jvo

検索Abstract:
We present a science use case of Virtual Observatory, which is actually achieved to examine environment of AGN up to redshift of 3.0. We used theJapanese 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 environment of higher galaxy density than that of typical galaxies. The current observations, however, indicate that AGNs
do not reside in particularly high density environment. We investigated ~1,000 AGNs, which is about ten times larger samples than previous studies
covering redshifts larger than 0.6. We successfully found significant excess of galaxies around AGNs at redshifts of 0.3 through 1.8.
If this work was done in a classical manner, that is, raw data were retrieved from the archive through a web interface in an interactive way and the data
were reduced in a local poor machine, it might have taken several years to finish it. Since the Virtual Observatory system is accessible through thestandard interfaces, it would be easy to query and retrieve observed data in an automatic way. We have constructed a pipeline for retrieving the data andcalculating 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 provides astronomers with a powerful tool to conduct a data-incentive astronomical research.

SubaruData Archive(raw)

Step 0 (Admin)

Step 1

Parallel processing oflarge amount of data

Multiple database query
Suprime-Cam images and UKIDSS catalog data are searched
for around known AGNs.

Data reduction of all the SuprimeCam data on the JVO gridcomputing system (12 servers, 48CPU cores)

The following JVO Query Language (JVOQL) is an example toexecute a coordinate join between an AGN catalog table and a
Suprime-Cam metadata table:

10 TB of RAW data are reduced
through the JVO web interface. The
processing time is ~10 days.

SELECTFROMThe metadata of the processed
images are registered to a databaseand exposed through the VOinterface.

WHERE

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)

JVO Portal

SubaruData Archive(processed)
Subaru SkyNode

Step 2
Workflow for calculating galaxy density
around each AGN.

AGN SkyNode

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

UKIDSS SkyNode

3. Calculate galaxy number density around the AGN position
This script is executed for every AGN found in the step 1:

Step 3

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

Detailed analysis on a localmachine.

Conclusion

1. Stack the galaxy density profiles
around each AGN
2. Calculate correlation length between
AGN and galaxies for each redshift
and luminosity range.
3. Write a paper…

Combination of all the Subaru archival data and the dataobtained by medium-sized survey telescopes has successfullyrevealed AGN environment at intermediate redshift range withhigher statistical significance than ever achieved. The featureof the VO service that enables automated queries is crucial for
conducting data-incentive astronomical studies in the 21stcentury.