Neutral Hydrogen 21cm Absorption Line And Radio Structure Study Of Nearby Galaxies

Hydrogen is one of the most abundant elements in the universe,most of which exist in the form of neutral hydrogen atoms.The study of neutral hydrogen is very helpful to understand the structure and evolution of galaxies.The study of neutral hydrogen requires VLBI(very long baseline interferometry).With its high resolution,this technology can be used to explore the spatial distribution and kinematics of galactic media.In this paper,in order to explore the absorption lines and radio structures of neutral hydrogen in the nearby galaxies(z<0.06),we used the survey data of 40%ALFALFA(Arecibo legacy fast Arecibo L-band feed array)extragalactic neutral hydrogen from the Arecibo radio telescope.The VLBI technique is used to detect 10 candidate sources of neutral hydrogen absorption in nearby galaxies,and the characteristics of their 21cm neutral hydrogen absorption lines and their radio structures and properties are analyzed.In this paper,the research status and development of neutral hydrogen are described.The spectral characteristics of the nearby neutral hydrogen galaxies are analyzed by using the survey data of Arecibo telescope.In the process of data processing,we use AIPS and Difmap software to edit and map the original data of VLBA,EVN and VLA observation data.The parameters of the neutral hydrogen absorption line,radio spectrum image,fitting flow and the angle diameter of the fitting component are obtained.In the ALFALFA survey,we found 10 nearest neighbor neutral hydrogen absorption candidates.Five of the 10 candidate sources(NGC 315,IC 860,NGC5363,CGCG 049-057,UGC 6081)have been confirmed earlier.The neutral hydrogen absorption lines of the other five candidate sources(UGC 613,ASK 378291,CGCG049-033,J1534+2513,PGC 070403)have been confirmed by FAST,VLA and WSRT telescopes in China.Through the investigation,we find that the FWHM of most of the10 sources belongs to narrow line,indicating that the absorption line at the system speed is probably generated by a regular rotating neutral hydrogen disk or neutral hydrogen cloud.And three of them have blue shifts.In radio structure,most of them are dense nuclear structure,and some of them have less obvious extended structure.However,there are jets in NGC 315,UGC 613,NGC 5363 and CGCG 049-033 on pc and Kpc scales.The jets of three galaxies are in the same direction on these two scales.The direction of NGC 5363 is not consistent in these two scales,which indicates that the source has Doppler enhancement effect.We pass three important indexes(brightness temperature T_B,The ratio of fir to radio flux q,Wide-field Infrared Survey Explorer(WISE))classifies the properties of these galaxies.We find that almost all the sources have higher brightness temperatures in the galactic nuclei,which indicates that AGN may be in the nucleus.However,from the infrared q-value and WISE,it is found that IC 860,CGCG 049-057 and UGC 6081A may be dust rich star explosion galaxies,and IC 860 has been identified as the galaxy remains of the late explosion period,which is consistent with our results.