Galaxies and cosmology: the promise of ALMA

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Galaxies and cosmology the promise of ALMA

• Andrew Blain
• Caltech
• 14th May 2004

ALMA North American Workshop
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Contents

• CMB and SZ cosmology aspect
• Examples of what we know ALMA can see
• Sub-arcsec resolution
• microJy sensitivities
• No confusion noise
• Continuum and line surveys
• Advances over all existing/proposed capabilities
• Sensitivity is not infinite!
• Relatively small field of view

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Fine angular scale CMB and SZ

• ALMA (with compact array) will be extremely
  sensitive to arcmin-scale CMB power, from
  clusters, filaments and primordial fluctuations

SZ effect
X-ray
ALMA
Carlstrom et al. Arcmin resolution
Chandra low-z Hydra cluster with substructure
Fine resolution will reveal features in the
intracluster medium to resolve physical
conditions in cluster gas
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Example target the Antennae
ISOCAM

• Excellent example of distinct opt/UV and IR
  luminosity
• Interaction long known, but great luminosity
  unexpected
• 90 energy escapes at far-IR
  wavelengths
• Resolved images important
• Relevant scales 1 at high
  redshift

HST WFPC2
CSO/SHARC-2 Dowell et al.
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Observed far-IR/submm SEDs

• Non-thermal radio
• Thermal dust
• Dominates luminosity
• Hotter in AGN?
• See Spitzer
• Molecular and atomic lines
• Mm CO / HCN
• IR C/N/O/H2
• IR CC PAH

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Submm population backgrounds

• Many sources of data
• Total far-IR and optical background intensity
  comparable
• Most of submm background detected by SCUBA
• Backgrounds yield weaker constraints on evolution
  than counts

ISO
SCUBA
SCUBA
Model BJSLKI
Models BJSLKI 99
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ALMA will resolve the most distant galaxies down
to L

• Example objects known from existing ground based
  observations
• High-redshift continuum emission
• Marginally resolved CO spectra reveal internal
  structure, and dynamical masses
• Spitzer will reveal a huge sample to follow up
• Redshifts are moderate z2-3
• ALMA will see CO structure in detail
• ALMA will probe fainter, still unconfused

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Example Deep Submm Image

• Abell 1835
• Hale 3-color optical
• 850-micron SCUBA
• Contrast
• Image resolution
• Visible populations
• Orthogonal submm and optical views
• One of 7 images from Smail et al. SCUBA lens
  survey (97-02)
• About 25 SCUBA cluster images

Ivison et al. (2000)
2.5 square
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Example IDed submm galaxy
Ivison et al (2000, 2001)

• Unusually bright example
• May not see most important region in the optical
• J2 is a Lyman-break galaxy (Adelberger Steidel
  2000)
• J1 is a cluster member post-starburst (Tecza et
  al. 2004)
• J1n is an Extremely Red Object (ERO Ivison 2001)
• Remains red in deeper Keck-NIRC data
• Both J1n J2 are at z 2.55 radio and mm from
  J1n

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High-redshift CO
Abell 2218 ISO 15µm and optical image (2.5
across) Metcalf et al. Orange left image Red
bottom image

• SAFIR field exceeds extent of the ISO image, yet
  has spatial resolution as good as the
  inteferometer, plus spectral information

40 square
Note submm, optical and mid-IR show different
populations
?
K band image (8 square), with IRAM CO contours
of an ultraluminous galaxy at z3.35
Upper submm continuum lower optical HST
Abell 851
Genzel et al. (2004)
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Submm galaxies in CO(3-2),(4-3)

Chapman et al.
Smail et al. N2.4
Frayer et al. N4
Neri et al. ApJ (2003) IRAM interferometer
source of detections given on individual frames 8
more now have CO measurements
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Population of submm galaxies

• Most data is at 850 µm
• New bright limit from Barnard et al
• Very few are Galactic contaminating clouds
• First limit was at 2.8 mm (BIMA)
• Also bright 95/175 µm counts (ISO), that will be
  dramatically improved by Spitzer
• Also data at 1.2mm (MAMBO) 1.1mm (BOLOCAM) and
  450µm

Orange stars Barnard et al (2004) 850-µm upper
limit
Blain et al (2002) updated
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Unique submm access to highest z

• Redshift the steep submm SED
• Counteracts inverse square law dimming
• Detect high-z galaxies as easily as those at z0
• Low-z galaxies do not dominate submm images
• Unique high-z access in mm and submm
• Ultimate limit is CMB heating

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Existing limits to information

• Limited few arcsec positional accuracy from
  10-m class submm telescopes
• challenges accurate identification and makes it
  difficult to target for spectroscopy
• So far VLA radio positions required for
  spectroscopy
• Optical spectroscopy has provided redshifts for
  more of this population that might have been
  expected (Chapman et al 2003 2004)
• ALMA will not be limited in this way
• To only cooler, more luminous, lower redshift
  systems

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850-µm redshift distribution

• Histogram sample expanded from Nature list
• Expected submm radio redshift distributions
  from Scott Chapmans model
• Consistent with studeis of star-formation history
  that show far-IR domiates optical at z2, but
  result now MUCH more robust
• z1.5 gap is the spectroscopic desert
• Bias against highest z is likely modest, but
  still uncertain

Chapman et al. (2003 Nature 2004 ApJ subm.)
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Signs of large-scale structure

• HDF-N/GOODS field submm/radio spectroscopic
  survey (Chapman et al 2004)
• Geometry is extreme pencil beam
• 5 x 3000 Mpc
• Same for ALMA
• Circles all galaxies with redshifts
• Empty z known
• Colored z in associations within 1200 km/s
• Note more associations than expected unless
  powerful galaxy-galaxy correlation
• r0 7h-1 Mpc
• ALMA will resolve less luminous associated
  structure and map the regions in detail

Blain et al. (astro-ph/0405035)
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ALMAs resolution puts it ahead

• Resolution is very fine, both to avoid confusion
  from overlapping sources, and resolve their
  internal structure
• The second absolutely demands ALMA
• The first can also be achieved by large aperture
  single-antenna telescopes on the ground and in
  space
• These can provide wide-field finder images
• 25-m submm Atacama Telescope Cornell-Caltech
  study

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Confusion noise

• Model based on SCUBA/ISO populations
• Flux for 1 source per beam RMS noise
• Extragalactic sources dominate for small
  apertures
• When lt 500µm 25-m aperture very important
• lt0.1mJy sure to find submm counterparts to high-z
  optical galaxies

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Time to reach confusion limit

• Galactic extragalactic confusion limits
• Sensitivity a D-1
• Practical limit 10-100hr in any field
• At shortest wavelengths need large aperture to
  allow deep surveys
• Note speed at 850µm
• 9 resolution

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Confusion is avoided with ALMA

• Current missions in black
• Spitzer is \
• Green bar is just a 500m baseline ALMA
• Red bar is 10-m SAFIR
• Confusion from galaxies not met for many minutes
  or hours
• At shortest wavelengths very deep observations
  are possible
• Factor of 10 in resolution over existing
  facilities is very powerful

?
?
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Submm observations of galaxies mature in ALMA era

• Resolution to match HST/JWST and resolve internal
  structure of high-z galaxies
• 3-D spectral information of even the most
  obscured regions
• Reveals astrophysics at work
• Provides direct redshifts
• ALMA astrophysical probes are self contained
• New populations of objects, and pre-reionization
  galaxies
• H2 lines / first metals dust and fine-structure
  lines

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Photometric redshifts

• Combine different bands to estimate T z
  together
• No strong far-IR spectral breaks or features
• Strongest lever from 200-600µm
• Based on knowledge of galaxies/site, can
  probably design 2 optimal bands
• Once z known, get accurate luminosity
• ALMA can do this, but combined with real redshift
  information from spectra

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SMGs SEDs FIR-radio assumed
Squares low-z, Dunne et al. Empty circles
moderate z, mainly Stanford et al. Crosses
variety of known redshifts (vertical
lensed) Solid circles Chapman SMGs Lines
low-z trends Scatter in T by gt40
Radio loud caveat above 60K
ALMA can explore new region here
ALMA can explore new region here
Solid circles new Submm sources
Blain, Barnard Chapman 2003 Blain et al (2004
astro-ph/0404438)
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Line emission

• Optical spectroscopy will probably never be able
  to keep up with mid-IR discoveries
• Especially the hard cases, deeply enshrouded in
  dust at zgt5
• Far-IR emission lines and CO rotational emission
  reveal astrophysics of gas involved in star
  formation
• Heterodyne Rgt106 and 8-GHz bandwidth ALMA can
  see details
• ALMA can make spatially spectrally resolved
  images of the most interesting galaxies found in
  lt1hr
• Little information on far-IR lines available so
  far
• SOFIA will test this science
• Spitzer covers restframe spectra of low-redshift
  galaxies
• CII and OI pair can give redshifts for z4.5 CO
  may be exhausted / not excited / not present at
  these redshifts
• High redshift AGN LBGs show metallicities are
  high early on

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Lines available for detection

• Left 870µm window 5x10-21 Wm-2 (10-s 18 min)
• Right 350µm window 4-10x10-20 Wm-2 (10-s 8.7
  hr)
• Long wavelength in blind searches detect 1
  hour -1
• ALMA is fastest planned instrument working at
  longer wavelengths
• Gives resolved spectroscopy redshift and
  dynamical information

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Summary

• ALMA will detect huge numbers of galaxies, deeper
  than any other facility
• Probe astrophysics
• during most active phase at z2-3
• Prior to re-ionization
• Resolved spectral images will reveal masses and
  mass assembly of galaxies
• DRSM shows demand will be high
• All areas of extragalactic astrophysics will
  benefit from ALMA