Far-infrared line imaging of the starburst ring in NGC 1097 with theHerschel/PACS spectrometer

Abstract

NGC 1097 is a nearby SBb galaxy with a Seyfert nucleus and a bright starburst ring. We study the physical properties of the interstellar medium (ISM) in the ring using spatially resolved far-infrared spectral maps of the circumnuclear starburst ring of NGC 1097, obtained with the PACS spectrometer on board the <i>Herschel<i/> Space Observatory. In particular, we map the important ISM cooling and diagnostic emission lines of [OI] 63 <i>μ<i/>m, [OIII] 88 <i>μ<i/>m, [NII] 122 <i>μ<i/>m, [CII] 158 <i>μ<i/>m and [NII] 205 <i>μ<i/>m. We observe that in the [OI] 63 <i>μ<i/>m, [OIII] 88 <i>μ<i/>m, and [NII] 122 <i>μ<i/>m line maps, the emission is enhanced in clumps along the NE part of the ring. We observe evidence of rapid rotation in the circumnuclear ring, with a rotation velocity of ~220 km s<sup>-1<sup/> (inclination uncorrected) measured in all lines. The [OI] 63 <i>μ<i/>m/[CII] 158 <i>μ<i/>m ratio varies smoothly throughout the central region, and is enhanced on the northeastern part of the ring, which may indicate a stronger radiation field. This enhancement coincides with peaks in the [OI] 63 <i>μ<i/>m and [OIII] 88 <i>μ<i/>m maps. Variations of the [NII] 122 <i>μ<i/>m/[NII] 205 <i>μ<i/>m ratio correspond to a range in the ionized gas density between 150 and 400 cm<sup>-3<sup/>.