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[120.05] The Relationship Between OVI WHIM Absorption and Galaxies from Hydrodynamic Simulations

R. Ganguly (University of Wyoming), R. Cen (Princeton University), T. Fang (University of California, Berkeley), K. R. Sembach (The Space Telescope Science Institute)

Hydrodynamic simulations predict that roughly half of the baryons at low redshift should reside in a warm-hot (T~ 10^5-7 K) intergalactic medium (WHIM). This gas is readily detectable in ultraviolet absorption by OVI and HI Lyman-alpha (and X-ray absorption by OVII and OVIII) toward background quasars. Interestingly however, observations in the fields of these sight lines reveal the presence of galaxies at similar redshifts as the absorbers. This begs the question, then, does the absorption trace inherently galactic or intergalactic material? We address this question by tracing the relationship between OVI absorption and galaxies within a hydrodynamical simulation. The simulation uses an Eulerian algortihm with a self-consistent galaxy/star-formation treatment and metal enrichment of the IGM. The box size is 85 Mpc/h, with a mass resolution of 3.5 x 10⁶ M_sun. We probe the box with 10000 evenly spaced sight lines of 1024 bins each, producing OVI absorption spectra for each sight-line. (The spatial resolution of our sight lines is 83 kpc/h.) To compare with observations, the synthetic spectra are convolved to two different resolving powers (R=20,000 and 45,000) each with a sampling rate of 2 pixels per resolution element. Gaussian noise is introduced at the level of S/N=20 per resolution element. We detect OVI absorption using an equivalent width-based unresolved feature detection algorithm following the HST Quasar Absorption Line Key Project. For each OVI profile we compute the equivalent width, integrated column density, centroid redshift, velocity width, and position along the sight line. We present comparisons of the distributions of these parameters with observations. We will also compare the spatial distribution of the OVI absorbing gas with the positions of galaxies produced within the simulation.

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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.