arXiv subjects

T. Fang

Publications and source records attributed to T. Fang.

21 records · Page 2Linked to original sources

arXiv2001

Chandra Observations of a Cluster and Two Quasars at High Redshift

We observed MS 1054-0321, the highest redshift cluster of galaxies in the Einstein Medium Sensitivity Survey (EMSS), with the Chandra ACIS-S detector. We find the X-ray temperature of the cluster to be 10.4^{+1.7}_{-1.5} keV, slightly lower than that inferred previously and in agreement with the observed velocity dispersion and that found from weak lensing. We confirm significant substructure in the form of two distinct clumps in the X-ray distribution. We find the virial mass of the cluster to be at least 4.5 x 10^{14} h^{-1} M_{\odot} and the existence of this cluster constrains Omega_m to be less than one. If Omega_m = 1 and assuming Gaussian initial perturbations, we find the probability of observing MS 1054 in the EMSS is ~ 7 x 10^{-4}. We also present the first high-resolution X-ray spectra of two high-redshift quasars, S5 0836+710 and PKS 2149-306, obtained with the Chandra HETGS. The primary goal of this observation is to use the high spectral resolving power of the HETGS to detect X-ray absorption produced by a hot intergalactic medium. No significant emission or absorption feature is detected in either source at +/-3sigma level. Based on the detection limits we constrain the properties of possible emitters and absorbers. We propose a method to constrain the cosmological parameters via the X-ray forest theory, but current data do not give significant constraints. We also find that combined with the constraints from the distortion of the CMB spectrum, the X-ray Gunn-Peterson test can marginally constrain a uniform, enriched IGM.

astro-ph↗

arXiv2001

Chandra Observations of Two High-Redshift Quasars

We report the first high-resolution X-ray spectra of two high-redshift quasars, S5 0836+710 and PKS 2149-306, obtained with the Chandra High Energy Transmission Grating Spectrometer (HETGS). The primary goal of this observation is to use the high spectral resolving power of the HETGS to detect X-ray absorption produced by a hot intergalactic medium. The continuum of both quasars can be fitted by absorbed power laws. The power law photon index (Gamma) of S5 0836+710 is consistent with that found in previous observations with ROSAT and ASCA, while the power law of PKS 2149-306 is harder than found in a previous observation by ASCA. Excess continuum absorption above the Galactic value is found in S5 0836+710, as evidenced in ASCA and ROSAT observations. No significant emission or absorption feature is detected in either source at 3 sigma level. Based on the detection limits we constrain the properties of possible emitters and absorbers. The upper limit of the equivalent width of Fe K emission lines could be as low as ~ 10 eV. Absorbers with a column density higher than 8e16 cm^{-2} for O VIII or 5e16 cm^{-2} for Si XIV would have been detected. We propose a method to constrain the cosmological parameters (namely Omega_0 and Omega_b) via the X-ray forest theory, but current data do not give significant constraints. However, we estimate that observing ~ 7 bright quasars should give at least one O VIII and more O VII absorption lines at 95% possibility. We also find that combined with the constraints from the distortion of the CMB spectrum, the X-ray Gunn-Peterson test can marginally constrain a uniform, enriched IGM.

astro-ph↗

arXiv2000

Probing Cosmology with the X-ray Forest

There is a growing consensus that in the present universe most baryons reside in galaxy clusters and groups in the form of highly ionized gas at temperatures of 10^6 ~ 10^8 K. The H-like and He-like ions of the heavy elements can produce absorption features - the so-called ``X-ray Forest'' - in the X-ray spectrum of a background quasar. We investigate the distribution of the X-ray absorption lines produced by this gas under three different cosmological models: the standard CDM with Omega_0=1, a flat model with Omega_0=0.3 and an open model with with Omega_0=0.3. We give a semi- analytic calculation of the X-ray forest distribution based on the Press- Schechter formalism, following Perna & Loeb (1998). We choose three ions (O VIII, Si XIV and Fe XXV) and calculate the distribution functions, the number of absorbers along the LOS to a distant quasar vs. redshift and column density in a given ion. We find that significant differences in the evolution of the distribution functions among the three cosmological models. Using Monte Carlo simulations, we simulate the distribution of X-ray absorption lines for 10,000 random LOS. We find there are at least several O VIII lines with column density higher than 10^16 cm^-2. Finally we explore the possibility of detecting the X-ray forest with current and upcoming X-ray missions and we present an XMM RGS simulation of a representative quasar X-ray spectrum.

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