1. Clustering of galaxies around AGN in the HSC Wide survey
published in PASJ HSC special issue
arXiv:
Yuji Shirasaki (NAOJ), Masayuki Akiyama (Tohoku U.),
Tohru Nagao (Ehime U.), Yoshiki Toba (ASIAA), Wanqiu He (Tohoku U.),
Masatoshi Ohishi (NAOJ), Yoshihiko Mizumoto (NAOJ),
Satoshi Miyazaki (NAOJ), Atsushi J. Nishizawa (Nagoya U.),
Tomonori Usuda (NAOJ)

2. Introduction
SMBHs (MBH = 106~1010 M☉) reside at the center of most galaxies.
Evidence of co-evolution between host galaxy and SMBH has been obtained.
Evolution of galaxies and SMBHs need to be discussed under a unified picture.
Important open questions
mechanism of the gas accretion to SMBH
How is the evolution of a host galaxy and SMBH regulated : AGN feed back ?

3. Model of the gas accretion to SMBH
secular process in the galaxy
bar and disk instability
external process
tidal interaction with nearby galaxy
major/minor galaxy merger
quiescent accretion of
hot halo gas from intra-cluster medium (ICM)
recycled gas from evolving stars
Alexander+12
#1 could operate in lower-luminosity AGNs (Seyfert)
#2 can explain the activity of higher-luminosity AGNs (QSO)
#3 is a plausible mechanism to evolve SMBH above 109M

4. Clustering of galaxies around AGN
Measure of the local density where gas accretion to SMBH occurring
dependence of local density (frequency of merger) on MBH (mass accretion history)
Previous studies (z < 1.0)
Komiya+13 and Shirasaki+16 detected a clustering dependence on MBH.
Krumpe+15 also detected a weak clustering dependence with MBH in 2.7 s.
Shirasaki+16
Krumpe+15

5. Objective of this work
extends the works of Komiya+13 and Shirasaki+16 (z < 1.0) up to redshift ~3
The epoch covering the peak of star formation and mass accretion rate for SMBH
Using the data of Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP)
Measure the environment of AGNs
clustering of galaxies
red / blue galaxy fraction
luminosity function
their dependence on MBH
First opportunity to derive those properties from a statistically significant number of AGN samples (~ thousands).

6. Data set AGN Shen+11 “QSO properties from SDSS-DR7”
Paris+17 “SDSS DR12 Quasar Catalog (DR12Q)”
RA, Dec, z, MBH (single epoch virial mass, DMBH ~ 0.4dex)
Galaxy
HSC-SSP Survey (Deep) (S15b)
240 deg2、i ~ 25.5 mag
detection in griz-band
# of AGN
5,345 (griz-band)
Grouped by z & MBH
z0 ~ z4
M8 : lower mass group
M9 : higher mass group

7. Analysis method (1/2) AGN-Galaxy cross-correlation function (1) (2)
r(r) : galaxy density at r from AGN
r0 : average density at the AGN redshift
r0 : cross-correlation length
g : fixed to 1.8
(2)
(3)
Measure the projected number densities of HSC sources at distance rp from each AGN : n(rp)
Calculate the average <n(rp)> for each AGN group.
Fit the Eq. (3) to <n(rp)>, then obtain r0. r0

8. Analysis method (2/2)
Color and Magnitude distribution of galaxies around AGN
Subtract the color/magnitude distribution at lower density region (7 - 9 Mpc) from that at higher density region (0.2 – 2 Mpc) : On-Off subtraction
 distribution for galaxies associated with the corresponding AGN
SED fit at a fixed redshift (=AGN’s z) for all HSC sources at rp < 10 Mpc
EAZY (Brammer+08) 　
Definition of color (D) and absolute magnitude (Ml)
z = 0.6~2.0 D1 = Ml270 – Ml380, Ml310
z = 1.5~3.0 D2 = Ml165 – Ml270, Ml220 D Ml

9. Result (1/4) : r0 vs z, Ml Dependence of r0 on z and Ml
For galaxies brighter than a given threshold value
Plotted as a function of M* - <Ml> for each redshift group
Galaxies more luminous than M* are clustered more than less- luminous galaxies.
Clustering of luminous galaxies increases as redshift increases.
Clustering of galaxies less luminous than M* is constant within stat. error (~6h-1Mpc)

10. Result (2/4) : LF of clustering galaxies
Derived by On-Off subtraction
Compared with LFs scaled by the factor corresponding to r0.
Over-density of luminous galaxies (M<M*)
Fit the Schechter function  M*
Deviation of M* from the average is larger for higher redshift.

11. Result (3/4) : r0 vs MBH
Crucial to remove the effect of z and Ml dependence
AGN samples matched in redshift (dz = 0.02) are used
Galaxies of Ml < M90% (> 90% completeness) are used
No significant dependence on MBH for whole galaxy sample
Red galaxies  tendency of increase in clustering with MBH

12. Result (4/4) : fblue vs MBH
on-off subtraction
Fraction of blue galaxy in our sample > 70% (each redshift group)
MBH dependence
Higher red fraction for larger MBH group

13. Discussion (1/3)
Too large clustering was measured for luminous galaxies
r0 = 10 ~ 40 h-1Mpc for M < M*
Consistent with previous clustering studies ?
r0 ~ 10 h-1Mpc at most for the brightest galaxies (Zehavi+11, Ishikawa+15).
To be consistent, the measured strong clustering should be localized around the AGNs
Clustering of less luminous galaxies
r0 ~ 6 h-1Mpc for M > M*
Mh = ~13.0 M (DM halo mass)
Consistent with previous clustering studies.

14. Discussion (2/3)
Implication of the association between AGNs and luminous galaxies
Direct interaction between them  unrealistic to affect to galaxies separated by a few Mpc ?
Environmental effect in a cluster or group
Interaction with ICM or cluster potential
Interaction between clusters/groups
Concurrent interactions between galaxies at multiple sites

15. Discussion (3/3) Different MBH dependence for blue/red galaxies
Star-formation  shift the LF to brighter side: mild increase in the # of typical (M>M*) blue galaxies, while significant increase in the # of luminous (M<M*) ones.
Quenching  conversion of blue to red: decrease in blue and increase in red
Total number of galaxies will change only mildly, while the
3 / 10
5 / 11
increase in the fraction of red can be significant in the case that the red fraction is small before the transition.

16. Summary Environment of AGN (MBH>108M, z= 0.6~3.0) was examined.
clustering, color, LF, and their MBH dependence,
Over-density of luminous galaxies around the AGNs.
Environmental effect in ICM
Cluster/Group interaction
Indication of MBH dependence
Red galaxy fraction is larger for the large MBH
Simple toy model of star-formation followed by quenching may fit to the observation qualitatively
Environment has an important role in the evolution of SMBH to MBH > 108 M