Variability of Low-ionization Broad Absorption Line Quasars Based on Multi-epoch Spectra from The Sloan Digital Sky Survey. (arXiv:1905.01573v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yi_W/0/1/0/all/0/1">Weimin. Yi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brandt_W/0/1/0/all/0/1">W. N. Brandt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hall_P/0/1/0/all/0/1">P. B. Hall</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vivek_M/0/1/0/all/0/1">M. Vivek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Grier_C/0/1/0/all/0/1">C. J. Grier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ak_N/0/1/0/all/0/1">N. Filiz Ak</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schneider_D/0/1/0/all/0/1">D. P. Schneider</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McGraw_S/0/1/0/all/0/1">S. M. McGraw</a>
We present absorption variability results for 134 bona fide mgii broad
absorption line (BAL) quasars at 0.46~$lesssim z lesssim$~2.3 covering days
to $sim$ 10 yr in the rest frame. We use multiple-epoch spectra from the Sloan
Digital Sky Survey, which has delivered the largest such BAL-variability sample
ever studied. mgii-BAL identifications and related measurements are compiled
and presented in a catalog. We find a remarkable time-dependent asymmetry in EW
variation from the sample, such that weakening troughs outnumber strengthening
troughs, the first report of such a phenomenon in BAL variability. Our
investigations of the sample further reveal that (i) the frequency of BAL
variability is significantly lower (typically by a factor of 2) than that from
high-ionization BALQSO samples; (ii) mgii BAL absorbers tend to have
relatively high optical depths and small covering factors along our line of
sight; (iii) there is no significant EW-variability correlation between mgii
troughs at different velocities in the same quasar; and (iv) the EW-variability
correlation between mgii and aliii BALs is significantly stronger than that
between mgii and civ BALs at the same velocities. These observational
results can be explained by a combined transverse-motion/ionization-change
scenario, where transverse motions likely dominate the strengthening BALs while
ionization changes and/or other mechanisms dominate the weakening BALs.
We present absorption variability results for 134 bona fide mgii broad
absorption line (BAL) quasars at 0.46~$lesssim z lesssim$~2.3 covering days
to $sim$ 10 yr in the rest frame. We use multiple-epoch spectra from the Sloan
Digital Sky Survey, which has delivered the largest such BAL-variability sample
ever studied. mgii-BAL identifications and related measurements are compiled
and presented in a catalog. We find a remarkable time-dependent asymmetry in EW
variation from the sample, such that weakening troughs outnumber strengthening
troughs, the first report of such a phenomenon in BAL variability. Our
investigations of the sample further reveal that (i) the frequency of BAL
variability is significantly lower (typically by a factor of 2) than that from
high-ionization BALQSO samples; (ii) mgii BAL absorbers tend to have
relatively high optical depths and small covering factors along our line of
sight; (iii) there is no significant EW-variability correlation between mgii
troughs at different velocities in the same quasar; and (iv) the EW-variability
correlation between mgii and aliii BALs is significantly stronger than that
between mgii and civ BALs at the same velocities. These observational
results can be explained by a combined transverse-motion/ionization-change
scenario, where transverse motions likely dominate the strengthening BALs while
ionization changes and/or other mechanisms dominate the weakening BALs.
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