Photoionized OVI absorbers toward the bright QSO HE 0515-4414

We report on detailed Monte Carlo inversion analysis of five OVI systems from the spectrum of the bright quasar HE 0515-4414 (z_e = 1.71). The associated system at z_a = 1.697 with the neutral hydrogen column density N(HI)= 4.4 10^{13} cm^{-2} shows pronounced absorption from highly ionized transitions of CIII, CIV, NV, OVI, SiIV, and probably SVI. We found that only a power law type ionizing spectrum (J_nu propto nu^{-1.5}) is consistent with the observed sample of the line profiles, i.e. the system is definitely intrinsic. The relative metal abundances give almost the solar pattern and the metallicity of about 5 times solar. The system originates in a thin shell of the line-of-sight thickness L <= 16 pc. Two OVI systems at z_a = 1.674 ([C/H] = -1.6) and 1.602 ([O/H] = -1.1), arising in intervening halos, have linear sizes of L = 3-14 kpc and 17 kpc, respectively. Absorption systems at z_a = 1.385 ([C/H] = -0.3, L = 1.7-2.5 kpc) and z_a = 1.667 ([C/H] = -0.5, L = 1 kpc) exhibit characteristics very similar to that observed in metal-enriched high velocity clouds in the Milky Way.These systems are probably embedded in extremely metal-poor halos with [C/H] < -2.4 (z_a = 1.667) and [C/H] < -3.7 (z_a = 1.385). We also found two additional extremely metal-poor Ly-alpha systems at z_a = 1.500 and 1.681 with, respectively, N(HI) = 1.7 10^{15} and 1.8 10^{15} cm^{-2} and [C/H] < -4.0 and <-3.0, - an indication that the distribution of metals in the metagalactic medium is utterly patchy. Our results show that the ionization states in the analyzed OVI absorbers, ranging from z = 1.4 to 1.7, can be maintained by photoionization only and that the fraction of the shock-heated hot gas with temperature T > 10^5 K is negligible in these systems.Comment: 16 pages, including 11 PostScript figures. Accepted for publication in A&

FeII/MgII Emission Line Ratio in High Redshift Quasars

We present results of the analysis of near infrared spectroscopic observations of 6 high-redshift quasars (z > 4), emphasizing the measurement of the ultraviolet FeII/MgII emission line strength in order to estimate the beginning of intense star formation in the early universe. To investigate the evolution of the FeII/MgII ratio over a wider range in cosmic time, we measured this ratio for composite quasar spectra which cover a redshift range of 0 < z < 5 with nearly constant luminosity, as well as for those which span ~6 orders of magnitude in luminosity. A detailed comparison of the high-redshift quasar spectra with those of low-redshift quasars with comparable luminosity shows essentially the same FeII/MgII emission ratios and very similar continuum and line spectral properties, i.e. a lack of evolution of the relative iron to magnesium abundance of the gas in bright quasars since z=5. Current nucleosynthesis and stellar evolution models predict that alpha-elements like magnesium are produced in massive stars ending in type II SNe, while iron is formed predominantly in SNe of type Ia with intermediate mass progenitors. This results in an iron enrichment delay of 0.2 to 0.6 Gyr. We conclude that intense star formation activity in the host galaxies of z>4 quasars must have started already at an epoch corresponding to z_f = 6 to 9, when the age of the universe was ~0.5 Gyr (H_o = 72 km/s/Mpc, Omega_M = 0.3, Omega_Lambda = 0.7). This epoch corresponds well to the re-ionization era of the universe.Comment: 22 pages, 5 figures, accepted for publication in ApJ (vol.596, Oct03

Effects of CMB temperature uncertainties on cosmological parameter estimation

We estimate the effect of the experimental uncertainty in the measurement of the temperature of the cosmic microwave background (CMB) on the extraction of cosmological parameters from future CMB surveys. We find that even for an ideal experiment limited only by cosmic variance up to l = 2500 for both the temperature and polarisation measurements, the projected cosmological parameter errors are remarkably robust against the uncertainty of 1 mK in the FIRAS instrument's CMB temperature monopole measurement. The maximum degradation in sensitivity is 20%, for the baryon density estimate, relative to the case in which the monopole is known infinitely well. While this degradation is acceptable, we note that reducing the uncertainty in the current temperature measurement by a factor of five will bring it down to the per cent level. We also estimate the effect of the uncertainty in the dipole temperature measurement. Assuming the overall calibration of the data to be dominated by the dipole error of 0.2% from FIRAS, the sensitivity degradation is insignificant and does not exceed 10% in any parameter direction.Comment: 12 pages, 2 figures, uses iopart.cls, v2: added discussion of CMB dipole uncertainty, version accepted by JCA

Using BBN in cosmological parameter extraction from CMB: a forecast for Planck

Data from future high-precision Cosmic Microwave Background (CMB) measurements will be sensitive to the primordial Helium abundance $Y_p$. At the same time, this parameter can be predicted from Big Bang Nucleosynthesis (BBN) as a function of the baryon and radiation densities, as well as a neutrino chemical potential. We suggest to use this information to impose a self-consistent BBN prior on $Y_p$ and determine its impact on parameter inference from simulated Planck data. We find that this approach can significantly improve bounds on cosmological parameters compared to an analysis which treats $Y_p$ as a free parameter, if the neutrino chemical potential is taken to vanish. We demonstrate that fixing the Helium fraction to an arbitrary value can seriously bias parameter estimates. Under the assumption of degenerate BBN (i.e., letting the neutrino chemical potential $\xi$ vary), the BBN prior's constraining power is somewhat weakened, but nevertheless allows us to constrain $\xi$ with an accuracy that rivals bounds inferred from present data on light element abundances.Comment: 14 pages, 4 figures; v2: minor changes, matches published versio

Direct evidence for radar reflector originating from changes in crystal-orientation fabric

International audienceThe origin of a strong continuous radar reflector observed with airborne radio-echo sounding (RES) at the EPICA deep-drilling site in Dronning Maud Land, Antarctica, is identified as a transition in crystal fabric orientation from a vertical girdle- to increased single-pole orientation seen along the ice core. The reflector is observed with a 60 ns and 600 ns long pulse at a frequency of 150 MHz, spans one pulse length, is continuous over 5 km, and occurs at a depth of about 2020?2030 m at the drill site. Changes in conductivity as reflector origin are excluded by investigating the ice-core profile and synthetic RES data. Our observations allow to extrapolate the crystal orientation feature along the reflector in space, with implications for ice-sheet dynamics. As the conductivity profile of the EPICA shows no distinctive peak at this depths, we exclude changes in conductivity as the reflector origin. This is supported by application of numerical forward modelling of electromagnetic wave propagation, based on the conductivity profile, which is able to reproduce nearby reflections, but fails to reproduce this one. Because of background noise, the permittivity profile based on dielectric does not show prominent signals at these depths. We therefore interpret the observed reflector to originate from this change in crystal fabric

Direct evidence for continuous radar reflector originating from changes in crystal-orientation fabric

International audienceThe origin of a strong continuous radar reflector observed with airborne radio-echo sounding (RES) at the EPICA deep-drilling site in Dronning Maud Land, Antarctica, is identified as a transition in crystal fabric orientation from a vertical girdle to an increased single-pole orientation seen along the ice core. The reflector is observed with a 60 ns and 600 ns long pulse at a frequency of 150 MHz, spans one pulse length, is continuous over 5 km, and occurs at a depth of about 2025?2045 m at the drill site. Changes in conductivity as reflector origin are excluded by investigating the ice-core profile, synthetic RES data, and a RES profile with different electromagnetic polarisation azimuths. The reflector's magnitude shows maximum values for polarisation parallel to the nearby ice divide and disappears for polarisation perpendicular to it, identifying the orientation of the girdle to lie in the vertical plane parallel to the ice divide. Observations allow us to extrapolate the crystal orientation feature along the reflector in space, with implications for ice-sheet dynamics and modeling

A representative sample of Be stars III: H band spectroscopy

We present H band (1.53 - 1.69 micron) spectra of 57 isolated Be stars of spectral types O9-B9 and luminosity classes III,IV & V. The HI Brackett (n-4) series is seen in emission from Br 11-18, and FeII emission is also apparent for a subset of those stars with HI emission. No emission from species with a higher excitation temperature, such as He II or CIII is seen, and no forbidden line emission is present. A subset of 12 stars show no evidence for emission from any species; these stars appear indistinguishable from normal B stars of a comparable spectral type. In general the line ratios constructed from the transitions in the range Br 11-18 do not fit case B recombination theory particularly well. Strong correlations between the line ratios with Br-gamma and spectral type are found. These results most likely represent systematic variations in the temperature and ionization of the circumstellar disc with spectral type. Weak correlations between the line widths and projected rotational velocity of the stars are observed; however no systematic trend for increasing line width through the Brackett series is observed.Comment: accepted for publication in A&A (this version correctly formatted