An improved method of determining photometric

redshift of “blended” galaxies

Ashley Marie ParkerMentor: Deborah Bard

What is redshift?• Redshift is an increase in the wavelength of light coming

from an object due to its motion away from Earth.

Absorption lines

• 393 & 397 nm from Ca II [ionized calcium]• 410, 434, 486 & 656 nm from H I [atomic hydrogen]• 518 nm from Mg I [neutral magnesium]• 589 nm from Na I [neutral sodium]

Standard methods for determining redshift

• Spectroscopic - view spectrum, measure shift in absorption lines– Developed in 1970’s – Is very time consuming to determine

• Photometric – more of an estimate– Developed in 1960’s– Uses u g r i z filters– large amounts of data

Why are more accurate photometric redshift measurements necessary?

• Application– Evolution of Universe– Gravitational lensing– Various others…

What is a “blended” galaxy?

Where did data come from?

• No distinction between “blended” and Not when SDSS photometric redshift is calculated

Data acquisition and format

• CasJobs for SDSS• Converting data type

TMVA

 regression analysis 

•Regression target•Variables•Spectator variables•Training and testing

•Various methods•PDERS•PDERSkNN•KNN•LD•FDA_GA•FDA_MC•FDA_MT•FDA_GAMT•MLP•SVM•BDT•BDTG

Spectroscopic vs. Photometric

Redshifts from training methods Not “Blended”

Redshifts from training methods “Blended”

RMS of methods

Best methods “Blended”

Best Methods Not “Blended”

Results

• Expecting to improve “blended”• Actually improved not “blended”• More accurate Photometric redshift willlead to increased precision in many scientific measurements• KNN is method with lowest RMS for “Blended” galaxies• MLP is the method with lowest RMS for NOT “Blended”

galaxies

Acknowledgements• Dr. Deborah Bard• SULI/DOE • SLAC/Stanford

• http://sqlpl.com • http://sdss.org • http://www.physorg.com• http://tmva.sourceforge.net/• http://www.astro.ucla.edu• http://ned.ipac.caltech.edu • http://arxiv.org/pdf/astro-ph/0106476v2• www.astro.princeton.edu/~rhl/photomisc/deblender.ps.gz• http://root.cern.ch • http://arxiv.org/PS_cache/astro-ph/pdf/0605/0605303v2.pdf

Errors for Not “Blended”

Errors for “Blended”

Differences Not “Blended”

Differences “Blended”

MLP feed-forward network according to the following propagation schema:

BDT