jvo

0. Abstract

1. Introduction
According to the hierarchical galaxy formation
model, it is assumed that a large galaxy has been
formed through the collisions and mergers of smaller
galaxies. During the galaxy evolution, a massive BH isformed at the center of the galaxy, and accretion ofmatters into the BH radiates large amount of energy,
which is observed as an AGN. It is, therefore,
expected that the AGN is located at higher density
region where probability of the galaxy collision ishigh.
Using the SDSS data, the clustering property of AGN
and galaxy has been measured upto z~0.6. To extend
this measurement to higher redshifts AGN, deep imaging
observations are necessary. Using the data archive ofSubaru Suprime-Cam, it is possible to measure thedistribution of galaxies around an AGN at theintermediate redshift (z=1~2), which is difficult tobe carried out with a smaller telescope. At thisredshift range, the formation rate of the AGN reaches
a maximum, so it is interesting to see the relation of
AGN activity and its environment, which may reveal afundamental clue for the mechanism of AGN evolution
and also for the evolution of large scale structure ofthe universe.

2. Dataset
We used the following dataset: AGN Catalog by Veron et al (2006)

Far and Bright AGN

Near and Dimmer AGN

Figure 2: Absolute magnitude-redshift distribution of theanalyzed AGNs.

Figure 2 : K-corrected V or g’ band absolute magnitude vsredshift of the AGNs used in this work.

3. Analysis method
1. Create a catalog from Suprime-Cam image using theSextractor. Create a multi-band catalog which
consists of data in nine bands (B, V, R, I, i’, z’,J, H, K) at maximum.

Figure 3: The average of Galaxy number density around AGNs ofeach absolute magnitude and redsfhit range.

2. Create a number density histogram of galaxy as afunction of distance from the AGN. Unobserved area,unused data suffered by a bright object, and bad
pixel fraction are corrected.
3. Remove samples which is strongly affected by theunassociated cluster of galaxies and/orinhomogeneity of the observations by applying 3
sigma deviation cut and c2 cut to the histogram.
4. For each subset of AGN samples grouped by its
redshift and brightness, the averaged number density
histogram is calculated. Assuming the number density
profile of the form of Eq (1), we derive correction
length r0 for a fixed value of γ = 0.8.
(1)Figure 4: Measured correlation length r0 as a function ofredshift.
3. Mass assembly
terminates and thegalaxy with amassive BH falls
into the center of thecluster (group).

(2)

(3)
ρ0 : average number density of galaxy at AGN’s redshiftρ(r) : observed number density as a function of distance from the AGN.
rp : perpendicular distance from the AGN
Γ: The Gamma function

mass scale

Japanese Virtual Observatory (JVO) is an
integrated database system developed byAstronomy Data Center of NAOJ. By accessing
the JVO, one can retrieve reduced Subaru
Suprime-Cam images, and also can accessseamlessly to any Virtual Observatorycompliant data services of the world. This
poster describes an early science result ofthe JVO; study of the clustering of galaxies
around an AGN. Using the data obtained throughthe JVO, we measured correlation length
between AGN and galaxy in ten times higher
statistics than ever achieved at intermediateredshifts (z=1~2).We find an indication thatthe clustering is stronger at higher redshifts.

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2. Merger of galaxies triggers generation ofa bright AGN
1. Downsizing of massassembly large cluster rapidly build up small cluster slowly …

Ni(rp) : projected number count of galaxies at distance rp from i-th AGN.
Si(rp) : effective area corresponding to the number of Ni(rp)ρi,0 : ρ0 for the i-th AGN
nbg : Back and foreground galaxy number densitytimeFigure 5: A picture of galaxy clustering and AGN evolution
inferred from this observational result.

 QSO Catalog (SDSS DR-5)
 Subaru Suprime-Cam reduced image
 UKIDSS DR2
We searched the Suprime-Cam images and UKIDSS IR
data around the AGNs listed in the Veron et al andSDSS AGN catalog, .
We analyzed for 750 AGN samples.
The celestial distribution of the AGNs are shown inFigure 1.

ρ0 is derived from Luminocity Function obtained by Gabaschet al.(2004,2007)、Cirasuolo et al (2007).

5. Discussion & Conclusions

4. Result• This observation result is compatible with the major
merger scenario which incorporates the downsizing ofmass assembly (Figure 5).

• We detected a clustering signals for datasetswith redsfhit 0.3 to 1.8 (Figure 3).
• When compared among the same brightness
datasets, the clustering is stronger at higher
redshift. Blue (Dark AGN) and red (Bright AGN)
markers of Figure 4.
• The distribution of galaxies around brighthigh-z (z=1.5-1.8) AGNs is almost flat at <1Mpc, which indicates that the AGNs are notnecessarily located at the center of galaxy
distribution.
ReferencesFigure 1 : The celestial distribution of the AGN analyzed
in this work.(in equatorial coordinate)

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• At higher redshift, assembly of larger systems aredominant, so the AGN produced at this epoch has adenser environment.The assembly of the larger systemterminates more rapidly than the smaller system, sothe smaller scale assembly becomes dominant at lower
redshift. The AGN produced during the low-massassembly has a sparser environment.
•AGNs may have similar brightness when they are
produced, regardless of their environment. The brightphase of the AGN terminates when gas accreting to the
BH is exhausted. The environment of a dimmer AGN
reflect the environment where it was produced.
• To be more confident about this scenario, more
observational data should be obtained both
qualitatively and quantitatively. The observations ofhuge number of AGN fields with the Hyper Suprime-Cam
will give more definite observational evidence on theevolution of a massive BH.