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The History of the Universe according to CANDELS. Mark Dickinson (NOAO). CANDELS and high redshift star f ormation. CANDELS fields offer the deepest multiwavelength data to measure SF UV rest frame (all fields; better in some than others) H a (3D-HST+AGHAST; all fields)

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candels and high redshift star f ormation
CANDELS and high redshiftstar formation
  • CANDELS fields offer the deepest multiwavelength data to measure SF
    • UV rest frame (all fields; better in some than others)
    • Ha (3D-HST+AGHAST; all fields)
    • Mid-IR (Spitzer MIPS 24 mm; 3 fields very deep)
    • Far-IR (Herschel 100-500 mm; 4 fields very deep)
    • Radio (VLA; decent 1.4 GHz in all fields, deepest in GOODS-N)
  • But, there’s room for improvement
    • Better UV @ z < 1 from WFC3-UVIS
    • Deeper U-band (LBT/LBC in progress)
    • Deeper WFC3 grism for Ha
    • More spectroscopic Ha (e.g., MOSDEF)
    • Deep, uniform submm (S2CLS? LMT?)
    • Deeper radio (JVLA, 1.4 GHz– 10 GHz)
candels data sensitivity to sfr1
CANDELS data: sensitivity to SFR

Assumes no extinction!

candels data sensitivity to sfr2
CANDELS data: sensitivity to SFR

L*(IR) (Magnelli+2011)

Assumes no extinction!

cosmic sf history
Cosmic SF history

Mostly GOODS +




Madau & Dickinson

what s not well known
What’s not well known
  • Peak redshift of cosmic SFR(z) – still uncertain!
    • “Precision” measurements needed
  • Measurements at z < 1 surprisingly poor
    • Improving recently for stellar mass functions
    • Still embarrassingly poor for SFR(z) given availability of GALEX data etc.
  • Faint end of the IR LF
    • Not well measured at z >> 1
  • Direct measurement of dusty SF at z >> 2
    • Only rare, most luminous objects detected individually
    • Even stacking limits are bright (e.g., Magdis), although room for improvement
    • UV slopes are bluer, hinting at less dust; extinction seems to peak at z=1-2, but highly biased samples at z > 2
    • Submm sources (incl. lensed) hint at a larger population of dusty SF galaxies at z > 3
  • Still much too heavy reliance on photo-z’s

CANDELS fields at 160 mm

HST WFC3 region outlined in red

The deepest far-IR observations at 100 – 500 mm:

Elbaz et al. (GOODS), Dickinson et al. (COSMOS, UDS)

GOODS-Herschel data products now public @ HeDaM

COSMOS+UDS data newly obtained and are now being analyzed together with CANDELS HST data





candels herschel cosmos

Red square: CANDELS WFC3 region

Thanks to HanaeInami, Paola Popesso, Ivan Valtchanov, Daniela Coia!

CANDELS+Herschel: Daring to detect the ordinary!

GOODS+CANDELS fields are unique for PACS and SPIRE 250 mm data deep enough to detect ~L*IR galaxies at z ≈ 2

L*(IR) vsz.

Magnelli et al. 2009, 2011

Gemini Science Meeting

the infrared luminosity function state of the art from herschel
The Infrared Luminosity Function:state of the art from Herschel

Magnelli et al. 2013: GOODS-Herschel + PEP, 0 < z < 2.3

Direct far-IR measurements down to LIR≈ 1011Lo at z=2 and LIR ≈ 1012 Lo at z=2

But faint end at z > 1 is only constrained by stacking on 24mm sources.

Slope and integrated r(LIR) are still quite uncertain

global evolution of ir luminosity density
Global evolution of IR luminosity density

The decline of the ULIRGs at z < 2 is well determined, but the bulk of the IR luminosity density at z > 1.5 is not yet directly resolved

Magnelli et al. 2013

herschel stacking and the cib
Herschel stacking and the CIB
  • Resolved SPIRE sources detect only a 5 to 15% of the FIRAS CIB
  • Stacking on 24mm sources (mostly z < 3) appears to resolve most (55-73%) of the CIB
  • Nothing left to find?

Bethermin et al. 2012

herschel stacking and the cib1
Herschel stacking and the CIB

Bethermin et al. 2012; Berta et al. 2011

uv luminosity functions at z 4
UV luminosity functions at z ≥ 4

Lots of work to date both by CANDELS team members + community using CANDELS data

Very little direct information on dust-obscured star formation at these high redshifts

(inferences on extinction from UV spectral slopes)

Bouwens et al. 2012

uv extinction for uv selection
UV extinction (for UV-selection)

See talks by Sandy Rogers; Paola Santini; MaurilioPannella; Marco Castellano

Global dust attenuation inferred from UV spectral slopes peaks strongly at z ≈ 1 to 2

Finkelstein et al. 2012

Bluing trend at z > 4, but the galaxies are entirely UV-selected LBGs

Bouwens et al. 2009, 2012,Dunlop et al. 2011

Finkelstein et al. 2012, etc. etc.

but not everything at z 3 is dust free
But, not everything at z > 3 is dust-free

Williams et al. 1996: HST optical

Hughes et al. 1998: SCUBA 850 mm

hdf 850 1 a hyperluminous ir galaxy in a protocluster at z 5 183
HDF 850.1: a hyperluminous IR galaxy in a protocluster at z=5.183

F. Walter et al. 2012, Nature

SFR ≈ 850 Mo/yr

many new smgs turning up at z 4
Many new SMGs turning up at z > 4

This is the tip … but how big is the iceberg?

GN20: z(CO) = 4.055

GN10: z(CO) = 4.0425

Magdis et al. 2012

Daddi et al. 2009

Capak et al. 2008, Daddi et al. 2009a,b, Coppin et al. 2009, Capak et al. 2011, Combes et al. 2012, Walter et al. 2012, Maroney et al. (submitted), etc. etc.



IRAC 4.5mm

stellar mass density
Stellar mass density
  • Stellar mass density is the time integral of the cosmic star formation history
  • Complements direct measurement of SFR(z), avoiding some of the multi-wavelength complexities and limitations of SFR measurements
    • But, of course it has its own model dependences, potential biases, etc.

Madau & Dickinson

stellar mass functions
Stellar mass functions

Much early work was done in GOODS thanks to the very deep IRAC, near-IR (ISAAC) and optical (ACS) photometry, but other, wider surveys now have very deep data too and are playing an important role.

Ilbert et al. arXiv:1301.1357 COSMOS + UltraVISTA, K < 24

stellar masses in candels
Stellar masses in CANDELS
  • The CANDELS “niche” is at very faint (infrared) magnitudes, thanks to CANDELS WFC3-IR and GOODS/SEDS IRAC
  • Low stellar masses at high redshifts; sensitivity to quiescent/passive galaxies (see talk by Veronica Sommariva)

Photo-z’s & masses: Janine Pforr

z > 3: the faint guys win!

candels stellar mass functions
CANDELS stellar mass functions

“Raw” measurements – very preliminary!

  • Broad dynamic range in mass, probing the faint end
  • Good agreement between fields (in broad redshift bins!)
  • Apparent steep evolution at high mass for z > 3
    • But: F160W is rest-frame UV… what are we missing?

See talk by Andrea Grazian

stellar mass densities
Stellar mass densities
  • Good agreement between fields
  • Decent agreement with previous literature results
  • “Bright” galaxies dominate at z ≤ 2
  • Faint galaxies dominate at z > 3
    • Here detected & measured directly
    • Previous analyses required large mass function extrapolation
  • What are we missing by UV rest-frame selection at z > 3 ?
s trong nebular line emission at z 4
Strong nebular line emission at z > 4

Flux excesses in Spitzer IRAC bands give evidence for (very!) strong Ha and [OIII] in LBGs at z > 4

Not seen (to this extent) in most comparable LBGs at z < 3 – strong evolution?

This can have a significant impact on derived stellar masses, ages, and SFRs

z ≈ 7 – 8 (stacking)

3.8 < z < 5: individual sources

IRAC ch1:






Shim et al. 2011

Labbé et al., submitted

Stark et al., submitted

the farthest frontier
The farthest frontier

Candidates at the highest redshifts (z ≈ 10) are generally extremely faint single-band detections. They have come and gone in different data, and their interpretation is hotly debated (e.g., Bouwens et al. 2008, 2011, 2012, Ellis et al. 2012, Brammer et al. 2012).

See Jim Dunlop’s talk, next…

Ellis et al. 2012

the galaxies we can see now at z 7 must be exceptional
The galaxies we can see now at z ≥ 7 must be exceptional

Progenitors of today’s Milky Way at z ≥ 7 would be have < 1% of their present-day DM halo masses

Boylan-Kolchin et al. 2010

z = 0: M(halo) = 1012 Mo

z = 7: M(progenitor) ≈ 1010 Mo

Millennium II simulations used here have high s8 compared to current estimates, making progenitor masses too large

  • z = 10: M(progenitor) ≈ 109.5 Mo
    • Bullock, Boylan-Kolchan et al. priv. comm.
    • (or even smaller, Behroozi et al. 2010)
milky way progenitors at z 7 should be fainter than the hudf limits
Milky Way progenitors at z ≥ 7should be fainter than the HUDF limits

Abundance matching between DM halo mass function and observed UV luminosity function predicts Milky Way progenitors at z = 7 to 10 should be 1 – 3 mags fainter than the current HUDF limits.

z = 7

Current HUDF limits

z = 10

z = 7

z = 10

Kuhlen & Faucher-Giguere 2012


Beyond CANDELS and the HUDF


Beyond CANDELS and the HUDF

Coe et al. 2013: Candidate triply lensed galaxy

zphot = 10.7

cluster lenses open a new window to study the faintest most distant galaxies
Cluster lenses open a new window to study the faintest, most distant galaxies

Zitrin et al. 2011

50 pc resolution!

Zheng et al. 2012

zphot = 9.6

Bradley et al. 2012

zphot = 6.7

H = 24.0 !

zspec = 4.92

the hubble frontier fields
The Hubble Frontier Fields
  • STScI organized a working group to advise on a new HST deep field Director’s discretionary initiative
    • James Bullock (chair, UC Irvine), Mark Dickinson (NOAO), Steven Finkelstein (UT Austin), Adriano Fontana (INAF, Rome), Ann Hornschemeier Cardiff (NASA/GSFC), Jennifer Lotz (STScI), PriyaNatarajan (Yale), Alexandra Pope (U. Mass), Brant Robertson (University of Arizona), Brian Siana (UC Riverside), Jason Tumlinson (STScI), Michael Wood-Vasey (University of Pittsburgh) + Neill Reid, Ken Sembach (STScI, ex-officio)
  • Recommended a program of optical-NIR deep field imaging targeting 6 massive galaxy clusters as gravitational lenses, plus 6 parallel “blank” fields.
  • Cluster lensing extends the reach of HST to probe JWST flux limits and scientific territory.

“JWST now with HST”

cluster lenses can boost hst s aperture to jwst size and larger
Cluster lenses can boost HST’s aperture to JWST size (and larger!)

Optimal cluster lenses provide a magnification factor of ~2.5 (1 mag) for high redshift background sources over most of the field of view for an HST or JWST instrument.

This is equivalent to boosting HST’s aperture to JWST size.

Smaller areas / volumes receive much larger magnification boosts of 2-3 magnitudes (or more).

hst frontier fields exploring the z 7 10 universe
HST Frontier Fields exploring the z = 7 – 10 universe
  • Detect significant numbers of galaxies 1 – 5 mags fainter than the HST HUDF limit
  • Reach fainter than the JWST NIRCAM blank deep field imaging limit
  • z = 7-10 galaxies lensed bright enough for detailed study (spectroscopy, ALMA, etc.)
  • Outstanding calibration of these lenses for future use (e.g., JWST, ALMA)
  • Prospects for probing faint IR-luminous galaxies at high redshift

Blank fields



JWST NIRCAM blank field limit

AB < 26.5

some questions to keep us awake at night
Some questions to keep us awake at night…

Part I: topics that I touched upon

  • Do we really know enough about dusty star formation at z > 2 ?
    • (and even z > 1) ??
    • What are our prospects of improving this ? (Is ALMA enough ?)
  • What was the peak redshift of cosmic SF, anyway, dammit ?
  • How biased is our view of SF and stellar populations at z >> 3 ?
    • UV selection, and the dreaded specter of surface brightness limits…
  • Are LBGs really very different at z > 4 ?
    • What do very strong nebular lines tell us about their star formation ?
  • Will we measure any redshifts at z > 8 before JWST (dammit) ?
    • Or even with JWST ? ALMA ?
  • Why is the main sequence (MS) tight, and why does it evolve as it does ?
    • Is SSFR(z) really so flat at z >> 2 ?
  • What drives starburstingoutliers to the MS ?
  • How does SF quenching really happen ?
  • Do dormant (quiescent, passive) galaxies ever return from the dead ?
  • Is there a tight MS at z >> 2 ?
  • Does the IMF vary? Where, when, why and how ? What the hell will we do about it ?

Part II: topics that I didn’t discuss (but which many of you will!)