77 research outputs found
A Vega--like disk associated with the planetary system of rho (1) CNC
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Improved constraints on the expansion rate of the Universe up to z~1.1 from the spectroscopic evolution of cosmic chronometers
We present new improved constraints on the Hubble parameter H(z) in the
redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic
evolution of early-type galaxies as a function of redshift. We extract a large
sample of early-type galaxies (\sim11000) from several spectroscopic surveys,
spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We
select the most massive, red elliptical galaxies, passively evolving and
without signature of ongoing star formation. Those galaxies can be used as
standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002),
whose differential age evolution as a function of cosmic time directly probes
H(z). We analyze the 4000 {\AA} break (D4000) as a function of redshift, use
stellar population synthesis models to theoretically calibrate the dependence
of the differential age evolution on the differential D4000, and estimate the
Hubble parameter taking into account both statistical and systematical errors.
We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in
H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z
\sim 1.1; for the first time, we place a constraint on H(z) at z \neq 0 with a
precision comparable with the one achieved for the Hubble constant (about 5-6%
at z \sim 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial
to distinguish many different quintessence cosmologies. These measurements have
been tested to best match a \Lambda CDM model, clearly providing a
statistically robust indication that the Universe is undergoing an accelerated
expansion. This method shows the potentiality to open a new avenue in constrain
a variety of alternative cosmologies, especially when future surveys (e.g.
Euclid) will open the possibility to extend it up to z \sim 2.Comment: 34 pages, 15 figures, 6 tables, published in JCAP. It is a companion
to Moresco et al. (2012b, http://arxiv.org/abs/1201.6658) and Jimenez et al.
(2012, http://arxiv.org/abs/1201.3608). The H(z) data can be downloaded at
http://www.physics-astronomy.unibo.it/en/research/areas/astrophysics/cosmology-with-cosmic-chronometer
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. 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 XVIII: The power spectrum of cosmic infrared background anisotropies
Using Planck maps of six regions of low Galactic dust emission with a total area of about 140 deg2, we determine the angular power spectra of
cosmic infrared background (CIB) anisotropies from multipole â = 200 to â = 2000 at 217, 353, 545 and 857 GHz. We use 21-cm observations of
Hi as a tracer of thermal dust emission to reduce the already low level of Galactic dust emission and use the 143 GHz Planck maps in these fields
to clean out cosmic microwave background anisotropies. Both of these cleaning processes are necessary to avoid significant contamination of the
CIB signal. We measure correlated CIB structure across frequencies. As expected, the correlation decreases with increasing frequency separation,
because the contribution of high-redshift galaxies to CIB anisotropies increases with wavelengths. We find no significant difference between the
frequency spectrum of the CIB anisotropies and the CIB mean, with âI/I=15% from 217 to 857 GHz. In terms of clustering properties, the
Planck data alone rule out the linear scale- and redshift-independent bias model. Non-linear corrections are significant. Consequently, we develop
an alternative model that couples a dusty galaxy, parametric evolution model with a simple halo-model approach. It provides an excellent fit to
the measured anisotropy angular power spectra and suggests that a different halo occupation distribution is required at each frequency, which
is consistent with our expectation that each frequency is dominated by contributions from different redshifts. In our best-fit model, half of the
anisotropy power at â=2000 comes from redshifts z 2 at 353
and 217 GHz, respectively
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. 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 âŒ10â60 GHz. Using Planck maps
and multi-frequency ancillary data, we have constructed spectra for two known AME regions: the Perseus and Ï 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 20â40 GHz and are detected at high significances of 17.1Ï for Perseus and 8.4Ï for Ï 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 Ï Ophiuchi, the âŒ30 GHz peak is dominated by dense molecular gas, but there is an indication of an extended tail at frequencies 50â100 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
- âŠ