The temperature of the intergalactic medium (IGM) is an important factor in determining the line-widths of the absorption lines in the Lyα forest. We present a method to characterise the line-widths distribution using a decomposition of a Lyα spectrum in terms of discrete wavelets. Such wavelets form an orthogonal basis so the decomposition is unique. We demonstrate using hydrodynamic simulatio...

Recently Lu presented tentative evidence for C IV lines in QSO Lyα forest systems with strong lines. We have performed a similar search for C IV in our 10 km s −1 echelle spectra of the bright QSO HS 1946+7658. We shifted the spectra to align the expected positions of the C IV lines in 65 Lyα systems, then added them. The resulting composite spectrum, equivalent to 390 hours of exposure time on...

At redshifts z2, most of the baryons reside in the smooth intergalactic medium which is responsible for the low column density Lyα forest. This photoheated gas follows a tight temperature-density relation which introduces a cut-off in the distribution of widths of the Lyα absorption lines (b-parameters) as a function of column density. We have measured this cut-off in a sample of nine high reso...

The high redshift galaxy MS1512–cB58 (z = 2.724, m V = 20.64) has been observed with the very efficient high resolution echelle spectrograph VLT/UVES. Although this is a very challenging observational program for a Southern hemisphere telescope (the galaxy is located at +36 • declination), high resolution spectra (FWHM ≃ 26 km s −1) have revealed, with unprecedented detail along a galaxy sight ...

Recent measurements of the autocorrelation function of the Lyα clouds are analyzed from the point of view of a simple model with strong clustering on the small scales. It is shown that this toy model reproduces fairly well the important linear relation between amplitude of the absorber autocorrelation function and neutral hydrogen column density. In addition, it predicts a correct evolutionary ...

The observed dynamics of gas and stars on galactic and larger scales cannot be accounted for by self-gravity, indicating that there are large quantities of unseen matter, or that gravity is non-Newtonian in these regimes. Milgrom’s MOdified Newtonian Dynamics (MOND) postulates that Newton’s laws are modified at very low acceleration, and can account for the rotation curves of galaxies and some ...

We present spectroscopic observations of the damped Lyα absorber at redshift z = 1.9342 seen in the spectrum of the quasar Q0151+048A. The redshift of the absorber is greater than the redshift of the quasar, so the system resembles the zabs ≈ zem damped absorber at z = 2.81 towards the quasar PKS0528-250. We have previously reported the detection of Lyα emission from the latter absorber, one of...

The case is made that the intracluster medium (ICM) in spiral-rich galaxy groups today probably has undergone much slower evolution than that in elliptical-rich groups and clusters. The environments of proto-clusters and proto-groups at z > 2 are likely similar to spiral-rich group environments at lower redshift. Therefore, like the ICM in spiral-rich groups today, the ICM in proto-groups and p...

We present a study of the Lyα forest at z . 0.4 from which we conclude that at least 20% of the total baryons in the universe are located in the highly-ionized gas traced by broad Lyα absorbers. The cool photoionized low-z intergalactic medium (IGM) probed by narrow Lyα absorbers contains about 30% of the baryons. We further find that the ratio of broad to narrow Lyα absorbers is higher at z . ...