Fine-Scale Structure of the Neutral Hydrogen Absorption in NGC1275

Author: Romney, Jonathan Daniel MacLeish

Year: 1979

Degree: Dissertation (Ph.D.)

Advisor: Cohen, Marshall H.

Committee Member: Unknown, Unknown

Option: Astronomy

DOI: 10.7907/ytaj-x179

Abstract

The high-velocity 21-cm absorption feature in NGC1275 (=3C84) has been mapped at an angular resolution of a few milliarcseconds with an intercontinental very-long-baseline interferometer. The method of analysis makes use of both the absolute amplitude of the visibility function in the continuum, and the relative amplitude and phase between the line and continuum.

Fine-scale structure in the continuum is determined from the observations, and the 21-cm structure of 3C84 on angular scales covering almost six orders of magnitude is reviewed.

The HI absorption is found to arise in a cloud covering part of the intense, compact continuum nucleus. Although absorption is seen against the brightest part of the continuum structure, the cloud is displaced to the northeast from the nucleus, reaching optical depths of at least 0.83. The cloud is at least 5.6 pc in diameter, with a deduced volume density between 12 and 120 cm[superscript -3].

Two basic hypotheses which have been advanced to elucidate the 21-cm absorption and other high-velocity features in NGC1275 are discussed. The results of the present investigation strongly support the interpretation that all the high-velocity features arise in a superposed galaxy in the Perseus Cluster. The alternative model, in which the high-velocity gas is ejected from the active nucleus, is inconsistent with the structure observed in the HI absorption.

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