Interferometer phase calibration sources — III. The regions +20 ≤ δ B1950 ≤ + 35° and +75 ≤ δ B1950 ≤ + 90°

We present a catalogue of 540 compact radio sources in the declination ranges +20 ≤ δ _B1950 ≤ + 35° and +75 ≤ δ _B1950 ≤ + 90°, the positions of which have been measured to an rms accuracy of about 55 mas with the Very Large Array (VLA). These sources are primarily intended for use as phase calibration sources for MERLIN. However, they will also be suitable as phase calibrators for the VLA and can be considered as candidate phase calibrators for very long baseline interferometry (VLBI) networks.     

The 7C(G) survey of radio sources at 151 MHz — the Galactic plane at 80° < l < 104° and 126° < l < 180°, for |b|≤ 55°.

Results from a survey of the northern Galactic plane (at declination ≳ 30°) at 151 MHz made with the Cambridge Low Frequency Synthesis Telescope are presented. This survey is designated the 7C(G) — i.e. the Galactic portion of the ongoing 7C surveys. This covers the regions 80° <  l  104° and 126° <  l  < 180°, for | b | ≤ 55^°_., and has some coverage to | b | ≈ 9°, with a resolution of ≈ 70 × 70 cossec (δ) arcsec² (RA × Dec.). The observations, data reduction and calibration of this survey are described, and a catalogue of 6262 compact sources, with a completeness limit of ≈ 0.25 Jy over most of the survey region, is presented. The catalogue has an rms positional accuracy of better than 10 arcsec, and the flux densities are tied to the scale of Roger, Bridle & Costain with an accuracy of better than 10 per cent.     

The 7C survey of radio sources at 151 MHz: three regions centred at RA 10h05m, Dec. 53°54', RA 10h42m, Dec. 57°36' and RA 13h32m,Dec. 38°10'

The Cambridge Low Frequency Synthesis Telescope has been used at 151 MHz to survey three regions centred at RA 10^h05^m, Dec. 53°54', RA 10^h42^m, Dec. 57°36' and RA 13^h32^m, Dec. 38°10', each of area 7.3×7.3 cosec δ deg². The resolution is 70×70 cosec δ arcsec², and the rms noise on the maps is typically 15 mJy beam⁻¹. We present positions and flux densities for 2381 sources which have signal-to-noise ratios >5.5.     

A 408-MHz variability study of two fields in the region 6h30m, +45°

Variability in 408-MHz flux density, over a 1-yr interval between 1995 and 1996, has been investigated using the DRAO Synthesis Telescope for a complete sample of 322 sources with S _408 MHz > 80 mJy at galactic latitude b  = 15°; four sources are found to show significant flux density variations. These results, taken with those from a similar study at b  = 58°, indicate that 408-MHz variability over a time-scale of 1 yr is more uncommon than has previously been thought; variations at a level >10 per cent could have been detected in a statistically complete sample of about 150 of these sources and none was found. Variability over a period of 18 yr has also been investigated by comparing the DRAO data with those from the B3 catalogue for 182 sources with S _408 MHz > 200 mJy; five variables are found. Large flux density variations over a period of 18 yr are much more common than over 1 yr, with roughly one source in 15 showing variations at the 15 per cent level or greater. The statistics are not good enough to show any conclusive evidence for a dependence of variability on galactic latitude. Roughly half of the variable sources have spectra that are steep at high frequencies and flatten at low frequencies; the other half have flat radio spectra over the entire frequency range. Simultaneous observations at 1420 MHz, also with the DRAO Synthesis Telescope, have been used to investigate variability at this frequency as well, and indicate that over a period of 1 yr roughly half of the flat-spectrum sources vary at the 5 per cent level or greater.     

Compact radio sources variable at 151 MHz – I. Catalogue of sources

The Cambridge Low-Frequency Synthesis Telescope has been used to produce a representative sample of low-frequency variable sources. 20 fields, each covering an area of approximately 9°×9° cosec  δ , have been observed at 151 MHz at between 2 and 10 epochs over the period from 1984 to 1996. At each epoch, maps were made with rms noise levels of typically 10–15 mJy beam⁻¹. From a total of ∼6000 sources detected on these maps, 207 are found for which the flux density variations between at least two epochs appear significant at greater than the 3 σ level. A numerical model is used to assess the true significance of the variability, given the analysis method adopted. This shows that for about half of the sources which appear to vary by >3 σ the variability is genuine. For the other half it is caused by random statistical fluctuations; most of the spurious variables vary by ≲3.5 σ between a single pair of epochs. A catalogue of the variable sources is presented, which includes an estimate of the probability that a given source is a genuine variable. Fractional flux density variations of between 5 and 100 per cent (typically 15–25 per cent) have been detected on a range of time-scales from 1 to 12 years.     

Faint UBVRI CCD sequences for wide-field surveys – II. UBVR sequences at δ=−30°

We present results from a continuing campaign to secure deep multi-colour CCD sequences for photometric calibration in UK Schmidt fields with galactic latitudes | b |>50°. In this paper we present UBVR photometry in 12 fields and BR photometry in a further 14 fields observed within UK Schmidt survey fields centred at δ =−30°. Photometric errors are at the 0.05 level at 20.2, 21, 20.5 and 20 mag for UBVR sequences respectively. Our observations were carried out with the 0.9-m telescope at the Cerro-Tololo Inter-American Observatory. These data are not intended for use as highly accurate individual photometric standards, but rather for use as sequences, using a large number of stars to calibrate wide-area data such as photographic plates. The data are available electronically at http://icstar5.ph.ic.ac.uk/~scroom/phot/photom.html .     

A 610-MHz survey of the Lockman Hole with the Giant Metrewave Radio Telescope – I. Observations, data reduction and source catalogue for the central 5 deg2

We present observations of the Lockman Hole taken at 610 MHz with the Giant Metrewave Radio Telescope (GMRT). Twelve pointings were observed, covering a total area of ∼5 deg² with a resolution of  6 × 5 arcsec²  , position angle  +45°  . The majority of the pointings have a rms noise of ∼60 μJy beam⁻¹ before correction for the attenuation of the GMRT primary beam. Techniques used for data reduction and production of a mosaicked image of the region are described, and the final mosaic is presented along with a catalogue of 2845 sources detected above 6σ. Radio source counts are calculated at 610 MHz and combined with existing 1.4-GHz source counts, in order to show that pure luminosity evolution of the local radio luminosity functions for active galactic nuclei and starburst galaxies is sufficient to account for the two source counts simultaneously.     

A sharper view of the outer Galaxy at 1420 and 408 MHz from the Canadian Galactic Plane Survey – I. Revisiting the KR catalogue and new Gigahertz Peaked Spectrum sources

Arcminute-resolution radio continuum images at 408 and 1420 MHz from the Canadian Galactic Plane Survey (CGPS) have been used to re-examine radio sources listed in the Kallas & Reich catalogue. This catalogue is of particular interest to Galactic studies as it lists both extended and compact radio sources found in the second Galactic quadrant. We have determined the nature (extended versus compact, Galactic versus extragalactic) of all of these bright radio sources. A number of large H  ii regions with no optical counterparts are highlighted along with a sample of large radio galaxies. Many sources previously thought to be extended Galactic objects are shown to be point sources. A sample of point sources with flat or rising spectra between 408 and 1420 MHz has been compiled, and within this sample likely Gigahertz Peaked Spectrum sources have been identified.     

The Millennium Galaxy Catalogue: 16 ≤BMGC < 24 galaxy counts and the calibration of the local galaxy luminosity function

The Millennium Galaxy Catalogue (MGC) is a 37.5 deg², medium-deep, B -band imaging survey along the celestial equator, taken with the Wide Field Camera on the Isaac Newton Telescope. The survey region is contained within the regions of both the Two Degree Field Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey Early Data Release (SDSS-EDR). The survey has a uniform isophotal detection limit of 26 mag arcsec⁻² and it provides a robust, well-defined catalogue of stars and galaxies in the range  16 ≤ B _MGC < 24 mag  .
Here we describe the survey strategy, the photometric and astrometric calibration, source detection and analysis, and present the galaxy number counts that connect the bright and faint galaxy populations within a single survey. We argue that these counts represent the state of the art and use them to constrain the normalizations (φ*) of a number of recent estimates of the local galaxy luminosity function. We find that the 2dFGRS, SDSS Commissioning Data (CD), ESO Slice Project, Century Survey, Durham/UKST, Mt Stromlo/APM, SSRS2 and NOG luminosity functions require a revision of their published φ* values by factors of  1.05 ± 0.05, 0.76 ± 0.10, 1.02 ± 0.22, 1.02 ± 0.16, 1.16 ± 0.28, 1.75 ± 0.37, 1.40 ± 0.26  and  1.01 ± 0.39  , respectively. After renormalizing the galaxy luminosity functions we find a mean local b _J luminosity density of     . ¹     

Spin vector orientation of galaxies in the region 15h 48m≤α(2000) ≤ 19h 28m, −68°≤δ(2000) ≤−62°

We present an analysis of the orientations of 1433 galaxies found in the region  15^h 48^m≤α(2000) ≤ 19^h 28^m, −68°≤δ(2000) ≤−62°  . In this region we investigated three Abell clusters (S0794, S0797, S0805) of richness Class 0 and the Triangulum Australis cluster. Our aim is to examine non-random effects in galaxy orientations in clusters. In addition, we classified the investigated galaxies into subsamples on the basis of their axial ratio, major diameter and morphology. The spin vector orientations of total galaxies in the investigated region is found to be random. No preferred orientation is found in the clusters. We could not note any morphological dependence of the galaxy orientations in our samples. No preferred orientations can be seen for the spiral galaxies. The morphologically unidentified galaxies, galaxies having major diameters of <47 arcsec, and the nearly edge-on galaxies  ( b / a < 0.5, 0.4 < b / a ≤ 0.5)  show anisotropy: spin vectors of galaxies tend to be oriented perpendicular to the Local Supercluster plane and spin vector projections tend to point radially with respect to the Virgo cluster centre.     

Compact radio sources variable at 151 MHz – II. High-resolution observations of an unbiased sample

High‐resolution observations, made with the Very Large Array (VLA) at 330 MHz, 1.4 GHz and 8.4 GHz and with the Ryle Telescope at 15 GHz, are presented of a sample of 23 sources which are variable at 151 MHz, concluding the observations of an unbiased sample of 40 such sources. The 8.4 GHz emission of almost all of the sources is dominated by structure on a scale ≲0.1 arcsec – the spectra of these compact components are such that they will also dominate the emission at 151 MHz; the number of sources for which this is not the case is consistent with the number of spurious variables expected to be found in the sample. About two-thirds of the sources have the self-absorbed, or flat, spectra expected from their size. The majority (∼75 per cent) of the sources belong to the compact steep-spectrum (CSS) class, but are generally more compact than other CSS sources; the CSS variables also appear to exhibit more spectral ageing than typical CSS sources, which may indicate a difference in the nature of the sources.     

A survey of polarization in the JVAS/CLASS flat-spectrum radio source surveys – I. The data and catalogue production

We have used the very large JVAS/CLASS 8.4-GHz surveys of flat-spectrum radio sources to obtain a large, uniformly observed and calibrated, sample of radio source polarizations. These are useful for many investigations of the properties of radio sources and the interstellar medium. We discuss comparisons with polarization measurements from this survey and from other large-scale surveys of polarization in flat-spectrum sources.     

Radio imaging of the Subaru/XMM–Newton Deep Field – I. The 100-μJy catalogue, optical identifications, and the nature of the faint radio source population

We describe deep radio imaging at 1.4 GHz of the 1.3-deg² Subaru/ XMM–Newton Deep Field (SXDF), made with the Very Large Array in B and C configurations. We present a radio map of the entire field, and a catalogue of 505 sources covering 0.8 deg² to a peak flux density limit of 100 μJy. Robust optical identifications are provided for 90 per cent of the sources, and suggested identifications are presented for all but 14 (of which seven are optically blank, and seven are close to bright contaminating objects). We show that the optical properties of the radio sources do not change with flux density, suggesting that active galactic nuclei (AGN) continue to contribute significantly at faint flux densities. We test this assertion by cross-correlating our radio catalogue with the X-ray source catalogue and conclude that radio-quiet AGN become a significant population at flux densities below 300 μJy, and may dominate the population responsible for the flattening of the radio source counts if a significant fraction of them are Compton-thick.     

A sample of 6C radio sources designed to find objects at redshift z > 4 — I. The radio data

We describe the selection of a sample of 34 radio sources from the 6C survey from a region of sky covering 0.133 sr. The selection criteria for this sample, hereafter called 6C*, were chosen to optimize the chances of finding radio galaxies at redshift z  > 4. Optical follow-up observations have already led to the discovery of the most distant known radio galaxy at z  = 4.41. We present VLA radio maps and derive radio spectra for all the 6C* objects.