Search

As part of the GLOSTAR survey we have used the VLA in its B-configuration to observe the part of the Galactic plane between longitudes of 28d and 36d and latitudes from -1d to +1d at the C-band (4--8 GHz). To reduce the contamination of extended sources that are not well recovered by our coverage of the (u, v)-plane we discarded short baselines that are sensitive to emission on angular scales $, 25 pages, 15 figures, and 6 tables, Accepted for publication in the Astronomy \& Astrophysics

We made two new sensitive (rms noise sigma_n ~ 1 microJy/beam) high resolution (theta = 3.0" and theta = 0.66" FWHM) S--band (2 < nu < 4 GHz) images covering a single JVLA primary beam (FWHM ~ 14') centered on J2000 RA = 10 46, Dec = 59 01 in the Lockman Hole. These images yielded a catalog of 792 radio sources, 97.7 +/- 0.8% of which have infrared counterparts stronger than S ~ 2 microJy at lambda = 4.5 micron. About 91% of the radio sources found in our previously published, comparably sensitive low resolution (theta = 8" FWHM) image covering the same area were also detected at 0.66" resolution, so most radio sources with S_3GHz >~ 5 microJy have angular structure phi = 0.3" +/- 0.1" FWHM and an rms scatter sigma_phi ~ /2.43 ~ 0.12", so the median effective radius of star-forming galaxies at redshifts z~1 is ~ 1.0 kpc., 20 pages, 8 figures

Magnetized plasmas traversed by linearly polarized light will reveal their presence by the frequency dependent Faraday rotation of the angle of polarization. The regions surrounding the black holes powering the jets in AGNs are expected to have dense magnetized plasmas, possibly giving rise to very large Faraday rotations. Compact steep spectrum (CSS) sources are good candidates to search for very large Faraday rotated components as they contain compact emission from close to the black hole and many are strongly depolarized at centimeter wavelengths as expected from strong Faraday effects. We present data on several CSS sources (3C48, 3C138 and 3C147) observed with the VLA at frequencies between 20 and 48 GHz in the most extended configuration. Large, but not excessive rotation measures are reported.

We describe the motivation, design, and implementation of the CORNISH survey, an arcsecondresolution radio continuum survey of the inner galactic plane at 5 GHz using the Very Large Array (VLA). It is a blind survey coordinated with the northern SpitzerGLIMPSE I region covering 10°

The most X-ray luminous cluster known, RXJ1347-1145 (z=0.45), has been the object of extensive study across the electromagnetic spectrum. We have imaged the Sunyaev-Zel'dovich Effect (SZE) at 90 GHz (3.3 mm) in RXJ1347-1145 at 10" resolution with the 64-pixel MUSTANG bolometer array on the Green Bank Telescope (GBT), confirming a previously reported strong, localized enhancement of the SZE 20" to the South-East of the center of X-ray emission. This enhancement of the SZE has been interpreted as shock-heated (> 20 keV) gas caused by an ongoing major (low mass-ratio) merger event. Our data support this interpretation. We also detect a pronounced asymmetry in the projected cluster pressure profile, with the pressure just east of the cluster core ~1.6 times higher than just to the west. This is the highest resolution image of the SZE made to date., 9 pages, 7 figures; accepted for publication in The Astrophysical Journal

This white paper offers cautionary observations about the planning and development of new, large radio astronomy instruments. Complexity is a strong cost driver so every effort should be made to assign differing science requirements to different instruments and probably different sites. The appeal of shared resources is generally not realized in practice and can often be counterproductive. Instrument optimization is much more difficult with longer lists of requirements, and the development process is longer and less efficient. More complex instruments are necessarily further behind the technology state of the art because of longer development times. Including technology R&D in the construction phase of projects is a growing trend that leads to higher risks, cost overruns, schedule delays, and project de-scoping. There are no technology breakthroughs just over the horizon that will suddenly bring down the cost of collecting area. Advances come largely through careful attention to detail in the adoption of new technology provided by industry and the commercial market. Radio astronomy instrumentation has a very bright future, but a vigorous long-term R&D program not tied directly to specific projects needs to be restored, fostered, and preserved.

Sgr A* is variable at radio and submillimeter wavelengths on hourly time scales showing time delays between the peaks of flare emission as well as linearly polarized emission at millimeter and sub-mm wavelengths. To determine the polarization characteristics of this variable source at radio frequencies, we present VLA observations of Sgr A* and report the detection of polarized emission at a level of 0.77\pm0.01% and 0.2\pm0.01% at 43 and 22 GHz, respectively. The change in the time averaged polarization angle between 22 and 43 GHz corresponds to a RM of -2.5\pm0.6 x10^3 rad m{-2} with no phase wrapping (or \sim 5x10^4 rad m^2 with 2\pi phase wrap). We also note a rise and fall time scale of 1.5 -- 2 hours in the total polarized intensity. The light curves of the degree of linearly polarized emission suggests a a correlation with the variability of the total intensity at 43 GHz. The available polarization data at radio and sub-mm wavelengths suggest that the rotation measure decreases with decreasing frequency. This frequency dependence, and observed changes in polarization angle during flare events, may be caused by the reduction in rotation measure associated with the expansion of synchrotron-emitting blobs., Comment: 11 pages, 3 figures, ApJL (in press)

We have measured non-zero closure phases for about 29% of our sample of 56 nearby Asymptotic Giant Branch (AGB) stars, using the 3-telescope Infrared Optical Telescope Array (IOTA) interferometer at near-infrared wavelengths (H band) and with angular resolutions in the range 5-10 milliarcseconds. These nonzero closure phases can only be generated by asymmetric brightness distributions of the target stars or their surroundings. We discuss how these results were obtained, and how they might be interpreted in terms of structures on or near the target stars. We also report measured angular sizes and hypothesize that most Mira stars would show detectable asymmetry if observed with adequate angular resolution., Comment: Accepted by ApJ

Compact Steep Spectrum (CSS) sources are known to show strong optical line emission \citep{Gelderman1994} which is generally considered to be due to the interaction between the radio jet and the ISM. This argument is strengthened by the HST observations of \citet{Axon-2000} which show this emission is frequently associated with the radio jet. Previous observations of the CSS quasar 3C 138 \citep{Cotton1997} have shown that the bulk of the jet has very low amounts of Faraday rotation whereas the inner jet shows very high Faraday rotation (~ -5000 rad m-2). The inner jet is dominated by moving components which allows observing the fine scale of the Faraday screen as the components move behind it. We report the results of such a monitoring campaign which indicated that there is structure in the Faraday screen on the pc and possibly sub pc scale. Motions of the polarized component slowed dramatically during the course of these observations, limiting the region probed. The observations also strongly suggest that the polarized emission from the inner jet is seen through limited holes in a dense Faraday screen. In this case, the observed variations in Faraday rotation are possibly the result of jet-ISM interactions.

We present a new complete sample of radio sources selected from the B2 and 3CR catalogues, with no bias respect to the jet velocity and orientation. Using preliminary data we investigate the parsec scale properties of radio sources with different radio power and kpc scale morphology. We stress the evidence for high velocity pc scale jets in all sources and conclude that the properties of parsec scale jets are similar regardless of the source total power and large scale morphology. Moreover we show two epoch images of two nearby radio galaxies: a low power compact source and a CSO. The comparison of the two epoch images suggests that in both sources the size is increasing with time. We derive a possible advance speed and estimate their dynamic age., Comment: 4 pages, 5 figures. Contributed paper to the 6th European VLBI Network Symposium held on June 25th-28th in Bonn (D)

We report the most important results on the parsec-scale properties of a complete sample of radio galaxies carried out at radio frequencies with the Global VLBI array and with the VLBA. Relativistic parsec-scale jets are common both in FRI and FRII radio galaxies, and their orientation to the line of sight is in agreement with the expectations from the unified schemes for radio loud AGNs. Proper motion has been detected in a few FRI galaxies in the sample. FRI and FRII radio galaxies exhibit very similar properties on the parsec-scale. Finally a few radio sources in the sample show evidence of velocity structure in the parsec-scale jet, i.e. a central spine with high Lorentz factor $\gamma$ and slower layers., Comment: 4 pages, 2 figures, Proceedings of the 5th EVN Symposium, Eds. John Conway, A. Polatidis, R. Booth, Chalmers Technical University

Sub-arcsecond radio continuum observations of the Galactic center region at $\lambda$6 and 2cm reveal a 0.5$^{\prime\prime}$ diameter source with a shell-like morphology. This source is linearly polarized at a level of 16% at $\lambda$6cm and has a steep nonthermal spectrum with spectral index 1.6 between $\lambda$6 and 2 cm. The distance to this source is not known but the large rotation measure value of 3000 rad m$^{-2}$ suggests that G359.87+0.18 is likely to be located in the inner Galaxy or at an extragalactic distance. We discuss possible interpretations of this object as a recent supernova, a very young supernova remnant, a nova remnant, or an extragalactic source. All possibilities are highly problematic., Comment: 11 pages, 3 figures, ApJ Lett in press

We present here two epochs of Space VLBI observations at 18 cm of the BL-Lac type object Mkn 501. Thanks to the high resolution of these new data we have found that the inner jet is centrally brightened at its beginning but becomes extended and limb brightened at ~ 8 mas from the core. Moreover a comparison between the two epochs shows the presence of a possible proper motion with apparent velocity = 6.7c. VLBI data at 6 and 18 cm of the BL-Lac type object Mkn 421 are also presented. Observational data have been used to constrain the jet velocity and orientation., Comment: to appear in the Proceedings of the "Bl Lac Phenomenon" Conference, held in Turku, 1998 - June 22,26 - ed. Leo Takalo

We present here two epochs of Space VLBI Observations at 18 cm of the BL-Lac type object MKN 501. Thanks to the high resolution of these new data, we have found that the inner jet is centrally brightened at its beginning, but becomes extended and limb brightened at ~8 mas from the core. Moreover a comparison between the two epochs shows the presence of a proper motion with apparent velocity = 6.7c. Observational data have been used to constrain the jet velocity and orientation., Comment: 4 Pages, Figures included. To appear in the proceedings of the 32nd COSPAR Scientific Assembly, Sect. E1.3, Nagoya, Japan, July 13-18 1998. Adv. in Space Research

The parsec scale properties of low power radio galaxies are reviewed here, using the available data on 12 FR I galaxies. The most frequent radio structure is an asymmetric parsec-scale morphology, i.e. core and one-sided jet. It is shared by 9 (possibly 10) of the 12 mapped radio galaxies. One (possibly 2) of the other galaxies has (have) a two-sided jet emission. Two sources are known from published data to show a proper motion; we present here evidence for proper motion in two more galaxies. Therefore, in the present sample we have 4 radio galaxies with a measured proper motion. One of these has a very symmetric structure and therefore should be in the plane of the sky. The results discussed here are in agreement with the predictions of the unified scheme models. Moreover, the present data indicate that the parsec scale structure in low and high power radio galaxies is essentially the same., Comment: 9 pages, TEX, figures available only by FAX, e-mail address GGIOVANNINI@ASTBO1.BO.CNR.IT Invited paper at the National Academy of Sciences Colloquium: "Quasars and AGN: High Resolution Radio Imaging" Irvine (CA) March 24-25 1995 - to appear in the Proceedings of the National Academy of Sciences

The Fanaroff-Riley type I radio galaxies (Fanaroff & Riley, 1974) presented in this paper belong to the complete sample of low-intermediate luminosity radio galaxies published in Giovannini, Feretti & Comoretto (1990). This sample includes radio galaxies with different morphologies on the arcsecond scale, such as compact sources, core-halos, FRIs and FRIIs.

We present radio and optical observations of the peculiar radio galaxy J1835+620, a member of a new sample of large angular size radio galaxies selected from the NRAO VLA Sky Survey. Its optical counterpart is in a group of at least three galaxies and shows strong, narrow emission lines which allow us to measure its redshift as z=0.518. The derived cosmological distance places J1835+620 among the giant radio galaxies. The outstanding aspect of J1835+620 at radio wavelengths is the existence of two symmetric bright components within a typical Fanaroff-Riley type II structure. We interpret the source as the result of two distinct phases of core activity. Radio maps and radio polarization properties are consistent with a dense new ejection evolving through an older underlying jet. We suggest that interaction with nearby galaxies could be the reason for restarting the activity in J1835+620., 7 pages, 3 figures. To appear in Astronomy & Astrophysics, Main Journal