The Herschel Exploitation of Local Galaxy Andromeda (HELGA) - I. Global far-infrared and sub-mm morphology

摘要: We have obtained Herschel images at five wavelengths from 100 to 500 micron of a ~5.5x2.5 degree area centred on the local galaxy M31 (Andromeda), our nearest neighbour spiral galaxy, as part guaranteed time project 'HELGA'. The main goals HELGA are study characteristics extended dust emission, focusing larger scales than studied in previous observations Andromeda an increased spatial resolution, and obscured star formation. In this paper we present data reduction provide description far-infrared morphology, comparing it with features seen other wavelengths. use high-resolution maps atomic hydrogen, fully covering fields, identify emission that genuinely belong M31, distinguishing them coming foreground Galactic cirrus. Thanks very large extension detect, for first wavelengths, three ring-shaped structures extending out ~21, ~26 ~31 kpc respectively, south-western innermost structure also having counterpart opposite side. presence these is safely confirmed by their detection HI maps. Due unfortunate coincidence M31's systemic velocity rotation speed its outermost parts, together bright cirrus heavily contaminating north-eastern side, fainter side more uncertain. find significantly extends beyond previously mapped emission. An annular-like segment, already known 15-kpc ring, clearly detected both sides similar annular undoubtedly south-west well.