Studies of the extended
Hαemission in Blue Compact
Dwarf Galaxies
S.R. Knollmann1, P. Papaderos1, A. Gil de Paz2, K.J. Fricke1
1: Universitäts-Sternwarte Göttingen, Germany
2: IPAC, Caltech, USA
Motivation
Sample
Methods
First results
Outlook
NGC1569
ESA, NASA, P. Anders (Göttingen Univ.) et al.
see also Hunter et al., AJ, 120, 2000
Overview
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004
from: Martin et al., ApJ, 574, 2002
The distribution and structure
of
the warm interstellar
medium (ISM) in blue compact
dwarf galaxies (BCDGs) is a
manifestation of the release of
energy and momentum from
young stellar populations and
SNe.
Therefore a close investigation
of its spatial properties is of
great interest. This may hold
crucial information to the
understanding
of
feedback
processes in dwarf galaxies.
Motivation
Central star
clusters
Studies
o
Interaction between
hot and warm gas
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004
BCDGs show Hα emission on kpc scales from the central star-forming
regions. How does the radial intensity distribution (as traced by the Hα
line) of BCDs look like?
In the Strömgren Model one would expect:
Motivation
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004
from: Papaderos et al., A&A, 393, 2002
There are clear indications that the extended Hα
emission in BCDGs shows a roughly exponential
intensitiy decrease for large radii (Papaderos et al.
2002, shown here). This was also reported for the
metal deficient BCDs SBS0335-052E/W (Pustilnik et al.
2004).
from: Papaderos et al., A&A, 393, 2002
Hα surface brightness µ of a sample of
BCDGs (shifted vertical by an arbitrary
amount for the sake of clarity) vs.
galactocentric radius R* in units of the
exponential scale length of the stellar
host galaxy in the B Band.
Motivation
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004
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Is an exponential Hα intensity decrease in the
outermost regions of the ionized halo of BCDs a typical
property of these systems?
Is there a clear change in the profile slope between the
inner, high surface brightness and the outer,
exponential low surface brightness part? Or do we
rather observe a smooth transition?
How is the concentration of the Hα emission or its
outer exponential scale length related to the burst
properties?
Motivation
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004
Our sample is composed of the “Palomar/Las Campanas Imaging Atlas of Blue
Compact Dwarf Galaxies” (Gil de Paz et al. 2003).
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114 images in B,R,Hα
images are reduced and calibrated
nearby objects (d < 60Mpc)
Hα surface brightness ≤ 10-17 erg/s/cm²/arcsec²
MB spanning from -12mag to -18mag
Additionally we include a number of other BCDs observed by us previously and
we plan to further enlarge the sample by including archival data.
Sample
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004
We first improve on the sky and
continuum subtraction of the
images.
Then different methods to extract
Hα profiles are used. The most
simple approach is to derive radial
intensitiy profiles within circular
apertures. The result – especially
in the inner, bright part – can be
highly dependent on the selected
center.
Therefore in order to warrant
reproducibility of our results, we
first determine a “minimum
asymmetry center” of each Hα
map which is then used as the
aperture's center.
Methods
NGC1705
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004
NGC3125 (Tol3)
Asymmetry parameter dependent on
different centers (displayed in pixel
coordinates). The Asymmetry A was
calculated using:
∑ ∣Ii , j−I i , j∣
A=
i, j
NGC3125 (Tol3)
Hα map with coordinate system
centered at the asymmetry minimum.

2 ∑ ∣Ii , j∣
i, j
(see eg. Lotz et al., AJ, 128, 2004 and
references therein)
Methods
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004
Some results
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004
Future work:
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Completing the profile derivation for the whole sample using
sets of circular apertures; test the result using another profile
extraction method.
Systematic analysis of the Hα surface brightness profiles;
possible parametrizations?
Determination of the profile slope (scale length) in its outer
part; comparison with other galactic properties (scale length of
the stellar component, burst duration and strength, ...)
Outlook
Studies of the extended Hα emission in blue compact dwarf galaxies
S.R. Knollmann, P. Papaderos, A. Gil de Paz, K.J. Fricke
JENAM2004