A new view of the Cygnus X region

Abstract

Context. The Cygnus X region is one of the richest star formation sites in the Galaxy. There is a long-standing discussion about whether the region is a chance superposition of several complexes along the line of sight or a single coherent complex at a distance of 1.5 to 2 kpc. Aims. Combining a 13 CO 2 → 1 survey taken with the KOSMA 3 m telescope with mid-IR images from MSX provides a way to improve our understanding of the spatial structure of the complex. The physical properties of the molecular gas can be derived in more detail as it was done in former studies. Methods. Cygnus X has been mapped in 13 CO J = 2 → 1 (10.8 deg 2 ) at an angular resolution of 130 , as well as for smaller areas in 12 CO and 13 CO J = 3 → 2 (90 ), using the KOSMA 3 m submm-telescope. Results. We identified 91 clumps in 13 CO 2 → 1 that have a typical excitation temperature of 10−30 K, an average density of 1.3 × 10 3 cm −3 , radii of 1−8 pc, and masses of a few hundred to several ten thousand M . The main cloud complexes, the northern part (M 2.8 × 10 5 M ) including DR21 and W75N and the southern region (M 4.5 × 10 5 M ) with IC 1318 b/c and AFGL2591, show differences in their physical properties. The 13 CO emission is closely associated with mid-IR emission seen with MSX. We find evidence that Cygnus OB2 and Cygnus OB9 are affecting the molecular material in Cygnus X. Conclusions. Since essentially all molecular cloud complexes in Cygnus X form groups that are connected by molecular emission (visible in channel and position-velocity maps) and partly show evidence of interaction with UV radiation, we conclude that most of the objects seen in this region are located at the same distance, i.e., that of the OB2 cluster at ∼1.7 kpc, which is also consistent with the distances of other OB associations (OB9, OB1) in Cygnus X.

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

“…The CO survey of Schneider et al (2006), the present MAMBO-2 maps, and our small-scale analysis trace various cloud structures (see Sects. 3.1-3.2).…”

“…In CygX-North (280 × 10 3 M ⊙ , cf. Schneider et al 2006), the concentration factor is 8 for each step while in CygX-South (480 × 10 3 M ⊙ ) it is 18 for each step. Therefore, when considering the mass involved in dense cores, the CygX-North region is 5 times more concentrated (CO clouds concentrate into 0.1 pc cores with an efficiency of ∼ 1.5%) than CygX-South (concentration efficiency of ∼ 0.3%).…”

“…Leung & Thaddeus 1992). Found to be part of the local spiral arm, this complex has been located at 1.7 kpc from the Sun by the recent 13 CO study of Schneider et al (2006). Cygnus X has a rich collection of H ii regions (see centimeter free-free emission maps by Wendker et al 1991, and infrared images from MSX presented in Figs.…”

“…Cygnus X has a rich collection of H ii regions (see centimeter free-free emission maps by Wendker et al 1991, and infrared images from MSX presented in Figs. 7-9 of Schneider et al 2006), indicating recent high-mass star formation. It is associated with several OB associations (see Uyaniker et al 2001 and references therein), amongst them one of the largest in our Galaxy (Cyg OB2, cf.…”

“…The high-extinction regions are yellow and outlined by the 15 mag contour level. The three molecular cloud ensembles identified by Schneider et al (2006) are labeled and the nearby Cygnus OB2 association is indicated. The fields mapped with MAMBO or MAMBO-2 are schematically outlined and add up to ∼ 3 • 2 .…”