An unbiased deep search for small-area molecular structures

Abstract

Small-area molecular structures (SAMS) resembling those clumpuscules, proposed by Pfenniger and Combes (1994) as candidate for baryonic dark matter, have recently been detected (Heithausen 2002, 2004) in an area where the shielding is too low for them to survive for a long time. To study the frequency of occurence of such structures I present the results of an unbiased deep search for molecular clumpuscules. The area surrounding these structures has been surveyed using the FCRAO 14m telescope in the CO J=1-0 transition. The field covered is 20' by 20'. The resulting rms of the data is only 0.04K in a 0.127 km/s wide channel. Also, high-angular resolution observations of the 13CO and C18O (J=1-0) transitions were obtained with the IRAM Plateau-de-Bure Interferometer. 3 new SAMS have been detected. The structures have very low intensities which makes it impossible to detect them in large scale CO surveys conducted to map the molecular gas of the Milky way. They move with a similar radial velocity as the surrounding HI gas. The clouds follow the same size-linewidth relation as found for giant molecular clouds or Galactic cirrus clouds. The observations clearly show that most of the large linewidths observed at low angular resolution is caused by a large velocity difference among the clumps seen at highest angular resolution. At an adopted distance of 100pc the structures have masses of only Jupiter mass or below. My observations show that SAMS might be an abundant phenomenon in the interstellar medium however not recognized as such due to their small size. If they are made of ordinary interstellar matter with solar metallicity they likely contribute only little to the total interstellar mass.

5 pages, 3 figures, accepted by Astronomy & Astrophysics

References in corpus (10)

• Extreme scattering events and Galactic dark matter
• Baryonic Dark Halos: Machos and Cold Gas?
• A FUSE Survey of Molecular Hydrogen in Intermediate-Velocity Clouds in the Milky Way Halo
• Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo
• The Globular Cluster Systems of NGC 3258 and NGC 3268 in the Antlia Cluster
• Absorption-Line Systems and Galaxies in Front of the Second Brightest Quasar, PHL 1811
• Small-area molecular clouds without shielding
• H_2 absorption in a dense interstellar filament in the Milky Way halo
• Molecular hydrogen as baryonic dark matter
• A tiny Galactic dust cloud projected onto NGC 3269?

Cited by in corpus (8)

• Turbulent molecular clouds
• Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions
• Intermittency of interstellar turbulence: extreme velocity-shears and CO emission on milliparsec scale
• Formation and Fractionation of CO (carbon monoxide) in diffuse clouds observed at optical and radio wavelengths
• Toward Understanding the Origin of Turbulence in Molecular Clouds: Small Scale Structures as Units of Dynamical Multi-Phase Interstellar Medium
• Molecular gas in high-velocity clouds: revisited scenario
• On the nature of dust clouds in the region towards M81 and NGC3077
• ALMA detection of the dusty object silhouetted against the S0 galaxy NGC 3269 in the Antlia cluster