Matching SDSS and UKIDSS Photometry for ... - AstroGrid wiki
Matching SDSS and UKIDSS Photometry for ... - AstroGrid wiki
Matching SDSS and UKIDSS Photometry for ... - AstroGrid wiki
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<strong>Matching</strong> <strong>SDSS</strong> <strong>and</strong> <strong>UKIDSS</strong><br />
<strong>Photometry</strong> <strong>for</strong> Luminous Red<br />
Galaxies<br />
Tim Higgs<br />
ICG, Portsmouth<br />
6 th Jan 2011
LRGs<br />
<br />
<br />
<br />
Luminous Red Galaxies<br />
Most massive galaxies in the<br />
universe<br />
– Efficient tracers of large scale<br />
structure<br />
– Small sample of LRGs can<br />
measure most of the mass in<br />
galaxies<br />
Most massive LRGs <strong>for</strong>med in<br />
early universe<br />
– Downsizing<br />
– Interesting from galaxy evolution<br />
point of view<br />
6/1/2011 Creating Matched Aperture <strong>Photometry</strong> 2
Why Match<br />
<br />
Galaxy at redshift of 0.7 emits an r-b<strong>and</strong><br />
(0.6µm) photon<br />
– This gets redshifted to 0.6 x (1+0.7) = 1 micron<br />
• Observers frame Y b<strong>and</strong><br />
– Observed r b<strong>and</strong> is galaxy rest frame u b<strong>and</strong><br />
• Most of the light from old stars<br />
• Most of the flux redshifted into NIR<br />
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Surveys<br />
<br />
<br />
<strong>SDSS</strong> III BOSS<br />
– 10,000 deg 2<br />
– Redshifts of 1.5<br />
million LRGs out<br />
z=0.7<br />
<strong>UKIDSS</strong> LAS<br />
– 4000 deg 2<br />
– Millions sources in<br />
DR5+<br />
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Surveys II<br />
• Galaxy photometry<br />
– <strong>SDSS</strong><br />
• Modelmag<br />
• Petrosian<br />
• Fibermag<br />
– <strong>UKIDSS</strong><br />
• Petrosian<br />
• Sersic mag<br />
• Circular Apermags<br />
r-b<strong>and</strong> defined<br />
H-b<strong>and</strong> defined<br />
• 0.5”< r
GAMA Matched Catalogue<br />
• Ideal solution is full re-extraction<br />
• Hill et al 2010 did this <strong>for</strong> GAMA fields<br />
– R-b<strong>and</strong> defined Kron aperture photometry<br />
• “Correct” method, expensive though<br />
– Time<br />
– Computationally<br />
• 4 hours to create 20GB mosaic<br />
• “a few days” to create catalogue <strong>for</strong> each mosaic in<br />
dual image mode<br />
Hill et al MNRAS 2010 (Arxiv 1009.0615)<br />
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GAMA DR1<br />
Hill et al MNRAS 2010<br />
Arxiv 1009.0615<br />
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GAMA Matched Catalogue<br />
Hill et al<br />
MNRAS 2010<br />
Arxiv 1009.065<br />
6/1/2011 Creating Matched Aperture <strong>Photometry</strong> 8
Alternative Approach<br />
• Can we take a short cut <strong>for</strong> LRGs<br />
– Small observed sizes<br />
• Average radius ~6 arcsec<br />
– Low ellipticities<br />
• How much can we get from catalogues<br />
6/1/2011 Creating Matched Aperture <strong>Photometry</strong> 9
Method<br />
• Get <strong>SDSS</strong> photoprofile<br />
– Flux within annuli<br />
– Generate curve of growth<br />
<strong>for</strong> galaxy<br />
– truncate curve at chosen<br />
radius<br />
• <strong>UKIDSS</strong> Apermags<br />
– Radius from 0.5” to 12”<br />
– Choose one of these radii<br />
Can produce circular aperture<br />
photometry to same radius<br />
– Matched aperture<br />
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Data<br />
• Focus on GAMA fields<br />
– <strong>UKIDSS</strong> DR4+<br />
– <strong>SDSS</strong> DR7<br />
– GAMA DR1<br />
• ~300 common LRGs<br />
• 144 deg 2<br />
• Use as test area<br />
– Compare my photometry to GAMA<br />
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Results<br />
GAMA use kron apertures, leading to slight offset<br />
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Stellar Mass<br />
• How do we know if<br />
we are doing well<br />
– Use Stellar<br />
masses as<br />
metric<br />
– Compute these<br />
by fitting to M09<br />
LRG template<br />
– Can compare to<br />
known stellar<br />
masses<br />
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Stellar Masses<br />
• Compare to MPA JHU mass catalog<br />
– Well tested stellar masses <strong>for</strong> <strong>SDSS</strong> galaxies<br />
– Uses Fiber photometry <strong>for</strong> fits<br />
• Assume Stellar Mass proportional to flux<br />
– Scale masses<br />
– Compare derived masses to scaled MPA-JHU<br />
masses<br />
log mass_MPA_JHU scaled =log mass_MPA_JHU −0.4r fiber<br />
−r photo <br />
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Comparisons<br />
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Conclusions<br />
• LRGs important <strong>for</strong> Cosmology <strong>and</strong> Galaxy<br />
Evolution<br />
• Can create a simple matched aperture <strong>SDSS</strong>-<br />
<strong>UKIDSS</strong> catalogue<br />
• Early results looking good<br />
– Good <strong>SDSS</strong> colour agreement<br />
– GAMA colours close<br />
– Stellar masses are close<br />
• Improvements to come from degrading <strong>UKIDSS</strong><br />
profiles to the same PSF as <strong>SDSS</strong> galaxies<br />
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Thank you<br />
6/1/2011 Creating Matched Aperture <strong>Photometry</strong> 17