Research Project
The goal of research project is to understand how observations of
X-ray diffuse emission can be used to measure oxygen line emission
and constrain models of the hot halo of the Milky Way galaxy. We
will do this by replicating the work done for several papers in the
scientific literature. It will be necessary to read those papers
(and perhaps others), learn to work with X-ray data analysis
software, understand how to predict the oxygen line emission for a
selected field given a particular model of the halo, write software
to implement such predictions and tune the model parameters to match
a given set of oxygen line emission measurements, and understand how
this work fits into the current searches for missing baryons.
The papers of interest are:
Steps in the project:
- Learn to use the X-ray spectral fitting package xspec and
apply it in the analysis of a spectrum of diffuse X-ray emission
obtained with Suzaku to measure the strength of the oxygen O VII
and O VIII lines. This is the topic of the data analysis session. This
should be done individually and handed in individually.
(20 points)
- Learn to generate fake spectra in xspec. Using the apec model,
generate spectra for various temperatures in the range from 105
K to 107 K. Fit each spectrum to measure the strength
of the oxygen O VII and O VIII lines, then plot the strength of
those lines and their ratio as a function of temperature. This
is the topic of the assignment generating
fake data in xspec. This should be done individually
and handed in individually. (20 points)
- Learn to reduce data from the Suzaku satellite and perform
analysis of one observation from Yoshino et al. (2009). Fit your
resulting spectrum to measure the strength of the oxygen O VII
and O VIII lines. This is the topic of the data reduction session. This
should be done individually and handed in individually.
(20 points)
- Write a python program to read in the table of oxygen emission
lines strengths from Henley and Shelton (2012). Plot the line
intensities and their ratio versus Galactic latitude and
longitude. Discuss the implications of your results for the
geometry of the halo emission. You may wish to address what can
be learned from repeated observations of the same field.
This is the topic of the assignment Using Python to Read and Plot
Data. This should be done individually and
handed in individually. (20 points)
- Using the AtomDB website http://www.atomdb.org/
, find the emissivity for O VII and O VIII as a function of
temperature and download the data to your computer. Write a
Python program to read in the emissivities and plot them and
their ratio versus temperature. Follow the instructions in
the emissivity
assignment. This should be done individually and
handed in individually. (20 points)
- Following Miller and Bregman (2015), write Python code to
calculate the oxygen emission line intensities for any given
line of sight using a spherical β-model to represent the Milky
Way’s hot gas halo density profile. Consider only the optically
thin case. Plot the line intensities versus Galactic latitude
and longitude for a specific choices of β-model parameters
following the instructions in the Models
of Halo Emission assignment. This should be done as a
group. (60 points).
- Write python code to fit the spherical β-model to a list of
line intensities. To practice, we will generate a
fake set of data using your spherical β-model and fit those fake
data following the instructions in the fitting
halo models assignment. This should be done as a group.
(100 points).
- We will now fit halo models to the data from Henley and
Shelton. This is described in the fitting
halo models with real data assignment. In the real
universe, there is emission from the local bubble, so we will
need to add this to our model of the total emission. You will
write python code to fit the spherical β-halo plus local bubble
model to the list of line intensities from Henley and Shelton
(2012). You will then fit the Henley and Shelton data to your
model of halo plus local bubble emission and find the best fit
parameters and estimates on their errors. Fit the data for O VII
and O VIII separately. The write up for this project
should include all of the group projects. Re-use your text from
the previous projects and add an introduction that covers all
parts of the projects, a detailed write up of fitting model to
the real data, and a conclusion section that covers all parts of
the project. There will be no separate written assignment
for this part of the project. Also, you should prepare a
presentation on the whole project. The presentations will
be made on the last day of class. If desired, we can
schedule a day to practice the presentations in advance of the
final presentation. All group members must contribute to
the final project write up and the project presentation. This
should be done as a group. (200 points).
Optional - use the HaloSat response Python code to generate response
matrices for various energy resolutions and determine the effect
that the energy resolution has on the accuracy of measurements of
the strength of the oxygen O VII and O VIII lines.