CONCAP 4: A Complex Autonomous Payload (CAP) for growing organic thin films in microgravity

A GAS facility has been developed for carrying out low temperature experiments. The arrangement being used on CONCAP IV-01 is designed for thin film growth in microgravity and can process up to twelve samples per mission. The nonlinear optical oven hardware can also be made suitable for other low temperature applications, such as gradient freeze and solution growth of crystals

The enrichment history of the intergalactic medium: O VI in Ly-alpha forest systems at redshift z ~ 2

A search for O VI at redshifts corresponding to Ly-alpha lines in the z_em ~ 2.4 QSOs HE1122-1648 and HE2217-2818 reveals that a substantial fraction of those with H I column densities log N(HI) > 14 (cm^{-2}) are highly ionized and show some heavy element enrichment. If these two sight lines are typical, then the O VI systems contain a cosmologically significant fraction of the baryons and the metals in the universe. For most systems the temperatures derived from the line widths are too low for collisional ionization to be responsible for the O VI lines. Photoionization models with a substantial hard ultraviolet flux can reproduce the observations for densities that are in good agreement with a model assuming local, hydrostatic equilibrium and heavy element abundances in the range ~ 10^{-3} - 10^{-2} solar. Photoionization by a UV flux much softer than that predicted by Haardt & Madau (1996) for a background dominated by quasars can be ruled out. Finally, we find one system with a very low H I column density for which both photoionization and collisional ionization models yield a metallicity close to solar and a density that is inconsistent with gravitational confinement, unless the gas fraction is negligible.Comment: 16 pages, 16 figures, 7 tables. Accepted for publication in the Astrophysical Journal. Minor change

The evolution of HI and CIV quasar absorption line systems at 1.9 < z < 3.2

We have investigated the distribution and evolution of ~3100 intergalactic HI absorbers with HI column densities log N(HI) = [12.75, 17.0] at 1.9 < z < 3.2, using 18 high resolution, high S/N quasar spectra obtained from the ESO VLT/UVES archive. We used two sets of Voigt profile fitting analysis, one including all the available high-order Lyman lines to obtain reliable HI column densities of saturated lines, and another using only the Ly-alpha lines. There is no significant difference between the results from the two fits. Combining our results with literature data, the mean number density at 0 < z < 4 is not well described by a single power law and strongly suggests that its evolution slows down at z < 1.5 at the high and low column density ranges. We also divided our entire HI absorbers at 1.9 < z < 3.2 into two samples, the unenriched forest and the CIV-enriched forest, depending on whether HI lines are associated with CIV at log N(CIV) > 12.2 within a given velocity range. The entire HI column density distribution function (CDDF) can be described as the combination of these two well-characterised populations which overlap at log N(HI) ~ 15. At log N(HI) < 15, the unenriched forest dominates, showing a similar power-law distribution to the entire forest. The CIV-enriched forest dominates at log N(HI) > 15, with its distribution function proportional to N(HI)^(-1.45). However, it starts to flatten out at lower N(HI), since the enriched forest fraction decreases with decreasing N(HI). The deviation from the power law at log N(HI) = [14, 17] shown in the CDDF for the entire HI sample is a result of combining two different HI populations with a different CDDF shape. The total HI mass density relative to the critical density is Omega(HI) ~ 1.6 x 10^(-6) h^(-1), where the enriched forest accounts for ~40% of Omega(HI).Comment: 26 pages, 20 figures, accepted for AA, in pres

The power spectrum of the flux distribution in the Lyman-alpha forest of a Large sample of UVES QSO Absorption Spectra (LUQAS)

The flux power spectra of the Lyman-alpha forest from a sample of 27 QSOs taken with the high resolution echelle spectrograph UVES on VLT are presented. We find a similar fluctuation amplitude at the peak of the ``3D'' flux power spectrum at k ~ 0.03 (km/sec)^(-1) as the study by Croft et al. (2002), in the same redshift range. The amplitude of the flux power spectrum increases with decreasing redshift if corrected for the increase in the mean flux level as expected if the evolution of the flux power spectrum is sensitive to the gravitational growth of matter density fluctuations. This is in agreement with the findings of McDonald et al. (2000) at larger redshift. The logarithmic slope of the "3D" flux power spectrum, P_F(k), at large scales k < 0.03 (km/sec)^(-1), is 1.4 +- 0.3, i.e. 0.3 shallower than that found by Croft et al. (2002) but consistent within the errors.Comment: 18 pages, 9 PS figures, 6 tables. Note that the k-values of the 1D flux power spectrum had been erroneously shifted by half a bin size (in log k) in the previous version. All the other results are unaffected. New tables can be found at http://www.ast.cam.ac.uk/~rtnigm/luqas.ht

Mapping Low-Density Intergalactic Gas: a Third Helium Lyman-alpha Forest

We present a new HST/STIS spectrum of the z=3.18 quasar PKS 1935-692 and summarize the spectral features shortwards of 304A in the rest frame likely to be caused by foreground HeII Lyman-alpha absorption. In accord with previous results on two other quasars at similar redshifts, we demonstrate a correlation with the HI Lyman-alpha forest absorption, and show that much of the helium absorption is caused by a comparable quantity of more diffuse gas with Omega~0.01, that is not detected in HI. The helium ionization zone around the quasar is detected as well as a void seen in both HI and HeII. The properties of the absorption are in broad agreement with those of the other quasars and with models of the protogalactic gas distribution and ionization at this redshift.Comment: 17 pages including 5 figures. As accepted for publication in The Astronomical Journal (minor revisions

A re-analysis of the spectrum of 2206-199

Recently Pettini, Hunstead, Smith and Mar, (PHSM 1991) performed an analysis of the Ly-alpha forest of QSO 2206-199N at very high resolution. On the basis of their observations they concluded that most Doppler parameters b = (square root of 2)(sigma) of Ly-alpha forest lines are below 22 km/s, with a range down to a few km/s and a median of 17 km/s. They also found a strong intrinsic correlation between Doppler parameter b and column density N. These results are in contrast to those of a similar study by Carswell, Lanzetta, Parnell, and Webb (CLPW 1991) at comparable resolution with the same instruments, who find that most of the Ly-alpha lines towards QSO 1100-264 have Doppler parameters above 15 km/s (median b = 34 km/s), and that there is no significant correlation between b and N. Whilst an intrinsic difference between the lines of sight to 2206-199 and to other QSO's can not be excluded a priori, previous disagreement between Doppler parameter estimates obtained by both groups pointed to a potential difference in estimation techniques and in the interpretation of the results. To investigate this possibility, the AAT/UCLES spectrum of 2206-199 obtained by PHSM were reanalyzed. The spectrum was extracted from the raw data and determined the line parameters using the method described by CLPW