PHYSICAL PROPERTIES OF DENSE CORES IN THE Ρ OPHIUCHI MAIN CLOUD AND a SIGNIFICANT ROLE OF EXTERNAL PRESSURES IN CLUSTERED STAR FORMATION

Abstract

Using the archive data of the H 13 CO + (J = 1-0) line emission taken with the Nobeyama 45 m radio telescope with a spatial resolution of ∼ 0.01 pc, we have identified 68 dense cores in the central dense region of the ρ Ophiuchi main cloud. The H 13 CO + data also indicate that the fractional abundance of H 13 CO + relative to H 2 is roughly inversely proportional to the square root of the H 2 column density with a mean of 1.72 × 10 −11 . The mean radius, FWHM line width, and LTE mass of the identified cores are estimated to be 0.045 ± 0.011 pc, 0.49 ± 0.14 km s −1 , and 3.4 ± 3.6 M , respectively. The majority of the identified cores have subsonic internal motions. The virial ratio, the ratio of the virial mass to the LTE mass, tends to decrease with increasing LTE mass and about 60% of the cores have virial ratios smaller than 2, indicating that these cores are not transient structures but self-gravitating. The detailed virial analysis suggests that the surface pressure often dominates over the self-gravity and thus plays a crucial role in regulating core formation and evolution. By comparing the ρ Oph cores with those in the Orion A molecular cloud observed with the same telescope, we found that the statistical properties of the core physical quantities are similar between the two clouds if the effect of the different spatial resolutions is corrected. The line widths of the ρ Oph cores appear to be nearly independent of the core radii over the range of 0.01-0.1 pc and deviate upward from the Heyer & Brunt relation. This may be evidence that turbulent motions are driven by protostellar outflows in the cluster environment.

The JCMT Gould Belt Survey: first results from the SCUBA-2 observations of the Ophiuchus molecular cloud and a virial analysis of its prestellar core population

“…This is equivalent to Pext /kb ≈ 1.8 × 10 7 K cm −3 , an order of magnitude higher pressure than that found by Maruta et al (2010), but similar to the total pressure in Ophiuchus P/kb ∼ 2 × 10 7 K cm −3 estimated by Johnstone et al (2000).…”

Submillimetre Studies of Prestellar and Starless Cores in the Ophiuchus, Taurus and Cepheus Molecular Clouds

“…This is equivalent to P ext /k b ≈ 1.8 × 10 7 K cm −3 , an order of magnitude higher pressure than that found by Maruta et al (2010), but similar to the total pressure in Ophiuchus P/k b ∼ 2 × 10 7 K cm −3 estimated by Johnstone et al (2000).…”

“…Maruta et al (2010) estimate a typical surface pressure on cores in Ophiuchus of P ext /k b ≈ 3 × 10 6 K cm −2 , sufficient to influence the energy balance of the cores. Similarly, Johnstone et al (2000) estimate core surface pressures P ext /k b ∼ 10 6−7 K cm −3 by treating the starless cores they identify in Ophiuchus as pressure-confined Bonnor-Ebert spheres.…”

“…However, the external pressure is often a dominant term in the energy balance of starless cores (e.g. Johnstone et al 2000;Maruta et al 2010), and so it is necessary to parameterise this effect, typically in the manner described herein.…”

The JCMT Gould Belt Survey: first results from SCUBA-2 observations of the Cepheus Flare region

“…Previous studies of starless cores suggested that external gas pressure might be instrumental in confining dense cores in at least some cases (Maruta et al 2010;Pattle et al 2015). We apply the method used by Pattle et al (2015) to estimate the external pressure on starless cores in the Ophiuchus molecular cloud to our sample of starless cores.…”