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Register a new userA comprehensive and uniform sample of broad-line active galactic nuclei from the SDSS DR7
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A new, complete sample of 14,584 broad-line AGNs at $z<0.35$ is presented, which are uncovered homogeneously from the complete database of galaxies and quasars observed spectroscopically in the Sloan Digital Sky Survey Seventh Data Release. The stellar continuum is properly removed for each spectrum with significant host absorption line features, and careful analyses of the emission-line spectra, particularly in the H$rm alpha$ and H$rm beta$ wavebands, are carried out. The broad Balmer emission line, particularly, H$rm alpha$, is used to indicate the presence of an AGN. The broad H$rm alpha$ lines have luminosities in a range of $10^{38.5}$-$10^{44.3}$ erg s$^{-1}$, and line widths (FWHMs) of 500-34,000 km s$^{-1}$. The virial black hole masses, estimated from the broad line measurements, span a range of $10^{5.1}$-$10^{10.3}$ $M_odot$, and the Eddington ratios vary from $-3.3$ to $1.3$ in logarithmic scale. Other quantities such as multi-wavelength photometric properties and flags denoting peculiar line profiles are also included in this catalog. We describe the construction of this catalog and briefly discuss its properties. The catalog is publicly available online. This homogeneously selected AGN catalog, along with the accurately measured spectral parameters, provide the most updated, largest AGN sample data, which will enable further comprehensive investigations of the properties of the AGN population in the low-redshift universe.
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Apart from viewing-dependent obscuration, intrinsic broad-line emission from active galactic nuclei (AGNs) follows an evolutionary sequence: Type $1 to 1.2/1.5 to 1.8/1.9 to 2$ as the accretion rate onto the central black hole is decreasing. This spectral evolution is controlled, at least in part, by the parameter $L_{rm bol}/M^{2/3}$, where $L_{rm bol}$ is the AGN bolometric luminosity and $M$ is the black hole mass. Both this dependence and the double-peaked profiles that emerge along the sequence arise naturally in the disk-wind scenario for the AGN broad-line region.
Most results of the reverberation monitoring of active galaxies showed a universal scaling of the time delay of the Hbeta emission region with the monochromatic flux at 5100 A, with very small dipersion. Such a scaling favored the dust-based formation mechanism of the Broad Line Region (BLR). Recent reverberation measurements showed that actually a significant fraction of objects exhibits horter lags than the previously found scaling. Here we demonstrate that these shorter lags can be explained by the old concept of scaling of the BLR size with the ionization parameter. Assuming a universal value of this parameter and universal value of the cloud density reproduces the distribution of observational points in the time delay vs. monochromatic flux plane, provided that a range of black hole spins is allowed. However, a confirmation of the new measurements for low/moderate Eddington ratio sources is strongly needed before the dust-based origin of the BLR can be excluded.
Broad emission lines in active galactic nuclei (AGNs) mainly arise from gas photoionized by continuum radiation from an accretion disk around a central black hole. The shape of the broad-line profile, described by ${cal D}_{_{rm Hbeta}}={rm FWHM}/sigma_{_{rm Hbeta}}$, the ratio of full width at half maximum to the dispersion of broad H$beta$, reflects the dynamics of the broad-line region (BLR) and correlates with the dimensionless accretion rate ($dot{mathscr{M}}$) or Eddington ratio ($L_{rm bol}/L_{rm Edd}$). At the same time, $dot{mathscr{M}}$ and $L_{rm bol}/L_{rm Edd}$ correlate with ${cal R}_{rm Fe}$, the ratio of optical Fe II to H$beta$ line flux emission. Assembling all AGNs with reverberation mapping measurements of broad H$beta$, both from the literature and from new observations reported here, we find a strong bivariate correlation of the form $log(dot{mathscr{M}},L_{rm bol}/L_{rm Edd})=alpha+beta{cal D}_{_{rm Hbeta}}+gamma{cal R}_{rm Fe},$ where $alpha=(2.47,0.31)$, $beta=-(1.59,0.82)$ and $gamma=(1.34,0.80)$. We refer to this as the fundamental plane of the BLR. We apply the plane to a sample of $z < 0.8$ quasars to demonstrate the prevalence of super-Eddington accreting AGNs are quite common at low redshifts.
Most of the variability studies of active galactic nuclei (AGNs) are based on ensemble analyses. Nevertheless, it is interesting to provide estimates of the individual variability properties of each AGN, in order to relate them with intrinsic physical quantities. A useful dataset is provided by the Catalina Surveys Data Release 2 (CSDR2), which encompasses almost a decade of photometric measurements of $sim500$ million objects repeatedly observed hundreds of times. We aim to investigate the individual optical variability properties of 795 AGNs originally included in the Multi-Epoch XMM Serendipitous AGN Sample 2 (MEXSAS2). Our goals consist in: (i) searching for correlations between variability and AGN physical quantities; (ii) extending our knowledge of the variability features of MEXSAS2 from the X-ray to the optical. We use the structure function (SF) to analyse AGN flux variations. We model the SF as a power-law, $text{SF}(tau)=A,(tau/tau_0)^gamma$, and we compute its variability parameters. We introduce the V-correction as a simple tool to correctly quantify the amount of variability in the rest frame of each source. We find a significant decrease of variability amplitude with increasing bolometric, optical and X-ray luminosity. We obtain the indication of an intrinsically weak positive correlation between variability amplitude and redshift, $z$. Variability amplitude is also positively correlated with $alpha_text{ox}$. The slope of the SF, $gamma$, is weakly correlated with the bolometric luminosity $L_text{bol}$ and/or with the black hole mass $M_text{BH}$. When comparing optical to X-ray variability properties, we find that X-ray variability amplitude is approximately the same for those AGNs with larger or smaller variability amplitude in the optical. On the contrary, AGNs with steeper SF in the optical do present steeper SF in the X-ray, and vice versa.
We present results from the fitting of infrared (IR) spectral energy distributions of 21 active galactic nuclei (AGN) with clumpy torus models. We compiled high spatial resolution ($sim 0.3$--$0.7$ arcsec) mid-IR $N$-band spectroscopy, $Q$-band imaging and nuclear near- and mid-IR photometry from the literature. Combining these nuclear near- and mid-IR observations, far-IR photometry and clumpy torus models, enables us to put constraints on the torus properties and geometry. We divide the sample into three types according to the broad line region (BLR) properties; type-1s, type-2s with scattered or hidden broad line region (HBLR) previously observed, and type-2s without any published HBLR signature (NHBLR). Comparing the torus model parameters gives us the first quantitative torus geometrical view for each subgroup. We find that NHBLR AGN have smaller torus opening angles and larger covering factors than those of HBLR AGN. This suggests that the chance to observe scattered (polarized) flux from the BLR in NHBLR could be reduced by the dual effects of (a) less scattering medium due to the reduced scattering volume given the small torus opening angle and (b) the increased torus obscuration between the observer and the scattering region. These effects give a reasonable explanation for the lack of observed HBLR in some type-2 AGN.
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