PENN STATE UNIVERSITY
This is a three color image of colliding galaxies, obtained with the Wide Field Planetary Camera on the Hubble Space Telescope. Stephan's quintet is one of Hickson's compact groups of galaxies. The image shows two interacting galaxies that are members of the group. Let's zoom in on the region to the lower left of the galaxy to the left.
close-up image shows the tidal debris drawn from a galaxy in the course
of the "galactic train wreck". Stars are forming in the gas of the
tidal debris; the blue colored clumps are regions of recent stellar birth.
red galaxy that lies behind the tidal debris, from what we can see in this
image, could be a dwarf galaxy that is a member of this group of galaxies,
or it could be a giant galaxy in the distant background. Our
Hobby-Eberly Telescope spectrum of this region reveals which is the case!
Here is the long-slit spectrum obtained with the Marcario
Low Resolution Spectrograph on the Hobby Eberly Telescope. The light
is dispersed horizontally along the spectrum, that is the wavelength scale
runs from blue to red along the image of the spectrum, from left to right.
The horizontal lines along the spectrum represent the "continuum" light
of the clump of light, while the very bright structures in the spectrum
represent "emission lines" that are characteristic of particular chemical
elements present in the gas. The long slit allows us to capture several
objects in the same spectrum, which are represented by the different lines
and bands in the vertical direction.
Here is a line plot of the spectrum of the brightest blue
clump right next to the red galaxy in the HST image. The emission
lines are those characteristic of the Balmer series of Hydrogen, and forbidden
lines of singly ionized Oxygen, Nitrogen, and Sulfur.
Four different regions have been probed with this single long slit spectrum of the tidal debris. Not only can the velocities of the regions be compared, as shown above, but we can also compare the build-up of metals and the ages of the populations of stars that have formed in this region.
Thanks to everyone at the
HET, especially to Grant Hill and Matt Shetrone for obtaining these data,
to Gary Hill for the LRS, and to Larry Ramsey for the HET.