Photometric redshifts in the SWIRE Survey - the need for infrared bands

1. Photometric redshifts in the SWIRE Survey - the need for infrared bands Michael Rowan-Robinson Imperial College London UCL, Sept 16th 2008

2. IMPz photometric redshift ‘code’ • designed to exploit Spitzer IRAC (3.6-160 mm) data, in addition to broad-band optical (Rowan-Robinson et al 2003,2004, 2008, Babbedge et al 2004) • template fitting method, with priors: first create colour table as function of z • two passes through data, separate template fits to starlight in optical/near ir and to dust emission in infrared, extinction AV as optional free parameter • Pass 1: 6 galaxy, 3 QSO templates, fit zph, using 3.6 and 4.5 if lg10{S(3.6)/S(r)} < 0.5, then fit ir templates to bands with an excess relative to starlight model • Pass 2: 11 galaxy, 3 QSO templates, higher S(3.6)/S(r) limit for galaxies, 3.6 and 4.5 not used if Pass 1 indicated dominant AGN dust torus in the infrared • use priors on absolute magnitude range, AV • known spectroscopic redshifts used to estimate in-band correction factors (Ilbert et al 2006) • good performance for galaxies, use of infrared bands significantly reduced catastrophic outlier rate (not so good for QSOs) • problem is presence of AGN dust torus, which can affect wavelengths down to rest-frame 1 mm UCL, Sept 16th 2008

3. SWIRE (Spitzer Wide-Area IR Extragalactic Survey) • SWIRE: 49 sq deg in ELAIS-N1,-N2,-S1, Lockman, XMM-LSS, CDFS areas surveyed at 3.6,4.5,5.8,8.0,24,70 and 160 mm • Reliable catalogues released in Dec 05 • Final catalogues being prepared, photometric redshift catalogue released UCL, Sept 16th 2008

4. optical templates for photometric redshifts t optical templates (Babbedge et al 2004, RR et al 2008) original templates were empirically modified from Yoshii and Takahari (1988) these were fitted with stellar synthesis models supplied by Stefano Berta these are convolved with filter set to create colour table AGN1 AGN2 UCL, Sept 16th 2008

5. Photometric redshifts SWIRE-VVDS sample (with VVDS team, PI LeFevre) VIRMOS-VLT Deep Survey spectra >1000 sources ~3% rms in (1+z) <2% outliers phot z method of RR 03, Babbedge et al 04, RR et al 05, some refinements 10 optical bands, 3.6, 4.5 mm ~ IRAC 3.6 and 4.5 mm big help in reducing outliers UCL, Sept 16th 2008

6. Photometric redshifts whole SWIRE catalogue, galaxies, 6 bands, r<23.5, S(3.6)>7.5 mJy UCL, Sept 16th 2008

7. Photometric redshifts for quasars whole SWIRE catalogue, at least 4 bands at least 6 bands UCL, Sept 16th 2008

8. redshift error as function of r-magnitude UCL, Sept 16th 2008

9. Photometric redshifts Percentage redshift error, (zph-zsp)/(1+zsp) v. zsp, v. I for VVDS Lockman, 4 optical bands, z from Keck/ Gemini (Smith et al 06) Lockman field red: gals, blue: QSOs UCL, Sept 16th 2008

10. Photometric redshifts gri ugri ugri 3.6,4.5 gri 3.6,4.5 UCL, Sept 16th 2008

11. rms and % outliers, as function of c2 threshold Histogram of c2 for SWIRE sources with 7 photometric bands rms as function of c2 threshold (dotted) % catastrophic outliers (>15% in 1+z) as function of c2 threshold (solid curves, upper: r<24, lower: r<21.5) UCL, Sept 16th 2008

12. rms and % outliers, as function of no. of bands UCL, Sept 16th 2008

13. Redshift distributions left: Suburu XDS, R<27.5 below: ELAIS-N1, r<23.5: for optically blank sources use 3.6-8 mm for phot-z >=3 bands from U-8mm UCL, Sept 16th 2008

14. AV distribution • filled circles: galaxies, crosses: quasars • definite improvement in c2 when use AV • histogram of AV in SWIRE catalogue is consistent with star-formation history UCL, Sept 16th 2008

15. Infrared templates estimation of sfr from 24 mu not very accurate, since galaxies have a range of mid-to-far ir seds (Rowan-Robinson 2001) UCL, Sept 16th 2008

16. modelling ir excess with dust emission templates SEDs of SWIRE galaxies and AGN • use optical and IRAC 3.6, 4.5 to fit optical SEDs and derive redshifts Sources with IR excess • where there is a mid-IR excess, fit infrared templates to the excess (Rowan-Robinson et al, 2005,AJ 129, 1183) UCL, Sept 16th 2008

17. SPITZER-IRS spectra of ELAIS sources • IRS spectra for 70 ELAIS-N1 and -N2 sources with S15> 1mJy validate the template fits • most are ULIRGs, with z =1-3 • Filled circles: optical, ISO, SWIRE ( and MAMBO) data • Solid curves: model seds • Red curve: calibrated IRS data (Hernan-Caballero et al 2006, Perez-Fournon et al, 2007, in prep) UCL, Sept 16th 2008

18. seds of submilllimetre galaxies SHADES SXDS Clements et al 2007 UCL, Sept 16th 2008

19. can use ir template fits to predict fluxes at longer wavelengths, for comparison with expected AKARI, PLANCK and HERSCHEL survey limits projections based on N1 Predicted fluxes at 160, 350 and 850 mm 850 mm 850 mm 160 mm 70 mm Babbedge et al. in prep. UCL, Sept 16th 2008

20. conclusions • over one million galaxies in SWIRE photometric redshift catalogue, includes stellar mass, star-formation rate, luminosities in infrared components (cirrus, M82 and A220 starburst, AGN dust torus), predicted far ir and submillimetre fluxes, full c2(z) • use of infrared bands reduces percentage of catastrophic outliers • need AV for optimal solution • SWIRE Photometric Redshift Catalogue is huge resource for high redshift galaxies: 10% have z > 2, 4% have z > 3 UCL, Sept 16th 2008