39 research outputs found
Differential interferometry of QSO broad line regions I: improving the reverberation mapping model fits and black hole mass estimates
Reverberation mapping estimates the size and kinematics of broad line regions
(BLR) in Quasars and type I AGNs. It yields size-luminosity relation, to make
QSOs standard cosmological candles, and mass-luminosity relation to study the
evolution of black holes and galaxies. The accuracy of these relations is
limited by the unknown geometry of the BLR clouds distribution and velocities.
We analyze the independent BLR structure constraints given by super-resolving
differential interferometry. We developed a three-dimensional BLR model to
compute all differential interferometry and reverberation mapping signals. We
extrapolate realistic noises from our successful observations of the QSO 3C273
with AMBER on the VLTI. These signals and noises quantify the differential
interferometry capacity to discriminate and measure BLR parameters including
angular size, thickness, spatial distribution of clouds, local-to-global and
radial-to-rotation velocity ratios, and finally central black hole mass and BLR
distance. A Markov Chain Monte Carlo model-fit, of data simulated for various
VLTI instruments, gives mass accuracies between 0.06 and 0.13 dex, to be
compared to 0.44 dex for reverberation mapping mass-luminosity fits. We
evaluate the number of QSOs accessible to measures with current (AMBER),
upcoming (GRAVITY) and possible (OASIS with new generation fringe trackers)
VLTI instruments. With available technology, the VLTI could resolve more than
60 BLRs, with a luminosity range larger than four decades, sufficient for a
good calibration of RM mass-luminosity laws, from an analysis of the variation
of BLR parameters with luminosity.Comment: 19 pages, 14 figures, accepted by MNRAS on December 5, 201
A diversity of dusty AGN tori: Data release for the VLTI/MIDI AGN Large Program and first results for 23 galaxies
The AGN-heated dust distribution (the "torus") is increasingly recognized not
only as the absorber required in unifying models, but as a tracer for the
reservoir that feeds the nuclear Super-Massive Black Hole. Yet, even its most
basic structural properties (such as its extent, geometry and elongation) are
unknown for all but a few archetypal objects. Since most AGNs are unresolved in
the mid-infrared, we utilize the MID-infrared interferometric Instrument (MIDI)
at the Very Large Telescope Interferometer (VLTI) that is sensitive to
structures as small as a few milli-arcseconds (mas). We present here an
extensive amount of new interferometric observations from the MIDI AGN Large
Program (2009 - 2011) and add data from the archive to give a complete view of
the existing MIDI observations of AGNs. Additionally, we have obtained
high-quality mid-infrared spectra from VLT/VISIR. We present correlated and
total flux spectra for 23 AGNs and derive flux and size estimates at 12 micron
using simple axisymmetric geometrical models. Perhaps the most surprising
result is the relatively high level of unresolved flux and its large scatter:
The median "point source fraction" is 70 % for type 1 and 47 % for type 2 AGNs
meaning that a large part of the flux is concentrated on scales smaller than
about 5 mas (0.1 - 10 pc). Among sources observed with similar spatial
resolution, it varies from 20 % - 100 %. For 18 of the sources, two nuclear
components can be distinguished in the radial fits. While these models provide
good fits to all but the brightest sources, significant elongations are
detected in eight sources. The half-light radii of the fainter sources are
smaller than expected from the size ~ L^0.5 scaling of the bright sources and
show a large scatter, especially when compared to the relatively tight
size--luminosity relation in the near-infrared.Comment: A&A in press; 93 pages, 63 figures, 39 tables; data available only
via CD
A dust-parallax distance of 19 megaparsecs to the supermassive black hole in NGC 4151
The active galaxy NGC 4151 has a crucial role as one of only two active
galactic nuclei for which black hole mass measurements based on emission line
reverberation mapping can be calibrated against other dynamical methods.
Unfortunately, effective calibration requires an accurate distance to NGC 4151,
which is currently not available. Recently reported distances range from 4 to
29 megaparsecs (Mpc). Strong peculiar motions make a redshift-based distance
very uncertain, and the geometry of the galaxy and its nucleus prohibit
accurate measurements using other techniques. Here we report a dust-parallax
distance to NGC 4151 of Mpc. The measurement is
based on an adaptation of a geometric method proposed previously using the
emission line regions of active galaxies. Since this region is too small for
current imaging capabilities, we use instead the ratio of the
physical-to-angular sizes of the more extended hot dust emission as determined
from time-delays and infrared interferometry. This new distance leads to an
approximately 1.4-fold increase in the dynamical black hole mass, implying a
corresponding correction to emission line reverberation masses of black holes
if they are calibrated against the two objects with additional dynamical
masses.Comment: Authors' version of a letter published in Nature (27 November 2014);
8 pages, 5 figures, 1 tabl
Resolving the AGN and host emission in the mid-infrared using a model-independent spectral decomposition
We present results on the spectral decomposition of 118 Spitzer Infrared
Spectrograph (IRS) spectra from local active galactic nuclei (AGN) using a
large set of Spitzer/IRS spectra as templates. The templates are themselves IRS
spectra from extreme cases where a single physical component (stellar,
interstellar, or AGN) completely dominates the integrated mid-infrared
emission. We show that a linear combination of one template for each physical
component reproduces the observed IRS spectra of AGN hosts with unprecedented
fidelity for a template fitting method, with no need to model extinction
separately. We use full probability distribution functions to estimate
expectation values and uncertainties for observables, and find that the
decomposition results are robust against degeneracies. Furthermore, we compare
the AGN spectra derived from the spectral decomposition with sub-arcsecond
resolution nuclear photometry and spectroscopy from ground-based observations.
We find that the AGN component derived from the decomposition closely matches
the nuclear spectrum, with a 1-sigma dispersion of 0.12 dex in luminosity and
typical uncertainties of ~0.19 in the spectral index and ~0.1 in the silicate
strength. We conclude that the emission from the host galaxy can be reliably
removed from the IRS spectra of AGN. This allows for unbiased studies of the
AGN emission in intermediate and high redshift galaxies -currently inaccesible
to ground-based observations- with archival Spitzer/IRS data and in the future
with the Mid-InfraRed Instrument of the James Webb Space Telescope. The
decomposition code and templates are available at
http://www.denebola.org/ahc/deblendIRS.Comment: 16 pages, 15 figures, 2 tables, accepted for publication in Ap
The role of grain size in AGN torus dust models
Fits the infrared spectra from the nuclear regions of AGN can place
constraints on the dust properties, distribution, and geometry by comparison
with models. However, none of the currently available models fully describe the
observations of AGN currently available. Among the aspects least explored, here
we focus on the role of dust grain size. We offer the community a new spectral
energy distribution (SED) library, hereinafter [GoMar23] model, which is based
on the two-phase torus model developed before with the inclusion of the grain
size as a model parameter, parameterized by the maximum grain size Psize or
equivalently the mass-weighted average grain size . We created 691,200
SEDs using the SKIRT code, where the maximum grain size can vary within the
range Psize = 0.01 - 10.0um ( = 0.007 - 3.41um). We fit this new and
several existing libraries to a sample of 68 nearby and luminous AGNs with
Spitzer/IRS spectra dominated by AGN-heated dust. We find that the [GoMar23]
model can adequately reproduce up to 85-88% of the spectra. The dust grain size
parameter significantly improves the final fit in up to 90% of these spectra.
Statistical tests indicate that the grain size is the third most important
parameter in the fitting procedure (after the size and half opening angle of
the torus). The requirement of a foreground extinction by our model is lower
compared to purely clumpy models. We find that 41% of our sample requires that
the maximum dust grain size is as large as Psize =10um (= 3.41um).
Nonetheless, we also remark that disk+wind and clumpy torus models are still
required to reproduce the spectra of a non-negligible fraction of objects,
suggesting the need for several dust geometries to explain the infrared
continuum of AGN. This work provides tentative evidence for dust grain growth
in the proximity of the AGN.Comment: 26 pages, 14 figures, 4 tables, accepted for publication in A&
Expectations for time-delay measurements in active galactic nuclei with the Vera Rubin Observatory
The Vera Rubin Observatory will provide an unprecedented set of
time-dependent observations of the sky. The planned Legacy Survey of Space and
Time (LSST) operating for 10 years will provide dense lightcurves for thousands
of active galactic nuclei (AGN) in Deep Drilling Fields (DDFs) and less dense
lightcurves for millions of AGN. We model the prospects for measuring time
delays for emission lines with respect to the continuum, using these data. We
model the artificial lightcurves using Timmer-Koenig algorithm, we use the
exemplary cadence to sample them, we supplement lightcurves with the expected
contamination by the strong emission lines (Hbeta, Mg II and CIV as well as
with Fe II pseudo-continuum and the starlight). We choose the suitable
photometric bands appropriate for the redshift and compare the assumed line
time delay with the recovered time delay for 100 statistical realizations of
the light curves. We show that time delays for emission lines can be well
measured from the Main Survey for the bright tail of the quasar distribution
(about 15% of all sources) with the accuracy within 1 sigma error, for DDFs
results for fainter quasars are also reliable when all 10 years of data are
used. There are also some prospects to measure the time delays for the faintest
quasars at the smallest redshifts from the first two years of data, and
eventually even from the first season. The entire quasar population will allow
obtaining results of apparently high accuracy but in our simulations, we see a
systematic offset between the assumed and recovered time delay depending on the
redshift and source luminosity which will not disappear even in the case of
large statistics. Such a problem might affect the slope of the
radius-luminosity relation and cosmological applications of quasars if
simulations correcting for such effects are not performed.Comment: Submitted to Astronomy & Astrophysics, comments wellcom
The Differences in the Torus Geometry Between Hidden and Non-Hidden Broad Line Active Galactic Nuclei
We present results from the fitting of infrared (IR) spectral energy distributions of 21 active galactic nuclei (AGNs) with clumpy torus models. We compiled high spatial resolution (~0.3–0.7 arcsec) mid-IR (MIR) N-band spectroscopy, Q-band imaging, and nuclear near- and MIR photometry from the literature. Combining these nuclear near- and MIR 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 AGNs have smaller torus opening angles and larger covering factors than HBLR AGNs. 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 AGNs