Extragalactic HⅠSurvey with FAST:First Look at the Pilot Survey Results

We present the first data release of HⅠsources extracted from a pilot extragalactic survey using the Five-hundredmeter Aperture Spherical radio Telescope(FAST).We extracted sources from three-dimensional(3D)spectral data cubes datacubes to perform interactive searching and computing,yielding global parameters for each source,extending redshift ranges of HⅠemission up to z=0.04.A total of 544 extragalactic HⅠsources has been detected by the pilot FAST HⅠdrift scan survey covering part of the sky region in R.A.(R.A.orα)and decl.(decl.orδ)range 00^(h)47^(m)<R.A.(J2000)<23^(h)22^(m)and+24°<decl.(J2000)<+43°.Of which,528 sources are matched with optical counterparts via examination of digital optical survey databases collected from NED and Vizier data center,and 449 of them have optical velocities.Furthermore,we detect 36 galaxies with HⅠmass<10^(8)M⊙,which is significant for the study of low-mass systems in the local universe.We present catalogs for all HⅠdetections with signal-to-noise ratio(S/N)greater than 5.1.The data are classified into four categories based on their S/N and baseline qualities,which are flagged with code 1 to 4:(1)422 sources with S/N>6.5;(2)61 sources with 5.1■S/N■6.5;(3)28 sources with relatively poor baselines;(4)33 sources that are partly masked by strong radio frequency interferences(RFIs).In addition,we find 16 HⅠsources that have not been matched with any counterparts in the existing galaxy catalogs.This data release can provide guidance for the future extragalactic HⅠsurvey with FAST.

Integrated HI emission in galaxy groups and clusters

The integrated HI emission from hierarchical structures such as groups and clusters of galax- ies can be detected by FAST at intermediate redshifts. Here we propose to use FAST to study the evolution of the global HI content of clusters and groups over cosmic time by measuring their integrated HI emissions. We use the Virgo Cluster as an example to estimate the detection limit of FAST, and have estimated the integration time to detect a Virgo type cluster at different redshifts （from z = 0.1 to z ---- 1.5）. We have also employed a semi-analytic model （SAM） to simulate the evolution of HI contents in galaxy clusters. Our simulations suggest that the HI mass of a Virgo-like cluster could be 2-3 times higher and the physical size could be more than 50% smaller when redshift increases from z = 0.3 to z = 1. Thus the integration time could be reduced significantly and gas rich clusters at intermediate redshifts can be detected by FAST in less than 2 hours of integration time. For the local Universe, we have also used SAM simulations to create mock catalogs of clusters to predict the outcomes from FAST all sky surveys. Comparing with the optically selected catalogs derived by cross matching the galaxy catalogs from the SDSS survey and the ALFALFA survey, we find that the HI mass distribution of the mock catalog with 20 s of integration time agrees well with that of observations. However, the mock catalog with 120 s of integration time predicts many more groups and clusters that contain a population of low mass HI galaxies not detected by the ALFALFA survey. A future deep HI blind sky survey with FAST would be able to test such prediction and set constraints on the numerical simulation models. The observational strategy and sample selections for future FAST observations of galaxy clusters at high redshifts are also discussed.

Properties of the UCHII region G25.4NW and its associated molecular cloud

Ultra compact HII （UCHII） G25.4NW is a bright IR source in the region of the inner Galaxy. New HI images from the Very Large Array Galactic Plane Survey show clear absorption features associated with the UCHII region up to 95 km s^-1, and there are no other absorptions up to the tangential velocity. This reveals that G25.4NW has a near-side distance of 5.7 kpc, and it is located in the region of the inner Galactic molecular ring. Using the new distance, the bolometric luminosity of G25.4NW is estimated as 105.6 L⊙, which corresponds to an 06 star. It contains 460 M⊙ of ionized gas. A high-resolution ^13CO image from the Galactic Ring Survey reveals that G25.4NW is part of a more extended star-forming complex with about 104 M⊙ of molecular gas.

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.

HiFAST:An HIdata calibration and imaging pipeline for FAST

The Five-hundred-meter Aperture Spherical radio Telescope(FAST)has the largest aperture and a 19-beam L-band receiver,making it powerful for investigating the neutral hydrogen atomic gas(HI)in the universe.We present HiFAST(https://hifast.readthedocs.io),a dedicated,modular,and self-contained calibration and imaging pipeline for processing the H?data of FAST.The pipeline consists of frequency-dependent noise diode calibration,baseline fitting,standing wave removal using an FFT-based method,flux density calibration,stray radiation correction,and gridding to produce data cubes.These modules can be combined as needed to process the data from most FAST observation modes:tracking,drift scanning,On-The-Fly mapping,and most of their variants.With HiFAST,the root-mean-square(RMS)noises of the calibrated spectra from all 19 beams were only slightly(~5%)higher than the theoretical expectation.The results for the extended source M33 and the point sources are consistent with the results from Arecibo.The moment maps(0,1 and 2)of M33 agree well with the results from the Arecibo Galaxy Environment Survey(AGES)with a fractional difference of less than 10%.For a common sample of 221 sources with signal-to-noise ratio S/N>10 from the Arecibo Legacy Fast ALFA(ALFALFA)survey,the mean value of fractional difference in the integrated flux density,Sint,between the two datasets is approximately 0.005%,with a dispersion of 15.4%.Further checks on the integrated flux density of 23 sources with seven observations indicate that the variance in the flux density of the source with luminous objects(Sint>2.5 Jy km s-1)is less than 5%.Our tests suggest that the FAST telescope,with the efficient,precise,and user-friendly pipeline HiFAST,will yield numerous significant scientific findings in the investigation of the H?in the universe.

Brugada syndrome:a fatal disease with complex genetic etiologies–still a long way to go

Brugada syndrome(BrS)is an arrhythmogenic disorder which was first described in 1992.This disease is a channelopathy characterized by ST-segment elevations in the right precordial leads and is susceptible to sudden death.BrS is a fatal disease with gender and age preferences.It occurs mainly in young male subjects with a structurally normal heart and silently progresses to sudden death with no significant symptoms.The prevalence of BrS has been reported in the ranges of 5-20 per 10000 people.The disease is more prevalent in Asia.Nowadays,numerous variations in 23 genes have been linked to BrS since the first gene SCN5A has been associated with BrS in 1998.Not only can clinical specialists apply these discoveries in risk assessment,diagnosis and personal medicine,but also forensic pathologists can make full use of these variations to conduct death cause identification.However,despite the progress in genetics,these associated genes can only account for approximately 35%of the BrS cases while the etiology of the remaining BrS cases is still unexplained.In this review,we discussed the prevalence,the genes associated with BrS and the application of molecular autopsy in forensic pathology.We also summarized the present obstacles,and provided a new insight into the genetic basis of BrS.

The forensic pathological analysis of sport-related sudden cardiac death in Southern China

Studies regarding sport-related sudden cardiac death(SCD)mainly focus on competitive ath-letes;similar data are rare in the general population,especially in China.We conducted a retrospective study(from September 1998 to August 2013)to investigate the aetiological distribution and epidemiological features of sport-related SCD in Southern China.Selections of cases are based on details,and two subgroups were established:one was the sport-related SCD group,and the other was the disease-free accident victims group which was matched with the sport-related SCD group in gender,age and year of death.Among the 3770 sudden-death cases,1656 cases were SCD cases.A total of 65 cases(57 males)out of 1656 SCD cases were sport-related.The age range of the 65 sport-related SCD cases was from 12 to 68 years old with a mean(35.92±14.23)years old.Only two of these cases were competitive athletes.The most common circumstances of the 65 sport-related SCD cases were heavy physical labour(46.15%)and running(30.77%).The three leading forensic diag-noses were the coronary atherosclerotic disease(CAD,28 cases),cardiomyopathy(CM,14 cases)and sudden unexplained death(7 cases).CM was the most common forensic diagno-sis in those?35 years old,while CAD was the most common one in those>35 years old.Left anterior descending in which atherosclerotic plaques was most commonly found was the principal artery branch associated with sport-related SCD.There was a statistically signifi-cant difference in the weight of hearts between the 65 sport-related SCD cases and 65 dis-eases-free accidental cases.This study highlights the need to attract public attention to sport-related SCD and to issue a prevention strategy to the public,and to make the SCD-related genetic sequencing a routine tool in both forensic pathological examination and clinic screening.