1,721,223 research outputs found
Geometry and inclination of the broad-line region in blazars
No full textWe study the properties of the broad-line region in blazars by comparing the virial estimate of black hole masses with that derived from the mass of the host galaxies. The former is sensitive to the width of broad lines, i.e. to the projection of the velocity of line-emitting clouds along the line of sight; the latter is not. This comparison allows us to constrain the deprojection factor f, thus revealing general properties of the geometry of the broad-line region. We show that blazars tend to have (1) higher f values than the quasars of our reference sample: <fBLLacs>= 6.9 ñ 2.3; <fblazars>= 5.6 ñ 1.3 and <fquasars>= 2.0 ñ 0.3, (2) relatively narrow broad emission lines and (3) modest equivalent widths, as expected because of the occurrence of jet emission at very low inclination angles. In a disc-like sketch of the broad-line region, these results indicate a pole-on view of a flat geometry in blazars. This consistently extends the orientation-dependent unified model of active nuclei to the geometry of the broad-line region
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Are the black hole masses in narrow-line Seyfert 1 galaxies actually small?
No full textNarrow-line Seyfert 1 galaxies (NLS1s) are generally considered peculiar objects among the broad class of type 1 active galactic nuclei, due to the relatively small width of the broad lines, strong X-ray variability, soft X-ray continua, weak [O iii], and strong Fe ii line intensities. The mass MBH of the central massive black hole (MBH) is claimed to be lighter than expected from known MBH–host galaxy scaling relations, while the accretion rate on to the MBH larger than the average value appropriate to Seyfert 1 galaxies. In this Letter, we show that NLS1 peculiar MBH and L/LEdd turn out to be fairly standard, provided that the broad-line region is allowed to have a disc-like, rather than isotropic, geometry. Assuming that NLS1s are rather ‘normal’ Seyfert 1 objects seen along the disc axis, we could estimate the typical inclination angles from the fraction of Seyfert 1 classified as NLS1s, and compute the geometrical factor relating the observed full width at half-maximum of broad lines to the virial mass of the MBH. We show that the geometrical factor can fully account for the ‘black hole mass deficit’ observed in NLS1s, and that L/LEdd is (on average) comparable to the value of the more common broad-line Seyfert 1 galaxies
High-redshift quasars and their host galaxies - II. Multiphase gas and stellar kinematics
Full text linkObservations of z ≳ 6 quasars provide information on the early phases of the most massive black holes (MBHs) and galaxies. Current observations at sub-mm wavelengths trace cold and warm gases, and future observations will extend information to other gas phases and the stellar properties. The goal of this study is to examine the gas life cycle in a z ≳ 6 quasar: From accretion from the halo to the galaxy and all the way into the MBH, to how star formation and the MBH itself affect the gas properties. Using a very high resolution cosmological zoom-in simulation of a z = 7 quasar, including state-of-the-art non-equilibrium chemistry, MBH formation, growth, and feedback, we investigate the distribution of the different gas phases in the interstellar medium across cosmic time. We assess the morphological evolution of the quasar host using different tracers (star- or gas-based) and the thermodynamic distribution of the MBH accretion-driven outflows, finding that obscuration in the disc is mainly due to molecular gas, with the atomic component contributing at larger scales and/or above/below the disc plane. Moreover, our results also show that molecular outflows, if present, are more likely the result of gas being lifted near the MBH than production within the wind because of thermal instabilities. Finally, we also discuss how different gas phases can be employed to dynamically constrain the MBH mass, and argue that resolutions below ∼100 pc yield unreliable estimates because of the strong contribution of the nuclear stellar component to the potential at larger scales
Downsizing of supermassive black holes from the SDSS quasar survey - II. Extension to z ~ 4
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