5 research outputs found
Photometric studies of some starburst galaxies
We present the results of a detailed morphological analysis of ten starburst
galaxies selected from the Markarian catalogue of uv-excess objects. CCD
surface photometry of these galaxies was carried out based on observations made
in B, V (Johnson) and R, I (Kron-Cousins) band passes. We present the radial
variations of surface brightness, ellipticity, position angle and the colour
indices for each galaxy obtained using ellipse fitting isophotal analysis. The
residual images constructed for extracting the fine structure are also
presented. A variety of morphological types are found to host the starburst
phenomenon. The star formation activity is not confined to the nuclear region
alone, but it also occurs at various locations in the galaxy and is seen as
clumpy regions. The colour index and the residual images are used for deriving
information about the sites of enhanced star formation activity and the
triggers of the starburst. The luminosity profiles show an exponential
behaviour in the outer region. The disk scale lengths and the half-light radii
are derived. The contribution of the burst component has been estimated and the
colours of the burst component are presented. Strong isophotal twisting is
detected in all the S0 and E galaxies: Mrk 1002, Mrk 1308 and Mrk 14, in the
sample. This is accompanied by boxiness in some cases, suggesting that a merger
is responsible for the starburst activity in these galaxies. In case of
isolated spirals, a bar or a central oval distortion appear to be the likely
trigger for the starburst.Comment: 12 pages of text and 28 figures. Uses aastex. To be published in A&A
Spiral-like Light Profiles but Elliptical-like Kinematics in Mergers of Galaxies
It is commonly accepted that a merger of two spiral galaxies results in a
remnant with an elliptical-like surface-brightness profile. Surprisingly, our
recent study (Chitre & Jog 2002) of the 2MASS data for twenty-seven advanced
mergers of galaxies has shown that half of these have a light distribution that
decreases exponentially with radius. Such a distribution normally characterizes
a rotationally supported disk in a spiral galaxy. Here we show from kinematic
data for two of these mergers, Arp 224 and Arp 214, that the main support
against gravitational collapse comes from pressure due to random motion of
stars as seen in an elliptical galaxy rather than from rotation. The origin of
the unusual combination of properties seen here is a puzzle. The standard
theoretical N-body models in the literature cannot account for these systems.
Further observational and dynamical studies of this new class of merger
remnants are needed, and would be important for understanding merger dynamics
and galaxy evolution.Comment: 13 pages, 2 .eps figures, To appear in A & A Letters, Vol. 393,
October 200