The high-velocity cloud complex Galactic center negative as seen by EBHIS and GASS

I. Cloud catalog and global properties

B. Winkel^1,2, N. Ben Bekhti¹, V. Darmstädter¹, L. Flöer¹, J. Kerp¹ and P. Richter³

¹ Argelander-Institut für Astronomie (AIfA), Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
e-mail: bwinkel@mpifr.de
² Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
³ Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Golm, Germany

Received: 27 May 2011
Accepted: 7 July 2011

Abstract

Using Milky Way data of the new Effelsberg-Bonn H i Survey (EBHIS) and the Galactic All-Sky Survey (GASS), we present a revised picture of the high-velocity cloud (HVC) complex Galactic center negative (GCN). Owing to the higher angular resolution of these surveys compared to previous studies (e.g., the Leiden Dwingeloo Survey), we resolve complex GCN into lots of individual tiny clumps, that mostly have relatively broad line widths of more than 15 km s^-1. We do not detect a diffuse extended counterpart, which is unusual for an HVC complex. In total 243 clumps were identified and parameterized which allows us to statistically analyze the data. Cold-line components (i.e., Δv_fwhm < 7.5 km s^-1) are found in about 5% only of the identified cloudlets. Our analysis reveals that complex GCN is likely built up of several subpopulations that do not share a common origin. Furthermore, complex GCN might be a prime example for warm-gas accretion onto the Milky Way, where neutral H i clouds are not stable against interaction with the Milky Way gas halo and become ionized prior to accretion.