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Abstrat: We present a science use case of Virtual Observatory, which is actually achieved to examine an environment of AGN upto redshift of 3.0. We
used the Japanese Virtual Observatory (JVO) to obtain the Subaru Suprime-Cam images around known AGNs. According to the hierarchical galaxy
formation model, AGNs are expected to be found in an environment of higher galaxy density than that of typical galaxies. The current observations,however, indicates that AGNs do not reside in a particularly high density environment. We investigated ~1000 AGNs, which is about ten times larger
samples than the other studies covering the redshifts larger than 0.6. We successfully found significant excess of galaxies around AGNs at redshifts of 0.3
to 1.8.
If this work is done in a classical manner, that is, raw data are retrieved from the archive through a web interface in an interactive way and the data are
reduced in a local poor machine, it may take several years to finish it. Since the Virtual Observatory system is accessible through the standard interface, itis easy to query and retrieve the data in an automatic way. We have constructed a pipeline for retrieving the data and calculating the galaxy number
density around a given coordinate. This procedure was executed in parallel on ~10 quad core PCs, and it took only one day for obtaining the final result.
Our result implies that the Virtual Observatory can be a powerful tool to do an astronomical research based on large amount of data.

SubaruData Archive(raw)

Step 0 (Admin)

Step 1

Parallel processing oflarge amount of data

Multiple database query

Data reduction of all the SuprimeCam data on the JVO gridcomputing system (12 servers, 48CPU cores) .
10 TB of RAW data are reduced
through the JVO web interface. The
processing time is ~10 days.
The metadata of the processed
image are registered to thedatabase and exposed through theVO interface.

Suprime-Cam image and UKIDSS catalog data are searchedaround known AGNs.
The following JVO Query Language (JVOQL) is an example to
do a coordinate join between AGN catalog table and SuprimeCam metadata table:
SELECT
FROMWHERE

qso.*, img.*
ivo://jvo/vizier/VII/235:qso_veron_2006 qso
ivo://jvo/skynode/spcam:image AS img
qso.z >= 1.0 and qso.z < 1.1AND
img.region = Circle((qso.raj2000, qso.dej2000) 0.14)

SubaruData Archive(processed)
Subaru SkyNode

Step 2
Workflow for calculating galaxy density
around each AGN.

AGN SkyNode

A script “qso-dataset.sh” which executes the following workflow:
1. retrieve images and catalog data around a specified coordinateof AGN. This query is directory sent to the SkyNode.
2. extract objects from the images, and cross-match to create amulti-bands catalog

UKIDSS SkyNode3. Calculate galaxy number density around the AGN coordinate
This script is executed for every AGN found in the step 1:

Step 3
Detailed analysis on a localmachine.
1. Stack the galaxy density profiles
around each AGN
2. Calculate a correlation length
between AGN and galaxies for each
AGN’s redshift and luminosity range.
3. Write a paper…

qso-dataset.sh --ra <qso_ra> --dec <qso_dec> --rad <img_radius>-z <qso_z>

Conclusion
Combination of all the Subaru archival data with data producedwith medium-sized survey telescopes succeeded to reveal theAGN environment at intermediate redshift with higher statistic
than ever achieved. The feature of the VO service that enables
automated query is essential for achieving astronomical study
based on huge amount of data.