ALMA reveals the magnetic field evolution in the high-mass star forming complex G9.62+0.19

Abstract

Context. The role of magnetic fields during the formation of high-mass stars is not yet fully understood, and the processes related to the early fragmentation and collapse are as yet largely unexplored. The high-mass star forming region G9.62+0.19 is a well known source, presenting several cores at different evolutionary stages. Aims. We seek to investigate the magnetic field properties at the initial stages of massive star formation. We aim to determine the magnetic field morphology and strength in the high-mass star forming region G9.62+0.19 to investigate its relation to the evolutionary sequence of the cores. Methods. We made use of Atacama Large Millimeter Array (ALMA) observations in full polarisation mode at 1 mm wavelength (Band 7) and we analysed the polarised dust emission. We estimated the magnetic field strength via the Davis-Chandrasekhar-Fermi and structure function methods. Results. We resolve several protostellar cores embedded in a bright and dusty filamentary structure. The polarised emission is clearly detected in six regions: two in the northern field and four in the southern field. Moreover the magnetic field is orientated along the filament and appears perpendicular to the direction of the outflows. The polarisation vectors present ordered patterns and the cores showing polarised emission are less fragmented. We suggest an evolutionary sequence of the magnetic field, and the less evolved hot core exhibits a stronger magnetic field than the more evolved hot core. An average magnetic field strength of the order of 11 mG was derived, from which we obtain a low turbulent-to-magnetic energy ratio, indicating that turbulence does not significantly contribute to the stability of the clump. We report a detection of linear polarisation from thermal line emission, probably from methanol or carbon dioxide, and we tentatively compared linear polarisation vectors from our observations with previous linearly polarised OH masers observations. We also compute the spectral index, column density, and mass for some of the cores. Conclusions. The high magnetic field strength and smooth polarised emission indicate that the magnetic field could play an important role in the fragmentation and the collapse process in the star forming region G9.62+019 and that the evolution of the cores can be magnetically regulated. One core shows a very peculiar pattern in the polarisation vectors, which can indicate a compressed magnetic field. On average, the magnetic field derived by the linear polarised emission from dust, thermal lines, and masers is pointing in the same direction and has consistent strength.

Discs and outflows in the early phases of massive star formation: Influence of magnetic fields and ambipolar diffusion

“…A milliGauss magnetic field amplitude is consistent with estimates in other massive star forming regions (e.g. Girart et al 2013;Dall'Olio et al 2019;Beltrán et al 2019). Last but not least, Girart et al (2009) and Qiu et al (2014) concluded that their observations are consistent with magnetic braking; that is, a magnetically regulated collapse.…”

“…There is no clear consensus on which physical process regulates the fragmentation level. There is, however, a trend in which massive dense cores are not as fragmented as expected (Wang et al 2014;Csengeri et al 2017;Nony et al 2018) and magnetic fields have an important role in fragmentation (Li et al 2015;Dall'Olio et al 2019). Using state-of-the-art multi-dimensional and multiphysics numerical models, it has also been demonstrated that magnetic fields, radiative transfer, and turbulence all play role in setting the fragmentation level of massive star forming regions (Hennebelle et al 2011;Commerçon et al 2011b;Myers et al 2013;Fontani et al 2018).…”

Discs and outflows in the early phases of massive star formation: influence of magnetic fields and ambipolar diffusion

“…A mG magnetic field amplitude is consistent with estimates in other massive star forming region (e.g. Girart et al 2013;Dall'Olio et al 2019;Beltrán et al 2019). Last but not least, Girart et al (2009) and Qiu et al (2014) conclude that their observations are consistent with magnetic braking, i.e.…”

“…There is no clear consensus on which physical processes is regu-lating the fragmentation level. There is however a trend in which massive dense cores are not as fragmented as expected (Wang et al 2014;Csengeri et al 2017;Nony et al 2018), and that magnetic fields has an important role in the fragmentation (Li et al 2015;Dall'Olio et al 2019). Using state-of-the-art multidimensional and multi-physics numerical models, it has also been demonstrated that magnetic fields, radiative transfer and turbulence all play role in setting the fragmentation level of massive star forming regions (Hennebelle et al 2011;Myers et al 2013;Fontani et al 2018).…”

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- VIII. A search for hot cores by using C$_2$H$_5$CN, CH$_3$OCHO and CH$_3$OH lines

“…We then confirm the 60 cores as hot cores, and give their coordinates, rotation temperatures and column densities in Table 1. We have checked the literature and found that 15 of these hot cores have been reported before (I18089-1732, Beuther et al 2004;I18032-2032I18032- /G9.62+0.19, Liu et al 2015Dall'Olio et al 2019;I18507+0110/G34.43+0.24, Beltrán et al 2009;Fu & Li 2017;Calcutt et al 2014; I17441-2822/Sgr B2(M), Sánchez-Monge et al 2017;IRAS18056-1952/G10.47+0.03, Rolffs et al 2011; I18507+0121/G34.26+0. 15 , Sakai et al 2013;Mookerjea et al 2007;I16060-5146, I16065-5158, I12326-6245, I14498-5856, I15254-5621, Araya et al 2005;Dedes et al 2011;I16547-4247, I17233-3606, I18182-1433, Hernández-Hernández et al 2014I17175-3544/NGC6334I, Brogan et al 2016).…”