J. González-Nuevo

The detection of a population of submillimeter-bright, strongly lensed galaxies

Through a Lens Brightly Astronomical sources detected in the submillimeter range are generally thought to be distant, dusty galaxies undergoing a vigorous burst of star formation. They can be detected because the dust absorbs the light from stars and reemits it at longer wavelengths. Their properties are still difficult to ascertain, however, because the combination of interference from dust and the low spatial resolution of submillimeter telescopes prevents further study at other wavelengths. Using data from the Herschel Space Telescope, Negrello et al. (p. 800) showed that by searching for the brightest sources in a wide enough area in the sky it was possible to detect gravitationally lensed submillimeter galaxies with nearly full efficiency. Gravitational lensing occurs when the light of an astronomical object is deflected by a foreground mass. This phenomenon increases the apparent brightness and angular size of the lensed objects, making it easier to study sources that would be otherwise too faint to probe. Data from the Herschel Space Observatory unveils distant, dusty galaxies invisible to optical telescopes. Gravitational lensing is a powerful astrophysical and cosmological probe and is particularly valuable at submillimeter wavelengths for the study of the statistical and individual properties of dusty star-forming galaxies. However, the identification of gravitational lenses is often time-intensive, involving the sifting of large volumes of imaging or spectroscopic data to find few candidates. We used early data from the Herschel Astrophysical Terahertz Large Area Survey to demonstrate that wide-area submillimeter surveys can simply and easily detect strong gravitational lensing events, with close to 100% efficiency.

Predictions for high-frequency radio surveys of extragalactic sources

We present detailed predictions of the contributions of the various source populations to the counts at frequen- cies of tens of GHz. New evolutionary models are worked out for flat-spectrum radio quasars, BL Lac objects, and steep- spectrum sources. Source populations characterized by spectra peaking at high radio frequencies, such as extreme GPS sources, ADAF/ADIOS sources and early phases of γ-ray burst afterglows are also dealt with. The counts of different populations of star-forming galaxies (normal spirals, starbursts, high-z galaxies detected by SCUBA and MAMBO surveys, interpreted as proto-spheroidal galaxies) are estimated taking into account both synchrotron and free-free emission, and dust re-radiation. Our analysis is completed by updated counts of Sunyaev-Zeldovich effects in clusters of galaxies and by a preliminary estimate of galactic-scale Sunyaev-Zeldovich signals associated to proto-galactic plasma.

Component separation methods for the PLANCK mission

Context. 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. Aims. 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” with different physical origins (Galactic synchrotron, free-free and dust emissions; extra-galactic and far-IR point sources; Sunyaev-Zeldovich effect, etc.) Methods. A component separation challenge has been organised, 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. Results. Different methods proved to be effective in cleaning the CMB maps of 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 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. Conclusions. 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.

Simultaneous Planck, Swift, and Fermi observations of X-ray and γ-ray selected blazars

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and -ray bands, and we compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set has allowed us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by Fermi Large Area Telescope (LAT), whereas 30 to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the -ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, withh i 0 up to about 70 GHz, above which it steepens toh i 0:65. BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency ( S ) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples withh S i = 10 13:1 0:1 Hz, while the mean inverse-Compton peak frequency,h IC i, ranges from 10 21 to 10 22 Hz. The distributions of S and of IC of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method, with -ray selected blazars peaking at 7 or more, and radio-selected blazars at values close to 1, thus implying that the common assumption that the blazar power budget is largely dominated by high-energy emission is a selection e ect. A comparison of our multi-frequency data with theoretical predictions shows that simple homogeneous SSC models cannot explain the simultaneous SEDs of most of the -ray detected blazars in all samples. The SED of the blazars that were not detected by Fermi-LAT may instead be consistent with SSC emission. Our data challenge the correlation between bolometric luminosity and S predicted by the blazar sequence.

The pre-launch Planck Sky Model: a model of sky emission at submillimetre to centimetre wavelengths

We present the Planck Sky Model (PSM), a parametric model for generating all-sky, few arcminute resolution maps of sky emission at submillimetre to centimetre wavelengths, in both intensity and polarisation. Several options are implemented to model the cosmic microwave background, Galactic diffuse emission (synchrotron, free-free, thermal and spinning dust, CO lines), Galactic HII regions, extragalactic radio sources, dusty galaxies, and thermal and kinetic Sunyaev-Zeldovich signals from clusters of galaxies. Each component is simulated by means of educated interpolations/extrapolations of data sets available at the time of the launch of the Planck mission, complemented by state-of-the-art models of the emission. Distinctive features of the simulations are spatially varying spectral properties of synchrotron and dust; different spectral parameters for each point source; modelling of the clustering properties of extragalactic sources and of the power spectrum of fluctuations in the cosmic infrared background. The PSM enables the production of random realisations of the sky emission, constrained to match observational data within their uncertainties. It is implemented in a software package that is regularly updated with incoming information from observations. The model is expected to serve as a useful tool for optimising planned microwave and sub-millimetre surveys and testing data processing and analysis pipelines. It is, in particular, used to develop and validate data analysis pipelines within the Planck collaboration. A version of the software that can be used for simulating the observations for a variety of experiments is made available on a dedicated website.

Herschel-ATLAS: Dust Temperature and Redshift Distribution of SPIRE and PACS Detected Sources Using Submillimetre Colours

We present colour-colour diagrams of detected sources in the Herschel-ATLAS science demonstration field from 100 to 500 mu m using both PACS and SPIRE. We fit isothermal modified black bodies to the spectral energy distribution (SED) to extract the dust temperature of sources with counterparts in Galaxy And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a photometric redshift. For a subsample of 330 sources detected in at least three FIR bands with a significance greater than 3 sigma, we find an average dust temperature of (28 +/- 8) K. For sources with no known redshift, we populate the colour-colour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters, and compare to colours of observed sources to establish the redshift distribution of this sample. For another subsample of 1686 sources with fluxes above 35 mJy at 350 mu m and detected at 250 and 500 mu m with a significance greater than 3s, we find an average redshift of 2.2 +/- 0.6.

Herschel -ATLAS: extragalactic number counts from 250 to 500 microns

Aims. The Herschel-ATLAS survey (H-ATLAS) will be the largest area survey to be undertaken by the Herschel Space Observatory. It will cover 550 sq. deg. of extragalactic sky at wavelengths of 100, 160, 250, 350 and 500 μm when completed, reaching flux limits (5σ) from 32 to 145 mJy. We here present galaxy number counts obtained for SPIRE observations of the first ∼14 sq. deg. observed at 250, 350 and 500 μm. Methods. Number counts are a fundamental tool in constraining models of galaxy evolution. We use source catalogs extracted from the H-ATLAS maps as the basis for such an analysis. Correction factors for completeness and flux boosting are derived by applying our extraction method to model catalogs and then applied to the raw observational counts. Results. We find a steep rise in the number counts at flux levels of 100−200 mJy in all three SPIRE bands, consistent with results from BLAST. The counts are compared to a range of galaxy evolution models. None of the current models is an ideal fit to the data but all ascribe the steep rise to a population of luminous, rapidly evolving dusty galaxies at moderate to high redshift.

The Mexican hat wavelet family: application to point-source detection in cosmic microwave background maps

We propose a detection technique in 2D images based on an isotropic wavelet family. This family is naturally constructed as an extension of the Gaussian-Mexican Hat Wavelet pair and for that reason we call it the Mexican Hat Wavelet Family (MHWF). We show the performance of these wavelets for dealing with the detection of point extragalactic sources in cosmic microwave background (CMB) maps: a very important issue within the most general problem of the component separation of the microwave sky. In particular, simulations for one channel (44 GHz) of the forthcoming Planck mission have been analysed. We present the results and compare them with those obtained using the Mexican Hat Wavelet technique (MHW), which has been proven a suitable tool for detecting point sources. The MHWF provides a point source catalogue at 44 GHz of 690 sources. Under the same conditions, the MHW provides 604 sources.

Predictions on the high-frequency polarization properties of extragalactic radio sources and implications for polarization measurements of the cosmic microwave background

We present a method to simulate the polarization properties of extragalactic radio sources at microwave frequencies. Polarization measurements of nearly 2 x 10 6 sources at 1.4 GHz are provided by the NVSS survey. Using this catalogue and the GB6 survey, we study the distribution of the polarization degree of both steep- and flat-spectrum sources. We find that the polarization degree is anticorrelated with the flux density for the former population, while no correlation is detected for the latter. The available high-frequency data are exploited to determine the frequency dependence of the distribution of polarization degrees. Using such information and the evolutionary model developed by Toffolatti and coworkers, we estimate the polarization power spectra of extragalactic radio sources at ≥30 GHz and their contamination of CMB polarization maps. Two distinct methods to compute point-source polarization spectra are presented, extending and improving the one generally used in previous analyses. While extragalactic radio sources can significantly contaminate the CMB E-mode power spectrum only at low frequencies (ν? 30 GHz), they can severely constrain the detectability of the CMB B mode up to ν ≃ 100 GHz.

Herschel-ATLAS: The dust energy balance in the edge-on spiral galaxy UGC 4754

We use Herschel PACS and SPIRE observations of the edge-on spiral galaxy UGC4754, taken as part of the H-ATLAS SDP observations, to investigate the dust energy balance in this galaxy. We build detailed SKIRT radiative models based on SDSS and UKIDSS maps and use these models to predict the far-infrared emission. We find that our radiative transfer model underestimates the observed FIR emission by a factor of two to three. Similar discrepancies have been found for other edge-on spiral galaxies based on IRAS, ISO, and SCUBA data. Thanks to the good sampling of the SED at FIR wavelengths, we can rule out an underestimation of the FIR emissivity as the cause for this discrepancy. Instead we support highly obscured star formation that contributes little to the optical extinction as a more probable explanation.