the growth of galaxies: ways forward toward a more robust understanding at high redshift
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The Growth of Galaxies:Ways Forward toward a More Robust
Understanding at High Redshift
Mark Dickinson (NOAO)
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
The demographics of galaxy growth
• Star formation• Stellar mass• Galaxy merging
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Cosmic star formation: a plethora of measurements…
Hopkins & Beacom 2006
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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 ((M*) vs. z)– Depletion of gas ((HI) vs. z)– Build-up of metals ((Z) vs. z)– Supernova rates vs. z– Ionizing background radiation– Extragalactic background light
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
SFR(z) vs. *(z): tension at all redshifts?
SFR(z) stars(z)
Derived SFR(z) may overproduce derived W*(z) at most redshifts
Hopkins & Beacom 2006; see also Chary & Elbaz 2001; Dickinson et al. 2003; Ferguson et al. 2003
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Stellar mass density, z~5 to 6
Stark et al.
Eyles et al.
Wiklind et al.
*(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)
Estimates for * at z=5-6 are 5-50x smaller than at z~2-3
Yan et al. 2006
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
SFR demographics:GALEX UV at z < 1.2
Schiminovich et al. 2005
Arnouts et al. 2005
HDF N+S,Steidel’99
GALEX
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Deep ISO surveys
Chary & Elbaz 2001: Modeled deep number counts from ISO 15, 90, 170m, SCUBA 850m 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.
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Into the Spitzer era
Vastly improved statisticsDeeper dataRedshifts!
Le Floc’h et al. 2005
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Evolution of the IR luminosity density, 0 < z
< 1
0 < z < 1:UV(z) ~ (1+z)2.5
(Schiminovich et al. 2005)IR(z) ~ (1+z)3.9
(Le Floc’h et al. 2005)
Infrared/UV emitted energy from star formation:
z=0 ~1.5 : 1z=1 ~ 4 : 1
LIRGs
ULIRGs
Normal Galaxies
Total IR
- - - UV - - -
Le Floc’h et al. 2005
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Challenges: going deep enough
24m-derived IR LFs, z < 1.2: Le Floc’h et al. 2004Spitzer 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 (SFR) at z ~ 1 ?
Deep surveys (GOODS) cover small area and volume (cosmic variance).
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
GOODS MIPS 24 m
~2000 24m sources with spectroscopic z
GOODS MIPS data detects dust + PAH emission from LIRGs at z ~ 2-3
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
GOODS MIPS 24 m
At 1 < z < 2.5, MIPS 24m is ~10 to 1000x more sensitive to star formation than are deep VLA or SCUBA surveys.
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
z ~ 2-3: the ULIRG era?
Chary et al. - Work in progress!
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
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Ways forward: SF demographics
Forthcoming:– Deeper MIPS surveys over wider areas: Far-IR Legacy Survey; S-COSMOS
• Deeper at 24 m: 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 z.• Many of the galaxies which may dominate (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
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Challenges: MIR/SFR calibrationrest frame 12 m at z ~ 1
z ~ 0 IRAS BGS12 mL12 ~ LIR
0.91
0.8 < z < 1.2 GOODS 24m vs. 1.4 GHz
20 cm fluxes -> LIR assuming z~0 radio/FIR correlation (Yun et al. 2001)MIPS 24m -> L(12m) with minimal k-correctionSignificant number of radio-loud outliers at z~1 (e.g., Donley et al. 2005)
L1.4GHz > 1023 WHz-1 : 38% outliers(>7% of z~1 sources with f(24m) > 20Jy)
z=0
rela
tion
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
PAH emission and SF
SWIRE+SDSS: Tight 8m / 70m correlation, but with strong Z dependence
12+log(O/H) > 8.8:L8 ~ LIR
0.9, < 0.126 dex
Lower O/H -> low L8/L70
Trend starts just below Zsolar
Monekiewicz et al. 2006
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Challenges: calibrating 24m/SFR at z~2
MIPS: <f(24m)>=125 Jy, <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 Jy<LIR> = 2e12 Lo, <SFR> ~ 340 Mo/yr
Sub-mm: stacked <f(850m)> = 1.0 mJy (5) <LIR> = 1.0e12 Lo, <SFR> ~ 170 Mo/yr
X-ray: stacked 8.5 soft-band detection, no significant hard-band. Far below expected AGN level. <SFR> = 100 - 500 Mo/yr (Ranalli 2003, Persic 2004 conversions)
On average, multiwavelength SFR tracers agree reasonably wellwith expectations from low-z correlations, templates & analogs.
Daddi et al. 2005
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Object by object SF comparisons at z~2
Daddi et al. in prep.Reddy et al. in prep.
24 m vs. H
24 m vs. radio
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Submm emission, dust temperatures, etc.
“warm” CE01“cool” CE01 (+ extra mid-IR extinction)
850mm too bright relative to radio or 24mm when comparedWith “warm” local ULIRG templates appropriate for these large L(IR).
Pope et al. 2006
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Implied dust temperatures
Chapman et al. 2005850m/20cm flux ratios suggest cooler dust temperatures for the implied FIR luminosities, compared to the local LIR-T correlation.
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Ways forward: SF calibration
• Measure true thermal far-IR dust emission: luminosities and temperatures– Deeper, wider Spitzer 70 m surveys– Herschel (70-500 m)– SHARC2, SCUBA2, etc. (e.g. 350-450 m)– ALMA
• Improved cross-calibration & diagnostic checks of SF:– Mid-IR vs. far-IR, submm, radio– Extensive mid-IR spectroscopy - Spitzer IRS
MIPS 24 mM81 = NGC 3031 24 m
H + RM81 = NGC 3031 H+ R
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
24 m rest frame emission traces star
formation
Calzetti et al. 2005M51
Calzetti et al. in prep.
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
600s GTO exposure
Ultradeep 70m imagingFrayer et al. 2006 + new MIPS Legacy Survey
10800s GO exposure, ~10’x10’
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Spitzer Far-IR Legacy Survey
GOODS-S
E-CDFS: 30’x30’EGS/AEGIS: 90’x10’
~2000 arcmin2 total
10x current GOODS 70m6.5x deep GOODS 24m
Sensitivities: ~3 mJy @ 70m~30 Jy @ 24m
LIR ~ 1011.5Lo at z=1LIR ~ 1012.5Lo at z=2
+160 arcmin2 in GOODS-N
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Deep 70 m matched to radio and submm
450m
70m70m survey limit well matched to very deep SCUBA-2 450m surveys and to very deep 20cm VLA surveys:
• LIRGs at z~1• ULIRGs at z~2
24m survey will reach “near-GOODS” depth over much larger areas:
• Normal galaxies at z~1• LIRGs at z~2
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
70m constrains dust properties at high redshift
70m/24m: warm dust properties450m/70m: bulk dust temperatures
SCUBA-2!Dusty AGN
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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: H 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
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Mass from light
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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 populationsFortunately, so far there’s not much convincing evidence for
IMF slope variations.
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
SFR(z) vs. *(z): tension at all redshifts?
SFR(z) stars(z)
Derived SFR(z) may overproduce derived W*(z) at most redshifts
Hopkins & Beacom 2006; see also Chary & Elbaz 2001; Dickinson et al. 2003; Ferguson et al. 2003
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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.
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Mass from light
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Composite stellar populations
Significant mass from an older stellar population could be hidden by ongoing star formation.
Papovich et al. 2001
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
IRAC observations of galaxies at z ~ 4-5
z~4 B-dropouts z~5 V-dropouts
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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 temperaturesRedder colors and lower red/near-IR M/L at t < 2 GyrBluer colors at later times
This reduces derived stellar pop. masses and ages at high redshift
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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.
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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.
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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+
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Stellar mass density, z~5 to 6
Stark et al.
Eyles et al.
Wiklind et al.
*(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)
Estimates for * at z=5-6 are 5-50x smaller than at z~2-3
Yan et al. 2006
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
Ways Forward: a summary
• Fully exploit existing surveys: the era of “precision L(z)”• More redshifts! (and more reliable redshifts!)• Extend multi- correlation studies at all redshifts
– MIR, FIR, radio, UV, X-ray, H, etc.– Deeper radio and FIR vital: SCUBA-2, Herschel, ALMA…
• Mid-IR improvements:– Better mid-IR spectral templates– IRS spectral diagnostics for large high-z samples– Figure out the physics!!! (esp. MIR, PAHs, etc.)
• Measure dust temperatures at high z• Get stellar evolution straight (stellar pop. models)• It’s the IMF, dummy (esp. at intermediate & high masses)• Better measurements of merger rates (vs. z & other properties)• Insanely deep surveys at z~5-6 and beyond (WFC3; JWST; ALMA;
TMT)
3 November 2006 Mark Dickinson - MGCT2
GOODS: Great Observatories Origins Deep Survey
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