The software is written by Herve Bourdin, a post-doc at the University of Rome Tor Vergata. Bourdin works at the cosmology group of Rome Tor Vergata. From Herve Bourdin’s tutorial:

“The X-Ray Wavelet Spectral Mapping (XWSM) package is a set of tools dedicated to the mapping of spectroscopic observables associated with the X-ray emission of the Inter- Galactic Medium (IGM), within clusters and groups of galaxies. Spectroscopic observables like the IGM brightness, temperature and metallicity can be estimated within specific re- gions of the field of view, or mapped by means of wavelet algorithms. These tools have been developped by Herv ́e Bourdin1, in collaboration with Albert Bijaoui2, Eric Slezak2 and Jean-Luc Sauvageot3. The present version of XWSM is specific to XMM-Newton data. Please notice that while the bulk of this work has been developped as a free software, some proprietary softwares, namely the Numerical Recipes and IDL have been used, so that the relative licenses are required. Moreover, some HEASARC softwares (FTOOLS) may be useful for further applications.”

Basic commands of XWSM are as follows:

xwsm_start, ‘ms1455_zoom’, acis_aoff_file=aoff, acis_evt_files=evt2, badpix_files=bpx, redshift=0.257800, T_inter=[0.1,60], /nh_ftools, /clean, /detect, /acis_i, n_bin=512

xwsm_lx ’obs_id’

xwsm_spec, ’obs_id’

xwsm_fit obs_id -Z

xwsm_map obs_id -bspline -donoho -ns_min.7

xwsm_map obs_id -Z -bspline -donoho -ns_min.7

xwsm_chandra,’obs_id’,/rebuild_cxb

xwsm_map_image, ‘a1835_zoom’, lx_min=.5, zoom=5, offset=[-.25,0], sigma=2

xwsm_map a1835_zoom -bspline -sigma2

- http://cxc.harvard.edu/ciao/download/
From here download ciao-install script. Create a different folder for everything of your data analysis namely, chandra. Copy this script file to that folder. enter into that folder and run the script. It’s better to install ciao also in this directory. Better not to install as root, I don’t know why.

For running the script, open terminal and go to that folder. Than type “bash ciao-install”, without the inverted commas of course. After than everything will be normal if the script works. Terminal will ask for Ciao installation directory, give the directory, chandra.

After installation go to the directory where ciao is installed. Go to the bin directory and run this code to see complete ciao configuration.
. ciao.bash

Then you have to edit the .bashrc file in your home to make an alias for ciao with which you will open ciao every time. The file is hidden so u have to use ls -a to see it. Than to edit write this,
sudo gedit .bashrc

Heasoft with Xspec

- http://heasarc.gsfc.nasa.gov/lheasoft/download.html

In this page first select what kind of package you want to download. I downloaded source codes instead of binary files. Because after downloading source code I can configure it according to my OS. But binary is already configured and maybe not properly for my OS.

After selecting “Source code distribution” selct operating system and select the tools that you need. I selected all “General-Use FTOOLS” and “XANADU”. Clisk on Submit and download the file. It will take time. More than 300 MB.

After downloading move the tar file to chandra directory and untar it. Go to the untarred directory and than to the BUILD_DIR directory. Configure file is situated here. So run the “./configure” command on terminal.

This configuration will not be easy. It will give errors if it does not find some package file that it needs. Than it will stop. We have to install that package file and then again give the configure command. Dunno how many times it will give errors, depend on your software resources. I had to install the following packages while configuring Heasoft: (using sudo apt-get install or Synaptic package manager)

# gfortran
# libncurses-dev
# X11 development packages (libxkbfile-dev, x11proto-core-dev, libxdmcp-dev, libxau-dev)

After configuration makefile was created. So run the “make” command. It gave me an error at first. Could not find X11-intrinsic.h. So went to synaptic and searched for this. Installed the following packages and it worked:
# libxt-dev, libxt6-dbg, libxbfile1-dbg

Funtools

- https://www.cfa.harvard.edu/~john/funtools/

Download this tar file and copy to your chandra folder. Than extract at the same place. Go inside the folder and run the ./configure command. It will configure the program. Step by step commands will be:

./configure
make
make install

Finished. Funtools is installed. Now we need to integrate this with ds9. In the terminal open ciao. Than open ds9. Go to

Edit –> Preferences –> Analysis –> Preload analysis file –> Browse

Go to your funtools folder and show the funtools.ds9 file. That’s all.

– Read more >>>>

One key finding comes from a paper online now in the journal Icarus that shows hydrogen molecules flowing down through Titan’s atmosphere and disappearing at the surface. Another paper online now in the Journal of Geophysical Research maps hydrocarbons on the Titan surface and finds a lack of acetylene.

This lack of acetylene is important because that chemical would likely be the best energy source for a methane-based life on Titan, said Chris McKay, an astrobiologist at NASA Ames Research Center, Moffett Field, Calif., who proposed a set of conditions necessary for this kind of methane-based life on Titan in 2005. One interpretation of the acetylene data is that the hydrocarbon is being consumed as food. But McKay said the flow of hydrogen is even more critical because all of their proposed mechanisms involved the consumption of hydrogen.

“We suggested hydrogen consumption because it’s the obvious gas for life to consume on Titan, similar to the way we consume oxygen on Earth,” McKay said. “If these signs do turn out to be a sign of life, it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth.”

To date, methane-based life forms are only hypothetical. Scientists have not yet detected this form of life anywhere, though there are liquid-water-based microbes on Earth that thrive on methane or produce it as a waste product. On Titan, where temperatures are around 90 Kelvin (minus 290 degrees Fahrenheit), a methane-based organism would have to use a substance that is liquid as its medium for living processes, but not water itself. Water is frozen solid on Titan’s surface and much too cold to support life as we know it.

The list of liquid candidates is very short: liquid methane and related molecules like ethane. While liquid water is widely regarded as necessary for life, there has been extensive speculation published in the scientific literature that this is not a strict requirement.

The new hydrogen findings are consistent with conditions that could produce an exotic, methane-based life form, but do not definitively prove its existence, said Darrell Strobel, a Cassini interdisciplinary scientist based at Johns Hopkins University in Baltimore, Md., who authored the paper on hydrogen.

Strobel, who studies the upper atmospheres of Saturn and Titan, analyzed data from Cassini’s composite infrared spectrometer and ion and neutral mass spectrometer in his new paper. The paper describes densities of hydrogen in different parts of the atmosphere and the surface. Previous models had predicted that hydrogen molecules, a byproduct of ultraviolet sunlight breaking apart acetylene and methane molecules in the upper atmosphere, should be distributed fairly evenly throughout the atmospheric layers.

Strobel found a disparity in the hydrogen densities that lead to a flow down to the surface at a rate of about 10,000 trillion trillion hydrogen molecules per second. This is about the same rate at which the molecules escape out of the upper atmosphere.

“It’s as if you have a hose and you’re squirting hydrogen onto the ground, but it’s disappearing,” Strobel said. “I didn’t expect this result, because molecular hydrogen is extremely chemically inert in the atmosphere, very light and buoyant. It should ‘float’ to the top of the atmosphere and escape.”

Strobel said it is not likely that hydrogen is being stored in a cave or underground space on Titan. The Titan surface is also so cold that a chemical process that involved a catalyst would be needed to convert hydrogen molecules and acetylene back to methane, even though overall there would be a net release of energy. The energy barrier could be overcome if there were an unknown mineral acting as the catalyst on Titan’s surface.

The hydrocarbon mapping research, led by Roger Clark, a Cassini team scientist based at the U.S. Geological Survey in Denver, examines data from Cassini’s visual and infrared mapping spectrometer. Scientists had expected the sun’s interactions with chemicals in the atmosphere to produce acetylene that falls down to coat the Titan surface. But Cassini detected no acetylene on the surface.

In addition Cassini’s spectrometer detected an absence of water ice on the Titan surface, but loads of benzene and another material, which appears to be an organic compound that scientists have not yet been able to identify. The findings lead scientists to believe that the organic compounds are shellacking over the water ice that makes up Titan’s bedrock with a film of hydrocarbons at least a few millimeters to centimeters thick, but possibly much deeper in some places. The ice remains covered up even as liquid methane and ethane flow all over Titan’s surface and fill up lakes and seas much as liquid water does on Earth.

“Titan’s atmospheric chemistry is cranking out organic compounds that rain down on the surface so fast that even as streams of liquid methane and ethane at the surface wash the organics off, the ice gets quickly covered again,” Clark said. “All that implies Titan is a dynamic place where organic chemistry is happening now.”

The absence of detectable acetylene on the Titan surface can very well have a non-biological explanation, said Mark Allen, principal investigator with the NASA Astrobiology Institute Titan team. Allen is based at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Allen said one possibility is that sunlight or cosmic rays are transforming the acetylene in icy aerosols in the atmosphere into more complex molecules that would fall to the ground with no acetylene signature.

“Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed,” Allen said. “We have a lot of work to do to rule out possible non-biological explanations. It is more likely that a chemical process, without biology, can explain these results — for example, reactions involving mineral catalysts.”

“These new results are surprising and exciting,” said Linda Spilker, Cassini project scientist at JPL. “Cassini has many more flybys of Titan that might help us sort out just what is happening at the surface.”

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL.

“We used a brand new technique for determining that an object orbits a nearby star, a technique that’s a nice nod to Galileo,” says Ben R. Oppenheimer, Curator and Professor in the Department of Astrophysics at the Museum. “Galileo showed tremendous foresight. Four hundred years ago, he realized that if Copernicus was right — that the Earth orbits the Sun — they could show it by observing the “parallactic motion” of the nearest stars. Incredibly, Galileo tried to use Alcor to see it but didn’t have the necessary precision.” If Galileo had been able to see change over time in Alcor’s position, he would have had conclusive evidence that Copernicus was right. Parallactic motion is the way nearby stars appear to move in an annual, repeatable pattern relative to much more distant stars, simply because the observer on Earth is circling the Sun and sees these stars from different places over the year.

Alcor is a relatively young star twice the mass of the Sun. Stars this massive are relatively rare, short-lived, and bright. Alcor and its cousins in the Big Dipper formed from the same cloud of matter about 500 million years ago, something unusual for a constellation since most of these patterns in the sky are composed of unrelated stars. Alcor shares a position in the Big Dipper with another star, Mizar. In fact, both stars were used as a common test of eyesight — being able to distinguish “the rider from the horse” — among ancient people. One of Galileo’s colleagues observed that Mizar itself is actually a double, the first binary star system resolved by a telescope. Many years later, the two components Mizar A and B were themselves determined each to be tightly orbiting binaries, altogether forming a quadruple system.

Now, Alcor, which is near the four stars of the Mizar system, also has a companion. This March, members of Project 1640 attached their coronagraph and adaptive optics to the 200-inch Hale Telescope at the Palomar Observatory in California and pointed to Alcor. “Right away I spotted a faint point of light next to the star,” says Neil Zimmerman, a graduate student at Columbia University who is doing his PhD dissertation at the Museum. “No one had reported this object before, and it was very close to Alcor, so we realized it was probably an unknown companion star.”

The team retuned a few months later and re-imaged the star, hoping to prove that the two stars are companions by mapping the tiny movement of both in relation to very distant background stars as the Earth moves around the Sun, in other words, by mapping its parallactic motion. If the proposed companion were just a background star, it wouldn’t move along with Alcor.

“We didn’t have to wait a whole year to get the results,” says Oppenheimer. “We went back 103 days later and found the companion had the same motion as Alcor. Our technique is powerful and much faster than the usual way of confirming that objects in the sky are physically related.” The more typical method involves observing the pair of objects over much longer periods of time, even years, to show that the two are moving through space together.

Alcor and its newly found, smaller companion Alcor B are both about 80 light-years away and orbit each other every 90 years or more. Over one year, the Alcor pair moves in an ellipse on the sky about 0.08 arc seconds in width because of the Earth’s orbit around the Sun. This amount of motion, 0.08 arcsec, is about 1,000 times smaller than the eye can discern, but a fraction of this motion was easily measured by the Project 1640 scientists.

The team was also able to determine the color, brightness, and even rough composition of Alcor B because the novel method of observation that Project 1640 uses records images at many different colors simultaneously. The team determined that Alcor B is a common type of M-dwarf star or red dwarf that is about 250 times the mass of Jupiter, or roughly a quarter of the mass of our Sun. The companion is much smaller and cooler than Alcor A.

“Red dwarfs are not commonly reported around the brighter higher mass type of star that Alcor is, but we have a hunch that they are actually fairly common,” says Oppenheimer. “This discovery shows that even the brightest and most familiar stars in the sky hold secrets we have yet to reveal.”

The team plans to use parallactic motion again in the future. “We hope to use the same technique to check that other objects we find like exoplanets are truly bound to their host stars,” says Zimmerman. “In fact, we anticipate other research groups hunting for exoplanets will also use this technique to speed up the discovery process.”

In addition to Zimmerman and Oppenheimer, authors include Anand Sivaramakrishnan, Sasha Hinkley, and Douglas Brenner of the Astrophysics Department at the Museum; Lynne Hillenbrand, Charles Beichman, Justin Crepp, Antonin Bouchez and Richard Dekany of the California Institute of Technology; Ian Parry, David King, and Stephanie Hunt of the Institute of Astronomy at Cambridge University; Rémi Soummer of the Space Telescope Institute in Baltimore; and Gautam Vasisht, Rick Burruss, Michael Shao, Lewis Roberts, and Jennifer Roberts of the Jet Propulsion Laboratory at California Institute of Technology. Project 1640 is funded by the National Science Foundation.

By analyzing Chandra’s X-ray spectrum — akin to a fingerprint of energy — and applying it to theoretical models, Ho and his colleague Craig Heinke, from the University of Alberta, determined that the neutron star in Cassiopeia A, or Cas A for short, has an ultra-thin coating of carbon. This is the first time the composition of an atmosphere of an isolated neutron star has been confirmed.

The Chandra “First Light” image of Cas A in 1999 revealed a previously undetected point-like source of X-rays at the center. This object was presumed to be a neutron star, the typical remnant of an exploded star, but researchers were unable to understand its properties. Defying astronomers’ expectations, this object did not show any X-ray or radio pulsations or any signs of radio pulsar activity.

By applying a model of a neutron star with a carbon atmosphere to this object, Ho and Heinke found that the region emitting X-rays would uniformly cover a typical neutron star. This would explain the lack of X-ray pulsations because — like a lightbulb that shines consistently in all directions — this neutron star would be unlikely to display any changes in its intensity as it rotates.

Scientists previously have used a neutron star model with a hydrogen atmosphere giving a much smaller emission area, corresponding to a hot spot on a typical neutron star, which should produce X-ray pulsations as it rotates. Interpreting the hydrogen atmosphere model without pulsations would require a tiny size, consistent only with exotic stars made of strange quark matter.

“Our carbon veil solves one of the big questions about the neutron star in Cas A,” said Craig Heinke. “People have been willing to consider some weird explanations, so it’s a relief to discover a less peculiar solution.”

Unlike most astronomical objects, neutron stars are small enough to understand on a human scale. For example, neutron stars typically have a diameter of about 14 miles, only slightly longer than a half-marathon. The atmosphere of a neutron star is on an even smaller scale. The researchers calculate that the carbon atmosphere is only about 4 inches thick, because it has been compressed by a surface gravity that is 100 billion times stronger than on Earth.

“For people who are used to hearing about immense sizes of things in space, it might be a surprise that we can study something so small,” said Ho. “It’s also funny to think that such a thin veil over this star played a key role in frustrating researchers.”

In Earth’s time frame, the estimated age of the neutron star in Cas A is only several hundred years, making it about ten times younger than other neutron stars with detected surface emission. Therefore, the Cas A neutron star gives a unique window into the early life of a cooling neutron star.

The carbon itself comes from a combination of material that has fallen back after the supernova, and nuclear reactions on the hot surface of the neutron star which convert hydrogen and helium into carbon.

The X-ray spectrum and lack of pulsar activity suggest that the magnetic field on the surface of this neutron star is relatively weak. Similarly low magnetic fields are implied for several other young neutron stars by study of their weak X-ray pulsations. It is not known whether these neutron stars will have low magnetic fields for their entire lives, and never become radio pulsars, or whether processes in their interior will lead to the development of stronger magnetic fields as they age.

[The above article was published on Science Daily]

Links

- Dr. Craig Heinke’s resource page on the topic
- Nature paper by Craig Heinke and Wynn C. G. Ho

Finally I have finished the final thesis report of mu undergraduate project. Honestly, I am not satisfied with it myself. Because I could not do any real research I mean something innovative. But now I am trying to do some simulation using Java. This report can be considered as a theoretical database of 21-cm cosmology and observation which will be helpful for me in the coming years, at least I think so. Here I am presenting the report. Link of the pdf file is attached. Abstract and content is mentioned separately.

Undergraduate thesis report

- Review of constraining cosmological parameters using 21-cm signal from the era of Reionization.pdf

Supervisor

Mr. Shafiqur Rahman
Assistant professor, Dept. of EEE
Islamic University of Technology, OIC
Bangladesh

Co-supervisor

Mr. Syed Ashraf Uddin Shuvo
Teaching assistant and PhD student
University of Kentucky, USA.

Submitted By

Khan Muhammad (Bin Asad) (052413)
Ahmed Raihan Abir (052470)
Md. Emon Hossain Khan (052401)

Abstract

We were very ambitious regarding the outcome of our project. In fact we tried to improvise the necessity of a radio telescope on the far side of the Moon. But later we realized the importance of SKA (Square Kilometer Array) as a feasible tool for unveiling the mystery of the Universe. So we tried to calculate the precise error margins of the cosmological parameters that SKA will give us. As far as we know Fisher4Cast is an efficient tool to constrain the error margins in a astrophysical survey. But we didn’t get enough time to use this tool efficiently. So we studied a very important paper by Yi Mao, Max Tegmark et al. to understand the constraints. We learned that, for future experiments, marginalizing over nuisance parameters may provide almost as tight constraints on the cosmology as if 21 cm tomography measured the matter power spectrum directly. Before studying about the constraining process we studied the basic physics of Early Universe, Reionization era, Dark Ages and 21-cm signal. We have written a review on the physics and observational constraints promised by the future telescopes in this thesis report.

Contents

1 – Introduction

2 – Physics of the Early Universe
2.1 – Hubble’s law
2.2 – Cosmological principle
2.3 – Comoving co-ordinates
2.4 – Cosmic Microwave Background Radiation (CMBR)
2.4.1 – Source of CMB
2.5 – Friedmann models
2.6 – Simple cosmological solutions
2.6.1 – Empty de Sitter universe
2.6.2 – Vacuum energy dominated universe
2.6.3 – Radiation dominated universe
2.6.4 – Matter dominated universe
2.6.5 – General equation of state
2.7 – Effects of curvature and cosmological constant
2.7.1 – Open, flat space (k=0)
2.7.2 – Closed, spherical space (k=1)
2.7.3 – Open, hyperbolic space (k=-1)
2.7.4 – Effects of cosmological constant
2.8 – Matter density of the universe

3 – Physics of the Dark Ages
3.1 – Linear gravitational growth
3.2 – Post-linear evolution of density fluctuations
3.2.1 – Spherical top-hat collapse
3.2.2 – Coupled Dark Energy (cDE) models
3.2.3 – Spherical collapse model
3.3 – Nonlinear growth

4 – Physics of Reionization
4.1 – Radiative feedback from the first sources of light
4.2 – Propagation of ionization fronts in the IGM
4.3 – Reionization of Hydrogen
4.3.1 – Pre-overlap
4.3.2 – Overlap
4.4 – Characteristic observed size of ionized bubbles
4.5 – Reionization can give important information about Early Universe

5 – 21-cm Cosmology
5.1 – Fundamental physics of 21-cm line
5.1.1 – Brightness temperature
5.1.2 – Flux density
5.1.3 – Spin temperature
5.1.4 – Optical depth
5.1.5 – Contrast between high-redshift Hydrogen cloud and CMB
5.2 – Temperatures of Dark Ages
5.2.1 – Three temperatures
5.2.2 – Ménage a trios
5.3 – Global history of IGM
5.3.1 – Five critical points in 21-cm history
5.4 – Advantages of 21-cm tomography

6 – 21-cm Power spectrum
6.1 – Fractional perturbation to brightness temperature
6.2 – Fluctuations in 21-cm signal
6.2.1 – Isotropic fluctuations
6.2.2 – Anisotropy in 21cm signal
6.3 – Redshift space distortions
6.4 – Alcock-Paczynski effect
6.5 – Separating out the AP effect on 21-cm fluctuations

7 – Interferometer arrays and sensitivity
7.1 – Interferometric visibility
7.2 – Detector noise
7.3 – Average observing time
7.4 – Angular averaged sensitivity
7.5 – Foreground
7.6 – Sensitivity of future interferometers
7.7 – SKA specifications

8 – Constraining cosmological parameters
8.1 – Reference experiment for simulation
8.2 – Lambda-CDM model
8.3 – Optimistic reference model
8.4 – Simulation
8.4.1 – Varying redshift ranges
8.4.2 – Varying array layout
8.4.3 – Varying collecting area
8.4.4 – Varying observation time and system temperature
8.5 – Graphs of fractional error
8.5.1 – Fractional error at z = 8
8.5.2 – Fractional error at z = 12
8.6 – Significance of constraining cosmological parameters

9 – Conclusion

Appendices
References

The Outer Disk of the Milky Way Seen in 21-cm Absorption
(download pdf)

Authors: John M. Dickey, Simon Strasser, B.M. Gaensler, Marijke Haverkorn, Dain Kavars, N. M. McClure-Griffiths, Jeroen Stil, A. R. Taylor

(Submitted on 8 Jan 2009) on arXiv

Abstract: Three recent surveys of 21-cm line emission in the Galactic plane, combining single dish and interferometer observations to achieve resolution of 1 arcmin to 2 arcmin, 1 km/s, and good brightness sensitivity, have provided some 650 absorption spectra with corresponding emission spectra for study of the distribution of warm and cool phase H I in the interstellar medium. These emission-absorption spectrum pairs are used to study the temperature of the interstellar neutral hydrogen in the outer disk of the Milky Way, outside the solar circle, to a radius of 25 kpc.

The cool neutral medium is distributed in radius and height above the plane with very similar parameters to the warm neutral medium. In particular, the ratio of the emission to the absorption, which gives the mean spin temperature of the gas, stays nearly constant with radius to 25 kpc radius. This suggests that the mixture of cool and warm phases is a robust quantity, and that the changes in the interstellar environment do not force the H I into a regime where there is only one temperature allowed. The mixture of atomic gas phases in the outer disk is roughly 15% to 20% cool (40 K to 60 K), the rest warm, corresponding to mean spin temperature 250 to 400 K.

The Galactic warp appears clearly in the absorption data, and other features on the familiar longitude-velocity diagram have analogs in absorption with even higher contrast than for 21-cm emission. In the third and fourth Galactic quadrants the plane is quite flat, in absorption as in emission, in contrast to the strong warp in the first and second quadrants. The scale height of the cool gas is similar to that of the warm gas, and both increase with Galactic radius in the outer disk.

An Automated Method for the Detection and Extraction of HI Self-Absorption in High-Resolution 21cm Line Surveys
(download pdf)

Authors: Steven J. Gibson, A. Russell Taylor, Lloyd A. Higgs, Christopher M. Brunt, Peter E. Dewdney

(Submitted on 5 Mar 2005)

Abstract: We describe algorithms that detect 21cm line HI self-absorption (HISA) in large data sets and extract it for analysis. Our search method identifies HISA as spatially and spectrally confined dark HI features that appear as negative residuals after removing larger-scale emission components with a modified CLEAN algorithm. Adjacent HISA volume-pixels (voxels) are grouped into features in (l,b,v) space, and the HI brightness of voxels outside the 3-D feature boundaries is smoothly interpolated to estimate the absorption amplitude and the unabsorbed HI emission brightness. The reliability and completeness of our HISA detection scheme have been tested extensively with model data. We detect most features over a wide range of sizes, linewidths, amplitudes, and background levels, with poor detection only where the absorption brightness temperature amplitude is weak, the absorption scale approaches that of the correlated noise, or the background level is too faint for HISA to be distinguished reliably from emission gaps. False detection rates are very low in all parts of the parameter space except at sizes and amplitudes approaching those of noise fluctuations. Absorption measurement biases introduced by the method are generally small and appear to arise from cases of incomplete HISA detection. This paper is the third in a series examining HISA at high angular resolution. A companion paper (Paper II) uses our HISA search and extraction method to investigate the cold atomic gas distribution in the Canadian Galactic Plane Survey.

A Self-Absorption Census of Cold HI Clouds in the Canadian Galactic Plane Survey
(download pdf)

Authors: Steven J. Gibson, A. Russell Taylor, Lloyd A. Higgs, Christopher M. Brunt, Peter E. Dewdney

(Submitted on 5 Mar 2005)

Abstract: We present a 21cm line HI self-absorption (HISA) survey of cold atomic gas within Galactic longitudes 75 to 146 degrees and latitudes -3 to +5 degrees. We identify HISA as spatially and spectrally confined dark HI features and extract it from the surrounding HI emission in the arcminute-resolution Canadian Galactic Plane Survey (CGPS). We compile a catalog of the most significant features in our survey and compare our detections against those in the literature. Within the parameters of our search, we find nearly all previously detected features and identify many new ones. The CGPS shows HISA in much greater detail than any prior survey and allows both new and previously-discovered features to be placed into the larger context of Galactic structure. In space and radial velocity, faint HISA is detected virtually everywhere that the HI emission background is sufficiently bright. This ambient HISA population may arise from small turbulent fluctuations of temperature and velocity in the neutral interstellar medium. By contrast, stronger HISA is organized into discrete complexes, many of which follow a longitude-velocity distribution that suggests they have been made visible by the velocity reversal of the Perseus arm’s spiral density wave. The cold HI revealed in this way may have recently passed through the spiral shock and be on its way to forming molecules and, eventually, new stars. This paper is the second in a series examining HISA at high angular resolution. A companion paper (Paper III) describes our HISA search and extraction algorithms in detail.

The Canadian Galactic Plane Survey
(download pdf)

Author: Taylor, A. R., Gibson, S. J., Peracaula, M., Martin, P. G., Landecker, T. L., Brunt, C. M., Dewdney, P. E., Dougherty, S. M., Gray, A. D., Higgs, L. A., Kerton, C. R., Knee, L. B. G., Kothes, R., Purton, C. R., Uyaniker, B., Wallace, B. J., Willis, A. G., & Durand, D.

2003, Astronomical Journal, 125, 3145.

Abstract: The Canadian Galactic Plane Survey (CGPS) is a project to combine radio, millimetre and infrared surveys of the Galactic Plane to provide arc-minute scale images of all major components of the interstellar medium over a large portion of the Galactic disk. We describe in detail the observations for the low-frequency component of the CGPS, the radio surveys carried out at the Dominion Radio Astrophysical Observatory (DRAO), and summarize the properties of the merged database of surveys that comprises the CGPS.

The DRAO Synthesis Telescope surveys have imaged a 73 degree section of the Galactic Plane, using ~85% of the telescope time between April 1995 and June 2000. The observations provide simultaneous radio continuum images at two frequencies, 408 MHz and 1420 MHz, and spectral-line images of the 21cm transition of neutral atomic hydrogen. In the radio continuum at 1420 MHz dual-polarization receivers provide images in all four Stokes parameters. The surveys cover the region 74.2 < l < 147.3 degrees, with latitude extent of -3.6 < b < +5.6 degrees at 1420 MHz and -6.7 < b < +8.7 degrees at 408 MHz. By integration of data from single-antenna observations, the survey images provide complete information on all scales of emission structures down to the resolution limit, which is just below 1' x 1' cosec(DEC) at 1420 MHz, and 3.4' x 3.4' cosec(DEC) at 408 MHz. The continuum images have dynamic range of several thousand, yielding essentially noise-limited images with rms of ~0.3 mJy/beam at 1420 MHz and ~3 mJy/beam at 408 MHz. The spectral-line data are noise limited with rms brightness temperature dTB ~ 3 K in a 0.82 km/s channel.

The complete CGPS data set, including the DRAO surveys and data at similar resolution in 12CO (1–0) and in infrared emission from dust, all imaged to an identical Galactic co-ordinate grid and map projection, are being made publicly available through the Canadian Astronomy Data Centre.

A New View of Cold HI Clouds in the Milky Way
(download pdf)

Author: S. J. Gibson, A. R. Taylor, L. A. Higgs, & P. E. Dewdney

2000, Astrophysical Journal, 540, 851.

Abstract: We reveal cold Galactic clouds of neutral hydrogen in unprecedented detail. Our 21cm synthesis maps, taken from the Canadian Galactic Plane Survey, show a numerous and diverse population of H I self-absorption (HISA) features in gas outside the Solar circle. These objects vary in size, shape, and contrast against the background H I. All display a high level of angular and velocity structure, and most would appear significantly diluted, if not invisible, in lower-resolution H I surveys. A number of Perseus arm features remain unresolved by the 1′ beam of our survey, with apparent diameters < 0.6 pc at 2 kpc distance. The majority of HISA features we detect have no obvious 12CO emission counterparts. This suggests either HISA is not found predominantly in molecular clouds, as has often been presumed in the past, or CO is not a good tracer of H2. Some HISA lacking CO shows far-infrared dust emission, though whether this arises from shielded molecular gas or diffuse atomic clouds is not clear. Constraining the gas properties of HISA remains a difficult problem, but we introduce a new method which aids this process. Our approach relates a number of physical parameters via gas law and line integral relationships, and should prove powerful if the input variables are sufficiently well known. We explore the current allowed parameter ranges for three sample features of very different appearance. We find spin temperatures ~102 cm-3.

Cover page
Abstract
Acknowledgments
Contents

1. Introduction

2. 21cm Cosmology

- First light
- In the beginning
- Wouthuysen-Field effct
- Detecting the earliest galaxies
- HI 21cm probe
- Cosmology at low frequencies

3. Constraining cosmological parameters

- How accurately can 21cm tomography constrain cosmology
- Cosmology at low frequencies

4. Assumptions and their effects

- How accurately can 21cm tomography constrain cosmology

5. Antenna sensitivity

- Cosmological parameter estimation using 21cm radiation

6. Future of 21cm observations

- Probing Dark Ages with SKA
- Low frequency Radio Astronomy from the Moon

7. Conclusion

References
Appendices
A -
B -
C -
D -
E -

All the resources of our project are presented below:

- Power point presentation of 7th semester
- Homework from Abraham Loeb paper

Here are the online resources that helped us

- Constraining cosmological and gravitational parameters with upcoming astrophysical data – Yi Mao, MIT
- The Epoch of Reionization and the 21cm signal – Mario Santos
- Cosmological parameter estimation using 21cm Radiation from the Epoch of Reionization – McQuinn