Synthetic observations of first hydrostatic cores in collapsing low-mass dense cores

Abstract

Context. First hydrostatic cores are predicted by theories of star formation, but their existence has never been demonstrated convincingly by (sub)millimeter observations. Furthermore, the multiplicity in the early phases of the star formation process is poorly constrained. Aims. The purpose of this paper is twofold. First, we seek to provide predictions for ALMA dust continuum emission maps from early Class 0 objects. Second, we show to what extent ALMA will be able to probe the fragmentation scale in these objects. Methods. Following our companion paper, we post-processed three state-of-the-art radiation-magneto-hydrodynamic 3D adaptive mesh refinement calculations to compute the emanating dust emission maps. We then produced synthetic ALMA observations of the dust thermal continuum from first hydrostatic cores. Results. We present the first synthetic ALMA observations of dust continuum emission from the first hydrostatic cores. We analyze the results given by the different bands and configurations and we discuss for which combinations of the two the first hydrostatic cores would most likely be observed. We also show that observing dust continuum emission with ALMA will help in identifying the physical processes occurring within collapsing dense cores. If the magnetic field is playing a role, the emission pattern will show evidence of a pseudo-disk and even of a magnetically driven outflow, which pure hydrodynamical calculations cannot reproduce. Conclusions. The capabilities of ALMA will enable us to make significant progress towards understanding the fragmentation at the early Class 0 stage and discovering first hydrostatic cores.

REVEALING H2D+DEPLETION AND COMPACT STRUCTURE IN STARLESS AND PROTOSTELLAR CORES WITH ALMA

“…The SM1N condensation is similar in extent, however, to that expected from theoretical predictions for a pseudodisk, a flattened, disequilibrium structure expected to form around FHSCs and young protostars as material is accreting onto the central source in the presence of a magnetic field (Galli & Shu 1993a,b). Commerçon et al (2012) simulate ALMA observations of FHSCs from radiation-magneto-hydrodynamic models of collapsing dense cores at 150 pc, and find detectable accretion disks with sizes similar to the SM1N condensation for cores with initial moderate and strong magnetic fields. While the predicted flux density in the simulated extended structure is similar to what we find toward SM1N, the predicted peak flux from the central FHSC is ∼ 10 times brighter than the observed peak flux toward SM1N.…”

Detection of Irregular, Submillimeter Opaque Structures in the Orion Molecular Clouds: Protostars within 10,000 yr of Formation?

“…These objects are the FH-SCs first described by Larson (1969). Only simulations invoking large amounts of rotational energy, resulting in the formation of highly flattened pre-stellar disks instead of spherical HSCs, predict masses and radii comparable to those of the envelopes (Bate 2011;Commerçon et al 2012). As we will discuss in the remainder in this section, there are several areas of tension between the observed results and existing models.…”

Evidence for disks at an early stage in class 0 protostars?

“…We post-processed the simulation using the the RADMC-3D radiative transfer code (Dullemond 2012) to compute the expected 350 GHz emission. Following Commerçon et al (2012a,b), we assumed that the gas and dust temperature are perfectly coupled and that the dust-to-gas ratio is uniform and equal to 1%. We used the dust opacity from Semenov et al (2003) for the homogeneous spheres model (with Fe/Fe+Mg=0.3 "normal" silicate composition).…”