Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.272..355m&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 272, Issue 2, pp. 355-362.
Astronomy and Astrophysics
Astronomy
70
Galaxies, Individual, Ngc 4151-Galaxies, Jets-Galaxies, Seyfert-Radio Lines, Galaxies.
Scientific paper
We present neutral hydrogen absorption measurements of the radio source associated with the nucleus of NGC 4151, with an angular resolution of ~0.15 arcsec. We find that only the component containing the nucleus shows significant absorption, whereas no measurable absorption is seen against other components within the 4-arcsec radio jet. Hence any neutral hydrogen disc, in which the nucleus is embedded, can be no thicker than 50 pc. The strongest component shows a mean integrated absorption of 21.4+/-3 km s^-1, which corresponds to a column density of (3.9+/-0.5)x10^21 atom cm^-2 (T_spin=100 K). There is structure in the absorption on scales as small as 0.1 arcsec, with column densities in excess of 6x10^21 atom cm^-2 over parts of the radio nucleus. The neutral hydrogen column densities are much higher than suggested by UV absorption measurements, which implies that the optical/UV continuum nucleus is not coincident with the strongest radio component. We suggest that the radio nucleus is associated with a weak VLBI component which is ~0.1 arcsec (~7 pc) to the west of the deepest absorption.
Baum Stefi A.
Brinks Elias
Gallimore Jack F.
Mundell Carole G.
O'Dea Christopher P.
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