Herschel study of the dust content of Cassiopeia A

Ref: arxiv:1005.2688v1Oliver 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 um2. SPIRE (Spectral and Photometric Imaging Receiver) 194 to 672 um3. HIFI (Heterodyne Instrument for the Far Infrared) 240 to 625 umR=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) 8-

100um 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 M had already been destroyed by the reverse shock)

A conclusion image

Thanks

Jacobus Kapteyn TelescopeNik Szymanek (of the amateur UK Deep Sky CCD imaging team of Nik Szymanek and Ian King) in summer 1997

William Herschel TelescopeNik Szymanek

Lagoon nebula (M8), Triffid Nebula (M20) and the Jacobus Kapteyn and Isaac Newton TelescopesNik 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)∝