Optical observations of Dwingeloo 1, a nearby barred spiral galaxy behind the Milky Way

Abstract

We present new optical observations of the nearby barred spiral galaxy Dwingeloo 1 (Dw1) obtained with the Isaac Newton, William Herschel and Wise telescopes. Dw1 lies at Galactic coordinates (l = 138°.52, b = - 0°.11) and it is heavily obscured by dust and gas in the Milky Way. We infer that Dw1 is of morphological type SBb or SBc (T = 4), has an inclination i ≈ 50°, a position angle PA ≈ 110°, and a recession velocity relative to the Milky Way VMW = 256±9 km s-1. The measured total apparent magnitudes of Dw1 are V= 14.0 ± 0.5, R = 12.2 ± 0.2 and I = 10.7 ± 0.2. The extinction estimate towards Dw1 is highly uncertain. The extinction in the B band, derived from Galactic H I column density measurements, is AB≈ 5.8. Estimated from Galactic 100-μm emission, the extinction is Lambda;B%4.3, while the reddened colours of Dw1 yield an estimate of AB ≈ 10.4. Assuming AB = 5.8, TullyFisher relations in the I and R bands lead to a distance estimate for Dw1 of D ≈ 300 km s-1. However, for the derived range of extinction estimates 4.3 ∼ AB ∼ 10.4, the distance varies from 100 to 500 km s-1. We also report the detection of numerous H II regions associated with Dw1, and present data from the Infrared Astronomical Satellite (IRAS) archive.