The Westerbork Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) survey

I. Survey description and pilot observations

¹ Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands
e-mail: heald@astron.nl
² University of New Mexico, 800 Yale Blvd, Albuquerque, NM, USA
³ Astronomy Department, Bologna University, via Ranzani 1, 40127 Bologna, Italy
⁴ Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
⁵ Department of Astronomy, New Mexico State University, PO Box 30001, MSC 4500, Las Cruces, NM 88003, USA
⁶ Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany
⁷ Sterrenkundig Observatorium, Ghent University, Krijgslaan 281, S9, 9000 Ghent, Belgium

Received: 15 October 2010
Accepted: 27 November 2010

Abstract

We introduce a new, very deep neutral hydrogen (H i) survey being performed with the Westerbork Synthesis Radio Telescope (WSRT). The Westerbork Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) Survey is producing an archive of some of the most sensitive H i observations available, on the angular scales which are most useful for studying faint, diffuse gas in and around nearby galaxies. The survey data are being used to perform careful modeling of the galaxies, characterizing their gas content, morphology, and kinematics, with the primary goal of revealing the global characteristics of cold gas accretion onto spiral galaxies in the local Universe. In this paper, we describe the survey sample selection, the data acquisition, reduction, and analysis, and present the data products obtained during our pilot program, which consists of UGC 2082, NGC 672, NGC 925, and NGC 4565. The observations reveal a first glimpse of the picture that the full HALOGAS project aims to illuminate: the properties of accreting H i in different types of spirals, and across a range of galactic environments. None of the pilot survey galaxies hosts an H i halo of the scale of NGC 891, but all show varying indications of halo gas features. We compare the properties of detected features in the pilot survey galaxies with their global characteristics, and discuss similarities and differences with NGC 891 and NGC 2403.