Sciences with Hyper Suprime-Camand survey parameters
Version 1

HSC survey design working groupmanuscript deadline: 2008 September 30
October 3, 2008

Summary
Summary

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Contents
1 Science cases and survey parameters
1.1 Subaru Wide-Field AGN Survey . . . . . . . . . . . . . . . . . . . . . . . . .

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3
4

Chapter 1
Science cases and survey parameters

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1.1

Subaru Wide-Field AGN Survey

Author(s)Masayuki Akiyama (Tohoku), Motohiro Enoki (Tokyo Keizai), Tomotsugu Goto (Hawaii),
Tetsuya Hashimoto (Kyoto), Masatoshi Imanishi (NAOJ), Nobunari Kashikawa (NAOJ),
Nozomu Kawakatu (NAOJ), Yoshiki Matsuoka (Tokyo), Tomoki Morokuma (NAOJ), Takashi
Murayama (Tohoku), Tohru Nagao (Ehime), Masahiro Nagashima (Nagasaki), Takao Nakagawa (JAXA/ISAS), Ken Ohsuga (NAOJ), Masahiro Takada (Tohoku), Yoshiaki Taniguchi(Ehime), Yuichi Terashima (Ehime), Yoshihiro Ueda (Kyoto), Masayuki Umemura (Tsukuba),
Keiichi Wada (NAOJ), Atsunori Yonehara (Kyoto Sangyo)

Abstract
We propose new AGN surveys, that consist of very-wide 5-band imaging observations andmoderately-deep 3-band imaging observations. Through these observations, we identify
numerous relatively-faint AGNs at 1 < z < 5 and bright AGNs at z > 6. The former
sample (1 < z < 5) is used to study the faint end of the AGN luminosity function, theAGN correlation function, and the environment around high-z AGNs. These statisticalproperties are crucial to constrain the AGN triggering mechanism, the typical lifetime of
AGN activities, the growth history of supermassive black holes, and the effects of the AGN
feedback onto galaxies. The latter sample (z > 6) is used to study detail processes of thecosmic reionization and to extend the cosmic redshift frontier where super-massive black
holes are growing rapidly.

1.1.1

Science Goals

Search for AGNs at z > 6
In this decade AGNs at z > 6 are enthusiastically focused on, because they are crucially
important to (1) constrain the formation/evolutionary scenarios of supermassive black holes(SMBHs), (2) prove the physical conditions of the IGM in terms of its neutral fraction, (3)provide a landmark of highest-z (proto-)clusters of galaxies, and (4) trace the earliest stageof the cosmic chemical evolution. While the most distant AGN identified so far has been
discovered with CFHT (z = 6.43; Willott et al. 2007), most of luminous AGNs at z > 6
ever found have been discovered through the SDSS photometric survey with follow-up
spectroscopy and/or near-infrared imaging observations (e.g., Fan et al. 2006; Goto 2006;
see Figure 1). Consequently the above three issues have been extensively investigated inthese years based on mainly the SDSS sample. The mass of SMBHs in some of SDSS AGNs
at z > 6 has been measured and it turned out to be > 109 M⊙ (e.g., Willott et al. 2003;
Kurk et al. 2007), that indeed gives strong constraints on some theoretical scenarios forthe evolution of SMBHs (e.g., Li et al. 2007; Tanaka & Haiman 2008). The evolutionof the Gunn-Peterson optical depth in SDSS high-z AGNs suggests that the end of thecosmic reionization process is at around z ∼ 6 and the neutral hydrogen fraction at z > 6 issignificantly more than zero (Fan et al. 2006). Possible overdensity regions around the SDSS
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high-z AGNs have also identified through follow-up deep multi-color imaging observations(Zheng et al. 2006; Ajiki et al. 2006). The metallicity of SDSS AGNs at z > 6 has been
examined through Feii/Mgii ratio (e.g., Maiolino et al. 2004; Iwamuro et al. 2004; Kurk et
al. 2007) and Nv/Civ ratio (Jiang et al. 2007); both of which show no chemical evolution,
surprisingly. All of these observational progress strongly suggests that AGNs at z > 6 are
extremely important objects to extend our knowledge on the cosmic frontier toward theso-called the cosmic dark age.

Figure 1.1: Spectra of the SDSS AGNs at 5.7 < z < 6.4 (Fan et al. 2006). AGNs at the higher redshift(upper panel in this figure) show the weaker (or nearly zero) flux at bluer side of Lyα, suggesting that thefraction of the neutral hydrogen increases significantly at z > 6. Note that strong Nv emission is also seenat the red side of Lyα. This emission is the crucial metallicity indicator, and the existence of Nv suggeststhat the SDSS AGNs are already metal-enriched even at z > 6.
However, there are three fatal drawbacks in the SDSS high-z AGN sample. The firstone is that the SDSS sample contains only extremely luminous AGNs due to the shallow
limiting magnitude of the SDSS images. This limitation prevents us from investigating thewhole shape of the AGN luminosity function, that is important to study the evolution of the
UV background and the SMBH mass function. Since the number density of such luminous
AGNs is extremely low, currently we cannot investigate the correlation function of AGNs
at z > 6 and the inhomogeneousness of the cosmic reionization. The lack of observational
evidence of the chemical evolution in the SDSS AGNs may be owing to the bias toward
the high luminosity. The second problem in the SDSS sample is that the selection method5

of the SDSS high-z AGNs assumes very red i′ − z ′ colors, that may miss relatively “blue”
AGNs; i.e., AGNs whose spectra are less absorbed by the intervenung hydrogen (maybe
due to the fractuation of the cosmic reionization or to the relatively low redshift, z ∼ 5.5).
Note that it is difficult to search for such blue high-z AGNs with the SDSS data due to its
large photometric errors. The third problem is a very simple one; the current AGN sample
discovered so far does not contain any AGNs at z > 6.5.
All of these three serious problems in the orevious highest-z AGN surveys are completely
solved by a very wide multi-color photometric survey with deeper limiting magnitudes thanthe SDSS imaging observations. To search for relatively blue and/or lower-luminosity AGNs
at 6 < z < 7, wide y-band imaging data are crucial. By performing ∼ 1000 deg2 survey
with limiting magnitudes of i = 25.8, z = 24.7, y = 23.4, ∼300 faint AGNs at 6 < z < 7 are
expected. Since the sample size is > 10 times larger than the current SDSS sample, thisnew survey will bring a breakthrough in this research field. For instance, we will investigate
the possible fractuation of the cosmic reionization by investigating the spectra of AGNs atz > 6 in various line-of-sights. Also we may give a preliminary constraint on the AGN
clustering amplitude at z > 6, which is usufut to infer the dark halo mass in which theAGNs (and also their SMBHs, of course) are located. In addition to the “wide” 5-band
photometric observation, we also propose relatively deep imaging observations for ∼ 50 deg2
with limiting magnitudes of i = 26.6, z = 25.9, y = 24.6 to extend the luminosity functionof AGNs at 6 < z < 7 toward the low-luminosity direction. It is no longer possible tosearch for AGNs at z > 7 with optical photometric surveys since the Lyα wavelength shifts
to λobs > 1µm. However such z > 7 AGNs should be moderately bright in the infrared.
Therefore, by combining ∼ 2000 deg2 z-band imaging data proposed here with the UKIRTWFCAM large area survey (http://www.ukidss.org/)1 , we will identify ∼10 AGNs at z > 7(see Figure 2).
Search for Low-Luminosity AGNs at 4 < z < 5This redshift range is extremely interesting to study the evolution of AGN activities and
SMBHs, because this range is just beyond the peak of the number density of bright AGNs
(e.g., Richards et al. 2006; see Figure 3) and thus it corresponds to the growing-up phaseof SMBHs. To investigate SMBHs in this epoch is also important to study the formationand evolution of galaxies, because galaxies and SMBHs hosted by them experienced “coevolution” as inferred by the MBH − Mbulge relation (e.g., Marconi & Hunt 2003). Notethat some theoretical models predict a higher MBH /Mbulge ratio at a higher redshift (e.g.,
Wyithe & Loeb 2003; Croton 2006) while some other models predict no evolution in the
MBH /Mbulge ratio (e.g., Robertson et al. 2006). Although some observations suggest a
constant MBH /Mbulge ratio up to z ∼ 3 (e.g., Shields et al. 2003), some other observations
1

The UKIRT WFCAM infrared large area survey has started in 2005 and will end in 2012(http://www.ukidss.org/). A total of 4000 deg2 will be covered (see Figure 2) with the limiting magnitudes of Y (1.05 µm) = 20.5, J (1.25 µm) = 20.0, H (1.65 µm) = 18.8, and K (2.2 µm) = 18.4. Notethat AGNs at z > 7 cannot be identified only by using the WFCAM data, because galactic cool stars also
display red optical − inf rared colors as AGNs at z > 7 and their number density is much much larger thanthat of z > 7 AGNs. To effectively separate z > 7 AGNs from Galactic cool stars, z-band imaging survey
proposed in this program is essential (see Glikman et al. 2008).

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Figure 1.2: The area shown in the orange color is covered with the UKIRT WFCAM large area survey.
The northern and equatorial stripe at Right Ascension (R.A.) = 7–18 hr each consists of 1907.6 deg2 . The
small area (212.5 deg2 ) at R.A. = 22–4 hr is also covered.

report a possible redshift evolution in the MBH /Mbulge ratio (e.g., Woo et al. 2008). This
problematic situation is largely due to the difficulty in measuring the MBH /Mbulge directly
at high redshifts. We therefore focus on the following statistical properties of AGNs at 4 <z < 5 to study the co-evolution of SMBHs and galaxies; “the environment of AGNs”,“the spatial correlation of AGNs”, and “the luminosity function of AGNs”.
The environment of AGNs provides important parameters of the AGN evolution such as
the lifetime of the AGN activity, specifically through the number densities of galaxies around
AGNs and the biases of AGNs and galaxies. This is because the formation and evolution of
AGNs are closely related with the merger process of galaxies, since a major merger carriesa large amount of gas in a galaxy disk inward to the central region and then ignite the
AGN activity (e.g., Kauffmann & Haehnelt 2000). Therefore some crucial parameters of
the AGN evolution such as the AGN lifetime are constrained through observations of thenumber density of galaxies around AGNs and the biases of AGNs and galaxies. Basedon the semi-analytic model of AGN formation by Enoki et al. (2003), the quasar/galaxy
number ratio in a dark matter halo depends on the mass of the dark matter halo and
the AGN lifetime. Therefore, by measuring the number of galaxies around AGNs, we will
constrain the typical timescale of the SMBH growth even at z > 3. On the other hand,
Kashikawa et al. (2007) reported the habitat segregation between Lyman break galaxies(LBGs) and Lyα-emitting galaxies around a luminous AGN at z ∼ 5 (Figure 4). Thisis a strong evidence of the (negative) AGN feedback on the star-formation activity in theneighboring galaxies around AGNs. Such an interplay between AGN activity and galaxy
evolution will be directly explored based on new observations of the environments around
AGNs.
By measuring the spatial distribution of AGNs and its evolution, we can give strong
constraints on some of crucial parameters in the AGN evolutionary scenario such as the7Figure 1.3: Integrated i-band luminosity function of AGNs (with Mi < −27.6) as a function of redshift,obtained with the SDSS dataset (Richards et al. 2006) combined with the 2dF quasar survey dataset (Boyleet al. 2000). The number density of luminous AGNs show its peak at z ∼ 2 − 3. This suggests that themain growing-up phase of SMBHs should be at z > 3, which is the main target of this proposed project.

AGN lifetime, efficiency of the SMBH growth, bias parameters for AGNs and host halo
masses. Since the number density of AGNs is quite small, wide surveys are crucial toobtain the AGN auto-correlation function. Croom et al. (2004) found a significant increasein the AGN clustering amplitude and AGN bias parameter in the range of 0.3 < z < 2.2,
based on the 2dF QSO survey. They also claimed that at all redshifts in this range AGNs
inhibit approximately the same mass dark matter halos (∼ 3 × 1012 M⊙ ), and that the AGN
lifetime is tQ ∼ 2 × 107 yr. However, currently there is no statistically relevant data to
study the AGN correlation functions beyond z = 3 because the SDSS AGNs contains only
very luminous object, whose number density is too low for the analysis of their correlation
functions. The proposed new survey will find numerous less-luminous AGNs at 4 < z < 5,which enables us to derive the AGN auto-correlation function accurately in this redshift
range.
Another approach to assess the evolution of SMBHs is to utilize the luminosity function(LF) of AGNs, which provides the “average” evolutionary process of AGNs and SMBHs.
Recent hard X-ray observations have shown the evolution of AGN LF at z < 3; it is foundthat the number density of luminous AGNs with LX = 1011−13 L⊙ decreased rapidly at z < 2while the epoch of the decrease of less-luminous AGNs was delayed, z ∼ 1 (“downsizing
evolution” or “luminosity-dependent density evolution”; e.g., Ueda et al. 2003). The shapeand its evolution of AGN LFs are closely related with the evolutionary process of AGNs,
especially with the AGN lifetime, as demonstrated by semi-analytic models (e.g., Enoki etal. 2003). However, although the AGN LF has been measured to the low-luminosity range
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Figure 1.4: Spatial distributions of LBGs (blue circles and contours) and Lyα emitters (red triangles
and contours) around a luminous AGN SDSS J0211–0009 (central orange square). Only LBGs are seen at
the vicinity of SDSS J0211–0009 (see Kashikawa et al. 2007 for more details).

at up to z ∼ 2 by previous optical and X-ray surveys, the low-luminosity part of AGN LFs at
z > 3 have not yet been investigated. This is because previous optical AGN survey such as
SDSS were too shallow to select such low-luminosity AGNs and previous deep X-ray surveys
were too narrow to find low spatial density objects as AGNs. The proposed new AGN survey
with HSC will enable us to measure the faint-side of AGN LFs even at z > 3. Note that
we will constrain the AGN contribution to the UV background radiation by integrating theobtained AGN LFs. The AGN contribution to the UV background radiation determines its
averaged spectral energy distribution, because the UV spectral shape of AGNs is completely
different from that of star-forming galaxies. Since the spectral shape of the UV backgroundradiation affects the star-formation activity in forming galaxies significantly, understanding
the AGN contribution to the UV background based on the AGN faint-end LFs is crucial
also to investigate the galaxy formation.
All of these three statistical properties of AGNs at 4 < z < 5, i.e., “the environmentof AGNs”, “the spatial correlation of AGNs”, and “the luminosity function ofAGNs”, will be firmly constrained by this proposed “Subaru Wide-Field AGN Survey”,
aiming to detect low-luminosity AGNs whose luminosity is ∼ 2 mag fainter than the SDSS
AGNs. The target AGNs will be identified by color-selection methods that is basicallythe same as the strategy adopted in the SDSS AGN survey. Specifically, the gri selection
identifies AGNs at 3.6 < z < 4.4 and the riz selection identifies AGNs at 4.6 < z < 5.1.
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Figure 1.5: Based on a semi-analytic model for AGN formation by Enoki et al. (2003), predictions fornumber fraction of AGNs to galaxies in a dark matter halo at z = 4 are estimated as shown in this figure.
In this model, lifetime of AGNs (tQ ) is assumed to proportional to the dynamical time scale. The tQ value
at z = 0 is set to be 3 × 107 yr and 3 × 108 yr, and denoted by the labels t03 and t30, respectively.

To reject contaminations of cool stars, y-band data is very useful. In addition to AGNs,
we also identify LBGs in the same redshift ranges to examine the AGN environment. We
will select at least a few hundreds AGNs at each redshift range, based on ∼ 1000 deg2
multi-band imaging survey. This number is necessary to investigate the AGN correlation
function accurately. The limiting magnitudes given in Table 1 is required to select LBGs
around the identified AGNs.
In addition to the ∼ 1000 deg2 multi-band imaging survey proposed above, we propose
another complementary survey to search for low-luminosity AGNs at 3 < z < 5. Morokuma(2007) showed that the time-variation selection is very efficient to search for low-luminosity
AGNs at 3 < z < 5. Based on the deep multi-epoch imaging data in the SXDS field,
he found a few low-luminosity AGNs at this redshift range, and most of their redshift are
confirmed spectroscopically. To construct a large sample of such variability-selected high-z
AGNs, we propose deeper imaging observations with HSC. By obtaining ∼ 50 deg2 i andz-band imaging data with the limiting magnitudes of i = 26.6 and z = 25.9, we will detect∼ 50 variability-selected low-luminosity AGNs at 3 < z < 5. Note that at least 3 year
duration is required to identify such variability-selected AGNs.

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Figure 1.6: UV luminosity functions of SDSS AGNs at z > 4 (Fan et al. 2001). Since the SDSS AGNs
are limited in extremely luminous AGNs, only the bright end of luminosity functions is seen.

Search for Very Faint AGNs at 1 < z < 3
As shown in Figure 3, the density evolution of relatively bright AGNs reached its peak atz ∼ 2−3 and therefore the growing-up phase of SMBHs in such relatively bright AGNs (butstill fainter than SDSS high-z AGNs) is at z > 3. However, as mentioned above, the density
evolution depends on the AGN luminosity (e.g., Ueda et al. 2003). More specifically, thefainter AGNs show their density peak at the lower redshift. This means that the growing-up
phase of SMBHs in faint AGNs should be at much lower-z, i.e., 1 < z < 3. The nature of
SMBHs in such very faint AGNs is particularly interesting, because faint AGNs are very
“common” objects among galaxies. In the local universe, a large fraction of galaxies show
low-level AGN activities (including our Milky Way, although its activity level is extremelylow). Therefore, it is crucial to study the evolving stage of SMBHs in very faint AGNs at
1 < z < 3, in order to understand the co-evolution of SMBHs and galaxies generally.
One difficulty to examine the accreting process in very faint AGNs in moderate-z (butstill distant) universe is that their mass-accretion rate normalized by their Eddington accretion limit (Ṁ /ṀEdd ) is too uncertain. To solve this issue, it is a good idea to focus on
X-ray sources in the fields with previous X-ray surveys. This is because the X-ray spectral
slope is a good indicator of Ṁ /ṀEdd (e.g., Shemmer et al. 2006, 2008). Especially AGNs
in a super-critical accretion phase (i.e., Ṁ /ṀEdd > 1 is interesting to study the growing-up
phase of SMBHs in faint AGNs. Note that we will identify such faint AGNs at 1 < z < 3

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Figure 1.7: Two-color selection diagrams for high-z AGNs. AGNs at 3.6 < z < 4.4 are selected throughthe r − i vs g − r diagram (left panel) while AGNs at 4.6 < z < 5.1 are selected through the i − z
vs r − i diagram (right panel). The hatched areas in both panels show the selection criteria for high-z
AGNs. Solid line in the panels are the predicted track for high-z AGNs and the filled black symbols denote
spectroscopically confirmed SDSS AGNs (Fan et al. 2001).

among the detected objects in ∼ 50 deg2 relatively deep images, basically through the AGN
photometric redshift technique (e.g., Richards et al. 2008). Note that AGNs in this redshift
range show very blue continuum colors and point-line nuclei.
Another interesting population is variability-selected AGNs in 1 < z < 3 since thevariability-selection method can pick up very low-level AGN activities. Recent observations
show that some of such variability-selected AGNs are in a special accretion phase, i.e.,
harboring a radiation-inefficient accretion flow (RIAF) in their nuclei (e.g., Totani et al.
2005; Morokuma et al. 2008). Their statistical properties are particularly interesting
because the feedback processes by AGNs in the RIAF phase are recently focused on as a“radio-mode AGN feedback” (e.g., Sijacki et al. 2007; Okamoto et al. 2008). Observational
studies on the interplay between the variability-selected AGNs and star-formation activities
in galaxies around the RIAF-mode AGNs will bring us a new insight in this topic.

1.1.2

Survey Parameters• Area:– Wide survey: 1,000 [deg2 ] for g, r, i, y, and 2,000 [deg2 ] for z.
– Deep survey: 50 [deg2 ] for i, z, y.
• Field(s):– Wide survey: A part of the UKIRT WFCAM large area survey (see Figure 2).
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Table 1.1: Survey parameters. (a) Acceptable seeing FWHM [arcsec]
g1
r1
i1
z1
y1
i2
z2
y2
Texp [min]
15
15
15
15
15
60
120 120depth[AB]26.5 26.2 25.8 24.7 23.4
26.6 25.9 24.6
lunar phasedddd/g d/gdd/g d/g(a)seeing[arcsec]
1.0
1.0
0.7
1.0
1.0
0.7 1.0 1.0
area[deg2 ]1000 1000 1000 2000 1000
50
50
50
– Deep survey: Including the XMM large sky survey area and other wide X-ray
imaging survey areas.
• Scheduling Requirements:– Wide survey: Each FoV should be completed in the continuous observing run;i.e., all of the 5 bands (g, r, i, z, y) for a certain FoV should be observed without
a time interval of a few weeks. This is required to avoid the effects of time
variation of AGNs, since the time variation of AGNs makes the color-selection
strategy inaccurate and inefficient.
– Deep survey: Each FoV should be observed at least three times in each band,with a time interval of at least 1 year. This is necessary to identify the AGNs
through the time-variation selection. Consequently the observation campaign
should continue at least 3 years.

Observing Method and Technical Details
No preferences for the unit exposure time and the dithering pattern. Note that better seeingnights are requested for i-band observations (both in “wide” and “deep” surveys). Sharp
images of the target objects is useful to distinguish high-z AGNs and extremely brightgalaxies (e.g., gravitationally magnified objects).

1.1.3

Comparison with Other Survey Plan(s)The most important on-going multi-color optical imaging survey is the CFHT legacy survey(CFHTLS; http://www.cfht.hawaii.edu/Science/CFHLS/). The limiting magnitudes of the
CFHTLS are u = 26.4, g = 26.6, r = 25.9, i = 25.5, and z = 24.8 for “Wide” survey(170 deg2 ), and g = 25.5, r = 25.0, and z = 24.4 for “Very Wide” survey (410 deg2 ). Our“Wide” survey is ×2.5 wider and ∼ 1.0 mag deeper than than “CFHTLS-Very Wide”. Thisdifference in the limiting magnitudes is essential to detect not only AGNs but also (relatively
bright) LBGs at z > 3. Although the limiting magnitudes of our “Wide” survey are similar
to those of “CFHTLS-Wide”, our survey area is × ∼ 10 wider than the CFHTLS. Thisdifference is crucial to study very rare objects such as high-z AGNs. Therefore, although
CFHTLS will also find AGNs at z > 3, the environment of the detected AGNs is still
statistically unclear. To investigate the co-evolution between SMBHs and galaxies, our13proposed observations is essencial to provide crucial statistical information. Note that the
CFHTLS lacks y data. This is critical to search for AGNs at z > 6.5, and thus our project
has a significant advantage with respect to the CFHTLS especially in this issue.
The dark energy survey (planned survey period is 2010–2014) will be the most competitive optical project for our survey. Its 5σ limiting magnitudes are g = 25.4, r = 24.9,
i = 25.1, z = 24.7, and y = 22.4 (Banerji et al. 2008). Although its z-band limiting
magnitude is comparable to ours, g, r, and y limiting magnitudes are ∼1 mag shallower
than ours. The deeper blue-side images are crucial to select AGNs at z > 3 because thecolor-color selection technique utilizes the Lyman-break feature in the spectra. The deeper
y image is significantly important to search for AGNs at z > 6.5. Therefore we would stressthat y-band observations with HSC is critically important, not only in terms of the AGN
science but also in terms of the survey originality.
There is another powerful future survey based on near-infrared wide-field imaging observations, that is the VISTA/VIKING 1500 deg2 survey. Its limiting magnitudes are z = 23.1,
y = 22.3, J = 22.1, H = 21.5, and K = 21.2. However, its z and y limiting magnitudes
are also ∼ 1 mag shallower than ours. This difference is crucial especially to search for
extremely rare objects (e.g., z > 7 QSOs), since the AGN luminosity function shows basically a power-law shape and thus the fainter AGNs are more numerous. Although the “first
discovery” of AGNs at z > 7 may be achieved by other survey projects, our AGN survey
with HSC will constract the “statistical” sample of AGNs at z > 7, for the first time.

1.1.4

Follow-up/Collaborative Survey Plan(s)To search for AGNs at z > 7, we will combine the Subaru HSC z-band data with UKIRTWFCAM LAS infrared data, which will surely be available in 2012. After getting thephotometric sample of z > 7 AGNs found though this project, we will perform follow-up
near-infrared spectroscopy. This will tell us various breakthrough information, including
the mass of SMBHs and metallicity in the z > 7 universe.
Also for the photometric sample of AGNs at 1 < z < 7, follow-up optical spectroscopic
observations are required. We will select a part of the whole survey area and carry out
complete spectroscopic observations for AGNs in the sub-area, because it is unrealistic toperform follow-up observations for all AGNs. Through the optical spectroscopic observations, we will confirm the accuracy, efficiency, and contamination of our color-based AGN
selection strategy. The spectra are also used to derive the metallicity, mass of SMBHs, andṀ /ṀEdd .

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