### 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.
```SELECT
p.ra, p.dec,s.z,p.petroMag_g,p.petroMag_i,p.modelMag_g,p.modelMag_i,
p.lnLExp_r, p.lnLDeV_r, s.zWarning,p.objID
FROM PhotoObj p, SpecObj s, SpecLine l
WHERE
p.SpecObjID = s.SpecObjID AND
p.SpecObjID = l.specobjID AND
s.specClass=2 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 in 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 an ESO press release.

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.