1. High-z (z > 3) QSOs studied with Subaru/HSC
Masa Imanishi (NAOJ)
Tohru Nagao (NAOJ)

2. Outline Importance and current understanding of high-z QSOs (AGNs)
2. QSOs at z > 7
(M.Imanishi)
(Subaru/HSC + UKIRT/WFCAM)
3. Low-luminosity QSOs at z = 3-6
(Subaru/HSC)
(T.Nagao)

3. IGM properties (re-ionization)
Why High-z QSOs(AGNs) ?
(1) Very bright
MBH =106-9Msun
DLA, LyA forest
IGM properties (re-ionization)
(2) Co-Evolution of SMBHs
and Galaxies
SMBHs are ubiquitous
in spheroid galaxies
M(gal)
M(BH)
Various observational surveys and investigations for high-redshift QSOs have been carried out extensively, up to now. This is partly because high-redshift QSOs can be used as luminous background sources. This means that high-redshift QSOs are important to study properties of absorption-line systems such as DLAs and optical depths of the IGMs, which are then used to discuss more fundamental issues such as cosmic metal-enrichment history and cosmic re-ionization history. The background UV and X-ray emission from high-redshift QSOs plays a role as both positive and negative feedback to star-formation in primordial galaxies. Another reason why we care of high-redshift QSOs is our interests on SMBHs and their link with galaxy evolution. The typical mass of SMBHs is 10^6-9 Msun, but we do not know at all how such huge SMBHs formed. This question would be probably linked with some fundamental parameters such as mass accretion history onto SMBHs and a typical lifetime of AGN phenomena. And recently it is widely recognized that some observations suggest the co-evolution of SMBHs and galaxies, that enhances our interests on QSOs and SMBHs among them.

4. High-z QSO found by SDSS z>7 QSO not detectable
>1000 QSOs
at z>3
Bright QSOs
only !
z>7 QSO not detectable
in the optical
z=6.42:
Most distant
Fan 2006

5. Post SDSS QSO Survey (1) Search for z > 7 QSOs
What next?
(1) Search for z > 7 QSOs
NIR data required
(UKIRT/WFCAM)
(2) Search for lower-Luminosity QSOs
at z = 3-6
Even though the SDSS QSO survey is a major breakthrough in this research field, there are still some crucial open issues. One is the lack of QSOs at z>6. Specifically, the number of QSOs at z>6 ever found is only 9, and the highest redshift of them is currently This redshift range corresponds to the cosmic re-ionization epoch, and thus the QSOs in this redshift range is extremely important to constrain the ionization degree of the universe as shown here. This redshift range is also interesting to examine the SMBH formation, since the available time for the SMBH growth is more limited at higher redshift. However, searching QSOs at z>7 requires NIR imaging data, that prevents us from performing wide surveys for QSOs at z>7. Another interesting issue at the post-SDSS era is searching for rather lower luminosity QSOs that were not explored by the SDSS QSO survey.

6. 1. z>7 QSOs
filters
optical
NIR
Very deep
Moderately deep Z Y J H K

7. UKIRT/WFCAM/LAS Y=20.5,J=20.0, H=18.8,K=18.4 z>7 QSOs:
~10 expected
Northern: deg^2
Equatorial: deg^2

8. z>7 QSO candidates cannot be selected
No deep z-band image:
z>7 QSO candidates cannot be selected
z’ - J
z’ - J
z>7 QSO:
z– NIR =
very large
SDSS + >2 mag
needed
J - K
J - K

9. Y-J color difference (small) i ,Y: limiting mag differs only 2mag
WFCAM team compromise
Y-band
Green：QSO Y z i
Red：BD J
i’ - Y
Y-J color difference (small)
Severe contamination
i ,Y: limiting mag differs only 2mag
Y - J

10. Proposal >1000 deg 2(wide), z>23.5mag (deep) survey DEC RA
Possible only with Subaru/HSC
The planned Subaru/HSC >1000 deg 2 survey
be executed at (northern) WFCAM/LAS
RA widely distributed RA
DEC

11. Why Japan? Deep, wide z-band survey Southern VISTA :
only possible with HSC
Southern VISTA :
Z<21.5 （?）
At z~7, z-ID requires um spectroscopy
Subaru/MOIRCS can
Japan can lead this area, if we do follow-up
before HSC data become archival !

12. Issues to be solved
SDSS z or Z
SDSS z
Z-band 1
(um)
0.8
Y dwarf

13. 2. low-luminosity QSOs (z=3-6)
Croom et al. (2001)
２ｄＦ
z<2.3
faint
bright
QSO LF:
bright end only
at z>3
QSO UV background:
dominated by faint end
Fan et al. (2001)
bright
SDSS
z>3.6
Actually the depth of the SDSS QSO survey is too shallow to cover a wide luminosity range and to draw whole shapes of luminosity functions at z>3. In general QSO luminosity functions are characterized by double power-law, as shown in the upper right panel. This is the QSO luminosity functions at z<2, derived by the 2dFQSO survey. You can see that the QSO luminosity function is well expressed by double power-low, and the QSO number density increases monotonically from z=0 to z=2 without a significant change in the functional shape. This information is strongly linked to the mass accretion history onto SMBHs, and accordingly the QSO luminosity function gives strong constraints on some fundamental parameters of QSOs such as the typical QSO lifetime. In the left panel, theoretical QSO luminosity functions predicted by semi-analytic models, adopting different QSO lifetimes, are shown. You can see how the QSO luminosity function is sensitive to the QSO lifetime. However at z>3, only the bright part of QSO luminosity function has been investigated as shown in the right lower panel, that prevents us from studying the nature of QSO activities at z>3. Another interesting issue related with the faint part of the QSO luminosity function is the UV background radiation from QSOs.

14. UV Background from QSOs at z=3-6
QSO (Mathews & Ferland 1989)
Starburst, Z=0.05 Zsolar
Starburst, Z=1.00 Zsolar
13.6eV
24.6eV
54.4eV
(Leitherer et al. 1999)
QSO UV is hard
HeII re-ionization
Effect on galaxy
formation
QSOs
Now it is widely believed that the cosmic re-ionization of hydrogen is accounted mostly by UV radiation from star-forming galaxies. However the UV radiation from QSOs is still important taking its very distinct SED into account, partly because the hardness of the UV background is sensitive to the galaxy formation, especially the star-formation in dwarf galaxies at their very early evolutionary stage. As shown in this panel, the SED of star-forming galaxies and that of QSOs is completely different, and the difference is crucial when focusing on a higher energy part. Specifically, UV emission from star-forming galaxies contains small number of photons responsible to singly-ionized helium and almost no photons responsible to doubly-ionized helium, while UV emission from QSOs contains significantly larger number of photons responsible to doubly-ionized helium. Since the SED of the total UV background radiation is the sum of UV from star-forming galaxies and that from QSOs, we have to know the QSO luminosity function in a wide luminosity range and then integrate it to derive the contribution of QSOs to the whole UV background. Note that the hardness of the UV background is important also to understand the cosmic He_II re-ionization.
Stars
Energy (Rydberg)

15. Corr.Func.  bias  M(halo)
QSO Correlation Func.
Faint, numerous QSOs
Corr.Func.  bias  M(halo)
 QSO lifetime
z > 3:unknown
Enoki et al. (2003)
108yr
107yr b e f 4 5 6 7 z 3 .
log MDH/Msun=12.5
12.0
11.5
bias
Redshift
Croom et al. (2005)
Redshift 1 2
bias
z < 3
Surveys for high-z low-luminosity QSOs are important also to derive QSO correlation functions at high redshift. We can calculate a so-called bias parameter from the inferred QSO correlation function, and the bias parameter tells us a typical mass of dark halos hosting QSOs. This is interesting to understand the nature of QSOs in the paradigm of the CDM cosmology, since the halo mass distribution in the universe can be precisely predicted as a function of redshift, by modern numerical simulations. The bias parameter is interesting also because it is related with the QSO lifetime. The left panel shows the expected QSO bias parameters as functions of redshift predicted by semi-analytic models, and you can see how the bias parameter is sensitive to the QSO lifetime. The QSO correlation function have been investigated at z<3, and then the bias parameter and the typical halo mass have been inferred as shown in the right panel. However the QSO correlation function has not studied at z>3, because the SDSS QSO survey identifies only very luminous QSOs and thus the QSO number density is too low to examine the correlation function. Obtaining QSO samples including less-luminous objects are essential to study the QSO correlation function at z>3.

16. Moderately Wide QSO Surveys
Strategy
Moderately Deep and
Moderately Wide QSO Surveys
SDSS
~ too shallow…
Deep Surveys (UDF, SDF)
~ too narrow…
Summarizing, to understand the nature of QSOs and SMBHs, we have to study the triggering mechanism of QSO activity, the mass-accretion timescale onto SMBHs, and their relation with the galaxy evolution. Such studies require QSO luminosity functions with a wide luminosity coverage, QSO correlation functions, environmental parameters around QSOs, and some other spectroscopic properties. In other words, we definitely need a QSO sample including less-luminous objects and enough sample size, at high redshift. As mentioned already, the SDSS QSO survey is too shallow to identify less-luminous QSOs at z>3. Although there are various deep surveys such as HDF, UDF and SDF, such surveys are too narrow to search for low number density objects like QSOs. Therefore, these considerations tell us that we have to promote a completely new QSO survey, with a moderately deep sensitivity and enough wide survey area.

17. Survey Strategy g u r i z Multi-band Selection g’ — r’ r’ — i’ i’ — z’
Selection in Color-Color Diagram
g’r’i’  3.6 < z < 4.4
r’i’z’  4.6 < z < 5.1 g u r i z
3000 Wavelength(A)
Richards et al. (2001)
g’ — r’
r’ — i’
i’ — z’
Here we propose a new QSO survey, based on multi-band very wide imaging observations with Hyper Suprime-Cam. Actually the strategy is almost the same as that adopted by the SDSS QSOs but simply deeper than SDSS. Specifically, by utilizing the Lyman break feature in the QSO spectra, we select high-z QSOs in color-color diagrams. Here the colors of SDSS QSOs are shown in two color-color diagrams, suggesting that QSOs at 3.6 < z < 4.4 show distinct colors in the GRI diagram while QSOs at 4.6 < z < 5.1 can be identified in the RIZ diagram. Of course this method does not have a perfect completeness and also select some contamination. However, we can estimate the completeness and contamination as functions of redshift and magnitude, as already performed in the SDSS QSO survey.

18. Multi-band HSC Survey HSC g’ r’ i’ z’ (3mag deeper than SDSS) g’ r’ i’
20min/band/FOV
(5σ, 0.7”seeing, 2”φ)
100 QSOs
~ 140 sq.deg.
~ 100 FOV
~ 400 pointing
~ 2 weeks
In this survey, we want to identify not only QSOs but also non-active galaxies around QSOs, at 3.6 < z < 5.1. This requires wide imaging data of four photometric bands, g, r, i, and z, with limiting magnitudes of 3 mag deeper than those of SDSS. With color-color diagrams we identify high-z objects at first, and then classify them into QSOs and galaxies. Since the luminosity function of LBGs is already understood very well, and therefore we can say that almost all of the selected objects brighter than a certain magnitude must be QSOs while objects fainter than L_star of the LBG luminosity function should be non-active galaxies. The required limiting magnitudes are summarized here, and compared with the SDSS magnitude at each band given in the parenthesis. By using hyper suprime-cam on the Subaru Telescope, these limiting magnitudes are achieved with a 20 minutes exposure for each band and FOV. To sample at least 100 QSOs at redshift around 5, the minimum required area for this survey is 140 deg^2, that corresponds to 100 FOVs of Hyper Suprime-Cam. Therefore the 400 pointing observations are necessary in total, that can be completed in 2 weeks, roughly speaking. We believe that this completely new QSO survey proposed here will contribute significantly to further understandings of the nature of QSOs, evolution of SMBHs, and co-evolution of QSOs and galaxies.

19. (Subaru/HSC + UKIRT/WFCAM) 2. Low-luminosity QSOs at z = 3-6
Summary
1. QSOs at z > 7
(Subaru/HSC + UKIRT/WFCAM)
2. Low-luminosity QSOs at z = 3-6
(Subaru/HSC)

20. End

21. QSO Environment Bright galaxy number excess around QSOs Blank-field
QSO Activity  Interaction
Borne et al. (2000)
Blank-field
QSOs
excess
Bright galaxy
number excess
around QSOs
The environment around QSOs is also an important aspect to understand the nature of QSOs. Now it is widely believed that the QSO activity is triggered by galaxy interactions. This is because we can see the evidence of interactions in QSO host galaxies directly, at least in the low-redshift universe as shown in this panel. However, at higher-z where the QSO activity is much more extensive with respect to that in the local universe, it is not feasible to identify the signature of galaxy interactions. Therefore we have to select more statistical approaches, rather than direct imaging observations toward individual QSOs. One possible way to investigate this issue is examining the QSO environment, quantified by the number of galaxies around QSOs. Actually at z=0.2, the galaxy number count is significantly different between in blank fields and around QSOs, as shown in these figures. To investigate this trends in high-z universe, surveys with an enough sensitivity to identify not only QSOs but also non-active galaxies at the same redshift are crucial.
Results at z=0.2 　(McLure & Dunlop 2001)

22. Strategy Moderately Deep and Moderately Wide QSO Surveys
Trigger of QSO Activity
Growth of SMBHs in QSOs
Relation with Galaxy Evolution
SDSS
~ too shallow…
Deep Surveys (UDF, SDF)
~ too narrow…
Luminosity Function of QSOs
Correlation Function of QSOs
Environments of QSOs
Summarizing, to understand the nature of QSOs and SMBHs, we have to study the triggering mechanism of QSO activity, the mass-accretion timescale onto SMBHs, and their relation with the galaxy evolution. Such studies require QSO luminosity functions with a wide luminosity coverage, QSO correlation functions, environmental parameters around QSOs, and some other spectroscopic properties. In other words, we definitely need a QSO sample including less-luminous objects and enough sample size, at high redshift. As mentioned already, the SDSS QSO survey is too shallow to identify less-luminous QSOs at z>3. Although there are various deep surveys such as HDF, UDF and SDF, such surveys are too narrow to search for low number density objects like QSOs. Therefore, these considerations tell us that we have to promote a completely new QSO survey, with a moderately deep sensitivity and enough wide survey area.
Moderately Deep
and
Moderately Wide
QSO Surveys
We need a QSO sample
~ with wide luminosity range
~ with enough number density

23. QSO Correlation Func. ～ Corr.Func.  bias  Mhalo
Croom et al. (2005)
～ Corr.Func.  bias  Mhalo
～ bias  QSO Lifetime
— mass-accretion timescale b e f 4 5 6 7 z 3 .
log MDH/Msun=12.5
12.0
11.5
tQ=3x108 yr
tQ=3x107 yr
Enoki et al. (2003)
Surveys for high-z low-luminosity QSOs are important also to derive QSO correlation functions at high redshift. We can calculate a so-called bias parameter from the inferred QSO correlation function, and the bias parameter tells us a typical mass of dark halos hosting QSOs. This is interesting to understand the nature of QSOs in the paradigm of the CDM cosmology, since the halo mass distribution in the universe can be precisely predicted as a function of redshift, by modern numerical simulations. The bias parameter is interesting also because it is related with the QSO lifetime. The left panel shows the expected QSO bias parameters as functions of redshift predicted by semi-analytic models, and you can see how the bias parameter is sensitive to the QSO lifetime. The QSO correlation function have been investigated at z<3, and then the bias parameter and the typical halo mass have been inferred as shown in the right panel. However the QSO correlation function has not studied at z>3, because the SDSS QSO survey identifies only very luminous QSOs and thus the QSO number density is too low to examine the correlation function. Obtaining QSO samples including less-luminous objects are essential to study the QSO correlation function at z>3.
Redshift

24. MBH/Mgal～0.002 Non-AGNs Co-Evolution of SMBHs and Galaxies
Marconi & Hunt (2004)
log Mgal [Msun]
log MBH [Msun]
MBH/Mgal～0.002
Ferrarese & Meritt (2000)
MBH [Msun]
stellar velocity dispersion
Non-AGNs
One of the most important evidence suggesting the co-evolution of SMBHs and galaxies is the tight relation between the mass of galaxies and that of SMBHs. This relation strongly infers the evolutionary link between SMBHs and galaxies. Interestingly, this relation is seen also in non-AGN galaxies, not only in active galaxies, suggesting that every galaxies may once experienced an AGN phase during their evolutionary process.
～ Evolutionary link between SMBHs and galaxies
～ Every galaxies may once experienced an AGN phase

25. SDSS QSO Survey: Redshift Distribution
Richards et al. (2006)
Schneider et al. (2005)
u’-dropout
g’-dropout
Motivated by these issues, many efforts have been performed to search for high-z QSOs so far. Among various important QSO surveys conducted up to now, the most intense QSO survey is apparently the SDSS QSO survey. This is the redshift distribution of QSOs in the SDSS DR3. The redshift distribution shown here is not smooth. This is due to the selection function of the SDSS QSO survey, since the SDSS QSO survey utilizes the so-called dropout method for high-z QSOs. However, once corrected for incompleteness and possible contamination, we can see true redshift distribution of the number density of luminous QSOs as shown in the right panel.
46420 QSOs
in SDSS DR3
Redshift