WHAT CONTROLS THE Fe II STRENGTH IN ACTIVE GALACTIC NUCLEI
We used a large, homogeneous sample of 4178 z <= 0.8 Seyfert 1 galaxies and QSOs selected from the Sloan Digital Sky Survey to investigate the strength of Fe II emission and its correlation with other emission lines and physical parameters of active galactic nuclei. We find that the strongest correlations of almost all the emission-line intensity ratios and equivalent widths (EWs) are with the Eddington ratio (L/L-Edd), rather than with the continuum luminosity at 5100 angstrom (L-5100) or black hole mass (M-BH); the only exception is the EW of ultraviolet Fe II emission, which does not correlate at all with broad-line width, L-5100, M-BH, or L/L-Edd. By contrast, the intensity ratios of both the ultraviolet and optical Fe II emission to MgII lambda 2800 correlate quite strongly with L/L-Edd. Interestingly, among all the emission lines in the near-UV and optical studied in this paper (including MgII lambda 2800, H beta, and [O III]lambda 5007), the EW of narrow optical Fe II emission has the strongest correlation with L/L-Edd. We hypothesize that the variation of the emission-line strength in active galaxies is regulated by L/L-Edd because it governs the global distribution of the hydrogen column density of the clouds gravitationally bound in the line-emitting region, as well as its overall gas supply. The systematic dependence on L/L-Edd must be corrected when using the Fe II/MgII intensity ratio as a measure of the Fe/Mg abundance ratio to study the history of chemical evolution in QSO environments.

title: ESTIMATING BLACK HOLE MASSES IN ACTIVE GALACTIC NUCLEI USING THE Mg II λ2800 EMISSION LINE
abstract: We investigate the relationship between the linewidths of broad Mg II lambda 2800 and H beta in active galactic nuclei (AGNs) to refine them as tools to estimate black hole (BH) masses. We perform a detailed spectral analysis of a large sample of AGNs at intermediate redshifts selected from the Sloan Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra for nearby sources monitored with reverberation mapping (RM). Careful attention is devoted to accurate spectral decomposition, especially in the treatment of narrow-line blending and Fe II contamination. We show that, contrary to popular belief, the velocity width of Mg II tends to be smaller than that of H beta, suggesting that the two species are not cospatial in the broad-line region. Using these findings and recently updated BH mass measurements from RM, we present a new calibration of the empirical prescriptions for estimating virial BH masses for AGNs using the broad Mg II and H beta lines. We show that the BH masses derived from our new formalisms show subtle but important differences compared to some of the mass estimators currently used in the literature.

title: EDDINGTON RATIO GOVERNS THE EQUIVALENT WIDTH OF Mg II EMISSION LINE IN ACTIVE GALACTIC NUCLEI
abstract: We have investigated the ensemble regularities of the equivalent widths (EWs) of Mg II lambda 2800 emission line of active galactic nuclei (AGNs), using a uniformly selected sample of 2092 Seyfert 1 galaxies and quasars at 0.45 <= z <= 0.8 in the spectroscopic data set of the Sloan Digital Sky Survey Fourth Data Release. We find a strong correlation between the EW of Mg II and the AGN Eddington ratio (L/L(Edd)): EW(Mg II) proportional to (L/L(Edd))(-0.4). Furthermore, for AGNs with the same L/L(Edd), their EWs of Mg II show no correlation with luminosity, black hole mass, or line width, and the Mg II line luminosity is proportional to continuum luminosity, as expected by photoionization theory. Our result shows that Mg II EW is not dependent on luminosity, but is solely governed by L/L(Edd).

title: Broad‐line Balmer decrements in blue active galactic nuclei
abstract: We have investigated the broad-line Balmer decrements (H alpha/H beta) for a large, homogeneous sample of Seyfert 1 galaxies and quasi-stellar objects (QSOs) using spectroscopic data obtained in the Sloan Digital Sky Survey. The sample, drawn from the Fourth Data Release, comprises 446 low-redshift (z less than or similar to 0.35) active galactic nuclei (AGN) that have blue optical continua as indicated by the spectral slopes in order to minimize the effect of dust extinction. We find that (i) the distribution of the intrinsic broad-line H alpha/H beta ratio can be well described by log-Gaussian, with a peak at H alpha/H beta = 3.06 and a standard deviation of about 0.03 dex only; (ii) the Balmer decrement does not correlate with AGN properties such as luminosity, accretion rate and continuum slope, etc.; (iii) on average, the Balmer decrements are found to be only slightly larger in radio-loud sources (3.37) and sources having double-peaked emission-line profiles (3.27) compared to the rest of the sample. We therefore suggest that the broad-line H alpha/H beta ratio can be used as a good indicator for dust extinction in the AGN broad-line region; this is especially true for radio-quiet AGN with regular emission-line profiles, which constitute the vast majority of the AGN population.

title: The origin and physical mechanism of the ensemble Baldwin effect
abstract: 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.

title: Optical identification of radio-loud active galactic nuclei in the ROSAT-Green-Bank sample with SDSS spectroscopy
abstract: Results of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank (RGB) catalog are presented (Brinkmann et al. 1997) which have been spectroscopically observed in the Sloan Digital Sky Survey (SDSS) DR5. The SDSS spectra of the optical counterparts are modeled in a careful and self-consistent way by incorporating the host galaxy's starlight. Optical emission line parameters are presented, which are derived accurately and reliably, along with the radio 1.4-5 GHz spectral indices estimated using (non-simultaneous) archival data. For 72 sources, the identifications are presented for the first time. It is confirmed that the majority of strong radio/X-ray emitters are radio-loud active galactic nuclei (AGNs), particularly blazars. Taking advantage of the high spectral quality and resolution and our refined spectral modeling, we are able to disentangle narrow line radio galaxies (NLRGs), as vaguely termed in most previous identification work, into Seyfert II galaxies and LINERs (low-ionization nuclear emission regions), based on the standard emission line diagnostics. The NLRGs in the RGB sample, mostly belonging to 'weak line radio galaxies', are found to have optical spectra consistent predominantly with LINERs, and only a small fraction with Seyfert II galaxies. A small number of LINERs have radio power as high as 10(23)-10(26) W Hz(-1) at 5 GHz, being among the strongest radio emitting LINERs known so far. Two sources are identified with radio-loud narrow line Seyfert I galaxies (NLS1s), a class of rare objects. The presence is also confirmed of flat-spectrum radio quasars whose radio-optical-X-ray effective spectral indices are similar to those of High-energy peaked BL Lacs (HBLs), as suggested by Padovani et al., although it is still a debate as to whether this is the case for their actual spectral energy distributions.

title: Evidence for gluon interference in hadronic Z decays
abstract: We present evidence for soft gluon interference, as required by QCD. This interference is expected to manifest itself in an angular ordering of the gluons radiated within a jet. Using hadronic decays of the Z boson in the L3 detector at LEP, we compare variables sensitive to such an angular ordering, namely the energy-energy correlation asymmetry and the newly introduced particle-particle correlation asymmetry, with the predictions of various parton shower models. Only those models which incorporate the expected interference agree with the data.

title: Measurements of the exclusive decays of the upsilon(5S) to meson final states and improved B(s)* mass measurement.
abstract: Using 420 pb(-1) of data collected on the upsilon(5S) resonance with the CLEO III detector, we reconstruct B mesons in 25 exclusive decay channels to measure or set upper limits on the decay rate of upsilon(5S) into B meson final states. We measure the inclusive B cross section to be sigma(upsilon(5S) --> BB(X)) = (0.177 +/- 0.030 +/- 0.016) nb and make the first measurements of the production rates of sigma(upsilon(5S) --> B*B*) = (0.131 +/- 0.025 +/- 0.014) nb and sigma(upsilon(5S) --> BB*) = (0.043 +/- 0.016 +/- 0.006) nb, respectively. We set 90% confidence level limits of sigma(upsilon(5S) -->BB) < 0.038 nb, sigma(upsilon(5S) --> B(*)B(*)pi) < 0.055 nb and sigma(upsilon(5S) --> BBpipi) < 0.024 nb. We also extract the most precise value of the B(s)* mass to date, M(B(s)*) = (5411.7 +/- 1.6 +/- 0.6) MeV/c2.

title: First observation of the sigma(*+)(c) baryon and a new measurement of the sigma(*+)(c) mass.
abstract: Using data recorded with the CLEO II and CLEO II.V detector configurations at the Cornell Electron Storage Rings, we report the first observation and mass measurement of the Sigma(*+)(c) charmed baryon, and an updated measurement of the mass of the Sigma(+)(c) baryon. We find M(Sigma(*+)(c))-M(Lambda(+)(c)) = (231.0+/-1.1+/-2.0) MeV, and M(Sigma(+)(c))-M(Lambda(+)(c)) = (166.4+/-0.2+/-0.3) MeV, where the errors are statistical and systematic, respectively.

title: Outflows from active galactic nuclei: the BLR–NLR metallicity correlation
abstract: The metallicity of active galactic nuclei (AGNs), which can be measured by emission line ratios in their broad- and narrow-line regions (BLRs and NLRs), provides invaluable information about the physical connection between the different components of AGNs. From the archival data bases of the International Ultraviolet Explorer, the Hubble Space Telescope and the Sloan Digital Sky Survey, we have assembled the largest sample available of AGNs which have adequate spectra in both the optical and ultraviolet bands to measure the narrow-line ratio [N ii]/H alpha and also, in the same objects, the broad-line N v/C iv ratio. These permit the measurement of the metallicities in the NLRs and BLRs in the same objects. We find that neither the BLR nor the NLR metallicity correlate with black hole masses or Eddington ratios, but there is a strong correlation between NLR and BLR metallicities. This metallicity correlation implies that outflows from BLRs carry metal-rich gas to NLRs at characteristic radial distances of similar to 1.0 kpc. This chemical connection provides evidence for a kinetic feedback of the outflows to their hosts. Metals transported into the NLR enhance the cooling of the ISM in this region, leading to local star formation after the AGNs turn to narrow-line low-ionization nuclear emission-line regions. This post-AGN star formation is predicted to be observable as an excess continuum emission from the host galaxies in the near-infrared and ultraviolet, which needs to be further explored.

title: CHANDRA HIGH-ENERGY GRATING OBSERVATIONS OF THE Fe Kα LINE CORE IN TYPE II SEYFERT GALAXIES: A COMPARISON WITH TYPE I NUCLEI
abstract: We present a study of the core of the Fe K{alpha} emission line at {approx}6.4 keV in a sample of type II Seyfert galaxies observed by the Chandra high-energy grating. The sample consists of 29 observations of 10 unique sources. We present measurements of the Fe K{alpha} line parameters with the highest spectral resolution currently available. In particular, we derive the most robust intrinsic line widths for some of the sources in the sample to date. We obtained a weighted mean full width at half-maximum (FWHM) of 2000 {+-} 160 km s{sup -1} for 8 out of 10 sources (the remaining sources had insufficient signal to noise). From a comparison with the optical emission-line widths obtained from spectropolarimetric observations, we found that the location of Fe K{alpha} line-emitting material is a factor of {approx}0.7-11 times the size of the optical broad-line region. Furthermore, compared to 13 type I active galactic nuclei (AGNs) for which the best Fe K{alpha} line FWHM constraints were obtained, we found no difference in the FWHM distribution or the mean FWHM, and this conclusion is independent of the central black hole mass. This result suggests that the bulk of the Fe K{alpha} line emission may originatemore » from a universal region at the same radius with respect to the gravitational radius, {approx}3 x 10{sup 4} r{sub g} on average. By examining the correlation between the Fe K{alpha} luminosity and the [O IV] line luminosity, we found a marginal difference in the Fe K{alpha} line flux between type I and type II AGNs, but the spread in the ratio of L{sub Fe} to L{sub [OIV]} is about two orders of magnitude. Our results confirm the theoretical expectation that the Fe K{alpha} emission-line luminosity cannot trivially be used as a proxy of the intrinsic AGN luminosity, unless a detailed comparison of the data with proper models is applied.« less