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Introductory Overview of SDSS Data Products
Introductory Overview of SDSS Data Products
SDSS Documentation
SDSS Documentation
A Little SDSS Nomenclature
A Little SDSS Nomenclature
Runs comprising Stripe 30, N and S strips
Runs comprising Stripe 30, N and S strips
SDSS DR4 Sky Coverage
SDSS DR4 Sky Coverage
SDSS Images
SDSS Images
Image-Related Products
Image-Related Products
Field Information
Field Information
Object Lists
Object Lists
Primary Survey Objects
Primary Survey Objects
SDSS asinh Magnitudes
SDSS asinh Magnitudes
SDSS Magnitudes
SDSS Magnitudes
SDSS Magnitudes (cont’d)
SDSS Magnitudes (cont’d)
Example Magnitude Usage
Example Magnitude Usage
Star/Galaxy Separation
Star/Galaxy Separation
Target Selection Flags
Target Selection Flags
primTarget flags
primTarget flags
primTarget flags
primTarget flags
Photometric Processing Flags
Photometric Processing Flags
Spectra
Spectra
Spectroscopic Information
Spectroscopic Information
Matching Spectroscopic and Photometric Data
Matching Spectroscopic and Photometric Data
Introductory Overview of SDSS Data Products
Introductory Overview of SDSS Data Products
Southern Survey and Special Spectroscopic Programs
Southern Survey and Special Spectroscopic Programs
Value-Added Data Products
Value-Added Data Products
SDSS Documentation Redux
SDSS Documentation Redux

Презентация на тему: «Introductory Overview of SDSS Data Products». Автор: Huan Lin. Файл: «Introductory Overview of SDSS Data Products.ppt». Размер zip-архива: 129 КБ.

Introductory Overview of SDSS Data Products

содержание презентации «Introductory Overview of SDSS Data Products.ppt»
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1 Introductory Overview of SDSS Data Products

Introductory Overview of SDSS Data Products

Huan Lin Experimental Astrophysics Group Fermilab

2 SDSS Documentation

SDSS Documentation

PLEASE make use of extensive SDSS documentation available on the web SDSS DR4 web site http://www.sdss.org/dr4/ Data Products Sky Coverage Data Access Algorithms SDSS collaboration DR4 Catalog Archive Server (CAS) http://cas.sdss.org/collabDR4/en/ Schema Browser

3 A Little SDSS Nomenclature

A Little SDSS Nomenclature

Run: a scan made by the imaging camera Runs make up a strip, 2 interleaved N and S strips make up each 2.5 deg wide survey stripe Rerun: number assigned to each (re)processing of the same run Camcol: 1 of the 6 camera columns comprising each run Field: 2048 pixel x 1361 pixel areas dividing each run Target: reduction used for spectroscopic target selection Best: best available reduction

4 Runs comprising Stripe 30, N and S strips

Runs comprising Stripe 30, N and S strips

Good

Target Chunk (“resolved” of overlaps)

Bad

5 SDSS DR4 Sky Coverage

SDSS DR4 Sky Coverage

See sky coverage page for the lists of target/best stripes, runs, fields, …

Imaging Area 6670 sq. deg.

Use “Foot” (footprint) server to convert RA/Dec to run/rerun/camcol/field

Spectroscopic Area 5320 sq. deg.

6 SDSS Images

SDSS Images

“Corrected frames”: fpC-$run-$filter$camcol-$field.fit E.g., fpC-002126-g6-0428.fit 0.396 arcsec/pixel 2048 x 1489 pixels (note adjacent fpC images overlap; e.g., along field direction primary area is only 1361pixels long) Retrieve from Data Archive Server (DAS), or via http with, say, wget Convert counts to calibrated magnitudes as on later slide A “sofbias” = 1000 counts is included in the background of the fpC images (subtract it off first to get real sky) See DR4 web site for astrometric calibration beyond the WCS given in the header

7 Image-Related Products

Image-Related Products

Atlas images fpAtlas*.fit: “postage-stamp” images of individual objects PSF files psField*.fit: PSF information Image masks fpM*.fit: binary masks indicating saturation, interpolation, detected objects, etc. Code to read fpAtlas, psField, and fpM files are available on the DR4 web site Bad region masks mask*.csv: ascii files indicating regions affected by saturation/bright stars, satellite trails, bad seeing, and survey holes

8 Field Information

Field Information

Field table in CAS tsField-$run-$camcol-$rerun-$field.fit binary fits tables Field quality (good, acceptable, bad, …) Photometric calibration zeropoints and extinction coefficients PSF and seeing information Sky (atmospheric extinction corrected) Astrometric transformation Plus other stuff …

9 Object Lists

Object Lists

PhotoObj and similar tables/views in CAS tsObj-$run-$camcol-$rerun-$field.fit binary fits tables Readable using standard fits I/O routines; see web site for example using SM Field quality, seeing, sky are also in fits header Fits tables contain Run, rerun, camcol, field, id Position: RA/Dec, etc. Object classifications and photometric processing flags Target selection flags Various calibrated SDSS magnitudes Surface brightness, concentration index, radial profiles Adaptive moments Lots of other quantities … see data model

10 Primary Survey Objects

Primary Survey Objects

Objects in the SDSS can be duplicated because of geometric overlaps between adjacent runs, fields, etc., and because of details of how photo defines detected objects In tsObj files, to avoid duplicate objects, select objects with the their status flag set as PRIMARY In the CAS, similarly select on the status flag or use views like PhotoPrimary, Galaxy, or Star, which are comprised of only primary survey objects

11 SDSS asinh Magnitudes

SDSS asinh Magnitudes

Count rate f/f0 = counts/exptime * 100.4*(aa + kk * airmass) exptime=53.907456, aa=zeropoint, kk=extinction coefficient tsField file or Field table Conventional magnitude = -2.5 * log10(f/f0) asinh magnitude = -(2.5/ln(10)) * [asinh((f/f0)/2b)+ln(b)] Lupton, Gunn, & Szalay 1999, AJ, 118 b is a softening parameter, set to be about 1 sigma of sky noise in each filter (see DR4 web site) Difference between asinh and conventional mag < 1% for objects brighter than asinh mag m(f/f0 = 10b) = 22.12, 22.60, 22.29, 21.85, 20.32 for ugriz

12 SDSS Magnitudes

SDSS Magnitudes

PSF: Fit of a PSF model to the object Petrosian: Magnitude w/i the Petrosian radius rP, where the ratio of the local surface brightness in an annulus at rP to the mean surface brightness within rP is 0.2 (aperture set by r band) Model: The better of the fits to a PSF-convolved deVaucouleurs (deV) or exponential (exp) galaxy profile (aperture set by r band) cmodel: The best linear combination of the deVaucouleurs and exponential fits in each band; the flux is Fcomposite= fracDeV FdeV + (1 - fracDeV) Fexp Fiber: Magnitude inside the 3”-diameter spectroscopic fiber aperture (images convolved to 2” seeing first)

13 SDSS Magnitudes (cont’d)

SDSS Magnitudes (cont’d)

Magnitudes are in general not corrected for Milky Way extinction Corrections are computed following Schlegel, Finkbeiner & Davis (1998) Given as reddening in the tsObj files or extinction in the CAS To compute magnitudes in arbitrary circular aperture, can use the radial surface brightness profiles Given as the average surface brightness in a series of annuli Units are maggies/sq. arcsec, where 1 maggie of flux has an AB magnitude of 0 See profMean in the tsObj files and the PhotoProfile table in CAS

14 Example Magnitude Usage

Example Magnitude Usage

Photometry of bright galaxies: e.g. for main sample galaxies, use Petrosian magnitudes (model independent, S/N remains good to r=20 or so) Photometry of galaxies: cmodel magnitude (close to optimal S/N, better cf. Petrosian magnitudes esp. at faint magnitudes) Colors of galaxies: model magnitudes (aperture from r band applied to all filters, unlike for cmodel magnitudes) Photometry of distant quasars: PSF magnitude (unresolved objects) Colors of stars: PSF magnitude

15 Star/Galaxy Separation

Star/Galaxy Separation

Star/galaxy separation criterion used by photo An object with psfMag - cmodelMag > 0.145 is classified as a galaxy, otherwise it’s a star (in each filter, or for summed flux in each band with a detection) Classification given as objc_type in the tsObj files or type in the CAS (3 = galaxy, 6 = star) Star/galaxy separation criteria used by target is different and more conservative for galaxies Main galaxies, Cut I LRGs: rPSF - rmodel > 0.24 Cut II LRGs: rPSF - rmodel > 0.4

16 Target Selection Flags

Target Selection Flags

Flags are used extensively to indicate type, status, quality, etc., etc. primTarget: 32-bit primary target selection flag Main galaxies, quasars, high-z quasars, luminous red galaxies (LRGs) , … E.g., to select main sample galaxies: (primTarget & 64) > 0 secTarget: secondary target selection flag Used to indicate calibration stars, skies, guide stars, etc. Southern Survey targets indicated with highest bit set in secTarget and primTarget

17 primTarget flags

primTarget flags

Stoughton et al. (2002)

18 primTarget flags

primTarget flags

secTarget flags

Stoughton et al. (2002)

Stoughton et al. (2002)

19 Photometric Processing Flags

Photometric Processing Flags

Flags objc_flags, objc_flags2 in tsObj files, flags in CAS (also flags for each individual filter) Important to check flags to eliminate problem objects or junk Detailed documentation on DR4 web site Examples given to derive clean samples of stars and galaxies Primary objects to avoid duplicates Reject saturated objects Reject objects with deblending problems Reject objects with interpolation problems Other cuts …

20 Spectra

Spectra

2D spPlate-$plate-$mjd.fit fits images and binary tables 640 spectra together in single fits file for each plate Flux-calibrated spectra, inverse variance, quality masks, and other supporting information No measured parameters (e.g., redshifts) 1D spSpec-$plate-$mjd-$fiber.fit image and binary tables 1 fits file for each fiber of each plate Calibrated spectrum, continuum-subtracted spectrum, noise, quality mask Spectral classification, redshift, redshift error and confidence Binary tables with line measurements, line indices, emission-line and cross-correlation redshift information, … spDiag-$mjd-$plate.par ascii file Summary information for all 640 spectra on each plate Object id, target flags Spectral classification, redshift, redshift error and confidence

21 Spectroscopic Information

Spectroscopic Information

Generate vacuum wavelengths using ? = 10(COEFF0 + COEFF1*i), where i denotes the (zero indexed) pixel number, and COEFF1 and COEFF2 are from file headers Check redshift confidence z_Conf, and also status z_Status and warning z_Warnin flags (I like z_Conf > 0.7 based on eye checks of galaxy spectra) In CAS, use the SpecObj, SpecLine, and SpecLineIndex tables/views to get spectroscopic parameters The spectrophotometry is good (e.g., overall residual offsets vs. gri fiber magnitudes/colors of < a few percent); see documentation on DR4 web site for details

22 Matching Spectroscopic and Photometric Data

Matching Spectroscopic and Photometric Data

Done in CAS joining the appropriate tables, or using SQS or IQS (now parts of CAS) first and then the DAS to retrieve the spectra and image fits files Also available for each plate are the packaged spectral data and corresponding object lists and atlas images: spPlate, spSpec, spDiag, spObj (analogous to tsObj), … Get from DAS (tsObjFromMap option) or via http (e.g. with wget)

23 Introductory Overview of SDSS Data Products
24 Southern Survey and Special Spectroscopic Programs

Southern Survey and Special Spectroscopic Programs

Mostly on Stripe 82, including u-selected galaxies, low-z galaxies, deep LRGs, faint quasars, spectra of everything, stellar programs, … Retrieve from DAS or using PlateX table in CAS; see sdss-archive/2511, and instructions are forthcoming on DR4 web site See the Southern Equatorial Survey plates page at http://www-sdss.fnal.gov/targetlink/southernEqSurvey/ See Ivan Baldry’s page and catalogs at http://mrhanky.pha.jhu.edu/~baldry/sdss-southern/

25 Value-Added Data Products

Value-Added Data Products

DR3 Quasar Catalog Composite and unusual quasar spectra White dwarf catalog Moving Object Catalog Cut & Enhance galaxy cluster catalog Value-added galaxy catalogs: NYU, CMU-Pitt, MPA/JHU Orion data release Princeton spectra SuperCosmos Science Archives

26 SDSS Documentation Redux

SDSS Documentation Redux

PLEASE make use of extensive SDSS documentation available on the web SDSS DR4 web site http://www.sdss.org/dr4/ Data Products Sky Coverage Data Access Algorithms SDSS collaboration DR4 Catalog Archive Server (CAS) http://cas.sdss.org/collabDR4/en/ Schema Browser

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