Cold gas in massive early-type galaxies: The case of NGC 1167

Abstract

We present a study of the morphology and kinematics of the neutral hydrogen in the gas-rich (MHI = 1.5 × 1010 M ⊙), massive earlytype galaxy NGC 1167, which was observed with the Westerbork Synthesis Radio Telescope (WSRT). The Hi is located in a 160 kpc disk (≈3 × D25) and has low surface density (≤2 M⊙ pc-2). The disk shows regular rotation for r < 65 kpc but several signs of recent and ongoing interaction and merging with fairly massive companions are observed. No population of cold gas clouds is observed - in contrast to what is found in some spiral galaxies. This suggests that currently the main mechanism bringing in cold gas to the disk is the accretion of fairly massive satellite galaxies, rather than the accretion of a large number of small gas clumps. NGC 1167 is located in a (gas-) rich environment: we detect eight companions with a total H I mass of ∼6 × 109 M ⊙ within a projected distance of 350 kpc. Deep optical images show a disrupted satellite at the northern edge of the Hi disk. The observed rotation curve shows a prominent bump of about 50 km s-1 (in the plane of the disk) at r ≈ 1.3 × R25. This feature in the rotation curve occurs at the radius where the Hi surface density drops significantly and may be due to large-scale streaming motions in the disk. We suspect that both the streaming motions and the Hi density distribution are the result of the interaction/accretion with the disrupted satellite. Like in other galaxies with wiggles and bumps in the rotation curve, H I scaling describes the observed rotation curve best. We suggest that interactions create streaming motions and features in the H I density distribution and that this is the reason for the success of H I scaling in fitting such rotation curves. © ESO 2010.