Quasar spectroscopy in UV and X-ray- probing the intergalactic medium using helium and oxygen

We employ ultraviolet (UV) and X-ray quasar spectroscopy to study the physical state of the Intergalactic Medium (IGM). First, we quantify the possibility of measuring the temperature of moderately over-dense regions of the IGM at high redshift (z [approx.] 2) using the strongest resonant absorption lines of neutral hydrogen ([lambda]HI = 1215.67 A[ngstroms]) and neutral helium ([lambda]HeI = 584.33 A[ngstroms]). We calculate the fraction of neutral helium in the IGM at z [approx.] 2 by solving a set of photoionization equilibrium equations. Using known distributions of the redshift, column density and Dopper [beta]-parameter of Lyman-[alpha] ac lines, we perform Monte Carlo simulation to create a line list, from which we calculate the number of observable HeI lines. We expect that 4.5% of the HI lines have observable HeI counterparts. Future ultraviolet (UV) telescope with wavelength coverage from 1400 A[ngstroms] to 2400 A[ngstroms] should be able to observe [approx.] 16 HelI lines per line of sight observation. Second, we analyze a combined 171 ksec. spectroscopic observation of the low redshift quasar 3C 273 by the Chandra X-ray Observatory. We search for the high ionization state lines of OVII and OVIII at redshifts of known intervening OVI absorbers. Detection of associated OVII or OVIII absorptions in the X-ray would suggest the existence of a warm hot component of the Intergalactic Medium at temperature T [approx.] 106 - 107 K. We observe an unresolved OVII line at z [approx.]0 with a maximum Doppler [beta] parameter of 190 km/s. We do not see any associated OVII absorption for a z [approx.] 0.12 OVI absorber at the -3.5[sigma] level. We provide most stringent to date (Chandra resolution limited) upper limit on the temperature of the z [approx.] 0.12 absorber and discuss the possibilities of photoionization and collisional ionization.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Gong, Donglai, 1977-

Advisor dc:contributor.advisor

• Scott M. Burles and Claude R. Canizares.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/30116

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/30116