photometric catalog i-band selected photometric catalog containing ~800,000 galaxies (i (ab) < 26...

Photometric CatalogI-band selected photometric catalog

containing ~800,000 galaxies

(I (AB) < 26 mag)

in 8 bands (UBVgRizK)

Star-Galaxy separation using magnitude-surface brightness diagram/Stellarity parameter

Astrometry accurate to < 0.05 arcsec

Photometry accurate to ~ 0.04 mag

Survey DepthAB (5 sigma)

U = 27.45

B = 27.75

V = 26.85

R = 26.85

I = 26.55

Z =25.45

Ks = 22.55

The photometric catalog has multi- aperture and ‘total’ magnitudes (and

their corresponding errors) in UBVgRizK bands.

This catalog is used to estimate photometric redshifts and spectral

types of galaxies

Future improvements

Do we need to incorporate ACS data into the ground-based catalog ?

Include the GALEX and radio data ?

We need to use the TFIT technique developed for GOODS

include morphologies into the catalog? GALFIT, A C G ?

Do we need U and K-band selected catalogs ?

Photometric Redshifts

1. Phot-z technique

2. Comparison between different phot-z codes

3. COSMOS Phot-z measures

4. Accuracy of phot-z’s

5. Spectral types

6. Future improvements

COSMOS Phot-z Code

• six templates used• Luminosity function used as prior• Cosmic opacity from Madau et al.• Extinction allowed as a free parameter,

estimating E(B-V) for each galaxy• Interpolates the spectral types• Easily extended to other bands (ie IRAC,

GALEX etc)

Input: Galaxy magnitudes, magnitude errors, templates, filter response

functions

Output: z(phot), spectral types, redshift probability distribution,

conventional and prior-based redshifts, extinction

COSMOS phot-z’s: UBVgRizK bands, E, Sa, Sb, Sc, Im, Starburst

templates

Rest-frame absolute magnitudes

M(B)=m + K-correction -Distance modulus(z)

Luminosity functions are calculated using* 1/Vmax method* Maximum likelihood method

Traditionally (ideally): each galaxy has one redshift-> one absolute magnitude-> one galaxy added to magnitude bin in LF

Using phot-z's:Phot-z's have relatively large errorsEach galaxy is represented by a redshift distribution

How Best use the Phot-z’s

• Only use redshifts based on > 4 photometric bands• Use redshifts for I (AB) < 25 mag.• Detection in U and K-bands are important in

improving phot-z estimate• The present COSMOS data do not provide

accurate phot-z’s for z > 1.5• SEDs for objects with smaller range in their

confidence intervals are better constrained

Tests…

• Do the LFs and 3D corr. Functions agree with independent measurements

• Do the phot-z’s agree with BzK technique ?

• How well we could estimate redshifts for LBGs and LAEs ?

Conclusions

• Phot-z’s from the COSMOS code are more accurate than those from the BPZ

• using over 680 galaxies with multi-band photometric data and spectrsocopic redshifts are used to calibrate the technique

• We estimate phot-z’s to COSMOS galaxies to (z(phot)-z(spec)/(1+z(spec)) )=0.1

• Spectral types agree with independent measurements of the types of galaxies

Future Plans

• Need J-band observations to improve redshifts at z > 1.5

• Require MORE spectroscopic redshifts• Incorporate local extinction • Check AGN templates- does it improve the phot-

z’s ?• Measure phot-z’s for all the one million galaxies• Estimate galaxy masses