skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Friday, May 17 until 8:00 AM ET on Saturday, May 18 due to maintenance. We apologize for the inconvenience.

Search for: All records

Creators/Authors contains: "Lu, Xing"

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    In this work, we constrain the star-forming properties of all possible sites of incipient high-mass star formation in the Milky Way’s Galactic Center. We identify dense structures using the CMZoom 1.3 mm dust continuum catalog of objects with typical radii of ∼0.1 pc, and measure their association with tracers of high-mass star formation. We incorporate compact emission at 8, 21, 24, 25, and 70μm from the Midcourse Space Experiment, Spitzer, Herschel, and SOFIA, cataloged young stellar objects, and water and methanol masers to characterize each source. We find an incipient star formation rate (SFR) for the Central Molecular Zone (CMZ) of ∼0.08Myr−1over the next few 105yr. We calculate upper and lower limits on the CMZ’s incipient SFR of ∼0.45 and ∼0.05Myr−1,respectively, spanning roughly equal to and several times greater than other estimates of CMZ’s recent SFR. Despite substantial uncertainties, our results suggest the incipient SFR in the CMZ may be higher than previously estimated. We find that the prevalence of star formation tracers does not correlate with source volume density, but instead ≳75% of high-mass star formation is found in regions above a column density ratio (NSMA/NHerschel) of ∼1.5. Finally, we highlight the detection ofatoll sources, a reoccurring morphology of cold dust encircling evolved infrared sources, possibly representing Hiiregions in the process of destroying their envelopes.

    more » « less
    Free, publicly-accessible full text available February 1, 2025
  2. Abstract

    The peptide-like molecule cyanoformamide (NCCONH2) is the cyano (CN) derivative of formamide (NH2CHO). It is known to play a role in the synthesis of nucleic acid precursors under prebiotic conditions. In this paper, we present a tentative detection of NCCONH2 in the interstellar medium with the Atacama Large Millimeter/submillimeter Array (ALMA) archive data. 10 unblended lines of NCCONH2 were seen around 3σ noise levels toward Sagittarius B2(N1E), a position that is slightly offset from the continuum peak. The column density of NCCONH2 was estimated to be 2.4 × 1015 cm−2, and the fractional abundance of NCCONH2 toward Sgr B2(N1E) was 6.9 × 10−10. The abundance ratio between NCCONH2 and NH2CHO is estimated to be ∼0.01. We also searched for other peptide-like molecules toward Sgr B2(N1E). The abundances of NH2CHO, CH3NCO and CH3NHCHO toward Sgr B2(N1E) were about 1/10 of those toward Sgr B2(N1S), while the abundance of CH3CONH2 was only 1/20 of that toward Sgr B2(N1S).

    more » « less
  3. Abstract

    We report JWST NIRCam observations of G0.253+0.016, the molecular cloud in the Central Molecular Zone known as “The Brick,” with the F182M, F187N, F212N, F410M, F405N, and F466N filters. We catalog 56,146 stars detected in all six filters using thecrowdsourcepackage. Stars within and behind The Brick exhibit prodigious absorption in the F466N filter that is produced by a combination of CO ice and gas. In support of this conclusion, and as a general resource, we present models of CO gas and ice and CO2ice in the F466N, F470N, and F410M filters. Both CO gas and ice contribute to the observed stellar colors. We show, however, that CO gas does not absorb the Pfβand Huϵlines in F466N, but that these lines show excess absorption, indicating that CO ice is present and contributes to observed F466N absorption. The most strongly absorbed stars in F466N are extincted by ∼2 mag, corresponding to >80% flux loss. This high observed absorption requires very high column densities of CO, and thus a total CO column that is in tension with standard CO abundance and/or gas-to-dust ratios. This result suggests the CO/H2ratio and dust-to-gas ratio are greater in the Galactic Center than in the Galactic disk. Ice and/or gas absorption is observed even in the cloud outskirts, implying that additional caution is needed when interpreting stellar photometry in filters that overlap with ice bands throughout galactic centers.

    more » « less
  4. Abstract One of the most poorly understood aspects of low-mass star formation is how multiple-star systems are formed. Here we present the results of Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations toward a forming quadruple protostellar system, G206.93-16.61E2, in the Orion B molecular cloud. ALMA 1.3 mm continuum emission reveals four compact objects, of which two are Class I young stellar objects and the other two are likely in prestellar phase. The 1.3 mm continuum emission also shows three asymmetric ribbon-like structures that are connected to the four objects, with lengths ranging from ∼500 to ∼2200 au. By comparing our data with magnetohydrodynamic simulations, we suggest that these ribbons trace accretion flows and also function as gas bridges connecting the member protostars. Additionally, ALMA CO J = 2−1 line emission reveals a complicated molecular outflow associated with G206.93-16.61E2, with arc-like structures suggestive of an outflow cavity viewed pole-on. 
    more » « less
    Free, publicly-accessible full text available July 1, 2024
  5. Abstract We observed the high-mass protostellar core G335.579–0.272 ALMA1 at ∼200 au (0.″05) resolution with the Atacama Large Millimeter/submillimeter Array (ALMA) at 226 GHz (with a mass sensitivity of 5 σ = 0.2 M ⊙ at 10 K). We discovered that at least a binary system is forming inside this region, with an additional nearby bow-like structure (≲1000 au) that could add an additional member to the stellar system. These three sources are located at the center of the gravitational potential well of the ALMA1 region and the larger MM1 cluster. The emission from CH 3 OH (and many other tracers) is extended (>1000 au), revealing a common envelope toward the binary system. We use CH 2 CHCN line emission to estimate an inclination angle of the rotation axis of 26° with respect to the line of sight based on geometric assumptions and derive a kinematic mass of the primary source (protostar+disk) of 3.0 M ⊙ within a radius of 230 au. Using SiO emission, we find that the primary source drives the large-scale outflow revealed by previous observations. Precession of the binary system likely produces a change in orientation between the outflow at small scales observed here and large scales observed in previous works. The bow structure may have originated from the entrainment of matter into the envelope due to the widening or precession of the outflow, or, alternatively, an accretion streamer dominated by the gravity of the central sources. An additional third source, forming due to instabilities in the streamer, cannot be ruled out as a temperature gradient is needed to produce the observed absorption spectra. 
    more » « less

    We present an overview and data release of the spectral line component of the SMA Large Program, CMZoom. CMZoom observed 12CO (2–1), 13CO (2–1), and C18O (2–1), three transitions of H2CO, several transitions of CH3OH, two transitions of OCS, and single transitions of SiO and SO within gas above a column density of N(H2) ≥ 1023 cm−2 in the Central Molecular Zone (CMZ; inner few hundred pc of the Galaxy). We extract spectra from all compact 1.3 mm CMZoom continuum sources and fit line profiles to the spectra. We use the fit results from the H2CO 3(0, 3)–2(0, 2) transition to determine the source kinematic properties. We find ∼90 per cent of the total mass of CMZoom sources have reliable kinematics. Only four compact continuum sources are formally self-gravitating. The remainder are consistent with being in hydrostatic equilibrium assuming that they are confined by the high external pressure in the CMZ. We find only two convincing proto-stellar outflows, ruling out a previously undetected population of very massive, actively accreting YSOs with strong outflows. Finally, despite having sufficient sensitivity and resolution to detect high-velocity compact clouds (HVCCs), which have been claimed as evidence for intermediate mass black holes interacting with molecular gas clouds, we find no such objects across the large survey area.

    more » « less