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

¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France e-mail: wim.vandriel@obspm.fr
² Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, 18330 Nançay, France
³ University of Massachusetts, Astronomy Program, 536 LGRC, Amherst, MA 01003, USA e-mail: schneide@messier.astro.umass.edu
⁴ Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa e-mail: kraan@ast.uct.ac.za
⁵ Laboratoire de l'Accélérateur Linéaire, Université Paris-Sud, Bâtiment 200, BP 34, 91898 Orsay Cedex, France e-mail: monnier@lal.in2p3.fr

Received: 20 March 2009
Accepted: 27 April 2009

Abstract

Aims. A pilot survey has been made to obtain 21 cm H i 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), as well as a further 16 2MASS pre-release working database sources that did not make it into 2MASX.

Methods. One hundred sixteen of the 2MASX sources and the 16 working database sources were observed using the Nançay radio telescope, usually in the 325 to 11 825 km s^-1 range, and the other 81 2MASX sources were observed with the Arecibo radio telescope in the –500 to 11 000 km s^-1 range, and for 9 also in the 9500 to 21 000 km s^-1 range.

Results. Global H i line parameters are presented for the 22 and 29 2MASX objects that were detected at Nançay and Arecibo, respectively, as well as upper limits for the undetected 2MASX objects. Another galaxy (ESO 371-27) was detected in the Nançay beam centred on an undetected target, ESO 371-26. Nançay data on 12 sources could not be used due to high rms noise levels, most likely caused by strong nearby continuum sources. None of the 16 working database sources were detected at Nançay. Whereas object 2MASX J08170147-3410277 appears to be a very massive galaxy with an H i mass of 4.6 10¹⁰  and an inclination-corrected rotation velocity of 314 km s^-1, it is clear that only radio synthesis H i imaging observations will allow a firm conclusion on this.

Conclusions. Overall, the global properties of the detected galaxies match those of other ZoA H i 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 H i 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 |b| 5°, but increasingly less so for lower latitudes.