2019ApJS..245....2S

We present 0.''25 resolution (35 au) ALMA 1.3 mm dust polarization observations for 37 young stellar objects (YSOs) in the Ophiuchus molecular cloud. These data encompass all the embedded protostars in the cloud and several flat-spectrum and Class II objects to produce the largest, homogeneous study of dust polarization on disk scales to date. The goal of this study is to study dust polarization morphologies down to disk scales. We find that 14/37 (38%) of the observed YSOs are detected in polarization at our sensitivity. Nine of these sources have uniform polarization angles, and four sources have azimuthal polarization structure. We find that the sources with uniform polarization tend to have steeper inclinations (>60°) than those with azimuthal polarization (<60°). Overall, the majority (9/14) of the detected sources have polarization morphologies and disk properties consistent with dust self-scattering processes in optically thick disks. The remaining sources may be instead tracing magnetic fields. Their inferred field directions from rotating the polarization vectors by 90° are mainly poloidal or hourglass shaped. We find no evidence of a strong toroidal field component toward any of our disks. For the 23 YSOs that are undetected in polarization, roughly half of them have 3σ upper limits of <2%. These sources also tend to have inclinations <60°, and they are generally compact. Since lower-inclination sources tend to have azimuthal polarization, these YSOs may be undetected in polarization owing to unresolved polarization structure within our beam. We propose that disks with inclinations >60° are the best candidates for future polarization studies of dust self-scattering, as these systems will generally show uniform polarization vectors that do not require very high resolution to resolve. We release the continuum and polarization images for all the sources with this publication. Data from the entire survey can be obtained from Dataverse.