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Toward a Direct Measurement of the Cosmic Acceleration:The Pilot Observation of HI 21 cm Absorption Line at FAST
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作者 jiangang kang Chang-Zhi Lu +1 位作者 Tong-Jie Zhang Ming Zhu 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第7期47-55,共9页
This study presents results on detecting neutral atomic hydrogen(H I)21 cm absorption in the spectrum of PKS PKS1413+13 at redshift z=0.24670041.The observation was conducted by FAST,with a spectral resolution of10 Hz... This study presents results on detecting neutral atomic hydrogen(H I)21 cm absorption in the spectrum of PKS PKS1413+13 at redshift z=0.24670041.The observation was conducted by FAST,with a spectral resolution of10 Hz,using 10 minutes of observing time.The global spectral profile is examined by modeling the absorption line using a single Gaussian function with a resolution of 10 kHz within a 2 MHz bandwidth.The goal is to determine the rate of the latest cosmic acceleration by directly measuring the redshift evolution of the H I 21 cm absorption line with Hubble flow toward a common background quasar over a decade or longer time span.This will serve as a detectable signal generated by the accelerated expansion of the Universe at redshift z<1,referred to as redshift drift z(5)or the SL effect.The measured H I gas column density in this DLA system is approximately equivalent to the initial observation value,considering uncertainties of the spin temperature of a spiral host galaxy.The high signal-to-noise ratio of 57,obtained at a 10 kHz resolution,strongly supports the feasibility of using the H I 21 cm absorption line in DLA systems to accurately measure the redshift drift rate at a precision level of around 10~(-10)per decade. 展开更多
关键词 (cosmology)cosmological parameters-cosmology observations-cosmology theory-(cosmology)dark energy-radio lines ISM-radio lines galaxies-ISM clouds
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Extragalactic HⅠSurvey with FAST:First Look at the Pilot Survey Results
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作者 jiangang kang Ming Zhu +2 位作者 Mei Ai Haiyang Yu Chun Sun 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2022年第6期215-233,共19页
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 ... 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. 展开更多
关键词 GALAXIES formation-radio lines galaxies-surveys-galaxies distances and redshifts-radiation dynamics-galaxies evolution
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