ABSTRACT
We analyse several large samples of active galactic nuclei (AGNs) in order to establish the best tools required to study the evolution of black hole mass (MBH) and normalized accretion rate ...(L/LEdd). The data include spectra from the Sloan Digital Sky Survey, 2dF QSO Redshift survey and 2dF SDSS LRG And QSO survey public surveys at z < 2, and a compilation of smaller samples with 0 < z < 5. We critically evaluate the usage of the Mg ii λ2798 and C iv λ1549 lines, and adjacent continuum bands, as estimators of MBH and L/LEdd, by focusing on sources where one of these lines is observed together with Hβ. We present a new, luminosity‐dependent bolometric correction for the monochromatic luminosity at 3000 Å, L3000, which is lower by a factor of ∼1.75 than those used in previous studies. We also re‐calibrate the use of L3000 as an indicator for the size of the broad emission‐line region (RBLR) and find that R BLR ∝L30000.62, in agreement with previous results. We find that FWHM ( Mg ii)≃ FWHM (Hβ) for all sources with FWHM ( Mg ii)≲6000 km s−1. Beyond this full width at half‐maximum (FWHM), the Mg ii line width seems to saturate. The spectral region of the Mg ii line can thus be used to reproduce Hβ‐based estimates of MBH and L/LEdd, with negligible systematic differences and a scatter of ∼0.3 dex. The width of the C iv line, on the other hand, shows no correlation with either that of the Hβ or the Mg ii lines and we could not identify the reason for this discrepancy. The scatter of MBH(C iv), relative to MBH(Hβ), is of almost 0.5 dex. Moreover, 46 per cent of the sources have FWHM (Civ)≲ FWHM (Hβ), in contrast with the basic premise of the virial method, which predicts FWHM (Civ)/ FWHM (Hβ)≃3.7, based on reverberation mapping experiments. This fundamental discrepancy cannot be corrected based on the continuum slope or any C iv‐related observable. Thus, the C iv line cannot be used to obtain precise estimates of MBH. We conclude by presenting the observed evolution of MBH and L/LEdd with cosmic epoch. The steep rise of L/LEdd with redshift up to z ≃ 1 flattens towards the expected maximal value of L/LEdd ≃ 1, with lower MBH sources showing higher values of L/LEdd at all redshifts. These trends will be further analysed in a forthcoming paper.
This is the second in a series of papers aiming to test how the mass (M
BH), accretion rate (Ṁ) and spin (a
*) of supermassive black holes (SMBHs) determine the observed properties of type I active ...galactic nuclei (AGN). Our project utilizes a sample of 39 unobscured AGN at z ≃ 1.55 observed by Very Large Telescope/X-Shooter, selected to map a large range in M
BH and L/L
Edd and covers the most prominent UV–optical (broad) emission lines, including Hα, Hβ, Mg ii λ2798 and C iv λ1549. This paper focuses on single-epoch, ‘virial’ M
BH determinations from broad emission lines and examines the implications of different continuum modelling approaches in line width measurements. We find that using a local power-law continuum instead of a physically motivated thin disc continuum leads to only slight underestimation of the full width at half-maximum (FWHM) of the lines and the associated M
BH(FWHM). However, the line dispersion σline and associated M
BH(σline) are strongly affected by the continuum placement and provides less reliable mass estimates than FWHM-based methods. Our analysis shows that Hα, Hβ and Mg ii can be safely used for virial M
BH estimation. The C iv line, on the other hand, is not reliable in the majority of the cases; this may indicate that the gas emitting this line is not virialized. While Hα and Hβ show very similar line widths, the mean FWHM(Mg ii) is about 30 per cent narrower than FWHM(Hβ). We confirm several recent suggestions to improve the accuracy in C iv-based mass estimates, relying on other UV emission lines. Such improvements do not reduce the scatter between C iv-based and Balmer-line-based mass estimates.
The physics of active super massive black holes (BHs) is governed by their mass (M...), spin (a*), and accretion rate (M). This work is the first in a series of papers with the aim of testing how ...these parameters determine the observable attributes of active galactic nuclei (AGN). We have selected a sample in a narrow redshift range, centred on z ~ 1.55, that covers a wide range in M... and M, and are observing them with X-shooter, covering rest wavelengths ~1200-9800 A. The current work covers 30 such objects and focuses on the origin of the AGN spectral energy distribution (SED). After estimating M... and M ... based on each observed SED, we use thin accretion disc (AD) models and a Bayesian analysis to fit the observed SEDs in our sample. We are able to fit 22/30 of the SEDs. Out of the remaining eight SEDs, three can be fit by the thin AD model by correcting the observed SED for reddening within the host galaxy and four can be fit by adding a disc wind to the model. In four of these eight sources, Milky Way-type extinction, with the strong 2175 A feature, provides the best reddening correction. The distribution in spin parameter covers the entire range, from -1 to 0.998, and the most massive BHs have spin parameters greater than 0.7. This is consistent with the 'spin-up' model of BH evolution. Altogether, these results indicate that thin ADs are indeed the main power houses of AGN, and earlier claims to the contrary are likely affected by variability and a limited observed wavelength range. (ProQuest: ... denotes formulae/symbols omitted.)
We use Herschel 70 to 160 μm images to study the size of the far-infrared emitting region in about 400 local galaxies and quasar (QSO) hosts. The sample includes normal “main-sequence” star-forming ...galaxies, as well as infrared luminous galaxies and Palomar-Green QSOs, with different levels and structures of star formation. Assuming Gaussian spatial distribution of the far-infrared (FIR) emission, the excellent stability of the Herschel point spread function (PSF) enables us to measure sizes well below the PSF width, by subtracting widths in quadrature. We derive scalings of FIR size and surface brightness of local galaxies with FIR luminosity, with distance from the star-forming main-sequence, and with FIR color. Luminosities LFIR~ 1011 L⊙ can be reached with a variety of structures spanning 2 dex in size. Ultraluminous LFIR≳ 1012 L⊙ galaxies far above the main-sequence inevitably have small Re,70~ 0.5 kpc FIR emitting regions with large surface brightness, and can be close to optically thick in the FIR on average over these regions. Compared to these local relations, first ALMA sizes for the dust emission regions in high redshift galaxies, measured at somewhat longer rest wavelengths, suggest larger sizes at the same IR luminosity. We report a remarkably tight relation with 0.15 dex scatter between FIR surface brightness and the ratio of Cii 158 μm emission and FIR emission – the so-called Cii-deficit is more tightly linked to surface brightness than to FIR luminosity or FIR color. Among 33 z ≤ 0.1 PG QSOs with typical LFIR/LBol,AGN ≈ 0.1, 19 have a measured 70 μm half light radius, with median Re,70 = 1.1 kpc. This is consistent with the FIR size for galaxies with similar LFIR but lacking a QSO, in accordance with a scenario where the rest FIR emission of these types of QSOs is, in most cases, due to host star formation.
ABSTRACT We present an analysis of 43 years (1972 to 2015) of spectroscopic observations of the Seyfert 1 galaxy NGC 5548. This includes 12 years of new unpublished observations (2003 to 2015). We ...compiled about 1600 Hβ spectra and analyzed the long-term spectral variations of the 5100 continuum and the Hβ line. Our analysis is based on standard procedures, including the Lomb-Scargle method, which is known to be rather limited to such heterogeneous data sets, and a new method developed specifically for this project that is more robust and reveals a ∼5700 day periodicity in the continuum light curve, the Hβ light curve, and the radial velocity curve of the red wing of the Hβ line. The data are consistent with orbital motion inside the broad emission line region of the source. We discuss several possible mechanisms that can explain this periodicity, including orbiting dusty and dust-free clouds, a binary black hole system, tidal disruption events, and the effect of an orbiting star periodically passing through an accretion disk.
We employ optical and ultraviolet (UV) observations to present spectral energy distributions (SEDs) for two reverberation-mapped samples of super-Eddington and sub-Eddington active galactic nuclei ...(AGN) with similar luminosity distributions. The samples are fitted with accretion disc (AD) models in order to look for SED differences that depend on the Eddington ratio. The fitting takes into account measured black hole (BH) mass and accretion rates, BH spin and intrinsic reddening of the sources. All objects in both groups can be fitted by thin AD models over the range 0.2–1 μm with reddening as a free parameter. The intrinsic reddening required to fit the data are relatively small, E(B − V) ≤ 0.2 mag, except for one source. Super-Eddington AGN seems to require more reddening. The distribution of E(B − V) is similar to what is observed in larger AGN samples. The best-fitting disc models recover very well the BH mass and accretion for the two groups. However, the SEDs are very different, with super-Eddington sources requiring much more luminous far-UV continuum. The exact amount depends on the possible saturation of the UV radiation in slim discs. In particular, we derive for the super-Eddington sources a typical bolometric correction at 5100 Å of 60–150 compared with a median of ∼20 for the sub-Eddington AGN. The measured torus luminosity relative to λL
λ(5100 Å) are similar in both groups. The αOX distribution is similar too. However, we find extremely small torus covering factors for super-Eddington sources, an order of magnitude smaller than those of sub-Eddington AGN. The small differences between the groups regarding the spectral range 0.2–22 μm, and the significant differences related to the part of the SED that we cannot observe may be consistent with some slim disc models. An alternative explanation is that present day slim-disc models overestimate the far-UV luminosity of such objects by a large amount.
The optical classification of a Seyfert galaxy and whether it is considered X-ray absorbed are often used interchangeably. There are many borderline cases, however, and also numerous examples where ...the optical and X-ray classifications appear to be in disagreement. In this article we revisit the relation between optical obscuration and X-ray absorption in active galactic nuclei (AGNs). We make use of our “dust colour” method to derive the optical obscuration AV, and consistently estimated X-ray absorbing columns using 0.3–150 keV spectral energy distributions. We also take into account the variable nature of the neutral gas column NH and derive the Seyfert subclasses of all our objects in a consistent way. We show in a sample of 25 local, hard-X-ray detected Seyfert galaxies (log LX/ (erg / s) ≈ 41.5−43.5) that there can actually be a good agreement between optical and X-ray classification. If Seyfert types 1.8 and 1.9 are considered unobscured, the threshold between X-ray unabsorbed and absorbed should be chosen at a column NH = 1022.3 cm-2 to be consistent with the optical classification. We find that NH is related to AV and that the NH/AV ratio is approximately Galactic or higher in all sources, as indicated previously. However, in several objects we also see that deviations from the Galactic ratio are only due to a variable X-ray column, showing that (1) deviations from the Galactic NH/AV can be simply explained by dust-free neutral gas within the broad-line region in some sources; that (2) the dust properties in AGNs can be similar to Galactic dust and that (3) the dust colour method is a robust way to estimate the optical extinction towards the sublimation radius in all but the most obscured AGNs.
The broadening of atomic emission lines by high-velocity motion of gas near accreting supermassive black holes is an observational hallmark of quasars
. Observations of broad emission lines could ...potentially constrain the mechanism for transporting gas inwards through accretion disks or outwards through winds
. The size of regions for which broad emission lines are observed (broad-line regions) has been estimated by measuring the delay in light travel time between the variable brightness of the accretion disk continuum and the emission lines
-a method known as reverberation mapping. In some models the emission lines arise from a continuous outflow
, whereas in others they arise from orbiting gas clouds
. Directly imaging such regions has not hitherto been possible because of their small angular size (less than 10
arcseconds
). Here we report a spatial offset (with a spatial resolution of 10
arcseconds, or about 0.03 parsecs for a distance of 550 million parsecs) between the red and blue photo-centres of the broad Paschen-α line of the quasar 3C 273 perpendicular to the direction of its radio jet. This spatial offset corresponds to a gradient in the velocity of the gas and thus implies that the gas is orbiting the central supermassive black hole. The data are well fitted by a broad-line-region model of a thick disk of gravitationally bound material orbiting a black hole of 3 × 10
solar masses. We infer a disk radius of 150 light days; a radius of 100-400 light days was found previously using reverberation mapping
. The rotation axis of the disk aligns in inclination and position angle with the radio jet. Our results support the methods that are often used to estimate the masses of accreting supermassive black holes and to study their evolution over cosmic time.
The physics of active super massive black holes (BHs) is governed by their mass (M_BH), spin (a_*), and accretion rate (M). This work is the first in a series of papers with the aim of testing how ...these parameters determine the observable attributes of active galactic nuclei (AGN). We have selected a sample in a narrow redshift range, centred on z similar to 1.55, that covers a wide range in M_BH and M, and are observing them with X-shooter, covering rest wavelengths similar to 1200-9800 A. The current work covers 30 such objects and focuses on the origin of the AGN spectral energy distribution (SED). After estimating M_BH and M based on each observed SED, we use thin accretion disc (AD) models and a Bayesian analysis to fit the observed SEDs in our sample. We are able to fit 22/30 of the SEDs. Out of the remaining eight SEDs, three can be fit by the thin AD model by correcting the observed SED for reddening within the host galaxy and four can be fit by adding a disc wind to the model. In four of these eight sources, Milky Way-type extinction, with the strong 2175 A feature, provides the best reddening correction. The distribution in spin parameter covers the entire range, from -1 to 0.998, and the most massive BHs have spin parameters greater than 0.7. This is consistent with the 'spin-up' model of BH evolution. Altogether, these results indicate that thin ADs are indeed the main power houses of AGN, and earlier claims to the contrary are likely affected by variability and a limited observed wavelength range.
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