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تسجيل مستخدم جديدBroad Balmer-line Absorption in SDSS J172341.10+555340.5
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Kentaro Aoki
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I present the discovery of Balmer-line absorption from H alpha to H9 in iron low-ionizaton broad absorption line (FeLoBAL) quasar, SDSS~J172341.10+555340.5 by near-infrared spectroscopy with the Cooled Infrared Spectrograph and Camera for OHS (CISCO) attached to the Subaru telescope. The redshift of the Balmer-line absorption troughs is 2.0530 +/- 0.0003, and it is blueshifted by 5370 km s^{-1} from the Balmer emission lines. It is more than $4000$ km s^{-1} blueshifted from the previously known UV absorption lines. I detect relatively strong (EW_rest=20A) [O III] emission lines which are similar to those found in other broad absorption line quasars with Balmer-line absorption. I derived a column density of neutral hydrogen of 5.2x10^{17} cm^{-2} by using the curve of growth and taking account of Ly alpha trapping. I searched for UV absorption lines which have the same redshift with Balmer-line absorption. I found Al II} and Fe III absorption lines at z=2.053 which correspond to previously unidentified absorption lines, and the presence of other blended troughs that were difficult to identify.
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I report the discovery of blueshifted broad absorption line (BAL) troughs in at least six transitions of the Balmer series of hydrogen (Hbeta to H9) and in CaII, MgII and excited FeII in the quasar SDSS J125942.80+121312.6. This is only the fourth ac
tive galactic nucleus known to exhibit Balmer absorption, all four in conjunction with low-ionization BAL systems containing excited Fe II. The substantial population in the n=2 shell of H I in this quasars absorber likely arises from Ly-alpha trapping. In an absorber sufficiently optically thick to show Balmer absorption, soft X-rays from the quasar penetrate to large tau_Lyalpha and ionize H I. Recombination then creates Ly-alpha photons that increase the n=2 population by a factor tau_Lyalpha since they require about tau_Lyalpha scatterings to diffuse out of the absorber. Observing Ly-alpha trapping in a quasar absorber requires a large but Compton-thin column of gas along our line of sight which includes substantial H I but not too much dust. Presumably the rarity of Balmer-line BAL troughs reflects the rarity of such conditions in quasar absorbers.
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