Extragalactic 1 millimeter sources: Simultaneous observations at centimeter, millimeter, and visual wavelengths

Observations simultaneously made at visual (B, V, and R) wavelengths, at 1, 1.4, and 3.4 mm and at 1.3, 2, 6, and 20 cm of 9 QSOs and BL Lac objects are reported. The range of the millimeter visual spectral index ɑ_(mv) was only 0.65-0.82, typical of optically thin synchrotron emission. This may indicate that the electrons radiating synchrotron emission in this portion of the spectrum are not subjected to large radiative losses, and therefore relativistic bulk motion with Doppler factors ~10 are required. The visual spectral index is much more broadly distributed and typically larger than ɑ_(mv). The spectral energy distributions have not changed much in the last 2-5 years except for 2251 + 15 and perhaps 0235 + 164. Only 1749 +09 shows a sharp spectral break shortward of 1 mm. Sixteen other sources were observed at 1 mm, of which seven were detected

EVN observations of low-luminosity flat-spectrum AGNs

We present and discuss the results of VLBI (EVN) observations of three low-luminosity (P(5 GHz)<10^25 W/Hz) Broad Emission Line AGNs carefully selected from a sample of flat spectrum radio sources (CLASS). Based on the total and the extended radio power at 5 GHz and at 1.4 GHz respectively, these objects should be technically classified as radio-quiet AGN and thus the origin of their radio emission is not clearly understood. The VLBI observations presented in this paper have revealed compact radio cores which imply a lower limit on the brightness temperature of about 3X10^8 K. This result rules out a thermal origin for the radio emission and strongly suggests an emission mechanism similar to that observed in more powerful radio-loud AGNs. Since, by definition, the three objects show a flat (or inverted) radio spectrum between 1.4 GHz and 8.4 GHz, the observed radio emission could be relativistically beamed. Multi-epoch VLBI observations can confirm this possibility in two years time.Comment: Accepted for publication in MNRA

Two Multifrequency Observations of 3C 371

We present observations of 3C 371, made at frequencies from the radio to the ultraviolet, which were coordinated during two short time intervals separated by 3 months. We also present 1 keV X-ray flux densities measured at a different time. The multifrequency measurements indicate spectral steepening at visual wavelengths, and that an extrapolation of the ultraviolet continuum falls below the X-ray data. We explain the infrared through X-ray data as relativistically beamed synchrotron self-Compton emission and derive source parameters for two possible models. Our ultraviolet spectra both show strong Lyɑ emission at the same redshift as weak optical emission lines reported previously. We favor production of these lines by recombination of gas after its ionization by the ultraviolet to X-ray continuum radiation. We tentatively identify C IV and N v absorption lines in one of our ultraviolet spectra, which, if real, suggest the presence of a hot (~ 3 x 10^5 K) gaseous halo in 3C 371

Accurate photometric redshifts for the CFHT Legacy Survey calibrated using the VIMOS VLT Deep Survey

We present photometric redshifts for an uniquely large and deep sample of 522286 objects with i'_{AB}<25 in the Canada-France Legacy Survey ``Deep Survey'' fields, which cover a total effective area of 3.2 deg^2. We use 3241 spectroscopic redshifts with 0<z<5 from the VIMOS VLT Deep Survey as a calibration to derive these photometric redshifts. We devise a robust calibration method which removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. For a sample selected at i'_{AB}<24, we reach a redshift accuracy of \sigma_{\Delta z/(1+z)}=0.037 with \eta=3.7% of catastrophic error. The reliability of our photometric redshifts is lower for fainter objects: we find \sigma_{\Delta z/(1+z)}=0.029, 0.043 and \eta=1.7%, 5.4% for samples selected at i'_{AB}=17.5-22.5 and 22.5-24 respectively. We find that the photometric redshifts of starburst galaxies in our sample are less reliable: although these galaxies represent only 18% of the spectroscopic sample they are responsible for 54% of the catastrophic errors. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at i'_{AB}<24. Finally, we compare the redshift distributions of i' selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is already present on fields of 0.8 deg^2.Comment: 19 pages, 17 figures, submitted to A&A. The photometric redshifts described in this paper will be made publicly available from 1st may 2006 at http://terapix.iap.fr and http://cencosw.oamp.fr

CFHTLenS: Improving the quality of photometric redshifts with precision photometry

Here we present the results of various approaches to measure accurate colours and photometric redshifts (photo-z's) from wide-field imaging data. We use data from the Canada-France-Hawaii-Telescope Legacy Survey (CFHTLS) which have been re- processed by the CFHT Lensing Survey (CFHTLenS) team in order to carry out a number of weak gravitational lensing studies. An emphasis is put on the correction of systematic effects in the photo-z's arising from the different Point Spread Functions (PSF) in the five optical bands. Different ways of correcting these effects are discussed and the resulting photo-z accuracies are quantified by comparing the photo-z's to large spectroscopic redshift (spec-z) data sets. Careful homogenisation of the PSF between bands leads to increased overall accuracy of photo-z's. The gain is particularly pronounced at fainter magnitudes where galaxies are smaller and flux measurements are affected more by PSF-effects. We also study possible re- calibrations of the photometric zeropoints (ZPs) with the help of galaxies with known spec-z's. We find that if PSF-effects are properly taken into account, a re-calibration of the ZPs becomes much less important suggesting that previous such re-calibrations described in the literature could in fact be mostly corrections for PSF-effects rather than corrections for real inaccuracies in the ZPs. The implications of this finding for future surveys like KiDS, DES, LSST, or Euclid are mixed. On the one hand, ZP re-calibrations with spec-z's might not be as accurate as previously thought. On the other hand, careful PSF homogenisation might provide a way out and yield accurate, homogeneous photometry without the need for full spectroscopic coverage. This is the first paper in a series describing the technical aspects of CFHTLenS. (abridged)Comment: 15 pages, 10 figures, accepted by MNRAS, minor revision

Integrating On-board and Vicarious Calibration with the Improved Radiometric Calibration of Land Imaging Systems (IRIS)

As part of Raytheon’s effort to provide innovative calibration capabilities that advance the performance of future earth imaging systems, an on-board Jones source calibrator integrated with vicarious SPecular ARray Calibration (SPARC) is introduced. The Improved Radiometric calibration of land Imaging Systems (IRIS) is a compact full-spectrum calibration system that reduces the size, weight, and power of conventional on-board radiometric sources into a single flat panel format providing high spatial illumination uniformity. Combining both carbon nanotube and LED technology within a Jones source design, IRIS offers a common assembly calibration reference covering the spectral range from 0.4 to 12 μm. On-board calibrator degradation from the effects of launch and lifetime exposure to the space environment impacts performance, making it difficult to maintain absolute knowledge of the sensor radiometry. What has been missing from past on-board lamp calibration systems is an operational capability for establishing and maintaining absolute SI traceability in the solar reflective spectral range after launch and over the sensor lifetime. Introduced in this presentation is a methodology that sustains traceability through a fusion of the on-board IRIS LED reference with Labsphere’s FLARE vicarious system. In this process, the imager collects an on-board calibration source image nearly simultaneously with observations of the sun safely reflected by a FLARE array of convex mirrors on the ground. The process known as IRIS-V provides data for recalibration of the onboard VSWIR system, as needed, in-flight without affecting operational land or coastal image collection. A prototype of the IRIS on-board calibrator and IRIS-V methodology will be described. IRIS is funded by the NASA Earth Science Technology Office (ESTO) through the Sustainable Land Imaging-Technology 2019 (SLIT19) Program