interstellar dust observations from planck and hersche€¦ · interstellar dust observations from...

Interstellar dust observations from Planck and Herschel A. Abergel Paris, Planck 2011

Interstellar dust observations

from Planck and Herschel A. Abergel,

IAS, University Paris-Sud/CNRS, Orsay, France


“DUSTEM” model, Compiègne et al. 2011 (one of the dust models developed after Spitzer to predict the emission and the extinction)

Emission spectrum of interstellar dust

BG: Thermal dust Large Amorphous Silicate (aSil)

Large Amorphous Carbon (LamC)

VSG Small Amorphous Carbon (SamC)

PAH Polycyclic Aromatic Hydrocarbons

PAH VSG

PACS-SPIRE, Planck/HFI ISO / Spitzer

BG


- Emission dominated by thermal dust - Emission properties, nature and structure of thermal dust :

- Emission Spectrum :

- Variations of the spectral index β ?

- Variations of the dust opacity σ from place to place ?

composition, form (amorphous, crystalline), shape, inclusions, disorder,

mantles, porosity, coagulation, …

- Relationship with the local conditions

- Dust as a tracer of the ISM : Structure (diffuse clouds to dense cores) Local physical conditions

Interstellar dust with Planck/HFI and Herschel

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Iν = τν0

νν0

⎛

⎝ ⎜

⎞

⎠ ⎟ β

Bν T( ) , with τν0=σν0

NH ?


1. Thermal dust in nearby molecular cloud

Planck early results paper submitted to A&A

on behalf of the Planck collaboration

2. Selection of a few Herschel results Illustrating the complementarity with Planck

Outlines of the presentation


Thermal dust in nearby molecular clouds Complete and unbiased survey

All angular scales, with an unprecedneted control of the photometry Unprecedented Signal to Noise ratio Angular resolution comparable to IRAS

Emission Spectrum of thermal dust

Temperature, spectral index and optical depth for each line of sight

Evolution of the emitting properties

Impact of the emitting properties on the temperature

First results in the Taurus molecular cloud, d=140 pc, b=-15°, no high mass star


IRAS 100 µm (3000 GHz) and HFI maps of the Taurus molecular complex

Noise analysis using simulations: Calibration errors: systematic errors , Statistical errors + CIBA: statistical noise

CMB removed data


Some examples of emission spectra

Square= data, Red square= fitted data (100 µm, 857, 545, 353 and 143 GHz), Error bars not visible (calibration errors, statistical noise, Cosmic IR Background Anisotropies)

Solid line: fitted model, Crosses= fitted model integrated within the bands.

Atomic region Molecular region

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Iν = τν0νν0

⎛

⎝ ⎜

⎞

⎠ ⎟ βBν T( )


A single modified black body gives a reasonable representation of IRAS 100 µm & HFI data

Residuals around 0 and below 1-3%, except: at 353 GHz: around -7 % Distribution of temperature along the lines of sight at 143 GHz: around +13.5 % Flatenning at low frequencies (in the millimeter)

Some examples of emission spectra Atomic region Molecular region


Residual at 217 and 100 GHz…

Some examples of emission spectra Atomic region Molecular region


Residual maps at 217 and 100 GHz

12CO J = 1-0, CfA, Dame et al. 2001

Mainly CO molecular lines : 12CO, but also 13CO, …


Black: all Green: without 12CO. Red: with 12CO but no 13CO Blue: with detected 13CO

Temperature & spectral index maps

13CO J = 1-0, FCRAO Narayanan et al. 2008 & Goldsmith et al. 2008

β around 1.78, systematic error 0.07


Systematic errors: T : 0.7 K, β : 0.07

Noise: T : 0.1 K, β : 0.025

Temperature & spectral index anti-correlation

- Real effect on the emerging spectra - Could reveal intrinsic properties of the emission

mechanisms

For bright pixels (I100 µm > 10 MJy/sr)

Solid line: Archeops (Désert et al. 2008) Dashed line: PRONAOS (Dupac et al. 2003)


Optical depth map

- σ = Opacity Standard value for the diffuse ISM from FIRAS: σ = 1 X 10-25 cm2 , at 250 µm (Boulanger et al. 1996)

Depends on the nature, the structure, the size, the shape of the dust grains (carbon, silicate) and also:

- the presence of mantles - the effects of porosity and coagulation

€

Iν = τν0

νν0

⎛

⎝ ⎜

⎞

⎠ ⎟ β

Bν T( ) , with τν0 =σν0

NH

- Increase of τ / NH (from NIR extinction) by factors 1.5-4 reported in translucent to dense clouds by several authors (from PRONAOS; ISOPHOT, Spitzer)

- Where the transition happens from the diffuse to the dense ISM ? On which angular scale ?

Important for dust physics & proper conversion τ to NH conversion

- Unbiased mapping of the optical depth, from the most diffuse regions to the densest parts.


Optical depth to Opacity 1

€

τ =σ H I

NH I

+ σ H2

NH2

HI 21 cm (Hartmann & Burton 1997), beam: 36’

Pixels with no detected 12CO :

In the atomic phase: σ = (1.1 +/-0.3) X 10-25 cm2 : “standard value”



€

τ H2

=σ H2

NH2

1 X 10-25 cm2

2 X 10-25 cm2

NIR extinction from 2MASS, corrected from the HI contribution (Pineda et al. 2010)

In the molecular phase, where W(12CO) > 3 K km s-1 :



€

τ H2

=σ H2

NH2

NIR extinction from 2MASS, corrected from the HI contribution (Pineda et al. 2010)

1 X 10-25 cm2

2 X 10-25 cm2

where W(12CO) > 3 K km s-1

Impact on the temperature distribution For constant incident radiation field, T α σ - 1 / (4+β)


- Strong impact of opacity variations on the temperature distribution - In the dense filaments : - Decrease of the incident radiation field,

- Decrease of the NIR extinction (increase of Rv) - Tmeasured > Taveraged and σ measured < σ averaged


Comparison FIR maps – T, β, τ Temperature Spectral index β Optical depth τ

The 100 µm emission is very sensitive to the temperature

Interstellar dust with Herschel Main advantages:

Angular resolution SPIRE: 18.1'', 25.2’’ & 36.6'’ at 250, 350 and 500 µm PACS: 5'', 6.7'' & 11''’ at 70, 110 and 170 µm

Spectral coverage of the peak emission of thermal dust: 70, 110, 170, 250 µm

Spectroscopic performances (talk by Edith Falgarone)

Spectral mapping capabilities SPIRE FTS: 194 - 313 µm and 303-671µm, R= 370-1290 (high), 60-200 (Medium), 18-82 (low) PACS: 55 - 210 µm, R=1000-5000

Combination of Mapping and Spectroscopy (SPIRE and PACS) Dust SED: Continuum Physical conditions : Gas lines (mainly CII, OI, NII, high-level lines of CO, … )



Dust emission across the NGC7023 PDR

Nor

mal

ised

pro

files

SPIRE 250 µm

- Density profile + dust model+ Radiative transfert !! ! Evidence abundance variations of the different dust populations Next step: combined analysis of dust & gas observations…

" " " " " " SPIRE ISM consortium/Abergel et al. 2010, initial results "" "

SPIRE & PACS mapping of the RCW 120 hot PDR

SPIRE consortium/Anderson et al. 2010, initial results

24 µm, 70 µm, 250 µm"- Coolling of the dust behind the edge of the PDR"- Indication of T-β anti-correlation"

18ʼ"


SPIRE mapping of the diffuse ISM !


• Thermal dust emission as a tracer of the structure of the ISM

SPIRE ISM & Goult belt consortia Processed using an updated version of SANEPIC (Beelen et al, in prep)

SPIRE mapping of the diffuse ISM !


• Thermal dust emission as a tracer of the structure of the ISM

• Initial results in the Polaris cloud (central square) • SPIRE consortium, Miville-Deschênes et al. 2010

- Power spectrum slope -2.7 ±0.1 - At all scales from 8° to 30”

SPIRE ISM & Goult belt consortia Processed using an updated version of SANEPIC (Beelen et al, in prep)


Conclusions Planck - Precise measurement of the emission spectrum Single modified black body at first order, compatible with post-Spitzer dust models - Unbiased maps of the temperature, of the spectral index and the optical depth Cooling of the dust particles T-β anti correlation on the measured spectra (line of sight averaged) Opacity variations: Systematic increase by a factor around 2 in the molecular phase Av > 1 Indication of coagulation processes Strong impact on the temperature distribution

Herschel - Angular resolution - Combined dust and and gas observations ISM at small angular scales Resolve interfaces : abundance, excitation conditions, physical conditions, …

Planck & Herschel: Uncertainties of the models generally higher than the noise in the data (optical properties, radiative transfert, physical conditions, geometry…)

Emission of thermal dust: powerful tracer of the interstellar matter

Acknowledgements: Planck Collaboration

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