Xing Lu

FRAGMENTATION OF MOLECULAR CLUMPS AND FORMATION OF A PROTOCLUSTER

Sufficiently massive clumps of molecular gas collapse under self-gravity and fragment to spawn a cluster of stars that have a range of masses. We investigate observationally the early stages of formation of a stellar cluster in a massive filamentary infrared dark cloud, G28.34+0.06 P1, in the 1.3mm continuum and spectral line emission using the ALMA. Sensitive continuum data reveal further fragmentation in five dusty cores at a resolution of several 10^3 AU. Spectral line emission from C18O, CH3OH, 13CS, H2CO and N2D+ are detected for the first time toward these dense cores. We found that three cores are chemically more evolved as compared with the other two; interestingly though, all of them are associated with collimated outflows as suggested by evidence from the CO, SiO, CH3OH, H2CO and SO emissions. The parsec-scale kinematics in NH3 exhibit velocity gradients along the filament, consistent with accretion flows toward the clumps and cores. The moderate luminosity and the chemical signatures indicate that the five cores harbor low- to intermediate-mass protostars that likely become massive ones at the end of the accretion. Despite the fact that the mass limit reached by the 1\sigma dust continuum sensitivity is 30 times lower than the thermal Jeans mass, there is a lack of a distributed low-mass protostellar population in the clump. Our observations indicate that in a protocluster, low-mass stars form at a later stage after the birth of more massive protostars.

The Galactic Center Molecular Cloud Survey - I. A steep linewidth-size relation and suppression of star formation

The Central Molecular Zone (CMZ; inner

DEEPLY EMBEDDED PROTOSTELLAR POPULATION IN THE 20 km s−1 CLOUD OF THE CENTRAL MOLECULAR ZONE

\sim{}200~\rm{}pc

The Molecular Gas Environment in the 20 km s−1 Cloud in the Central Molecular Zone

) of the Milky Way is a star formation (SF) environment with very extreme physical properties. Exploration of SF in this region is important because (i) this region allows us to test models of star formation under exceptional conditions, and (ii) the CMZ clouds might be suitable to serve as templates to understand the physics of starburst galaxies in the nearby and the distant universe. For this reason we launched the Galactic Center Molecular Cloud Survey (GCMS), the first systematic study that resolves all major CMZ clouds at interferometer angular resolution (i.e., a few arc seconds). Here we present initial results based on observations with the Submillimeter Array (SMA) and the Atacama Pathfinder Experiment (APEX). Our study is complemented by dust emission data from the Herschel Space Telescope and a comprehensive literature survey of CMZ star formation activity. Our research reveals (i) an unusually steep linewidth-size relation,

The Galactic Center Molecular Cloud Survey - II. A lack of dense gas and cloud evolution along Galactic center orbits

\sigma(v)\propto{}r_{\rm{}eff}^{0.66\pm{}0.18}

INITIAL FRAGMENTATION IN THE INFRARED DARK CLOUD G28.53−0.25

, down to velocity dispersions

Filamentary fragmentation and accretion in high-mass star-forming molecular clouds

\sim{}0.6~\rm{}km\,s^{-1}

Deeply Embedded Protostellar Population in the Central Molecular Zone Suggested by H

at 0.1 pc scale. This scaling law potentially results from the decay of gas motions to transonic velocities in strong shocks. The data also show that, relative to dense gas in the solar neighborhood, (ii) star formation is suppressed by factors

_2

\gtrsim{}10

O Masers and Dense Cores

in individual CMZ clouds. This observation encourages exploration of processes that can suppress SF inside dense clouds for a significant period of time.