Oct 2007

Introduction to the Sloan SurveyIntroduction to the Sloan Survey

Title

Rita SinhaRita SinhaIUCAAIUCAA

Oct 2007

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.

SDSSThe 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.

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.

Oct 2007

Title

DATA FLOW

Oct 2007

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.

http://www.sdss.org/iotw/archive.html

Interesting images from Sloan

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.

Oct 2007

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.

Oct 2007

Data Release 6 (DR6)Data Release 6 (DR6)

SDSS DR6 Imaging Sky Coverage (Aitoff projection of Equatorial coordinates)

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 ]

u g r i z3551Å 4686Å 6165Å 7481Å 8931Å22.0 22.2 22.2 21.3 20.5

Average wavelengths and magnitude limits

Oct 2007

Data Release 6 (DR6)Data Release 6 (DR6)

SDSS DR6 Imaging Sky Coverage (Aitoff projection of Equatorial coordinates)

SDSS DR6 Spectral Sky Coverage (Aitoff projection of Equatorial coordinates)

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 ]

Spectroscopy Area 7425 sq. deg.Wavelength coverage 3800-9200ÅTarget magnitude limits for main samples:Galaxies: Petrosian r <17.77, Quasars: PSF i <19.1 [Data volume: 310 GB]

Catalogof

1,271,680spectra

790,860 Galaxies, 154,925 Stars90,108 Quasars (redshift <2.3)13,539 Quasars (redshift >=2.3)69,052 M stars and later68,770 Sky spectra, 21,332 Unknown class

u g r i z3551Å 4686Å 6165Å 7481Å 8931Å22.0 22.2 22.2 21.3 20.5

Average wavelengths and magnitude limits

Oct 2007

SDSS data products Images - using SDSS as your telescopeSDSS 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 catalogThe 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 productsThese include astrometric calibrations, photometric calibrations, gif and postscript plots of spectra, and finding charts in postscript/jpeg/fits formats.

Oct 2007

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).

SDSS data products

Oct 2007

DR5 Schema

Oct 2007

Title

DEMOhttp://cas.sdss.org/astro/en/

Oct 2007

Schema Browser http://cas.sdss.org/astro/en/

Oct 2007

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.

Oct 2007

Search

* 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

You can search the SDSS database by using several predefined queries to find specific objects.

Oct 2007

Search ...

For the query pages we require:

* ra, dec (in either degrees or in the h:m:s, d:m:s 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 objectsSelecting all will return all objectsSelecting top N will return the first N objects satisfying the query

* Format: output formatIt can be HTML, CSV, or can be XML(not yet implemented)

Oct 2007

SQL

• SQL: Structured Query Language,a standard means of asking for data from databases

Syntax:“Select” .................“From” .................“Where” .................

Sample Query:

SELECTObjID, ra,dec,psfmag_i, psfmag_r, psfmag_u, psfmag_g,psfmag_z, zFROM SpecPhotoWHEREpsfmag_u between 10 and 24 AND (specclass = 1 and type = 6)

http://cas.sdss.org/astro/en/tools/search/sql.asp

Oct 2007

Data Access

DASThe Data Archive Server, which provides access to the imaging and spectroscopic products of the survey.

CASThe Catalog Archive Server contains the measured parameters from all objects in the imaging survey and the spectroscopic survey.

Create account in Casjobs