Space distribution and clustering of 345 Cepheids in the Milky Way from 2MASS data

JHKS photometry from the 2MASS survey is used for investigation of the distribution of Milky Way Cepheids. The diameter and thickness of the explored region of the Milky Way disk is about 10 kpc and about 1 kpc, respectively. This paper presents: 1) recalibrated period-luminosity relation in the KS band, based on 29 well studied Cepheids, 2) reestimated distances for 345 Cepheids, 3)a method for detecting dense groups of Cepheids in 3D space and 4) 18 newly revealed large Cepheid groups. It is found that the characteristic size of the largest groups is about 700 pc. Many other young objects are found around the centers of the Cepheid groups: OB stars, WR stars, associations, open clusters, HII regions. It is concluded that the Cepheid groups are good indicators of the locations and sizes of the star forming complexes.