target selection for despec
DESCRIPTION
Target Selection for DESpec. Filipe Abdalla, Stephanie Jouvel, With input from many from the DESpec target selection team. A DESspec target selection?. 1)100% spectroscopic completeness of DES galaxies to r=21stmagnitude with resolution 50 km/s. - PowerPoint PPT PresentationTRANSCRIPT
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Target Selection for DESpec
Filipe Abdalla, Stephanie Jouvel, With input from many from the DESpec target selection team.
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A DESspec target selection?
1)100% spectroscopic completeness of DES galaxies to r=21stmagnitude with resolution 50 km/s.
2)Case 1 plus 50% completeness to r=22.5 magnitude evenly distributed over all redshift bins
3)~300 km/s redshift precision with 100% completeness to r=22ndmagnitude
Q: on what parameters give the most improvement on FoM and advice as to what new techniques are opened up.
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Largest FOM’s are always with a constant number density.
1- Constant density 0.2<z<1.7, 10^7galaxies
2- Constant density 0.2<z<0.5, plus I<22.5 for 0.5<z<1.7 @65% eff’y. Total 10^7galaxies. Note redshiftcut-off (right)
3- Constant density 0.2<z<0.7, plus emission line galaxies for 0.7<z<1.7. Total 10^7galaxies.
Is FOM the best way to asses these
Large difference between different target selection techniques.
Best is to reach a magic number of n=~2.10^-4Mpc^-2
This magic number ranges from a few hundred to a few thousand galaxies per sqdeg depending on z range
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LRG target selection
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Strawman LRG target selection from Jim...
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- Sensitivities for 30 mins exposure time on 2 arcsec ø fibers (70% light fraction)- Resolution R=2500 at 0.9um.- Calculation include DES throughput + sky noise and atmospheric lines from Hanuschik (2003)
Line sensitivities from Huan Lin
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Line sensitivities from Huan Lin 0.6-1um
- Sensitivities for 30 mins exposure time on 2 arcsec ø fibers (70% light fraction)- Resolution R=2500 at 0.9um.- Calculation include DES throughput + sky noise and atmospheric lines from Hanuschik (2003)
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Redshift distribution / em lines gal
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Redshift distribution / em lines gal
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Redshift distribution from em linesRedshift distribution of emission line galaxies selected with :- I (DES) < 23- 1 < photoz < 2- at least one em line detected at 5 sigma
Photoz with Le Phare (template fitting method) u DES+VISTA
Can we select the emission line galaxies based on DES+VISTA photometry only ?
Total of roughly1200 gal/deg2
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Can we do color-color cut ?g-r vs r-i r-i vs i-z
It looks difficult to select the OII line in a color-color cut. We need a higher dimensional kind of cut such as photoz codes can provide
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Multidimensional method based on NN selection
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Photo-z’s, target selection and Neural networks:
Has an architecture: defined by a number of inputs/ outputs and nodes in hidden layers
Collister & Lahav 2004
http://www.star.ucl.ac.uk/~lahav/annz.html
Internally values range from 0 to 1 roughly
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Use of NN to select em line galaxies
We assign a value of :- 1 for targetted em line galaxies- 0 for non targetted galaxies
We then use ANNz and train a NN on a sample of 10000 galaxies from the CMC (DES+VISTA)
Results for i(DES) < 24
Using Huan Lin sensitivities cut between 0.6-1um
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Which ANNz selection criterion ?
Fig : Cumulated nbr galaxies/deg2 fct ANNz target probability
We suggest a selection criterion of 0.8 yielding to : -7500 emission line galaxies / deg2 i(DES)<24- and a contamination of 800 gal/deg2 i(DES)<24
0.8Using sensitivities cut between 0.6-1um
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Which ANNz selection criterion ?
Solid : percentage of galaxies for which we will measure a redshift/total nbr gal & Dashed : SSR fct ANNz target probability
We suggest a selection criterion of 0.8 yielding to : -7500 emission line galaxies / deg2 i(DES)<24- and a contamination of 800 gal/deg2 i(DES)<24
Using sensitivities cut between 0.6-1um
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Redshift distribution of ANNz sel 0.8Using sensitivities cut between 0.6-1um
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Redshift distribution / em lines gal
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Target selection
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Target selection in wordsOut of the high redsfhit EL
galaxies, use the photo-z to obtain a nP=1 survey out to z=1.7 use photo-z from DES to “shape that distribution” ~1000 sq deg?
Obtain a high nP sample at low z as it overlaps the lensing kernel. ~1500 sq deg?
Some could be EL galaxies to have low bias for RSDs ~750 deg sq? Can be Ha or OIII lines
Some could be LRG’s & RG’s ~ 750 deg sq? so that we probe down the luminosity function of groups and relate lenses and lensing galaxies.
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ConclusionWe simulated a DES+VISTA catalogue using the CMC
which include emission line fluxes.Used derived a fiber sensitivities including all instruments
troughput and sky noise including astmospheric lines for a DESpec instrument (Huan Lin).
Using these sensitivities we can select emission line galaxies from DES+VISTA photometry using ANNz. They are complementary to the LRG selection.
We suggest a selection criterion of 0.8 with a yield of 8000gal/deg2 for i(DES)<24 and a success rate of 93% or 5000gal/deg2 i(DES)<23 and a success rate of 95% ~ 1000 of which at z>1.
To do this would need a pilot survey to identify the successful galaxies or trust the mocks.
A color-color cut does not seem the optimal solution to select target for DESpec.