INCIDENCE OF ABSORPTION AT THE INTERFACE OF GALAXIES AND IGM

INCIDENCE OF ABSORPTION AT THE INTERFACE OF GALAXIES AND IGM

Ramiz AhmadIndian Institute of Space Science and Technology

May, 2012

Plan of the talk 1. Introduction.2. Details about data.3. Data analysis.4. Method of measurement.5. Results and observations.6. Conclusion.

What is out there?

What is it made up of?

What is out there?

What is it made up of?

What is out there?

Composition of the universe (present day)

Distribution of the baryonic matter:

~ 6-10 % are in the form of galaxies.

Distribution of the baryonic matter:

~ 6-10 % are in the form of galaxies.

=> 90-93 % of the baryonic matter are in the form of IGM

Owing to the high temperature of the IGM, the UV region of the electromagnetic spectra is the best region to study it.

Owing to the high temperature of the IGM, the UV region of the electromagnetic spectra is the best region to study it.

Cosmic Origin Spectrograph- Aboard the Hubble Space Telescope

COS is capable of producing high sensitivity medium and low resolution far-UV and near-UV spectra

The data was obtained from the public archive of the COS (Cosmic Origin Spectrograph) available at Multi-mission Archive (MAST) at Space Telescope Science Institute (STScI) webpage : http://archive.stsci.edu/

The data was obtained from the public archive of the COS (Cosmic Origin Spectrograph) available at Multi-mission Archive (MAST) at Space Telescope Science Institute (STScI) webpage : http://archive.stsci.edu/

COS Grating Parameters

Data Analysis

Sample table

Data Analysis

Step1: The data is converted into either ASCII or the .sav format depending upon the requirement.

Step2: The data is re-binned.

Step3: Then various rebinned files are co-added with the exposure time as the weightage factor.

Step4: The spectra is then plotted using the co-added files and from the spectra the continuum normalized spectra is obtained on which all the final analysis is done.

Data Analysis

Continuum Normalized Spectra of HE0153-4520

Line Measurements Using Apparent Optical Depth Method

The direct integration of the observed optical path difference is done

Line Measurements Using Apparent Optical Depth Method

The direct integration of the observed optical path difference is done

Line Measurements Using Apparent Optical Depth Method

The first moment of the optical depth gives the central velocity of the absorption line

Line Measurements Using Apparent Optical Depth Method

The first moment of the optical depth gives the central velocity of the absorption line

And we get the Doppler width from the second moment of the apparent optical depth

Line Measurements Using Apparent Optical Depth Method

The first moment of the optical depth gives the central velocity of the absorption line

And we get the Doppler width from the second moment of the apparent optical depth

Where,

Line Measurements Using Apparent Optical Depth Method

The general expression for the calculation of equivalent width is

Where f(v) is the continuum normalised flux of the spectra in the velocity space.

Observations and Results

Observations and Results

1. HE0153-4520

2. HE0226-4110

3. HE0238-1904

4. MS0117.2-2837

Observations and Results

System plot for HE0153-4520

Observations and Results

System plot for HE0226-4110

Observations and Results

System plot for HE0238-1904

Observations and Results

System plot for MS0117.2-2837

Observations and Results

If the line is clearly resolved, a value of the parameter can be obtained. In case of the absence of the absorption line or unresolved line, only an upper limit could be calculated.

Observations and Results

If the line is clearly resolved, a value of the parameter can be obtained. In case of the absence of the absorption line or unresolved line, only an upper limit could be calculated.

The table shows the measured values and the upper limit of the various parameters(Wr (mA)= Equivalent width in milli-angstrom, ba= Doppler parameter)

Observations and Results

The table shows a list of the line of the sights, associated absorbers, impact parameters and the equivalent width.

Observations and Results

Variation of the equivalent depth with impact parameter.

Conclusion

1. There is no obvious relation between the impact parameters of the galaxies and the equivalent width of the absorption lines.

Conclusion

1. There is no obvious relation between the impact parameters of the galaxies and the equivalent width of the absorption lines.

2. Based on the measurement of the Doppler parameter, the average value of the temperature was found to be 5 x 10^4 K, which is consistent with the temperature of the photoionized component of the IGM.

Conclusion

1. There is no obvious relation between the impact parameters of the galaxies and the equivalent width of the absorption lines.

2. Based on the measurement of the Doppler parameter, the average value of the temperature was found to be 5 x 10^4 K, which is consistent with the temperature of the photoionized component of the IGM.

3. Although in none of the case any other absorption line by any metal ion is detected, from the measurement an upper limit was calculated for the ions in all the cases and is in agreement with the model of cosmic abundance percentage. The absence of metal absorption is consistent with low metallicity (of ~1/10 solar) typical of low-z IGM.

Conclusion

1. There is no obvious relation between the impact parameters of the galaxies and the equivalent width of the absorption lines.

2. Based on the measurement of the Doppler parameter, the average value of the temperature was found to be 5 x 10^4 K, which is consistent with the temperature of the photoionized component of the IGM.

3. Although in none of the case any other absorption line by any metal ion is detected, from the measurement an upper limit was calculated for the ions in all the cases and is in agreement with the model of cosmic abundance percentage. The absence of metal absorption is consistent with low metallicity (of ~1/10 solar) typical of low-z IGM.

4. Though as of now, nothing can be said about the relation between the impact parameter and the equivalent width because of the lack of the number of data points, one conclusion that can be drawn based on the above graphs is that there is a possibility that the IGM surrounding the galaxies is patchy.

References:

1. Penton, Steven V.; Stocke, John T.; Shull, J. Michael, “The Local Lyα Forest. IV. Space Telescope Imaging Spectrograph G140M Spectra and Results on the Distribution and baryon Content of H I Absorbers”, The Astrophysical Journal Supplement Series , 152:29-62, 2004 May.

2. Lehner, N.; Savage, B. D.; Wakker, B. P.; Sembach, K. R.; Tripp, T. M. “Low-Redshift Intergalactic Absorption Lines in the Spectrum of HE 0226-4110”, The Astrophysical Journal Supplement Series , 164:1 – 37, 2006 May

3. Blair D. Savage, Kenneth R. Sembach, “The Analysis of Apparent Optical Depth Profiles for Interstellar Absorption Lines”, The Astrophysical Journal, 379: 245-259,1991 September 20

4. Joel N. Bregman, "The Search for the Missing Baryons at Low Redshift", Annu. Rev. Astron. Astrophys. 2007. 45:221–59

5. Anand Narayanan, Bart P. Wakker, Blair D. Savage, Brian A. Keeney, J. Michael Shull, John T. Stocke, and Kenneth R. Sembach, "Cosmic Origins Spectrograph And Fuse Observations of T 10^5 K Gas In A Nearby Galaxy Filament", The Astrophysical ∼Journal, 721:960–974, 2010 October

Thank You!