Finding active galaxies in the cluster Abell 1238
In this exercise, we will examine the spectra of four objects found in the field of A1238 for which spectra
are available in the SDSS Data Release #4. Note that the SDSS is still in progress, and remember that not all galaxies
found in the imaging survey are targeted for spectroscopy.
- -- Go to the SDSS DR4 site: http://cas.sdss.org/dr4/en/
Orient yourself; if you have questions, this will be the basic place to
return to look up information.
2.1. NED gives the center position of Abell 1238 as RA = 11h22m58.0s, Dec = +01d05m32s in J2000 equatorial coordinates.
This position is based on Abell's original eyeball estimate of the cluster center, so it is not very accurate.
What does J2000 refer to?
2.2. Convert RA, Dec in these units to decimal degrees and record the answer here. You will need this
conversion, because the SDSS Navigator Tool works in this system.
2.3. Go the SDSS Navigator Tool
http://cas.sdss.org/dr4/en/tools/chart/navi.asp and input the coordinates. You may also which to set
various Drawing Options, and explore using the Zoom, Recenter,
and Explore utilities. Comment on the appearance of the cluster in the SDSS image.
2.4. Use the SpecObjs option to identify the objects which have spectra already
in the SDSS database. Comment on how this result might relate to your answer to question 1.4.
We have identified four objects in the vicinity of the cluster for which you should examine both the morphological appearance, the
spectral information and the location in the cluster. To make things easier for you, we provide direct links to the objects, but you'll
have to explore a bit beyond the two links we provide. Be sure to check
the NED link also; one of the objects is a background QSO.
2.5. Using the SDSS images and spectra, comment separately on the stellar population, star formation rate,
and "activity" in each of the four objects A, B, C and D
and explain what evidence obtained from the images and spectra lead you to your conclusion.
Last modified: Tue Jan 23 08:58:34 2007
by martha