Properties of dense cores in clustered massive star-forming regions at high angular resolution

Abstract

We aim at characterising dense cores in the clustered environments associated with intermediate/high-mass star-forming regions. For this, we present an uniform analysis of Very Large Array NH 3 (1,1) and (2,2) observations towards a sample of 15 intermediate/high-mass star-forming regions, where we identify a total of 73 cores, classify them as protostellar, quiescent starless, or perturbed starless, and derive some physical properties. The average sizes and ammonia column densities of the total sample are ∼ 0.06 pc and ∼ 10 15 cm −2 , respectively, with no significant differences between the starless and protostellar cores, while the linewidth and rotational temperature of quiescent starless cores are smaller, ∼ 1.0 km s −1 and 16 K, than linewidths and temperatures of protostellar (∼ 1.8 km s −1 and 21 K), and perturbed starless (∼ 1.4 km s −1 and 19 K) cores. Such linewidths and temperatures for these quiescent starless cores in the surroundings of intermediate/high-mass stars are still significantly larger than the typical linewidths and rotational temperatures measured in starless cores of low-mass star-forming regions, implying an important non-thermal component. We confirm at high angular resolutions (spatial scales ∼ 0.05 pc) the correlations previously found with single-dish telescopes (spatial scales 0.1 pc) between the linewidth and the rotational temperature of the cores, as well as between the rotational temperature and the linewidth with respect to the bolometric luminosity. In addition, we find a correlation between the temperature of each core and the incident flux from the most massive star in the cluster, suggesting that the large temperatures measured in the starless cores of our sample could be due to heating from the nearby massive star. A simple virial equilibrium analysis seems to suggest a scenario of a self-similar, self-graviting, turbulent, virialised hierarchy of structures from clumps (∼ 0.1-10 pc) to cores (∼ 0.05 pc). A closer inspection of the dynamical state taking into account external pressure effects, reveal that relatively strong magnetic field support may be needed to stabilise the cores, or that they are unstable and thus on the verge of collapse.

Deuteration and evolution in the massive star formation process

“…The average τ m (1, 1) is ∼1 with no significant differences between the three evolutionary groups, while τ m (2, 2) is usually smaller than 1. The average line widths of the (1,1) lines are ∼1.7, ∼2.3, and ∼2.6 km s −1 for the HMSC, HMPO, and UC Hii groups (standard deviations 0.5, 0.6, and 0.7 km s −1 , respectively), and tend to increase with evolution, as expected (Sánchez-Monge et al 2013).…”

“…This is suggested by Figs. 5 and 6, where we plot D frac (NH 3 ) against the gas temperature and the line widths of the (1,1) transition, both known to increase with time (e.g., Sánchez-Monge et al 2013): by applying statistical tests, we even find that D frac (NH 3 ) could be slightly correlated with both the ammonia rotation temperature (Pearson's linear correlation coefficient ρ ∼ 0.2) and line widths (Pearson's linear correlation coefficient ρ ∼ 0.4). In contrast, D frac (N 2 H + ) is anti-correlated with both parameters, as shown in Fig.…”

Ongoing star formation in the protocluster IRAS 22134+5834

“…The T rot map derived from NH 3 observations shows that the main part of HMSC-E has a temperature of ∼20 to 25 K, which achieves its highest value of 30 K at the position close to the UCH region. The western clump HMSC-W has a much lower T rot of ∼14 K. These results are consistent with the values reported in Sánchez- Monge et al (2013), where the temperature increases when approaching the UV-radiation source. For the N 2 H + observations, the excitation temperature T ex also shows a higher temperature at a position close to the UCH region of ∼17 K and a lower value toward HMSC-W of ∼10 K. The deuterated fraction (hereafter D frac ) of N 2 H + , defined as the column density ratio of the species containing deuterium to its counterpart containing hydrogen, is reported to be anticorrelated with the evolutionary stages of the high-mass cores .…”

“…Imaging was performed using natural weighting, and the resulting rms and synthesized beams are listed in Table 3. The same data were also presented in Sánchez-Monge et al (2013).…”

“…The NIR K-band images reveal a ring-shaped embedded cluster made of early-to late-B type young stars with a central dark region (Kumar et al 2003). Furthermore, multiple starless cores are found around the centimeter source and the NIR cluster Sánchez-Monge 2011;Sánchez-Monge et al 2013). Therefore, the protocluster associated with I22134 represents an excellent laboratory to study the influence of massive YSOs on nearby starless dense cores.…”