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Register a new userProbing the Origins of the CIV and Fe Kalpha Baldwin Effect
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We use UV/optical and X-ray observations of 272 radio-quiet Type 1 AGNs and quasars to investigate the CIV Baldwin Effect (BEff). The UV/optical spectra are drawn from the Hubble Space Telescope, International Ultraviolet Explorer and Sloan Digital Sky Survey archives. The X-ray spectra are from the Chandra and XMM-Newton archives. We apply correlation and partial-correlation analyses to the equivalent widths, continuum monochromatic luminosities, and alpha_ox, which characterizes the relative X-ray to UV brightness. The equivalent width of the CIV 1549 emission line is correlated with both alpha_ox and luminosity. We find that by regressing l_UV with EW(CIV) and alpha_ox, we can obtain tighter correlations than by regressing l_UV with only EW(CIV). Both correlation and regression analyses imply that l_UV is not the only factor controlling the changes of EW(CIV); alpha_ox (or, equivalently, the soft X-ray emission) plays a fundamental role in the formation and variation of CIV. Variability contributes at least 60% of the scatter of the EW(CIV)-l_UV relation and at least 75% of the scatter of the of the EW(CIV)-alpha_ox relation. In our sample, narrow Fe Kalpha 6.4 keV emission lines are detected in 50 objects. Although narrow Fe Kalpha exhibits a BEff similar to that of CIV, its equivalent width has almost no dependence on either alpha_ox or EW(CIV). This suggests that the majority of narrow Fe Kalpha emission is unlikely to be produced in the broad emission-line region. We do find suggestive correlations between the emission-line luminosities of CIV and Fe Kalpha, which could be potentially used to estimate the detectability of the Fe Kalpha line of quasars from rest-frame UV spectroscopic observations.
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Using the properties of SDSS DR7 QSOs catalog from Shen et al., the Baldwin effect, its slope evolution, the underlying drive for a large sample of 35019 QSOs with reliable spectral analysis are investigated. We find that the Baldwin effect exists in this large QSOs sample, which is almost the same in 11 different redshift bins, up to $zsim 5$. The slope is -0.238 by the BCES (civ EW depends on the continuum), -0.787 by the BCES bisector. For 11 redshift-bins, there is an increasing of the Baldwin effect slope from $zsim1.5$ to $zsim2.0$. From $zsim2.0$ to $zsim5.0$, the slope change is not clear considering their uncertainties or larger redshift bins. There is a strong correlation between the rest-frame civ EW and civ-based mbh while the relation between the civ EW and mgii-based mbh is very weak. With the correction of civ-based mbh from the civ blueshift relative to mgii, we suggest that this strong correlation is due to the bias of the civ-based mbh, with respect to that from the mgii line. Considering the mgii-based mbh, a medium strong correlation is found between the civ EW and the Eddington ratio, which implies that the Eddington ratio seems to be a better underlying physical parameter than the central black hole mass.
The relationship between the emission-line equivalent width and the continuum luminosity, so called the Baldwin effect, plays an important role in studying the physics of the broad line region of AGNs. Using the archived ultraviolet spectra obtained by IUE, HST, and HUT in 1978-2002, we investigated the intrinsic CIV Baldwin effect of a well-studied Seyfert 1 galaxy NGC 4151. Both its continuum flux and CIV emission-line flux varied about two orders of magnitude in more than two decades, making it one of the best targets for studying the slope variation of the Baldwin effect. We fitted the CIV line profile of the 490 archived UV spectra of NGC 4151 with the same model consisting of a few Gaussian components, and derived the slope in the log-log plot for the total flux of CIV emission line against the UV continuum flux in different observation epochs.We found that the slope is not constant for NGC 4151, as it varies from 0.58 in the highest flux epoch to 0.83 in the lowest flux epoch. The slope evidently decreases as the continuum flux increases, which reinforces the previous findings of the non-constant slope in the H_beta Baldwin effect of NGC 5548 and the CIV Baldwin effect of Fairall 9. Our result suggests that such a non-constant slope may not be unusual for AGNs. Its physical origin is probably related to the different non-linear responses of the emission line to the variable ionizing continuum caused by the different accretion modes at different luminosity levels. We briefly discuss the effects of various absorption components in the CIV line profile of NGC 4151 and argue that the slope variation is not driven mainly by the absorption effect. Intensive, long-term and high resolution spectral observations of strongly variable AGNs are needed in the future to confirm our result.
Broad emission lines is a prominent property of type I quasi-stellar objects (QSOs). The origin of the Baldwin effect for civ $lambda1549~$AA broad emission lines, i.e., the luminosity dependence of the civ equivalent width (EW), is not clearly established. Using a sample of 87 low-$z$ Palomar-Green (PG) QSOs and 126 high-$z$ QSOs across the widest possible ranges of redshift ($0<z<5$), we consistently calculate hb-based single-epoch supermassive black hole (SMBH) mass and the Eddington ratio to investigate the underlying driver of the civ Baldwin effect. An empirical formula to estimate the host fraction in the continuum luminosity at 5100 AA is presented and used in hb-based mbh calculation for low-$z$ PG QSOs. It is found that, for low-$z$ PG QSOs, the Eddington ratio has strong correlations with PC1 and PC2 from the principal component analysis, and civ EW has a strong correlation with the optical feii strength or PC1. Expanding the luminosity range with high-$z$ QSOs, it is found that civ Baldwin effect exists in our QSOs sample. Using hb-based single-epoch SMBH mass for our QSOs sample, it is found that civ EW has a strong correlation with the Eddington ratio, which is stronger than that with the SMBH mass. It implies that the Eddington ratio seems to be a better underlying parameter than the SMBH mass to drive the civ Baldwin effect.
Using a large sample of 26623 quasars with redshifts in the range $1.5 le zle 5.1$ with civ $lambda$1549 AA emission line in Fifth Data Release of the Sloan Digital Sky Survey (SDSS), we investigate the cosmological evolution of the Baldwin Effect, i.e. the relation between the equivalent width (EW) of the civ emission line and continuum luminosity. We confirm the earlier result that there exists a strong correlation between the civ EW and the continuum luminosity, and we find that, up to $zapprox 5$, the slope of the Baldwin Effect seems to have no effect of cosmological evolution. A sub-sample of 13960 quasars with broad civ $lambda$1549 AA emission line from SDSS is used to explore the origin of the Baldwin Effect. We find that civ EW have a strong correlation with the mass of supermassive black hole (SMBH), and a weak correlation with the Eddington ratio, $lb/ledd$. This suggests that the SMBH mass is probably the primary drive for the Baldwin Effect.
We have conducted a systematic investigation of the origin and underlying physics of the line--line and line--continuum correlations of AGNs, particularly the Baldwin effect. Based on the homogeneous sample of Seyfert 1s and QSOs in the SDSS DR4, we find the origin of all the emission-line regularities is Eddington ratio (L/Ledd). The essential physics is that L/Ledd regulates the distributions of the properties (particularly column density) of the clouds bound in the line-emitting region.
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