Star-formation, Chemical Enrichment, and Feedback at z~2-3

Star-formation, Chemical Enrichment, and Feedback at z~2-3Alice Shapley (Princeton)Collaborators: Chuck Steidel, Max Pettini, Dawn Erb, Naveen Reddy, Kurt Adelberger

Overview and Motivation UV-color-selected galaxies at z~1.5-3.0 (9-11 Gyr) Lots of progress in understanding their global and detailed properties, their effects on the IGM New results: The origin of the ionizing background at z~3, direct spectroscopic measurement of ionizing radiation from galaxies at z~3, constraints on fesc, Jn , G Robust measurement of mass-metallicity relation at z~2. Plus: new info on physical conditions in star-forming regions at z~2, implications for inferred chemical abundances, nature of star-formation

z>2 color-selection Adjust z~3 UGR crit. for z~2 (Adelberger et al. 2004) Spectroscopic follow-up with optimized UV-sensitive setup (Keck I/LRIS-B) (Steidel et al. 2004)

Redshift DistributionsUnsmoothed

LBG: z~3 (940) SLBG=1.7/arcmin2 nLBG=1.4x10-3Mpc-3 BX: z=2-2.5 (816) SBX=5.2/arcmin2 nBX=2.0x10-3 Mpc-3BM: z=1.5-2.0 (118) SBM=3.8/arcmin2 nBM=1.7x10-3Mpc-3750 gals at z=1.4-2.5(Steidel et al. 2004; Adelberger et al. 2004)BX/BM/LBG with R

Contribution of LBGs to the Ionizing Background at z~3

Origin of the Ionizing Background Major question: how did the universe transform from having a neutral to highly ionized IGM? Many new observational results (SDSS QSOs, WMAP), plus theoretical work (i.e. predictions for future 21 cm telescopes) Nature of the ionizing background important for understanding reionization and inferring physical properties of Lya forest Measured with QSO proximity effect: current estimates J912~10-21erg/s/cm2/Hz/sr , G~10-12s-1 (Scott et al. 2000) Questions: What are relative contribution of QSOs & gals vs. z? (drop-off in QSO number density at high redshift) What is fesc for galaxies???

Definitions of fesc What is fesc? fesc= Llyc,out/Llyc,in= exp(-tISM,lyc) What is fesc,rel and why?fesc,rel= fesc x (LUV,out/LUV,in)-1 = fesc x exp(tISM,UV) Useful for deriving global quantities, such as J912,gal, based on LBG UV luminosity function fesc,rel can be re-written:fesc,rel= (LUV/Llyc)in/(FUV/Flyc)obs x exp(tIGM,lyc)Stellar pop. models:1.5-5.5We measure thisSimulations of z~3 IGM opacity in Lyc range

Search for Lyman-Continuum EmissionLyman-Continuum Observations of Galaxies z~0: HUT spectra at z~0, fesc

Detection of Ly-C Emission?Lyman Cont. Leakage 29 gals at =3.4+/-0.09 Significant Ly-cont flux in composite spectrum 5 times more ionizing flux than QSOs at z~3 Bluest quartile in (G-R)0, strong Lya emission, IS abs lines weaker than cB58: is it representative? fesc different from local SB (Leitherer et al. 1995)(Steidel et al. 2001)

Search for Lyman-Continuum EmissionLyman-Continuum Observations of Galaxies z~0: HUT spectra at z~0, fesc

New Ly-C Observations Deep Keck/LRIS spectra for a sample of 14 objects Red side: detailed obs of interstellar lines (17 hr, 2x resolution) Blue side: sensitive observations of Lyman Continuum region (22 hr, 8 hr with New Blue Camera, 1.3x resolution) Observations approach the quality of cB58, but larger sample Deep Sample (bright LBGs): =3.06, =23.92, =0.11, WLya=2 (em/abs) Steidel et al. Ly-cont sample:=3.40, =24.33, =0.07, WLya=15 Composite Sample of Shapley et al. (811 galaxies w/ spectra):=2.96, =24.60, =0.13, WLya=15

Examples of Deep LBG Spectra LRIS-R spectra (LRIS-B covers Lya and Lyman continuum), 1-1.5 res. Use these spectra to measure physical properties of abs. lines; connect with UV-color, Lya, Lyman continuum

New Ly-C ObservationsMain observational results: Ionizing flux is detected for 2 out of 14 objects. Why? F900/F1500 (i.e. Flyc/FUV) quite large for these two galaxies --> significant galaxy-to-galaxy variation in fesc? Ratio of F900/F1500 in average spectrum is four times lower than that in Steidel et al. (2001)

Detections: 2D SpectraLyman limit, 912 AA 3950 AA 3350 AAD3, z=3.07 Rs=23.37C49, z=3.15 Rs=23.85

Detections: 1D Spectra D3, double, z=3.07, Rs=23.37 F1500/F900=5.1 (7.1 if you add F1500 from both components), 15% uncertaintyYet, IS lines are black! Reddest galaxy in sample IGM correction x3 (starts to strain stellar pop. models)Steidel et al. (2001) found =17.7, then corrected by factor of 3.8 for IGM opacity.

Detections: SSA22a-D3HST/NIC F160WD3 (z=3.07, Rs=23.37) is double, and upper brighter component appears to have significant flux below 912 Lots of additional info: near-IR imaging &spectra, HST, Lya blob

Detections: SSA22a-D3P200 Rs HST/NICMOS F160W

Detections: 1D Spectra C49, z=3.15, Rs=23.85 F1500/F900=12.7, 15% uncertainty One of the bluest galaxies in the sample, with weakest IS lines (non-unity covering fraction), but others with even less, and no Lyman Cont. emission IGM correction x3Steidel et al. (2001) found =17.7, then corrected by factor of 3.8 for IGM opacity.

Detections: 1D Spectra D3 has very young inferred age (

Non-Detections: 1D SpectraC32, z=3.29, Rs=23.68Weak IS lines (covering fraction smaller than in C49)C35, z=3.10, Rs=24.18

The Average SpectrumStack 15 deep spectra, normalized by F1500WLya=2 (plus abs), WIS=2.2 absF1500/F900=65 (25% uncertainty), four times larger than S01Systematics of sky subtraction VERY IMPORTANT, comparable to avg detectionRMS 2.5 times lower than S01 (red curve)

The Average SpectrumBenefits of Averaging. Recover information bluewards of Lya, such as Lyman series (independent estimate of typical N(HI) )Possibly molecular HOther metal lines

Implications S01 measured =17.7, and applied a factor of 3.8 correction for z=3.4 IGM opacity -->F1500/F900,corr=4.6 We now measure =65.5, and z=3 IGM correction factor is more like ~3 --> F1500/F900=22. So, we measure fesc,rel that is 4-5 times lower (~10%). If F1500/F900 is representative (which we still need to establish), we can use it to convert LBG 1500 AA luminosity density into 912 AA luminosity function, and then from e(912) to J912 (and then to G)If we scale S01 results for J912, we get 3x10-22 erg/s/cm2/Hz/sr, and G~8x10-13 s-1, which is more consistent with recent estimates (Bolton et al. 2005) of G(z=3) based on Lya forest optical depth

The Future Understand ISM/outflow properties of sample (based on red-side data of interstellar absorption lines), try to connect to emergent Lyman continuum radiation Understand spectroscopic sky-subtraction systematics Compare with AGN contribution -- new value of J912 is comparable to that from QSOs (Hunt et al. 2004), but depends on fesc in faint QSOs While we have a larger sample of deep z~3 spectra now, we are also trying to detect Lyman continuum in an independent manner: NB imaging just below the Lyman Limit (Inoue et al. 2005) Special opportunity because of large structure of galaxies at z=3.09, unparalleled U-band sensitivity of LRIS-B

Metallicities & Gas Fractions

Other redshift desert surveysOther surveys with galaxies at z~1.4-2.5 K20/BzK (Cimatti et al.) (K

Evolution of Galaxy Metallicities Gas phase oxygen abundance in star-forming galaxies Fundamental metric of galaxy formation process, reflects gas reprocessed by stars, metals returned to the ISM by SNe explosions (HII regions in sf-galaxies, stars in early-type). Galaxies display universal correlations between Luminosity (L), Stellar mass (M), and metallicity (Z) Departures from closed-box expectations can reveal evidence for outflow/inflow Closed box: Z = y x ln (1/m)(Z=metallicity, y=yield, m=gas fraction=Mgas/(Mgas+M*))

Evolution of Galaxy Metallicities 10,000s of galaxies in the local universe with O/H Now the challenge is to obtain these measurements at high redshift (evolution will give clues, compare metal census with inferred metal density from integrating the global star-formation history) Measuring gas fractions is very important to quantify how much material has been processed into stars -- currently very indirectPhysical conditions may be different in high-redshift HII regions: implications for inferred metallicities!!!

Abundance Measurements vs. z(Tremonti et al. 2004) Lots of local emission line measurements (10000s, 2dF, Sloan) At z=0.5-1, 4 groups (>=200 gals, CFRS, DGSS, CADIS, TKRS) At z>2 there were < 10 measurements (mainly LBGs) DLAs provide metallicity information from abs lines, but hard to relate

Near-IR spectroscopy of z~2 gals z~2 ideal for measuring several neb lines in JHK evidence of M-Z relation at z~2, intriguing information about HII region physics

[NII]/Ha ratios: z~2 metallicities relationship between [NII]/Ha and O/H N is mixture of primary and secondary origin age, ionization, N/O effects, integ. spectra, DIG, AGN(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

Near-IR spectroscopy of z~2 gals Ha spectra of 101 z~2 gals KeckII/NIRSPEC Kinematics: linewidths, Mdyn, some spatially-resolved, tilted lines, compare with stellar masses Line ratios: HII region metallicities, physical conditions Ha fluxes: SFRs, compare with UV, models Offsets between nebular, UV abs and Lya em redshifts -> outflowsM*=41011 MK=19.3, J-K=2.3M*=5109 M

Local M-Z Relationship(Tremonti et al. 2004) M-Z possibly more fundamental than L-Z relationship closed box model relates gas fraction and metallicity, according to the yield SDSS sample revealed lower effective yield in lower mass galaxies importance of feedback

Local M-Z Relationship(Tremonti et al. 2004) We have metallicity information for a large sample of (~100) galaxies at z~2 For the majority of these, we have used broadband optical and IR photometry to estimate stellar masses (see next slides) Therefore we can construct a z~2 M-Z relationship

Opt/NIR SED: Age/Dust Degeneracy Only optical photometry cant distinguish between age/dust Balmer break is sensitive to A/O stars ageK-band probes other side of Balmer break More discriminating power, IRAC gives you even more (???)(Shapley et al. 2001, Papovich et al. 2001)

Stellar Populations & Masses Near/Mid-IR Imaging

Deep J, K imaging with WIRC, Palomar 5-m, to Ks~22.5, J~23.8 4 fields, ~420 galaxies with zsp> 1.4 Spitzer IRAC data in Q1700 field, 3.6, 4.5, 5.4, 8 m Combine optical and IR SED to model stellar populations, massesKs (2.15 mm)(Barmby et al. 2004, Steidel et al. 2005)

Stellar Populations & Masses Near/Mid-IR Imaging

Deep J, K imaging with WIRC, Palomar 5-m, to Ks~22.5, J~23.8 4 fields, ~420 galaxies with zsp> 1.4 Spitzer IRAC data in Q1700 field, 3.6, 4.5, 5.4, 8 m Combine optical and IR SED to model stellar populations, massesIRAC (4.5 mm)(Barmby et al. 2004, Steidel et al. 2005)

z~2 M-Z Relationship(Erb et al. 2005) New sample of 87 star-forming galaxies at z~2 with both M* and [NII[/Ha (gas phase O/H) measurements Divide into 6 bins in M* , which increases as you move down clear increase in [NII]/Ha with increasing M* M-Z at z~2!!

z~2 M-Z Relationship(Erb et al. 2005) Evol. Comparison with SDSS, where Z is based on [NII]/Ha (for both samples) Clear offset in relations --> at fixed stellar mass, z~2 galaxies significantly less metal rich than local gals Not evolutionary (z~2 probably red&dead by z~0)

z~2 M-Z Relationship(Erb et al. 2005) Important: measure change of Z with m (gas fraction) Must estimate Mgas, which we do from SHa, to Ssfr, to Sgas (assuming Schmidt law) Very indirect! Low stellar mass objects have much higher m

z~2 M-Z Relationship Different models for feedback, using different yields and different outflow rates Data are best fit by model with super-solar yield and outflow rate greater than SFR (for all masses) Rate of change of m with metallicity gives evidence for feedback ; m is very important (estimated indirectly)(Erb et al. 2005)

z~2 M-Z Relationship Increase of Z with decreasing m is shallower than expected for no outflow. Same thing goes for increase of Z with M* Important: SDSS sample showed evidence for preferential loss of metals from lower mass galaxies (would be steeper) While the range of baryonic masses in the z~2 sample is small, we see NO evidence for preferential metal loss for less massive galaxies Remember: outflows generic feature of UV-selected gals, metals in cluster gas(Erb et al. 2005)

HII Region Physical Conditions

z~2 Physical Conditions Well-defined sequence in [OIII]/Hb vs. [NII]/Ha in local galaxies (SDSS) (star-formation vs. AGN) small sample of z~2 star-forming galaxies with [OIII]/Hb are offset from this locus (as is DRG) ne, ionization parameter, ionizing spectrum (IMF, star-formation history) Implications for derived O/H(Erb et al. 2005)

z~1 Physical Conditions Well-defined sequence in [OIII]/Hb vs. [NII]/Ha in local galaxies (SDSS) (star-formation vs. AGN) z~1.4 star-forming galaxies are offset from this locus (as is DRG) ne, ionization parameter, ionizing spectrum (IMF, star-formation history) Implications for derived O/H(Shapley et al. 2005)

z~2 Physical Conditions Among K

Beyond [NII]/Ha: All the lines(van Dokkum et al. 2005)H NOHO Deriving Oxygen Abundance from [NII]/Ha relied on several assumptions Physical conditions appear different. Observations of full set of lines important for constraining sfr in high redshift objects GNIRS/Gemini

Summary Lots of new results from UV-selected surveys, including At z~3, we have detected leaking ionizing radiation from individual galaxies. Global contribution from LBGs may be lower than previous estimates. At z~2, using IR imaging (J,K, IRAC) and spectroscopy, we have measured a strong correlation between stellar mass and gas phase metallicity. This arises from increase in metallicity as gas fraction decreases, modulated by metal loss at all masses (high mass too!). Physical conditions may be different in high-redshift star-forming regions!

Q1700+64: Distribution of M* Mstar,med=2.0x1010 Msun Distributions with and without IRAC data very similar (uncertainties smaller with IRAC data) Stellar mass density of z~2 BX/MD galaxies is ~108MsunMpc-3 16% of z=0 stellar mass density (Cole et al. 2001) caveats: IMF, bursts relate to z~3, evolution (???? Weak constraints) Better constraints for most massive gals (8%)(Steidel et al. 2005) 6/72 have M*>1011M & contain 50% of the mass

Q1700+64 Field QSO field (V~16, zem=2.72), very sensitive obs. of IGM Optical, near-IR imaging and spectra Spitzer/IRAC photometry 3.6-8.0 mm (Barmby et al. 2004) BIG ???: HOW MUCH DOES SPITZER HELP US? 72 gals at z=1.4-2.9 (most are at z stellar populations, masses BC2003 exp(-t/t) and CSF models, Calzetti extinction Serendipity: Large redshift spike at z=2.299+/-0.015 (20 galaxies) --> study properties vs. environment

Q1700+64: Distribution Mstar,med=2.0x1010 Msun Distributions with and without IRAC data very similar (uncertainties smaller with IRAC data) Stellar mass density of z~2 BX/MD galaxies is ~108MsunMpc-3 16% of z=0 stellar mass density (Cole et al. 2001) caveats: IMF, bursts relate to z~3, evolution (???? Weak constraints) Better constraints for most massive gals (8%)(Steidel et al. 2005) 6/72 have M*>1011M & contain 50% of the mass

Q1700+64: M/L (optical, near-IR) At z~2, even mid-IR observations not direct tracers of stellar mass

Inferred stellar mass can differ by factor of ~10 at a given 4.5 m luminosity, ~70 at K-band(Steidel, Shapley et al. 2005)

Q1700+64: Weak Constraints6/72 have M*>1011M & contain 50% of the massLow-massMedianHigh-mass M/L related to relative amount of rest-UV to opt/IR For low-mass (young) and typical galaxies, very weak constraints on sf-histories, and therefore ages, E(B-V), sfr More robust constraints for most massive galaxies(Shapley et al. 2005)

Q1700+64: Six M*>1011Gals: UV-selection DOES find massive galaxies Most of sample, no constraints on t, but these must have t>=0.2 Gyr Best-fit implies t=2-3Gyr, already massive at z~3 z=2.2-2.4, n~2x10-4 /Mpc3, Descendants of z~3 SMG? LBG? Progenitors of old, red galaxies at =1.7 (Cimatti, McCarthy)?IRAC (4.5 mm)(Steidel et al. 2005)

Q1700+64: The z=2.3 Spike Only identified ~25% of galaxies in the field -> >80 galaxies in the spike Galaxy redshift overdensity, d=6 in spike is x2 larger than outside in spike is 1.4 Gyr, whereas it is 0.7 Gyr outside zform earlier in spike?

Q1700+64: Implications Typical stellar mass of z~2 UV-selected galaxy, 2x1010 M, z~2 sample contains ~16% of z=0 stellar mass density Weak constraints on SF-histories for most of population. Timescales are TOUGH. Masses are EASIER (assuming no past burst). Typical galaxies could be hiding upper limit 2-3 times stellar mass in old burst Clustering strength indicates that UV-selected z~2 gals are hosted by the descendants of DM halos hosting z~3 LBGs (Adelberger et al. 2004) Lack of constraints on timescales (and possible hidden mass from past bursts) makes it difficult to determine if z~2 galaxies are the direct descendants of LBGs, based on stellar populations. With CSF (longest timescale for given set of colors), >50% had not turned on by z=2.7 (end of LBG era) may imply shorter, episodic timescale for SF.

Q1700+64: Implications

UV-selection translates into a large range of inferred stellar masses and star-formation histories. High mass tail, 8% with M>1011 M, t~1-3 Gyr, n=2x10-4/Mpc3, cant hide much mass in such galaxies, already have the masses of large elliptical galaxies and are metal rich

Massive UV-selected galaxies are old, were already massive during z~3 LBG era, could have been SMGs, can become red-dead gals by z=1.7 (Cimatti, McCarthy) (right # density)

Proto-cluster enables study of galaxy properties vs. environment

z~3 LBG Metallicities: R23 Measure [OIII] and Hb in the K-band with KeckII/NIRSPEC Measure [OII] in the H-band Relative flux-calibration is difficult, dust extinction Measurements for fewer than 10 gals at z>2(Pettini et al. 2001; Kobulnicky & Koo 2000)

z~3 LBG Metallicities: R23LBG nebular O/H ~ 0.1-1.0 Zsun,2-4 mags brighter than local L-Z relation(Pettini et al. 2001)

[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(Pettini & Pagel 2004)O3N2=log([NII] 6584/Ha)12+log(O/H)=8.73-0.32xO3N2 s~0.14

Schematic model of superwinds Collective effect of multiple SNe: mechanical energy input causes shock-heated expanding superbubble with T~108 K, expands, entrains cold ISM (radiation pressure) Superwind seen in local starbursts with S>0.1 Msun/year/kpc2(Heckman et al. 1990, Heckman 2002)

Outflows: Local StarburstsM82 Nearby starburst galaxy Red is Ha emission from ionized gas above the plane of the galaxy outflow speed: >500 km/s plenty of detailed spatial information(Subaru Image)

Importance of feedback/outflows Enrichment and heating of IGM Enrichment and entropy floor in ICM Problems in models of galaxy formation: overcooling and angular momentum Feedback often invoked as solution, but crudely modeled in both semi-analytic and numerical codes Observationally important to constrain mass, energy, metals escaping, and how these depend on galaxy properties

Typical L* LBG SpectrumUnsmoothedSmoothed by 5 pixRAB=24-25.51.5 hr exposure S/N ~ 2/pix, 9-12 AA resolution

Deep in the Desert 10 hr LRIS-B integration for 25 obj, 20 hr for 5 obj 4-5 AA resolution, S/N=20-25 / res. element IMF, stellar metallicity, outflow properties (cB58)

Implications of Winds ICM metals in clusters of galaxies: these are after all the progenitors of rich environments todayEntropy 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 surprisingwhat 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).

Measuring Redshifts: z~3 High redshift Lya em/abs, IS abs at z>2.5 At z =1.4-2.5, these features are in the near UV, while strong rest-frame optical emission lines have shifted into the near-IR

Redshift DesertLow redshift Emission-line z [OII], [OIII], Hb, Ha At z > 1.4, [OII] moves past 9000 AA, while Lya below 4000 AA at z

Redshift DesertLow redshift Abs-line z 4000 AA break, Ca H&K, Mg At z > 1.4, 4000AA break moves past 9000 AA SDSS galaxy at z=0.38

Keck/LRIS-B EfficiencyUnsmoothed LRIS-B + 400/3400 grism --> 40% efficiency from 3800-5000 AA Low night-sky background in near-UV (~3 mag fainter than at 9000 AA)(Steidel et al. 2004)

Measuring Redshifts: z~2 Low- and high-ionization outflow lines He II emission, CIII] emission Fewer galaxies have Lya emission (57% have no Lya) than in z~3 sample (cf. SMG!)(Steidel et al. 2004)

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

Abundance Indicators: Bright (R23)(Kobulnicky et al. 1999) High-Z branch: R23 decreases as Z increases Low-Z branch: R23 decreases as Z decreases Uncertainty in which branch R23 corresponds to Systematic differences from direct method

Star-formation, Chemical Enrichment, and Feedback at z~2-3

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