A CO survey on a sample ofHerschelcold clumps

Abstract

Context. The physical state of cold cloud clumps has a great impact on the process and efficiency of star formation and the masses of the forming stars inside these objects. The sub-millimetre survey of the Planck space observatory and the far-infrared follow-up mapping of the Herschel space telescope provide an unbiased, large sample of these cold objects. Aims. We have observed 12 CO(1−0) and 13 CO(1−0) emission in 35 high-density clumps in 26 Herschel fields sampling different environments in the Galaxy. We derive the physical properties of the objects and estimate their gravitational stability. Methods. The densities and temperatures of the clumps were calculated from both the dust continuum and the molecular line data. Kinematic distances were derived using 13 CO(1−0) line velocities to verify previous distance estimates and the sizes and masses of the objects were calculated by fitting 2D Gaussian functions to their optical depth distribution maps on 250 µm. The masses and virial masses were estimated assuming an upper and lower limit on the kinetic temperatures and considering uncertainties due to distance limitations. Results. The derived excitation temperatures are between 8.5−19.5 K, and for most clumps between 10−15 K, while the Herschel-derived dust colour temperatures are more uniform, between 12−16 K. The sizes (0.1−3 pc), 13 CO column densities (0.5−44 × 10 15 cm −2 ) and masses (from less than 0.1 M to more than 1500 M ) of the objects all span broad ranges. We provide new kinematic distance estimates, identify gravitationally bound or unbound structures and discuss their nature. Conclusions. The sample contains objects on a wide scale of temperatures, densities and sizes. Eleven gravitationally unbound clumps were found, many of them smaller than 0.3 pc, but large, parsec-scale clouds with a few hundred solar masses appear as well. Colder clumps have generally high column densities but warmer objects appear at both low and higher column densities. The clump column densities derived from the line and dust observations correlate well, but are heavily affected by uncertainties of the dust properties, varying molecular abundances and optical depth effects.

The effects of ionization feedback on star formation: a case study of the M 16 H II region

“…where T kin is the kinetic temperature in the core. If the densities of the cores are high enough so that LTE conditions hold, T ex can be adopted as T kin (Fehér et al 2017). For the dense Table 3.…”

SCOPE: SCUBA-2 Continuum Observations of Pre-protostellar Evolution – survey description and compact source catalogue

“…CO clumps have been detected towards PGCCs (e.g. Liu et al 2013;Meng, Wu & Liu 2013;Parikka et al 2015;Zhang et al 2016;Fehér et al 2017), as well as detections of line emission from dense gas tracers (Yuan et al 2016). There can be, however, low levels of active star formation within PGCCs (Tóth et al 2014;Liu et al 2015;Tang et al 2018;Yi et al 2018;Zhang et al 2018).…”

Galactic cold cores

“…Studies have already been carried out on the structure of filaments (Rivera-Ingraham et al 2016 and high-latitude clouds, especially the cloud LDN 1642 (Malinen et al 2014(Malinen et al , 2016, and the kinematics (e.g. the internal turbulence of the clumps) through molecular line observations (Parikka et al 2015;Fehér et al 2017;Saajasto et al 2017).…”