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Deep VLBI Imaging of Faint Radio Sources in the NOAO Bootes Field
We have conducted a deep, very long baseline interferometry (VLBI)observation at 1.4 GHz of an area of sky located within the NOAO Bootesfield, using the NRAO Very Long Baseline Array and 100 m Green BankTelescope. Applying wide-field VLBI techniques, a total of 61 sources,selected from a Westerbork Synthesis Radio Telescope (WSRT) image, weresurveyed simultaneously with a range of different sensitivities andresolutions. The survey covered a total of 1017 arcmin2=0.28deg2 divided into annular fields centered onα=14h29m27s0,δ=+35deg28'30.00" (J2000.0). The inner 0-2'of the field reached an unprecedented 1 σ rms noise level of 9μJy beam-1 and yielded two detections. VLBI J142923.6466and VLBI J142934.7033 have brightness temperatures in excess of106 K, and we locate the active nuclei of their host galaxies(NDWFS J142923.6+352851 and NDWFS J142934.7+352859, with I~16.3 and 19.6mag, respectively). Further deep surveys of the inner 2'-4' and 4'-6' ofthe field, with 1 σ rms noise levels of 11-19 μJybeam-1, detected a previously known source, VLBIJ142910.2224, a quasar with a brightness temperature in excess of109 K, that was also used during these observations as anin-beam phase calibrator. The deep VLBI survey between 0' and 6' thusdetected three radio sources, drawn from a total of 24 targets. Ashallower VLBI survey, conducted between 6' and 18' of the field center,and with 1 σ rms noise levels of 37-55 μJy beam-1,detected a further six radio sources, drawn from 37 additional targets.Each of those six VLBI detections has a brightness temperature in excessof 105 K; this hints that those six are accretion-powered, asuggestion reinforced by the double structure of three of them.Combining the deep and shallow VLBI surveys, optical identifications areavailable for eight of the nine VLBI detections. Only VLBI J142906.6095remains unidentified (I>25.6 mag), quite unusually, as its integratedWSRT flux density is 20 mJy. Two other sources are not detected in theK-band (K>18.5 mag), suggesting that some significant fraction ofthese compact radio sources may be located at z>1. The VLBI detectionrate for sub-mJy WSRT radio sources is 8+4-5%. TheVLBI detection rate for mJy WSRT sources is higher,29+11-12%. This observational trend is expectedfrom a rapidly evolving radio source population. Moreover, this trendsupports deep radio surveys, at lower resolution, which have suggestedthat the radio emission associated with fainter sub-mJy and μJysources arises via processes associated with extended regions of starformation. The nine VLBI detections reported here pinpoint the preciselocation of active nuclei or candidate active nuclei, and their VLBIpositions can help to anchor the NOAO Bootes field to the InternationalCelestial Reference Frame. The simultaneous detection of several sub-mJyand mJy radio sources, in a single observation, suggest that theircombined response may be used to self-calibrate wide-field VLBI data.There is every prospect that future deep VLBI observations will be ableto take advantage of this wide-field technique, in any random directionon the sky, thereby generating large-area, unbiased surveys of the faintradio source population.
| The deepest and widest VLBI survey yet: VLBA+GBT 1.4 GHz observations in Bootes
We present preliminary results from the deepest VLBI observations yetconducted. VLBA+GBT 1.4 GHz observations of a region within NOAO-N,reach an r.m.s. noise level of 9 microJy per beam. Three sources areclearly detected (/>7σ) within the inner 2 arcmin of the GBTprimary beam, including two sub-mJy sources and the `in-beam'calibrator. In addition, by tapering the data, we map out a much largerarea of sky, reaching well beyond the half-power point of the GBTprimary beam. An additional 6 sources are detected in the extendedfield. We comment briefly on the scientific motivation for even deeperand wider VLBI surveys, and note that the summed response of sources inthe field will permit self-calibration techniques to be employed in anyregion of the radio sky, including so-called `blank' fields.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Deep Westerbork 1.4 GHz Imaging of the Bootes Field
We present the results from our deep (16×12 hr) WesterborkSynthesis Radio Telescope (WSRT) observations of the approximately 7deg2 Bootes Deep Field, centered at14h32m05.75s, 34°16'47.5"(J2000.0). Our survey consists of 42 discrete pointings, with enoughoverlap to ensure a uniform sensitivity across the entire field, with alimiting sensitivity of 28 μJy (1 σrms). The catalogcontains 3172 distinct sources, of which 316 are resolved by the13''×27'' beam. The Bootes field is part ofthe optical/near-infrared imaging and spectroscopy survey effortconducted at various institutions. The combination of these data setsand the deep nature of the radio observations will allow unique studiesof a large range of topics including the redshift evolution of theluminosity function of radio sources, the K-z relation, the clusteringenvironment of radio galaxies, the radio/far-infrared correlation fordistant starbursts, and the nature of obscured radio-loud activegalactic nuclei.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| The CfA Redshift Survey: Data for the NGP +36 Zone
We have assembled redshifts for a complete sample of 719 galaxies withm_zw_ <= 15.5 in the declination range 32.5^deg^ <= δ <=38.5^deg^ and right ascension range 8^h^ <= α <= 17^h^. Wehave determined morphological types for all galaxies in the magnitudelimited sample by direct inspection of the POSS-O plates. 576 of theredshifts are measurements from Mount Hopkins, and 405 are newredshifts. We also include new redshifts for 77 fainter galaxies in thesame strip.
| H I observations of galaxies in the Hercules supercluster
An H-I survey of the Hercules supercluster region was conducted using21-cm line observations of galaxies listed in the Uppsala GeneralCatalog of Galaxies (Nilson, 1973). It is found that thethree-dimensional distribution of the sample deviates markedly from thatexpected for a randomly distributed sample, and that the sample volumecontains an underdense region in front of the supercluster. An upperlimit to the expansion velocity of this underdense region of 400 km/s isobtained.
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