A common way to explore the properties of a population of galaxies involves constructing
its color-magnitude diagram (CMD). A nice example which we will use for reference
is the work of ALFALFA team member Peppo
Gavazzi and his co-workers who constructed the CMD of a large sample of galaxies within
420 square degrees of sky covering
the Coma supercluster and its member groups and clusters of galaxies as presented
Gavazzi+ (2010), A&A 517, 73 and shown here to the right. Taken from Fig. 3 of
that paper, the figure shows the "g-i color versus i-band absolute magnitude
relation of all galaxies in the C[oma]S[upercluster] coded according to Hubble type: red = early-
type galaxies (dE-E-S0-S0a); blue = disk galaxies (Sbc-Im-BCD); green = bulge
galaxies (Sa-Sb)... Contours of equal
density are given. The continuum line g-i =
-0.0585 *(Mi + 16) + 0.78 represents the empirical separation between the
red-sequence and the remaining galaxies.
The dashed line illustrates the effect of the limiting magnitude r=17.77 of the
spectroscopic SDSS database, combined with the
color of the faintest E galaxies g-r ~0.70 mag.."
Your task is to construct a CMD for the α.40 population using colors and
magnitudes derived from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7).
Luckily for you, we will provide you with the data you need, but before you begin,
you should understand a bit about the SDSS photometric dataset.
Click for a larger view.
Figure 3 from Gavazzi+ (2010)