Far-infrared/millimetre emission in 3C sources - Dust in radio galaxies and quasars

We present far-infrared and millimetric observations of a sample of 3C objects. Millimetre data were taken at 1.25 mm with the IRAM 30 m antenna feeding the MPIfR bolometer array. Mid-infrared (MIR) and far-infrared (FIR) photometry were carried out with the ISOCAM and ISOPHOT cameras on the ISO Satellite. Additional FIR IRAS observations are also included. We present the entire Spectral Energy Distributions (SEDs) from the UV to radio and discuss the emitting mechanisms. Two composite spectra, one for the radio galaxies and one for the radio quasars, are built in the object rest frame. While the SEDs of the two classes differ, they are indistinguishable in the MIR and FIR range where they probably arise as thermal emission from a dusty torus and a larger-scale (cooler) dust distribution in the host galaxy.</p

rPICARD: A CASA-based Calibration Pipeline for VLBI Data

Currently, HOPS and AIPS are the primary choices for the time-consuming process of (millimeter) Very Long Baseline Interferometry (VLBI) data calibration. However, for a full end-to-end pipeline, they either lack the ability to perform easily scriptable incremental calibration or do not provide full control over the workflow with the ability to manipulate and edit calibration solutions directly. The Common Astronomy Software Application (CASA) offers all these abilities, together with a secure development future and an intuitive Python interface, which is very attractive for young radio astronomers. Inspired by the recent addition of a global fringe-fitter, the capability to convert FITS-IDI files to measurement sets, and amplitude calibration routines based on ANTAB metadata, we have developed the the CASA-based Radboud PIpeline for the Calibration of high Angular Resolution Data (rPICARD). The pipeline will be able to handle data from multiple arrays: EHT, GMVA, VLBA and the EVN in the first release. Polarization and phase-referencing calibration are supported and a spectral line mode will be added in the future. The large bandwidths of future radio observatories ask for a scalable reduction software. Within CASA, a message passing interface (MPI) implementation is used for parallelization, reducing the total time needed for processing. The most significant gain is obtained for the time-consuming fringe-fitting task where each scan be processed in parallel.Comment: 6 pages, 1 figure, EVN 2018 symposium proceeding

ISOPHOT observations of 3CR quasars and radio galaxies

In order to check for consistency with the radio-loud AGN unification scheme, ISOPHOT data obtained for two small sets of intermediate redshift steep-spectrum 3CR radio galaxies and quasars are being examined. Supplementary submillimeter and centimeter radio data for the quasars are also taken into account, in order to assess the magnitude of any beamed nonthermal radiation. The fact that we find broad-lined objects to be somewhat more luminous in their far-infrared output than narrow-lined objects, hints at a contradiction to the unification scheme. However, as the sample objects are not particularly well matched, the sample size is small, and the FIR radiation may still be partly anisotropic, this evidence is, at the moment, weak

Infrared emission in radio galaxy NGC 4261

We have analyzed the total and nuclear SED for NGC 4261 and find that the dominant process for the mid- and far-infrared emission in this object is non-thermal emission from the active nucleus. Modeling the emission from the optically detected 300 pc dust disk yields no significant disk contribution at any wavelength. To explain the observations, either the disk has an inflated inner region which partly absorbs the core, or the intrinsic core spectrum is curved. The inner 10 pc of the disk can potentially be conceived as an obscuring torus, albeit with optical depth around unity.Comment: 4 pages, 4 figures. To appear in the proceedings of: "The Spectral Energy Distribution of Gas-Rich Galaxies: Confronting Models with Data", Heidelberg, 4-8 Oct. 2004, eds. C.C. Popescu and R.J. Tuffs, AIP Conf. Ser., in pres

Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources

We have measured mid-infrared radiation from an orientation-unbiased sample of 3CRR galaxies and quasars at redshifts 0.4 < z < 1.2 with the IRS and MIPS instruments on the Spitzer Space Telescope. Powerful emission (L_24micron > 10^22.4 W/Hz/sr) was detected from all but one of the sources. We fit the Spitzer data as well as other measurements from the literature with synchrotron and dust components. The IRS data provide powerful constraints on the fits. At 15 microns, quasars are typically four times brighter than radio galaxies with the same isotropic radio power. Based on our fits, half of this difference can be attributed to the presence of non-thermal emission in the quasars but not the radio galaxies. The other half is consistent with dust absorption in the radio galaxies but not the quasars. Fitted optical depths are anti-correlated with core dominance, from which we infer an equatorial distribution of dust around the central engine. The median optical depth at 9.7 microns for objects with core-dominance factor R > 10^-2 is approximately 0.4; for objects with R < 10^-2, it is 1.1. We have thus addressed a long-standing question in the unification of FR II quasars and galaxies: quasars are more luminous in the mid-infrared than galaxies because of a combination of Doppler-boosted synchrotron emission in quasars and extinction in galaxies, both orientation-dependent effects.Comment: 42 pages, 14 figures plus two landscape tables. Accepted for publication in Ap

Clumpy tori around active galactic nuclei

We discuss the question whether the matter in dusty tori around active galactic nuclei has a smooth or a clumpy structure. Nenkova, Ivezic & Elitzur (2002) have argued that the lack of emission feature in the SEDs of type 1 AGN galaxies combined with a clear absorption feature in type 2 AGN can be explained if the circumnuclear dust is distributed in discrete clumps. Our aim is to verify this. We use multi-dimensional radiative transfer models of smooth and clumpy tori, and compare the SEDs of equivalent smooth and clumpy models. We find that the 10 micron emission feature of the clumpy models, when seen almost face-on, is not appreciably reduced compared to the equivalent smooth models. Some of the clumpy models have a weak or even absent 10 micron feature, but so do some of the smooth models. On the whole the SEDs of clumpy and smooth tori are similar, but some details are different. The absorption feature seen at edge-on inclinations appears to be less deep in the clumpy models than in the smooth models, and the average flux in the near-infrared regime is stronger in the clumpy models. Moreover, at these inclinations the clumpy models have a slightly wider SED. Whether these differences are unique enough to be used as a diagnostic for clumpiness of AGN tori is not yet clear.Comment: Accepted for publication in Astronomy & Astrophysic

The ISOPHOT-MAMBO survey of 3CR radio sources: Further evidence for the unified schemes

We present the complete set of ISOPHOT observations of 3CR radio galaxies and quasars, which are contained in the ISO Data Archive, providing 75 mid- and far-infrared spectral energy distributions (SEDs) between 5 and 200 micron. For 28 sources they are supplemented with MAMBO 1.2 mm observations and for 15 sources with new submillimetre data from the SCUBA archive. We check the orientation-dependent unified scheme, in which the powerful FR2 narrow line galaxies are quasars viewed at high inclination, so that their nuclei are hidden behind a dust torus intercepting the optical-ultraviolet AGN radiation and reemitting it in the infrared. We find that (1) both the quasars and the galaxies show a high mid- to far-infrared luminosity ratio typical for powerful AGNs and (2) -- when matched in 178 MHz luminosity -- both show the same ratio of isotropic far-infrared to isotropic 178 MHz lobe power. Therefore, from our large sample investigated here we find strong evidence for the orientation-dependent unification of the powerful FR2 galaxies with the quasars.Comment: 16 pages, 7 figures, 3 tables, accepted by Astronomy & Astrophysic

Ionospheric Calibration of Low Frequency Radio Interferometric Observations using the Peeling Scheme: I. Method Description and First Results

Calibration of radio interferometric observations becomes increasingly difficult towards lower frequencies. Below ~300 MHz, spatially variant refractions and propagation delays of radio waves traveling through the ionosphere cause phase rotations that can vary significantly with time, viewing direction and antenna location. In this article we present a description and first results of SPAM (Source Peeling and Atmospheric Modeling), a new calibration method that attempts to iteratively solve and correct for ionospheric phase errors. To model the ionosphere, we construct a time-variant, 2-dimensional phase screen at fixed height above the Earth's surface. Spatial variations are described by a truncated set of discrete Karhunen-Loeve base functions, optimized for an assumed power-law spectral density of free electrons density fluctuations, and a given configuration of calibrator sources and antenna locations. The model is constrained using antenna-based gain phases from individual self-calibrations on the available bright sources in the field-of-view. Application of SPAM on three test cases, a simulated visibility data set and two selected 74 MHz VLA data sets, yields significant improvements in image background noise (5-75 percent reduction) and source peak fluxes (up to 25 percent increase) as compared to the existing self-calibration and field-based calibration methods, which indicates a significant improvement in ionospheric phase calibration accuracy.Comment: 23 pages, 14 figures, 2 tables. Accepted for publication in A&A. Changes in v2: Corrected minor error in Equations A.3 and A.12. Extended acknowledgment

The dusty environment of Quasars. Far-IR properties of Optical Quasars

We present the ISO far-IR photometry of a complete sub-sample of optically selected bright quasars belonging to two complete surveys selected through multicolour (U,B,V,R,I) techniques. The ISOPHOT camera on board of the ISO Satellite was used to target these quasars at wavelengths of 7.3, 11.5, 60, 100 and 160 micron. Almost two thirds of the objects were detected at least in one ISOPHOT band. The detection rate is independent of the source redshift, very likely due to the negative K-correction of the far-IR thermal emission. More than a half of the optically selected QSOs show significant emission between 4 and 100 micron in the quasar rest-frame. These fluxes have a very likely thermal origin, although in a few objects an additional contribution from a non-thermal component is plausible in the long wavelength bands. In a colour-colour diagram these objects span a wide range of properties from AGN-dominated to ULIRG-like. The far-IR composite spectrum of the quasar population presents a broad far-IR bump between 10 and 30 micron and a sharp drop at wavelengths greater than 100 micron in the quasar restframe. The amount of energy emitted in the far-IR, is on average a few times larger than that emitted in the blue and the ratio L(FIR)/L(B) increases with the bolometric luminosity. Objects with fainter blue magnitudes have larger ratios between the far-IR (wavelengths > 60 micron) fluxes and the blue band flux, which is attributed to extinction by dust around the central source. No relation between the blue absolute magnitude and the dust colour temperature is seen, suggesting that the dominant source of FIR energy could be linked to a concurrent starburst rather than to gravitational energy produced by the central engine.Comment: Astronomical Journal, in pres

The heating mechanism for the warm/cool dust in powerful, radio-loud AGN

The uncertainty surrounding the nature of the heating mechanism for the dust that emits at mid- to far-IR (MFIR) wavelengths in active galaxies limits our understanding of the links between active galactic nuclei (AGN) and galaxy evolution, as well as our ability to interpret the prodigious infrared and sub-mm emission of some of the most distant galaxies in the Universe. Here we report deep Spitzer observations of a complete sample of powerful, intermediate redshift (0.05 < z < 0.7) radio galaxies and quasars. We show that AGN power, as traced by [OIII]5007 emission, is strongly correlated with both the mid-IR (24 micron) and the far-IR (70 micron) luminosities, however, with increased scatter in the 70 micron correlation. A major cause of this increased scatter is a group of objects that falls above the main correlation and displays evidence for prodigious recent star formation activity at optical wavelengths, along with relatively cool MFIR colours. These results provide evidence that illumination by the AGN is the primary heating mechanism for the dust emitting at both 24 and 70 microns, with starbursts dominating the heating of the cool dust in only 20 -- 30% of objects. This implies that powerful AGN are not always accompanied by the type of luminous starbursts that are characteristic of the peak of activity in major gas-rich mergers.Comment: 13 pages, 3 figures. Accepted for publication in astrophysical journal letter