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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

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Whitmore et al

Continuum Observing in the Submm/mm

Tracy Webb (McGill)


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

 examples of recent continuum science

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

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

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

limited by the atmosphere:

what wavelengths are possible from the ground?










Submillimeter Array

Detectors and Receivers: Bolometer Arrays

(not to scale)


(to scale)


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














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.

jiggle maps

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”









measures differences in flux

throws: 30-120 arcsec

frequency: many Hz

scan maps

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


SMA 8x6m Hawaii

IRAM PdB 5 x 15m France

CARMA California (BIMA+OVRO) 6x10m + 10x6m

ALMA (not yet operational) see later talk

submm emission: thermal radiation from cold dust

T = 10-100K dust peaks at


peaks where the atmosphere is

opaque but still substantial flux

in the submm (especially when


T=3K (CMB) peaks at 1mm

Wien’s displacement law:

never a simple single-temperature Black Body

small grains:

< 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:

>0.1 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

‘secondary’ sources of emission




 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

specific constraints provided by continuum measurements



(Dunne et al. 2002)

Md = S850 D2/(d() B(T))

dust mass

(Hildebrand 1983)

assuming optically thin dust

flux density



star formation

rate (Bell 2003)

(LTIR estimated from fitting SED to FIR/submm)

debris disks - extra-solar (proto) planetary systems

cold disks of dust debris around stars

Holland et al.

star forming regions in the Galaxy:

sites of obscured star formation in the Eagle nebula

450µm with SCUBA

White et al. 1999

HST image

the mass function of cold dusty clumps

consistent with a

Salpeter initial

mass function!

(Reid & Wilson)

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 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 starburst

red - dust added

Sanders & Mirabel review

Whitmore et al

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

high redshift galaxies: the advantage of the K-correction


redshift 1-9

at long wavelengths FIR-bright galaxies do not get

fainter as they get further away!


 high-resolution submm imaging:Iono et al. 2006

submm and UV emitting regions are different

no evolution


 filamentary structure on 400kpc scales around z=2 QSO

Stevens et al. 2005

 submm source counts: Scott et al. 2002

orders of magnitude evolution from z=0-3

galaxy clusters and the Sunyaev-Zel’dovich effect:

probes of cosmology

decrease in CMB


increase in CMB


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?

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.

25 nights with SCUBA



z > 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

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