jvo

http://jvo.nao.ac.jp/portal

0. Abstract
Japanese Virtual Observatory (JVO) is an
integrated database system developed by Astronomy
Data Center of NAOJ. From the JVO, one can retrieve
reduced archive data collected by the Subaru telescope,and also can access to any Virtual Observatories of theworld. This poster describes an early science result ofthe JVO; study of the clustering of galaxies around anAGN. Using the data obtained through the JVO, we
measured cross correlation between AGN and galaxy
based on 1809 AGN samples. We found that the highredshift AGNs reside in an environment of higher
galaxy density than AGNs in the local universe.

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, expectedthat the AGN is located at higher density region where
probability of the galaxy collision is high.
Based on large surveys such as SDSS and 2dF, theclustering property of AGN and galaxy has beenmeasured up to z~0.6. To extend this measurement tohigher redshifts, we need to carry out deep opticalobservations or medium deep infrared observations.
Using data archive of Subaru Suprime-Cam, it ispossible to measure the environment of AGN at
intermediate redshifts (z=1~2), which is difficult to be
carried out with a smaller telescope. At this redshift
range, the formation rate of AGN reaches a maximumand the super massive black holes were produced
mostly at this epoch. Thus it is expected that the AGNs
are found in the environment of high galaxy density, if
they were produced mostly by galaxy mergers.
The study of the AGN environment may reveal afundamental clue to the mechanism of AGN evolution
and also for the evolution of large scale structure ofthe universe.

2. Dataset
We used the following dataset:• 12th AGN Catalog by Veron-Cetty et al (AGN samples)• SDSS DR-5 QSO Catalog (AGN samples)• Subaru Suprime-Cam image archive (galaxy samples)• UKIDSS DR2 (galaxy samples)
We searched the Suprime-Cam images and UKIDSS IR dataaround the AGNs listed in the AGN catalogs.
We analyzed 1809 AGN samples for redshift from 0.3 to 3.0.
The celestial distribution of the AGNs are shown in Figure 1, andthe distribution of redshift and brightness of the AGNs areshown in Figure 2.

Far and Bright AGN

Near and Dimmer AGN

Table 1 : Fitting parameters of projected cross correlation
analysis.

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

3. Analysis method
Studies of cross-correlation analysis usually use amethod which compares the number count at eachseparation distance for an observed sample with that fora random catalog.
In this work, data of each AGN field are highly
inhomogeneous, and it is difficult to create a random
catalog to be compared with the observation. Thus weadopted the following method to estimate the projectedcross correlation function, w(rp).
The projected cross correlation function is calculated
by integrating the cross correlation function x along theline of sight as shown in Eq (1), where r(r) is the number
density of galaxies at a distance r from an AGN and nbg isthe surface density of background galaxies.
(1)

We derived a surface density n(rp) as a function ofprojected distance from an AGN, and calculated theaverage for each redshift and brightness group. We also
estimated the average number density r0 of detectablegalaxies at the AGN redshift from the luminosity
function of galaxies. Then average of w(rp) is expressedas:(2)

Figure 3: The average of
projected crosscorrelation of AGNs andgalaxies for eachabsolute magnitude andredsfhit range.

Figure 4: Measured correlation length r0 as a function ofredshift.

Assuming the power law model for the crosscorrelation function, we fit the model function to theobserved surface density with two free parameters,
correlation length and the average of the surface densityof background galaxy <nbg>.

4. Result• The projected cross correlation functions andcorrelation lengths were measured for seven redshift
and brightness groups (Table 1 and Figure 3).

Figure 4 : The s8 of the galaxies around AGNs as afunction of redshift.

• s8 , which is a root mean square of the correlation
function in the sphere with a comoving radius of 8h-1
Mpc, are compared in Figure 4.

5. Conclusions• s8 increases with the redshift and it shows nosignificant dependence on the brightness of the AGN.
• It should be noted that the type of galaxies analyzed
for each redshift group is not completely identical. The
samples of the higher redshift groups are expected tobe biased to the blue star-forming galaxies as they areobserved at UV spectrum range in the rest frame.

Figure 1 : The celestial distribution of the 1809 AGNs
analyzed in this work. (equatorial coordinate)

検索• The distribution of galaxies around bright high-z AGNs
(z4-B) is almost flat at < 2 Mpc, which indicates that theAGNs are not necessarily located at the center ofgalaxy distribution.

• We developed a method to measure the crosscorrelation function of AGN and galaxy from imaging
data only, which enabled to investigate the galaxy
distribution around an AGN at a small scale with highstatistic.
• We succeeded to measure the cross correlation atredshifts higher than 0.6 with better statistics than everachieved by using deep imaging data of Subaru
Suprime-Cam retrieved from the JVO.
• Our result shows that AGNs at higher redshift (z > 1.0)
reside in a denser environment than lower redshift
AGNs, which supports a galaxy merger scenario forevolution of a supermassive black hole.