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Register a new userObservations of Lyman-alpha Absorption in a Triple Quasar System
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P. A. Young Stewardn Observatory
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We have obtained follow-up observations of the quasar pair LBQS 0107-025A,B and new observations of the nearby quasar LBQS 0107-0232 with the Hubble Space Telescope Faint Object Spectrograph. Extended wavelength coverage of LBQS 0107-025A and B using the G270H grating was also obtained. This triple system is unique in providing sensitivity to coherent Ly-alpha absorption on transverse scales of approximately 1 Mpc at z < 1. Monte Carlo simulations were used to establish the confidence level for matches between absorption features in different lines of sight as a function of velocity separation. Pairwise, there are 8, 9, and 12 lines that match between spectra. Three instances of matches between all three lines of sight were found with velocity separations of less than 550 kms^-1. Two of the pairings have coincident lines within |Delta v| < 200 kms^-1 that would occur with less than 10% probability by chance. Taking into account the equivalent widths of the lines, one of these triple coincidences is significant at the 99.99% confidence level, based on Monte Carlo simulations with random line placements. Matches with strong lines preferentially have small velocity separations. These same simulations are used to demonstrate that the distribution of matches for a population of absorbers randomly distributed in velocity space is peaked toward |Delta v| = 0, which has implications for the statistical significance of matches. One of the triple coincidences appears to be a strong absorber with a sheet-like, but inhomogeneous, geometry and a coherence length approaching or exceeding 1 Mpc.
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We report on the discovery of a bright Lyman alpha blob associated with the z=3 quasar SDSSJ124020.91+145535.6 which is also coincident with strong damped Lyman alpha absorption from a foreground galaxy (a so-called proximate damped Lyman alpha system; PDLA). The one dimensional spectrum acquired by the Sloan Digital Sky Survey (SDSS) shows a broad Lyman alpha emission line with a FWHM ~ 500 km/s and a luminosity of L_{Lya} = 3.9e43 erg/s superposed on the trough of the PDLA. Mechanisms for powering this large Lyman alpha luminosity are discussed. We argue against emission from HII regions in the PDLA galaxy since this requires an excessive star-formation rate ~ 500 Msun/yr and would correspond to the largest Lyman alpha luminosity ever measured from a damped Lyman alpha system or starburst galaxy. We use a Monte Carlo radiative transfer simulation to investigate the possibility that the line emission is fluorescent recombination radiation from the PDLA galaxy powered by the ionizing flux of the quasar, but find that the predicted Lyman alpha flux is several orders of magnitude lower than observed. We conclude that the Lyman alpha emission is not associated with the PDLA galaxy at all, but instead is intrinsic to the quasars host and similar to the extended Lyman alpha fuzz which is detected around many AGN. PDLAs are natural coronagraphs that block their background quasar at Lyman alpha, and we discuss how systems similar to SDSSJ124020.91+145535.6 might be used to image the neutral hydrogen in the PDLA galaxy in silhouette against the screen of extended Lyman alpha emission from the background quasar.
We have observed three quasars, PKS 1127-145, Q 1331+171 and Q0054+144, with the ACIS-S aboard the Chandra X-ray Observatory, in order to measure soft X-ray absorption associated with intervening 21-cm and damped Ly$alpha$ absorbers. For PKS 1127-145, we detect absorption which, if associated with an intervening z_{abs}=0.312 absorber, implies a metallicity of 23% solar. If the absorption is not at z_{abs}=0.312, then the metallicity is still constrained to be less than 23% solar. The advantage of the X-ray measurement is that the derived metallicity is insensitive to ionization, inclusion of an atom in a molecule, or depletion onto grains. The X-ray absorption is mostly due to oxygen, and is consistent with the oxygen abundance of 30% solar derived from optical nebular emission lines in a foreground galaxy at the redshift of the absorber. For Q1331+171 and Q 0054+144, only upper limits were obtained, although the exposure times were intentionally short, since for these two objects we were interested primarily in measuring flux levels to plan for future observations. The imaging results are presented in a companion paper.
We have identified a new Lyman limit absorption system towards PKS1937-1009, with log N(HI)=18.25 +/- 0.02 at z=3.256. It is suitable for measuring D/H, and we find a 68.3% confidence range for D/H of 1.6^{+0.25}_{-0.30} times 10^{-5}, and a 95.4% range of 1.6^{+0.5}_{-0.4} times 10^{-5}. The metallicity of the cloud where D/H was measured is low, [Si/H] = -2.0 +/- 0.5. At these metallicities we expect that D/H will be close to the primordial value. Our D/H disagrees at a level of 99.4% with the predicted D/H using the baryon density calculated from the cosmic background radiation measured by WMAP, 2.60^{+0.19}_{-0.17} times 10^{-5}. Our result also exacerbates the scatter in D/H values around the mean primordial D/H.
We present a new ultra-violet spectrum of the QSO 0013-004 with 0.9 AA resolution obtained with the MMT Blue spectrograph. The upsilon = 0 - 0, 1 - 0, 2 - 0 and 3 - 0 Lyman bands of H_2 associated with the z = 1.9731 damped Ly alpah absorption line system have been detected. The H_2 column density is N(H_2) = 6.9 (pm 1.6)times 10^{19} cm^{-2}, and the Doppler parameter b = 15pm 2 km/s. The populations of different rotational levels are measured and used to derive the excitation temperatures. The estimated kinetic temperature T_Ksim 70 K, and the total particle number density n(H) sim 300 cm^{-3}. The UV photoabsorption rate $beta_0 sim 6.7times 10^{-9}$ s^{-1}, about a factor of few times greater than that in a typical diffuse Milky Way interstellar cloud. The total hydrogen column density is $N(H) = 6.4(pm 0.5)times 10^{20} cm^{-2}$. The fractional H_2 abundance f = 2N(H_2)/(2N(H_2) + N(H I)) sim 0.22 pm 0.05 is the highest among all observed damped Lyal absorbers. The high fractional H_2 abundance is consistent with the inferred presence of dust and strong C I absorption in this absorber.
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