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

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Presentation on theme: "Star-Forming Galaxies and the IGM in the z= “Redshift Desert”"— Presentation transcript:

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~ 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: 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): Q , Q , Q , Q , Q 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= Two primary selection criteria, targeting: Z= (“BX” ) 750 redshifts Z= (“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= 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 12 hours, reaches K~22.3 (KAB~24.2), 5 sigma
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
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=

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. 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
GOODS-N Results 171 spec redshifts between z= 4 BX/BMZ galaxies are also SCUBA sources, 3 have spectroscopic redshifts 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=

27 The average z~2 galaxy in this sample is a “LIRG”, w/Lbol~few x 1011
X-Rays and Radio Emission from UV-selected Galaxies in CDF/GOODS-N Field Stacking of 171 spectroscopically confirmed z= 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~ , 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 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)= xN2 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)= xO3N2 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
Q field, 121 with spectroscopic z + K measurement 90% of UV-selected “BX” objects have Ks>20 Sample: 9 z= objects with Ks<20, 4 of which also have R-Ks>4 Obtained NIRSPEC/Ha spectra (Shapley et al. 2004)

38 [NII]/Ha ratios: z~2 metallicities
Selected 8 K<20 galaxies (z= ) 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 ~ Msun Shapley et al 2004

39 Other redshift desert surveys
Some other surveys with galaxies at z~ 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 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
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 ~ km/s with respect to nebular line redshifts, Differences between Ly alpha emission and interstellar absorption is ~ km/s Z~2 Z~3

47 dense shell of swept-up material
Vwind= 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 ( 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

51 Fraction of CIV systems that are within this distance of a LBG
Metals and Galaxies on Scales of 0.75 Mpc (co-moving), ±600 km/sec (the expected sphere of influence of winds from single LBGs) Fraction of CIV systems that are within this distance of a LBG Cross-correlation Adelberger, CS, Shapley, Pettini 2003

52 The “Galaxy Proximity Effect ”?
Galaxies “clear out” a region in the neutral H within ~700 kpc (co-moving)? There is an excess of HI absorption within ~6 Mpc of galaxies, on average Average flux in the Lyman alpha forest at z=3 Croft et al 2002 Adelberger, CS, Shapley, Pettini 2003

53 Metals in the Forest Metals, traced by CIV, are found in the same regions of space that contain detected LBGs Highest N(CIV) systems appear to be one and the same as LBGs (but with R ~150 kpc proper); extent consistent with expected sphere of influence of winds Even the weakest CIV systems are distributed like the observed LBGs Strongly suggests inhomogeneous enrichment of the IGM…and that most or all places that have observable metals have been recently “disturbed” at z~3

54 Other possible implications of winds from LBGs
ICM metals in clusters of galaxies: these are after all the progenitors of rich environments today… “Entropy floor” in galaxy clusters? Feedback regulates star formation, suppresses subsequent star formation while wind-affected regions cool (~1-2 Gyr) Suppress formation of small galaxies within ~200 kpc of large ones?. The existence of winds is not surprising—what may be surprising is their strength and the suggestion that relatively massive galaxies (as opposed to dwarfs) may dominate the effects on the IGM, and not all of the effects are confined to very high redshifts (z>>3).

55 Galaxies and the IGM at z~2
Much higher galaxy surface density (factor of 4 higher per unit solid angle) Further explore use of galaxy spectra to probe IGM Forest evolves extremely rapidly over the redshift range 3.51.8: how does the galaxy/forest relationship change? Many more QSO sightlines 17 lines of sight in 5 fields Simultaneously obtain first extensive information on z~2 galaxies. Epoch of peak star formation and black hole growth? Redshifts z= are ideal for near-IR spectroscopic follow-up

56 Multiple QSO Probes, z=1.8-2.5 IGM
Goal: IGM “Tomography”+Galaxy influence/correlations with IGM metals, HI Keck/LRIS-B 2002/3 255 Galaxy Spectra 7 QSO probes (HIRES/ESI/LRIS-B spectra) in 16’ by 12’ field

57 HIRES Spectrum of QSO: ∆v(CIV,NV)~570 km/s Weak associated Ly
∆(vneb-vism) = 460 km/s Dlos=115 kpc [O/H]~0 (i.e., solar metallicity) SFR~85 Msun/yr K~20.3, R~24 M*~6 x 1010 Msun

58 Other Examples: Individual Observations of Large-Scale Winds
Galaxy: Q1700-MD103 z=2.3148 D=115 kpc QSO spectra from Simcoe et al 2003 Galaxy: Q1700-BX717 Z=2.4353 D=218 kpc

59 Galaxy Proximity Effect at z~2?
Galaxies within 1h-1 co-moving Mpc of QSO sightline Adelberger et al 2004; sims by Kollmeier and Weinberg

60 A Special Case: The Pair at z=1.60/2.17
BX201 z=2.17 Keck/ LRIS spectra AA BM115 z=1.60 HST/WFPC2 F814W image Dq =2” 11 h-1 kpc at z=1.6 Two UV-selected z~2 galaxies on one slit Higher z galaxy probes outflow of lower-z gal at 11h-1 kpc Outflowing gas: velocity & abs strength difference vs. radius

61 Other (Undigested) Results
Far-UV Luminosity function, clustering in progress z~3 spectroscopic LBGs: r0=4.0±0.3 h-1 Mpc (Adelberger et al 2003). Spectral differences between z~3 and z~2: Lyman  emission becoming increasingly rare at the bright end of the L.F. Impact of star forming galaxies on the z~2 IGM, cross correlation of galaxies/metals/HI nearly ready. Deep multi-wavelength fields are not particularly useful for this sort of thing, which is a shame. AGN content of z~2 sample: fraction of objects with obvious AGN signatures is 3.2% (same as z~3). Includes two narrow lined AGN in CDF-N that are X-ray undetected.

62 Summary Galaxies at z= are easy to find and study; there is no redshift desert. There is a huge amount of accessible astrophysical information on these galaxies now, with much more to come in the next ~year from (e.g.) deep spectroscopy and from Spitzer. There are significant differences in the star forming galaxy population between z~3 and z~2, in the sense that there are many more “mature’’ galaxies by z~2 (that are still forming stars). Most massive galaxies at z~2 are still forming stars (?) But perhaps not for much longer… The IGM represents a laboratory for studying important aspects of the galaxy formation process that are otherwise inaccessible observationally.


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