35 research outputs found
Planck early results. IX. XMM-Newton follow-up for validation of Planck cluster candidates
We present the XMM-Newton follow-up for confirmation of Planck cluster candidates. Twenty-five candidates have been observed to date using
snapshot (∼10 ks) exposures, ten as part of a pilot programme to sample a low range of signal-to-noise ratios (4 < S/N < 6), and a further 15 in a
programme to observe a sample of S/N > 5 candidates. The sensitivity and spatial resolution of XMM-Newton allows unambiguous discrimination
between clusters and false candidates. The 4 false candidates have S/N ≤ 4.1. A total of 21 candidates are confirmed as extended X-ray sources.
Seventeen are single clusters, the majority of which are found to have highly irregular and disturbed morphologies (about ∼70%). The remaining
four sources are multiple systems, including the unexpected discovery of a supercluster at z = 0.45. For 20 sources we are able to derive a redshift
estimate from the X-ray Fe K line (albeit of variable quality). The new clusters span the redshift range 0.09 <∼ z <∼ 0.54, with a median redshift
of z ∼ 0.37. A first determination is made of their X-ray properties including the characteristic size, which is used to improve the estimate of
the SZ Compton parameter, Y500. The follow-up validation programme has helped to optimise the Planck candidate selection process. It has also
provided a preview of the X-ray properties of these newly-discovered clusters, allowing comparison with their SZ properties, and to the X-ray
and SZ properties of known clusters observed in the Planck survey. Our results suggest that Planck may have started to reveal a non-negligible
population of massive dynamically perturbed objects that is under-represented in X-ray surveys. However, despite their particular properties, these
new clusters appear to follow the Y500–YX relation established for X-ray selected objects, where YX is the product of the gas mass and temperature
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 IRAS–IRIS data at 100 μm 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 (β). The average spectral index is found to be
consistent with β =1.5 and β =1.2 below 500 μm 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 β =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. XIII. Statistical properties of extragalactic radio sources in the Planck Early Release Compact Source Catalogue
The data reported in Planck’s Early Release Compact Source Catalogue (ERCSC) are exploited to measure the number counts (dN/dS) of
extragalactic radio sources at 30, 44, 70, 100, 143 and 217 GHz. Due to the full-sky nature of the catalogue, this measurement extends to the
rarest and brightest sources in the sky. At lower frequencies (30, 44, and 70 GHz) our counts are in very good agreement with estimates based on
WMAP data, being somewhat deeper at 30 and 70 GHz, and somewhat shallower at 44 GHz. Planck’s source counts at 143 and 217 GHz join
smoothly with the fainter ones provided by the SPT and ACT surveys over small fractions of the sky. An analysis of source spectra, exploiting
Planck’s uniquely broad spectral coverage, finds clear evidence of a steepening of the mean spectral index above about 70 GHz. This implies
that, at these frequencies, the contamination of the CMB power spectrum by radio sources below the detection limit is significantly lower than
previously estimated
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 × 1022 cm−2, and with linear mass density covering a broad range, between 15 and 400 M pc−1. 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 pc−1, 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. XX. New light on anomalous microwave emission from spinning dust grains
Anomalous microwave emission (AME) has been observed by numerous experiments in the frequency range ∼10–60 GHz. 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. 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, but there is an indication of an extended tail at frequencies 50–100 GHz,
which can be accounted for by irradiated low density atomic gas. The dust parameters are consistent with those derived from other measurements.
We have also searched the Planck map at 28.5 GHz for candidate AME regions, by subtracting a simple model of the synchrotron, free-free, and
thermal dust. We present spectra for two of the candidates; S140 and S235 are bright Hii regions that show evidence for AME, and are well fitted
by spinning dust models
Planck early results. XV. Spectral energy distributions and radio continuum spectra of northern extragalactic radio sources
Spectral energy distributions (SEDs) and radio continuum spectra are presented for a northern sample of 104 extragalactic radio sources, based
on the Planck Early Release Compact Source Catalogue (ERCSC) and simultaneous multifrequency data. The nine Planck frequencies, from 30
to 857 GHz, are complemented by a set of simultaneous observations ranging from radio to gamma-rays. This is the first extensive frequency
coverage in the radio and millimetre domains for an essentially complete sample of extragalactic radio sources, and it shows how the individual
shocks, each in their own phase of development, shape the radio spectra as they move in the relativistic jet. The SEDs presented in this paper
were fitted with second and third degree polynomials to estimate the frequencies of the synchrotron and inverse Compton (IC) peaks, and the
spectral indices of low and high frequency radio data, including the Planck ERCSC data, were calculated. SED modelling methods are discussed,
with an emphasis on proper, physical modelling of the synchrotron bump using multiple components. Planck ERCSC data also suggest that the
original accelerated electron energy spectrum could be much harder than commonly thought, with power-law index around 1.5 instead of the
canonical 2.5. The implications of this are discussed for the acceleration mechanisms effective in blazar shocks. Furthermore in many cases the
Planck data indicate that gamma-ray emission must originate in the same shocks that produce the radio emission
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