Dust and ionized gas in NGC 3607

Abstract

We report the detection of a broad dust ring in the X-ray-bright elliptical galaxy NGC 3607, the dominant member of a nearby group of galaxies. The inner radius of the ring is approximately 1.3 kpc from the nucleus and has a width of approximately 0.75 kpc. The maximum extinction corresponds to E(B-V) = 0.12 +/- 0.023. We also confirm the existence of bright H-alpha nebulosity around the nuclear region of the galaxy, just inside the dust ring. The luminosity in H-alpha is approximately 1.5 x 1040 ergs/s. The estimated amount of neutral hydrogen in the galaxy is approximately 4 x 107 solar masses and ionized hydrogen approximately 1.1 x 105 solar masses. We rule out H-alpha emission due to cooling flow, heat conduction from hot gas to the cold gas, photoionization by post-Asymptotic Giant Branch (AGB) stars or an active nucleus, and suggest that photoionization by young stars is the most plausible cause. We also suggest that the dust and associated gas are acquired from an interacting neighbor NGC 3608. The results are based on CCD surface photometry of the galaxy carried out using the broad-band filters V and R and a narrow-band filter appropriate for the red-shifted H-alpha + (N II) emission.