Browsing by Author "Oosterloo, T"

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    A low H I column density filament in NGC 2403: signature of interaction or accretion
    (2014) de Blok, W J G; Keating, K M; Pisano, D J; Fraternali, F; Walter, F; Oosterloo, T; Brinks, E; Bigiel, F; Leroy, A
    Observed H i accretion around nearby galaxies can only account for a fraction of the gas supply needed to sustain the currently observed star formation rates. It is possible that additional accretion occurs in the form of low column density cold flows, as predicted by numerical simulations of galaxy formation. To constrain the presence and properties of such flows, we present deep H i observations obtained with the NRAO Green Bank Telescope of an area measuring 4° × 4° around NGC 2403. These observations, with a 5σ detection limit of 2.4 × 1018 cm-2 over a 20 km s-1 linewidth, reveal a low column density, extended cloud outside the main H i disk, about 17′ (~ 16 kpc or ~ 2 R25) to the NW of the center of the galaxy. The total H i mass of the cloud is 6.3 × 106 M⊙, or 0.15 percent of the total H i mass of NGC 2403. The cloud is associated with an 8 kpc anomalous-velocity H i filament in the inner disk, that was previously observed in deep VLA observations. We discuss several scenarios for the origin of the cloud, and conclude that it is either accreting from the intergalactic medium, or is the result of a minor interaction with a neigboring dwarf galaxy
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    HALOGAS: Extraplanar gas in NGC 3198
    (2013) Gentile, G; Józsa, G I G; Serra, P; Heald, G H; de Blok, W J G; Fraternali, F; Patterson, M T; Walterbos, R A M; Oosterloo, T
    We present the analysis of new, deep HI observations of the spiral galaxy NGC 3198, as part of the HALOGAS (Westerbork Hydrogen Accretion in LOcal GAlaxieS) 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/kpc (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 Halpha 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 MOND (Modified Newtonian Dynamics) and we 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.