continuum: flux integrated over a range in wavelength
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Transcript of continuum: flux integrated over a range in wavelength
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continuum:continuum:flux integrated over a range flux integrated over a range in wavelengthin wavelength
line: spectral resolution (Petitpas et al.)
Whitmore et al
HST850μm
Continuum Observing in the Submm/mmTracy Webb (McGill)
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how do we make continuum measurements?
some specific physics we can measure
examples of recent continuum science
Next 40 mins ...
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what is the submm/mm?
generally defined as: 200m-1mm “submillimeter” 1mm - 10mm “millimeter”
shorter wavelengths mid-far-infraredlonger 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!
> 1/2 the total energy in the cosmic background
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
1996 UKT14 1 pixel2007 SCUBA2 104 pixels!
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limited by the atmosphere:what wavelengths are possible from the ground?
350µm450µm
750µm850µm
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facilities:single-dish &interferometers
JCMT
Submillimeter Array
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Detectors and Receivers: Bolometer
Arrays
Transition Edge Sensorsfast, linear response, sensitive
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
SCUBA
SCUBA-2
(to scale)
(not to scale)
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Detectors and Receivers: heterodynes
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
RF amplifier
tunable local oscillator
mixer IF amplifier further
analysis/detectionelectronics
EMR
antenna
collapse over wavelengthto form image
Neri et al.
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creating a continuum maptwo 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 areoften only one pixel
A B C
measures differences in fluxthrows: 30-120 arcsecfrequency: many Hz
sky skysource
“chop and nod” mapping
scan mapsjiggle maps
throw
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a comparison of some submm continuum facilities
ground based
JCMT 15m SCUBA2 450µm/850µm 104 pixels NorthernCSO 10m SHARC-II 350µm 384 pixels NorthernApex 12m LaBoca 870µm 295 pixels SouthernLMT 50m AzTec 1.1mm/2.1mm 144 pixels SouthernIRAM 30m MAMBO-2 1.2mm 117 pixels Northern
airborne observatories
BLAST 2m 250µm -500µm SOFIA 2.5m 0.3µm -1.3mmHerschel 3.5m 60µm-700µm
interferometersSMA 8x6m HawaiiIRAM PdB 5 x 15m FranceCARMA California (BIMA+OVRO) 6x10m + 10x6mALMA (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 isopaque but still substantial flux in the submm (especially when redshifted)
T=3K (CMB) peaks at 1mm
Wien’s displacement law:
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never a simple single-temperature Black Body
small grains: < 0.1µm in sizenot in thermal equalibrium with the interstellar radiation field (ISRF) but are heated stochasticallymost of the time very cold, but spike to 100-1000K
large grains:>0.1 µm in sizein thermal equalibrium with ISRFgenerally 10-100K
dust temperature depends on heating mechanism and distribution:star formation, active galactic nucleus, old starscompact hot dust vs diffuse cold dust
emissivity (emission efficiency) where ~1-2thermal spectrum becomes S B(T)
hot dense cores in Orion
cold diffuse Galactic dust
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‘secondary’ sources of emission
synchrotron
free-free
thermal
CO line contaminationfrom molecular gas
relativistic electrons in supernova remnants ionized 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))
distance emissivityflux density
dust mass(Hildebrand 1983)assuming optically thin dust
star formation rate (Bell 2003)
(LTIR estimated from fitting SED to FIR/submm)
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debris disks - extra-solar (proto) planetary systemscold 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
HST image450µm with SCUBAWhite et al. 1999
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the mass function of cold dusty clumps
consistent with aSalpeter initialmass function!
(Reid & Wilson)
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continuum emission from supernova remnants
.
Dunne et al. 2004Dwek et al. 2004
evidence for dust in supernovae -- process of dust production at high redshift (ie z~6)?
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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 starburstred - dust added
Sanders & Mirabel review
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850m contours over optical images
Whitmore et al
spatial correlation between optical/UVand FIR/submm?
multi-temperature components multi-dust components dust mass estimates ...
(Dunne et al. 2002; Wilson et al. 2004)
what can we learn about nearby galaxies?
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high redshift galaxies: the advantage of the K-correction
850μmredshift 1-9
at long wavelengths FIR-bright galaxies do not getfainter as they get further away!
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high-resolution submm imaging:Iono et al. 2006submm and UV emitting regions are different
filamentary structure on 400kpc scales around z=2 QSOStevens et al. 2005
submm source counts: Scott et al. 2002orders of magnitude evolution from z=0-3
no evolution
ALMA
SCUBA2
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galaxy clusters and the Sunyaev-Zel’dovich effect: probes of cosmology
Carlstrom et al.
SZ facilities: Apex-SZ (Chile), ACBAR (South Pole)CBI (Chile), DASI (South Pole), ACT (Chile) ... SCUBA2?
hot electrons in intracluster gas inverse compton scatterbackground CMB photons tohigher energies
decrease in CMB intensity
increase in CMBintensity
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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.
large scale structure and statistical astronomyGovernato et al. 1998
dusty starbursts with HST in the opticalALMA has similar resolution in the submm!
25 nights with SCUBA
2 nights 2ith SCUBA2
z~0 z~1
z > 2