ASTRONOMY 3303   HW#5     due Wed Oct 18, 2017
Print a copy of this page and enter it in your portfolio.
Part I: FAST
new FAST radio telescope is
now nearing completion. Prepare a one-page handout of relevant
information about FAST directed to an audience of your peers (Cornell
undergrad phys/astro/engr/similar majors).
Include at least one
diagram, table or image; choose it to make a
technical point, not just for flash. Also, include a direct comparison
(not only in size) to other large single-dish radio telescopes in the
US, such as the Green Bank Telescope (GBT) and Arecibo.
Part II: The ALFALFA galaxy population
Arecibo Legacy Fast Arecibo L-band Feed Array survey, is a
survey of HI 21cm emission in nearby and low-redshift galaxies, led by
Cornell professors Martha Haynes and Riccardo Giovanelli.
Find here a CSV file containing useful information
extracted from the population of galaxies included in both the
2011 public ALFALFA survey catalog (α.40
Haynes et al.
2011) and the SDSS DR7 database. Let's use this file to explore some interesting characteristics of
the population of galaxies detected by ALFALFA. Examine the contents of the file before
you start working with it and be sure that you understand what all the columns mean (remember the SDSS help page);
if you don't understand any of them, ask. This information on the radio spectrum may be useful in the context of understanding and interpreting radio observations. In general, remember to use wikipedia with care - it is a useful source of information, but not a scholarly source like the textbook or refereed scientific publications.
- Spanhauer diagram: Make a plot of distance (the column "dist" in Mpc on the x-axis) versus
the log of the HI mass ("logM_HI" in solar masses on the y axis). So we can compare results,
set the scales to be: x-axis (0, 270 Mpc), y-axis (6.0, 11.0 Msun)
- There are two "gaps" (fewer than expected points) at
distances of about 85 Mpc and 230 Mpc. For the HI 21 cm line, what
frequencies do these gaps correspond to? Any ideas on what causes the gaps?
- There appears to be a vertical line-up of (more than expected)
points at a distance of 17 Mpc.
What might cause this?
- Why does the distribution of points appear as it does, both on the lower and upper ends?
Explain this in terms of the HI mass function. Assume here that more massive galaxies
are more luminous.
(If you don't understand what an HI mass function is, ask.).
- Color-magnitude diagram: Construct a (g-i) versus MI
color-magnitude diagram using
model magnitudes for the color and Petrosian magnitudes for the absolute magnitude.
Use the distances given in the data file, and correct the observed apparent
magnitudes for both Galactic (Gext) and internal extinction (Iext); the corrections
are given in the file.
- Make a first plot using the scaling x-axis (-14, -24), y-axis
- So that you can compare with the two similar CMDs
discussed in HW #4, set the axes to be: x-axis (-16, -23.5), y-axis
(0.0, 1.5). How many points (a few? a lot? any particular ones?)
get lost when you restrict the axis scales?
- If you did not get the CMD correct for the MKW11 system, please
redo it to produce a corrected version. If you don't understand
what went wrong the last time, ask for help.
- Compare the three CMDs: the one from Gavazzi et al. (2010); the one
for MKW 11 and the one for the α.40-SDSS sample. Explain
the differences in terms of the galaxy populations included in the
Part III: Group discussion: G2
In class, we had a detailed discussion about the Galactic center. A
few years ago, the exciting object G2 was discovered near the
supermassive black hole, as discussed, e.g., here:
http://www.eso.org/public/news/eso1332/ : 2013 ESO press release on G2
What did people think at the time the nature of this object is, and
its fate? Discuss with your group the relevance of these
observations, and how they were made. For possible paths of inquiry,
look at your previous discussions. After you have studied the press
release in detail, research on the web (including the astronomy query
tools you have encountered so far) what has happened to this discovery
since, and what other ideas have been proposed for the nature of the
object. Use at least one recent scientific publication in your
discussion. Also, as a group, be prepared to give a 3 minute summary
of your discussion during the lecture on October 18th, 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, as usual,
please provide a brief (1-2 page) write-up of your discussion.
NOTE: Self-organize in groups of up to 3-4 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!