Target Selection for DESpec Filipe Abdalla, Stephanie Jouvel, With input from many from the DESpec target selection team.
Jan 14, 2016
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.
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.
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
LRG target selection
Strawman LRG target selection from Jim...
- 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
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)
Redshift distribution / em lines gal
Redshift distribution / em lines gal
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
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
Multidimensional method based on NN selection
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
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
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
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
Redshift distribution of ANNz sel 0.8Using sensitivities cut between 0.6-1um
Redshift distribution / em lines gal
Target selection
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.
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.