%\documentclass[12pt,preprint]{aastex}
\documentclass[10pt,preprint]{aastex}
\usepackage{graphicx}
\usepackage{times}
\begin{document}

\subsection{Super-massive black hole growth and on-set of feedback}
\noindent
With the discovery of super massive black holes (SMBHs) at the center of
every massive galaxy, the issue of how these SMBHs formed and evolved over
the cosmic history become one of the major unanswerd questions in 
observational cosmology. The number density of the SMBHs in the local 
universe can be roughly explained as the relics of accretion activities
observed as AGNs. Accretion growth history of SMBHs inferred from 
the cosmic evolution of number density of AGNs implies major part of
the growth happened in the accretion during the violent era of the universe.
However, the observational understanding is not complete yet due to 
the existence of large number of obscured AGNs which can be missed in
the current surveys based on optical spectroscopic follow-ups.
FMOS SSP can reveal the obscured accretion with the NIR spectroscopic 
follow-ups of hard X-ray-selected AGNs and mass-selected galaxies in the 
violent era. 

In the local universe, the mass of the SMBHs is directly proportional 
to the mass of the spheroid of its host. The tight relation 
implies that galaxies and their central black holes grew concordantly. 
Galaxy-scale feeding and feedback processes to and from SMBHs 
should play crucial role in the physical link between the galaxy 
evolution and SMBH growth. One of such processes is galaxy-scale feedback 
from low-luminosity radio AGNs, so-called radio mode feedback. 
The radio mode feedback is thought to heat up the cooling accretion 
to massive galaxies and suppress their growth further. Following the 
assembly of massive galaxies and their SMBHs, radio mode feedback 
starts to play important role in shaping properties of massive galaxies.
FMOS SSP NIR spectroscopic suvey of radio-selected AGNs should detect 
the on-set of radio mode feedback happened during the assembly of
massive galaxies in the violent era.

\subsubsection{Obscured growth of super-massive black hole during the violent epoch}

The growth history of SMBHs with accretion process can be evaluated with the 
evolution of the comoving space density of AGNs as a function of cosmic time.
X-ray surveys provide the most efficient and the cleanest sample of AGNs. 
Intensive optical spectroscopic follow-ups of X-ray sources revealed
broad-/narrow-line AGNs out to $z\sim5$. Hard X-ray surveys with various depth 
revealed number density of non-obscured plus mildly-obscured AGNs as a 
function of redshift for each luminosity bin (e.g., Ueda et al. 2003,
ApJ, 598, 886, as shown in the left panel of Figure 1). Using the redshift 
evolution of the X-ray luminosity
functions of AGNs, the average growth history of SMBHs are 
quantitatively inferred (e.g., Marconi et al. 2004, MNRAS, 351, 169): massive 
$>10^{8}$M$_{\odot}$ SMBHs gain their mass around $z\sim2$, on the contrary, 
less-massive $<10^{8}$M$_{\odot}$ SMBHs increase their mass around $z\sim1$. 
During the epoch of violent galaxy evolution, SMBHs grew significantly as well.

However, the understanding on the accretion history is not
complete yet, due to the existence of large number of obscured AGNs
which are missed in the current optical spectroscopic follow-up 
observations of X-ray sources. FMOS SSP surveys will overcome the 
current limits of the understanding of the obscured accretion 
by 1) NIR spectroscopic follow-ups of optically-faint X-ray 
sources, and 2) emission line AGN survey of massive galaxies 
selected with photometric redshift method.

\begin{figure}[h]
\begin{center}
\includegraphics[width=0.67\linewidth]{ssp_agn_numden.eps}
\end{center}
\caption[]{Left) Number density of X-ray selected AGNs from Ueda et al. (2003).
Almost all of these AGNs are non-Compton-thick AGNs. Right) Estimated number
dentisy of Compton-thick AGNs in each luminosity bin as a function of redshift
(Vignali et al. 2010). The solid lines are predicted number density by Gilli 
et al. (2007) model. The proposed spectroscopic survey prove the redshift
and number density (=volume) range hatched with orange.
\label{fig:ssp_agn_numden}}
\end{figure}

\subsubsection*{Non-obscured and mildly-obscured accretion revealed with X-ray AGN survey}

\begin{figure}[h]
\begin{center}
% \includegraphics[width=0.67\linewidth]{ssp_agn_numden.eps}
\end{center}
\caption[]{SHOWING optically-faint X-ray sources.
\label{fig:ssp_agn_optfaint}}
\end{figure}

A significant fraction of the sources in the deep X-ray surveys 
remain unidentified even with the intensive spectroscopic observations 
due to the faintness of their optical counterparts. As shown in Figure 2, 
optical spectroscopic observation reveal the nature of X-ray sources with 
brighter than $i\sim$23.5mag, but there are large number of sources with
fainter optical counterpart. Typically 60\% of 
the CDF-N sample has been spectroscopically unidentified, which drops 
to $\sim$50\% completeness when only X-ray AGNs are included (i.e., 
X-ray starbursts are removed). 

Photometric redshift estimation suggests 
that the optically-faint optical-spectroscopically unidentified X-ray 
sources are located at $z>1$ (see right panel of Figure 2). Not only 
the faintness in the optical band but also the fact that the major 
emission lines of narrow-line AGNs are out of optical wavelength range 
in the redshift range between $z=1.3$ and $z=2.3$ prevent the 
spectroscopic identification of such population of X-ray sources.
Based on the photometric redshift estimation, it is suggested that
such obscured population outnumber the non-obscured AGNs in the redshift
range 1-3. The obscured fraction of X-ray-selected AGNs at $z>2$ can 
be 2 times higher than that in the local universe 
(Hasinger et al. 2008, A\&A, 905, 922).

In the SXDS/UDS region, conducting follow-up observations of X-ray sources, 
51 type-1 and 22 type-2 AGNs are spectroscopically identified
between $z=1.3-1.6$ and 64 candidates of type-2 AGNs with photometric
redshifts in the range (Akiyama et al. 2010, in prep). The 64 objects 
are primary targets of Sample 3, and ??? X-ray sources without spectroscopic 
redshifts are also observed as secondary targets of Sample 3. In addition 
to these obscured AGN candidates, 51 type-1 AGNs will be observed with 
lower priority, in order to estimate their black hole mass with rest-frame 
optical broad-emission line. Based on the black hole mass and multiwavelength 
photometry, typical Eddington ratio of the sample can be estimated. 
The Eddington ratio of the obscured AGNs may be assumed to be the same as
the typical Eddington ratio derived with the non-obscured AGNs with 
similar luminosity and redshift. 

\subsubsection*{Heavily-obscured accretion revealed with Compton-thick AGN survey}

\begin{figure}[h]
\begin{center}
\includegraphics[width=0.67\linewidth]{ssp_agn_detlim.eps}
\end{center}
\caption[]{Left) Observed unobscured hard X-ray luminosity
vs. [OIII] line luminosity (converted to corresponding 
X-ray luminosity using L[OIII]-Lx relation) of obscured QSOs
found in SDSS (Vignali et al. 2010). The thick vertical and horizontal
solid lines indicate the [OIII] and 2-10keV detection limits in this
survey. Right) Diagnostic diagram of optical emission lines
of $z\sim2$ galaxies (Kriek et al. 2007) overlayed on 
local SDSS galaxies shown in gray scale. The detection 
limit of the emission line survey is designed to reject
the region hatched with green color.\label{fig:ssp_agn_detlim}}
\end{figure}

Although X-ray selection is efficient to select 
mildly-obscured AGNs, still X-ray selection can miss and be biased 
against heavily-obscured AGNs with obscuration column density of
N$_{\rm H}>10^{24}$cm$^{-2}$, i.e., Compton-thick AGNs, for which
the high column density makes the optical depth of Compton-scattering 
for X-ray photons one. Even very hard X-ray 20-40~keV flux 
of AGNs can be diminished significantly by heavy obscuration 
and a sample selected in such high-energy band can be biased 
against Compton-thick AGNs (Malizia et al. 2009, MNRAS, 399, 944).

In the local universe, a significant fraction of [OIII]-line-selected
obscured AGNs is possibly Compton-thick AGNs. Candidates of obscured AGNs
are selected based on strong [OIII]-line from Sloan Digital Sky Survey
(SDSS) spectroscopic database (Zakamska et al. 2003, ApJ, 126,2125). 
% (L$_{\rm [OIII]}=1\times10^{42}-4\times10^{43}$ erg s$^{-1}$). 
X-ray fluxes of half of them are significantly smaller than that 
predicted from the strength of the [OIII]-line (see Figure 2, Vignali et al. 2010,
MNRAS, ). The large $L_{\rm [OIII]}$ / $L_{\rm 2-10keV}$ implies that their 
active nuclei are heavily-obscured even in the hard X-ray band.

Because summantion of X-ray emission of populations of non-obscured and 
mildly-obscured AGNs cannot explain the energy density of the
Cosmic X-ray Background (CXB) at around its peak energy range ($\sim$30~keV), 
Compton-thick AGNs are expected to contribute significantly to the energy 
density, and the number density of Compton-thick AGNs needs to be as high 
as that of mildly-obscured AGNs
(Ueda et al. 2003; Gilli et al. 2007). 
The redshift range of the FMOS SSP survey is especially important because 
the residual CXB spectrum implies that the contribution from the 
heavily-obscured AGNs peaked at $z\sim1.5$ (Worsley et al. 2005). 

High number density of Compton-thick AGNs at high-redshifts is inferred from 
24$\mu$m-excess (Daddi et al. 2007; Fiore et al. 2008; Alexander et al. 2008), 
MIR plus radio (Martinez-Sansigre et al. 2007), and MIR-SED 
(Polletta et al. 2006) selections of obscured AGNs. The estimated number 
density of Compton-thick AGNs is summarized in the right panel of Figure 1. 
Comparison with that of X-ray-selected AGNs as shown in the left panel implys that 
Compton-thick AGNs are as numerous as non-obscured and mildly-obscured AGNs, 
i.e., heavily-obscured accretion can significantly contribute
to the accretion growth of SMBHs. However, the current knowledge on the 
number density of obscured AGNs are rather heterogeneous and not 
conclusive.

FMOS SSP Sample 1 can constrain the number density of heavily-obscured 
AGNs similar to [OIII] emission line survey of SDSS in the local universe. 
The targets are selected based on the photometric redshift and
estimated stellar mass. Because almost all of the X-ray selected
luminous and low-luminosity AGNs are associated with relatively
massive galaxies (M$_{*}>10^{10.5}M_{\odot}$; Yamada et al. 2009, 
ApJ, 699, 1354), heavily-obscured AGNs are expected to also 
reside in such massive galaxies. The detection limit of Sample 1
corresponds to $L_{\rm [OIII]}$ of $2.8\times10^{43}$ erg s$^{-1}$ at $z=1.5$
with SN=10. The luminosity is equivalent to unobscured 
$L_{\rm 2-10keV}$ of $1.4\times10^{44}$ erg s$^{-1}$. 
Once H$\alpha$ and [OIII] emission lines are detected with SN$>10$,
secondary emission lines, such as [NII] and H$\beta$ are expected to have
SN$>3$ if they have strength 1/3 of the H$\alpha$ and [OIII] emission lines. 
Achieving the detection limit, AGN-like emission lines can be
distinguished clearly from HII-region-like lines as shown in right panel of Figure 3.
Combining the [OIII]-line selected AGNs with the deep X-ray data in the SXDS/UDS 
region which reach the detection limit of $L_{\rm 2-10keV}=1\times10^{43}$ erg s$^{-1}$,
we can directly identify heavily-obscured AGNs using the ratio $L_{\rm [OIII]}/L_{\rm 2-10keV}$ 
(or lower limit on the ratio) as shown in left panel of Figure 3. 
Selection with strong [OIII] line may miss obscured AGNs without strong 
optical emission line, like fully-covered less-luminous AGNs in the 
local universe (Ueda et al. 2007, ApJ, 664, 79). Such AGNs can be 
found among radio AGNs in Sample 3 and FIR-selected galaxies in Sample 2-3.

The fraction of AGNs among massive galaxies may be rather high in the
high-redshift universe. For example, NIR survey of 26 K-bright galaxies 
at $2.0<z_{\rm phot}<2.7$ by Kriek et al. (2007) found 11 emission line objects and
among them there are 4 classical AGNs and 3 possible AGNs (AGN+Starburst) as shown 
in Figure 3. Among the 7 objects, only 1 object is detected in 
X-ray. The result indicates that a significant fraction ($\sim$1/3) of the 
massive galaxies shows AGN activity detectable with rest-frame optical 
emission lines and most of them are missed in the deep X-ray surveys. 
The number of the sample is too small to conclude the statistical nature 
of heavily-obscured AGNs.
Assuming similar number of Compton-thick AGNs to X-ray-selected 
mildly-obscured (type-2) AGNs as mentioned above, it is expcted that
about 50 Compton-thick AGNs in the SXDS/UDS region above the [OIII] detection limit.

Finally, combining 
the X-ray-selected non-obscured/mildly-obscured AGNs mentioned above 
and the [OIII]-selected heavily-obscured AGNs, the entire population of
AGNs among galaxies in the violent era can be revealed.  

\subsection{Massive galaxy formation and the onset of radio-mode feedback}

It is now generally accepted that AGNs play a major role in shaping
the evolution of their host galaxies, via a process known as `AGN
feedback'. This feedback can take one of two forms, for which Croton
et al.\ (2006, MNRAS, 365, 11) coined the terms `quasar mode' and `radio mode'.
Quasar mode feedback occurs when the central supermassive black hole
is accreting close to its Eddington limit, and the infalling material
forms a hot accretion disk that, in turn, ionizes the surrounding gas
to produce a rich emission-line spectrum. This mode is associated with
mergers and interactions which also promote star formation, although
the precise relationship between the accretion and star formation
activities is not fully understood.

In contrast, the physics and energetics of radio mode feedback are far
clearer. This mode occurs when hot gas accretes directly onto the
black hole at a low rate, eliminating the need for an accretion disk,
and hence not producing strong emission lines (note that classical
powerful radio galaxies such as Cygnus~A are actually `quasar mode'
systems). Best et al.\ (2005, MNRAS, 362, 25) demonstrated that the fraction of
galaxies hosting a low-luminosity radio-loud AGN was a strong function
of stellar mass.  Inferring this to be a duty cycle of activity, Best
et al.\ (2006, MNRAS, 368, L67) showed that the energy output (making plausible
assumptions about the relationship between radio luminosity and
kinetic power) precisely balanced the observed X-ray cooling. This
mechanism, whereby radio `bubbles' inflate cavities in the surrounding
hot X-ray halo (as clearly seen in, e.g., the Perseus cluster; Fabian
et al.\ 2003, MNRAS 344, L43; Fabian et al.\ 2006, MNRAS, 366, 417) 
is therefore responsible for the curtailment of
baryonic cooling and hence star formation in massive galaxies, and
explains the steep cut-off at the bright end of the galaxy luminosity
function.

Radio mode feedback only becomes important once massive elliptical
galaxies have formed, and it therefore can be used to locate the epoch
of massive galaxy assembly. This is still a major problem in modern
cosmology, as the existence of massive galaxies at high redshift
continues to present difficulties for models of galaxy formation
(e.g., Collins et al.\ 2009 Nature, 458, 603; Stott et al.\ 2010, ApJ, 718, 23).  
Blank-field surveys
for massive galaxies are hampered by the reliance on photometric
redshifts and stellar mass estimates and hence their results are open
to debate without extensive confirmational spectroscopic follow-up
(see, e.g., van Dokkum et al.\ 2006, ApJ, 638, L59). By comparison, an observed
decline in the number of low-luminosity radio sources would pinpoint
the time at which the most massive galaxies have completed their
stellar build-up and found equilibrium between gas cooling and
radio-source heating. Locating this epoch provides an essential
constraint for models of galaxy formation.  Detecting such a decline
requires far less follow-up and, indeed, has been tentatively seen in
the SXDF/UDS sample of 505 radio sources (Simpson et al.\ 2011, in prep.;
Fig.~\ref{fig:simpson}). However, this result also hinges on the
reliability of photometric redshifts, and is also made slightly
ambiguous by the overlap between low-luminosity radio-loud AGN and
high-luminosity radio-quiet (quasar mode) sources, although these
evolve like the luminous AGN population and so are expected to peak at
$z\sim2.5$.

FMOS is the ideal instrument to tackle this problem, since it is able
to detect the strong 4000-\AA\ break in massive galaxies at $z\sim2$
with little or no line emission, and also detect the strong emission
lines of [O{\sc~ii}] and/or [O{\sc~iii}] at this redshift to eliminate
contaminating quasar-mode radio-quiet objects. Since the population we
are interested in does not have strong accretion, there is no hot dust
emission longward of 1\,$\mu$m and the \textit{Spitzer\/}/IRAC colours
provide robust (if rather uncertain) photometric redshift estimates
(Simpson \& Eisenhardt 1999, PASP, 111, 691). By selecting radio sources with
appropriate colours from the deep IRAC observations in the SXDS/UDS and
COSMOS fields, we will reliably and efficiently measure the evolution
of the radio-mode galaxy population and hence determine when the most
massive galaxies have fully assembled.


\begin{figure}
\caption[]{Figure from my new paper demonstrating the decline in
  low-luminosity radio sources.\label{fig:simpson}}
\end{figure}

\subsection*{Sample selection bit}

From Chris, this should be in the sample section.

We have selected radio sources in the SXDF/UDS (from a new radio map;
Ivison et al., in prep) and COSMOS (Schinnerer et al.\ 2010, ApJS, 188, 384) fields
which are believed to lie at $z>1.5$, based on their
\textit{Spitzer\/} [3.6]$-$[4.5] colours. This colour cut will also
include lower redshift `quasar mode' AGN (due to the hot dust emission
from the inner walls of the torus) and these objects have been
excluded based on their optical magnitudes. There are \textbf{XXX}
sources, with a range of $J$-band magnitudes, that therefore require
different exposure times. We aim to achieve S/N=5 in the continuum,
which will be sufficient to detect the strong 4000-\AA\ break.

\end{document}
