Abstract
Neutral hydrogen has been studied on sub-arcsecond scales in two Seyfert galaxies, NGC 7469 and NGC 7674. The 1.4-GHz continuum emission from these sources agree with higher frequency measurements and shows linear, triple source in NGC 7674 and a compact source surrounded by a weak ring of radio emission in NGC 7469. In both of these sources we detect deep localized H I absorption in front of a single continuum component. In the case of NGC 7674 the H I absorption is only seen against the central component and has a peak optical depth of 0.21 ± 0.03, a linewidth of 114 ± 7 km s-1 and a heliocentric velocity of 8623 ± 5 km s-1. The integrated H I absorption against the central component corresponds to a column density of 5.0 ± 0.7 × 1021 atom cm-2. We interpret the lack of H I absorption against the east and west components (τ <0.07 and 0.06) as evidence that the H I is localized within the central few hundred pc, similar to the H I observed against the nucleus of NGC 4151, and has an upper mass limit of ∼4 × 105 M⊙. We speculate that this H I may be associated with a dusty torus. Giant Meterwavelength Radio Telescope (GMRT) results show extended emission and give a rest velocity of 8699 ± 20 km s-1. The H I absorption against NGC 7469 shows a single deep feature against the strong central component. The line has a peak optical depth 0.25, a linewidth of 65 ± 6 km s-1 and a heliocentric velocity of 4843 ± 5 km s-1. The integrated column density is 3.6 ± 0.4 × 1021 atom cm-2. Unfortunately the other components in NGC 7469 are too weak to set significant limits to the H I optical depth, and hence, unlike NGC 7674, it is not possible to constrain the size of the absorbing gas.
Original language | English |
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Pages (from-to) | 1091-1099 |
Number of pages | 8 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 335 |
Issue number | 4 |
DOIs | |
Publication status | Published - 1 Oct 2002 |
Keywords
- Galaxies: active
- Galaxies: individual: NGC 7469
- Galaxies: individual: NGC 7674
- Galaxies: Seyfert
- Radio lines: galaxies