Herschel study of the dust
content of Cassiopeia A
Ref: arxiv:1005.2688v1
Oliver Krause PPT
Why study the dust in SNRs
• As important producers of the dust grains
– Ejecta dust is thought to play a key role as a
coolant in the formation of high-redshift galaxies
(Morgan & Edwards 2003)
– (0.1-1 Msun of dust per SNe is required to form to
explain large dust content (>108 Msun ) and rapid
enrichment)
• SNRs ejecta and the dust physics in the shock
• Need direct, observational evidence
Herschel space telescope
• 1,500,000 km from the Earth
• Probing the cold but animate
universe
• The Three Musketeers:
1. PACS (Photodetecting Array Camera
and Spectrometer) 55 to 210 um
2. SPIRE (Spectral and Photometric
Imaging Receiver) 194 to 672 um
3. HIFI (Heterodyne Instrument for the
Far Infrared) 240 to 625 um
R=107
PACS bands (top row) and in the
three SPIRE bands (bottom row)
Resemblistic analysis (image part)
• PACS 70um image
strongly resembles the
similar angular
resolution Spitzer 24um
MIPS image
• Fainter outer region—
forward shock
• A bright warm dust rim-reverse shock
• Longer wavelength-Knots, lanes of diffuse
Interstellar(IS) dust ,
morphology closely
matches molecular lines
Resemblistic analysis (SED part)
• Emission component decomposition
– nonthermal
– warm dust
– The cold interstellar
– cool Cas A dust
Nonthermal component
• Resemble: VLA 6 cm & IRAC
3.6um
• Convolving to 6’’
• Correspond very closely
– Indicating that both are
dominated by by the nonthermal
emission
• Mean spectral index:
– -0.70+/_0.05 (other ref: Dunne
et al. 2003)
Warm dust
• Resemble: 24 um & 70 um
– Pointing to a common emitting
warm dust component
– Peaking in bright rim /reverse
shock
– More emission from interior in
70 um image
• Originated from 3*10-3 Msun
of 82 K magnesium
protosilicate (Hines et al. 2004)
Cold component
• 70um(Cold dust):
– I70um-n*I24um (Normalised the 24
um image to the surface brightness
levels in the outer parts of Cas A in
70 um image and subtracted it) ??
– Total “warm dust” contribution at
70um is 120+/_6 Jy
• Longer wavelengh (Cold dust):
– Warm dust-Subtracted images
from 100 um
Cold Interstellar Component
• Resemble-_-!!!: 160/350/500um
– > indicating that they are emitted by the same cold IS dust particles.
– determined average 100/160 and 70/160um flux ratios for several
bright regions located outside the remnant.
– Then applied these ratios to the 160umimage and subtracted them
from 70um and 100um images
– In order to determine Cold dust contribution at 160 um, subtracted a
scaled image of the cool component at 70 m(where the ISM and line
contamination is smallest) from the 160-m map iteratively, until its
visible imprint was minimized.
Total and individual component
flux densities (in Jy) for Cas A
70-850um SED of the components
The mass of cool dust in Cas A
• The cold dust can be fitted by ~0.075 Msun of ~35K
silicate dust.
• Other studies:
– Sibthorpe et al. derived a 33-K cool dust mass of 0.055 M
– Nozawa et al. (2010) modelled the Hines et al. (2004) 8100um SED of Cas A with 0.008Msunof shock-heated warm
dust and 0.072Msun of unshocked cool dust in the
remnant’s interior.
(dust formation model for the Cas A ejecta predicted 0.17 M
of new dust, from which they suggested that 0.09 Mhad
already been destroyed by the reverse shock)
A conclusion image
Thanks
Jacobus Kapteyn Telescope
Nik Szymanek (of the amateur UK Deep Sky CCD imaging team of Nik
Szymanek and Ian King) in summer 1997
William Herschel Telescope
Nik Szymanek
Lagoon nebula (M8), Triffid Nebula (M20) and the
Jacobus Kapteyn and Isaac Newton Telescopes
Nik Szymanek
he Dutch Open Telescope (DOT) and the
Nordic Optical Telescope (NOT)
Nik Szymanek
Dunne et al .2003 Nature
• M = S D^2/k B (n, T)
• where S is the flux density measured at frequency n, D is the
distance, and k is the dust mass absorption coefficient. The value B
is the Planck function, and T is the dust temperature. (S ∝ Bv^beta)