The Central Regions of Sersic-Pastoriza Galaxies T. P. Prabhu [Ph.D Thesis]

Doctor of Philosophy Indian Institute of Astrophysics, Bangalore 1979

Apart from the sustained interest in the enhanced
forms of activity in the nuclei of galaxies, other
classes of phenomena occurring in the central regions
of galaxies have also drawn considerable interest. One
such aspect of investigations of the central regions of
galaxies is the system of 'hot spots' described
originally by Morgan. Though some enthusiasm was
derived at least once from the speculation that these
are the results of a split due to explosive activity in
the nucleus, the spectroscopic evidences obtained by the
Burbidges and others proved that the hot spots are simply
giant HII complexes.
Sersio and Pasteurize broadened the definition of
this olass of phenomena observed in the central regions
of galaxies to include bright amorphous formations ae well.
The purpose of the present investigations ia to test
whether the objects from the lists of Series and Pasteurize
form a homogeneous class, and to derive parameters which
assist in understanding their structure and content.
We begin with a brier over view of the principle of
superposition of quasi-independent subsystems in galaxies
in Chapter 1. We will also describe some of the classification
schemes describing the central regions of galaxies Following Morgan's operational approach. we show in
Chapter 2 that the central regions of galaxies listed by
Sersic and Pastoriza are morphologically intermediate
between the normal and Seyfert galaxies. We will also
compile an additional list similar central formations
based on the descriptions published by various authors.
The correlation of the occurrence of such 'pronuclear
formations' with the morphology of the parent galaxies
is also investigated.
The techniques o£ observation and of reduction
are presented. They include direct and filter photography,
and spectroscopy with a narrow as well as a wide slit.
The techniques used in obtaining equal intensity contours
are also presented.
A morphological classification of the central
regions of 50 galaxies from the lists of Series and
Pastoriza ia proposed in Chapter 4. The classes range from
the elliptioal appearance of ‘E’types, through the
formations with bright dist1nct hot spots to the
irregular pattern of hot spots of low surface brightness.
Some correlations with the types of the parent
galaxy are also investigated.
The surface photometric data is presented in Chapter 5
in terms of the equal intensity contours in the integrated light (~~4000-8700) for 27 galaxies from the finding list. The equivalent luminosity profiles have been presented for all these galaxies.
The blue-infrared colour distribution across the
nucleus and the 'perinuclear formation' have been presented
in Chapter 6 for one galaxy of type E (NGC 210) and for
five of class ~(NGC 613, 1097, 136,5, 1808 and 2903).
The nucleus appears reddest in all the casts. The perinuclear
formations of class ~ possess neutral colour with
respect to the main body of the galaxy. The hot spots of formations of class ~ are generally redder than the main body of the galaxy though a few hot spots are
distinctly bluer. The perinuclear regions of NGC t808
are the reddest among the galaxies investigated. The
nucleus of NGC 290) has been discovered on our infrared
photographs.
The mean profiles for different classes of formations
have also been computed in Chapter 6. and appear similar
to each other in all the oases except in the class ~ .
The formations of class ~ have a lower luminosity
Gradient than the other classes. A small difference noticed
in class or could be due to the existence of discrete
hot spots.