1,514 research outputs found
Reverberation Mapping of High-z, High-luminosity Quasars
We present Reverberation Mapping results after monitoring a sample of 17
high-z, high-luminosity quasars for more than 10 years using photometric and
spectroscopic capabilities. Continuum and line emission flux variability is
observed in all quasars. Using cross-correlation analysis we successfully
determine lags between the variations in the continuum and broad emission lines
for several sources. Here we present a highlight of our results and the
determined radius--luminosity relations for Ly_alpha and CIV.Comment: Contributed talk at conference "Quasars at all cosmic epochs", held
in Padova 2-7 April 2017, published in Frontiers in Astronomy and Space
Science
Black Hole Growth to z = 2 - I: Improved Virial Methods for Measuring M_BH and L/L_Edd
We analyze several large samples of AGN in order to establish the best tools
required to study the evolution of black hole mass (M_BH) and normalized
accretion rate (L/L_Edd). The data include spectra from the SDSS, 2QZ and 2SLAQ
surveys at z<2, and a compilation of smaller samples with 0<z<5. We critically
evaluate the usage of the MgII(2798A) and CIV(1549A) lines, and adjacent
continuum bands, as estimators of M_BH and L/L_Edd, by focusing on sources
where one of these lines is observed together with Hbeta. We present a new,
luminosity-dependent bolometric correction for the monochromatic luminosity at
3000A, L_3000, which is lower by a factor of 1.75 than those used in previous
studies. We also re-calibrate the use of L_3000 as an indicator for the size of
the broad emission line region (R_BLR) and find that R_BLR is proportional to
L_3000^0.62. We find that FWHM(MgII)\simeqFWHM(Hb) for all sources with
FWHM(MgII)<6000 km/s. Beyond this FWHM, the MgII line width seems to saturate.
The spectral region of the MgII line can thus be used to reproduce Hb-based
estimates of M_BH and L/L_Edd, with negligible systematic differences and a
scatter of 0.3 dex. The width of the CIV line, on the other hand, shows no
correlation with either that of the Hb or the MgII lines and we could not
identify the reason for this discrepancy. The scatter of M_BH(CIV), relative to
M_BH(Hb) is of almost 0.5 dex. Moreover, 46% of the sources have
FWHM(CIV)<FWHM(Hb), in contrast with the basic premise of the virial method,
which predicts FWHM(CIV)/FWHM(Hbeta)~1.9. Thus, the CIV line cannot be used to
obtain precise estimates of M_BH. We conclude by presenting the observed
evolution of M_BH and L/L_Edd with cosmic epoch. The steep rise of L/L_Edd with
redshift up to z~1 flattens towards the expected maximal value of L/L_Edd~1,
with lower-M_BH sources showing higher values of L/L_Edd at all redshifts.
[Abridged]Comment: 23 pages, including 2 appendices and 18 figures. Accepted for
publication in MNRAS (minor corrections
Disk Outflows and High-Luminosity True Type 2 AGN
The absence of intrinsic broad line emission has been reported in a number of
active galactic nuclei (AGN), including some with high Eddington ratios. Such
"true type 2 AGN" are inherent to the disk-wind scenario for the broad line
region: Broad line emission requires a minimal column density, implying a
minimal outflow rate and thus a minimal accretion rate. Here we perform a
detailed analysis of the consequences of mass conservation in the process of
accretion through a central disk. The resulting constraints on luminosity are
consistent with all the cases where claimed detections of true type 2 AGN pass
stringent criteria, and predict that intrinsic broad line emission can
disappear at luminosities as high as about 4x erg s and any
Eddington ratio, though more detections can be expected at Eddington ratios
below about 1%. Our results are applicable to every disk outflow model,
whatever its details and whether clumpy or smooth, irrespective of the wind
structure and its underlying dynamics. While other factors, such as changes in
spectral energy distribution or covering factor, can affect the intensities of
broad emission lines, within this scenario they can only produce true type 2
AGN of higher luminosity then those prescribed by mass conservation.Comment: To appear in MNRAS. The L and M columns were inadvertently switched
in the original version (Thank you Giovanni Miniutti for catching). Corrected
in this versio
Bloated Stars as AGN Broad Line Clouds: The Emission Line Profiles
The Bloated Stars Scenario proposes that AGN broad line emission originates
in the winds or envelopes of bloated stars (BS). Alexander and Netzer (1994)
established that ~ 5e4 BSs with dense, decelerating winds can reproduce the
observed emission line spectrum and avoid rapid collisional destruction. Here,
we use the observed properties of AGN line profiles to further constrain the
model parameters. In the BS model, the origin of the broad profiles is the
stellar velocity field in the vicinity of the central black hole. We use a
detailed photoionization code and a model of the stellar distribution function
to calculate the BS emission line profiles and compare them to a large sample
of AGN CIV, CIII] and MgII profiles. We find that the BSs can reproduce the
general shape and width of typical AGN profiles as well as the line ratios if
(i) The ionizing luminosity to black hole mass ratio is low enough. (ii) The
broad line region size is limited by some cutoff mechanism. (iii) The fraction
of the BSs in the stellar population falls off roughly as r^-2. (iv) The wind
density and/or velocity are correlated with the black hole mass and ionizing
luminosity. Under these conditions the strong tidal forces near the black hole
play an important role in determining the line emission properties of the BSs.
Some discrepancies remain: the calculated BS profiles tend to have weaker wings
than the observed ones, and the differences between the profiles of different
lines are somewhat smaller than those observed.Comment: 13 pages with 10 figures, LaTeX using mn.sty and epsf.sty, to appear
in MNRA
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