Fragmentation in the massive star-forming region IRAS 19410+2336

Abstract

Context. The core mass functions (CMFs) of low-mass star-forming regions are found to resemble the shape of the initial mass function (IMF). A similar result is observed for the dust clumps in high-mass star-forming regions, although on spatial scales of clusters that do not resolve the substructure that is found in these massive clumps. The region IRAS 19410+2336 is one exception, having been observed on spatial scales on the order of ∼2500 AU, which are sufficient to resolve the clump substructure into individual cores. Aims. We investigate the protostellar content of IRAS 19410+2336 at high spatial resolution at 1.4 mm, determining the temperature structure of the region and deriving its CMF. Methods. The massive star-forming region IRAS 19410+2336 was mapped with the PdBI (BCD configurations) at 1.4 mm and 3 mm in the continuum and several transitions of formaldehyde (H 2 CO) and methyl cyanide (CH 3 CN). The H 2 CO transitions were also observed with the IRAM 30 m Telescope. Results. We detect 26 continuum sources at 1.4 mm with a spatial resolution as low as ∼2200 AU, several of them with counterparts at near-and mid-infrared wavelengths, distributed in two (proto)clusters. With the PdBI CH 3 CN and PdBI/IRAM 30 m H 2 CO emission, we derive the temperature structure of the region, ranging from 35 K to 90 K. Using these temperatures, we calculate the core masses of the detected sources, ranging from ∼0.7 M to ∼8 M . These masses are strongly affected by the spatial filtering of the interferometer, which removes a common envelope with ∼90% of the single-dish flux. Considering only the detected dense cores and accounting for binning effects as well as cumulative distributions, we derive a CMF, with a power-law index β = −2.3 ± 0.2. We resolve the Jeans length of the (proto)clusters by one order of magnitude, and only find a small velocity dispersion between the different subsources. Conclusions. Since we cannot unambiguously differentiate between protostellar and prestellar cores, the derived CMF is not prestellar. Furthermore, because of the large fraction of missing flux, we cannot establish a firm link between the CMF and the IMF. This implies that future high-mass CMF studies will need to complement the interferometer continuum data with the short spacing information, a task suitable for ALMA. We note that the method of extracting temperatures using H 2 CO lines becomes less applicable when reaching the dense core scales of the interferometric observations because most of the H 2 CO appears to originate in the envelope structure.

SiO: Not the perfect outflow tracer

“…Fig. 1 well (see also Beuther et al 2002c;Beuther & Schilke 2004;Rodón et al 2012). The interferometric observation filters out large scale structure, but the comparison to older interferometric observation at 2.6 mm by Beuther et al (2003) shows very good agreement.…”

“…In the calculations, we assume that the excitation temperature is equal to the kinetic temperature, which should be approximately correct at the given high densities. As temperature, 40 K is used (Rodón et al 2012) and τ is the optical depth. For the assumption of optically thin lines holds τ 1, and the factor τ/(1 − e −τ ) approaches unity.…”

“…The total gas mass of this region is calculated by Beuther et al (2002c) and Beuther et al (2005) to be 5 × 10 M . The mean temperature was investigated by Rodón et al (2012) with several known gas temperature tracers, such as H 2 CO and CH 3 CN, with the result of an average temperature of 40 ± 15 K and a temperature of 80 ± 40 K for the dense cores. Early observations of the continuum of IRAS 19410+2336 were conducted by Beuther et al (2002c) and Beuther & Schilke (2004).…”

Global collapse of molecular clouds as a formation mechanism for the most massive stars

“…3 we inferred core masses of M MM1 = 545 Figure 6 shows a radius-versus-mass diagram for a significant (but not complete) sample of massive protostellar cores Rathborne et al 2007Rathborne et al , 2008Beuther et al 2002Beuther et al , 2003Beuther et al , 2005Beuther et al , 2012Molinari et al 1998;Rodón et al 2012), while the empty circles correspond to the same set of sources for which we recalculated the mass using the same dust opacity law as in this paper. The MM1 and MM2 sources are indicated as red filled circles.…”

Multiplicity and disks within the high-mass core NGC 7538IRS1

“…Peter et al (2012) find companion separations between 400 and several thousand AU, stressing the necessity of high spatial resolution, Furthermore, Sana et al (2012) infer that multiple system interactions dominate the evolution of massive stars. Interferometer studies have revealed that most high-mass starforming regions fragment into multiple objects, suggesting that massive monolithic cores larger than several 1000 AU are rare, however, the degree of fragmentation varies (e.g., Cesaroni et al 2005;Beuther et al 2007bBeuther et al , 2012Zhang et al 2009;Bontemps et al 2010;Wang et al 2011;Rodón et al 2012;Palau et al 2013;Sánchez-Monge et al 2014;Johnston et al 2015). Even regions that remain single continuum sources down to arcsec resolution, mostly fragment on even smaller scales.…”