arXiv subjects

J. Schaye

Publications and source records attributed to J. Schaye.

78 records · Page 5Linked to original sources

arXiv2008

Numerical simulations of the Warm-Hot Intergalactic Medium

In this paper we review the current predictions of numerical simulations for the origin and observability of the warm hot intergalactic medium (WHIM), the diffuse gas that contains up to 50 per cent of the baryons at z~0. During structure formation, gravitational accretion shocks emerging from collapsing regions gradually heat the intergalactic medium (IGM) to temperatures in the range T~10^5-10^7 K. The WHIM is predicted to radiate most of its energy in the ultraviolet (UV) and X-ray bands and to contribute a significant fraction of the soft X-ray background emission. While O VI and C IV absorption systems arising in the cooler fraction of the WHIM with T~10^5-10^5.5 K are seen in FUSE and HST observations, models agree that current X-ray telescopes such as Chandra and XMM-Newton do not have enough sensitivity to detect the hotter WHIM. However, future missions such as Constellation-X and XEUS might be able to detect both emission lines and absorption systems from highly ionised atoms such as O VII, O VIII and Fe XVII.

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arXiv2008

Clusters of galaxies: beyond the thermal view

We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the "missing baryon" problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations.

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arXiv2006

Probing unexplored territories with MUSE: a second generation instrument for the VLT

The Multi Unit Spectroscopic Explorer (MUSE) is a second-generation VLT panoramic integral-field spectrograph under preliminary design study. MUSE has a field of 1x1 arcmin**2 sampled at 0.2x0.2 arcsec**2 and is assisted by the VLT ground layer adaptive optics ESO facility using four laser guide stars. The simultaneous spectral range is 465-930 nm, at a resolution of R~3000. MUSE couples the discovery potential of a large imaging device to the measuring capabilities of a high-quality spectrograph, while taking advantage of the increased spatial resolution provided by adaptive optics. This makes MUSE a unique and tremendously powerful instrument for discovering and characterizing objects that lie beyond the reach of even the deepest imaging surveys. MUSE has also a high spatial resolution mode with 7.5x7.5 arcsec**2 field of view sampled at 25 milli-arcsec. In this mode MUSE should be able to obtain diffraction limited data-cubes in the 600-930 nm wavelength range. Although the MUSE design has been optimized for the study of galaxy formation and evolution, it has a wide range of possible applications; e.g. monitoring of outer planets atmosphere, environment of young stellar objects, super massive black holes and active nuclei in nearby galaxies or massive spectroscopic surveys of stellar fields in the Milky Way and nearby galaxies.

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arXiv2002

A feature at z ~ 3.2 in the evolution of the Ly-alpha forest optical depth

The effective optical depth in the Ly-alpha forest region of 1061 low-resolution QSO spectra drawn from the SDSS database decreases with decreasing redshift over the range 2.5 < z < 4. Although the evolution is relatively smooth, tau_eff ~ (1+z)^{3.8 pm 0.2}, at z ~ 3.2 the effective optical depth decreases suddenly, by about ten percent with respect to this smoother evolution. It climbs back to the original smooth scaling again by z ~ 2.9. We describe two techniques, one of which is new, for quantifying this evolution which give consistent results. A variety of tests show that the feature is not likely to be a consequence of how the QSO sample was selected, nor the result of flux calibration or other systematic effects. Other authors have argued that, at this same epoch, the temperature of the IGM also shows a departure from an otherwise smooth decrease with time. These features in the evolution of the temperature and the optical depth are signatures of the reionization of He II.

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arXiv2002

Detection of He II reionization in the SDSS quasar sample

The expansion of the Universe leads to a rapid drop in the mean hydrogen Ly-alpha opacity tau of the intergalactic medium (IGM), tau (1+z)^{3.8}, between redshifts 4 and 3. Measurements of the temperature evolution of the IGM and of the He II opacity both suggest that He II reionizes in this redshift range. We use hydrodynamical simulations to show that the temperature increase associated with He II reionization leads to a relatively sudden decrease in tau around the reionization epoch of ~ 10 per cent. We find clear evidence for such a feature in the evolution of tau determined from a sample of ~ 1100 quasars obtained from the SDSS. He II reionization starts at redshift ~ 3.4, and lasts for (Delta z) ~ 0.4. The increase in the IGM temperature also explains the widths of hydrogen absorption lines as measured in high-resolution spectra.

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arXiv2001

Enrichment of the High-Redshift IGM by Galactic Winds

This paper discusses a semi-numerical method of investigating the enrichment of the intergalactic medium by galactic winds. We find that most galaxies at z >~ 3 should be driving winds, and that (if these winds are similar to those at low-z) these winds should escape to large distances. Our calculations -- which permit exploration of a large region of model parameter space -- indicate that the wind velocity, the mass of the wind-driving galaxies, the fraction of ambient material entrained, and the available time (between wind launch and the observed redshift) all affect wind propagation significantly; other physical effects can be important but are sub-dominant. We find that under reasonable assumptions, the enrichment by 3 <~ z <~ 6 galaxies could account for the quantity of metals seen in the Ly-alpha forest, though it is presently unclear whether this enrichment is compatible with the intergalactic medium's detailed metal distribution or relative quiescence.

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