Gas infalling motions in the envelopes of Very Low Luminosity Objects

Abstract

We present the results of a single dish survey toward 95 VeLLOs in optically thick (HCN 1-0) and thin (${\mathrm{N}}_2{\mathrm{H}}^{+}$ 1-0) lines performed for the purpose of understanding the physical processes of inward motions in the envelopes of the VeLLOs and characterizing their true nature. The normalized velocity differences ($\delta V_{HCN}$) between the peak velocities of the two lines were derived for 41 VeLLOs detected in both lines. The $\delta V$ distribution of these VeLLOs is found to be significantly skewed to the blue, indicating the dominance of infalling motions in their envelopes. The infall speeds were derived for 15 infall candidates by using the HILL5 radiative transfer model. The speeds were in the range of 0.03 $\mathrm{km}{\mathrm{s}}^{-1}$ to 0.3 $\mathrm{km}{\mathrm{s}}^{-1}$, with a median value of 0.16 $\mathrm{km}{\mathrm{s}}^{-1}$, being consistent with the gravitational free-fall speeds from pressure-free envelopes. The mass infall rates calculated from the infall speeds are mostly of the order of $10^{-6}{M}_{\odot }y{r}^{-1}$ with a median value of $3.4\pm 1.5\times 10^{-6}{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$. These are found to be also consistent with the values predicted with the inside-out collapse model and show a fairly good correlation with the internal luminosities of the VeLLOs. This again indicates that the infall motions observed toward the VeLLOs are likely to be due to the gravitational infall motions in their envelopes. Our study suggests that most of the VeLLOs are potentially faint protostars while two of the VeLLOs could possibly be proto-brown dwarf candidates.

References in corpus (13)

• A Large Catalog of Accurate Distances to Local Molecular Clouds: The Gaia DR2 Edition
• A Compendium of Distances to Molecular Clouds in the Star Formation Handbook
• On the internal structure of starless cores. II. A molecular survey of L1498 and L1517B
• The dynamics of collapsing cores and star formation
• The Spitzer c2d Survey of Nearby Dense Cores: I: First Direct Detection of the Embedded Source in IRAM 04191+1522
• IC348-SMM2E: a Class 0 proto-brown dwarf candidate forming as a scaled-down version of low-mass stars
• Probing Inward Motions in Starless Cores Using The HCN J = 1-0 Hyperfine Transitions : A Pointing Survey Toward Central Regions
• Protostar Formation in Supersonic Flows: Growth and Collapse of Spherical Cores
• Molecular Line Observations of Infrared Dark Clouds: Seeking the Precursors to Intermediate and Massive Star Formation
• CARMA Large Area Star Formation Survey: Dense Gas in the Young L1451 Region of Perseus
• CO Outflow Survey of 68 Very Low Luminosity Objects: a Search for Proto-Brown Dwarf Candidates
• Properties of the Molecular Cores of Low Luminosity Objects
• Infall/Expansion Velocities in the Low-Mass Dense Cores L492, L694-2, and L1521F: Dependence on Position and Molecular Tracer

Cited by in corpus (4)

• TRAO Survey of the nearby filamentary molecular clouds, the universal nursery of stars (TRAO FUNS). II. Filaments and Dense cores in IC 5146
• A Catalog of Molecular Clumps and Cores with Infall Signatures
• In search for infalling clumps in molecular clouds -- A catalogue of CO blue-profiles
• Post-Outburst Chemistry in a Very Low-Luminosity Object: Peculiar High Abundance of Nitric Oxide