Continuum Observing

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Continuum Observing in the Submm/mm Tracy Webb
(McGill)
continuum flux integrated over a range in
wavelength
line spectral resolution (Petitpas et al.)
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Next 40 mins ...
? how do we make continuum measurements? ? some
specific physics we can measure ? examples of
recent continuum science
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what is the submm/mm?
generally defined as 200m-1mm submillimeter
1mm - 10mm
millimeter shorter wavelengths ?
mid-far-infrared longer wavelengths ? cm and
radio
sources of submm/mm radiation thermal
emission -- cold dust and CMB synchrotron
-- relativistic electrons in SNR free-free
(Bremstrahlung) -- ionized gas (inverse
compton scattering -- SZ clusters)
these mechanisms are generally associated with
structure formation physics, young objects, and
optically obscured regions
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why work in the submm/mm continuum?

• ? technology just becoming mature
• ? breakthrough science still possible
• JCMT-SCUBA citation rate rivals HST!
• ? gt 1/2 the total energy in the cosmic background

1996 UKT14 1 pixel 2007 SCUBA2 104 pixels!
science areas for continuum work -
debris/proto-planetary disks - Galactic star
formation regions - ISM in local galaxies -
high-redshift galaxy formation - high-redshift
clusters - SZ effect - CMB cosmology
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limited by the atmosphere what wavelengths are
possible from the ground?
750µm 850µm
350µm 450µm
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JCMT
facilities
single-dish interferometers
Submillimeter Array
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Detectors and Receivers Bolometer Arrays
(not to scale)
SCUBA
(to scale)
SCUBA-2
Incoming photons drive change in T and therefore
change in R. Signal is read as voltage or
current. ? used on single dish detectors ?
provide wide bandwidth ? can be wide-field
multi-pixel
Transition Edge Sensors fast, linear response,
sensitive
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Detectors and Receivers heterodynes
collapse over wavelength to form image
?IF ?RF - ?LO ?IF ?RF ?LO
preserves phase and spectral information
? useful for line and continuum work ? single
dish and arrays ? small bandwidth 1-2 GHz ?
single or very few pixels
Neri et al.
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creating a continuum map

• two basic and almost universal problems (cf
  SCUBA2)
• ? need to remove the sky absorption, emission,
  noise
• H20 molecular transitions, thermal emission,
  changing temporally spatially
• arrays usually under sample the sky and
  heterodynes are
• often only one pixel

chop and nod
mapping
throw
A
B
C
source
sky
sky
measures differences in flux throws 30-120
arcsec frequency many Hz
scan maps
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a comparison of some submm continuum facilities
ground based JCMT 15m SCUBA2 450µm/850µm
104 pixels Northern CSO 10m SHARC-II
350µm 384 pixels Northern Apex
12m LaBoca 870µm 295 pixels
Southern LMT 50m AzTec 1.1mm/2.1mm
144 pixels Southern IRAM 30m MAMBO-2 1.2mm
117 pixels Northern
airborne observatories BLAST 2m 250µm
-500µm SOFIA 2.5m 0.3µm -1.3mm Herschel
3.5m 60µm-700µm
interferometers SMA 8x6m Hawaii IRAM PdB 5 x
15m France CARMA California (BIMAOVRO) 6x10m
10x6m ALMA (not yet operational) see later talk
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submm emission thermal radiation from cold dust
T 10-100K dust peaks at
30µm-300µm peaks where the atmosphere is opaque
but still substantial flux in the submm
(especially when redshifted) T3K (CMB) peaks
at 1mm
Wiens displacement law
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never a simple single-temperature Black Body
small grains lt 0.1µm in size not in thermal
equalibrium with the interstellar radiation
field (ISRF) but are heated stochastically most
of the time very cold, but spike to
100-1000K large grains gt0.1 µm in size in
thermal equalibrium with ISRF generally 10-100K
dust temperature depends on heating mechanism
and distribution star formation, active galactic
nucleus, old stars compact hot dust vs diffuse
cold dust emissivity (emission efficiency) ? ??
where ?1-2 thermal spectrum becomes S? ?
??B?(T)
hot dense cores in Orion
cold diffuse Galactic dust
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secondary sources of emission
thermal
synchrotron
free-free
? relativistic electrons in supernova remnants ?
ionized gas
CO line contamination from molecular gas
these processes are often found together! dust
gas star formation supernovae/hard radiation
field
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specific constraints provided by continuum
measurements
dust temperature (Dunne et al. 2002)
Md S850 D2/(?d(?) B?(T))
dust mass (Hildebrand 1983) assuming optically
thin dust
distance
emissivity
flux density
star formation rate (Bell 2003)
(LTIR estimated from fitting SED to FIR/submm)
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debris disks - extra-solar (proto) planetary
systems cold disks of dust debris around stars
Holland et al.
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star forming regions in the Galaxy sites of
obscured star formation in the Eagle nebula
450µm with SCUBA White et al. 1999
HST image
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the mass function of cold dusty clumps
consistent with a Salpeter initial mass
function! (Reid Wilson)
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continuum emission from supernova remnants .
Dunne et al. 2004 Dwek et al. 2004
evidence for dust in supernovae -- process of
dust production at high redshift (ie z6)?
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Ultraluminous IR Galaxies (ULIRGs)
the most luminous systems are also the dustiest
and the most IR/submm bright -- 90 of their
energy is emitted in the FIR/submm
galaxy models of Silva et al. blue - no dust
starburst red - dust added
Sanders Mirabel review
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what can we learn about nearby galaxies?
? spatial correlation between optical/UV and
FIR/submm? ? multi-temperature components ?
multi-dust components ? dust mass estimates
... (Dunne et al. 2002 Wilson et al. 2004)
850m contours over optical images
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high redshift galaxies the advantage of the
K-correction
850µm
redshift 1-9
at long wavelengths FIR-bright galaxies do not
get fainter as they get further away!
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ALMA
? high-resolution submm imagingIono et al.
2006 submm and UV emitting regions are different
no evolution
SCUBA2
? filamentary structure on 400kpc scales around
z2 QSO Stevens et al. 2005
? submm source counts Scott et al. 2002 orders
of magnitude evolution from z0-3
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galaxy clusters and the Sunyaev-Zeldovich
effect probes of cosmology
decrease in CMB intensity increase in
CMB intensity
hot electrons in intracluster gas inverse
compton scatter background CMB photons to higher
energies
Carlstrom et al.
SZ facilities Apex-SZ (Chile), ACBAR (South
Pole) CBI (Chile), DASI (South Pole), ACT (Chile)
... SCUBA2?
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and of course the CMB!
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the future of continuum observing in the
submm (i.e. is there anything left to learn?)
we have be limited by large beams, low
sensitivity, slow mapping speed- no longer.
25 nights with SCUBA
z0
z1
z gt 2
2 nights 2ith SCUBA2
? dusty starbursts with HST in the optical ALMA
has similar resolution in the submm!
? large scale structure and statistical
astronomy Governato et al. 1998