We performed a radio recombination line ( RRL ) survey to construct a high-mass star-forming region ( HMSFR ) sample in the Milky Way based on the all-sky Wide-Field Infrared Survey Explorer ( All-WISE ) point source catalog .
The survey was observed with the Shanghai 65m Tianma radio telescope ( TMRT ) covering 10 hydrogen RRL transitions ranging from H98 \alpha to H113 \alpha ( corresponding to the rest frequencies of 4.5 - 6.9 GHz ) simultaneously .
Out of 3348 selected targets , we identified an HMSFR sample consisting of 517 sources traced by RRLs , a large fraction of this sample ( 486 ) locate near the Galactic plane ( | b | < 2 \degr ) .
In addition to the hydrogen RRLs , we also detected helium and carbon RRLs towards 49 and 23 sources respectively .
We cross-match the RRL detections with the 6.7 methanol maser sources built up in previous works for the same target sample , as a result , 103 HMSFR sources were found to harbor both emissions .
In this paper , we present the HMSFR catalog accompanied by the measured RRL line properties and a correlation with our methanol maser sample , which is believed to tracer massive stars at earlier stages .
The construction of an HMSFR sample consisting of sources in various evolutionary stages indicated by different tracers is fundamental for future studies of high-mass star formation in such regions .