1. Astronomical Imaging of Interacting Galaxies
Data Reduction
Data was reduced using python, IRAF, SExtractor and AstroimageJ.
We developed a script in python to perform overscan subtraction, bias
subtraction and flat field correction. After this processing was done, AstroimageJ
was used to get the world coordinates for the images and align them. Then
imcombine from IRAF was called to combine the images by color-band. Finally, a
second script was created to perform sky subtraction on the images.
From here the data must be calibrated using magnitudes We plan to perform low
surface brightness photometry to analyze the interacting pair.
NGC 3310 is a galaxy located in the constellation Ursa
Major. It is also a starburst galaxy, meaning it is
experiencing a high rate of star formation. NGC 3310
recently underwent a collision with a much smaller mass
galaxy, which was consumed creating tidal loops and
stimulating star formation. After we reduced the data, we
discovered previously unnoticed tidal loops. These loops
are speculated to be the remnants of the consumed
galaxy that have been caught in the orbit of NGC 3310.
Over-scan Subtraction:
The over-scan is a portion of the image created
by blank read out cycles, which appear on one or
two sides of the image. The over-scan contains
bias information specific to the camera's state
when the image was taken. HDI is unique
because the over-scan appears in two
dimensions. It is removed by finding the median
value within the over-scan sections and
subtracting that value from the image.
Bias Subtraction:
A bias frame is an image taken with the lens cap
on and a zero exposure time. This shows the bias
in the chip itself, which will appear in every
image. Bias subtraction is performed by median
combining all bias frames and subtracting that
median bias frame from all images.
Flat Field Correction:
Flat field frames are images that show imperfections
in the chip and optical path. The images used in this
process were Dome Flats. They contained dust or
marks, which may appear in all science frames as
well. These features must be divided out of the
image. To perform the correction, we median
combined the flat frames by color-band, normalized
each combined frame by the mean value, and
divided them out of the images.
Sky Subtraction:
When an image is taken there is a sky level that
must be taken into account. This "sky" contains any
gradients in the background as well as any other
unwanted illumination from the reflection of the sky.
Imsurfit from IRAF was used to remove this by
subtracting a 2D polynomial fit from the image.
Maria McQuillan and Dr Elizabeth Wehner
University of St. Thomas
Physics
NGC 2798 and 2799 are an interacting equal
mass spiral pair. A bridge with notable star
forming regions originates in NGC 2798 (right)
and connects to NGC 2799 (left). NGC 2799 also
has two tidal tails, north and south.
NGC 3310 in Z-scale which shows
the fainter structures
NGC 3310 log scale showing the
brighter structures
NGC 2798/9 in Z-scale which shows
the fainter structures
NGC 2798/9 in log scale showing the
brighter structures.
Process for Sky subtraction:
NGC 2798 and 2799
Before 2D surface fit After
The gradient in background of the image before sky
subtraction
The flat background after sky subtraction
NGC 3310
Acknowledgments:
This work was funded by the Minnesota Space Grant
Consortium. I would also like to thank the University
of St. Thomas Grants office for providing housing.