Neutral hydrogen absorption in the nucleus of NGC3079

Abstract

We present subarcsecond MERLIN 21cm neutral hydrogen absorption line measurements of a 4 × 3 arcseconds (300 × 200 pc) region associated with the active nucleus of the Sc galaxy NGC3079. Broad (200–400 km s⁻¹) and deep (τ ∼ 0.5–1) absorption is seen over much of the region, corresponding to column densities as high as 3 × 10²² atoms cm⁻². The absorption shows a velocity gradient which could be consistent with rotation about a central mass of ∼ 10⁹ M_⊙, however significant non-circular motions are also present which may be due to gas motions in a non-axisymetric potential.