVV.

Results. We report the discovery of 493 new infrared star cluster candidates. The analysis of the spatial distribution show that the clusters are very concentrated in the Galactic plane, presenting some local maxima around the position of large star-forming complexes, such as G305, RCW 95, and RCW 106. The vast majority of the new star cluster candidates are quite compact and generally surrounded by bright and/or dark nebulosities. IRAS point sources are associated with 59% of the sample, while 88% are associated with MSX point sources. GLIMPSE 8 μm images of the cluster candidates show a variety of morphologies, with 292 clusters dominated by knotty sources, while 361 clusters show some kind of nebulosity in this wavelength regime. Spatial cross-correlation with young stellar objects, masers, and extended green-object catalogs suggest that a large sample of the new cluster candidates are extremely young. In particular, 104 star clusters associated with methanol masers are excellent candidates for ongoing massive star formation. Also, there is a special set of sixteen cluster candidates that present clear signposts of star-forming activity having associated simultaneosly dark nebulae, young stellar objects, extended green objects, and masers.