Discovery of new Milky Way star clusters candidates in the 2MASS point source catalog

Abstract

Abstract.A systematic search of the 2MASS point source catalog, covering 47% of the sky, was carried out aiming to reveal any hidden globular clusters in our Galaxy. Eight new star clusters were discovered by a search algorithm based on finding peaks in the apparent stellar surface density, and a visual inspection of their vicinities yielded additional two. They all are concentrated toward the Galactic plane and are hidden behind up to A V = 20 mag which accounts for their late discovery. The majority of new clusters are associated with H regions or unidentified IRAS sources suggesting that they are young, probably similar to Arches or open clusters. Only one candidate has morphology similar to a globular cluster and the verification of its nature will require deeper observations with higher angular resolution than the 2MASS data.

Cluster candidates from the USNO-A2.0 catalogue

“…In order to discover stellar clusters that may have been missed in previous searches we follow the simple method of Ivanov et al (2002) and Reylé & Robin (2002). Firstly, we converted the USNO equatorial coordinates to Galactic coordinates since this is a more appropriate system for a cluster search.…”

“…Our choice of box size was based on Ivanov et al (2002). These authors found that the average half-mass radius for globular clusters in the Harris (1996) catalogue is 1.3±0.8 and the average size of Galactic open clusters in the Lyngå (1995) catalogue is 3.5 ± 2.5 .…”

“…The cluster candidate selection of Ivanov et al (2002) required that the number of stars in a bin was 3σ greater than the background and that there were more than 50 stars in the bin. In our search we did not use a uniform σ cut above the background level and the number of stars required for selection was also varied.…”

“…In recent years there have been a number of studies aimed at finding local star clusters using newly available imaging data and proper motion surveys (Ivanov et al 2002;Reylé & Robin 2002;Dutra & Bica 2000, 2001Hurt et al 2000). Many of these surveys have taken advantage of the new near-IR sky surveys DENIS (I, J and K) (Cioni et al 2000) and 2MASS (J, H and K s ) (Cutri et al 2003) 1 , as their observations are far less affected by high reddening in the Galactic plane than optical observations.…”

“…However, the average measured reddening is biased toward lower values because high extinctions would have made them undetectable at optical wavelengths. For example, Ivanov et al (2002) found cluster candidates with up to 20 mag of visual extinction, effectively undetectable in optical images. In Fig.…”