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    {\small\rm\thepage\hfill
    \quad\quad ACTA ASTRONOMICA SINICA \hfill
    \hspace{2mm} Vol.44\vspace{2mm}}}} %%%%%%%
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    {\small\rm  suppl.\hfill X.-B. Wu et al.: Black Hole Masses and Radio Properties of AGNs %%（作者：题目名称）
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    \normalsize\rm
\zihao{5}\songti

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    \zihao{6}\songti
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    \\%%%[-0.5 true mm]
    Vol.44~ Suppl.
    \hfill\hspace{8mm} %%% if ``October/January'' then \hspace{8/10 mm} July
    \small ACTA ASTRONOMICA SINICA
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      Feb.,~2003 \\[-1.5 true mm] %%January
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\vs\vs\vs \bc {\Large\bf
Black Hole Masses and Radio Properties of AGNs   %%（文题）
%\\[1ex]
%$\!\!^*$
}

\vs\vs{\normalsize Xue-Bing Wu\up{1},\hs\hs J. L. Han\up{2},\hs\hs F. K. Liu\up{1}\hs\&\hs T. Z. Zhang\up{1} }  %%（本文作者）

\vs
(\footnotesize 1~\pka)\\%%（本文作者单位）
 (\footnotesize 2~\nao )\\
\vs\vs \ec

\normalsize
\begin{quotation}

 \no{\bf A{\scriptsize\bf BSTRACT }}~~~\small
Supermassive black hole (SMBH) is believed to be an essential part
of AGN activities. Recently a lot of dynamical measurements have
shown that many nearby galaxies host SMBHs. Reverberation mapping
of about 40 AGNs also revealed that such SMBHs exist in AGNs.
 A tight relation between SMBH masses and
central velocity dispersions has been found for both nearby and
active galaxies. Using this correlation we can reliably estimate
the SMBH masses of a lot of AGNs for which other mass measurement
techniques can not apply. For a sample of Seyfert galaxies, we
found that the radio power increase with SMBH masses, similar as
that found for quasars and nearby galaxies. However, AGNs have 100
times more radio power than that of nearby galaxies at the given
black hole mass. For radio-loud AGNs, the nuclear radio-loudness
tends to increase with SMBH mass.  But such a relation
 has not been found for radio-quiet AGNs. In addition, we estimated the SMBH masses
and the Eddington ratios ($L/L_{\rm Edd}$) for a sample of AGNs
with elliptical host galaxies and found that radio-loud AGNs may
have lower Eddington ratios than radio-quiet AGNs. Some related
physics on black hole accretion  and jet formation mechanisms are
discussed.

 \vn
 \no{\bf Key words}~~  pulsar-mode  change-spectrum
\end{quotation}

%%%% 正文
 \para{\large\bf{1}~~ Introduction}

\vs\vs Supermassive black holes with masses in the range of $10^6$
to $10^9 M_\odot$, have been suggested to exist in the center
of quasars and active galactic nuclei (AGNs) in order to account
for the huge power
 of these energetic objects (Lynden-Bell 1969; Rees 1984). Recently, the
 masses of central
objects in 20 Seyfert galaxies and 17 nearby quasars have been
measured with the reverberation mapping technique (Ho 1999;
Wandel, Peterson \& Malkan 1999; Kaspi et al. 2000), which
confirmed the existence of  SMBHs in  these objects. On the other
hand, a lot of observations using gas and stellar dynamics
indicated that SMBHs  also exist in the center of our Galaxy (Ghez
et al. 1998; Genzel et al. 1997) and in the nuclei of many normal
galaxies (Kormendy \& Richstone 1995; Kormendy \& Gebhardt 2001).


One interesting result found recently for nearby galaxies is the
correlation of black hole masses with the properties of galactic bulges. Although with
large scatters, the black hole masses
 seem to correlate with  bulge luminosities (Kormendy \& Richstone 1995;
 Magorrian et al. 1998). This also leads to the finding
that the black hole mass, $  M_{\rm BH}$, is possibly proportional
to the bulge mass,
${  M}_{\rm bulge}$,  %%
though the mass ratio found by different authors was different, in
the range of 0.2\% to 0.6\% (Kormendy \& Richstone 1995; Magorrian
et al. 1998; Ho 1999).
 Recently, a significantly tight correlation
of $  M_{\rm BH}$ with the bulge velocity dispersion $\sigma$ was
also found for nearby galaxies (Gebhardt  et al. 2000a; Ferrarese
\& Merritt 2000). More recent studies indicated that 11 Seyfert
galaxies  with $ M_{\rm BH}$ measured by reverberation mapping
follow the same $ M_{\rm BH}-\sigma$ relation as for normal
galaxies (Gebhardt et al. 2000b; Ferrarese et al. 2001), implying
another  possible universal relation for both normal and active
galaxies. These correlations  strongly suggest a tight connection
between the formation and evolution of the SMBH and galactic
bulge, though the nature of this connection is still in debate.


Nonthermal radio emissions of quasars and AGNs  are believed to be
probably produced by relativistic electrons that are powered by
jets (Begelman, Blandford \& Rees 1984; Blundel \& Beasley 1998).
Similar radio emissions have been  detected in the nuclei of
normal elliptical galaxies (Sadler, Jenkins \& Kotanyi 1989) and
also in some spiral galaxies (Sadler et al. 1995). Recently, some
studies have indicated that the radio power may be directly
correlated with the black hole mass. Franceschini, Vercellone \&
Fabian (1998) found a very tight relation between black hole mass
and radio power in a small sample of nearby mostly non-active
galaxies. McLure et al. (1999) estimated the black hole masses for
a sample of AGNs using $  M_{\rm BH}$-bulge mass relation found by
Magorrian et al. (1998) and noted they follow the same correlation
with radio power as found by Franceschini et al. (1998). However,
Laor (2000) recently argued that the $ M_{\rm BH}$ and radio power
of a sample of 87 $z<0.5$ Palomar-Green (PG) quasars do not follow
the tight correlation suggested by Franceschini et al. (1998),
because quasars usually have over 100 times larger radio power
than normal galaxies at a given $ M_{\rm BH}$. He
 also noted that the radio-loud quasars seem to host more massive black
holes than radio-quiet quasars. Very recently, Ho \& Peng (2001) studied the
radio-loudness of bright Seyfert 1 galaxies using the nuclear
 radio and optical luminosities, and suggested
that the majority of Seyfert 1 nuclei in their sample are essentially radio loud.
Therefore, it is useful to check
 if these radio-loud Seyfert  nuclei  host more massive black holes than
radio-quiet ones
 and if the Seyfert galaxies still follow
the same correlation between the radio power and black hole masses of
 nearby galaxies and quasars (Wu \& Han 2001).

\para{\large\bf{2}~~SMBH Masses of Seyfert Galaxies}

\vs\vs Currently the SMBH masses of a few weak AGNs have been well
measured by stellar dynamics, ionized gas dynamics and water maser
dynamics (Kormendy \& Gebhardt 2001). Using the reverberation
mapping technique, the SMBH masses of 20 Seyfert galaxies and 17
bright quasars have been recently estimated (Ho 1999; Wandel et
al. 1999; Kaspi et al. 2000). However, for most Seyfert galaxies,
it is difficult to measure the SMBH mass using these methods
because of either the large nuclear luminosity or the lack of
long-term variability monitoring and precise measurements of
characteristic velocity dispersions in the broad emission line
region. Since the tight correlation between the SMBH mass and
bulge velocity dispersion has been found for both normal and
active galaxies (Gebhardt et al. 2000b; Ferrarese et al. 2001), it
may be straightforward to estimate the SMBH mass from the measured
bulge velocity dispersion. Here we adopt the $  M_{\rm
BH}$-$\sigma$ relation found by Merritt \& Ferrarese (2001),
namely,

\be
 M_{\rm BH}=1.3 \times 10^8 {\rm M}_\odot(\sigma/200\,{\rm km}\,{\rm s}^{-1})^{4.72}\,, %%
\ee
to derive the SMBH masses for Seyfert galaxies with measured
nuclear velocity dispersions.
Using a slightly flatter relation found by Gebhardt et al. (2000)  %%
does not cause significant changes in our results.


\begin{figure}[h]
\center {\includegraphics [bb=18 144 592
718,scale=0.6]{wuxbf1.eps}}

   \parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {%\center
   \footnotesize

      Fig.\,1~~ The nuclear radio-loudness and the nuclear radio power against the
black hole masses for
        Seyfert galaxies. The dashed line in the lower panel represents the tight
        correlation  for nearby galaxies found by Franceschini et al. (1998).}

    \end{figure}


We selected 37 Seyfert galaxies, including 22 Seyfert 1s and 15
Seyfert 2s from two well-studied  Seyfert samples, namely the
Palomar and CfA bright Seyfert samples (Ho et al. 1997a;
Osterbrock \& Martel 1993). These Seyfert galaxies have either the
measured SMBH masses or the measured central velocity dispersions.
Among them, three Seyfert 1s and two Seyfert 2s have dynamical
SMBH masses (Ho 1999; Gebhardt et al. 2000a), and ten Seyfert 1s
have SMBH masses measured by the reverberation mapping method
(Wandel et al. 1999; Ho 1999). Another Nine Seyfert 1s and 13
Seyfert 2s have measured central velocity dispersions but unknown
SMBH masses
 (Nelson \& Whittle 1995). The SMBH masses
 can be estimated by equation (1) using the measured central velocity
dispersions. Therefore, our sample consists of 37 Seyfert galaxies
with derived SMBH masses.

The radio properties of Seyfert galaxies have been investigated
using the Very Large Array (VLA) at 3.6\,cm by Kukula et al.
(1995) for the CfA sample, and at 6\,cm and 20 cm recently by Ho
\& Ulvestad (2001) for the Palomar sample.  Here we adopt the
radio data for Seyfert 1s from Ho \& Peng (2001) and the data for
Seyfert 2s from Ho \&  Ulvestad (2001) and Kukula et al. (1995).
The 6 cm data for
 some sources in the CfA sample (Kukula et al. 1995) were extrapolated from the 3.6cm data assuming
$f_{\nu} \propto
\nu^{-0.5}$.

Seyfert galaxies have been  considered usually as radio-quiet AGNs
because most of them have lower radio-loudness, defined as the
ratio of the radio to optical luminosities,
 $R = L_{6 cm}/L_B$. However, recently Ho \& Peng (2001) showed
that though the nuclear radio power for Seyfert 1 galaxies on
average accounts for about $75\%$ of the total radio emission, the
nuclear optical luminosity, measured by high-resolution optical
images, accounts for merely 0.01\% of the integrated light. If the
radio-loudness is measured by the nuclear
 radio and optical luminosities,
most Seyfert 1s are in the category of radio-loud AGNs (with
radio-loudness larger than 10). Their nuclear radio-loudness,
$R_c$, can be calculated by $R_c = L^{\rm nuc}_{6
cm}/L^{\rm nuc}_B$.  %%
The Hubble constant $H_0 =75 {\rm kms^{-1}Mpc^{-1}}$ and the
deceleration parameter of $q_0=0.5$ were adopted. For Seyfert 2s,
the measurements of their nuclear optical magnitudes are not
available
 in the literature.

Figure 1 shows the relation of SMBH masses with the nuclear
radio-loudness of Seyfert 1s and the radio power of Seyfert
galaxies. It is  clear  that the radio-loud Seyfert 1s with larger
nuclear radio-loudness seem to host more massive black holes. The
similar tendency has been found for nearby quasars by Laor (2000).
From Figure 1(b) we see a trend that Seyfert galaxies having a
larger radio power perhaps host a more massive black hole than
those of less radio power. With the same black hole mass, Seyfert
galaxies seem to have 100 to 1000 times greater radio power than
normal galaxies. Laor (2000) has shown that nearby quasars also
depart from such a correlation for nearby galaxies, with the radio
luminosity of quasars being $10^4$ larger at a given $\rm M_{\rm
BH}$. The difference of radio luminosities of  quasars,
Seyfert galaxies and nearby galaxies may be simply due to different levels  %%
of nuclear activity.

\begin{figure}[h]
\center {\includegraphics [bb=18 144 592
718,scale=0.6]{wuxbf2.eps}}

   \parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {%\center
   \footnotesize

      Fig.\,2~~ The radio-loudness (a) and radio power (b) against the black %%
   hole masses for Seyfert galaxies
in the sample of Nelson \& Whittle (1995). The dashed line in (b)
represents the tight
        correlation found by Franceschini et al. (1998) for nearby galaxies.}

    \end{figure}

We can also investigate the relation between SMBH masses and radio
properties using the Seyfert sample in Nelson \& Whittle (1995),
where the measurements of nuclear velocity dispersions of about 70
Seyfert galaxies were reported. After excluding several LINERs and
normal galaxies, we got 33 Seyfert 1s and 32 Seyfert 2s. We
estimated the SMBH masses of these Seyfert galaxies using the $\rm
M_{\rm BH}$-$\sigma$ relation (eq. (1)). The  total radio power at
5\,GHz of them was calculated from the 1.4 GHz data in Nelson \&
Whittle (1995) by assuming $f_\nu \propto \nu^{-0.5}$ and $H_0=80
{\rm kms^{-1}Mpc^{-1}}$. The radio-loudness was calculated by the
5 GHz radio luminosity and the B-band optical luminosity. The
radio-loudness and total radio power against the SMBH masses for
29 Seyfert 1s and 25 Seyfert 2s with available radio data in the
sample of Nelson \& Whittle (1995) are plotted in Fig.~2.
 Now we see
that most Seyfert galaxies  seem to be radio quiet ($R<10$) when
we adopted the total radio and optical luminosities to calculate
the radio-loudness. There is a weak tendency that Seyfert galaxies
with larger radio-loudness have larger SMBH masses. A comparison
with the result in Figure 1(a) indicates that the nuclear
radio-loudness may be more fundamental and reflect the nature of
central engine of Seyfert galaxies. From Figure 2(b) we see that
there is a strong correlation between the total radio power and
the SMBH mass, which confirms the previous result that AGNs with
larger radio power may host more massive SMBHs (Franceschini et
al. 1998; McLure et al. 1999). However,
  Seyfert galaxies depart significantly from the tight relation
between the radio power and SMBH mass found for normal galaxies by
Franceschini et al. (1998).


\para{\large\bf{3}~~SMBH Masses and Eddington Ratios of Radio Galaxies and
Quasars}

\vs\vs The tight M$_{BH}$-$\sigma$ relation suggests an
interesting possibility to estimate the central black hole masses
for galaxies using the measured values of bulge velocity
dispersions. This straightforward method is particularly important
for  AGNs because the dynamical method cannot be applied for the
determination of the black hole mass for most of them. However,
AGNs usually have very bright nuclear emission, which makes it
very difficult to measure their stellar velocity dispersions with
the spectroscopic method. For most AGNs, one has to look for other
methods to determine the central velocity dispersions of their
host galaxies.

Imaging studies on the host galaxies of AGNs with HST have
clearly revealed that a lot of  BL Lac objects, radio galaxies, radio-loud quasars, and
some radio-quiet quasars have massive elliptical hosts (Urry et al. 2000;
McLure et al. 1999; Dunlop et al. 2002).  It is well known for
ellipticals that three observables, the effective radius,
the corresponding average surface
brightness and the central velocity dispersion, follow a surprisingly
tight linear relation (so-called fundamental plane, see Djorgovski
\& Davis 1987; Dressler et al. 1987; Faber et al. 1989).
Some subsequent studies have shown that  the elliptical hosts of radio
galaxies follow the same fundamental plane
as normal ellipticals (Bettoni et al. 2001).
Because the fundamental plane is probably universal and  exists also for
elliptical hosts of AGNs, it is possible to estimate the central velocity dispersions
from the morphology parameters of the host galaxies (McLure \& Dunlop
2001). This provides
another possible way to derive the SMBH masses of AGNs for which
high quality images of their host galaxies have been obtained (Wu, Liu \& Zhang 2002).

A deep HST imaging study of the host galaxies of a sample of 10
radio galaxies (RGs), 10 radio-loud quasars (RLQs) and 13
radio-quiet quasars (RQQs) has been  performed recently (McLure et
al. 1999; Dunlop et al. 2002).  The hosts of both radio-loud AGNs
and bright radio-quiet AGNs were found to be virtually all massive
ellipticals. The basic properties of these host galaxies are
indistinguishable from those of normal ellipticals. Therefore,
using the fundamental plane relation, we can  derive the central
velocity dispersions and black hole masses for this sample of AGNs
based on the morphology parameters of their host galaxies. The
average SMBH masses of RGs, RLQs and RQQs were estimated to be
$10^{8.13}{\rm M}_\odot$, $10^{8.22}{\rm M}_\odot$ and
$10^{7.90}{\rm M}_\odot$ respectively. The mean SMBH mass of 9
RQQs is smaller by only a factor of two than that of 10 RLQs. Most
of these AGNs have black hole masses in the range of $10^{7.5}{\rm
M}_\odot$ to  $10^{9}{\rm M}_\odot$.

\begin{figure}[h]
\center {\includegraphics [bb=19 160 550
679,scale=0.4]{wuxbf3.eps}}

   \parbox[tb]{9cm}
   %{\hspace{3.5cm}
   {%\center
   \footnotesize

      Fig.\,3~~ Comparisons of Eddington ratios of radio-loud quasars, radio-quiet quasars
and radio galaxies.}

    \end{figure}

Using the derived SMBH masses, we can estimate the Eddington ratio
(defined as the ratio of bolometric luminosity and Eddington
luminosity) of the source in our sample of RGs, RLQs and RQQs. We
adopted the assumptions of $L_{\rm bol}\simeq 10 \lambda
L_{5100\AA}$ (Kaspi et al. 2000) and $f_\nu \propto \nu^{-0.2}$
(Dunlop et al. 2002) to convert the R-band luminosity to the
bolometric luminosity for the nuclear component of AGNs. Figure 3
shows the distributions of Eddington ratios of 9 RGs, 10 RLQs and
9 RQQs. It is clear that the Eddington ratios of RGs are
systematically smaller than those of RLQs and RQQs by two orders,
while there is less significant difference in Eddington ratios for
RLQs and RQQs. Our result is  qualitatively consistent with that
obtained by Ho (2002) who recently suggested that the strongly
active AGNs have larger Eddington ratios. Figure 3 shows that both
RLQs and RQQs have a bolometric luminosity comparable to the
Eddington luminosity. A t-test also shows a significance of 56\%
that the Eddington ratios of RLQs and RQQs are from the same
population. Therefore, our results indicate that the SMBH masses
of RLQs may be slightly larger than those of RQQs; their Eddington
ratios may not be significantly different. However, we must noted
that these results were obtained with a small sample of radio-loud
and radio-quiet quasars. More definitive conclusions can be
reached only with larger and more complete samples.


\para{\large\bf{4}~~Discussions}

\vs\vs With a larger sample of Seyfert galaxies, we show
 that AGNs %%
with a larger nuclear radio-loudness seem to have more massive
black holes. This conclusion was obtained recently by Laor (2000)
for nearby quasars and was supported by our study for Seyfert
galaxies. Our results also strengthen the argument made by Ho \&
Peng (2001) that the majority of Seyfert 1s are essentially
radio-loud AGNs. The total radio power of Seyfert galaxies
increases with the black hole mass. At a given $ M_{\rm BH}$,
quasars and Seyfert galaxies seem to have greater radio power than
that of nearby galaxies. These difference may  simply be due to
the different level of nuclear activity. A recent study using the
quasars from the FIRST Bright Quasar Survey  found evidence for
the dependence of radio-luminosity on accretion rate and SMBH mass
(Lacy et al. 2001). This may help us to understand the origin of
scatters in the relation
 between the radio power and SMBH %%
mass. If we describe the nuclear activity of galaxies using the
accretion rate $\dot{M}$, the difference of radio power at a given
$ M_{\rm BH}$ may show that quasars and Seyfert galaxies have
larger $\dot{M}$  than nearby galaxies. This seems also consistent
with the idea that the accretion process in these systems may be
different (Fabian \& Rees 1995; Di Matteo \& Fabian 1996). Most
likely ADAFs with very low accretion rate exist in the nuclei of
nearby galaxies, while quasars and most AGNs probably host
standard geometrically thin accretion disks with higher accretion
rate. However, the radio emissions from radio-quiet AGNs and
nearby galaxies are  not well understood at present. Whether they
are from ADAFs (Narayan et al. 1998) or from weak jets (Falcke \&
Biermann 1996, 1999) still remains uncertain. For radio-loud AGNs,
the radio emissions are thought to be mainly from the jet and are
probably related to the magnetic fields or black hole spin
(Blandford \& Payne 1982; Blandford \& Znajek 1977). If the radio
emissions correlate with the black hole mass and accretion rate,
we need to explain the possible relations of these parameters with
magnetic fields and black hole spin. However, no satisfactory
theory can provide
 clear physics about these relations at present.

In addition, our study on the Eddington ratios for quasars and radio galaxies
implies that
the importance of accretion rates in the evolutionary sequences of AGNs.
The different observational
appearances among  radio-loud AGNs cannot be dominated by the different
SMBH masses. Theoretical investigations have pointed
out that accretion  near the Eddington limit may
produce optically thick accretion disks extending all the way to the innermost
stable orbit, while accretion at very lower accretion rate may lead to advection
dominated accretion mode ( Narayan et al. 1998). Recently Ghisellini \& Celotti
(2001) also proposed
that the separation of FR I and FR II radio galaxies may be closely related to the
critical accretion rates. In addition, the state transition of Galactic black hole
X-ray transients has been explained according to the different accretion modes
at the different accretion rates (Esin et al. 1998).
From all these points we suspect that
the main reason for the evolutionary sequence of radio-loud AGNs may be accretion rate rather
than the SMBH mass.
 In addition, our results show that there may still be a difference in SMBH masses of
radio-loud and radio-quiet quasars, but such a difference is not significant as previously claimed.
The Eddington ratios of these two sub-classes of quasars seem to be from the same population. These
points are very important for our understanding of the physics of quasars and obviously need to be
confirmed with larger samples.

\bc {\bf References} \ec

\vspace{-4mm} \no \fns

 \nref Begelman M.C., Blandford R.D., Rees M.J., Rev. Mod.
    Phys., 1984, 56, 255
\nref Bettoni D., Falomo R., Fasano G., et al. A\&A, 2001, 380,
471 \nref  Blandford R.D., Payne D.G., MNRAS, 1982, 199, 883 \nref
Blandford R.D., Znajek R.L., MNRAS, 1977, 179, 433 \nref  Blundell
K.M., Beasley A.J., MNRAS, 1998, 299, 165 \nref Di Matteo T.,
Fabian A.C., MNRAS, 1996, 286, 393
 \nref Djorgovski S., Davis M., ApJ, 1987, 313, 59
  \nref Dressler A., Lynden-Bell D., Burstein D., et al., ApJ, 1987, 313,
  42
\nref Dunlop J.S., McLure R.J., KuKula M.J., et al., MNRAS, 2002,
in press (atro-ph/0108397)
 \nref Esin A.A., Narayan R., Cui W., et al ApJ, 1998, 505, 854
\nref  Faber S.M., Wegner G., Burstein D., et al., ApJSS, 1989,
69, 763 \nref Fabian A.C., Rees M.J., MNRAS, 1995, 277, L55
 \nref
Falcke H., Biermann P.L., A\&A, 1996, 308, 321
 \nref
Falcke H., Biermann P.L., A\&A, 1999, 342, 49 \nref  Ferrarese L.,
Merritt D., ApJ, 2000, 539, L9
 \nref
Ferrarese L., Merritt D., ApJ, 2001, 547, 140
 \nref
Ferrarese L., et al., ApJ, 2001, 555, L79
 \nref
Franceschini A., Vercellone S., Fabian A.C., MNRAS, 1998, 297, 817
\nref Gebhardt K., et al., ApJ, 2000a, 539, L13
 \nref Gebhardt K., et al., ApJ, 2000b, 543, L5
  \nref Genzel R., et
al., MNRAS, 1997, 264, 455
 \nref Ghez A., et al.,
ApJ, 1998, 509, 678
 \nref  Ghisellini G., Celloti A.,
A\&A, 2001, 379, L1
 \nref  Ho L.C., in Observational
Evidence for Black Holes in the Universe,
    ed. S.K. Charkrabarti (Dordrecht: Kluwer), 1999, 157
\nref  Ho L.C., ApJ, 2002, 564, 120
 \nref Ho L.C., Filippenko A.V.,  Sargent W.L.W., ApJS, 1997a, 112,
    315
\nref Ho L.C., Peng C.Y., ApJ, 2001, 555, 650
 \nref Ho L.C., Ulvestad J.S., ApJS, 2001, 133, 77
\nref Kaspi S., Smith P.S., Netzer H., et al., ApJ, 2000, 533, 631
\nref Komendy J., Richstone D., ARA\&A, 1995, 33 581
 \nref Komendy J., Gebhardt K., Proceedings of The 20th Texas
Symposium on Relativistic Astrophysics, ed. H. Martel \& J.C.
Wheeler, in press (astro-ph/0105230), 2001 \nref  Kukula M.J.,
Pedlar A., Baum S.A., et al., MNRAS, 1995, 276, 1262 \nref  Lacy
M., Laurent-Muehleisen S.A., Ridgway S.E., et al.,
    ApJ, ???, 551, L17
\nref  Laor A., ApJ, 2000, 543, L111 \nref Lyden-Bell D., Nature,
1969, 223, 690
 \nref  Magorrian J., et al., AJ, 1998, 115, 2285
\nref  McLure R.J,  Dunlop J.S., MNRAS, 2001, 327, 199
 \nref
McLure R.J,  Dunlop J.S., MNRAS, 2002, 331, 795
 \nref McLure R.J, Kukula M.J., Dunlop J.S., et al., MNRAS, 1999, 308,
 377
\nref Nelson C.H., Whittle M., ApJS, 1995, 99, 67 \nref
Osterbrock D.E., Martel A., ApJ, 1993, 414, 552
 \nref Rees M.J., ARA\&A, 1984, 22 471
  \nref Sadler E.M., Jenkins C.R., Kotanyi C.G., MNRAS, 1989, 240, 591
   \nref  Sadler E.M., Slee O.B., Reynolds J.E., et al., MNRAS, 1995, 276,
1373
 \nref  Urry C.M., Scarpa R., O'Dowd M., et al.,
ApJ, 2000, 532, 816
 \nref  Wandel A., Peterson B.M.,  Malkan M.A., ApJ, 1999, 526,
 579
\nref  Wu X.B., Han J.L., A\&A, 2001, 380, 31
 \nref Wu X.B., Liu F.K., Zhang T.Z., A\&A, 2002, 389, 742

%\end{CJK}
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