Context. The High Frequency Instrument (HFI) is one of the two focal instruments of the Planck mission. It will observe the whole sky in six bands in the 100 GHz–1 THz range. Aims. The HFI instrument ...is designed to measure the cosmic microwave background (CMB) with a sensitivity limited only by fundamental sources: the photon noise of the CMB itself and the residuals left after the removal of foregrounds. The two high frequency bands will provide full maps of the submillimetre sky, featuring mainly extended and point source foregrounds. Systematic effects must be kept at negligible levels or accurately monitored so that the signal can be corrected. This paper describes the HFI design and its characteristics deduced from ground tests and calibration. Methods. The HFI instrumental concept and architecture are feasible only by pushing new techniques to their extreme capabilities, mainly: (i) bolometers working at 100 mK and absorbing the radiation in grids; (ii) a dilution cooler providing 100 mK in microgravity conditions; (iii) a new type of AC biased readout electronics and (iv) optical channels using devices inspired from radio and infrared techniques. Results. The Planck-HFI instrument performance exceeds requirements for sensitivity and control of systematic effects. During ground-based calibration and tests, it was measured at instrument and system levels to be close to or better than the goal specification.
Aims. We present data from the CFHTLS Strong Lensing Legacy Survey (SL2S). Due to the unsurpassed combined depth, area and image quality of the Canada-France-Hawaii Legacy Survey it is becoming ...possible to uncover a large, statistically well-defined sample of strong gravitational lenses which spans the dark halo mass spectrum predicted by the concordance model from galaxy to cluster haloes. Methods. We describe the development of several automated procedures to find strong lenses of various mass regimes in CFHTLS images. Results. The preliminary sample of about 40 strong lensing candidates discovered in the CFHTLS T0002 release, covering an effective field of view of 28 deg super(2) is presented. These strong lensing systems were discovered using an automated search and consist mainly of gravitational arc systems with splitting angles between 2 and 15 arcsec. This sample shows for the first time that it is possible to uncover a large population of strong lenses from galaxy groups with typical halo masses of about 10 6h 6M_\odot. We discuss the future evolution of the SL2S project and its main scientific aims for the next 3 years, in particular our observational strategy to extract the hundreds of gravitational rings also present in these fields.
The existence of strong lensing systems with Einstein radii covering the full mass spectrum, from ∼$1{-}2\arcsec$ (produced by galaxy scale dark matter haloes) to >$10\arcsec$ (produced by galaxy ...cluster scale haloes) have long been predicted. Many lenses with Einstein radii around $1{-}2\arcsec$ and above $10\arcsec$ have been reported but very few in between. In this article, we present a sample of 13 strong lensing systems with Einstein radii in the range $3\arcsec{-}8\arcsec$ (or image separations in the range $6\arcsec{-}16\arcsec$), i.e. systems produced by galaxy group scale dark matter haloes. This group sample spans a redshift range from 0.3 to 0.8. This opens a new window of exploration in the mass spectrum, around 1013–1014 $M_{\odot}$, a crucial range for understanding the transition between galaxies and galaxy clusters, and a range that have not been extensively probed with lensing techniques. These systems constitute a subsample of the Strong Lensing Legacy Survey (SL2S), which aims to discover strong lensing systems in the Canada France Hawaii Telescope Legacy Survey (CFHTLS). The sample is based on a search over 100 square degrees, implying a number density of ~0.13 groups per square degree. Our analysis is based on multi-colour CFHTLS images complemented with Hubble Space Telescope imaging and ground based spectroscopy. Large scale properties are derived from both the light distribution of elliptical galaxies group members and weak lensing of the faint background galaxy population. On small scales, the strong lensing analysis yields Einstein radii between 2.5″ and 8″. On larger scales, strong lens centres coincide with peaks of light distribution, suggesting that light traces mass. Most of the luminosity maps have complicated shapes, implying that these intermediate mass structures may be dynamically young. A weak lensing signal is detected for 6 groups and upper limits are provided for 6 others. Fitting the reduced shear with a Singular Isothermal Sphere, we find $\sigma_{\rm SIS}\,\sim 500$ km s-1 with large error bars and an upper limit of ~900 km s-1 for the whole sample (except for the highest redshift structure whose velocity dispersion is consistent with that of a galaxy cluster). The mass-to-light ratio for the sample is found to be $M/L_i$ ~ 250 (solar units, corrected for evolution), with an upper limit of 500. This compares with mass-to-light ratios of small groups (with $\sigma_{\rm SIS} \sim 300$ km s-1) and galaxy clusters (with $\sigma_{\rm SIS} > 1000$ km s-1), thus bridging the gap between these mass scales. The group sample released in this paper will be complemented with other observations, providing a unique sample to study this important intermediate mass range in further detail.
Context. The Strong Lensing Legacy Survey (SL2S) provides a sample of the strong lensing events associated with massive distant galaxies, some of which lie in the outskirts of galaxy groups and ...clusters. Aims. We investigate the internal structure of early-type galaxies in overdense environments, where tidal forces are expected to alter dark matter haloes of infalling galaxies. Methods. SL2SJ02176-0513 is a remarkable lens for the presence of two multiply-imaged systems at different redshifts lensed by a foreground massive galaxy at zlens = 0.656: a bright cusp arc at zarc = 1.847 and an additional double-image system at an estimated redshift of zdbl ~ 2.9 based on photometry and lensing geometry. The system is located about 400 kpc away from the centre of a massive group of galaxies. Mass estimates for the group are available from X-ray observations and satellite kinematics. Multicolour photometry provides an estimate of the stellar mass of the main lens galaxy. The lensing galaxy is modelled with two components (stars and dark matter), and we include the perturbing effect of the group environment and all available constraints. Results. We find that classic lensing degeneracies, e.g. between external convergence and mass density slope, are significantly reduced with respect to standard systems and infer tight constraints on the mass density profile: (i) the dark matter content of the main lens galaxy is in line with that of typical galaxies $f_{\rm dm}({<}R_{\rm e})=0.41^{+0.09}_{-0.06}$; (ii) the required mass associated with the dark matter halo of the nearby group is consistent with X-ray $(\sigma_{\rm grp}=550^{+130}_{-240})$; (iii) accounting for the group contribution in the form of an external convergence, the slope of the mass density profile of the main lens galaxy alone is found to be $\alpha=-1.03^{+0.22}_{-0.16}$, consistent with the isothermal (α = -1) slope. Conclusions. We demonstrate that multiple source plane systems together with good ancillary dataset can be used to disentangle local and environmental effects.
Context. The new generation of wide-field optical imaging as the Canada France Hawaii Telescope Legacy Survey (CFHTLS) enables discoveries of all types of gravitational lenses present in the sky. The ...Strong Lensing Legacy Survey (SL2S) project has started an inventory of clusters or groups of galaxies lenses and of Einstein rings around distant massive ellipticals. Aims. Here we attempt to extend this inventory by finding lensing events produced by massive edge-on disk galaxies that remain a poorly documented class of lenses. Methods. We implemented and tested an automated search procedure of edge-on galaxy lenses in the CFHTLS Wide fields with magnitude 18<i<21, inclination angle lower than $25\degr$, and a photometric redshift determination. This procedure estimated the lensing convergence of each galaxy from the Tully-Fisher law and selected only those few candidates that exhibit a possibly nearby arc configuration at a radius compatible with this convergence ($r_\mathrm{arc}$ ≲ 2 $r_\mathrm{E}$). The efficiency of the procedure was tested after a visual examination of the whole initial sample of 30 444 individual edge-on disks. Results. After calculating the surface density of edge-on lenses possibly detected in a survey for a given seeing, we deduce that this theoretical number is about 10 for the CFHTLS Wide, a number in broad agreement with the 2 good candidates detected here. We show that the Tully-Fisher selection method is very efficient at finding valuable candidates, though its accuracy depends on the quality of the photometric redshift of the lenses. Finally, we argue that future surveys will detect at least a hundred of such lens candidates.
Planck has produced detailed all-sky observations over nine frequency bands between 30 and 857 GHz. These observations allow robust reconstruction of the primordial cosmic microwave background (CMB) ...temperature fluctuations over nearly the full sky, as well as new constraints on Galactic foregrounds, including thermal dust and line emission from molecular carbon monoxide (CO). This paper describes the component separation framework adopted by Planck for many cosmological analyses, including CMB power spectrum determination and likelihood construction on large angular scales, studies of primordial non-Gaussianity and statistical isotropy, the integrated Sachs-Wolfe effect, gravitational lensing, and searches for topological defects. We test four foreground-cleaned CMB maps derived using qualitatively different component separation algorithms. The quality of our reconstructions is evaluated through detailed simulations and internal comparisons, and shown through various tests to be internally consistent and robust for CMB power spectrum and cosmological parameter estimation up to ℓ = 2000. The parameter constraints on ΛCDM cosmologies derived from these maps are consistent with those presented in the cross-spectrum based Planck likelihood analysis. We choose two of the CMB maps for specific scientific goals. We also present maps and frequency spectra of the Galactic low-frequency, CO, and thermal dust emission. The component maps are found to provide a faithful representation of the sky, as evaluated by simulations, with the largest bias seen in the CO component at 3%. For the low-frequency component, the spectral index varies widely over the sky, ranging from about β = −4 to − 2. Considering both morphology and prior knowledge of the low frequencycomponents, the index map allows us to associate a steep spectral index (β< −3.2) with strong anomalous microwave emission, corresponding to a spinning dust spectrum peaking below 20 GHz, a flat index of β> −2.3 with strong free-free emission, and intermediate values with synchrotron emission.
Rotational transition lines of CO play a major role in molecular radio astronomy as a mass tracer and in particular in the study of star formation and Galactic structure. Although a wealth of data ...exists for the Galactic plane and some well-known molecular clouds, there is no available high sensitivity all-sky survey of CO emission to date. Such all-sky surveys can be constructed using the Planck HFI data because the three lowest CO rotational transition lines at 115, 230 and 345 GHz significantly contribute to the signal of the 100, 217 and 353 GHz HFI channels, respectively. Two different component separation methods are used to extract the CO maps from Planck HFI data. The maps obtained are then compared to one another and to existing external CO surveys. From these quality checks the best CO maps, in terms of signal to noise ratio and/or residual contamination by other emission, are selected. Three different sets of velocity-integrated CO emission maps are produced with different trade-offs between signal-to-noise, angular resolution, and reliability. Maps for the CO J = 1 → 0, J = 2 → 1, and J = 3 → 2 rotational transitions are presented and described in detail. They are shown to be fully compatible with previous surveys of parts of the Galactic plane as well as with undersampled surveys of the high latitude sky. The Planck HFI velocity-integrated CO maps for the J = 1 → 0, J = 2 → 1, and J = 3 →2 rotational transitions provide an unprecedented all-sky CO view of the Galaxy. These maps are also of great interest to monitor potential CO contamination of the Planck studies of the cosmological microwave background.
Planck intermediate results Adam, R; Ade, P A R; Aghanim, N ...
Astronomy and astrophysics (Berlin),
02/2016, Letnik:
586
Journal Article
Recenzirano
Odprti dostop
The role of the magnetic field in the formation of the filamentary structures observed in the interstellar medium (ISM) is a debated topic owing to the paucity of relevant observations needed to test ...existing models. The Planck all-sky maps of linearly polarized emission from dust at 353 GHz provide the required combination of imaging and statistics to study the correlation between the structures of the Galactic magnetic field and of interstellar matter over the whole sky, both in the diffuse ISM and in molecular clouds. We focus our study on structures at intermediate and high Galactic latitudes, which cover two orders of magnitude in column density, from 1020 to 1022 cm-2. We use analytical models to account for projection effects. We discuss our results in the context of models and MHD simulations, which attempt to describe the respective roles of turbulence, magnetic field, and self-gravity in the formation of structures in the magnetized ISM.
This paper describes the methods used to produce photometrically calibrated maps from the Planck High Frequency Instrument (HFI) cleaned, time-ordered information. HFI observes the sky over a broad ...range of frequencies, from 100 to 857 GHz. To obtain the best calibration accuracy over such a large range, two different photometric calibration schemes have to be used. The 545 and 857 GHz data are calibrated by comparing flux-density measurements of Uranus and Neptune with models of their atmospheric emission. The lower frequencies (below 353 GHz) are calibrated using the solar dipole. A component of this anisotropy is time-variable, owing to the orbital motion of the satellite in the solar system. Photometric calibration is thus tightly linked to mapmaking, which also addresses low-frequency noise removal. By comparing observations taken more than one year apart in the same configuration, we have identified apparent gain variations with time. These variations are induced by non-linearities in the read-out electronics chain. We have developed an effective correction to limit their effect on calibration. We present several methods to estimate the precision of the photometric calibration. We distinguish relative uncertainties (between detectors, or between frequencies) and absolute uncertainties. Absolute uncertainties lie in the range from 0.54% to 10% from 100 to 857 GHz. We describe the pipeline used to produce the maps from the HFI timelines, based on the photometric calibration parameters, and the scheme used to set the zero level of the maps a posteriori. We also discuss the cross-calibration between HFI and the SPIRE instrument on board Herschel. Finally we summarize the basic characteristics of the set of HFI maps included in the 2013 Planck data release.
Wedescribe the processing of the 531 billion raw data samples from the High Frequency Instrument (HFI), which we performed to produce six temperature maps from the first 473 days of Planck-HFI survey ...data. These maps provide an accurate rendition of the sky emission at 100, 143, 217, 353, 545, and 857GHz with an angular resolution ranging from 9.́7 to 4.́6. The detector noise per (effective) beam solid angle is respectively, 10, 6 , 12, and 39 μK in the four lowest HFI frequency channels (100−353GHz) and 13 and 14 kJy sr-1 in the 545 and 857 GHz channels. Relative to the 143 GHz channel, these two high frequency channels are calibrated to within 5% and the 353 GHz channel to the percent level. The 100 and 217 GHz channels, which together with the 143 GHz channel determine the high-multipole part of the CMB power spectrum (50 <ℓ < 2500), are calibrated relative to 143 GHz to better than 0.2%.
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