HALOGAS: Extraplanar gas in NGC 3198

¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, 9000 Gent, Belgium
e-mail: gianfranco.gentile@ugent.be
² Department of Physics and Astrophysics, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
³ Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴ Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
⁵ Astrophysics, Cosmology and Gravity Centre (ACGC), Astronomy Department, University of Cape Town, Private Bag X3, 7700 Rondebosch, Republic of South Africa
⁶ Astronomy Department, University of Bologna, Bologna, Italy
⁷ Kapteyn Astronomical Institute, University of Groningen, AD Groningen, The Netherlands
⁸ Department of Astronomy, New Mexico State University, PO Box 30001, MSC 4500, Las Cruces, NM 88003, USA

Received: 16 January 2013
Accepted: 4 April 2013

Abstract

We present the analysis of new, deep Hi observations of the spiral galaxy NGC 3198 as part of the Westerbork Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) survey, with the main aim of investigating the presence, amount, morphology, and kinematics of extraplanar gas. We present models of the Hi observations of NGC 3198. The model that matches best the observed data cube features a thick disk with a scale height of ~3 kpc and an Hi mass of about 15% of the total Hi mass; this thick disk also has a decrease in rotation velocity as a function of height (lag) of 7–15 km s^-1 kpc^-1 (though with large uncertainties). This extraplanar gas is detected for the first time in NGC 3198. Radially, this gas appears to extend slightly beyond the actively star-forming body of the galaxy (as traced by the Hα emission), but it is not more radially extended than the outer, fainter parts of the stellar disk. Compared to previous studies, thanks to the improved sensitivity we trace the rotation curve out to larger radii. We model the rotation curve in the framework of modified Newtonian dynamics (MOND) and confirm that, with the allowed distance range we assumed, fit quality is modest in this galaxy, but the new outer parts are explained in a satisfactory way.