Measurements of Flux

------SDSS photometry

周志民

The SDSS asinh magnitude system

SDSS Magnitudes

PSF magnitudes（psfMag）

postage-stamp pipeline

Fiber magnitudes (fiberMag)The flux contained within the aperture of a spectroscopic fiber (3" in

diameter) is calculated in each band.

▷ Petrosian magnitudes (petroMag)to measure a constant fraction of the total light, independent of the

position and distance of the object.

Petrosian ratio

Petrosian flux ,

▷ Petrosian magnitudes (petroMag)

Theoretically, the Petrosian magnitudes defined here should recover essentially all of the flux of an exponential galaxy profile and about 80% of the flux for a de Vaucouleurs profile.

Model magnitudesa pure de Vaucouleurs profile

A pure exponential profile

At bright magnitudes (r* < 18), the model magnitudes are a poor measure of the total flux of the galaxy, because of the fact that the fits are restricted to the central parts of objects (Strateva et al. 2001).

fitting procedures: r_deV and r_exp, the effective radii of the models;

ab_deV and ab_exp, the axis ratio of the best fit models;

phi_deV and phi_exp, the position angles of the ellipticity (in degrees East of North).

deV_L and exp_L, the likelihoods associated with each model from the chi-squared fit;

deVMag and expMag, the total magnitudes associated with each fit.

apply aperture corrections to make these model magnitudes equal the PSF magnitudes in the case of an unresolved object.

ModelMagchoose the model (exponential or de Vaucouleurs) of higher likelihood in the r filter, and we apply that model (i.e., allowing only the amplitude to vary) in the other bands after convolving with the appropriate PSF in each band.

Cmodel magnitudes

Fcomposite = fracDeV FdeV + (1 - fracDeV) Fexp

There is now excellent agreement between cmodel and Petrosian magnitudes of galaxies, and cmodel and PSF magnitudes of stars

Cmodel and Petrosian magnitudes are not expected to be identical：bright galaxies：0.05-0.1 mag

star-galaxy separation using the difference between cmodel and PSF magnitudes, with the threshold at the same value (0.145 magnitudes).

Which Magnitude should I use?

the cmodel magnitude is now an adequate proxy to use as a universal magnitude for all types of objects.

Photometry of Bright Stars: PSFmag (annuli~7’’)

Photometry of Distant Quasars: psfMag

Photometry of Nearby Galaxies: petroMag

Photometry of distant galaxies: cmodel

Colors of stars: PSFmag

Colors of Galaxies: model (not cmodel) magnitudes

SDSS imaging pipelines

astrometric pipeline (astrom)

postage-stamp pipeline (psp)

Frames pipeline (frames)

final calibration pipeline (nfcalib)

monitor telescope pipeline (mtpipe)

All of the SDSS imaging software is built using a infrastructure package called Dervish (Kent et al. 1995) written in portable C, and using TCL as a command language.

photo

Dervish provides standard data structures such as linked lists and

vectors; a sophisticated memory manager with debugging

facilities; a set of astronomical data structures (such as 2-

dimensional images and ndimensional tables); FITS (Wells et al. 2001) reading and writing; utilities to parse C include (‘.h’) files and provide

access to the schema of the C data structures from TCL;

much of the processing is specified via input parameter files.

Photo pipeline

PSP The Point Spread Function (PSF)

Determining Bias Vectors, Scattered Light, and Flatfields.

Frames Removing the Instrumental Signature

Sky Subtraction and Object Detection

Photometry, Flux Measures

Object Classification (S/G)

Measurements of Objects Shapes

基于U波段（SCUSS）数据的星系研究

U-band as star formation tracer U-band vs UV、Hα、FIR

Sample: GOODS、COSMOS、SWIRE...

Bared galaxies in U band Star formation enhanced by bars

The misalign of different materials in bars

Bar vs AGN/BH

Low Surface Brightness galaxy

…

谢谢！