photometric catalog i-band selected photometric catalog containing ~800,000 galaxies (i (ab) < 26...
Post on 22-Dec-2015
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![Page 1: Photometric Catalog I-band selected photometric catalog containing ~800,000 galaxies (I (AB) < 26 mag) in 8 bands (UBVgRizK) Star-Galaxy separation using](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d7f5503460f94a634e2/html5/thumbnails/1.jpg)
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
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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
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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
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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 ?
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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
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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)
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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
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Rest-frame absolute magnitudes
M(B)=m + K-correction -Distance modulus(z)
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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
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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
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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 ?
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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
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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