High Redshift Galaxies

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High Redshift Galaxies

• Scott Chapman (Cambridge, IoA)
• Aug22, 2007

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Overview and Motivation

• 0. Introductory remarks about galaxy
  formation evolution
• Direct observations of galaxy progenitors
  forming at high redshift (z 1.5)
• Protoclusters at high redshift (z 1.5)

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Context Hierarchical Galaxy Formation (How/when
are the galaxy components assembled?)

• Big Bang Cosmic Microwave Background
• Galaxy Formation and Evolution Fossil
  Records today!

Submm/Radio is a superb probe of obscured forming
galaxies well defined SEDs unimpeded by dust
obscuration bolometric selection Andromeda
(M31) is ideal laboratory to study L galaxy
components.
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Galaxy Evolution - Gravity
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GALAXY FORMATION and EVOLUTION with baryons
Dark matter
Bright galaxies
N-body semi-analytic -gas cooling -star
formation -SNe feedback -galaxy mergers within
halos

• Success reproducing
• observed parameters
• at z0.
• High-z objects of various classes continue to be
  problematic -- SMGs, DRGs,
• (e.g., Sommerville et al. 2000 Baugh et al.
  2005)

Low SFR
High SFR
(Kauffmann et al. 1998)
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Progenitors of Massive Galaxies

• Until the mid-1990s the only zgt2 objects known
  were QSOs, radio galaxies, and QS0 absorbers
  (DLA/LLS)
• How can we go about isolating more normal
  galaxies during the epoch of star/galaxy
  formation?
• The study of high-redshift (lets say zgt1.5)
  galaxies has exploded in the last 10 years, with
  multiple techniques for isolating high redshift
  galaxies, making use of multi-wavelength data
  spanning from the radio to the X-ray
• As opposed to traditional magnitude-limited
  surveys, down to specific flux limit, new results
  utilize several complementary selection
  techniques for finding high-z galaxies, selecting
  overlapping yet complementary populations --gt
  must determine how they overlap/complement each
  other to describe entire galaxy population at a
  given epoch.

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Foreground (zlt2) Galaxies
NB IAB25 ?? 1 photon/year/cm2/A
From LeFevre, Vettolani et al 2003
? Brute force spectroscopy is inefficient for
zgt2!
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The Laboratory for studying high-z galaxies
UKIRT CSO JCMT Subaru
Keck-I/II IRTF CFHT Gemini
Spitzer
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Ground-based vs. space-based?

• NB in addition to transmissivity, the emissivity
  of the Earths atmosphere is a big problem sky
  at 2mm is 10,000 brighter than at 0.5mm

Some sub-mm windows from good sites
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(Spitzer Space Telescope)
10-m mirror
0.85-m mirror
2-m astronomer
2.4-m mirror
(Hubble Space Telescope)
(Keck Telescope)
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Local Galaxies - e.g. Luminous Elliptical Galaxies

• the most massive galaxies in the local
  Universe
• Pressure-supported, metal-rich stellar systems.
  Simple galactic-scale stellar systems
• Extremely homogeneous and old (implies zgt2
  formation)
• Live in the highest density regions (clusters)
• Largest stellar mass of any galaxies ( up to 10
  M)
• Host the most massive Black Holes in local
  Universe, gt109Mo
• HOW ARE THEY MADE ???
• -observations of the high-z Universe

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Formation Mechanisms

• Wide range of proposed mechanisms for forming big
  galaxies
• (pseudo-)monolithic collapse (TmergeltTSF)
• major merger of two existing galaxies
  (TmergeTSF)
• an extended series of minor mergers (TmergegtTSF)
• Can we observationally distinguish between these
  scenarios?

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Dust obscured, merging galaxies e.g.,The
Antennae
ISOCAM
ISO 15um

• Distinct opt/UV and far-IR luminosity
• 90 emitted at far-IR
• Dust obscures UV
• absorbs and re-radiates at longer
  wavelengths
• (100-200 microns)

HST WFPC2
CSO/SHARC-2 350um
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The Extragalactic Background
?

• FIRB opt/UV EBL -gt half of the energy
  production (from SF or AGN) over history of the
  Universe arises in highly obscured regions
• Much of the star formation in the Universe might
  be obscured resolve FIRB into constituent
  components

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Components of FIRB (to be studied
directly and indirectly)
350
850
Dole et al. 2005
Submm is almost all high-z galaxies (80
zlt4) MidIR and FarIR is 80 zlt1.7 Radio is
extremely useful, BUT submm best (only?) way to
probe the high-z components of FIRB
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Studying the obscured activity
SED of an ageing stellar population of solar
metalicity with dust
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f(24mm) vs Lbol
Papovich and Bell 2003
At far-IR wavelengths, Spitzer can only observe
well at 24 mm what are the bolometric
corrections? theyre large! And especially bad
for the most luminous, dust-obscured
populations. (leave aside for now)
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Progenitors of Massive Galaxies

• Review of techniques
• (focus on submm/radio selection, UV, nearIR)
• Some key questions and results

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zgt1.5 Submm Selection (100 zs)
(courtesy I. Smail)
(Smail 2005)

• Submm galaxies dusty, most of luminosity comes
  out in submm waveband
• First detected by SCUBA/JCMT in 1997 at 850 ?m
  (Smail1997)
• Counts 1000/sq. degree at 5 mJy (limit of
  bright SCUBA survey) a few 100 submm galaxies
  IDd
• In principle, SCUBA sensitive to dusty galaxies
  to zgt6 (negative K-correction) but we now know
  that almost no SCUBA galaxies are that distant!

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Submm/Radio bolometric selection of galaxies?
Identify SMGs (although Spitzer proving very
useful -- Pope06) -Known tight correlation with
FIR -Good spatial resolution (MERLIN 0.3, VLA
1.4)
FarIR/radio correlation roughly holds at z2.5
(Kovacs et al. 2006)
Far-IR correlates with synchrotron radio (SNe
shock accelerates electrons)
1.4GHz
(Ivison et al. 2002)
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SCUBA galaxies (SMGs)
High resolution RADIO and HST reveal large,
merging galaxies.
Smail1999,2004 Chapman2003,2004)
greyscale
contours
JCMT/SCUBA
HST
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SCUBA galaxies (SMGs)
Redshift surveys have given us tremendous insight
into a hyper-luminous population of cool dust
SB-dominated galaxies.
ltzgt2.3
Massive/merging
Chapman03,05, Swinbank04 Pope05
Neri03, Greve05 Genzel02, Tacconi05
IRAM
Keck 10m
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zgt1.5 Submm Selection
(courtesy I. Smail)
(Chapman et al. 2005)

• Breakthrough using radio (1.4 GHz) positions
  for optical spectroscopy (ameliorates ambiguity
  from 15 SCUBA beam), 50 of sources have zs
• Redshifts of 100 SMGs enable study of physical
  properties
• Typical LIR8x1012L? and dust temperature Td38K
  (confirmed by 350 ?m observations)
• Less than 10 of submm galaxies are at zgtgt3

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zgt1.5 Submm Selection
(courtesy I. Smail)
(Chapman et al. 2005)

• IR luminosities correspond to sfr gt1000 M?/yr
  (Salpeter) if bulk of FIR is powered by star
  formation. If SF lasts for 108 yr, significant
  stellar mass formed
• Much rarer than other samples, but higher
  inferred SFR, likely contribute significantly to
  SFR density at high z

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zgt1.5 Submm Selection
(Chapman et al. 2003)

• Rest-frame UV spectra obtained with Keck/LRIS-B
  (like UV-selected samples)
• Spectra show features of star-formation and AGN
  (Ly?, NV, CIV, SIV), rest-frame optical spectra
  sometimes NII/H?????or broad H?
• Raises question of AGN contribution to
  bolometric luminosity, Deep (Chandra 2 Msec
  image) X-ray emission indicates presence of Fe
  K??line, and absorbed non-thermal continuum slope
• BUT AGN appears not to be energetically
  important -gt submm emission dominated by star
  formation

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zgt1.5 Submm Selection
Note galaxies w/ smaller star formation rates
not detected yet in CO
(Tacconi et al. 2006)

• Masses stellar masses estimated from
  SED-fitting (how does AGN affect stellar mass
  estimates?) dynamical masses estimated from H?,
  CO-linewidths cold molecular gas masses
  estimated from CO line luminosities
• Dynamical masses w/in 10kpc, 2x1011 M?(Swinbank
  et al. 2004, 2006), molecular gas masses 5x1010
  M? (Tacconi et al. 2006)

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zgt1.5 Submm Selection

• Submm galaxies appear to be massive systems with
  prodigious star-formation rates, may also be
  strongly clustered (but uncertain because of
  small number of redshifts)
• Could be progenitors of QSOs, and massive
  galaxies at lower redshift
• Interesting note several years ago, a lot was
  made of the fact that there was so little overlap
  between submm galaxies and z3 UV-selected
  galaxies. But now we know that most submm
  galaxies are at zlt3, and have similar redshift
  distribution to z2 UV-selected galaxies. gt50
  of submm galaxies have colours of UV-selected
  galaxies (but bigger SFRs)

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Photometric Pre-selection UV

• 50 objects/square arcmin down to R25. How do
  you pick out the high-redshift galaxies?
• Lyman discontinuity at rest-frame 912 A gives
  z3 galaxies very distinctive observed UGR colours

(Steidel et al. 1992, 1993, 1995, 1996, 2003)
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zgt1.5 Rest-UV Color Selection

• z3 UGR Lyman Break criteria, adjusted for z2
  (Adelberger et al. 2004)
• Spectroscopic follow-up with optimized
  UV-sensitive setup (Keck I/LRIS-B)
• 1000 galaxies at z3, gt750 galaxies with
  spectroscopic redshifts at z1.4-2.5, in what was
  previously called the Redshift Desert

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Measuring Redshifts z3

• Meaure Lya em/abs, IS abs at zgt2.5
• At z 1.4-2.5, these features are in the near
  UV bonus strong rest-frame optical emission
  lines have shifted into the near-IR
• formerly called THE REDSHIFT DESERT

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Redshift Desert

• Low redshift
• Emission-line z
• OII, OIII, Hb, Ha
• At z gt 1.4, OII moves past 9000 AA,
  while Lya below 4000 AA at zlt2.3 no strong
  features in the optical

SDSS galaxy at z0.09
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Redshift Desert

• Low redshift
• Abs-line z
• 4000 AA break, Ca HK, Mg
• At z gt 1.4, 4000AA break moves past 9000 AA

SDSS galaxy at z0.38
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Keck/LRIS-B Efficiency

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

Unsmoothed
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Measuring Redshifts z2

• Low- and high-ionization outflow lines, Ly?
• He II emission, CIII emission
• Fewer galaxies have Lya emission (57 have no
  Lya) than in z3 sample (cf. SMG!)
• (Steidel et al. 2004)

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Outflow Kinematics z3 vs. z2

• Kinematic evidence for large-scale outflows is a
  generic feature of UV and submm-selected galaxies
  at zgt2
• Signature of feedback, perhaps fundamental to
  understanding galaxy formation
• (Steidel et al. 2004)

z3
z2
Unsmoothed
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zgt1.5 Rest-UV Color Selection

• z3 UGR criteria (Lyman Break), adjusted for
  z2 (Adelberger et al. 2004)
• Spectroscopic follow-up with optimized
  UV-sensitive setup (Keck I/LRIS-B)
• 1000 galaxies at z3, gt750 galaxies with
  spectroscopic redshifts at z1.4-2.5, in what was
  previously called the Redshift Desert

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Evolution of Clustering to z1, 0
(Adelberger et al. 2004)
(Blain et al. 2004)

• Follow evolution of DM halo clustering in
  simulation
• Matches early-type absorption line DEEP2
  galaxies at z1 (Coil et al. 2003) SDSS Es at
  z0.2
• Typical UV-selected galaxy at z2-3 will evolve
  into an elliptical by z0

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Summaryzgt1.5 Rest-UV Colour Selection

• (typical sfr50-100M?/yr)
• (typical stellar mass few x 1010M?, large range)
• What does UV-selection mean in terms of physical
  properties?
• Star-formation thats only moderately (factor of
  few-100) extinguished by dust, but a large range
  of stellar masses (smaller range of baryonic
  masses), clustering implies that these will
  correspond to early-type galaxies at z0.

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zgt1.5 Near-IR selection

• Extension of K20 survey group (i.e., get zs for
  everything with Klt20), use B-z, z-K color
  criteria to select both star-forming galaxies and
  passive galaxies at zgt1.4
• Incomplete for fainter objects with small Balmer
  Breaks, weighted more towards fairly massive
  objects
• Significant overlap of BzK/SF with UV-selected
  samples

(Daddi et al. 2004)
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zgt1.5 FIRES/J-K selection (20 zs)
(Franx et al. 2003)
(Reddy et al. 2005)

• J-Kgt2.3 criteria meant to select massive evolved
  galaxies with significant Balmer/4000 Å breaks at
  zgt2 turns out selection also yields massive
  dusty starbursts
• 25 appear to contain AGN (much higher than
  fraction of UV-selected population)
• Only limited number of spectroscopic redshifts

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zgt1.5 Summary

• In addition to UV-selected, BzK, J-K, submm,
  there are other techniques, such as the
  K-band/photo-z technique of the Gemini Deep Deep
  Survey (GDDS), and new Spitzer capabilities IRAC
  (mass-selected), MIPS/24 micron (sfr-selected,
  analogous to SCUBA)
• Now that there are several groups using
  different selection techniques to find galaxies
  at z2, we need to understand how the samples
  relate to each other (each sample has certain
  benefits but is incomplete e.g., UV-selected
  sample has largest set of redshifts and spectra)
• Reddy et al. (2005) considered the overlap among
  different samples, and contribution of each to
  the sfr density at z2-2.5

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At the highest redshifts?
Hard stuff to study! (e.g., contamination)
Controversy at z 6? Did the star formation rate
change from z 6 to z 3? If so, did it
increase or decrease? Each possibility
(increase, decrease, stay the same) had been
claimed by various groups studying z 6 galaxies.
For z 6, Lyais between I z bands, so we are
looking for I-drops R. J. Bouwens, G.D.
Illingworth, J. P. Blakeslee, M. Franx set out
to do the most careful analysis possible and
thereby come to some firm conclusions about such
galaxies.
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The Star Formation History of the Universe

• Millimeter/Radio galaxies form most of the stars
  we see today in big bursts
• 2-5 billion years after the big bang.
• LESSONS
• we still dont even know about all the galaxies
  in the Universe!
• Local galaxies (M31) show unexpected components!
• Simulations of how galaxies form are not always
  very predictive!

UV-selected
Radio/submm
(Chapman et al. 2005)
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Key Questions

• What is the evolution in global sfr and stellar
  mass density vs. z?
• What is the evolution in number density of
  galaxies as a function of (stellar) mass and
  star-formation rate?
• What are the star-formation histories of
  galaxies (burst/episodic, continuous), and how do
  they accumulate their stellar mass?
• What are the origins of different morphological
  types?
• What is the chemical enrichment in galaxies vs.
  z, and by how much do they enrich their
  surroundings (vs. mass)?
• What is the effect of supernovae/AGN feedback on
  gas in galaxies and the surrounding IGM?
• How do we make a continuous timeline of galaxies
  from high redshift to z0 (map one sample to
  another)?

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Key Techniques/Goals

• New multi-wavelength technologies are helping us
  address these questions, beyond ground-based
  optical imaging and spectroscopy
• Wide-field near-IR imaging (stellar masses) and
  near-IR spectroscopy (dynamical masses, sfr,
  chemical abundances)
• Chandra X-ray observations (sfr and AGN)
• Spitzer/IRAC (stellar masses) and MIPS (dust
  luminosity, sfr)
• HST ACS/NICMOS (morphologies)
• Full understanding of energetics and stellar and
  metal content is a multi-wavelength endeavor
• Detailed comparison with numerical simulations
  and semi-analytic models

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Concluding Philosophical Comment

• Rich set of observations of galaxies in the
  early universe, for statistical samples of
  galaxies selected with different techniques
  (though its still a challenge to get spectra)
• Theres much more that I could have presented
• Field of zgt1.5 galaxy evolution is completely
  different since just 10 years ago, when
  UV-selection technique was first implemented
• Whats happening in the next 10 years?
  (feedback, connecting to samples at other
  redshift, building mass/sfr-limited samples, disk
  galaxies)