Try to finish this hunt by 7pm on Wednesday evening

UAT13.01 Scavenger Hunt #3:
Introduction to how we can use ALFALFA in combination with other datasets to explore the local galaxy population

This scavenger hunt will provide an introduction to the ALFALFA and SDSS catalogs, deriving galaxy properties from observational data, what the ALFALFA galaxy population is like compared to an optically selected one and investigating the large scale structure. As an example of the kind of science the UAT groups project is doing, we will take a quick look at the galaxy population in ALFALFA, in the SDSS database and in the vicinity of the nearby "poor" cluster known as MKW 11.

In a departure from previous Scavenger Hunts, each team will be assigned a separate project dealing with the use of ALFALFA data to learn about galaxies in the local universe. We will then reassemble Wednesday evening when team will have 10 minutes to present their results.

Team C:       Large scale structure around the poor cluster MKW 11

The Undergraduate ALFALFA Team groups project is a joint effort to explore how local galaxy environment impact the evolution of galaxies. In this activity, you will examine the large scale structure and membership of the nearby "poor" cluster known as MKW 11. One of the other teams will be looking at the properties of the galaxies in the region of the cluster. Your task is to study the structure of the cluster itself and its position within the local large scale structure.

3.C.1     The cluster MKW 11

Use this link to the NASA Extragalatic Database (NED) to find out some of the basic information about MKW 11 that you will need. Notice that it has numerous other names, but this is the structure we want to examine.

Recessional velocity in heliocentric rest frame  
Recessional velocity in CMB rest frame  
Distance to the cluster (quoted in NED)  
Galactic latitude  
Galactic extinction in g-band  
Galactic extinction in i-band  

Using the information and links in NED, learn what you can about the cluster. Here are some questions to get you started. To review the large scale structure in and around MKW 11, we can use the "Arecibo General Catalog", the private database of galaxies maintained by Martha and Riccardo at Cornell which is made available to members of the ALFALFA team with the usual caveat that you get what you pay for: be sure to understand the limitations of the AGC and read about its conditions of use.

We have used the AGC to create two CSV files for use in this activity: The files contain the galaxy AGC number, RA, Dec, Vhelio and the projected separation of the galaxy from the cluster center in arcminutes. You can use these files to explore the structure of the cluster.

3.C.2     The sky distribution of galaxies in the cluster MKW 11

First, let's take a look at the distribution of galaxies in the vicinity of MKW 11. Using the AGC/α.40 data files (linked above), plot (on the same graph) the sky distribution of galaxies in the (a) optical sample and (b) the α.40 galaxies. Plot the optical sample first, since it is much bigger. Be sure to plot the distribution so that east is to the left and west is the right; why do we do that? Consider the result: what do you notice and how can you explain what you see?

Clusters of galaxies have a typical radius of 2 Mpc. At the distance of MKW 11, what is the angular extent of 2 Mpc?

Make a second plot, zooming in on the region around the center. Comment on what you see. Is the cluster evident in both samples?

3.C.3     The distribution of heliocentric velocity with projected separation

In the previous plots, we did not make use of the redshift information; it's time to do that. Using the same data files (linked above), plot (on the same graph) the variation in heliocentric velocities (y-axis) with the projected separation from the cluster center (x-axis) for the (a) optical sample and (b) the α.40 galaxies. Consider the result: what do you notice and how can you explain what you see?

3.C.4     The velocity structure of MKW 11

Now, let's focus on the cluster itself. Using the same data files again, plot (on the same graph) the distribution of heliocentric velocities (using the histogram option) for the (a) optical sample and (b) the α.40 galaxies. Consider the result: what do you notice and how can you explain what you see?

Now let's examine just the galaxies within 2 Mpc of the cluster center. If time permits, try to figure out how you can generate the file you need within TOPCAT. If you are rushed for time, you can use these two files already made up for you: Comment on what you see and discuss how you might use this result.

Next focus in on the cluster itself to make a histogram of only the galaxies within 2 Mpc of MKW 11 and in the velocity range Vhelio: (5850 to 7850 km/s), for either Vopt or V21. Again, you can figure out how to generate the file you need in TOPCAT or if time is short, use this one.

Again comment on what you see and discuss how you might use this result.

3.C.5     The large scale structure around MKW 11

Now, let's examine the very large scale structure you see. A convenient way to examine large scale structure is to make a "cone diagram" of an almost-2-D "slice". For this purpose, there are two more files containing galaxies in a 5 degree wide "slice" of the universe: RA: (7.5 to 16.5 hours), Dec: (10.5 to 15.5deg), Vhelio: (0, 18000 km/s). As before, there are two files: Consider the result: what do you notice and how can you explain what you see?

3.C.6     Make an image of the MKW 11 cluster using Montage

Note: this may take a little while to run, because system use at IPAC is unpredictable. We suggest you not wait until the last minute to start it.

Note also: Someone in your group will have already be registered to use this facility, or else one of you will have to setup up an account; find someone in your group to be the registered user and then proceed.

Montage is a Virtual Observatory tool that allows you to make images up to 1 degree in size from selected public databases via a web-based interface. Read about the full capabilities of the service here.

Use the Montage web service to create a 1 degree image of the SDSS i-band data for MKW 11. How many original SDSS images go into making up this mosaic? How long does it take for the job to run (seconds, minutes, hours, days)? What kinds of output are produced? Figure out a way to show us the "result page".

Note: during UAT13, we are having some trouble access the Montage Web service. If that is the case, you can download the resulting FITS file here, keeping in mind that it is a fairly large file (618 MB).

Team D is going to be looking at the g-band image of the inner 0.5 degrees of the cluster; it will be interesting to compare results with them.

If someone in your group has access to ds9, you can examine the FITS image.

Assignments given to the other teams:

This page created by and for the members of the ALFALFA Survey Undergraduate team

Last modified: Thu Jan 10 08:37:34 EST 2013 by Martha