Issue |
A&A
Volume 504, Number 1, September II 2009
|
|
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Page(s) | 73 - 79 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/200912023 | |
Published online | 09 July 2009 |
The bolometric luminosity of type 2 AGN from extinction-corrected [OIII]
No evidence of Eddington-limited sources
A. Lamastra1 - S. Bianchi1 - G. Matt1 - G. C. Perola1 - X. Barcons2 - F. J. Carrera2
1 - Dipartimento di Fisica ``E. Amaldi'', Università degli Studi
Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
2 -
Instituto de Física de Cantabria (CSIC-UC), Avenida de los Castros, 39005
Santander, Spain
Received 10 March 2009 / Accepted 27 May 2009
Abstract
Context. There have been recent claims that a significant fraction of type 2 AGN accrete close to or even above the Eddington limit. In type 2 AGN, the bolometric luminosity ()
is generally inferred from the [OIII] emission line luminosity (
). The key issue in estimating the bolometric luminosity in these AGN, is therefore to know the bolometric correction to be applied to
.
A complication arises from the observed
being affected by extinction, most likely from dust within the narrow line region. The extinction-corrected [OIII] luminosity (
)
is a better estimator of the nuclear luminosity than
.
However, only the bolometric correction to be applied to the uncorrected
has been evaluated so far.
Aims. This paper is devoted to estimating the bolometric correction
/
for deriving the Eddington ratios for the type 2 AGN in a sample of SDSS objects.
Methods. We collected 61 sources from the literature with reliable estimates of both
and X-ray luminosities (
). To estimate
,
we combined the observed correlation between
and
with the X-ray bolometric correction.
Results. In contrast to previous studies, we found a linear correlation between
and
.
We estimated
using an earlier luminosity-dependent X-ray bolometric correction, and we found a mean value of
in the luminosity ranges log
= 38-40, 40-42, and 42-44 of 87, 142, and 454, respectively. We used it to calculate the Eddington ratio distribution of type 2 SDSS AGN at 0.3<z<0.4 and found that these sources are not accreting near their Eddington limit, contrary to previous claims.
Key words: galaxies: active - galaxies: Seyfert - X-rays: galaxies
1 Introduction
Active galactic nuclei (AGN) are believed to be powered by gas accretion
onto the black hole located at the centre of galaxies.
The AGN bolometric luminosity ()
depends on the mass accretion rate and on the efficiency for the conversion of gravitational energy into radiation.
In this scenario, the luminosity produced by a black hole has a physical
limit, the Eddington limit
(
(
/
)
erg/s), at which
the radiation pressure from accretion of the infalling matter balances
the gravitational force of the black hole.
The ratio between the bolometric and Eddington luminosities,
/
,
is referred to as the Eddington ratio.
The knowledge of the Eddington ratio distribution and its evolution is very
important for constraining the predictions of theoretical models which link the evolution of the galaxies in the hierarchical clustering
scenario with the quasar evolution (e.g. Menci et al. 2003, 2004). In fact,
all predictions regarding AGN, such as the luminosity function or the black-hole mass
function of AGN relics, depends on the assumptions about this quantity. The
estimate of the Eddington ratio
requires measurements of the black hole
mass,
,
and of the bolometric luminosity,
.
According to the unification model (Antonucci 1993), the optical/UV continuum source and the surrounding broad emission line region (BLR) in the AGN classified as type 1 are viewed without any substantial obscuration, while in type 2 AGN these regions suffer obscuration along the observer's line of sight by intervening dusty material, most of which is likely associated with a circumnuclear structure often referred to as the torus. Even if some exceptions have been found (e.g. Bianchi et al. 2008), the unification model can be safely assumed to provide a useful reference frame for the vast majority of sources.
Progress in reverberation mapping of type 1 AGN (Peterson et al. 2004, 2005)
provided rather good evidence that the BLR size depends on the optical
continuum luminosity (Kaspi et al. 2000, 2005; Bentz et al. 2006).
This size-luminosity relation, combined with the gas
velocity derived from the width of the emission lines, under the assumption
that the BLR clouds are in Keplerian motion around the black hole, has been
widely used to estimate the black hole masses, in large samples of type 1 AGN
up to
(e.g. Woo & Urry 2002; McLure & Dunlop 2004; Warner
et al. 2004; Kollmeier et al. 2006; Vestergaard 2002, 2004; Netzer &
Trakhtenbrot 2007). The Eddington ratio is then obtained by applying a bolometric
correction to the optical luminosity. These authors seem to agree on a
practically constant value of
(
Kollmeier et al. 2006) at all z, irrespective of luminosity and black hole mass, after selection
effects had been properly taken into account (but see Netzer &
Trakhtenbrot 2007 for a recent result indicating a dependence of
on both
and z up to
).
In type 2 AGN, the BLR is not visible and the
estimate is usually obtained through the empirical
relationships between the black hole mass and the properties of the spheroidal
component of the host galaxy (e.g. Magorrian et al. 1998; Gebhardt
et al. 2000a; Ferrarese
Merritt 2000; Tremaine et al. 2002). This method has
been applied to a very large sample of type 2 AGN in the local Universe
(Kauffmann et al. 2003; Heckman et al. 2004 here-in-after H04; Kauffmann & Heckman 2009). At higher z, however, this
method becomes more difficult to apply, especially in spiral galaxies where it
is necessary to disentangle the contribution of the bulge from that of the
disk. A step forward in this direction has been recently made by Bian et al. (2006, here-in-after B06), which were able to estimate the black hole masses for a
subsample of SDSS type 2 AGN at
0.3< z <0.83 from the Zakamska et al. (2003) sample. The black hole mass estimate was obtained from the stellar
velocity dispersion measurements (
)
and the
-
relation of Tremaine et al. (2002).
In type 2 AGN, since the primary optical/UV radiation is strongly affected
by dust extinction, the bolometric luminosity is generally inferred from the [OIII] emission line luminosity (
).
The [OIII] emission line arises in the much larger narrow-line region (NLR),
where the gas is photoionized by the continuum radiation escaping within the opening angle of the torus. The observed flux is therefore
weakly affected by the viewing angle relative to the torus and its luminosity
indicates the nuclear luminosity. The key issue in estimating
in these AGN is therefore to have a
bolometric correction factor in hand to be applied to
.
After computing a mean bolometric correction factor to the
observed [OIII] luminosity, H04 used it to estimate the Eddington ratio
distribution of local (
)
type 2 AGN. This bolometric correction factor was also used by B06 to estimate the
-distribution of their sample. B06 found a mean
value for this distribution
,
which would reveal a population
of high Eddington ratio sources that differs from that observed in the local
Universe and in type 1 AGN. If confirmed, this result would have enormous
impact on the way that massive black holes grow along cosmic time, because most of
this growth is expected to occur at significant redshift and in obscured objects.
However,
is only an indirect estimator of the nuclear luminosity,
which depends on the geometry of the system, on the amount of gas, and on any
possible shielding effect that may affect the ionizing radiation seen by the NLR.
This implies an intrinsic scatter in the
-
relation and therefore an uncertainty in the
estimate.
A further complication arises from the [OIII] emission line being affected by extinction, likely due to dust within the NLR.
In some cases, the reddening due to the NLR can be evaluated, and the extinction-corrected [OIII] luminosity (
)
is a more direct estimator
of the nuclear luminosity than
.
We estimated the [OIII] bolometric
correction following a similar method adopted by H04, but we used the extinction-corrected [OIII] luminosity instead of
the observed one.
Then we used this bolometric correction to calculate the Eddington ratio of the sources from the B06 sample for which the extinction-corrections are available. Moreover, we observed 8 sources of the B06 sample with XMM-Newton, in order to have an independent estimate of the bolometric luminosity through X-ray luminosity.
The paper is organised as follows. In Sect. 2 the bolometric correction estimate is described. Section 3 is devoted to the estimate of the Eddington ratio distribution. Discussion and conclusions follow in Sect. 4.
2 The
-
luminosity relation
H04 estimated the bolometric
correction (BC) to the observed [OIII] luminosity,
,
in a two-step process. First they estimated the mean ratio between the monochromatic
continuum luminosity at 5000
and the [OIII]
luminosity, L5000/
,
in a sample of type 1 AGN. Then they calculated the mean ratio
between the bolometric luminosity and L5000 using the average type 1 AGN
intrinsic spectral energy distribution (SED) of Marconi et al. (2004).
They find /
0. As discussed in H04,
they did not correct
for dust extinction in the NLR,
because the extinction correction is usually made by measuring the observed Balmer
decrement (H
/H
), and in type 1 AGN this procedure requires deblending the narrow
components from the broad ones.
In Seyfert galaxies optically classified as type 1.5, 1.8, 1.9, and 2, in
which the narrow components of the H
and
H
lines dominate the line profiles (Osterbrock & Ferland 2006), the estimate of the
Balmer decrement can instead be considered reliable.
We therefore used these Seyfert types to estimate the BC to convert the
extinction-corrected [OIII] luminosity,
,
to the bolometric
luminosity.
In these Seyfert types, the bolometric luminosity
cannot be easily determined because the primary optical/UV radiation is highly obscured.
In X-rays, however, the nuclear emission could be directly estimated,
provided that the absorbing matter is Compton-thin (i.e.
cm-2); if the matter is Compton-thick,
no nuclear radiation is visible below 10 keV, with the Compton reflection
component usually dominating the spectrum.
Assuming that the X-ray bolometric correction is the same in type 1 and in
type 2 AGN, we used the relation between
and the absorption
corrected X-ray luminosity and the X-ray
bolometric correction of type 1 and Compton-thin type 2
AGN to estimate the [OIII] bolometric correction (
).
We have collected a sample from the literature for which reliable estimates of the Balmer decrement,
and
,
were available. We discarded Seyfert galaxies with optical classification
1.2 and X-ray Compton-thick sources.
The final sample consists of 61 sources: 5 from Mulchaey et al. (1994)
, 12 from Panessa et al. (2006, P06
hereafter), and 44 from Bassani et al. (1999, B99 hereafter, 8 of these 44 sources
are also included in the P06 sample).
We used the B99 relation to derive
from the Balmer decrement:
which assumes an intrinsic Balmer decrement equal to 3.0 as expected in the NLR (see Osterbrock & Ferland 2006).
In Fig. 1 (top panel) the distribution of the ratio between the
(2-10) keV luminosity and the extinction-corrected [OIII] luminosity for our sample is shown. The mean of this distribution is
and the dispersion is 0.63 dex.
![]() |
Figure 1:
Distribution of log( |
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The bottom panel of Fig. 1 shows
versus L
.
The
correlation is highly significant
(Spearman rank correlation coefficient
,
). To quantify any distance-driven
effects that may be present in a luminosity-luminosity correlation, we also
performed a ``scrambling test'' (see e.g. Bregman 2005; Merloni et al. 2006;
Bianchi et al. 2009b). The correlation does not appear to be affected by distance effects:
not even a data-set out of the 100 000 simulated ones has a correlation
coefficient as large as the one measured in the real data set.
An ordinary least-square bisector procedure gives
the following best fit:
i.e., we found a linear correlation between


P06 investigated the same correlation finding that L
.
They included in their analysis type 1 AGN, type 2 AGN, and
Compton-thick sources (in the latter case they assumed that the intrinsic X-ray
luminosity is 60 times higher than the observed one) and covered about five orders
of magnitude in both [OIII] luminosity and X-ray luminosity.
It should be recalled that the P06 sample is optically
selected, while our sample, mainly based on the B99 catalogue, includes both optically selected and
X-ray selected AGN. As discussed in several papers, most recently in Heckman et al. (2005) and Netzer et al. (2006, N06 hereafter), X-ray selected samples are likely to be biased towards X-ray bright
sources, hence produce a higher X/[OIII] ratio compared to
optically selected ones. The 44 sources that we have selected from the B99
catalogue all have log
.
The presence of X-ray selected
objects among these sources should therefore tend to make the
-L
relationship steeper than found by P06, which, as
can also be seen in Fig. 1, is exactly the opposite of what we found.
On the other hand, the high-luminosity ranges in P06 are nearly completely populated by type 1 AGN, for
which we consider the estimate of
unreliable. The steeper slope
of the
-
relation found by P06 could indeed
stem from an underestimate of the reddening in these AGN types.
N06 studied the relation between
and
in samples of type 1 and type 2 AGN. They found that the ratio
between
and
decreases with
,
and the
same result was obtained also for type 2 AGN using the extinction-corrected [OIII]
luminosity. In that case, they used the B99 catalogue but excluded sources
with optical classification
and Compton-thick sources. They found
log(
/
) = (
)
- (
)log
,
which
implies
1.61, i.e. a correlation with an even steeper slope
than that obtained by P06.
Our analysis only differs from N06 for the inclusion of the AGN
optically classified as type 1.5. Excluding these sources from our sample, we found
for the remaining 52 sources:
(
= 0.85,
), i.e. a significant linear correlation also in this
case. The discrepancy between the results may come from the narrower range of
luminosities covered by N06, which does not include sources with
1040erg/s. Unfortunately we
cannot make a clear comparison with N06, because they did not perform a simple
-
fit, an extrapolation of the resulting slope from their fit may be
misleading. Moreover N06 did not explicitly report the method they used to compute the
linear regression and the significance of the correlation they found.
The relation between
and L
can be combined with
the X-ray bolometric correction (XBC) to obtain the [OIII] bolometric correction factor,
.
Adopting the luminosity-dependent XBC of Marconi et al. (2004), we found a
mean value of
in the luminosity ranges log
,
40-42, and 42-44 of 87, 142, and 454, respectively.
As a cautionary remark, it must be noted that the XBC may suffer from large uncertainties.
Marconi et al. (2004) and Hopkins et al. (2007) accounted for variations
in AGN SEDs with luminosity using the anti-correlation between the optical-to-X-ray spectral index
(
)
and the luminosity at 2500
(L2500) (e.g. Vignali
et al. 2003a), but
Hopkins et al. (2007) find that the intrinsic spread in AGN SEDs could give
rise to variation of a factor of
2 in the XBC, even when luminosity
dependence is taken into account.
Moreover, the very dependence on luminosity of the X-ray bolometric correction has been questioned by Vasudevan & Fabian (2007), who estimate it from the observed SEDs of 54 AGNs. They find evidence of a large scatter in the XBC, with no simple dependence on luminosity, and suggest instead the Eddington ratio as the physical quantity the bolometric correction depends on.
Very recently, Kauffmann & Heckman (2009) have anticipated an estimate of
.
They find
in the range
500 to 800. Because the details of their
analysis have not been published yet, for the time being we are not able
to discuss the origin of this discrepancy.
3 The Eddington ratio distribution of type 2 SDSS AGN at 0.3 <z< 0.4
B06 measured the stellar velocity dispersion,
,
for 30 sources
of the 0.3<z<0.8 SDSS type 2 AGN sample of Zakamska et al. (2003). The
stellar velocity dispersion was obtained by fitting the profile of heavy
element absorption lines, which are mainly associated with the old stellar
population in the bulge. Then, they estimated the black hole masses from
,
adopting the Tremaine et al. (2002) relation.
The B06 subsample is representative of the total
sample of Zakamska et al. (2003) with respect to
.
Indeed, the observation of significant stellar absorption features, which is the key point in accurately measuring
,
does not appear to depend on the nuclear luminosity of the sources, as confirmed by a t-test (see B06).
For 15 sources, B06 calculated
the [OIII] line luminosity corrected for extinction using the observed Balmer
decrement and Eq. (1). Therefore all these sources have
,
because of the limited
wavelength coverage of the SDSS spectroscopy (
3800-9200
).
The ratio between
and
is between 0.6 and 17.8. The observed Balmer decrement
is lower in three objects than the theoretical value, most likely due to an imperfect
subtraction of the starlight.
We assigned zero extinction to these objects.
Figure 4 in B06 shows the distribution of the Eddington ratios of the 15
sources where we have a reliable estimate of
.
This distribution is surprising
for its mean value,
1; because it would reveal a population of
high Eddington ratio sources that are not observed in the local Universe, such
Eddington ratios are neither observed in type 1 AGN at higher redshift.
However, it is important to note that B06 obtained this distribution by
estimating the bolometric luminosity from
and the BC given by
H04. This bolometric correction applies to
and not to
,
therefore B06 overestimated
in a systematic manner and hence
.
In this section we use
,
as computed in Sect. 2, to calculate the Eddington ratio distribution of the
type 2 SDSS AGN of the B06 sample. First of all we have tested
the reliability of deriving
from the [OIII] line luminosity in an
optically selected sample, adopting the
we derived in a collection
of X-ray selected and optically selected sources.
To this aim we used the P06 subsample used in Sect. 2.
In the top panel of Fig. 2 the Eddington ratio estimates obtained from
and
(
)
are compared with those obtained from
and the XBC of Marconi et al. (2004,
;
the black hole masses taken from Table 2 of P06). We find good agreement between the X-ray and the [OIII] estimates.
For the 8 SDSS AGN of the B06 sample for which we have
XMM-Newton observations, we can repeat the above check.
The bottom panel of Fig. 2 shows
versus
obtained from
and
and versus
obtained by B06.
As expected, the
obtained by B06 are systematically
larger than those derived from the X-ray luminosity, while this effect
disappears when the proper bolometric correction is used.
The black hole mass, the [OIII] line luminosity, the extinction-corrected
[OIII] line luminosity, the (2-10) keV observed flux (
), and the
intrinsic (i.e. de-absorbed) (2-10) keV luminosity (
)
of the
X-ray observed sources are listed in Table 1. The X-ray data
reduction and the estimate of
either from X-ray spectral fitting
or extrapolated from the observed X-ray count rates (or upper limits) are
reported in the Appendix. The [OIII] luminosities are derived from the SDSS
spectra, except for SDSSJ083945.98+384319.0. This source has z=0.424 so the SDSS spectrum does not
cover the spectral range necessary to measure the H
line. The [OIII]
line luminosity and the Balmer decrement measurements are obtained from
observation collected with the 2.2 m telescope at the Centro Astronómico
Hispano Alemán (CAHA) at Calar Alto.
![]() |
Figure 2:
Top:
|
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Table 1: Properties of the SDSS type 2 AGN
Figure 3 shows the -distribution of the B06 sample
obtained using
and
to estimate the bolometric
luminosity. This distribution is obviously shifted to lower
values
with respect to that obtained by B06: the mean of this distribution is
,
a value that is similar to that
estimated in other AGN samples.
We have checked whether the width of the observed -distribution
indicates a physical spread in the Eddington ratios or can be due
to the dispersion in the
-
relation. In practice,
we checked that the observed distribution is consistent with a log-normal
distribution centred at log
and with width equal to the
dispersion in the
-
relation (0.63 dex). A
Kolmogorov-Smirnov test gives D=0.27, which
corresponds to a probability of 0.18 for the null hypothesis that the two
distributions are drawn from the same parent population.
![]() |
Figure 3:
Eddington ratio distribution of the B06 sample, which is obtained by estimating |
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4 Conclusions
In this paper we estimate the bolometric correction
factor,
,
needed to convert the extinction-corrected [OIII] line luminosity to
bolometric luminosity.
We determined
in a two-step process. First we studied the
-
relation in a sample of 61 Seyfert galaxies with
reliable measurements of both
and
;
i.e., we selected
galaxies with reliable measurement of the Balmer decrement
(Seyfert galaxies with optical classification
1.5) and X-ray Compton-thin
sources. The bolometric correction C
was then obtained by combining the mean
ratio between
and
with the luminosity-dependent X-ray bolometric
correction of Marconi et al. (2004). We found a
mean value of C
in the luminosity ranges log
,
40-42, and 42-44 of 87, 142, and 454, respectively.
Similarly, H04 estimated the [OIII] bolometric correction by combining
the mean ratio between L5000 and
in a sample of
type 1 AGN with the 5000 Angstrom continuum to
correction from Marconi et al. (2004). H04 did not correct
for the extinction in the NLR,
therefore their bolometric correction applies to the ``observed'' [OIII] luminosities.
Compared to H04 our estimate of the [OIII] bolometric correction is not
subject from the scatter due to the extinction in the NLR, which we estimated
to be about 0.6 dex from our sample.
The [OIII] line luminosity is an indirect estimator of the nuclear
luminosity, depending on the geometry of the system, and on any
possible shielding effect that may affect the ionizing radiation seen by the NLR.
The amount of gas that is exposed to the ionizing radiation depends on the
torus opening angle. Bianchi et al. (2007, and references therein) confirmed the
Iwasawa-Taniguchi (IT) effect, i.e. the anti-correlation between the iron line equivalent
width and the X-ray luminosity. The simplest explanation for the IT effect is in terms
of a decrease in the torus covering factor (and hence an increase in its opening angle)
with luminosity, which may also explain the observed decrease with
luminosity of the ratio between mid-IR and bolometric luminosities (Maiolino et al.
2007; Treister et al. 2008). If this explanation is correct, we would expect a less
than linear relation between
and
,
different from what we
found. The situation is even worse with the more than linear relations found by
P06 and N06. This problem will be addressed in a forthcoming paper.
We used
to estimate the Eddington ratio distribution of
type 2 SDSS AGN at 0.3<z<0.4 from the B06 sample. B06 find that the mean of
this distribution
is
1, thus revealing a population of high Eddington ratio
sources that is absent in the local Universe and in type 1 AGN at
higher redshift (e.g. Woo & Urry 2002; McLure & Dunlop 2004; Warner
et al. 2004; Kollmeier et al. 2006; Vestergaard 2002, 2004; Netzer &
Trakhtenbrot 2007).
However, we have demonstrated, with the help of the X-ray
luminosities, that B06 have sistematically overestimated the bolometric luminosities, hence the Eddington
ratios, which we found to be
,
similar to what is found in other AGN samples.
Acknowledgements
This work benefitted from an Italy-Spain Integrated Actions, reference HI-0079. A.L., G.M., and S.B. acknowledge financial support from ASI (grant I/088/06/0). X.B. and F.J.C. acknowledge financial support by the Spanish Ministerio de Ciencia e Innovación under project ESP2006-13608-C02-01. The authors thank Cristian Vignali for useful discussions, and the anonymous referee for constructive comments. The work is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA), and on observation collected with the 2.2 m telescope at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).
Appendix A: The X-ray data
Table A.1: X-ray count rates.
Of the 8 sources presented in this paper, 7 were observed as a part of our XMM-Newton proposal ID 050206 and ID 055120, and one was observed serendipitously. The data were processed using the XMM-Newton Science Analysis Software (SAS) v.8.0. The raw event files (the Observation Data Files, ODF), have been linearized with the XMM-SAS pipeline EPPROC for the PN camera, and we generated calibration files using the XMM-SAS pipeline CIFBUILD. Event files were cleaned from bad pixel (hot pixels and events out of the field of view), and we selected events spread at most in two contiguous pixels (pattern = 0-4). We removed periods of high background levels by analysing the light curves of the count rate at energies higher than 10 keV. Response functions (the ancillary response file and the redistribution matrix file) for spectral fitting were generated using the SAS tasks RMFGEN and ARFGEN. We extracted the PN counts in a circular region with radius of 15'', centred at the source position, and the background counts in the source-free regions close to the target.
The SDSS name, redshift, exposure times (filtered for good time intervals), and X-ray PN count rates (or 5
upper limits) in the rest frame energy ranges (0.5-2) keV and (2-10) keV are listed in Table A.1.
Of the 8 sources, two are detected (i.e. the Poisson probability of a spurious
background excess is less than 2.710-3) in the (0.5-10) keV band,
two only in the
soft band (0.5-2 keV) and one only in the hard band (2-10 keV).
Sufficient counts for a spectral fitting in the 2-10 keV band were only collected from three sources: SDSSJ075920.21+351903.4, SDSSJ143928.23+001538.0, and SDSSJ083945.98+384319.0.
Spectral analysis was carried out with XSPEC v.12.4.0 using data accumulated in energy bins with 5 counts each and the C-statistic (Cash 1979). The spectral fits are shown in Fig. A.1.
The X-ray spectra in the (0.5-10) keV band are fitted with an absorbed power-law continuum plus a Compton-reflection component and a soft-excess component, modelled with a power-law with photon index equal to the one of the primary continuum. The parameters of the fits along with the observed (2-10) keV flux, and the de-absorbed (2-10) keV luminosity are shown in Table A.2. In SDSSJ075920.21+351903.4 an iron line with equivalent width of about 2.6 keV is also detected, revealing that this source is Compton-thick. In these sources the primary X-ray emission is totally suppressed below 10 keV, the hard X-ray emission is accounted for by reflection of the primary nuclear emission off the inner walls of optically thick circumnuclear matter.
Table A.2: Best-fit parameters.
The luminosity reported in Table A.2 is obtained assuming that the ratio between the reflected and the primary component is 0.05, similar to what is observed in the Circinus galaxy, one of the best-studied Compton-thick sources (Matt et al. 1999).
The upper limits in the X-ray luminosity, listed in Table 1,
for the other sources are extrapolated from the observed count rates (Col. 5 of Table A.1) assuming a typical spectrum of Compton-thick
sources. The spectrum is assumed to be a power law with photon index
absorbed by column density of
,
plus a
pure Compton reflection component with an iron line (at 6.4 keV and with
equivalent width EW=1 keV with respect of the pexrav component). The ratio
between the reflected and the primary component is assumed to be 0.05. We
chose this spectrum because we wanted to study the extreme case of
obscuration that implies the higher intrinsic X-ray luminosities and
therefore the higher bolometric luminosities.
![]() |
Figure A.1: XMM- Newton spectra of SDSSJ083945.98+384319.0, SDSSJ143928.23+001538.0, and SDSSJ075920.21+351903.4 from top to bottom. |
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We used this method to also estimate
in the sources detected only in the soft band, because from the comparison
between the observed X-ray luminosity and that predicted from
and
Eq. (2), we argued that they are heavily absorbed sources. Therefore the soft X-ray emission is not the primary soft X-ray emissions but a soft excess component.
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Footnotes
- ...1994)
- We used
and Balmer decrement from Mulchaey et al. (1994) and the X-ray luminosities from Bianchi et al. (2009a).
- ... significant
- We consider those correlations statistically
significant whose null hypothesis probability, P, are lower
than 1
10-3, which correspond to a confidence level of 99.9
.
All Tables
Table 1: Properties of the SDSS type 2 AGN
Table A.1: X-ray count rates.
Table A.2: Best-fit parameters.
All Figures
![]() |
Figure 1:
Distribution of log( |
Open with DEXTER | |
In the text |
![]() |
Figure 2:
Top:
|
Open with DEXTER | |
In the text |
![]() |
Figure 3:
Eddington ratio distribution of the B06 sample, which is obtained by estimating |
Open with DEXTER | |
In the text |
![]() |
Figure A.1: XMM- Newton spectra of SDSSJ083945.98+384319.0, SDSSJ143928.23+001538.0, and SDSSJ075920.21+351903.4 from top to bottom. |
Open with DEXTER | |
In the text |
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