A multi-transition molecular line study of infrared dark cloud G331.71+00.59

Using archive data from the Millimeter Astronomy Legacy Team Survey at 90 GHz (MALT90),carried out using the Mopra 22-m telescope,we made the first multi-transition molecular line study of infrared dark cloud (IRDC) MSXDC G331.71+00.59.Two molecular cores were found embedded in this IRDC.Each of these cores is associated with a known extended green object (EGO),indicating places of massive star formation.The HCO + (1-0) and HNC (1-0) transitions show prominent blue or red asymmetric structures,suggesting outflow and inflow activities of young stellar objects (YSOs).Other detected molecular lines include H 13 CO + (1-0),C 2 H (1-0),HC 3 N (10-9),HNCO(4 0,4-3 0,3) and SiO (2-1),which are typical of hot cores and outflows.We regard the two EGOs as evolving from the IRDC to hot cores.Using public GLIMPS data,we investigate the spectral energy distribution of EGO G331.71+0.60.Our results support this EGO being a massive YSO driving the outflow.G331.71+0.58 may be at an earlier evolutionary stage.

Molecular outflows and gas rotation associated with G20.08–0.14N

We present the results of a high-resolution study with the Submillimeter Array(SMA)toward the massive star-forming complex G20.08–0.14N.With the SMA data,we have detected and analyzed the transitions in the12CO(3–2)and12CO(2–1)molecular lines as well as CH3CN.The millimeter observations reveal highly collimated bipolar molecular outflows,traced by high-velocity12CO(2–1)and12CO(3–2)emissions.Using a rotation temperature diagram,we derive that the rotational temperature and the column density of CH3CN are 244 K and 1.2×1015cm 2,respectively.We also suggest that the minor outflow is probably driven by the hypercompact(HC)HII region A that is inside.We find the molecular gas(traced by C17O,SO,CH3OH and SO2)surrounding G20.08–0.14N appears to be undergoing bulk rotation.The HCHII region A that is inside is most probably the main source of accretion and heating for G20.08–0.14N.

A multiwavelength study of the star forming HⅡ region Sh2-82

Based on a multiwavelength study,the interstellar medium and young stellar objects(YSOs) around the H Ⅱ region Sh2-82 have been analyzed.Two molecular clumps were found from the archival data of the Galactic Ring Survey,and using the Two Micron All-Sky Survey catalog,we found two corresponding young clusters embedded in the molecular clumps.The very good relations between CO emission,infrared shells and YSOs suggest that it is probably a triggered star formation region from the expansion of Sh2-82.We further used the data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire from Spitzer to study the YSOs within the two clumps,confirming star formation in this region.By spectral energy distribution fits to each YSO candidate with infrared excess,we derived the slope of the initial mass function.Finally,comparing the H Ⅱ region's dynamical age and the fragmentation time of the molecular shell,we discard the "collect and collapse" process as being the triggering mechanism for YSO formation.Sh2-82 can be a mixture of other processes such as radiative-driven implosion and/or collisions with pre-existing clumps.

HNCO： a molecule that traces low-velocity shocks

Using data from Millimetre Astronomy Legacy Team Survey at 90 GHz(MALT90), we present a molecular line study of a sample of APEX Telescope Large Area Survey of the Galaxy(ATLASGAL) clumps. Twelve emission lines have been detected in all. We found that in most sources,emissions of HC_3 N, HN^(13) C, CH_3 CN, HNCO and Si O show more compact distributions than those of HCO^+, HNC, HCN and N_2 H^+. By comparing with other molecular lines, we found that the abundance of HNCO(χ(HNCO)) correlates well with other species such as HC_3N, HNC, C_2H, H^(13) CO^+and N_2 H^+. Previous studies indicate the HNCO abundance could be enhanced by shocks. However, in this study, we find the abundance of HNCO does not correlate well with that of Si O, which is also a good tracer of shocks. We suggest this may be because HNCO and Si O trace different parts of shocks.Our analysis indicates that the velocity of a shock traced by HNCO tends to be lower than that traced by Si O. In the low-velocity shocks traced by HNCO, the HNCO abundance increases faster than that of Si O. While in the relatively high-velocity shocks traced by Si O, the Si O abundance increases faster than that of HNCO. We suggest that in the infrared dark cloud MSXDC G331.71^+00.59, high-velocity shocks are destroying the molecule HNCO.

Searching for initial stage of massive star formation around the HⅡ region G18.2–0.3

Sometimes,early star formation can be found in cold and dense molecular clouds,such as an infrared dark cloud.Considering that star formation often occurs in clusters,H II regions may be triggering a new generation of star formation,so we can search for the initial stage of massive star formation around H II regions.Based on the above,this work introduces one method to search for the initial stage of massive star formation around H II regions.Towards one section of the H II region G18.2–0.3,multiwavelength observations are carried out to investigate its physical properties.Through analysis,we find three potential initial stages of massive star formation,suggesting that it is feasible to use in searching for the initial stage of massive star formation around H II regions.

Radio recombination line observations at 1.0-1.5 GHz with FAST

H Ⅱ regions made of gas ionized by radiations from young massive stars,are widely distributed in the Milky Way.They are tracers for star formation,and their distributions are correlated with the Galactic spiral structure.Radio recombination lines(RRLs) of hydrogen and other atoms allow for the most precise determination of physical parameters such as temperature and density.However,RRLs at around 1.4 GHz from HⅡ regions are weak and their detections are difficult.As a result,only a limited number of detections have been obtained yet.The 19-beam receiver on board of the Five-hundred-meter Aperture Spherical radio Telescope(FAST) can simultaneously cover 23 RRLs for Hnα,Henα,and Cnα(n=164-186),respectively.This,combined with its unparalleled collecting area,makes FAST the most powerful telescope to detect weak RRLs.In this pilot survey,we use FAST to observe nine HⅡ regions at L band.We allocate20 minutes pointing time for each source to achieve a sensitivity of around 9 mK in a velocity resolution of2.0 km s^(-1).In total,21 RRLs for Hnα and Cnα at 1.0-1.5 GHz have been simultaneously detected with strong emission signals.Overall,the detection rates for the H167α and C167α RRLs are 100%,while that for the He167α RRL is 33.3%.Using hydrogen and helium RRLs,we measure the electron density,electron temperature,and pressure for three HⅡ regions.This pilot survey demonstrates the capability of FAST in RRL measurements,and a statistically meaningful sample with RRL detection,through which knowledge about Galactic spiral structure and evolution can be obtained,is expected in the future.

Probing star formation and feedback using CCOSMA and archival data in the CFG028.68–0.28 quasi-sinusoidal filament

We have performed a multi-wavelength study toward a quasi-sinusoidal filament(CFG028.68–0.28). A new large-scale ^12CO J = 3-2 map was obtained from the China-Cologne Observation for Sub Millimeter Astronomy(CCOSMA) 3m radio telescope. Based on the ATLASGAL catalog, we have identified 27 dust clumps in the filament. Through the relationship between the mass and radius of these clumps, 67% of these clumps are dense and massive enough to potentially form massive stars. The obtained CFE is ~11% in the filament. The filament has a linear mass density of ~305 M⊙pc^-1, which is smaller than its critical mass to length ratio. This suggests that the external pressure from the neighboring H Ⅱ regions may help prevent the filament from dispersing under the effects of turbulence. Comparing the energy injection from outflows and H Ⅱ regions in the filament, the ionization feedback from the H Ⅱ regions can help maintain the observed turbulence.

HI detection of J030417.78+002827.4 by the Five-hundred-meter Aperture Spherical Radio Telescope

We present the first HI 21 cm spectroscopy detection of J030417.78+002827.4,which is an active galactic nucleus(AGN)with an intermediate-mass black hole(IMBH)in the center.The observations were carried out with the Five-hundred-meter Aperture Spherical Radio Telescope(FAST)last year.We relied on the ON-OFF observing approach with the 19-beam receiver covering 1.05-1.45 GHz.Within a total integration time of about 20 min,the root mean square(RMS)of our data reaches 1.2 mJy beam-1,at a velocity resolution of 1.6 km s^(-1).Radio frequency interference(RFI)is checked and excluded during the data analysis.The detected HI spectroscopy shows a dual-horned profile with a line width of 223.5 km s^(-1),indicating gas rotation around this AGN.The redshift of this galaxy derived from our HI observation is0.0447.We calculate the atomic gas mass by the integrated flux of the HI emission line.The total gas mass in this galaxy is estimated to be 1.8×10^(10)M☉.We find the fraction of gas-to-stellar mass ratio in J030417.78+002827.4 is more than 50%.This ratio is much higher than the typical value found in other AGNs with supermassive black holes(SMBHs),and is comparable to some star-forming galaxies recently observed by FAST.

The FAST all sky HI survey(FASHI):The first release of catalog

The FAST All Sky HI survey(FASHI)was designed to cover the entire sky observable by the Five-hundred-meter Aperture Spherical radio Telescope(FAST),spanning approximately 22000 square degrees of declination between-14°and+66°,and in the frequency range of 1050-1450 MHz,with the expectation of eventually detecting more than 100000 HI sources.Between August 2020 and June 2023,FASHI had covered more than 7600 square degrees,which is approximately 35%of the total sky observable by FAST.It has a median detection sensitivity of around 0.76 m Jy beam-1and a spectral line velocity resolution of~6.4 km s-1at a frequency of~1.4 GHz.As of now,a total of 41741 extragalactic HI sources have been detected in the frequency range 1305.5-1419.5 MHz,corresponding to a redshift limit of z■0.09.By cross-matching FASHI sources with the Siena Galaxy Atlas(SGA)and the Sloan Digital Sky Survey(SDSS)catalogs,we found that 16972(40.7%)sources have spectroscopic redshifts and 10975(26.3%)sources have only photometric redshifts.Most of the remaining 13794(33.0%)HI sources are located in the direction of the Galactic plane,making their optical counterparts difficult to identify due to high extinction or high contamination of Galactic stellar sources.Based on current survey results,the FASHI survey is an unprecedented blind extragalactic H I survey.It has higher spectral and spatial resolution and broader coverage than the Arecibo Legacy Fast ALFA Survey(ALFALFA).When completed,FASHI will provide the largest extragalactic HI catalog and an objective view of HI content and large-scale structure in the local universe.