arXiv subjects

F. K. Hansen

Publications and source records attributed to F. K. Hansen.

At least 145 records · Page 8Linked to original sources

arXiv2011

Planck early results. III. First assessment of the Low Frequency Instrument in-flight performance

The scientific performance of the Planck Low Frequency Instrument (LFI) after one year of in-orbit operation is presented. We describe the main optical parameters and discuss photometric calibration, white noise sensitivity, and noise properties. A preliminary evaluation of the impact of the main systematic effects is presented. For each of the performance parameters, we outline the methods used to obtain them from the flight data and provide a comparison with pre-launch ground assessments, which are essentially confirmed in flight.

astro-ph.CO↗

arXiv2011

Planck early results. XXI. Properties of the interstellar medium in the Galactic plane

(abridged) Planck has observed the entire sky from 30 GHz to 857GHz. The observed foreground emission contains contributions from different phases of the interstellar medium (ISM). We have separated the observed Galactic emission into the different gaseous components (atomic, molecular and ionised) in each of a number of Galactocentric rings. Templates are created for various Galactocentric radii using velocity information from atomic (neutral hydrogen) and molecular (12CO) observations. The ionised template is assumed to be traced by free-free emission as observed by WMAP, while 408 MHz emission is used to trace the synchrotron component. Gas emission not traced by the above templates, namely "ark gas", as evidenced using Planck data, is included as an additional template, the first time such a component has been used in this way. These templates are then correlated with each of the Planck frequency bands, as well as other ancillary data. The emission per column density of the gas templates allows us to create distinct spectral energy distributions (SEDs) per Galactocentric ring and in each of the gaseous tracers from 1.4 GHz to 25 THz (12μm). Apart from the thermal dust and free-free emission, we have probed the Galaxy for anomalous (e.g., spinning) dust as well as synchrotron emission. We show that anomalous dust emission is present in the atomic, molecular and dark gas phases throughout the Galactic disk. The derived dust propeties associated with the dark gas phase are derived but do not allow us to reveal the nature of this phase. For all environments, the anomalous emission is consistent with rotation from polycyclic aromatic hydrocarbons (PAHs) and, according to our simple model, accounts for $(25\pm5)%$ (statistical) of the total emission at 30 GHz.

astro-ph.GA↗

arXiv2011

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 Rho 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 17.1 sigma for Perseus and 8.4 sigma for Rho 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 Rho 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.

astro-ph.GA↗

arXiv2011

Planck Early Results. V. The Low Frequency Instrument data processing

We describe the processing of data from the Low Frequency Instrument (LFI) used in production of the Planck Early Release Compact Source Catalogue (ERCSC). In particular, we discuss the steps involved in reducing the data from telemetry packets to cleaned, calibrated, time-ordered data (TOD) and frequency maps. Data are continuously calibrated using the modulation of the temperature of the cosmic microwave background radiation induced by the motion of the spacecraft. Noise properties are estimated from TOD from which the sky signal has been removed using a generalized least square map-making algorithm. Measured 1/f noise knee-frequencies range from 100mHz at 30GHz to a few tens of mHz at 70GHz. A destriping code (Madam) is employed to combine radiometric data and pointing information into sky maps, minimizing the variance of correlated noise. Noise covariance matrices required to compute statistical uncertainties on LFI and Planck products are also produced. Main beams are estimated down to the approx -10dB level using Jupiter transits, which are also used for geometrical calibration of the focal plane.

astro-ph.IM↗

arXiv2011

Planck Early Results XXIV: Dust in the diffuse interstellar medium and the Galactic halo

This paper presents the first results of comparison of Planck along with IRAS data with Green Bank Telescope 21-cm observations in 14 fields covering more than 800 square degrees at high Galactic latitude. Galactic dust emission for fields with average HI column density lower than 2 x 10^20 cm^-2 is well correlated with 21-cm emission. The residual emission in these fields, once the HI-correlated emission is removed, is consistent with the expected statistical properties of the cosmic infrared background fluctuations. Fields with larger column densities show significant excess dust emission compared to the HI column density. Regions of excess lie in organized structures that suggest the presence of hydrogen in molecular form, though they are not always correlated with CO emission. Dust emission from intermediate-velocity clouds is detected with high significance. Its spectral properties are consistent with, compared to the local ISM values, significantly hotter dust (T~20 K), lower sub-millimeter dust opacity, and a relative abundance of very small grains to large grains about four times higher. These results are compatible with expectations for clouds that are part of the Galactic fountain in which there is dust shattering and fragmentation. Correlated dust emission in HVCs is not detected; the average of the 99.9% confidence upper limits to the emissivity is 0.15 times the local ISM value at 857 and 3000 GHz, in accordance with gas phase evidence for lower metallicity and depletion in these clouds. Unexpected anti-correlated variations of the dust temperature and emission cross-section per H atom are identified in the local ISM and IVCs, a trend that continues into molecular environments. This suggests that dust growth through aggregation, seen in molecular clouds, is active much earlier in the cloud condensation and star formation processes.

astro-ph.GA↗

arXiv2011

Introducing Mexican needlets for CMB analysis: Issues for practical applications and comparison with standard needlets

Over the last few years, needlets have a emerged as a useful tool for the analysis of Cosmic Microwave Background (CMB) data. Our aim in this paper is first to introduce in the CMB literature a different form of needlets, known as Mexican needlets, first discussed in the mathematical literature by Geller and Mayeli (2009a,b). We then proceed with an extensive study of the properties of both standard and Mexican needlets; these properties depend on some parameters which can be tuned in order to optimize the performance for a given application. Our second aim in this paper is then to give practical advice on how to adjust these parameters in order to achieve the best properties for a given problem in CMB data analysis. In particular we investigate localization properties in real and harmonic spaces and propose a recipe on how to quantify the influence of galactic and point source masks on the needlet coefficients. We also show that for certain parameter values, the Mexican needlets provide a close approximation to the Spherical Mexican Hat Wavelets (whence their name), with some advantages concerning their numerical implementation and the derivation of their statistical properties.

astro-ph.CO↗

arXiv2011

Planck Early Results: 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 -7 % 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 to the contribution of the J=2-1 and J=1-0 12CO and 13CO emission lines. We derive maps of the dust temperature T, the dust spectral emissivity index beta, and the dust optical depth at 250 microns tau. The temperature map illustrates the cooling of the dust particles in thermal equilibrium with the incident radiation field, from 16-17 K in the diffuse regions to 13-14 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-beta 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 microns per hydrogen atom tau/NH. We report an increase of tau/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.

astro-ph.GA↗

arXiv2011

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 square degrees, we determine the angular power spectra of cosmic infrared background (CIB) anisotropies from multipole l = 200 to l = 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 Delta I/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 l=2000 comes from redshifts z<0.8 at 857 GHz and z<1.5 at 545 GHz, while about 90% come from redshifts z>2 at 353 and 217 GHz, respectively.

astro-ph.CO↗

arXiv2011

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.

astro-ph.CO↗

arXiv2011

Planck Early Results. VII. The Early Release Compact Source Catalog

(Abridged) A brief description of the methodology of construction, contents and usage of the Planck Early Release Compact Source Catalogue (ERCSC), including the Early Cold Cores (ECC) and the Early Sunyaev-Zeldovich (ESZ) cluster catalogue is provided. The catalogue is based on data that consist of mapping the entire sky once and 60% of the sky a second time by Planck, thereby comprising the first high sensitivity radio/submillimetre observations of the entire sky. A Monte-Carlo algorithm based on the injection and extraction of artificial sources into the Planck maps was implemented to select reliable sources among all extracted candidates such that the cumulative reliability of the catalogue is >=90%. The 10sigma photometric flux density limit of the catalogue at |b|>30 deg is 0.49, 1.0, 0.67, 0.5, 0.33, 0.28, 0.25, 0.47 and 0.82 Jy at each of the nine frequencies between 30 and 857 GHz. Sources which are up to a factor of ~2 fainter than this limit, and which are present in "clean" regions of the Galaxy where the sky background due to emission from the interstellar medium is low, are included in the ERCSC if they meet the high reliability criterion. The Planck ERCSC sources have known associations to stars with dust shells, stellar cores, radio galaxies, blazars, infrared luminous galaxies and Galactic interstellar medium features. A significant fraction of unclassified sources are also present in the catalogs. In addition, two early release catalogs that contain 915 cold molecular cloud core candidates and 189 SZ cluster candidates that have been generated using multi-frequency algorithms are presented. The entire source list, with more than 15000 unique sources, is ripe for follow-up characterisation with Herschel, ATCA, VLA, SOFIA, ALMA and other ground-based observing facilities.

astro-ph.CO↗

arXiv2011

Planck Early Results: 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.

astro-ph.CO↗

arXiv2011

Planck Early Results: The Planck View of Nearby Galaxies

The all-sky coverage of the Planck Early Release Compact Source Catalogue (ERCSC) provides an unsurpassed survey of galaxies at submillimetre (submm) wavelengths, representing a major improvement in the numbers of galaxies detected, as well as the range of far-IR/submm wavelengths over which they have been observed. We here present the first results on the properties of nearby galaxies using these data. We match the ERCSC catalogue to IRAS-detected galaxies in the Imperial IRAS Faint Source Redshift Catalogue (IIFSCz), so that we can measure the spectral energy distributions (SEDs) of these objects from 60 to 850 microns. This produces a list of 1717 galaxies with reliable associations between Planck and IRAS, from which we select a subset of 468 for SED studies, namely those with strong detections in the three highest frequency Planck bands and no evidence of cirrus contamination. The SEDs are fitted using parametric dust models to determine the range of dust temperatures and emissivities. We find evidence for colder dust than has previously been found in external galaxies, with T<20K. Such cold temperatures are found using both the standard single temperature dust model with variable emissivity beta, or a two dust temperature model with beta fixed at 2. We also compare our results to studies of distant submm galaxies (SMGs) which have been claimed to contain cooler dust than their local counterparts. We find that including our sample of 468 galaxies significantly reduces the distinction between the two populations. Fits to SEDs of selected objects using more sophisticated templates derived from radiative transfer models confirm the presence of the colder dust found through parameteric fitting. We thus conclude that cold (T<20K) dust is a significant and largely unexplored component of many nearby galaxies.

astro-ph.CO↗

arXiv2011

Planck Early Results: The Galactic Cold Core Population revealed by the first all-sky survey

We present the statistical properties of the first version of the Cold Core Catalogue of Planck Objects (C3PO), in terms of their spatial distribution, temperature, distance, mass, and morphology. We also describe the statistics of the Early Cold Core Catalogue (ECC, delivered with the Early Release Compact Source Catalogue, ERCSC) that is the subset of the 915 most reliable detections of the complete catalogue. We have used the CoCoCoDeT algorithm to extract 10783 cold sources. Temperature and dust emission spectral index β values are derived using the fluxes in the IRAS 100 \mum band and the three highest frequency Planck bands. Temperature spans from 7K to 17K, and peaks around 13K. Data are not consistent with a constant value of β over the all temperature range. β ranges from 1.4 to 2.8 with a mean value around 2.1, and several possible scenarios are possible, including β(T) and the effect of multiple T components folded into the measurements. For one third of the objects the distances are obtained. Most of the detections are within 2 kpc in the Solar neighbourhood, but a few are at distances greater than 4 kpc. The cores are distributed from the deep Galactic plane, despite the confusion, to high latitudes (>30$^{\circle}$). The associated mass estimates range from 1 to $10^5$ solar masses. Using their physical properties these cold sources are shown to be cold clumps, defined as the intermediate cold sub-structures between clouds and cores. These cold clumps are not isolated but mostly organized in filaments associated with molecular clouds. The Cold Core Catalogue of Planck Objects (C3PO) is the first unbiased all-sky catalogue of cold objects. It gives an unprecedented statistical view to the properties of these potential pre-stellar clumps and offers a unique possibility for their classification in terms of their intrinsic properties and environment.

astro-ph.GA↗

arXiv2011

Planck Early Results: All sky temperature and dust optical depth from Planck and IRAS: Constraints on the "dark gas" in our galaxy

We construct an all-sky map of the apparent temperature and optical depth of thermal dust emission using the Planck-HFI and IRAS data. The optical depth maps are correlated to tracers of the atomic and molecular gas. The correlation is linear in the lowest column density regions at high galactic latitudes. At high NH, the correlation is consistent with that of the lowest NH. In the intermediate NH range, we observe departure from linearity, with the dust optical depth in excess to the correlation. We attribute this excess emission to thermal emission by dust associated with a Dark-Gas phase, undetected in the available HI and CO measurements. We show the 2D spatial distribution of the Dark-Gas in the solar neighborhood and show that it extends around known molecular regions traced by CO. The average dust emissivity in the HI phase in the solar neighborhood follows roughly a power law distribution with beta = 1.8 all the way down to 3 mm, although the SED flattens slightly in the millimetre. The threshold for the existence of the Dark-Gas is found at NH = (8.0\pm 0.58) 10^{20} Hcm-2. Assuming the same dust emissivity at high frequencies for the dust in the atomic and molecular phases leads to an average XCO = (2.54\pm0.13) 10^{20} H2cm-2/(K km s-1). The mass of Dark-Gas is found to be 28% of the atomic gas and 118% of the CO emitting gas in the solar neighborhood. A possible origin for the Dark-Gas is the existence of a dark molecular phase, where H2 survives photodissociation but CO does not. The observed transition for the onset of this phase in the solar neighborhood (AV = 0.4 mag) appears consistent with recent theoretical predictions. We also discuss the possibility that up to half of the Dark-Gas could be in atomic form, due to optical depth effects in the HI measurements.

astro-ph.GA↗

arXiv2011

Planck Early Results: The submillimetre properties of a sample of Galactic cold clumps

(abridged) 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 (150pc) and remote (2kpc) 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.

astro-ph.GA↗

arXiv2009

Increasing evidence for hemispherical power asymmetry in the five-year WMAP data

(Abridged)Motivated by the recent results of Hansen et al. (2008) concerning a noticeable hemispherical power asymmetry in the WMAP data on small angular scales, we revisit the dipole modulated signal model introduced by Gordon et al. (2005). This model assumes that the true CMB signal consists of a Gaussian isotropic random field modulated by a dipole, and is characterized by an overall modulation amplitude, A, and a preferred direction, p. Previous analyses of this model has been restricted to very low resolution due to computational cost. In this paper, we double the angular resolution, and compute the full corresponding posterior distribution for the 5-year WMAP data. The results from our analysis are the following: The best-fit modulation amplitude for l <= 64 and the ILC data with the WMAP KQ85 sky cut is A=0.072 +/- 0.022, non-zero at 3.3sigma, and the preferred direction points toward Galactic coordinates (l,b) = (224 degree, -22 degree) +/- 24 degree. The corresponding results for l <~ 40 from earlier analyses was A = 0.11 +/- 0.04 and (l,b) = (225 degree,-27 degree). The statistical significance of a non-zero amplitude thus increases from 2.8sigma to 3.3sigma when increasing l_max from 40 to 64, and all results are consistent to within 1sigma. Similarly, the Bayesian log-evidence difference with respect to the isotropic model increases from Delta ln E = 1.8 to Delta ln E = 2.6, ranking as "strong evidence" on the Jeffreys' scale. The raw best-fit log-likelihood difference increases from Delta ln L = 6.1 to Delta ln L = 7.3. Similar, and often slightly stronger, results are found for other data combinations. Thus, we find that the evidence for a dipole power distribution in the WMAP data increases with l in the 5-year WMAP data set, in agreement with the reports of Hansen et al. (2008).

astro-ph.CO↗

arXiv2008

Power Asymmetry in Cosmic Microwave Background Fluctuations from Full Sky to Sub-degree Scales: Is the Universe Isotropic?

We repeat and extend the analysis of Eriksen et al 2004 and Hansen et al 2004 testing the isotropy of the Cosmic Microwave Background (CMB) fluctuations. We find that the hemispherical power asymmetry previously reported for the largest scales l=2-40 extend to much smaller scales. In fact, for the full multipole range l=2-600, significantly more power is found in the hemisphere centered at (theta=107 deg., phi=226 deg.) in galactic co-latitude and longitude than in the opposite hemisphere consistent with the previously detected direction of asymmetry for l=2-40. We adopt a model selection test where the direction and amplitude of asymmetry as well as the multipole range are free parameters. A model with an asymmetric distribution of power for l=2-600 is found to be preferred over the isotropic model at the 0.4% significance level taking into account the additional parameters required to describe it. A similar direction of asymmetry is found independently in all six subranges of 100 multipoles between l=2-600 and none of our 9800 isotropic simulated maps show a similarly consistent direction of asymmetry over such a large multipole range. No known systematic effects or foregrounds are found to be able to explain the asymmetry.

astro-ph↗

arXiv2008

Component separation methods for the Planck mission

The Planck satellite will map the full sky at nine frequencies from 30 to 857 GHz. The CMB intensity and polarization that are its prime targets are contaminated by foreground emission. The goal of this paper is to compare proposed methods for separating CMB from foregrounds based on their different spectral and spatial characteristics, and to separate the foregrounds into components of different physical origin. A component separation challenge has been organized, based on a set of realistically complex simulations of sky emission. Several methods including those based on internal template subtraction, maximum entropy method, parametric method, spatial and harmonic cross correlation methods, and independent component analysis have been tested. Different methods proved to be effective in cleaning the CMB maps from foreground contamination, in reconstructing maps of diffuse Galactic emissions, and in detecting point sources and thermal Sunyaev-Zeldovich signals. The power spectrum of the residuals is, on the largest scales, four orders of magnitude lower than that of the input Galaxy power spectrum at the foreground minimum. The CMB power spectrum was accurately recovered up to the sixth acoustic peak. The point source detection limit reaches 100 mJy, and about 2300 clusters are detected via the thermal SZ effect on two thirds of the sky. We have found that no single method performs best for all scientific objectives. We foresee that the final component separation pipeline for Planck will involve a combination of methods and iterations between processing steps targeted at different objectives such as diffuse component separation, spectral estimation and compact source extraction.

astro-ph↗