continuum: flux integrated over a range in wavelength
DESCRIPTION
HST. 850 μ m. Whitmore et al. Continuum Observing in the Submm/mm Tracy Webb (McGill). continuum: flux integrated over a range in wavelength. line: spectral resolution (Petitpas et al.). Next 40 mins. how do we make continuum measurements? some specific physics we can measure - PowerPoint PPT PresentationTRANSCRIPT
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)
how do we make continuum measurements?
some specific physics we can measure
examples of recent continuum science
Next 40 mins ...
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
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!
limited by the atmosphere:what wavelengths are possible from the ground?
350µm450µm
750µm850µm
facilities:single-dish &interferometers
JCMT
Submillimeter Array
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)
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.
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
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
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:
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
‘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
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)
debris disks - extra-solar (proto) planetary systemscold disks of dust debris around stars
Holland et al.
star forming regions in the Galaxy: sites of obscured star formation in the Eagle nebula
HST image450µm with SCUBAWhite et al. 1999
the mass function of cold dusty clumps
consistent with aSalpeter initialmass function!
(Reid & Wilson)
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)?
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
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?
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!
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
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
and of course the CMB!
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