63 research outputs found

    Molecular hydrogen from z = 0.0963 DLA towards the QSO J1619+3342

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    We report the detection of H2 in a zabs= 0.0963 Damped Lyman-{\alpha} (DLA) system towards zem = 0.4716 QSO J1619+3342. This DLA has log N(H I) = 20.55 (0.10), 18.13 < log N(H2) < 18.40, [S/H] = -0.62 (0.13), [Fe/S] = -1.00 (0.17) and the molecular fraction -2.11 < log f(H2) < -1.85. The inferred gas kinetic temperature using the rotational level population is in the range 95 - 132 K. We do not detect C I or C II* absorption from this system. Using R- and V-band deep images we identify a sub-L* galaxy at an impact parameter of 14 kpc from the line of sight, having consistent photometric redshift, as a possible host for the absorber. We use the photoionization code CLOUDY to get the physical conditions in the H2 component using the observational constrains from H2, C I, C II* and Mg I. All the observations can be consistently explained if one or more of the following is true: (i) Carbon is underabundant by more than 0.6 dex as seen in halo stars with Z ~ 0.1 Z_sun, (ii) H I associated with H2 component is less than 50% of the H I measured along the line of sight and (iii) the H2 formation rate on the dust grains is at least a factor two higher than what is typically used in analytic calculations for Milky Way interstellar medium. Even when these are satisfied, the gas kinetic temperature in the models are much lower than what is inferred from the ortho-to-para ratio of the molecular hydrogen. Alternatively the high kinetic temperature could be a consequence of contribution to the gas heating from non-radiative heating processes seen in hydrodynamical simulations.Comment: 10 pages, 4 figues, resubmitted to the MNRAS after minor revision suggested by the refere

    Discovery of an HI-rich Gas Reservoir in the Outskirts of SZ-effect Selected Clusters

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    We report on the detection of three strong HI absorbers originating in the outskirts (i.e., impact parameter, ρclβ‰ˆ(1.6βˆ’4.7)r500\rho_{\rm cl} \approx (1.6-4.7) r_{500}) of three massive (M500∼3Γ—1014MβŠ™M_{500}\sim3\times10^{14} M_{\odot}) clusters of galaxies at redshift zclβ‰ˆ0.46z_{\rm cl} \approx 0.46, in the HubbleSpaceTelescopeHubble Space Telescope Cosmic Origins Spectrograph (HSTHST/COS) spectra of 3 background UV-bright quasars. These clusters were discovered by the 2500 deg2^2 South Pole Telescope Sunyaevβˆ’-Zel'dovich (SZ) effect survey. All three COS spectra show partial Lyman limit absorber with N(HI)>1016.5Β cmβˆ’2N(HI) > 10^{16.5} \ \rm cm^{-2} near the photometric redshifts (βˆ£Ξ”z/(1+z)βˆ£β‰ˆ0.03|\Delta z/(1+z)| \approx 0.03) of the clusters. The compound probability of random occurrence of all three absorbers is <0.02<0.02%, indicating that the absorbers are most likely related to the targeted clusters. We find that the outskirts of these SZ-selected clusters are remarkably rich in cool gas compared to existing observations of other clusters in the literature. The effective Doppler parameters of the Lyman series lines, obtained using single cloud curve-of-growth (COG) analysis, suggest a non-thermal/turbulent velocity of a few Γ—10Β kmsβˆ’1\times10 \ \rm km s^{-1} in the absorbing gas. We emphasize the need for uniform galaxy surveys around these fields and for more UV observations of QSO-cluster pairs in general in order to improve the statistics and gain further insights into the unexplored territory of the largest collapsed cosmic structures.Comment: Accepted for publication in ApJ Letters (6 pages

    Implications of an updated ultraviolet background for the ionization mechanisms of intervening Ne VIII absorbers

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    Ne VIII absorbers seen in QSO spectra are useful tracers of warm ionized gas, when collisional ionization is the dominant ionization process. While photoionization by the ultraviolet background (UVB) is a viable option, it tends to predict large line-of-sight thickness for the absorbing gas. Here, we study the implications of the recently updated UVB at low-z to understand the ionization mechanisms of intervening Ne VIII absorbers. With the updated UVB, one typically needs higher density and metallicity to reproduce the observed ionic column densities under photoionization. Both reduce the inferred line-of-sight thicknesses of the absorbers. We find a critical density of β‰₯5Γ—10βˆ’5\geq5\times10^{-5} cmβˆ’3^{-3} above which the observed N(Ne VIII)/N(O VI) can be reproduced by pure collisional processes. If the gas is of near solar metallicity (as measured for the low ions) then the cooling timescales will be small (<10810^{8} yrs). Therefore, a continuous injection of heat is required in order to enhance the detectability of the collisionally ionized gas. Using photoionization models we find that in almost all Ne VIII systems the inferred low ion metallicity is near solar or supersolar. If we assume the Ne VIII phase to have similar metallicities then photoionization can reproduce the observed N(Ne VIII)/N(O VI) without the line-of-sight thickness being unreasonably large and avoids cooling issues related to the collisional ionization at these metallicities. However the indication of broad LyΞ±\alpha absorption in a couple of systems, if true, suggests that the Ne VIII phase is distinct from the low ion phase having much lower metallicity.Comment: 11 pages, 5 figures, 2 tables. Accepted for publication in MNRA

    MUSEQuBES: The relation between LyΞ±\alpha emitters and C IV absorbers at zβ‰ˆ3.3z \approx 3.3

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    We present a detailed study of the column density and covering fraction profiles of C IV absorption around 86 redshift zβ‰ˆ3.3z \approx 3.3 LyΞ±\alpha emitters (LAEs) detected in 8 Multi-Unit Spectroscopic Explorer (MUSE) fields of 1β€²Γ—1β€²1'\times 1' centered on 8 bright background quasars as part of the MUSEQuBES survey. Using Voigt profile fitting of all the C IV absorbers detected along these 8 sightlines, we generated a ``blind'' absorbers' catalog consisting of 489 C IV absorption components. We cross-matched this blind C IV catalog with the MUSE-detected LAE catalog and found a significant enhancement of C IV components within β‰ˆΒ±\approx \pm400 km sβˆ’1\rm km\, s^{-1} of the systemic redshifts of the LAEs. Neither the C IV column density (NN) nor the Doppler parameter (bb) of individual C IV components shows any significant anti-correlation with impact parameter (ρ\rho) of the LAEs in the 68 percentile range of 90≀ρ≀23090\leq \rho \leq 230 physical kpc (pkpc). We find a covering fraction of β‰ˆ60%\approx 60\% for a threshold NN(C IV) of 1012.5 cmβˆ’210^{12.5}\, \rm \rm cm^{-2}, which is roughly twice as high as in random regions. The C IV covering fraction remains constant at β‰ˆ50%\approx50\% for impact parameters in the range 150--250~pkpc (β‰ˆ3βˆ’6R200\approx 3-6 R_{200}). Using the covering fraction profile, we constrained the LAE--C IV absorber two-point correlation function, and obtained r0=3.2Β hβˆ’1r_0 = 3.2~h^{-1} comoving Mpc (cMpc) and Ξ³=1.2\gamma = 1.2 for a threshold NN(C IV) of 1013.0 cmβˆ’210^{13.0}\, \rm cm^{-2}. The C IV covering fraction is found to be enhanced for the LAEs that are part of a ``pair/group'' compared to the isolated ones.Comment: 18 (+15 in the appendix) pages, 15 (+2 in the appendix) figures. Submitted to MNRA

    The Extreme Ultraviolet Variability of Quasars

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    We study the extreme ultraviolet (EUV) variability (rest frame wavelengths 500 - 920 A˚\AA) of high luminosity quasars using HST (low to intermediate redshift sample) and SDSS (high redshift sample) archives. The combined HST and SDSS data indicates a much more pronounced variability when the sampling time between observations in the quasar rest frame is >2Γ—107> 2\times 10^{7} sec compared to <1.5Γ—107< 1.5\times 10^{7} sec. Based on an excess variance analysis, for time intervals <2Γ—107< 2\times 10^{7} sec in the quasar rest frame, 10%10\% of the quasars (4/40) show evidence of EUV variability. Similarly, for time intervals >2Γ—107>2\times 10^{7} sec in the quasar rest frame, 55%55\% of the quasars (21/38) show evidence of EUV variability. The propensity for variability does not show any statistically significant change between 2.5Γ—1072.5\times 10^{7} sec and 3.16Γ—1073.16\times 10^{7} sec (1 yr). The temporal behavior is one of a threshold time interval for significant variability as opposed to a gradual increase on these time scales. A threshold time scale can indicate a characteristic spatial dimension of the EUV region. We explore this concept in the context of the slim disk models of accretion. We find that for rapidly spinning black holes, the radial infall time to the plunge region of the optically thin surface layer of the slim disk that is responsible for the preponderance of the EUV flux emission (primarily within 0 - 7 black hole radii from the inner edge of the disk) is consistent with the empirically determined variability time scale.Comment: To appear in Ap
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