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?
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?
Detectors and Receivers: Bolometer Arrays
(not 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.
creating a continuum map
often only one pixel
“chop and nod”
measures differences in flux
throws: 30-120 arcsec
frequency: many Hz
a comparison of some submm continuum facilities
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
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
< 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
>0.1 µm in size
in thermal equalibrium with ISRF
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)
cores in Orion
‘secondary’ sources of emission
relativistic electrons in supernova remnants
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))
assuming optically thin dust
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
the mass function of cold dusty clumps
consistent with a
(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
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
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
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
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