The Galaxy Gallery Page 6: Comparative Morphology
This Is M33.
M33 is a High Surface Brightness Galaxy low mass spiral
Galaxy which is a member of the local group. Its distance is
approximately 2.5 million light years from the earth. Its an
important calibrator in the extragalactic distance scale although
it has somewhat high luminosity per unit mass compared to other
low mass spiral galaxies. The Left Image is an exposure is of 30 seconds duration
and again taken with a blue filter. It captures the central 2/3
of the total galaxy. There are lots of OB associations and other
signs of active star formation here.
H-alpha Emission in M33. Star formation is often best manifested by bright H II regions.These are regions of hydrogen which have been ionized by ultraviolet
photons which are emitted from massive stars (typically stars more than
20 times the mass of the Sun). As those UV photons ionize the hydrogen,
the free protons and electrons will later recombine and emit a photon
of wavelength 6562.8 Angstroms (this is call H-alpha). A narrowband
filter image centered on this wavelength will then readily reveal these
H II regions and hence the current sites of star formation in a galaxy,
The luminous blobs that can be seen here are all H II regions
The Right Image is the H-alpha Image of M33.
This Is The Large Magellanic Cloud.
The Large Magellanic Cloud (LMC) is the nearest other
galaxy to the Milky Way. It covers an angular size on the sky of
about 36 square degrees. It is best seen with the naked eye
using averted vision and provides a good example of what the concept
of low surface brightness is all about. This image is the only of
its kind. It is a narrow band (15 angstrom) H-alpha image of the
LMC taken with a single CCD exposure. No telescope is involved,
just an 85-mm Nikon Lens. It is interesting to compare the
morphology of this H-alpha image with the Red image of the LMC. Here the Red passband is measuring the
intensity and appearance of the galaxy in the light of 5 billion
year old stars whereas the H-alpha image is measuring the distribution
of stars with ages less than 10 Million years. The dramatic difference
in morphology between the two passbands is an important lesson.
Images From CTIO
The Electronic Universe Project
Obtained March 15, 1994.
- Low Surface Brightness spirals, in which N3558 appears to be one given the low
contrast of its disk.
This Is M106.
M106 has a High Surface Brightness Inner region and low
Surface Brightness outer region. The Left Most image is a blue band
exposure of the inner 1/2 of the galaxy where the dust is evident.
The Right Most image is an I-band image (effective wavelength around
8500 Angstroms) of the whole galaxy. The morphology in this image
appears much smoother as the old stellar population (more smoothly
distributed) dominates the light in this passband.
Image of M106
IR Image of M106