45 research outputs found
Planck early results III : First assessment of the Low Frequency Instrument in-flight performance
Peer reviewe
Planck early results XVII : Origin of the submillimetre excess dust emission in the Magellanic Clouds
Peer reviewe
Planck early results XXIV : Dust in the diffuse interstellar medium and the Galactic halo
Peer reviewe
Planck early results. XVII. Origin of the submillimetre excess dust emission in the Magellanic Clouds
The integrated spectral energy distributions (SED) of the Large Magellanic Cloud (LMC) and SmallMagellanic Cloud (SMC) appear significantly
flatter than expected from dust models based on their far-infrared and radio emission. The still unexplained origin of this millimetre excess is
investigated here using the Planck data. The integrated SED of the two galaxies before subtraction of the foreground (Milky Way) and background
(CMB fluctuations) emission are in good agreement with previous determinations, confirming the presence of the millimetre excess. In the context
of this preliminary analysis we do not propose a full multi-component fitting of the data, but instead subtract contributions unrelated to the galaxies
and to dust emission.
The background CMB contribution is subtracted using an internal linear combination (ILC) method performed locally around the galaxies. The
foreground emission from the Milky Way is subtracted as a Galactic Hi template, and the dust emissivity is derived in a region surrounding the
two galaxies and dominated by Milky Way emission. After subtraction, the remaining emission of both galaxies correlates closely with the atomic
and molecular gas emission of the LMC and SMC. The millimetre excess in the LMC can be explained by CMB fluctuations, but a significant
excess is still present in the SMC SED. The Planck and IRASâIRIS data at 100 ÎŒm are combined to produce thermal dust temperature and optical
depth maps of the two galaxies. The LMC temperature map shows the presence of a warm inner arm already found with the Spitzer data, but which also shows the existence of a
previously unidentified cold outer arm. Several cold regions are found along this arm, some of which are associated with known molecular clouds.
The dust optical depth maps are used to constrain the thermal dust emissivity power-law index (ÎČ). The average spectral index is found to be
consistent with ÎČ =1.5 and ÎČ =1.2 below 500 ÎŒm for the LMC and SMC respectively, significantly flatter than the values observed in the Milky
Way. Also, there is evidence in the SMC of a further flattening of the SED in the sub-mm, unlike for the LMC where the SED remains consistent
with ÎČ =1.5. The spatial distribution of the millimetre dust excess in the SMC follows the gas and thermal dust distribution. Different models are
explored in order to fit the dust emission in the SMC. It is concluded that the millimetre excess is unlikely to be caused by very cold dust emission
and that it could be due to a combination of spinning dust emission and thermal dust emission by more amorphous dust grains than those present
in our Galaxy
Planck early results. XXII. The submillimetre properties of a sample of Galactic cold clumps
We perform a detailed investigation of sources from the Cold Cores Catalogue of Planck Objects (C3PO). Our goal is to probe the reliability
of the detections, validate the separation between warm and cold dust emission components, provide the first glimpse at the nature, internal
morphology and physical characterictics of the Planck-detected sources. We focus on a sub-sample of ten sources from the C3PO list, selected to
sample different environments, from high latitude cirrus to nearby (150 pc) and remote (2 kpc) molecular complexes. We present Planck surface
brightness maps and derive the dust temperature, emissivity spectral index, and column densities of the fields. With the help of higher resolution
Herschel and AKARI continuum observations and molecular line data, we investigate the morphology of the sources and the properties of the
substructures at scales below the Planck beam size. The cold clumps detected by Planck are found to be located on large-scale filamentary (or
cometary) structures that extend up to 20 pc in the remote sources. The thickness of these filaments ranges between 0.3 and 3 pc, for column
densities NH2 ⌠0.1 to 1.6 Ă 1022 cmâ2, and with linear mass density covering a broad range, between 15 and 400 M pcâ1. The dust temperatures
are low (between 10 and 15K) and the Planck cold clumps correspond to local minima of the line-of-sight averaged dust temperature in these
fields. These low temperatures are confirmed when AKARI and Herschel data are added to the spectral energy distributions. Herschel data reveal
a wealth of substructure within the Planck cold clumps. In all cases (except two sources harbouring young stellar objects), the substructures are
found to be colder, with temperatures as low as 7 K. Molecular line observations provide gas column densities which are consistent with those
inferred from the dust. The linewidths are all supra-thermal, providing large virial linear mass densities in the range 10 to 300 M pcâ1, comparable
within factors of a few, to the gas linear mass densities. The analysis of this small set of cold clumps already probes a broad variety of structures
in the C3PO sample, probably associated with different evolutionary stages, from cold and starless clumps, to young protostellar objects still
embedded in their cold surrounding cloud. Because of the all-sky coverage and its sensitivity, Planck is able to detect and locate the coldest spots
in massive elongated structures that may be the long-searched for progenitors of stellar clusters
Planck early results. XXV. Thermal dust in nearby 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. We present an early analysis of the Taurus molecular complex, on line-of-sight-averaged data and without component separation. The
emission spectrum measured by Planck and IRAS can be fitted pixel by pixel using a single modified blackbody. Some systematic residuals are
detected at 353 GHz and 143 GHz, with amplitudes around â7% 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 â 1 and J = 1 â 0 12CO and 13CO emission lines. We derive maps of the
dust temperature T, the dust spectral emissivity index ÎČ, and the dust optical depth at 250 ÎŒm Ï250. The temperature map illustrates the cooling
of the dust particles in thermal equilibrium with the incident radiation field, from 16â17 K in the diffuse regions to 13â14 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. We detect a significant
T â ÎČ anti-correlation. The dust optical depth map reveals the spatial distribution of the column density of the molecular complex from the densest
molecular regions to the faint diffuse regions.We use near-infrared extinction and Hi data at 21-cm to perform a quantitative analysis of the spatial
variations of the measured dust optical depth at 250 ÎŒm per hydrogen atom Ï250/NH. We report an increase of Ï250/NH by a factor of about 2
between the atomic phase and the molecular phase, which has a strong impact on the equilibrium temperature of the dust particles