Mother of dragons. A massive, quiescent core in the dragon cloud (IRDC G028.37+00.07)

July 2023 • 2023A&A...675A..53B

Authors • Barnes, A. T. • Liu, J. • Zhang, Q. • Tan, J. C. • Bigiel, F. • Caselli, P. • Cosentino, G. • Fontani, F. • Henshaw, J. D. • Jiménez-Serra, I. • Kalb, D. -S. • Law, C. Y. • Longmore, S. N. • Parker, R. J. • Pineda, J. E. • Sánchez-Monge, A. • Lim, W. • Wang, K.

Abstract • Context. Core accretion models of massive star formation require the existence of massive, starless cores within molecular clouds. Yet, only a small number of candidates for such truly massive, monolithic cores are currently known.
Aims: Here we analyse a massive core in the well-studied infrared-dark cloud (IRDC) called the `dragon cloud' (also known as G028.37+00.07 or `Cloud C'). This core (C2c1) sits at the end of a chain of a roughly equally spaced actively star-forming cores near the center of the IRDC.
Methods: We present new high-angular-resolution 1 mm ALMA dust continuum and molecular line observations of the massive core.
Results: The high-angular-resolution observations show that this region fragments into two cores, C2c1a and C2c1b, which retain significant background-subtracted masses of 23 M_⊙ and 2 M_⊙ (31 M_⊙ and 6 M_⊙ without background subtraction), respectively. The cores do not appear to fragment further on the scales of our highest-angular-resolution images (0.2″, 0.005 pc ~ 1000 AU). We find that these cores are very dense (n_H2 > 10⁶ cm⁻³) and have only trans-sonic non-thermal motions (ℳ_s ~ 1). Together the mass, density, and internal motions imply a virial parameter of <1, which suggests the cores are gravitationally unstable, unless supported by strong magnetic fields with strengths of ~1-10 mG. From CO line observations, we find that there is tentative evidence for a weak molecular outflow towards the lower-mass core, and yet the more massive core remains devoid of any star formation indicators.
Conclusions: We present evidence for the existence of a massive, pre-stellar core, which has implications for theories of massive star formation. This source warrants follow-up higher-angular-resolution observations to further assess its monolithic and pre-stellar nature.

Links

• PREPRINT http://arxiv.org/abs/2303.15499
• POSTSCRIPT https://www.aanda.org/10.1051/0004-6361/202245668/postscript
• ELECTR https://doi.org/10.1051%2F0004-6361%2F202245668
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2023A%26A...675A..53B
• PDF https://www.aanda.org/10.1051/0004-6361/202245668/pdf
• DATA https://telbib.eso.org/detail.php?bibcode=2023A%26A...675A..53B