Bibcode
Tepper-García, Thorsten; Richter, Philipp; Schaye, Joop; Booth, C. M.; Dalla Vecchia, C.; Theuns, Tom; Wiersma, Robert P. C.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 413, Issue 1, pp. 190-212.
Fecha de publicación:
5
2011
Número de citas
61
Número de citas referidas
58
Descripción
We investigate the origin and physical properties of O VI absorbers at
low redshift (z= 0.25) using a subset of cosmological, hydrodynamical
simulations from the OverWhelmingly Large Simulations (OWLS) project.
Intervening O VI absorbers are believed to trace shock-heated gas in the
warm-hot intergalactic medium (WHIM) and may thus play a key role in the
search for the missing baryons in the present-day Universe. When
compared to observations, the predicted distributions of the different O
VI line parameters (column density ?, Doppler parameter ?, rest
equivalent width Wr) from our simulations exhibit a lack of
strong O VI absorbers, a discrepancy that has also been found by
Oppenheimer & Davé. This suggests that physical processes on
subgrid scales (e.g. turbulence) may strongly influence the observed
properties of O VI systems. We find that the intervening O VI absorption
arises mainly in highly metal enriched
(10-1≪Z/Z⊙≲ 1) gas at typical
overdensities of 1 ≪ρ/<ρ>≲ 102.
One-third of the O VI absorbers in our simulation are found to trace gas
at temperatures T < 105 K, while the rest arises in gas at
higher temperatures, most of them around T= 105.3 ±
0.5 K. These temperatures are much higher than inferred by
Oppenheimer & Davé, probably because that work did not take
the suppression of metal-line cooling by the photoionizing background
radiation into account. While the O VI resides in a similar region of
(ρ, T)-space as much of the shock-heated baryonic matter, the vast
majority of this gas has a lower metal content and does not give rise to
detectable O VI absorption. As a consequence of the patchy metal
distribution, O VI absorbers in our simulations trace only a very small
fraction of the cosmic baryons (<2 per cent) and the cosmic metals.
Instead, these systems presumably trace previously shock-heated,
metal-rich material from galactic winds that is now mixing with the
ambient gas and cooling. The common approach of comparing O VI and H I
column densities to estimate the physical conditions in intervening
absorbers from QSO observations may be misleading, as most of the H I
(and most of the gas mass) is not physically connected with the
high-metallicity patches that give rise to the O VI absorption.