Introduction to the Sloan Survey

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Introduction to the Sloan Survey

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Rita Sinha IUCAA
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SDSS
The SDSS uses a dedicated, 2.5-meter telescope on
Apache Point, NM, equipped with two powerful
special-purpose instruments. The 120-megapixel
camera can image 1.5 square degrees of sky at a
time, about eight times the area of the full
moon. A pair of spectrographs fed by optical
fibers can measure spectra of more than 600
galaxies and quasars in a single observation. A
custom-designed set of software pipelines keeps
pace with the enormous data flow from the
telescope.
The Sloan Digital Sky Survey (SDSS) will map
one-quarter of the entire sky and perform
redshift survey of galaxies, quasars and stars.
Now into its sixth major data release i.e. DR6.
Science goals fundamental questions about the
nature of the Universe, the origin of galaxies
and quasars, and the formation and evolution of
our own Galaxy, the Milky Way.
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DATA FLOW

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Interesting images from Sloan
Within the heart of the majestic Seyfert galaxy,
NGC 5033, lies a powerful engine. Seyfert
galaxies are a class of active galactic nuclei
(AGN) which produce large amounts of emission
line spectra in their core, often with variable
power. The driving source of this emission is
thought to be a supermassive black hole at the
centre.
Spiral galaxies NGC 3788 (top) and NGC 3786
(bottom) in the constellation Ursa Major. These
two galaxies, like many found throughout the SDSS
survey, are gravitationally interacting.
Interactions such as these are commonly observed
by the SDSS. They are thought to lead to the
formation of elliptical galaxies.
The Siamese twins, NGC 4567 and NGC 4568, look
like they are in the middle of a collision. But
yet these two members of the Virgo Cluster show
none of the usual signs of interaction such as
tidal tails or distortion. It may be that one is
just passing in front of the other.
http//www.sdss.org/iotw/archive.html
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Future sky coverage of SDSSSDSS- II
Imaging and spectroscopy of the North Galactic
Cap is continuing as part of the Sloan Legacy
Survey, one of three components of SDSS-II. The
Legacy Survey, which will continue through
mid-2008, will cover the small remaining imaging
gaps from DR5 and will complete spectroscopy over
the full DR5 region. The SEGUE (Sloan Extension
for Galactic Understanding and Exploration )
component of SDSS-II includes additional imaging,
and spectroscopy of stellar targets. The Sloan
Supernova Survey, the third component of SDSS-II,
carries out repeated imaging of the southern
equatorial stripe to discover and measure
supernovae. The first data from SDSS-II release
is DR6.
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Data Release 6 (DR6)
Imaging Footprint area 9583 sq. deg. Imaging
catalog 287 million unique objects Data volume
of images 10 TB catalogs (DAS, fits format) 2
TB catalogs (CAS, SQL database) 4 TB
Average wavelengths and magnitude limits
SDSS DR6 Imaging Sky Coverage (Aitoff projection
of Equatorial coordinates)
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Data Release 6 (DR6)
Imaging Footprint area 9583 sq. deg. Imaging
catalog 287 million unique objects Data volume
of images 10 TB catalogs (DAS, fits format) 2
TB catalogs (CAS, SQL database) 4 TB
Average wavelengths and magnitude limits
SDSS DR6 Imaging Sky Coverage (Aitoff projection
of Equatorial coordinates)
Spectroscopy Area 7425 sq. deg. Wavelength
coverage 3800-9200Å Target magnitude limits for
main samples Galaxies Petrosian r Quasars PSF i Catalog of 1,271,680 spectra
790,860 Galaxies, 154,925 Stars 90,108 Quasars
(redshift 2.3) 69,052 M stars and later 68,770 Sky
spectra, 21,332 Unknown class
SDSS DR6 Spectral Sky Coverage (Aitoff projection
of Equatorial coordinates)
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SDSS data products

• Images - using SDSS as your telescope
• SDSS provides FITS image files of the corrected
  frames in five bands, a mask that records how
  each pixel was used in the imaging pipelines,
  images of the corrected frames after detected
  objects have been removed, and "atlas" images,
  which include all significant pixels around each
  object.
• Object lists - using SDSS as your photometric
  catalog
• The calibrated object lists are FITS tables
  containing positions, fluxes, and shapes of all
  objects detected at 5 sigma on the images.
• Spectra and spectroscopic parameters - using SDSS
  as your spectrograph
• "2d" spectra FITS files of the flux- and
  wavelength-calibrated, sky-subtracted spectra,
  with error and mask arrays and resolution at each
  pixel.
• "1d" spectra FITS files with the calibrated
  spectra and error and mask arrays, redshift,
  spectral classification, and detected lines of
  each spectrum.
• Tiling - using SDSS as your complete survey
• "Tiling" means optimising the placement of
  spectroscopic tiles on the sky and assignment of
  spectroscopic fibers to targets in the
  spectroscopic survey.
• Other data products
• These include astrometric calibrations,
  photometric calibrations, gif and postscript
  plots of spectra, and finding charts in
  postscript/jpeg/fits formats.

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SDSS data products
Data Access All data products are available
from the data access page as fits images and
tables from the Data Archive Server (DAS). All
catalogs are also available through the Catalog
Archive Server (CAS) which provides fast search
capabilities.
Data model The flat-file data model contains
detailed descriptions of all data generated by
the data processing. The Archive Intro page and
the Schema Browser describe how data are stored
in the Catalog Archive Server (CAS).
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DR5 Schema
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http//cas.sdss.org/astro/en/
DEMO

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Schema Browser
http//cas.sdss.org/astro/en/
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Visual Tools
Finding Chart returns a JPEG image centered
on (ra,dec), of size (height x width) where the
image is scaled to an arbitrary scale (scale).
Various drawing options can be specified (opt).
Navigate lets you interactively navigate the
sky, by clicking and zooming. Image Lists
is a cutout service that generates small JPEG
images for up to 1000 user-provided positions on
the sky. Explore lets you interactively
explore the various properties of individual
objects.
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Search
You can search the SDSS database by using several
predefined queries to find specific objects.
Radial Search the sky around a given point
Rectangular Search the sky in a rectangular
region SQL Type in a SQL query directly
Imaging Query Form-based query on imaging
data Spectro Query Form-based query on
spectroscopic data
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Search ...
For the query pages we require ra,
dec (in either degrees or in the hms, dms
notation). radius is the search radius for
a radial query (arcminutes). u,g,r,i,z -
the magnitudes of the objects in the SDSS.

The output options and formats on the query
pages Return the number of objects
Selecting all will return all objects
Selecting top N will return the first N objects
satisfying the query Format output
format It can be HTML, CSV, or can be
XML(not yet implemented)
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SQL
http//cas.sdss.org/astro/en/tools/search/sql.asp

• SQL Structured Query Language,
• a standard means of asking for data from
  databases
• Syntax
• Select .................
• From .................
• Where .................

Sample Query SELECT ObjID, ra,dec,psfmag_i,
psfmag_r, psfmag_u, psfmag_g,psfmag_z, z FROM
SpecPhoto WHERE psfmag_u between 10 and 24 AND
(specclass 1 and type 6)
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Data Access
Create account in Casjobs
DAS The Data Archive Server, which provides
access to the imaging and spectroscopic products
of the survey.
CAS The Catalog Archive Server contains the
measured parameters from all objects in the
imaging survey and the spectroscopic survey.