Peering into the Milky Way by FAST:Ⅱ.Ionized gas in the inner Galactic disk revealed by the piggyback line observations of the FAST GPPS survey  

作　　者：LiGang Hou JinLin Han Tao Hong XuYang Gao Chen Wang 

机构地区：[1]National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100101,China [2]School of Astronomy,University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Science China(Physics,Mechanics & Astronomy)》2022年第12期18-38,共21页中国科学：物理学、力学、天文学（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.11988101,11933011,11833009,12133004,and 12003044);the National Key R&D Program of China(Grant No.2017YFA0402701);the Key Research Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSW-SLH021);the National SKA Program of China(Grant No.2022SKA0120103);the support from the Youth Innovation Promotion Association CAS;the financial support by the CAS-NWO Cooperation Programme(Grant No.GJHZ1865);the National Natural Science Foundation of China(Grant No.U1831103)。

摘　　要：As one of the major components of the interstellar medium,the ionized gas in our Milky Way,especially the low-density diffuse component,has not been extensively observed in the radio band.The Galactic Plane Pulsar Snapshot(GPPS)survey covers the sky area within the Galactic latitude of±10°around the Galactic plane visible by the Five-hundred-meter Aperture Spherical radio Telescope(FAST),and the spectral line data are simultaneously recorded during the pulsar survey observations.With an integration time of 5 min for each beam,the GPPS survey project provides the most sensitive piggyback spectra for tens of radio recombination lines(RRLs)in the band of 1000-1500 MHz for Hnα,Henα,Cnα,as well as Hnβand Hnγ.We processed the spectral data of RRLs,and obtained a sensitive averaged HnαRRL map of a sky area of 88 square degrees in the inner Galaxy of 33°≤l≤55°and∣b∣≤2°0.The final spectral data of the HnαRRLs have a spatial resolution of∼3′,a spectral resolution of 2.2 km s^(−1),and a typical spectral RMS noise of 0.25 mJy beam−1 or 6.3 mK in main-beam brightness temperature.The FAST GPPS HnαRRL observations are sensitive down to an emission measure of about 200 cm^(−6) pc if a 3σdetection limit is required.The new HnαRRL map shows complex structural features dominated by a number of HII regions and large extended diffuse ionized gas regions.We detect about 94%of the known HII regions and confirm 43 WISE HII regions in the observed sky area.Several large HII regions or star-forming complexes in the distant outer Galaxy are resolved in the map of HnαRRLs.Extended RRL features of the diffuse ionized gas are detected.In addition,the GPPS piggyback spectral-line data also provide sensitive detection for other kinds of RRLs,such as the Henα,Cnα,Hnβ,and HnγRRLs.The RRL data products of the GPPS survey will be published and updated at http://zmtt.bao.ac.cn/MilkyWayFAST/.

关 键 词：surveys ISM HII regions radio lines 

分 类 号：P156[天文地球—天文学]