Galactic science with the Planck Spacecraft

EWASS Torku Finland 1

Galactic science with the Planck Spacecraft

Richard Davis

8/7/2013


Thermal Dust in Molecular Clouds

• Planck allows unbiased mapping of Galactic sub-millimetre and millimetre emission from the most diffuse regions to the densest parts of molecular clouds.

• The emission spectrum measured by Planck and IRAS can be fitted pixel by pixel using a single modified blackbody.

8/7/2013



• The temperature map illustrates the cooling of the dust particles in thermal equilibrium with the incident radiation field, from 16−17 K in the diffuse regions to 13−14 K in the dense parts.

• The distribution of spectral indices is centred at 1.78, with a standard deviation of 0.08 and a systematic error of 0.07

8/7/2013



• Some systematic residuals are detected at 353 GHz and 143 GHz, with amplitudes around −7% and +13%, respectively, indicating that the measured spectra are likely more complex than a simple modified blackbody. Significant positive residuals are also detected in the molecular regions and in the 217 GHz and 100 GHz bands, mainly caused by the contribution of the J = 2 → 1 and J = 1 → 0 12CO and 13CO emission lines.

8/7/2013

EWASS Torku Finland 68/7/2013



Dust in the diffuse interstellar mediumand the Galactic halo

• This paper presents the first results from a comparison of Planck dust maps at 353, 545 and 857 GHz, along with IRAS data at 3000 (100 μm) and 5000 GHz (60 μm), with Green Bank Telescope 21-cm observations of Hi in 14 fields covering more than 800 deg2 at high Galactic latitude.

8/7/2013


Dust in the diffuse interstellar mediumand the Galactic halo

• Galactic dust emission for fields with average Hi column density lower than 2 × 1020 cm−2 is well correlated with 21-cm emission because in such diffuse areas the hydrogen is predominantly in the neutral atomic phase.

8/7/2013




The first all-sky surveyof Galactic cold clumps

• We present the statistical properties of the Cold Clump Catalogue of Planck Objects (C3PO), the first all-sky catalogue of cold objects, in terms of their spatial distribution, dust temperature, distance, mass, and morphology. We have combined Planck and IRAS data to extract 10 342 cold sources that stand out against a warmer environment.

8/7/2013



• These cold clumps are not isolated but clustered in groups. Dust temperature and emissivity spectral index values are derived from their spectral energy distributions using both Planck and IRAS data. The temperatures range from 7K to 19K, with a distribution peaking around 13K.

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• The data are inconsistent with a constant value of the associated spectral index β over the whole temperature range: β varies from 1.4 to 2.8, with a mean value around 2.1. Distances are obtained for approximately one third of the objects. Most of the detections lie within 2 kpc of the Sun, but more distant sources are also detected, out to 7 kpc. The mass estimates inferred from dust emission range from 0.4 M to 2.4 × 105 M.

8/7/2013


Properties of the interstellar mediumin the Galactic plane

• Planck has observed the entire sky from 30 GHz to 857 GHz. The observed foreground emission contains contributions from different phases of the interstellar medium (ISM). We have separated the observed Galactic emission into the different gaseous components (atomic, molecular and ionised) in each of a number of Galactocentric rings.

8/7/2013



• Apart from the thermal dust and free-free emission, we have probed the Galaxy for anomalous (e.g., spinning) dust as well as synchrotron emission. We find the dust opacity in the solar neighbourhood, τ/NH = 0.92±0.05×10−25 cm2 at 250 μm, with no significant variation with Galactic radius, even though the dust temperature is seen to vary from over 25 K to under 14 K.

8/7/2013



• For all environments, the anomalous emission is consistent with rotation from polycyclic aromatic hydrocarbons (PAHs) and, according to our simple model, accounts for (25 ± 5)% (statistical) of the total emission at 30 GHz.

8/7/2013




New light on anomalous microwaveemission from spinning dust grains

• Using Planck maps and multi-frequency ancillary data, we have constructed spectra for two known AME regions: the Perseus and ρ Ophiuchi molecular clouds. The spectra are well fitted by a combination of free-free radiation, cosmic microwave background, thermal dust, and electric dipole radiation from small spinning dust grains.

8/7/2013


New light on anomalous microwaveemission from spinning dust grains

• The spinning dust spectra are the most precisely measured to date, and show the high frequency side clearly for the first time. The spectra have a peak in the range 20–40 GHz and are detected at high significances of 17.1σ for Perseus and 8.4σ for ρ Ophiuchi.

• In Perseus, spinning dust in the dense molecular gas can account for most of the AME; the low density atomic gas appears to play a minor role.

• In ρ Ophiuchi, the 30 GHz peak is dominated by ∼dense molecular gas,

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All-sky temperature and dust opticaldepth from Planck and IRAS. Constraints on the “dark gas”

in our Galaxy

• An all sky map of the apparent temperature and optical depth of thermal dust emission is constructed using the Planck-HFI (350 μm to 2 mm) and IRAS (100 μm) data.

• The optical depth maps are correlated with tracers of the atomic (H i) and molecular gas traced by CO. The correlation with the column density of observed gas is linear in the lowest column density regions at high Galactic latitudes

8/7/2013


All-sky temperature and dust opticaldepth from Planck and IRAS. Constraints on the “dark gas”

in our Galaxy

• The average dust emissivity in the Hi phase in the solar neighbourhood is found to be τD/Ntot H = 5.2 × 10−26 cm2 at 857 GHz. It follows roughly a power law distribution with a spectral index β = 1.8 all the way down to 3 mm, although the SED flattens slightly in the millimetre. Taking into account the spectral shape of the dust optical depth, the emissivity is consistent with previous values derived from FIRAS measurements at high latitudes within 10%.

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• The 2D spatial distribution of the dark gas in the solar neighbourhood (|bII| > 10◦) is shown to extend around known molecular regions traced by CO.

• The mass of dark gas is found to be 28% of the atomic gas and 118% of the CO emitting gas in the solar neighbourhood. The Galactic latitude distribution shows that its mass fraction is relatively constant down to a few degrees from the Galactic plane.

8/7/2013




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Galactic science with the Planck Spacecraft

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