ALMA Observations of Dust Polarization and Molecular Line Emission from the Class 0 Protostellar Source Serpens SMM1

Abstract

We present high angular resolution dust polarization and molecular line observations carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these observations with new polarization observations from the Submillimeter Array (SMA) and archival data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare the magnetic field orientations at different spatial scales. We find major changes in the magnetic field orientation between large (∼0.1 pc) scales-where the magnetic field is oriented E-W, perpendicular to the major axis of the dusty filament where SMM1 is embedded-and the intermediate and small scales probed by CARMA (∼1000 au resolution), the SMA (∼350 au resolution), and ALMA (∼140 au resolution). The ALMA maps reveal that the redshifted lobe of the bipolar outflow is shaping the magnetic field in SMM1 on the southeast side of the source; however, on the northwestern side and elsewhere in the source, lowvelocity shocks may be causing the observed chaotic magnetic field pattern. High-spatial-resolution continuum and spectral-line observations also reveal a tight (∼130 au) protobinary system in SMM1-b, the eastern component of which is launching an extremely high-velocity, one-sided jet visible in both =  (J CO 2 1) and =  (J SiO 5 4); however, that jet does not appear to be shaping the magnetic field. These observations show that with the sensitivity and resolution of ALMA, we can now begin to understand the role that feedback (e.g., from protostellar outflows) plays in shaping the magnetic field in very young, star-forming sources like SMM1.

Indirect evidence of significant grain growth in young protostellar envelopes from polarized dust emission

“…Indeed, single dish observations of the dust polarized emission, probing ∼ 0.1 pc scales, show a decrease in polarization fraction in denser regions p ∝ I −α , with α ∼ 0.5 − 1.2 is usually found at those scales (Wolf et al 2003;Crutcher 2004;Soam et al 2018). High angular resolution observations suggest this is at least partly due to a beam averaging effect (unresolved structure of B) since larger polarization fractions are recovered when probing typical scales 1000 au in dense cores, thanks to interferometric facilities (Hull et al 2014(Hull et al , 2017bGalametz et al 2018). This was also suggested by early analysis of synthetic polarization maps from MHD simulations (Falceta- Gonçalves et al 2008;Padovani et al 2012).…”

“…Since 2016 the most sensitive sub-millimeter interferometer, ALMA, is producing exquisite polarized dust continuum emission maps from the high-density protostellar interiors, probing the properties of polarized emission down to scales of a few tens of au. Typically, polarization fractions of p ∼ 2 − 10% are recovered in envelopes at radii > 50 − 5000 au, when both self-scattering polarization and large filtering effects can be excluded (e.g., Kataoka et al 2015;Hull et al 2017a;Maury et al 2018;Cox et al 2018;Alves et al 2018;Sadavoy et al 2018).…”

Impact of Low-Energy Cosmic Rays on Star Formation

“…The magnetic configuration in dense cores and discs can be very complicated (e.g., Joos et al, 2012;Li et al, 2013;Padovani et al, 2013;Hull et al, 2017Hull et al, , 2018, and the field strength is usually much larger than the interstellar value (Crutcher, 2012). Dust polarisation observations of dense cores often display an hourglass shape, which can be created by gravitational contraction pinching the magnetic field (Girart et al, 2006(Girart et al, , 2009Hull et al, 2014).…”

Formation and Evolution of Disks Around Young Stellar Objects

“…This is particularly important because integration of polarized radiation along a line of sight often produces non-trivial structures as it is integration of vector, not scalar. For example, Hull et al (2017) compared dust polarization observations of a few star forming clouds in Serpens with simulations of turbulent clouds, and demonstrated that turbulence is dominating the dynamics in the molecular clouds. Maury et al (2018) calculated a synthetic polarization map based on an MHD simulation and compared it with B335, a very young Class-0 object with a very compact (or no) disk.…”