The VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems

We have searched for molecular hydrogen in damped Lyman-alpha (DLA) and sub-DLA systems at z>1.8 using UVES at the VLT. Out of the 33 systems in our sample, 8 have firm and 2 have tentative detections of associated H2 absorption lines. Considering that 3 detections were already known from past searches, H2 is detected in 13 to 20 percent of the newly-surveyed systems. We report new detections of molecular hydrogen at z=2.087 and 2.595 toward, respectively, Q 1444+014 and Q 0405-443, and also reanalyse the system at z=3.025 toward Q 0347-383. We find that there is a correlation between metallicity and depletion factor in both our sample and also the global population of DLA systems (60 systems in total). The DLA and sub-DLA systems where H2 is detected are usually amongst those having the highest metallicities and the largest depletion factors. Moreover, the individual components where H2 is detected have depletion factors systematically larger than other components in the profiles. In two different systems, one of the H2-detected components even has [Zn/Fe]>=1.4. These are the largest depletion factors ever seen in DLA systems. All this clearly demonstrates the presence of dust in a large fraction of the DLA systems. The mean H2 molecular fraction is generally small in DLA systems and similar to what is observed in the Magellanic Clouds. From 58 to 75 percent of the DLA systems have log f<-6. This can be explained if the formation rate of H2 onto dust grains is reduced in those systems, probably because the gas is warm (T>1000 K) and/or the ionizing flux is enhanced relative to what is observed in our Galaxy.Comment: 21 pages, 16 figures, MNRA

A collimated flow driven by radiative pressure from the nucleus of quasar Q~1511+091

High velocity outflows from quasars are revealed by the absorption signatures they produce in the spectrum of the quasar. Clues on the nature and origin of these flows are important for our understanding of the dynamics of gas in the central regions of the Active Galactic Nucleus (AGNs) but also of the metal enrichment of the intergalactic space. Line radiation pressure has often been suggested to be an important process in driving these outflows, however no convincing evidence has been given so far. Here we report observation of a highly structured flow, toward Q~1511+091, where the velocity separations between distinct components are similar to O VI, N V and C IV doublet splittings with some of the profiles matching perfectly. This strongly favors the idea that the absorbing clumps originate at similar physical location and are driven by radiative acceleration due to resonance lines. The complex absorption can be understood if the flow is highly collimated so that the different optically thick clouds are aligned and cover the same region of the background source. One component shows saturated H I Lyman series lines together with absorptions from excited levels from C II and Si II but covers only 40% of the source of continuum. The fact that clouds cover only part of the small continuum source implies that the flow is located very close to it.Comment: 6 pages, 5 figures to appear in MNRA

Neutral atomic-carbon QSO absorption-line systems at z>1.5: Sample selection, HI content, reddening, and 2175 A extinction feature

We present the results of a search for cold gas at high redshift along QSO lines-of-sight carried out without any a priori assumption on the neutral atomic-hydrogen (HI) content of the absorbers. To do this, we systematically looked for neutral-carbon (CI) 1560,1656 transition lines in low-resolution QSO spectra from the SDSS database. We built up a sample of 66 CI absorbers with redshifts 1.5<z<3.1 and equivalent widths 0.1<W_r(1560)<1.7 A. The completeness limit of our survey is W_r,lim(1560)~0.4 A. CI systems stronger than that are more than one hundred-times rarer than DLAs at z_abs=2.5. The number of CI systems per unit redshift increases significantly below z=2. We suggest that the CI absorbers are closely related to the process of star formation and the production of dust in galaxies. We derive the HI content of the CI systems and find that a majority of them are sub-DLAs with N(HI)~10^20 atoms cm^-2. The dust content of these absorbers is yet significant as seen from the redder optical colours of the background QSOs and their reddened SEDs. The overall N(HI) distribution of CI systems is relatively flat however. As a consequence, among the CI systems classifying as DLAs there is a probable excess of strong DLAs with log N(HI)>21 compared to systematic DLA surveys. We study empirical relations between W_r(CI), N(HI), E(B-V) and the strength of the 2175 A extinction feature, the latter being detected in about 30% of the CI absorbers. We show that the 2175 A feature is weak compared to Galactic lines-of-sight exhibiting the same amount of reddening. This is probably the consequence of current or past star formation in the vicinity of the CI systems. We also find that the strongest CI systems tend to have the largest amounts of dust and that the metallicity of the gas and its molecular fraction is likely to be high in a large number of cases.Comment: Accepted for publication in Astronomy & Astrophysics Main Journal on 20 April 201

Lyapunov Generation of Entanglement and the Correspondence Principle

We show how a classically vanishing interaction generates entanglement between two initially nonentangled particles, without affecting their classical dynamics. For chaotic dynamics, the rate of entanglement is shown to saturate at the Lyapunov exponent of the classical dynamics as the interaction strength increases. In the saturation regime, the one-particle Wigner function follows classical dynamics better and better as one goes deeper and deeper in the semiclassical limit. This demonstrates that quantum-classical correspondence at the microscopic level requires neither high temperatures, nor coupling to a large number of external degrees of freedom

The Nature of Associated Absorption and the UV-X-ray Connection in 3C 288.1

We discuss new Hubble Space Telescope spectroscopy of the radio-loud quasar, 3C 288.1. The data cover ~590 A to ~1610 A in the quasar rest frame. They reveal a wealth of associated absorption lines (AALs) with no accompanying Lyman-limit absorption. The metallic AALs range in ionization from C III and N III to Ne VIII and Mg X. We use these data and photoionization models to derive the following properties of the AAL gas: 1) There are multiple ionization zones within the AAL region, spanning a factor of at least ~50 in ionization parameter. 2) The overall ionization is consistent with the ``warm'' X-ray continuum absorbers measured in Seyfert 1 nuclei and other QSOs. However, 3) the column densities implied by the AALs in 3C 288.1 are too low to produce significant bound-free absorption at any UV-X-ray wavelengths. Substantial X-ray absorption would require yet another zone, having a much higher ionization or a much lower velocity dispersion than the main AAL region. 4) The total hydrogen column density in the AAL gas is log N_H (cm-2)= 20.2. 5) The metallicity is roughly half solar. 6) The AALs have deconvolved widths of ~900 km/s and their centroids are consistent with no shift from the quasar systemic velocity (conservatively within +/-1000 km/s). 7) There are no direct indicators of the absorber's location in our data, but the high ionization and high metallicity both suggest a close physical relationship to the quasar/host galaxy environment. Finally, the UV continuum shape gives no indication of a ``blue bump'' at higher energies. There is a distinct break of unknown origin at ~1030 A, and the decline toward higher energies (with spectral index alpha = -1.73, for f_nu ~ nu^alpha) is even steeper than a single power-law interpolation from 1030 A to soft X-rays.Comment: 27 pages with figures and tables, in press with Ap

Multiphase Plasma in Sub-Damped Lyman Alpha Systems: A Hidden Metal Reservoir

We present a VLT/UVES spectrum of a proximate sub-damped Lyman-alpha (sub-DLA) system at z=2.65618 toward the quasar Q0331-4505 (z_qso=2.6785+/-0.0030). Absorption lines of O I, Si II, Si III, Si IV, C II, C III, C IV, Fe II, Al II, and O VI are seen in the sub-DLA, which has a neutral hydrogen column density log N(H I)=19.82+/-0.05. The absorber is at a velocity of 1820+/-250 km/s from the quasar; however, its low metallicity [O/H]=-1.64+/-0.07, lack of partial coverage, lack of temporal variations between observations taken in 2003 and 2006, and non-detection of N V imply the absorber is not a genuine intrinsic system. By measuring the O VI column density and assuming equal metallicities in the neutral and ionized gas, we determine the column density of hot ionized hydrogen in this sub-DLA, and in two other sub-DLAs with O VI drawn from the literature. Coupling this with determinations of the typical amount of warm ionized hydrogen in sub-DLAs, we confirm that sub-DLAs are a more important metal reservoir than DLAs, in total comprising at least 6-22% of the metal budget at z~2.5.Comment: 5 pages, 3 color figures, accepted for publication in ApJ

On the Search for Quasar Light Echoes

The UV radiation from a quasar leaves a characteristic pattern in the distribution of ionized hydrogen throughout the surrounding space. This pattern or light echo propagates through the intergalactic medium at the speed of light, and can be observed by its imprint on the Ly-alpha forest spectra of background sources. As the echo persists after the quasar has switched off, it offers the possibility of searching for dead quasars, and constraining their luminosities and lifetimes. We outline a technique to search for and characterize these light echoes. To test the method, we create artificial Ly-alpha forest spectra from cosmological simulations at z=3, apply light echoes and search for them. We show how the simulations can also be used to quantify the significance level of any detection. We find that light echoes from the brightest quasars could be found in observational data. With absorption line spectra of 100 redshift z~3-3.5 quasars or galaxies in a 1 square degree area, we expect that ~10 echoes from quasars with B band luminosities L_B=3x10^45 ergs/s exist that could be found at 95% confidence, assuming a quasar lifetime of ~10^7 yr. Even a null result from such a search would have interesting implications for our understanding of quasar luminosities and lifetimes.Comment: 9 pages, 7 figures, ApJ in pres

Multi-epoch intra-night optical monitoring of 8 radio-quiet BL Lac candidates

For a new sample of 8 weak-line-quasars (WLQs) we report a sensitive search in 20 intranight monitoring sessions, for blazar-like optical flux variations on hour-like and longer time scale (day/month/year$-$like). The sample consists exclusively of the WLQs that are not radio$-$loud and have either been classified as `radio-weak probable BL Lac candidates' and/or are known to have exhibited at least one episode of large, blazar$-$like optical variability. Whereas only a hint of intra$-$night variability is seen for two of these WLQs, J104833.5$+$620305.0(z = 0.219) and J133219.6$+$622715.9 (z = 3.15), statistically significant inter$-$night variability at a few per cent level is detected for three of the sources, including the radio-intermediate WLQ J133219.6$+$622715.9 (z = 3.15) and the well known bona$-$fide radio$-$quiet WLQs J121221.5$+$534128.0 (z = 3.10) and WLQ J153259.9$-$003944.1 (z = 4.62). In the rest$-$frame, this variability is intra-day and in the far$-$UV band. On the time scale of a decade, we find for three of the WLQs large brightness changes, amounting to 1.655$\pm$0.009, 0.163$\pm$0.010 and 0.144$\pm$0.018 mag, for J104833.5$+$620305.0, J123743.1$+$630144.9 and J232428.4$+$144324.4, respectively. Whereas the latter two are confirmed radio-quiet WLQs, the extragalactic nature of J104833.5$+$620305.0 remains to be well established, thanks to the absence of any feature(s) in its available optical spectra. The present study forms a part of our ongoing campaign of intranight optical monitoring of radio quiet weak-line quasars, in order to improve the understanding of this enigmatic class of Active Galactic Nuclei and to look among them for a possible tiny, elusive population of radio-quiet BL Lacs.Comment: Accepted to MNRAS. 12 pages, 1 figure, 4 Tabl