Emission Line Galaxy Targeting for BigBOSS

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

2. 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

3. 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

4. COSMOS Mock Catalog Ilbert (2008) Ilbert (2008) • 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

5. [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 10-3 -10-4 (Mpc/h)-3 range

6. Target Selection Bands Adelberger (2004) • 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.

7. z=1.0 z=1.5 grz Selection Adelberger (2004) • 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 Reddening

8. ugr Selection 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 Reddening Redshift Reddyr (2006)

9. Survey Photometric Errors • Looked at the following surveys with available sensitivities, sky brightnesses, and median seeing: • PanStarrs (griz, PS1=360s, 30k deg2) • Palomar Transient Factory (gr, 3 hr, 12k deg2) • Theoretical CFHT survey (u, 400s, 14k deg2) • 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

10. Low redshift grz selection • 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 Note: PTF errors used here are larger than those quoted by Peter yesterday

11. r magnitude limit for grz cut • For a redshift distribution ~103 galaxies/deg2, we should expect a magnitude limit of ~23.5 and F[OII]~1E-16

12. grz-selectedRedshift Distribution

13. ugr Selection Bands • 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.deg2) from 0.8<z<2 • Overall selection of star-forming galaxies with F[OII]>5E-17 cgs is >90%

14. z=1.0 z=1.5 Life on the Blue Corner • 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)

15. ugr vs. grz blue corner ugr grz • 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

16. 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