G. Polenta

A simplified view of blazars: clearing the fog around long-standing selection effects

We propose a scenario where blazars are classified as flat-spectrum radio quasars (FSRQs), BL Lacs, low synchrotron, or high synchrotron peaked objects according to a varying mix of the Doppler boosted radiation from the jet, the emission from the accretion disk, the broad line region, and the light from the host galaxy. In this framework the peak energy of the synchrotron power (ν S ) in blazars is independent of source type and of radio luminosity. We test this new approach, which builds upon unified schemes, using extensive Monte Carlo simulations and show that it can provide simple answers to a number of long-standing issues including, amongst others, the different cosmological evolution of BL Lacs selected in the radio and X-ray bands, the larger ν S peak values observed in BL Lacs, the fact that high synchrotron peaked blazars are always of the BL Lac type, and the existence of FSRQ/BL Lac transition objects. Objects so far classified as BL Lacs on the basis of their observed weak, or undetectable, emission lines are of two physically different classes: intrinsically weak lined objects, more common in X-ray selected samples, and heavily diluted broad lined sources, more frequent in radio selected samples, which explains some of the confusion in the literature. We also show that strong selection effects are the main cause of the diversity observed in radio and X-ray samples, and that the correlation between luminosity and ν S , that led to the proposal of the “blazar sequence”, is also a selection effect arising from the comparison of shallow radio and X-ray surveys, and to the fact that high ν S peak - high radio power objects have never been considered because their redshift is not measurable.

A simplified view of blazars: the γ-ray case

We have recently proposed a new simplified scenario where blazars are classified as flat-spectrum radio quasars (FSRQs) or BL Lacs according to the prescriptions of unified schemes, and to a varying combination of Doppler boosted radiation from the jet, emission from the accretion disk, the broad line region, and light from the host galaxy. Here we extend our approach, previously applied to radio and X-ray surveys, to the gamma-ray band and, through detailed Monte Carlo simulations, compare our predictions to Fermi-LAT survey data. Our simulations are in remarkable agreement with the overall observational results, including the percentages of BL Lacs and FSRQs, the fraction of redshift-less objects, and the redshift, synchrotron peak, and gamma-ray spectral index distributions. The strength and large scatter of the oft-debated observed Gamma-ray -- radio flux density correlation is also reproduced. In addition, we predict that almost 3/4 of Fermi-LAT BL Lacs, and basically all of those without redshift determination, are actually FSRQs with their emission lines swamped by the non-thermal continuum and as such should be considered. Finally, several of the currently unassociated high Galactic latitude Fermi sources are expected to be radio-faint blazars displaying a pure elliptical galaxy optical spectrum.

Exploring the Relation between (Sub-)Millimeter Radiation and γ-Ray Emission in Blazars with Planck and Fermi

The coexistence of Planck and Fermi satellites in orbit has enabled the exploration of the connection between the (sub-)millimeter and γ-ray emission in a large sample of blazars. We find that the γ-ray emission and the (sub-)mm luminosities are correlated over five orders of magnitude, L γL (sub-)mm. However, this correlation is not significant at some frequency bands when simultaneous observations are considered. The most significant statistical correlations, on the other hand, arise when observations are quasi-simultaneous within two months. Moreover, we find that sources with an approximate spectral turnover in the middle of the mm-wave regime are more likely to be strong γ-ray emitters. These results suggest a physical relation between the newly injected plasma components in the jet and the high levels of γ-ray emission.

Intensity and polarization of the atmospheric emission at millimetric wavelengths at Dome Concordia

Atmospheric emission is a dominant source of disturbance in ground-based astronomy at millimetric wavelengths. The Antarctic plateau is recognized as an ideal site for millimetric and submillimetric observations, and the French/Italian base of Dome Concordia (Dome C) is among the best sites on Earth for these observations. In this paper, we present measurements at Dome C of the atmospheric emission in intensity and polarization at a 2-mm wavelength. This is one of the best observational frequencies for cosmic microwave background (CMB) observations when considering cosmic signal intensity, atmospheric transmission, detector sensitivity and foreground removal. Using the B-mode radiation interferometer (BRAIN)-pathfinder experiment, we have performed measurements of the atmospheric emission at 150 GHz. Careful characterization of the airmass synchronous emission has been performed, acquiring more than 380 elevation scans (i.e. skydip) during the third BRAIN-pathfinder summer campaign in 2009 December/2010 January. The extremely high transparency of the Antarctic atmosphere over Dome C is proven by the very low measured optical depth, = 0.050 ± 0.003 ± 0.011, where the first error is statistical and the second is the systematic error. Mid-term stability, over the summer campaign, of the atmosphere emission has also been studied. Adapting the radiative transfer atmosphere emission model am to the particular conditions found at Dome C, we also infer the level of the precipitable water vapor (PWV) content of the atmosphere, which is notoriously the main source of disturbance in millimetric astronomy (? mm). Upper limits on the airmass correlated polarized signal are also placed for the first time. The degree of circular polarization of atmospheric emission is found to be lower than 0.2 per cent [95 per cent confidence level (CL)], while the degree of linear polarization is found to be lower than 0.1 per cent (95 per cent CL). These limits include signal-correlated instrumental spurious polarization.

A comparison of CMB Angular Power Spectrum Estimators at Large Scales: the TT case

In the context of cosmic microwave background (CMB) data analysis, we compare the efficiency at large scale of two angular power spectrum algorithms, implementing, respectively, the quadratic maximum likelihood (QML) estimator and the pseudo spectrum (pseudo-Cl) estimator. By exploiting 1000 realistic Monte Carlo (MC) simulations, we find that the QML approach is markedly superior in the range l=[2-100]. At the largest angular scales, e.g. l < 10, the variance of the QML is almost 1/3 (1/2) that of the pseudo-Cl, when we consider the WMAP kq85 (kq85 enlarged by 8 degrees) mask, making the pseudo spectrum estimator a very poor option. Even at multipoles l=[20-60], where pseudo-Cl methods are traditionally used to feed the CMB likelihood algorithms, we find an efficiency loss of about 20%, when we considered the WMAP kq85 mask, and of about 15% for the kq85 mask enlarged by 8 degrees. This should be taken into account when claiming accurate results based on pseudo-Cl methods. Some examples concerning typical large scale estimators are provided.

THE SPECTRAL ENERGY DISTRIBUTION OF THE CARINA NEBULA FROM FAR-INFRARED TO RADIO WAVELENGTHS

Multi-wavelength observations are mandatory to understand the physical properties of astrophysical sources. In this paper we use observations in the far infrared to radio range to derive the spectral energy distribution (SED) of the Carina nebula. To do this, we carefully subtract the irregularly varying diffuse emission from the Galactic plane, which can be of the order of 10 of the nebula flux at these wavelengths. We find that the far infrared SED can be modeled as emission from a dust population with a single temperature T_d=(34.5^{+2.0}_{-1.8}), and with a spectral index of emissivity alpha=-1.37^{+0.09}_{-0.08}. We also find a total infrared luminosity of the Nebula of (7.4^{+2.5}_{-1.4})x10^6 L_{odot} and, assuming a single temperature of the dust, a mass of the dust of (9500^{+4600}_{-3500})M_odot.

Data reduction pipeline for the Hi-GAL survey

We present the data reduction pipeline for the Herschel Infrared Galactic Plane survey (Hi-GAL). Hi-GAL is a key project of the Herschel satellite, which is mapping the inner part of the Galactic plane (|l| ≤ 70° and |b| ≤ 1°), using two Photodetector Array Camera and Spectrometer (PACS) and three Spectral and Photometric Imaging Receiver (SPIRE) frequency bands, from 70 to 500 μm. Our pipeline relies only partially on the Herschel Interactive Processing Environment (hipe). It features several newly developed routines to perform data reduction, including accurate data culling, noise estimation and minimum variance map-making, the latter performed with the romagal algorithm, a deep modification of the roma code already tested on cosmological surveys. We discuss in depth the properties of the Hi-GAL science demonstration phase data.