H I line observations of 2MASS galaxies in the zone of avoidance

Abstract

A pilot survey has been made to obtain 21cm HI emission line profiles for 197 objects in the Zone of Avoidance (ZoA) that were classified as galaxies in the 2MASS all-sky near-infrared Extended Source Catalog (2MASX). 116 of the sources were observed using the Nancay radio telescope, in the 325 to 11,825 km/s range, and the other 81 sources were observed at Arecibo in the -500 to 11,000 km/s range, and for 9 also in the 9,500 to 21,000 km/s range. Global HI line parameters are presented for the 22 and 29 2MASX objects that were detected at Nancay and Arecibo, respectively, as well as upper limits for the undetected 2MASX objects. Whereas object 2MASX J08170147-3410277 appears to be a very massive galaxy with an HI mass of 4.6 x 10E10 Msun, it is clear that only radio synthesis HI imaging observations will allow a firm conclusion on this. Overall, the global properties of the detected galaxies match those of other ZoA HI surveys. Although the detections are as yet too sparse to give further insight into suspected or unknown large-scale structures in the ZoA, they already indicate that an extension of the present pilot survey is bound to quantify filaments, clusters, and voids behind this part of the Milky Way. It is shown that the number of candidate 2MASS-selected ZoA galaxies to be observed in HI could have been reduced by about 15% through examination of composite near-infrared images and the application of extinction-corrected near-infrared colour limits. Present results confirm that the Galactic extinction values from Schlegel et al. (1998) are valid for latitudes above |b|=5 degrees, but increasingly less so for lower latitudes.