Emission Line Galaxy Targeting for BigBOSS Nick Mostek Lawrence Berkeley National Lab BigBOSS Science Meeting Novemenber 19, 2009

Why Emission Line Galaxies? Strong emission line spectral features come from excited ISM gases, most commonly found in galaxies with ongoing star formation Lines fall at specific wavelengths which can be used for accurate redshift measurement Advantages: ELGs are numerous in the range of 1<z<2 as they do not require much hierarchical structure formation Bright, unique identifiers - ideal for measuring redshifts efficiently Evolution in the [OII] luminosity function is observed up to z=2 due to an increased SFR. (For a fixed volume density, the [OII] luminosity in distant ELGs is higher than rest-frame ELGs) Disadvantages: Accurate luminosity functions are difficult to measure beyond z>1.5 Single emission line detections can be ambiguous Must have sufficient spectroscopic resolution to achieve  z<0.001(1+z) AND efficiently detect the line over background noise

Target Selection Parameters Photometric depth required to target constant 3.4E-4 (h/Mpc) 3 number density Select brightest [OII] lines ELGs from 0.7<z<2 High completeness (>70%) for [OII] line flux Optical photometric selection 10-15k sq. deg targeting in the Northern Hemisphere within 3 years

COSMOS Mock Catalog Left panel shows template SEDs fit from 30 band photometry in the zCOSMOS survey field (Ilbert et al., 2008) Right panel shows the [OII] line fluxes from VVDS spectra and M(UV)-[OII] calibration LePhare photo-z code used to generate synthetic photometry in ugrizJHK bands Ilbert (2008)

[OII] Luminosity Function Zhu et al., 2008 Left figure shows the measured luminosity function of DEEP2 [OII]-emitting galaxies for 4 redshift bins. 14,000 [OII] emission line galaxies were used in this sample. Right figure shows the predicted redshift distribution for a fixed [OII] flux limit from DEEP2 and Ilbert/VVDS. Stage IV BAO experiments are considering densities in the (Mpc/h) -3 range

Strong [OII] emission comes from star forming, typically late type galaxies (Sb-Sd and Irregulars) Adelberger (2004) showed that such galaxies can be selected using optical bands from 1<z<3 These galaxies typically have relatively flat SEDs except for 2 regions: –Hydrogen Balmer absorption bands, rest frame ~4000 Å. –Ly  absorption, rest frame ~912 Å. Target Selection Bands Adelberger (2004)

grz Selection Reddening z=1.0 z=1.5 Figure at right shows grz color plane with F [OII] >5E-17 cgs for z>0.7 galaxies and a magnitude limit of r <23.5 mag Selection box is drawn around bulk of bright [OII] emitters at z<1.5 Adelberger (2004)

u-band can also provide a redshift color selection, although it works best for z>2 Synthetic photometry from Ilbert zCOSMOS code shows a selection box is drawn around F [OII] >5E-17 cgs for 1.5<z<2 galaxies and a magnitude limit of r <24 mag ugr Selection Adelberger (2004) Redshift Reddening Reddyr (2006)

Looked at the following surveys with available sensitivities, sky brightnesses, and median seeing: –PanStarrs (griz, PS1=360s, 30k deg 2 ) –Palomar Transient Factory (gr, 3 hr, 12k deg 2 ) –Theoretical CFHT survey (u, 400s, 14k deg 2 ) Errors are statistical. Only systematic considered is a floor on photometric error. Note: PTF errors used here are larger than those quoted by Peter yesterday Survey Photometric Errors

Figure at right shows grz color plane (PTF+PS1) with F [OII] >5E-17 cgs for 0.7<z<2 galaxies and a magnitude limit of r <23.5 mag Low redshift grz selection Note: PTF errors used here are larger than those quoted by Peter yesterday

r magnitude limit for grz cut r magnitude limit for grz cut For a redshift distribution ~10 3 galaxies/deg2, we should expect a magnitude limit of ~23.5 and F[OII]~1E-16

grz-selected Redshift Distribution

Used gr photometry from PTF and u-band from CFHT, mag limit of r<24 Marginal u-band data scatters lower redshift objects into selection box…could ugr alone be sufficient? Selection delivers a mean of 2400 N/(dz.deg 2 ) from 0.8<z<2 Overall selection of star-forming galaxies with F [OII] >5E-17 cgs is >90% ugr Selection Bands

Strong OII line emission and high redshift sample (z>1.5) can be found in the “blue corner” of the grz color plane Plot on right shows COSMOS objects with magnitude errors from PS1 (grz) Life on the Blue Corner z=1.0 z=1.5

ugr vs. grz blue corner ugr vs. grz blue corner ugrgrz r<24 for both color cuts, no additional color information used for lower redshifts ugr averages 90% in selection efficiency of bright [OII] for z>1.5, grz averages 85% For all practical purposes, the cuts are very similar with grz being more effective at weeding out lower redshifts but producing more targets beyond z>2

Summary Proof of Concept Target Selection ugr produces a ~flat redshift distribution from 1<z<2 at r<24, minimal number density grz produces a higher density redshift distribution from 0.7<z<1.5 at r<23.5 with a shot at extending to higher redshifts Limiting [OII] line flux ~1E-16 cgs flux Much to do: Alternative color selections Photometric surveys and real errors (PTF, PAN-STARRS) Observational tests of selection criteria Color selection optimization