Metallicities and dust content of proximate damped Lyman alpha systems in the Sloan Digital Sky Survey

Composite spectra of 85 proximate absorbers (log N(HI)>20 and velocity difference between the absorption and emission redshift, dv<10,000 km/s) in the SDSS are used to investigate the trends of metal line strengths with velocity separation from the QSO. We construct composites in 3 velocity bins: dv<3000 km/s, 30006000 km/s, with further sub-samples to investigate the metal line dependence on N(HI) and QSO luminosity. Low (e.g. SiII and FeII) and high ionization (e.g. SiIV and CIV) species alike have equivalent widths (EWs) that are larger by factors of 1.5 -- 3 in the dv<3000 km/s composite, compared to the dv>6000 km/s spectrum. The EWs show an even stronger dependence on dv if only the highest neutral hydrogen column density (log N(HI)>20.7) absorbers are considered. We conclude that PDLAs generally have higher metallicities than intervening absorbers, with the enhancement being a function of both dv and N(HI). It is also found that absorbers near QSOs with lower rest-frame UV luminosities have significantly stronger metal lines. We speculate that absorbers near to high luminosity QSOs may have had their star formation prematurely quenched. Finally, we search for the signature of dust reddening by the PDLAs, based on an analysis of the QSO continuum slopes relative to a control sample and determine a limit of E(B-V)<0.014 for an SMC extinction curve. This work provides an empirical motivation for distinguishing between proximate and intervening DLAs, and establishes a connection between the QSO environment and galaxy properties at high redshifts.Comment: Accepted for publication in MNRA

Searching for Dust Reddening in SDSS Spectra with Damped Lyman α\alpha{} Systems

We searched for evidence of reddening of background SDSS QSO spectra due to dust in intervening DLA systems. We utilise the Data Releases 5 and 7 to arrive at sample sizes of 475 (DR5) and 676 (DR7) absorbers, based on two different published lists of SDSS DLAs. Both samples span roughly the redshift range of 2.2 < z_abs < 5.2, with a mean of z~3.0, and the majority of the DLAs (75%) below z=3.3. We construct geometric mean spectra in the absorber restframes ranging from 1240 to ~2800 A, and composite spectra of samples matching the 'DLA' QSOs in i band magnitude and emission redshift z_em, but without absorption lines. By comparing the slopes of these composite spectra with their matched counterparts, we find no sign of reddening in the ensemble of the absorbers from these samples. Owing to both the unprecedently large sizes of the DLA samples themselves and the non-DLA SDSS QSO sample, from which we can draw our matching spectra, we can place very tight limits for this non-detection ( =-0.0013+-0.0025 (DR5) and =-0.0017+-0.0022 (DR7). Interestingly, when applying our technique to the samples of York et. al. (2006), vandenBerk et al. (2008) (intervening and intrinsic MgII absorbers) and the smaller DLA-subsample and pool of comparison QSOs of Vladilo et al. (2008), we do recover their results, i.e. detect the same amount of reddening as these authors do. Furthermore, we have tested whether subsamples of our large sample in categories involving the absorbers (HI column densities, presence or absence of accompanying metal absorption, absorber redshift) or the background quasars (emission redshift, brightness) do reveal dust extinction, but found no trends. These results are at odds with both detections of dust reddening from previous studies, and also with expectations from observations of high-redshift galaxies. (abridged)Comment: 16 pages, 12 figures, accepted for publication in MNRA

Precious Metals in SDSS Quasar Spectra I: Tracking the Evolution of Strong, 1.5 < z < 4.5 CIV Absorbers with Thousands of Systems

We have vastly increased the CIV statistics at intermediate redshift by surveying the thousands of quasars in the Sloan Digital Sky Survey Data-Release 7. We visually verified over 16,000 CIV systems with 1.46 < z < 4.55---a sample size that renders Poisson error negligible. Detailed Monte Carlo simulations show we are approximately 50% complete down to rest equivalent widths W_r ~ 0.6 \AA. We analyzed the sample as a whole and in ten small redshift bins with approximately 1500 doublets each. The equivalent width frequency distributions f(W_r) were well modeled by an exponential, with little evolution in shape. In contrast with previous studies that modeled the frequency distribution as a single power law, the fitted exponential gives a finite mass density for the CIV ions. The co-moving line density dN_CIV/dX evolved smoothly with redshift, increasing by a factor of 2.37+/-0.09 from z = 4.55 to 1.96, then plateauing at dN_CIV/dX ~ 0.34 for z = 1.96 to 1.46. Comparing our SDSS sample with z < 1 (ultraviolet) and z > 5 (infrared) surveys, we see an approximately 10-fold increase in dN_CIV/dX over z ~ 6 --> 0, for W_r >= 0.6 \AA. This suggests a monotonic and significant increase in the enrichment of gas outside galaxies over the 12 Gyr lifetime of the universe.Comment: 17 pages (emulateapj), 13 figures, 4 tables; accepted to ApJ and in press; also see http://igmabsorbers.inf

Star Formation Feedback and Metal Enrichment History Of The Intergalactic Medium

Using hydrodynamic simulations we compute the metal enrichment history of the intergalactic medium (IGM). We show that galactic superwind (GSW) feedback can transport metals to the IGM and that the properties of simulated metal absorbers match observations. The distance of influence of GSW is typically limited to >0.5Mpc and within regions of overdensity >10. Most CIV and OVI absorbers are located within shocked regions of elevated temperature (T>2x10^4K), overdensity (>10), and metallicity ([-2.5,-0.5]). OVI absorbers have typically higher metallicity, lower density and higher temperature than CIV absorbers. For OVI absorbers collisional ionization dominates over the entire redshift range z=0-6, whereas for CIV absorbers the transition occurs at moderate redshift z~3 from collisionally dominated to photoionization dominated. We find that the observed column density distributions for CIV and OVI in the range log N cm^2=12-15 are reasonably reproduced by the simulations. The evolution of mass densities contained in CIV and OVI lines, Omega_CIV and Omega_OVI, is also in good agreement with observations, which shows a near constancy at low redshifts and an exponential drop beyond redshift z=3-4. For both CIV and OVI, most absorbers are transient and the amount of metals probed by CIV and OVI lines of column log N cm^2=12-15 is only ~2% of total metal density at any epoch. While gravitational shocks from large-scale structure formation dominate the energy budget (80-90%) for turning about 50% of IGM to the warm-hot intergalactic medium (WHIM) by z=0, GSW feedback shocks are energetically dominant over gravitational shocks at z > 1-2. Most of the so-called "missing metals" at z=2-3 are hidden in a warm-hot (T=10^{4.5-7}K) gaseous phase, heated up by GSW feedback shocks. Their mass distribution is broadly peaked at $\delta=1-10$ in the IGM, outside virialized halos.Comment: 52 pages, 26 figures, published in the Astrophysical Journal, 2011, ApJ, 731, 1

Discovery of a compact gas-rich DLA galaxy at z = 2.2: evidences for a starburst-driven outflow

We present the detection of Ly-alpha, [OIII] and H-alpha emission associated with an extremely strong DLA system (N(HI) = 10^22.10 cm^-2) at z=2.207 towards the quasar SDSS J113520-001053. This is the largest HI column density ever measured along a QSO line of sight, though typical of what is seen in GRB-DLAs. This absorption system also classifies as ultrastrong MgII system with W2796_r=3.6 A. The mean metallicity of the gas ([Zn/H]=-1.1) and dust depletion factors ([Zn/Fe]=0.72, [Zn/Cr]=0.49) are consistent with (and only marginally larger than) the mean values found in the general QSO-DLA population. The [OIII]-Ha emitting region has a very small impact parameter with respect to the QSO line of sight, b=0.1", and is unresolved. From the Ha line, we measure SFR=25 Msun/yr. The Ly-a line is double-peaked and is spatially extended. More strikingly, the blue and red Ly-a peaks arise from distinct regions extended over a few kpc on either side of the star-forming region. We propose that this is the consequence of Ly-a transfer in outflowing gas. The presence of starburst-driven outflows is also in agreement with the large SFR together with a small size and low mass of the galaxy (Mvir~10^10 Msun). From the stellar UV continuum luminosity of the galaxy, we estimate an age of at most a few 10^7 yr, again consistent with a recent starburst scenario. We interpret the data as the observation of a young, gas rich, compact starburst galaxy, from which material is expelled through collimated winds powered by the vigorous star formation activity. We substantiate this picture by modelling the radiative transfer of Ly-a photons in the galactic counterpart. Though our model (a spherical galaxy with bipolar outflowing jets) is a simplistic representation of the true gas distribution and velocity field, the agreement between the observed and simulated properties is particularly good. [abridged]Comment: 15 pages, 18 figures, 4 tables, accepted for publication in Astronomy and Astrophysic

Hyperaccreting Neutron-Star Disks and Neutrino Annihilation

Newborn neutron stars surrounded by hyperaccreting and neutrino-cooled disks may exist in some gamma-ray bursts (GRBs) and/or supernovae (SNe). In this paper we further study the structure of such a neutron-star disk based on the two-region (i.e., inner & outer) disk scenario following our previous work, and calculate the neutrino annihilation luminosity from the disk in various cases. We investigate the effects of the viscosity parameter, energy parameter (measuring the neutrino cooling efficiency of the inner disk) and outflow strength on the structure of the entire disk as well as the effect of emission from the neutron star surface boundary emission on the total neutrino annihilation rate. The inner disk satisfies the entropy-conservation or the advection-dominated self-similar structure depending on the energy parameter. An outflow from the disk decreases the density and pressure but increases the thickness of the disk. Moreover, compared with the black-hole disk, the neutrino annihilation luminosity above the neutron-star disk is higher, and the neutrino emission from the boundary layer could increase the neutrino annihilation luminosity by about one order of magnitude higher than the disk without boundary emission. The neutron-star disk with the advection-dominated inner disk could produce the highest neutrino luminosity while the disk with an outflow has the lowest. Although a heavily mass-loaded outflow from the neutron star surface at early times of neutron star formation prevents the outflow material from being accelerated to a high bulk Lorentz factor, an energetic ultrarelativistic jet via neutrino annihilation can be produced above the stellar polar region at late times if the disk accretion rate and the neutrino emission luminosity from the surface boundary layer are sufficiently high.Comment: 46 pages, 11 figures, 4 tables, improved version following the referee's comments, accepted for publication in Ap

Non variability of intervening absorbers observed in the UVES spectra of the "naked-eye" GRB080319

The aim of this paper is to investigate the properties of the intervening absorbers lying along the line of sight of Gamma-Ray Burst (GRB) 080319B through the analysis of its optical absorption features. To this purpose, we analyze a multi-epoch, high resolution spectroscopic observations (R=40000, corresponding to 7.5 km/s) of the optical afterglow of GRB080319B (z=0.937), taken with UVES at the VLT. Thanks to the rapid response mode (RRM), we observed the afterglow just 8m:30s after the GRB onset when the magnitude was R ~ 12. This allowed us to obtain the best signal-to-noise, high resolution spectrum of a GRB afterglow ever (S/N per resolution element ~ 50). Two further RRM and target of opportunity observations were obtained starting 1.0 and 2.4 hours after the event, respectively. Four MgII absorption systems lying along the line of sight to the afterglow have been detected in the redshift range 0.5 < z < 0.8, most of them showing a complex structure featuring several components. Absorptions due to FeII, MgI and MnII are also present; they appear in four, two and one intervening absorbers, respectively. One out of four systems show a MgII2796 rest frame equivalent width larger than 1A. This confirms the excess of strong MgII absorbers compared to quasars, with dn/dz = 0.9, ~ 4 times larger than the one observed along quasar lines of sight. In addition, the analysis of multi-epoch, high-resolution spectra allowed us to exclude a significant variability in the column density of the single components of each absorber. Combining this result with estimates of the size of the emitting region, we can reject the hypothesis that the difference between GRB and QSO MgII absorbers is due to a different size of the emitting regions.Comment: 10 pages, 15 ps figures, submitted to MNRA

The Nature and Origin of Low-Redshift O VI Absorbers

The O VI ion observed in quasar absorption line spectra is the most accessible tracer of the cosmic metal distribution in the low redshift (z<0.5) intergalactic medium (IGM). We explore the nature and origin of O VI absorbers using cosmological hydrodynamic simulations including galactic outflows. We consider the effects of ionization background variations, non-equilibrium ionization and cooling, uniform metallicity, and small-scale (sub-resolution) turbulence. Our main results are 1) IGM O VI is predominantly photo-ionized with T= 10^(4.2+/-0.2) K. A key reason for this is that O VI absorbers preferentially trace over-enriched regions of the IGM at a given density, which enhances metal-line cooling such that absorbers can cool within a Hubble time. As such, O VI is not a good tracer of the WHIM. 2) The predicted O VI properties fit observables only if sub-resolution turbulence is added. The required turbulence increases with O VI absorber strength such that stronger absorbers arise from more recent outflows with turbulence dissipating on the order of a Hubble time. The amount of turbulence is consistent with other examples of turbulence observed in the IGM and galactic halos. 3) Metals traced by O VI and H I do not trace exactly the same baryons, but reside in the same large-scale structure. Observed alignment statistics are reproduced in our simulations. 4) Photo-ionized O VI traces gas in a variety of environments, and is not directly associated with the nearest galaxy, though is typically nearest to ~0.1L* galaxies. Weaker O VI components trace some of the oldest cosmic metals. 5) Very strong absorbers are more likely to be collisionally ionized, tracing more recent enrichment (<2 Gyr) within or near galactic halos.Comment: 33 pages, 18 figures, accepted to MNRAS. Two new figures adde

Acute exposure to nocturnal train noise induces endothelial dysfunction and pro-thromboinflammatory changes of the plasma proteome in healthy subjects

Nocturnal train noise exposure has been associated with hypertension and myocardial infarction. It remains unclear whether acute nighttime train exposure may induce subclinical atherosclerosis, such as endothelial dysfunction and other functional and/or biochemical changes. Thus, we aimed to expose healthy subjects to nocturnal train noise and to assess endothelial function, changes in plasma protein levels and clinical parameters. In a randomized crossover study, we exposed 70 healthy volunteers to either background or two different simulated train noise scenarios in their homes during three nights. After each night, participants visited the study center for measurement of vascular function and assessment of other biomedical and biochemical parameters. The three nighttime noise scenarios were exposure to either background noise (control), 30 or 60 train noise events (Noise30 or Noise60), with average sound pressure levels of 33, 52 and 54 dB(A), respectively. Flow-mediated dilation (FMD) of the brachial artery was 11.23 ± 4.68% for control, compared to 8.71 ± 3.83% for Noise30 and 8.47 ± 3.73% for Noise60 (p < 0.001 vs. control). Sleep quality was impaired after both Noise30 and Noise60 nights (p < 0.001 vs. control). Targeted proteomic analysis showed substantial changes of plasma proteins after the Noise60 night, mainly centered on redox, pro-thrombotic and proinflammatory pathways. Exposure to simulated nocturnal train noise impaired endothelial function. The proteomic changes point toward a proinflammatory and pro-thrombotic phenotype in response to nocturnal train noise and provide a molecular basis to explain the increased cardiovascular risk observed in epidemiological noise studies

Chasing the heaviest black holes of jetted Active Galactic Nuclei

We investigate the physical properties of the 10 blazars at redshift greater than 2 detected in the 3-years all sky survey performed by the Burst Alert Telescope (BAT) onboard the Swift satellite. We find that the jets of these blazars are among the most powerful known. Furthermore, the mass of their central black hole, inferred from the optical-UV bump, exceeds a few billions of solar masses, with accretion luminosities being a large fraction of the Eddington one. We compare their properties with those of the brightest blazars of the 3-months survey performed by the Large Area Telescope (LAT) onboard the Fermi satellite. We find that the BAT blazars have more powerful jets, more luminous accretion disks and larger black hole masses than LAT blazars. These findings can be simply understood on the basis of the blazar sequence, that suggests that the most powerful blazars have a spectral energy distribution with a high energy peak at MeV (or even sub-MeV) energies. This implies that the most extreme blazars can be found more efficiently in hard X-rays, rather than in the high energy gamma-ray band. We then discuss the implications of our findings for future missions, such as the New Hard X-ray Mission (NHXM) and especially the Energetic X-ray Imaging Survey Telescope (EXIST) mission which, during its planned 2 years all sky survey, is expected to detect thousands of blazars, with a few of them at z greater than 6.Comment: Accepted for publication in MNRAS. Absorption due to Lyman-alpha clouds calculated, and optical-UV data de-absorbed. 16 figures, 15 page