N₂H⁺(1–0) survey of massive molecular cloud cores

Abstract

Abstract. We present the results of N 2 H + (1-0) observations of 35 dense molecular cloud cores from the northern and southern hemispheres where massive stars and star clusters are formed. Line emission has been detected in 33 sources, for 28 sources detailed maps have been obtained. Peak N 2 H + column densities lie in the range: 3.6 × 10 12 −1.5 × 10 14 cm −2 . Intensity ratios of (01-12) to (23-12) hyperfine components are slightly higher than the LTE value. The optical depth of (23-12) component toward peak intensity positions of 10 sources is ∼0.2−1. In many cases the cores have elongated or more complex structures with several emission peaks. In total, 47 clumps have been revealed in 26 sources. Their sizes lie in the range 0.3-2.1 pc, the range of virial masses is ∼30−3000 M . Mean N 2 H + abundance for 36 clumps is 5 × 10 −10 . Integrated intensity maps with axial ratios <2 have been fitted with a power-law radial distribution ∼r −p convolved with the telescope beam. Mean power-law index for 25 clumps is close to 1.3. For reduced maps where positions of low intensity are rejected mean power-law index is close to unity corresponding to the ∼r −2 density profile provided N 2 H + excitation conditions do not vary inside these regions. In those cases where we have relatively extensive and high quality maps, line widths of the cores either decrease or stay constant with distance from the center, implying an enhanced dynamical activity in the center. There is a correlation between total velocity gradient direction and elongation angle of the cores. However, the ratio of rotational to gravitational energy is too low (4× 10 −4 -7.1 × 10 −2 ) for rotation to play a significant role in the dynamics of the cores. A correlation between mean line widths and sizes of clumps has been found. A comparison with physical parameters of low-mass cores is given.

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

“…We note that Pirogov et al (2003) our cores, but that a wide scatter about this abundance is to be expected, and hence our H2 column densities determined using this abundance are likely to be accurate to within a factor of 2−3 in regions without significant N2H + depletion. Figure 8 compares the masses derived from each of our tracers, and shows that the masses of cores measured in N2H + and in continuum emission correlate fairly well, although with significant scatter about the line of unity, whereas those from C 18 O do not.…”

“…However, due to the low abundance of N2H + relative to H2 (X(N2H + ) = 5.2 ± 0.5 × 10 −10 - Pirogov et al 2003), it is only detectable in regions of the highest H2 column density.…”

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

“…The equivalent H 2 column density is found using the conversion factor X(N 2 H + ) = 5.2 × 10 −10 (Pirogov et al 2003). We note that Pirogov et al (2003) determined this value of X(N 2 H + ) by considering the mean N 2 H + abundance across 36 massive molecular cloud cores; the applicability of this abundance to a low-to-intermediate mass star-forming region such as Ophiuchus is not certain.…”

“…We note that Pirogov et al (2003) determined this value of X(N 2 H + ) by considering the mean N 2 H + abundance across 36 massive molecular cloud cores; the applicability of this abundance to a low-to-intermediate mass star-forming region such as Ophiuchus is not certain. Friesen et al (2010) find N 2 H + abundances in the range 2.5 − 17 × 10 −10 in Oph B, Pirogov et al (2003) value of X(N 2 H + ) is applicable to our cores, but that a wide scatter about this abundance is to be expected, and hence our H 2 column densities determined using this abundance are likely to be accurate to within a factor of 2−3 in regions without significant N 2 H + depletion. This correlation indicates that N 2 H + and dust are tracing the same material.…”

Physical and chemical structure of dense cores in regions of high mass star formation

“…The variations of the CS/N 2 H + intensity ratio reach more than an order of magnitude. It is worth noting that the N 2 H + optical depth is usually small (Pirogov et al 2003) while the CS optical depth can be rather high. This means that the saturation effects can only decrease the apparent variations of the CS/N 2 H + ratio.…”