49 research outputs found
Planck intermediate results: IV. the XMM-Newton validation programme for new Planck galaxy clusters
Planck early results. XXVI. Detection with Planck and confirmation by XMM-Newton of PLCK G266.6-27.3, an exceptionally X-ray luminous and massive galaxy cluster at z ~ 1
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. 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
Planck early results. XIII. Statistical properties of extragalactic radio sources in the Planck Early Release Compact Source Catalogue
The data reported in Planckâs 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. Planckâs 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
Planckâs 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 XXVI: Detection with Planck and confirmation by XMM-Newton of PLCK G266.6-27.3, an exceptionally X-ray luminous and massive galaxy cluster at z~1
We present first results on PLCK G266.6-27.3, a galaxy cluster candidate
detected at a signal-to-noise ratio of 5 in the Planck All Sky survey. An
XMM-Newton validation observation has allowed us to confirm that the candidate
is a bona fide galaxy cluster. With these X-ray data we measure an accurate
redshift, z = 0.94 +/- 0.02, and estimate the cluster mass to be M_500 = (7.8
+/- 0.8)e+14 solar masses. PLCK G266.6-27.3 is an exceptional system: its
luminosity of L_X(0.5-2.0 keV)=(1.4 +/- 0.05)e+45 erg/s, equals that of the two
most luminous known clusters in the z > 0.5 universe, and it is one of the most
massive clusters at z~1. Moreover, unlike the majority of high-redshift
clusters, PLCK G266.6-27.3 appears to be highly relaxed. This observation
confirms Planck's capability of detecting high-redshift, high-mass clusters,
and opens the way to the systematic study of population evolution in the
exponential tail of the mass function.Comment: 6 pages, 3 figures; final version accepted for publication in A&A ;
minor changes in Sec.2.,3.2 and 4.1; Table 1: misprint on R500 error
corrected; abundance value adde