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|Paper IPM / Astronomy / 15222||
We present the results of our automatic search for proximate damped LyÎ± absorption (PDLA) systems in the quasar spectra from the Sloan Digital Sky Survey Data Release 12. We constrain our search to those PDLAs lying within 1500 km sâ1 from the quasar to make sure that the broad DLA absorption trough masks most of the strong LyÎ± emission from the broad line region (BLR) of the quasar. When the LyÎ± emission from the BLR is blocked by these so-called eclipsing DLAs, narrow LyÎ± emission from the host galaxy could be revealed as a narrow emission line (NEL) in the DLA trough. We define a statistical sample of 399 eclipsing DLAs with log N(H I) â¥ 21.10. We divide our statistical sample into three subsamples based on the strength of the NEL detected in the DLA trough. By studying the stacked spectra of these subsamples, we found that absorption from high ionization species are stronger in DLAs with stronger NEL in their absorption core. Moreover, absorption from the excited states of species like Si II are also stronger in DLAs with stronger NEL. We also found no correlation between the luminosity of the LyÎ± NEL and the quasar luminosity. These observations are consistent with a scenario in which the DLAs with stronger NEL are denser and physically closer to the quasar. We propose that these eclipsing DLAs could be the product of the interaction between infalling and outflowing gas. High resolution spectroscopic observation would be needed to shed some light on the nature of these eclipsing DLAs.
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