Star-Forming Galaxies and the IGM in the z=1.5-2.5 “Redshift Desert”

1. Star-Forming Galaxies and the IGM in the z=1.5-2.5 “Redshift Desert” C. Steidel, D. Erb, N. Reddy (Caltech) A. Shapley (Berkeley) M. Pettini (IoA, Cambridge) K. Adelberger (OCIW)

2. Overview • The “redshift desert” is largely a myth. The redshift range z~1.4-2.5 is actually quite easily observed and moreover there is (in principle) more information accessible on these objects than almost any other redshift • Summary of some new results (mostly) from observed UV/optical and near-IR observations . • Galaxies and the IGM at z~2: initial results • Upshot: this is a very important epoch for the assembly and maturity of the massive galaxies of the present epoch

3. Why z~2 is interesting…. • The peak of the QSO epoch, and (probably) of star formation in galaxies • Allows for simultaneous study of diffuse IGM in the same cosmic volumes [z~2.5 QSOs are much more common than z~3.5 QSOs]; galaxy surface density within spectroscopic limit is much higher than at z>3 • Large numbers of galaxies are bright enough for detailed spectroscopic study with 8m-class telescopes • Access to diagnostic spectroscopy in both the rest-frame far-UV and the rest-frame optical; well placed nebular lines in atmospheric windows!

4. The “Redshift Desert” DEEP2 LBGs “Team Keck” in GOODS-N

5. Why the “redshift desert”? • Familiar spectral features ([OII] 3727; 4000 Å break) used for redshift measurement at low redshift shift out of optical band for z>1.4. • Near-IR multi-object spectrographs planned or just coming on line • Sky is increasingly problematic in near-IR • Difficult photometric selection because of absence of broad-band spectral features in optical window • Wide-field near-IR to adequate depth extremely expensive • Most 8m-class optical spectrographs are optimized at visual and red wavelengths • Common mis-conception: that emission lines are necessary to measure redshifts without heroic effort (Ly alpha, rest-optical nebular lines)

6. Far-UV Spectra of LBGs (z~3) Shapley et al 2003

7. LBG Analogs at lower redshifts Pushing into the “Spectroscopic Desert” using optical (far-UV) color selection (poor man’s photo-z) Adelberger et al 2004

8. Optical Photometric Pre-Selection Green/yellow (LBGs): z=2.960.26 Cyan(“BX”): Z=2.200.32 Magenta (“BM”): Z=1.700.34 Total surface density is ~9 arcmin-2 to R=25.5

9. Why z~1.5-2.5 is now easy… • Sky is very dark (AB=22.5-23/arcsec2) • LRIS-B is very efficient right where it counts: 3100-4500 Å • Galaxies have lots of spectral features– mostly absorption lines Z=1.41, 90 min

10. “Redshift Desert” Survey Statistics • 7 fields, total ~0.5 sq. degrees • 5 are specially chosen to have several z~>2.5 QSOs for the purposes of probing the IGM through the same volume (primary program is galaxy/IGM cross-correlation): Q1307+28, Q1623+27, Q1700+64, Q2343+12, Q2346+00 • 2 are fields chosen to have extensive existing or planned multi-wavelength data (GOODS-N, Groth/Westphal field) • To date: total of 900 spectroscopic redshifts, z=1.4-2.6 • Two primary selection criteria, targeting: • Z=2.0-2.5 (“BX” ) 750 redshifts • Z=1.5-2.0 (“BM”) 150 redshifts [primarily in non-QSO fields] • Contamination by low-z interlopers and stars is ~8% to R=25.5

11. Spectroscopy of Star-Forming Galaxies in the ``Redshift Desert’’ • z=1.5-2.5 galaxies: • Surface density to R=25.5 (K~22.5) is ~9.5/arcmin2 • ~25% of the R-band surface density to R=25.5 750 950 150 CS et al 2004

12. All spectra 90 min, Keck/LRIS-B CS et al 2004

13. Another Method for Exploring the “Desert”:Spectroscopic Failures from the DEEP Survey, observed with LRIS-B, September 2003 z=1.657 z=1.958

14. DEEP Failure z-distribution [OII] outside of DEIMOS coverage (z>1.4) 18/25 gals [OII] falls within DEIMOS coverage(z<1.4) 7/25 gals, including 2 AGN <z>=1.62+/-0.42 LRIS-B z’s for 25/26 DF targets

15. Deep Near-IR Photometry from Palomar 5m/WIRC, 8.7’ x 8.7’ field of view, FWHM~0.6” 12 hours, reaches K~22.3 (KAB~24.2), 5 sigma ~85% of galaxies with spectroscopic z’s are detected in the K images (3 fields so far)

16. Near-IR Imaging of Spectroscopic z~2 Galaxies • ~10% have K<20 • (note these are not all red in R-K) • ~30% have K<20.6 (cf. Gemini Deep Deep Survey) • Distribution of K luminosities is not very different from z~3 sample

17. Near-IR Imaging of Spectroscopic z~2 Galaxies (283 gal) Optical/IR colors are significantly redder at z~2 than at z~3 (Galaxies with identical star formation histories would have identical R-K colors) (108 gal) more extensive star formation histories than z~3 analogs

18. Optical/IR Colors of z~2 Galaxies (283) (108) R=25.5 limit CS et al 2004; z~3 from Shapley et al 2001

19. Galaxy Kinematics at z~2 (Keck/NIRSPEC K- band Spectroscopy-May 2002) • 7 of 15 show extended H emission (w/shear) • Typical projected vc>150 km/sec • Minimum dynamical masses >5x1010 Msun in several cases • Intriguing differences compared to z~3 sample… Erb et al 2003

20. Ha kinematics: rotation curves? • Used ACS BViz images of GOODS-N field, in which we have 171 galaxies with z>1.4 • 10/13 galaxies targeted to have slit PA aligned with major axis. Only 2 show measurable shear. • Puzzling result: elongated galaxies have smaller velocity dispersions than randomly selected objects • (Erb et al. 2004) Galaxies at z=2.1-2.5

21. 2 GOODS-N w/measured shear Erb et al 2004

22. Ha kinematics: rotation curves? • Seeing has significant effect on measured tilt • In May 2002 seeing was 0.5”, and in May 2003 seeing was 0.9” • Reobserved Q1700-BX691 to test this effect • 1-d  is much more stable with respect to seeing Q1700-BX691, z=2.1895 May 2002 vc~220 km/s s~170 km/s May 2003 vc~120 km/s s~156 km/s Erb et al 2004

23. H-alpha Kinematics at z~2 • Z~2 galaxies have consistently larger 1-d velocity dispersions than z~3 sample • 50% of sample has sigma > 100 km/sec (cf. 1/30 @z~3) • H-alpha detections for ~80% of attempted targets in 1 hour with NIRSPEC • ~25-30% have rotation-like kinematics

24. 171 spec redshifts between z=1.4-2.6 • 4 BX/BMZ galaxies are also SCUBA sources, 3 have spectroscopic redshifts GOODS-N Results Z=2.098 Z=1.865 Z=1.989

25. 94 z=2-2.5 Galaxies in the GOODS-N Field

26. 50 GOODS-N Galaxies, z=1.5-2.0

27. X-Rays and Radio Emission from UV-selected Galaxies in CDF/GOODS-N Field • Stacking of 171 spectroscopically confirmed z=1.4-2.5 S.F. galaxies (excluding all direct detections, AGN) • 10 sigma detection <SFR(Xray)> = 42 Msun/yr • 5 sigma detection in radio<SFR(Radio)>=50Msun/yr • Corresponding <SFR(1500)> = 8.5 Msun/yr •  <A(1500)>= factor of 4.9, very similar to results at z~3, and to inference from UV colors Chandra Stack The average z~2 galaxy in this sample is a “LIRG”, w/Lbol~few x 1011 Reddy & CS 2004

28. Far-UV Spectroscopy of “Desert” Galaxies Blue: Starburst99 Solar Metallicity, Salpeter IMF 3250 4460 LRIS-B, June 2002

29. Far-UV Spectral Diagnostics: IMF constraints z=1.411 At z~1.4-2.5, spectra of the quality necessary for detailed modeling of the OB stellar population are accessible for much more than lensed galaxies Best fit model: Salpeter IMF, solar metallicity 0 CS et al 2004

30. Far-UV Spectral Diagnostics: Metallicity Constraints FeIII 1978 Index Q1307-BM1163 (z=1.410): Data: Black, LRIS-B Best fit model (blue):continuous star formation, Salpeter IMF, solar metallicity cB58 (z=2.72): Smoothed data (black) Best-fit model: continuous star formation, Salpeter IMF, 0.4 solar metallicity S. Rix, Pettini, CS, et al 2004

31. Rest UV + Rest Optical: What do you learn? H/[NII] ratio also implies [O/H]=0 (solar abundance) Keck/NIRSPEC UV stellar P-Cygni and photospheric absorption indicate solar abundances Keck/LRIS-B • SFR(H)=SFR(UV)=30 Msun/year • V(ISM)=270 km/sec with respect to both nebular lines and stellar photospheric lines

32. Direct Nebular Abundance Determination Z=1/25 Zsun • Use [OIII] 4363/(5007,4959) to get Te, [SII] to get ne • Problem: 4363 weak, even in local low-Z gals; high z star-forming gals are not very metal-poor--NO HOPE at high redshift • (figure from van Zee 2000)

33. Indirect: Bright Lines (R23) • High-Z branch: R23 decreases as Z increases • Low-Z branch: R23 decreases as Z decreases • Particularly ambiguous for near-solar abundances • Systematic differences from direct method • Practical issues for high-z galaxies (Kobulnicky et al. 1999)

34. [NII]/Ha ratios: z~2 metallicities • relationship between [NII]/Ha and O/H • after Denicolo et al 2002, but using only accurately determined values from literature • [NII]/H saturates at high metallicity • (Pettini & Pagel 2004) N2=log([NII] 6584/Ha) 12+log(O/H)=8.9+0.57xN2 s~0.18, factor of 2.5 in O/H

35. [NII]/Ha ratios: z~2 metallicities • at O/H greater than 0.25 solar O3N2 index is useful • N2 increases as O3 decreases, so very sensitive to O/H • Ratios are essentially reddening independent • (Pettini & Pagel 2004) O3N2=log([NII] 6584/Ha) 12+log(O/H)=8.73-0.32xO3N2 s~0.14

36. Metallicities in z~2 Galaxies: Keck/NIRSPEC results • solar to super-solar metallicities are not uncommon among z~2 star-forming galaxies • Initial indications are that choosing K-bright or R-K red objects is almost guaranteed to yield solar metallicities or greater… [NII]/H calibration from Denicolo et al 2002

37. Rest-frame Optical Selection • 90% of UV-selected “BX” objects have Ks>20 • Sample: 9 z=2.1-2.5 objects with Ks<20, 4 of which also have R-Ks>4 • Obtained NIRSPEC/Ha spectra • (Shapley et al. 2004) Q1623+268 field, 121 with spectroscopic z + K measurement

38. [NII]/Ha ratios: z~2 metallicities • Selected 8 K<20 galaxies (z=2.1-2.5) from among 12 with spectroscopic redshifts in a single (8’) field. • All have abundances consistent with solar; half may have super-solar abundances. • Population synthesis indicates stellar masses greater than 1011 Msun • All are best-fit by ages >1Gyr (most >2Gyr) despite current star formation rates of ~50-100 Msun Shapley et al 2004

39. Other redshift desert surveys • Some other surveys with galaxies at z~1.5-2.5 • K20 (Cimatti et al.) (K<20 selection)(~10) • Gemini Deep Deep (Abraham et al.) (K<20.6, photo-z)(34) • FIRES (Franx, van Dokkum et al.) (J-K selection) (4) • Radio-detected SCUBA sources (Chapman et al.)(~50) • Reminder: K band is rest frame R @ z~2. Can easily be dominated by current star formation and not formed stellar mass

40. Optical vs. Near-IR Selection in the Desert: What’s the difference? • Number for comparison are small, but: • Of 9 z>1.7 K<20 galaxies in K20 survey (Daddi et al 2003), at least 6 would have been selected by UV BX/BM color criteria • One of our fields (SSA22) is in common with GDDS; of 7 galaxies with z>1.6 (3 with spectr. Z and 4/photz), 6/7 satisfy BX/BM selection criteria. • Space density of UV-selected objects w/K<20 is very similar to that of K-selected objects in the same redshift range. • Most massive galaxies at z~2 are still forming stars • This might not be true at z=1.3, which is ~2 Gyr later Shapley et al 2004

41. Other Interesting Points about z~2 IR-bright galaxies • Change in R-K colors from z~3 to z~2.2, together with change in kinematics, suggests more than doubling of stellar mass of objects with the same range of star formation rates, on average, over that interval. • Inferred star formation ages indicate long star formation histories for massive z~2 galaxies, consistent with their being galaxies which would have been easily observable at z~3.

42. Using optical (rest-UV) and near-IR (rest optical) to quantify physical properties of z~2 galaxies • Optical spectra: • IMF • stellar photospheric abundances • ISM metallicity • ISM kinematics • Near-IR spectra: • Kinematics • Ionized gas metallicity • SFR estimate

43. Deep in the Desert: 10-20 hr Spectra w/LRIS-B (4-5 A resol’n)

44. Probing The Intergalactic Medium Using Quasar Absorption Lines Quasar Keck/HIRES Quasar Spectrum * H I C IV Observer

45. Galaxies and the IGM • Idea is to: • Observe the relative distribution of young galaxies and the diffuse IGM—(e.g., do they trace the same matter fluctuations, with different degrees of “bias”?) • Place constraints on the evironmental influences of galaxy formation and the feedback of star formation and AGN . • Directly measure the large-scale effects of “feedback”

46. Galactic Scale Winds: Still Going Strong at z~2 • The kinematics of outflowing ISM gas is similar in z~3 and z~2 star-forming galaxies • Typical velocities are ~200-400 km/s with respect to nebular line redshifts, • Differences between Ly alpha emission and interstellar absorption is ~500-1000 km/s Z~2 Z~3

47. dense shell of swept-up material Vwind=500-600 km s-1 Isotropic? • Holes in ISM to allow escape of ionizing photons? • Blow-out of dust and gas • As for local “superwind” galaxies, mass loss rate in wind is comparable to SFR (5-1000 Msun yr-1 for bright LBGs) estimated from observations of the blue-shifted IS lines. • Metals into IGM/ICM if Vwind > Vesc • Expect gas heated to >> 106 K • Expect metal mass ejected at ~SFR/100 ~ Msun yr-1 • Expected “sphere of influence” is Rwind~150 kpc (tSF/300 Myr) x (Vwind/600 km s-1)

48. Mapping the Galaxy Distribution in the Same Volumes as Probed by the QSO Absorption Line Techniques Map "On the Sky" Along Our Line of Sight ~200 Mpc (co-moving) ~20 Mpc (co-moving) ~10 Mpc (co-moving)

49. Metals in the IGM and Galaxies at z~3 Even compressed into one dimension, galaxy over-densities are closely related to metal “over-densities”

50. Galaxies and Metals at z~3 Galaxy-Galaxy Clustering Galaxy-Metals Cross-Correlation Adelberger, CS, Shapley, Pettini 2003