Compact Disks in a High Resolution ALMA Survey of Dust Structures in the Taurus Molecular Cloud (1906.10809v1)

Abstract: We present a high-resolution ($\sim0.''12$, $\sim16$ au, mean sensitivity of $50~\mu$Jy~beam$^{-1}$ at 225 GHz) snapshot survey of 32 protoplanetary disks around young stars with spectral type earlier than M3 in the Taurus star-forming region using Atacama Large Millimeter Array (ALMA). This sample includes most mid-infrared excess members that were not previously imaged at high spatial resolution, excluding close binaries and highly extincted objects, thereby providing a more representative look at disk properties at 1--2 Myr. Our 1.3 mm continuum maps reveal 12 disks with prominent dust gaps and rings, 2 of which are around primary stars in wide binaries, and 20 disks with no resolved features at the observed resolution (hereafter smooth disks), 8 of which are around the primary star in wide binaries. The smooth disks were classified based on their lack of resolved substructures, but their most prominent property is that they are all compact with small effective emission radii ($R_{\rm eff,95\%} \lesssim 50$ au). In contrast, all disks with $R_{\rm eff,95\%}$ of at least 55 au in our sample show detectable substructures. Nevertheless, their inner emission cores (inside the resolved gaps) have similar peak brightness, power law profiles, and transition radii to the compact smooth disks, so the primary difference between these two categories is the lack of outer substructures in the latter. These compact disks may lose their outer disk through fast radial drift without dust trapping, or they might be born with small sizes. The compact dust disks, as well as the inner disk cores of extended ring disks, that look smooth at the current resolution will likely show small-scale or low-contrast substructures at higher resolution. The correlation between disk size and disk luminosity correlation demonstrates that some of the compact disks are optically thick at millimeter wavelengths.

Compact Disks in a High Resolution ALMA Survey of Dust Structures in the Taurus Molecular Cloud

The paper by Long et al. investigates the properties of protoplanetary disks in the Taurus Molecular Cloud using high-resolution observations from the Atacama Large Millimeter Array (ALMA). The paper focuses on a sample of 32 protoplanetary disks around young stars with spectral types earlier than M3, offering a more representative look at disk properties in the 1-2 Myr age range. This paper provides crucial insights into the diversity of disk structures and their potential implications for planet formation processes.

Study Design and Observations

The authors conducted a snapshot survey with ALMA at a resolution of approximately 0.12 arcseconds and a mean sensitivity of 50 μJy/beam at 225 GHz. The selection criteria excluded close binaries and highly extincted objects to avoid complications in the analysis of disk structures. The primary aim was to identify and characterize the morphologies of dust distribution, specifically the presence of prominent dust gaps and rings, which play a significant role in the planet formation narrative.

Key Findings

1. Disk Morphologies: The survey revealed 12 disks with prominent dust gaps and rings, while 20 disks appeared smooth without resolved features at the observed resolution. All disks with significant radial extents (R_eff,95% ≥ 55 au) showed detectable substructures, whereas compact disks did not display such features.
2. Disk Size and Emission: The effective radii for 95% of the emission (R_eff,95%) highlight a clear distinction in the detectable substructures' presence between extended and compact disks. The correlation between disk size and disk luminosity further emphasizes that some compact disks are optically thick at millimeter wavelengths.
3. Inner Disk Similarities: Despite differences in outer structures, the inner emission cores of both smooth and substructured disks share similar properties. This similarity suggests that the primary difference lies in the presence or absence of outer substructures rather than the inner disk core features.

Implications and Future Directions

The research underscores the role of disk substructures, such as dust rings and gaps, in potentially trapping dust particles, thereby influencing planetesimal and planet formation. The absence of such substructures in compact disks suggests that these disks might either lose their outer layers through rapid radial drift or be originally small.

Theoretical implications point toward the need to understand better the mechanisms responsible for substructure formation and sustenance across different spatial scales and stellar ages. Practically, these findings suggest that future high-resolution ALMA observations should aim to capture finer details in disks, particularly around lower-mass stars and fainter disks, to ascertain the prevalence and characteristics of substructures in typical protoplanetary environments.

In summary, this paper contributes to our understanding of protoplanetary disk diversity, with a specific focus on the structural features that might dictate the early stages of planet formation. The paper serves as a springboard for further research into the correlations between disk properties and planet formation potential, especially within the context of varying stellar environments.