A star cluster at the edge of the Galaxy

Context. This paper is part of our ongoing study of star formation in the ( far-) outer Galaxy. Aims. Our goal in this paper is to study stars and molecular gas in the direction of IRAS 06145+ 1455 ( WB89- 789). The kinematic distance of the associated molecular cloud is 11.9 kpc. With a galactocentric distance of similar to 20.2 kpc, this object is at the edge of the ( molecular) disk of the Galaxy. Methods. We use near- IR ( J, H, K), molecular line-, and dust continuum observations. Results. The near- IR data show the presence of an ( embedded) cluster of about 60 stars, with a radius similar to 1.3 pc and an average stellar surface density similar to 12 pc(-2). We find at least 14 stars with NIR- excess, 3 of which are possibly Class I objects. The cluster is embedded in a similar to 1000 M-circle dot molecular/ dust core, from which a molecular outflow originates. The temperature of most of the outflowing gas is less than or similar to 40 K, and the total mass of the swept- up material is less than or similar to 10 M-circle dot. Near the center of the flow, indications of much higher temperatures are found, probably due to shocks. A spectrum taken of one of the probable cluster members shows a tentative likeness to that of a K3 III- star ( with an age of at least 20 Myr). If correct, this would confirm the kinematic distance. Conclusions. This cluster is the furthest one from the Galactic center yet detected. The combination of old and recent activity implies that star formation has been going on for at least 20 Myr, which is diffcult to understand considering the location of this object, where external triggers are either absent or weak, compared to the inner Galaxy. This suggests that once star formation is occurring, later generations of stars may form through the effect of the first generation of stars on the ( remnants of) the original molecular cloud.