Evidence for Photoionization Driven Broad Absorption Line Variability

We present a qualitative analysis of the variability of quasar broad absorption lines using the large multi-epoch spectroscopic dataset of the Sloan Digital Sky Survey Data Release 10. We confirm that variations of absorption lines are highly coordinated among different components of the same ion or the same absorption component of different ions for C IV, Si IV and N V. Furthermore, we show that the equivalent widths of the lines decrease or increase statistically when the continuum brightens or dims. This is further supported by the synchronized variations of emission and absorption line equivalent width, when the well established intrinsic Baldwin effect for emission lines is taken into account. We find that the emergence of an absorption component is usually accompanying with dimming of the continuum while the disappearance of an absorption line component with brightening of the continuum. This suggests that the emergence or disappearance of a C IV absorption component is only the extreme case, when the ionic column density is very sensitive to continuum variations or the continuum variability amplitude is larger. These results support the idea that absorption line variability is driven mainly by changes in the gas ionization in response to continuum variations, that the line-absorbing gas is highly ionized, and in some extreme cases, too highly ionized to be detected in UV absorption lines. Due to uncertainties in the spectroscopic flux calibration, we cannot quantify the fraction of quasars with asynchronized continuum and absorption line variations.Comment: 41 pages, 15 figures, accepted to Ap

The asymmetric effect of plasma response to variation of quasar radiation

Plasma is prevalent throughout the universe. The cosmic plasma serves as not only a crucial tracer for studying the evolution of the cosmos but also an ideal laboratory for investigating the properties of plasma in extreme conditions. As one of the important contributors to the re-ionization of the universe, the variability in quasar (driven by the supermassive black hole) radiation presents a convenient opportunity to study the response of gases ionized by them. Based on extensive statistical analysis using data from the Sloan Digital Sky Survey (SDSS), it has been demonstrated that the response of gases to quasar radiation exhibits asymmetry. Specifically, over 70\% of broad absorption lines (BALs) gas in quasar host galaxies exhibit a negative response. Through analytical calculations and photoionization simulations of C IV, we found that the response of gases to radiation is asymmetric for low and high ionization states. In high ionization states, the response time scale is shorter, leading to the detection of more negative responses. In actual case, the observation time interval is mostly greater than 1 day, and hence the asymmetric effect of the C IV response gives a typical gas density of upper limit of $\rm 10^7\ cm^{-3}$. Interestingly, this is consistent with the fact that most of the measured BAL gas densities are below $\rm 10^7\ cm^{-3}$. In principle, the detection of this asymmetric effect becomes easier with lower plasma density or shorter observation time intervals.Comment: 7 pages, 5 figures, comments welcom

Outflow and hot dust emission in high redshift quasars

Correlations of hot dust emission with outflow properties are investigated, based on a large z~2 non-broad absorption lines quasar sample built from the Wide-field Infrared Survey and the Sloan Digital Sky Survey data releases. We use the near infrared slope and the infrared to UV luminosity ratio to indicate the hot dust emission relative to the emission from the accretion disk. In our luminous quasars, these hot dust emission indicators are almost independent of the fundamental parameters, such as luminosity, Eddington ratio and black hole mass, but moderately dependent on the blueshift and asymmetry index (BAI) and full width at half-maximum (FWHM) of CIV lines. Interestingly, the latter two correlations dramatically strengthen with increasing Eddington ratio. We suggest that, in high Eddington ratio quasars, CIV regions are dominated by outflows so the BAI and FWHM(CIV) can reliably reflect the general properties and velocity of outflows, respectively. While in low Eddington ratio quasars, CIV lines are primarily emitted by virialized gas so the BAI and FWHM(CIV) become less sensitive to outflows. Therefore, the correlations for the highest Eddington ratio quasars are more likely to represent the true dependence of hot dust emission on outflows and the correlations for the entire sample are significantly diluted by the low Eddington ratio quasars. Our results show that an outflow with a large BAI or velocity can double the hot dust emission on average. We suggest that outflows either contain hot dust in themselves or interact with the dusty interstellar medium or torus.Comment: 14 page, 4 figures, accepted for publication in ApJ