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The Growth of Galaxies: Ways Forward toward a More Robust Understanding at High Redshift

The Growth of Galaxies: Ways Forward toward a More Robust Understanding at High Redshift. Mark Dickinson (NOAO). The demographics of galaxy growth. Star formation Stellar mass Galaxy merging. Cosmic star formation: a plethora of measurements…. Hopkins & Beacom 2006.

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The Growth of Galaxies: Ways Forward toward a More Robust Understanding at High Redshift

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  1. The Growth of Galaxies:Ways Forward toward a More Robust Understanding at High Redshift Mark Dickinson (NOAO)

  2. The demographics of galaxy growth • Star formation • Stellar mass • Galaxy merging Mark Dickinson - MGCT2

  3. Cosmic star formation: a plethora of measurements… Hopkins & Beacom 2006 Mark Dickinson - MGCT2

  4. The global history of cosmic star formation • The “cosmic” SFR(z): the comoving average SFR from galaxies, per unit volume, over cosmic time and redshift. • What does it relate to? • Growth of stellar mass in galaxies (W(M*) vs. z) • Depletion of gas (W(HI) vs. z) • Build-up of metals (W(Z) vs. z) • Supernova rates vs. z • Ionizing background radiation • Extragalactic background light Mark Dickinson - MGCT2

  5. Introduction, cont’d • The era of multiwavelength measurements • UV • Mid-IR • Far-IR • Submm • Radio • Nebular emission lines • X-ray • General challenges: • No one observable sees it all • Interpreting observables: model dependence • The IMF • Stellar population/evolution issues Mark Dickinson - MGCT2

  6. SFR(z) vs. W*(z): tension at all redshifts? Derived SFR(z) may overproduce derived W*(z) at most redshifts SFR(z) Wstars(z) Hopkins & Beacom 2006; see also Chary & Elbaz 2001; Dickinson et al. 2003; Ferguson et al. 2003 Mark Dickinson - MGCT2

  7. r*(reion.), 6 < z < 10, C=30, fesc=1 Stars whose formation produces sufficient reionizing photons at 6<z<10 for 100% Lyman contin. escape fraction (Madau, Haardt & Rees 1999) Wiklind et al. Stark et al. Eyles et al. Stellar mass density, z~5 to 6 Estimates for r* at z=5-6 are 5-50x smaller than at z~2-3 Yan et al. 2006 Mark Dickinson - MGCT2

  8. SFR demographics:GALEX UV at z < 1.2 HDF N+S, Steidel’99 GALEX Schiminovich et al. 2005 Arnouts et al. 2005 Mark Dickinson - MGCT2

  9. Deep ISO surveys • Chary & Elbaz 2001: Modeled deep number counts from ISO 15, 90, 170mm, SCUBA 850mm surveys, and the CIRB • Minimal redshift information; small statistics • Features: • LIRGs dominate SFR at z~1 • Fairly flat SFR(z) from 0.8 < z < 2; Turnover pushed toward lower z. Mark Dickinson - MGCT2

  10. Into the Spitzer era Vastly improved statistics Deeper data Redshifts! Le Floc’h et al. 2005 Mark Dickinson - MGCT2

  11. Evolution of the IR luminosity density, 0 < z < 1 Le Floc’h et al. 2005 0 < z < 1: rUV(z) ~ (1+z)2.5 (Schiminovich et al. 2005) rIR(z) ~ (1+z)3.9 (Le Floc’h et al. 2005) Infrared/UV emitted energy from star formation: z=0 ~1.5 : 1 z=1 ~ 4 : 1 Total IR Normal Galaxies LIRGs - - - UV - - - ULIRGs Mark Dickinson - MGCT2

  12. Challenges: going deep enough 24mm-derived IR LFs, z < 1.2: Le Floc’h et al. 2004 Spitzer wide surveys reach LIR ~ 1011 Lo at z~1, ~ 1012 Lo at z~2. Potentially large and uncertain LF extrapolation to total energy density: Have we really converged on r(SFR) at z ~ 1 ? Deep surveys (GOODS) cover small area and volume (cosmic variance). Mark Dickinson - MGCT2

  13. GOODS MIPS 24 mm ~2000 24mm sources with spectroscopic z GOODS MIPS data detects dust + PAH emission from LIRGs at z ~ 2-3 Mark Dickinson - MGCT2

  14. GOODS MIPS 24 mm At 1 < z < 2.5, MIPS 24mm is ~10 to 1000x more sensitive to star formation than are deep VLA or SCUBA surveys. Mark Dickinson - MGCT2

  15. z ~ 2-3: the ULIRG era? • Caveats: • Spectroscopic (and photo-?) z samples incomplete) • Templates for MIR-to-SFR conversion uncertain, esp. at higher L and higher z • AGN identification uncertain • SF component of AGN IR emission uncertain Chary et al. - Work in progress! Mark Dickinson - MGCT2

  16. Ways forward: SF demographics Forthcoming: • Deeper MIPS surveys over wider areas: Far-IR Legacy Survey; S-COSMOS • Deeper at 24 mm: hopefully below the LF knee at z~1; possibly convergence at z~2 • Multiple fields: controlling cosmic variance Desperately needed: • Redshifts!! Especially for dusty galaxies/AGN at z > 1. • Mid-IR K-corrections potentially very strong with small Dz. • Many of the galaxies which may dominate r(SFR) at z~2: • are not UV bright • have K > 20 • Multiplexed NIR spectroscopy and wild heroism? Let’s hope so… Open issues: • AGN contribution to IR emission • Star formation contribution from those AGN • Mid-IR to SFR conversions Mark Dickinson - MGCT2

  17. z=0 relation L1.4GHz > 1023 WHz-1 : 38% outliers (>7% of z~1 sources with f(24mm) > 20mJy) Challenges: MIR/SFR calibrationrest frame 12 mm at z ~ 1 20 cm fluxes -> LIR assuming z~0 radio/FIR correlation (Yun et al. 2001) MIPS 24mm -> L(12mm) with minimal k-correction Significant number of radio-loud outliers at z~1 (e.g., Donley et al. 2005) 0.8 < z < 1.2 GOODS 24mm vs. 1.4 GHz z ~ 0 IRAS BGS 12 mm L12 ~ LIR0.91 Mark Dickinson - MGCT2

  18. Lower O/H -> low L8/L70 Trend starts just below Zsolar PAH emission and SF SWIRE+SDSS: Tight 8mm / 70mm correlation, but with strong Z dependence 12+log(O/H) > 8.8: L8 ~ LIR0.9, s < 0.126 dex Monekiewicz et al. 2006 Mark Dickinson - MGCT2

  19. Challenges: calibrating 24mm/SFR at z~2 On average, multiwavelength SFR tracers agree reasonably well with expectations from low-z correlations, templates & analogs. MIPS: <f(24mm)>=125 mJy, <z>=1.9, and CE01 templates: <LIR> = 1.7e12 Lo, <SFR> ~ 300 Mo/yr UV continuum + reddening: <SFR> ~ 220 Mo/yr Radio: stacked VLA data <f(20cm)> = 17 mJy <LIR> = 2e12 Lo, <SFR> ~ 340 Mo/yr Sub-mm: stacked <f(850mm)> = 1.0 mJy (5s) <LIR> = 1.0e12 Lo, <SFR> ~ 170 Mo/yr X-ray: stacked 8.5s soft-band detection, no significant hard-band. Far below expected AGN level. <SFR> = 100 - 500 Mo/yr (Ranalli 2003, Persic 2004 conversions) Daddi et al. 2005 Mark Dickinson - MGCT2

  20. Object by object SF comparisons at z~2 24 mm vs. radio 24 mm vs. Ha Reddy et al. in prep. Daddi et al. in prep. Mark Dickinson - MGCT2

  21. Submm emission, dust temperatures, etc. 850mm too bright relative to radio or 24mm when compared With “warm” local ULIRG templates appropriate for these large L(IR). “warm” CE01 “cool” CE01 (+ extra mid-IR extinction) Pope et al. 2006 Mark Dickinson - MGCT2

  22. Implied dust temperatures 850mm/20cm flux ratios suggest cooler dust temperatures for the implied FIR luminosities, compared to the local LIR-T correlation. Chapman et al. 2005 Mark Dickinson - MGCT2

  23. Ways forward: SF calibration • Measure true thermal far-IR dust emission: luminosities and temperatures • Deeper, wider Spitzer 70 mm surveys • Herschel (70-500 mm) • SHARC2, SCUBA2, etc. (e.g. 350-450 mm) • ALMA • Improved cross-calibration & diagnostic checks of SF: • Mid-IR vs. far-IR, submm, radio • Extensive mid-IR spectroscopy - Spitzer IRS Mark Dickinson - MGCT2

  24. M81 = NGC 3031 24 mm MIPS 24 mm

  25. M81 = NGC 3031 Ha + R Ha + R

  26. 24 mm rest frame emission traces star formation Calzetti et al. 2005 M51 Calzetti et al. in prep. Mark Dickinson - MGCT2

  27. 600s GTO exposure 10800s GO exposure, ~10’x10’ Ultradeep 70mm imagingFrayer et al. 2006 + new MIPS Legacy Survey Mark Dickinson - MGCT2

  28. EGS/AEGIS: 90’x10’ E-CDFS: 30’x30’ GOODS-S Spitzer Far-IR Legacy Survey Sensitivities: ~3 mJy @ 70mm ~30 mJy @ 24mm LIR ~ 1011.5Lo at z=1 LIR ~ 1012.5Lo at z=2 ~2000 arcmin2total 10x current GOODS 70mm 6.5x deep GOODS 24mm +160 arcmin2 in GOODS-N Mark Dickinson - MGCT2

  29. Mark Dickinson - MGCT2

  30. 70mm 450mm Deep 70 mm matched to radio and submm • 70mm survey limit well matched to very deep SCUBA-2 450mm surveys and to very deep 20cm VLA surveys: • LIRGs at z~1 • ULIRGs at z~2 • 24mm survey will reach “near-GOODS” depth over much larger areas: • Normal galaxies at z~1 • LIRGs at z~2 Mark Dickinson - MGCT2

  31. 70mm constrains dust properties at high redshift 450mm/70mm: bulk dust temperatures 70mm/24mm: warm dust properties SCUBA-2! Dusty AGN Mark Dickinson - MGCT2

  32. SFR(z): the first 2 Gyr • At z > 3, UV is (almost) the only game in town: no direct measurement of reprocessed energy for most galaxies (yet). • Spitzer, Herschel, and near-term submm facilities can only detect hyperluminous (unlensed) objects • ALMA: LIR = 1011 Lo at z=6 in ~10 hours • JWST: Ha at z < 6.5 • Difficulties: • Uncertain extinction inferred from UV spectral slope alone. • Apparently very steep (but uncertain) UV LF slopes -> very large corrections to total luminosity density Mark Dickinson - MGCT2

  33. Mass from light Mark Dickinson - MGCT2

  34. Stellar mass:stellar population issues The IMF: • The IMF almost certainly flattens/turns over at low mass. We use Salpeter because we’re lazy. • Low-mass turnover is probably not a big problem: • It affects M*/L more or less uniformly at all wavelengths, including both stellar mass and SFR indicators. • Local evidence points to nearly universal low-mass IMF • IMF slope at intermediate/high mass is a big deal! • Affects different SFR indicators differently • Changes luminosity evolution of stellar populations Fortunately, so far there’s not much convincing evidence for IMF slope variations. Mark Dickinson - MGCT2

  35. SFR(z) vs. W*(z): tension at all redshifts? Derived SFR(z) may overproduce derived W*(z) at most redshifts SFR(z) Wstars(z) Hopkins & Beacom 2006; see also Chary & Elbaz 2001; Dickinson et al. 2003; Ferguson et al. 2003 Mark Dickinson - MGCT2

  36. Stellar population issues (2) Star formation histories: • Broad band SEDs are largely degenerate to a variety of possible past SF histories, which can lead to substantial M/L variations. • Modeling often assume smooth, monotonic SF histories, but recent SF can mask hide high-M/L starlight from older stars. • IRAC improves but does not eliminate this, especially for bluer, star-forming galaxies. Mark Dickinson - MGCT2

  37. Mass from light Mark Dickinson - MGCT2

  38. Composite stellar populations Significant mass from an older stellar population could be hidden by ongoing star formation. Papovich et al. 2001 Mark Dickinson - MGCT2

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  45. IRAC observations of galaxies at z ~ 4-5 z~4 B-dropouts z~5 V-dropouts Mark Dickinson - MGCT2

  46. Stellar population issues (3) The models: • No definite convergence on stellar population synthesis models yet. • In particular, Maraston 2006 models: • Larger red light contribution from TP-AGB stars at 0.2-2 Gyr • Different evolutionary tracks • Warmer RGB temperatures Redder colors and lower red/near-IR M/L at t < 2 Gyr Bluer colors at later times This reduces derived stellar pop. masses and ages at high redshift Mark Dickinson - MGCT2

  47. Stellar population models • Stellar mass may also be reduced by changing stellar population models: • Maraston 2005 models with substantial TP-AGB contribution to red/near-IR light at ages of 0.2-2 Gyr can reduce M/L significantly Mark Dickinson - MGCT2

  48. Testing stellar M/L at high z • Almost only SED modeling: at high redshift, almost no direct tests of stellar masses so far! • Galaxy kinematics to constrain M/L (mostly FP for early-type galaxies; see also RvdM talk) • Issues of dark matter effects in observed large-scale internal kinematics • AO-fed integral field spectroscopy may be the best way forward. Mark Dickinson - MGCT2

  49. Galaxy merging Galaxies grow their mass both by star formation and merging. A full understanding of galaxy growth requires understanding both. • Stellar mass (M*) + star formation (dM*/dt)SF distribution functions versus time (t, z) are in principle sufficient … • … but in practice real measurements of merger rates (ideally versus other galaxy properties (M*, SFR) would help a lot!! • Observationally, still a highly debated topic, even at z < 1 • In lieu of definitive data, models must guide us here. Mark Dickinson - MGCT2

  50. The near-infrared data gap • Near-IR data remain a huge bottleneck: • Much shallower than current deep optical or Spitzer/IRAC imaging. • Photo-z’s remain mandatory (unfortunately) and near-IR is the weakest link. • Wide-field IR ground-based imagers: • WFCAM, WIRCAM, NEWFIRM, VISTA, HAWK-I, MOIRCS, FLAMINGOS-2, etc. • HST/WFC3: • Detect fading red remnants of higher-z star formation • Differentiating stellar population components within galaxies • Measure UV spectral slopes (dust reddening) at z > 5 • Photometry/SEDs/photo-z’s for UV-faint galaxies at z > 5 • Reliable 2-color LBG selection at 6 < z < 10+ Mark Dickinson - MGCT2

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