arXiv subjects

Yunfan Jiao

Publications and source records attributed to Yunfan Jiao.

4 recordsLinked to original sources

arXiv2026

ALMA-QUARKS view of W49N: Multipolar episodic outflow associated with the most energetic Galactic water maser

We present a detailed investigation of a multipolar episodic molecular outflow in the mini-starburst region W49N, which hosts the most luminous water maser in the Galaxy. Using high-resolution ($\sim$0.3 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the $\mathrm{^{12}CO}$ emission as part of the ALMA-QUARKS survey, we analyze the morphology and kinematics of the outflow. Our observations reveal four newly identified outflow lobes in addition to the previously known central bipolar jet. These lobes appear more jet-like rather than exhibiting wide opening angles. Based on the $\mathrm{^{12}CO}$ (2-1) and $\mathrm{^{13}CO}$ (2-1) emission, we provide a more reliable estimate of the outflow's physical parameters, confirming it as one of the most energetic outflows in the Galaxy. Notably, these newly discovered lobes exhibit chains of knots, a characteristic signature of episodic ejection. Furthermore, two of the lobes display prominent S-shaped wiggles, suggestive of a precessing jet. The discovery of these features -- commonly observed in outflows from low-mass protostars -- in such an extreme massive star-forming environment provides compelling evidence that some underlying physical mechanisms for launching outflows are conserved across a wide range of stellar masses.

astro-ph.GA↗

arXiv2026

The Keplerian disk, envelope, and streamers surrounding an early O-type protostar in the Sagittarius C cloud of the Central Molecular Zone

Disk-mediated accretion is central to theories of massive star formation, setting the initial conditions for their evolution. Yet observations of Keplerian disks around early O-type protostars remain scarce, as they are often blended into complex surrounding structures. We report ALMA Band 6 observations (300 au resolution) of an accretion disk surrounding a high-mass protostar in the Sagittarius C (Sgr C) cloud in the Central Molecular Zone (CMZ) around the Galactic Center. We identify spectral lines and analyze the spatial distribution of the emission of the complex organic molecules. We use a dynamical model with an inner Keplerian disk and an outer free-fall envelope to fit the three-dimensional position-position-velocity data of the stacked CH$_3$OCHO molecular lines and constrain the mass of the central protostar to be $\sim40^{+2}_{-3} M_{\odot}$. The fitting results additionally show that the disk has a centrifugal radius at about 1300 au. Considering the infall velocity, radius, and mass of the envelope, we estimate the accretion rate from the envelope onto the disk to be $\sim7\times 10^{-3}\ M_{\odot}\,\mathrm{yr^{-1}}$. We also identify spiral-like structures in the disk that can be described by free-falling streamers. Our results highlight the critical role of accretion disks and streamers in the mass accumulation of early O-type stars in the CMZ.

astro-ph.GA↗

arXiv2026

Tracking Protostellar Variability in Massive Protoclusters with ALMA: I. Insights from QUARKS and MaMMOtH

Millimeter/submillimeter variability is often attributed to dynamical disk-mediated accretion, yet detection is limited to low-mass protostars in nearby clouds. Recent observations have also revealed significant (sub)millimeter variability in high-mass protostars, but the confirmed cases are scarce and lack systematic monitoring. In this work, we analyzed multi-epoch Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (1.3 mm) continuum observations of 22 massive protoclusters, with epoch separations ranging from a few hours to more than two years, while achieving a consistent angular resolution of approximately 0.3 arcsec. These data allow us to track variability of protostars across a broader mass range and in an environment markedly different from nearby clouds. Using a custom processing pipeline for data reduction, image alignment, and relative flux calibration, we achieve high-precision flux measurements and, for the first time, investigate millimeter variability in massive protoclusters based on interferometric data in a statistical manner. Applying the astrodendro algorithm, we identified 383 condensations and tracked their variations in peak intensities. Standard deviation analysis and difference maps reveal five variable sources, corresponding to a lower limit of 1.3% on the variable fraction. Among these, I13111-6228 stands out as it hosts a hypercompact H II region that exhibits a 68% increase in continuum peak intensity over one year, with an uncertainty of 2%.

astro-ph.GA↗

arXiv2025

The ALMA-ATOMS survey: A sample of weak hot core candidates identified through line stacking

Hot cores represent critical astrophysical environments for high-mass star formation, distinguished by their rich spectra of organic molecular emission lines. We aim to utilize high-angular resolution molecular line data from ALMA to identify hot cores, with a particular focus on weak-emission candidates, and to provide one of the largest samples of hot core candidates. We propose to use spectral stacking and imaging techniques of complex organic molecules (COMs) in the ALMA-ATOMS survey, including line identification & weights, segmentation of line datacubes, resampling, stacking and normalization, moment 0 maps, and data analysis, to search for hot core candidates. We classify cores with dense emission of CH3OH and at least one molecule from the other six molecules as hot core candidates. In addition to the existing sample of 60 strong hot cores from the ALMA-ATOMS survey, we have detected 40 new weak candidates through stacking. All hot core candidates display compact emission from at least one of the other six COM species. For the strong sample, the stacking method provides molecular column density estimates that are consistent with previous fitting results. For the newly identified weak candidates, all species except CH3CHO show compact emission in the stacked image, which cannot be fully resolved spatially. These weak candidates exhibit column densities of COMs that are approximately one order of magnitude lower than those of the strong sample. The entire hot core sample, including the weak candidates, reveals tight correlations between the compact emission of CH3OH and other COM species, suggesting they may share a similar chemical environment for COMs, with CH3OH potentially acting as a precursor for other COMs. The molecular line stacking technique is used to identify hot core candidates in this work, leading to the identification of 40 new hot core candidates.

astro-ph.GA↗