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

Abstract

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.