ASTRONOMY 3303   HW#4     due Wed Oct 04, 2017
Print a copy of this page and enter it in your portfolio. Answer the
questions (preferably type them or write legibly) separately; make sure to include
the graded answers in
your portfolio after they are handed back. In all cases, be sure that you give
complete derivations, showing the equations you use, including the values of any
constants you use and always giving the units involved.
Part I: The NASA Extragalactic Database NED
For this assignment, we will investigate the galaxies in the vicinity of the nearby "poor" cluster known as MKW 11.
Use the NED to record relevant information about the cluster and to answer these questions
- Record the R.A., Dec. and heliocentric radial velocity of the group as given in NED.
- What does "MKW" stand for?
- What are other names for this same group?
- What is the basic difference between the frame B1950.0 and J2000.0?
- What is the galactic latitude of MKW 11?
- What is the V-band extinction in this direction?
- What is the recessional velocity of the cluster in the CMB rest frame?
- What is the distance (in the frame of the CMB) quoted by NED? What distance do you get if you use the Cosmology Calculator? If you have not encountered the calculator before, make sure to read its tutorial, to understand the definitions of its input and output parameters.
Part II: Running a search using the SDSS SQL
Let's investigate the photometric dataset available from the Sloan Digital Sky Survey
(SDSS) in the region of MKW 11. Before you begin, take a look
at the SDSS
SQL help page and review the instructions on how to run a
SQL search of the SDSS database.
Below is the SQL search you should run; be sure you understand the syntax.
p.lnLExp_r, p.lnLDeV_r, s.zWarning,p.objID
FROM PhotoObj p, SpecObj s, SpecLine l
p.SpecObjID = s.SpecObjID AND
p.SpecObjID = l.specobjID AND
l.lineID = dbo.fSpecLineNames('Ha_6565') AND
p.ra >=198. AND p.ra <= 207. AND
p.dec >= 7. AND p.dec <= 16. AND
s.z <= 0.061
order by p.ra
Figure out what all the parameters listed above are, and how the SQL search is going to work.
- What is a Petrosian magnitude as derived by the SDSS?
- What is a "model" magnitude as derived by the SDSS?
- What is the difference between "lnLExp" and "lnLDeV" as derived by the SDSS?
- What are some reasons why the warning flag "z.Warning" is set by the SDSS?
- Run the SQL search and download the resultant file in CSV format.
Part III: The CMD of galaxies in the MKW 11 region
Next, let's explore the CMD of galaxies included in the SDSS in the region
of MKW 11 to a larger sample covering 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.."
Click for a larger view.
Figure 3 from Gavazzi+ (2010)
- Use TOPCAT to construct the CMD of the galaxies in the CSV file you downloaded
from the previous search. In order to compare what you find with Figure 3
of Gavazzi+ (2010), be sure to: (a) calculate distances from CMB velocities
and using Ho = 73 km/s/Mpc; and (b) generate the plot with the same
scaling and orientation they use.
- Compare the results from our SQL search with the general ones
found by Gavazzi+ (2010). Which galaxies are included in both plots? In only
one or the other, but not both?
Part IV: Group discussion: Active Galaxies.
In class, we had a detailed discussion about star formation in
galaxies, and signs of activity. Let's have a closer look at one case
with some interesting new data, based on
We will discuss active galactic nuclei in more detail in the following
lectures, so don't worry if you do not yet fully understand the
terminology used here.
Based on what you have learned in class, discuss with your group the
relevance of these observations, and what you find most interesting
about them. What is the VLT telescope? At what wavelengths does it
observe, and why? What made these observations challenging? In what
ways is this galaxy different from the Milky Way? What can we learn
from studies like this one? Using the astronomy query tools you have
encountered so far, try to find more information on this galaxy. Use
at least one scientific publication with different data in your
discussion. Also, as a group, be prepared to give a 3 minute summary
of your discussion during the lecture on October 4th, as a lead-in to
discussing your findings with the other groups. It may be useful to
assign a discussion leader and a note taker within your group. If you
require any form of media, please prepare handouts or anything
equivalent that is suitable for sharing at the table. Also, please
provide a brief (1-2 page) write-up of your discussion.
NOTE: Self-organize in groups of up to 3 students for
this discussion. Clearly indicate and give credit to all members of
the discussion group, and clearly reference all source materials you
consider in your discussion (e.g., specific parts of the press
release, newspaper articles based on this release, the textbook, class
notes, etc.). You may hand in only one copy of the report for your
group if preferred, but make sure that all names are provided!