A necklace of dense cores in the high-mass star forming region G35.20−0.74 N: ALMA observations

Abstract

Context. The formation process of high-mass stars (with masses >8 M ) is still poorly understood, and represents a challenge from both the theoretical and observational points of view. The advent of the Atacama Large Millimeter Array (ALMA) is expected to provide observational evidence to better constrain the theoretical scenarios. Aims. The present study aims at characterizing the high-mass star forming region G35.20−0.74 N, which is found associated with at least one massive outflow and contains multiple dense cores, one of them recently found associated with a Keplerian rotating disk. Methods. We used the radio-interferometer ALMA to observe the G35.20−0.74 N region in the submillimeter continuum and line emission at 350 GHz. The observed frequency range covers tracers of dense gas (e.g., H 13 CO + , C 17 O), molecular outflows (e.g., SiO), and hot cores (e.g., CH 3 CN, CH 3 OH). These observations were complemented with infrared and centimeter data. Results. The ALMA 870 μm continuum emission map reveals an elongated dust structure (∼0.15 pc long and ∼0.013 pc wide; full width at half maximum) perpendicular to the large-scale molecular outflow detected in the region, and fragmented into a number of cores with masses ∼1-10 M and sizes ∼1600 AU (spatial resolution ∼960 AU). The cores appear regularly spaced with a separation of ∼0.023 pc. The emission of dense gas tracers such as H 13 CO + or C 17 O is extended and coincident with the dust elongated structure. The three strongest dust cores show emission of complex organic molecules characteristic of hot cores, with temperatures around 200 K, and relative abundances 0.2-2 × 10 −8 for CH 3 CN and 0.6-5 × 10 −6 for CH 3 OH. The two cores with highest mass (cores A and B) show coherent velocity fields, with gradients almost aligned with the dust elongated structure. Those velocity gradients are consistent with Keplerian disks rotating about central masses of 4-18 M . Perpendicular to the velocity gradients we have identified a large-scale precessing jet/outflow associated with core B, and hints of an east-west jet/outflow associated with core A. Conclusions. The elongated dust structure in G35.20−0.74 N is fragmented into a number of dense cores that may form high-mass stars. Based on the velocity field of the dense gas, the orientation of the magnetic field, and the regularly spaced fragmentation, we interpret this elongated structure as the densest part of a 1D filament fragmenting and forming high-mass stars.

Warm C<sub>2</sub>H<sub>2</sub> toward NGC 7538 IRS9: Grain Surface Origin

“…These regions show evidence of complex molecules and in fall on spatial scales down to approximately 5000 -10,000 AU. Unfortunately, the temperatures observed toward these regions may be somewhat high (up to 200 K [39]) compared to the C 2 H 2 temperatures inferred here.…”

“…It is also possible that the C 2 H 2 ice may be transported via in falling filaments observed toward massive star-forming regions [38] [39]. These regions show evidence of complex molecules and in fall on spatial scales down to approximately 5000 -10,000 AU.…”

Filamentary structure and Keplerian rotation in the high-mass star-forming region G35.03+0.35 imaged with ALMA

“…The red star corresponds to core A in G35.03. Blue filled dots connected by a dotted line correspond to cores A and B in G35.20-0.74N, which occupy two different positions in the diagram depending on the value of the mass adopted (Sánchez-Monge et al 2014). The parameters of the HMC G29.96−0.02 have been recalculated for a more correct distance of 6.2 kpc (Russeil et al 2011) instead of 3.5 kpc, which was the one used by Beltrán et al (2011a).…”

Chemical segregation in hot cores with disk candidates

“…For details, see § 3.3 d :Calculated from source size, continuum flux density, and kinetic temperature ( § 3.3). e :Sources mass calculated as in Sánchez-Monge et al (2014) using the average kinetic temperatures. massive young objects as the higher temperature allows for endothermic reactions to take place more readily.…”

“…The digital correlator was configured in four spectral windows (with dual polarization) of 1875 MHz and 3840 channels each, providing a resolution of ∼0.4 km/s. The four spectral windows covered the frequency ranges [336 849.57-338 Sánchez-Monge et al (2014) and Beltrán et al (2014).…”