Sub-arcsecond atomic hydrogen absorption in the Seyfert galaxies NGC 7674 and NGC 7469

Details Sub-arcsecond atomic hydrogen absorption in the Seyfert galaxies NGC 7674 and NGC 7469 Sub-arcsecond atomic hydrogen absorption in the Seyfert galaxies NGC 7674 and NGC 7469

Oct 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002mnras.335.1091b&link_type=abstract

Monthly Notice of the Royal Astronomical Society, Volume 335, Issue 4, pp. 1091-1099.

Astronomy and Astrophysics

Astronomy

6

Galaxies: Active, Galaxies: Individual: Ngc 7469, Galaxies: Individual: Ngc 7674, Galaxies: Seyfert, Radio Lines: Galaxies

Scientific paper

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 Msolar. 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.

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