ALMA Observations of Starless Core Substructure in Ophiuchus

Abstract

Compact substructure is expected to arise in a starless core as mass becomes concentrated in the central region likely to form a protostar. Additionally, multiple peaks may form if fragmentation occurs. We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations of 60 starless and protostellar cores in the Ophiuchus molecular cloud. We detect eight compact substructures which are 15 >  from the nearest Spitzer young stellar object. Only one of these has strong evidence for being truly starless after considering ancillary data, e.g., from Herschel and X-ray telescopes. An additional extended emission structure has tentative evidence for starlessness. The number of our detections is consistent with estimates from a combination of synthetic observations of numerical simulations and analytical arguments. This result suggests that a similar ALMA study in the ChamaeleonI cloud, which detected no compact substructure in starless cores, may be due to the peculiar evolutionary state of cores in that cloud.

VLA cm-wave survey of young stellar objects in the Oph A cluster: constraining extreme UV- and X-ray-driven disk photoevaporation

“…The uncertainties correspond to the fit uncertainties only. The fluxes measured at 4.5 and 7.5 GHz come from Dzib et al (2013), while the ones at 107 GHz come from Kirk et al (2017). It should be noted that the The brightest source in our sample, J162634.17-242328.7 (S1, #32), has been already investigated in several studies and is known to be a completely non-thermal source.…”

“…It was, however, detected at 5 GHz with the VLA at an angular resolution of ∼10 (measured peak fluxes of 130 -200 µJy beam −1 ; Leous et al 1991;Gagné et al 2004), although, in the first study, the source appears slightly offset by 3 . More recent ALMA observations suggest that SM1 is actually protostellar and that it hosts a warm (∼30-50 K) accretion disk or pseudo-disk (Friesen et al 2014;Kirk et al 2017;Friesen et al 2018).…”

“…To determine the thermal contribution from dust, we assume that the ∼107 GHz continuum fluxes reported by Kirk et al (2017) are entirely due to dust thermal emission, and then extrapolate the contribution of dust emission at our observing frequency of 10 GHz by assuming a power-law with a spectral index α (see Table 3). We note that the angular resolution of the observations reported by Kirk et al (2017) is approximately 10 times coarser than that of our VLA observations. Therefore, our estimates of 10 GHz dust emission should be regarded as upper limits.…”

Dust Polarization toward Embedded Protostars in Ophiuchus with ALMA. III. Survey Overview

“…Figure 2 shows that there is substantial extended emission between IRS 47 and ALMA J162729.7. Kirk et al (2017) weakly detected similar extended emission at 3 mm in ∼ 2 resolution ALMA data, and Kamazaki et al (2019) strongly detected this structure in 1.3 mm continuum, 13 CO (2-1), and C 18 O (2-1) in their ALMA observations that combine the 12 m main array and the compact ACA. The arc structure curves further around IRS 47 in the two line tracers, forming a near bubble and the arc also coincides with 70 µm emission from Herschel (Kamazaki et al 2019).…”

“…The continuum source is well resolved, with a deconvolved size of 81 au × 37 au and a mass of 8 M Jupiter . Kirk et al (2017) found a much higher mass of 0.071 M (74 M Jupiter ) in lower resolution 3 mm observations, Figure A32. Same as Figure A1 except for VLA 1623A and VLA 1623B.…”