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The study of steep spectrum sources containing compact components has become increasingly popular as the number of papers on the topic in this volume indicates. I wish to discuss the properties of a number of steep spectrum sources which are dominated by compact components whose spectra remain steep to quite low frequencies. Most of the known sources of this type do not have optical counterparts to the limit of the Palomar Sky Survey prints and thus, with the implicit assumption that they are extragalactic, have been referred to as “Optically Quiet Quasars”.
On 1981 March 17–18 we undertook MkIII VLBI observations of the quasars 1038+528 A, B (Owen et al. 1979; Owen et al. 1980) with an array of 7 telescopes operating simultaneously at λ3.6 and λ13 cm with right circular polarization reception at each wavelength. Because the sources are ~33″ apart they could be observed simultaneously at every telescope. Thus the corrupting contributions of the propagation medium and the instrumentation were approximately the same for each of the quasars, hence allowing us to calibrate the structure phase of B with respect to a reference point chosen in the map of A using the expression
where φB and φA are the observed fringe phases, φGB and φGA are the geometric contribution with respect to the reference points chosen in each map and φSA is the structure phase contribution with respect to the reference point chosen in the A map.
On 1983 May 10–11 we undertook simultaneous λ3.6 and λ13 cm Mark III VLBI observations of the quasars 1038+528 A,B. Our experimental conditions (i.e., synthesized band, uv-coverage, etc.) were almost identical to those we used on 1981 March 17–18. Thus, we could make a direct comparison of the results from both epochs.
Far-infrared (FIR), ultraviolet (UV), and soft X-ray observations are easily degraded by dust and gas between the source and the telescope. They must be made from space, where they are still affected by the interstellar medium (ISM) of our Galaxy. Fortunately the ISM is quite patchy, with several “cosmic windows” covering ∼ 100 deg2 of sky having exceptionally low interstellar extinction and cirrus emission. Since the universe is nearly isotropic, these windows contain representative samples of cosmologically distant sources and will be the targets of deep multiwavelength studies including SWIRE, GALEX/DIS, and XMM-LSS. Overlapping optical and radio surveys provide essential source identifications, redshifts, morphologies, and continuum spectra. The prototype VLA survey (see http://www.cv.nrao.edu/sirtf_fls/) covers the 5 deg2 SIRTF First-Look Survey (FLS) and is being used to identify the expected FIR sources in advance. Most will be star-forming galaxies obeying the very tight far-infrared/radio correlation and thus continuum radio sources stronger than S ≈ 100 μJy at 1.4 GHz. Proposed VLA surveys covering the remaining “cosmic windows” will be useful for studying the evolution of obscured AGNs, clusters, and other uncommon objects.
In recent years a number of very steep spectrum, compact radio sources have been discovered (e.g. Cotton 1983, Cotton and Owen 1985, Ulvestad 1985) which have no optical counterpart to the limit of the Palomar Sky Survey. VLBI observations of a number of these have confirmed the very compact (<10 mas) nature of several of these sources. Analysis of the available data in terms of the standard synchrotron modal suggest that they contain very weak magnetic fields, large particle densities and may emit detectable infrared and optical emission by inverse Campton scattering in the compact radio source (Cotton 1983). This paper will report on an analysis including new VLBI observations, infrared and optical imaging at KPNO and low frequency radio observations at CLRO of a number of these objects.
Early large scale radio surveys of the sky were made with instruments with poor imaging quality and were limited to measuring positions and brightnesses of discrete sources. In recent decades radio interferometric arrays have dramatically increased their speed, sensitivity and ability to image the sky and several large scale radio surveys are currently being made with imaging instruments. One of these surveys is discussed in this paper.
Recently we focussed our attention on a sample of Compact Steep-spectrum Sources (CSSs) selected because of the large bent radio jets seen in the inner region of emission. The largest distortions are often seen in sources dominated by jets, and there are suggestions that this might to some extent be due to projection effects. However, superluminal motion is rare in CSSs. The only case we know of so far is 3C147 (Alef at al. 1990) with a mildly superluminal speed of ≃ 1.3v/c. Moreover, the core fractional luminosity in CSSs is ≃ 3% and ≤ 0.4% for quasars and radio galaxies respectively. Similar values are found for large size radio sources i.e. both boosting and orientations in the sky are similar for the two classes of objects. An alternative possibility is that these bent-jet sources might also be brightened by interactions with the ambient media. There are clear indications that intrinsic distortions due to interactions with a dense inhomogeneous gaseous environment play an important role. Observational support comes from the large RMs found in CSSs (Taylor et al. 1992; Mantovani et al. 1994; Junor et al. these proc.) and often associated with strong depolarization (Garrington & Akujor, t.p.). The CSSs also have very luminous Narrow Line Regions emission, with exceptional velocity structure (Gelderman, t.p.).
We analyze polarization observations of 3C 147 at milliarcsecond scale which we have made with the VLBA at L, S, and C band and with the MERLIN array at K band. Several constraints placed by the observations on the physical conditions of the magnetoionic gas which produces the Faraday rotation are briefly discussed. Our data show that the Faraday rotation increases towards the VLBI core component with a maximum observed value of RM~ 4600±80 rad m−2. Such a value does not support the inclusion of 3C 147 as a source with exceedingly-high faraday rotation (SEFR), as suggested from published low-resolution observations.
We discuss our VLBA observations at 5 and 2.7 GHz and our MERLIN observations at 1.6 and 5 GHz. A MERLIN+VLBA image provided good starting model for self-calibration and we obtained an unprecedent image of the bent jet of 3C 216. Our observations suggest the detection of strong polarization position angle variation across the observing band. If this is due to Faraday rotation then 3C216 may have a four-figure observed rotation measure, which is unlikely to be due to errors in the polarization position angle calibration.
The polarization structure of synchrotron sources provides information about the magnetic field structure and thermal particle distributions near the source. Such information is critical to a full understanding of compact sources in the nuclei of galaxies and quasars. VLBI maps of these objects are frequently interpreted as showing jets even though the maps are dominated by a few bright regions. If these sources do indeed contain jets then the jet should have a relatively well-ordered component of the magnetic field. The presence of this ordered magnetic field, as well as the presence of thermal plasma in and around the jet, should be revealed by the polarized radiation. We present below the results of the first successful VLBI measurements of the polarized emission from an extragalactic compact radio source.
Radio interferometric observations of extragalactic radio sources have been made with antennas at the Haystack Observatory in Massachusetts and the Owens Valley Radio Observatory in California during fourteen separate experiments distributed between September 1976 and May 1978. The components of the baseline vector and the coordinates of the sources were estimated from the data from each experiment separately. The root-weighted-mean-square scatter about the weighted mean (“repeatability”) of the estimates of the length of the 3900 km baseline was approximately 7 cm, and of the source coordinates, approximately or less, except for the declinations of low-declination sources. With the source coordinates all held fixed at the best available, a posteriori, values, and the analyses repeated for each experiment, the repeatability obtained for the estimate of baseline length was 4 cm. From analyses of the data from several experiments simultaneously, estimates were obtained of changes in the x component of pole position and in the Earth's rotation (UT1). Comparison with the corresponding results obtained by the Bureau International de l'Heure (BIH) discloses systematic differences. In particular, the trends in the radio interferometric determinations of the changes in pole position agree more closely with those from the International Polar Motion Service (IPMS) and from the Doppler observations of satellites than with those from the BIH.
Gram-negative bacilli frequently cause epidemics in high-risk newborn intensive care units. Recently, an epidemic caused by a multiply-resistant K. pneumoniae, serotype 21, occurred in the Vanderbilt University intensive care nursery. The background of this outbreak included an increasing endemic nosocomial sepsis rate, operation of the facility in excess of rated capacity, and increasingly inadequate nurse-to-patient staffing ratios. The epidemic lasted 11 weeks; 26 (12%) of the 232 infants at risk in the unit became colonized. Five infants developed systemic illness and one died. Cohorting, reinforcement of strict handwashing and isolation procedures, and closure of the unit to outborn admissions resulted in rapid termination of the outbreak. Followup studies performed on infants colonized with the epidemic bacterium demonstrated persistent fecal shedding up to 13 months following discharge from the hospital. This epidemic had a detrimental influence on high-risk newborn and obstetric health care delivery in an area encompassing portions of three states. Under a system of progressively more sophisticated referral units, nosocomial infections occurring at a tertiary center can have an impact on other hospitals within the network.
W. F. Grimes excavated a rectangular earthwork in advance of airport construction in 1944, at Heathrow, Middlesex, and found a timber building of unique ‘concentric-rectangle’ plan, together with penannular house gullies; all these features were thought to be part of the same settlement except for two Neolithic pits. Now it can be seen that a Late Bronze Age occupation attested by scattered pottery and small finds but next to no identifiable structures, was followed by 11 Middle Iron Age round houses, and one or two features that may be Late Iron Age. The rampart of the earthwork overlay at least some of the houses. The rectangular building may be Middle or Late Iron Age: though other Iron Age rectangular buildings are now known, its concentric plan remains unique in Britain and resembles that of some Romano–Celtic temples. The precise chronological relationship of the strong earthwork, the round houses and the rectangular building remains uncertain.
The role of radio polarimetry in the understanding of GPS and CSS sources is explored. After an initial discussion of what can be learned from polarimetry, the expectations of a simple evolutionary sequence of GPS/CSO to CSS to FR I/FR II sources are explored. Observational results are then compared with the expectations. Conclusions include: the GPS category is likely not a single homogeneous class of objects; Faraday depth effects are very strong inside the inner 3 kpc of CSS and CSO sources; in at least 3C 138 the Faraday screen has very fine scale (subparsec) structure; and there is evidence for increased ionisation near bends in some CSS jets probably due to jet–ISM interaction. New results on 3C 138, 3C 43, and 3C 454 are given.
Asymptotic Giant Branch Stars (AGB) are evolved, mass losing red giants with tenuous molecular envelopes which have been the subject of much recent study using infrared and radio interferometers. In oxygen rich stars, radio SiO masers form in the outer regions of the molecular envelopes and are powerful diagnostics of the extent of these envelopes. Spectroscopically resolved infrared interferometry helps constrain the extent of various species in the molecular layer. We made VLBA 7 mm SiO maser, Keck Interferometer near IR and VLTI/MIDI mid IR high resolution observations of the stars U Ari, W Cnc, RX Tau, RT Aql, S Ser and V Mon. This paper presents evidence that the SiO is depleted from the gas phase and speculate that it is frozen onto Al2O3 grains and that radiation pressure on these grains help drive the outflow.
In this chapter, Alpert–Stein Factor Separation (FS) Methodology is used to assess the significance of various land surface characteristics on the development and precipitation characteristics of convective storms occurring downwind of an urban region. In particular, the roles of topography, momentum fluxes, radiative heat fluxes, and latent and sensible heat fluxes are evaluated. The use of this technique in investigating the relative and interactive roles of different nucleating aerosols, including cloud condensation nuclei, giant cloud condensation nuclei, and ice nuclei, on the development, structure, and precipitation processes of tropical convection is also then described.
Numerical mesoscale simulations of urban enhanced convection
We briefly review the application of a three-dimensional, cloud-resolving, mesoscale model case study described in Rozoff et al. (2003) to the examination of the impacts of St. Louis, MO, USA, land use and topography on local convective storms. Located within a relatively moist and temperate climate, St. Louis is an ideal city for experimental study since it is relatively isolated from other substantial urban areas and its local geography is devoid of major topography and large bodies of water. Furthermore, St. Louis was the site for a large field campaign in 1971–5, called Project METROMEX (Changnon et al., 1981). That study was dedicated to questions regarding the role of urban areas on weather modification. It is believed the findings for St. Louis are widely applicable to other cities containing similar background conditions.
The origin of the far-infrared emission from the nearby radio galaxy M87 remains a matter of debate. Some studies find evidence of a far-infrared excess due to thermal dust emission, whereas others propose that the far-infrared emission can be explained by synchrotron emission without the need for an additional dust emission component. We observed M87 with PACS and SPIRE as part of the Herschel Virgo Cluster Survey (HeViCS). We compare the new Herschel data with a synchrotron model based on infrared, submm and radio data to investigate the origin of the far-infrared emission. We find that both the integrated SED and the Herschel surface brightness maps are adequately explained by synchrotron emission. At odds with previous claims, we find no evidence of a diffuse dust component in M87.
We observed four nearby AGN with MIDI at the VLTI to investigate the mid-infrared emission from these sources. With our measurements we resolve the dusty structure around the nucleus of the Circinus galaxy. We find two dust components: a hot, small elongated structure with a size of 0.4 pc and a cooler, almost round component with a size of 1.9 pc. We interpret the emission to be originating in a geometrically thick dusty torus oriented perpendicular to the ionisation cone. Hence our finding nicely confirms the unified picture. We also observed the nucleus of Centaurus A and find that 70% of the mid infrared flux originates from an unresolved source with a size of less than 0.2 pc. In this case, the majority of the emission comes from a synchrotron source at the base of the radio jet. Two further galaxies, Mrk 1239 (Seyfert 1) and MCG -05-23-016 (Seyfert 2), also show unresolved mid infrared sources limiting the size of the dust distribution to less than 5 and 2 pc respectively.
Not all students of the Roman world may have realized that, following extensive discoveries in the last few years, Egypt has ceased to be the only part of the Empire from which there are now substantial numbers of documentary texts written on perishable materials. This article is intended as a survey and hand-list of the rapidly-growing ‘papyrological’ material from the Roman Near East. As is normal, ‘papyrology’ is taken to include also any writing in ink on portable, and normally perishable, materials: parchment, wood, and leather, as well as on fragments of pottery (ostraka). The area concerned is that covered by the Roman provinces of Syria (divided in the 190s into ‘Syria Coele’ and ‘Syria Phoenice’); Mesopotamia (also created, by conquest, in the 190s); Arabia; and Judaea, which in the 130s became ‘Syria Palaestina’. These administrative divisions are valid for the majority of the material, which belongs to the first, second and third centuries. For the earlier part of the period we include also papyri from Dura under the Parthian kings (Nos 34, 36–43, and 166), since they belong to the century before the Roman conquest and illustrate the continuity of legal and administrative forms; and five papyri from the kingdom of Nabataea, which after its ‘acquisition’ in 106 was to form the bulk of the new province of Arabia, on the grounds that in some sense dependent kingdoms were part of the Empire (Nos 180–184). Both groups are listed in brackets. We also include the extensive material from the first Jewish revolt (Nos 230–256) and from the Bar Kochba war of 132–5 (Nos 293–331), even though it derives from regimes in revolt against Rome. The private-law procedures visible in the Bar Kochba documents are continuous with those from the immediately preceding ‘provincial’ period (that of the later items in the ‘archive of Babatha’ and other documents). What changes dramatically after the outbreak of the revolt is language use: Hebrew now appears alongside Aramaic and Greek. But even as late as the third year of the revolt we find contracts in Aramaic. Our list at this point will supplement and correct that given by Millar in The Roman Near East, App. B.