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1.
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.  相似文献   

2.
This paper introduces a new program to find high-redshift radio galaxies in the Southern hemisphere through ultrasteep spectrum (USS) selection. We define a sample of 234 USS radio sources with spectral indices α843408≤−1.0 ( S ν∝να) and flux densities S 408≥ 200 mJy in a region of 0.35 sr, chosen by cross-correlating the revised 408 MHz Molonglo Reference Catalogue, the 843 MHz Sydney University Molonglo Sky Survey and the 1400 MHz NRAO VLA Sky Survey in the overlap region −40° < δ < −30°. We present Australia Telescope Compact Array (ATCA) high-resolution 1384 and 2368 MHz radio data for each source, which we use to analyse the morphological, spectral index and polarization properties of our sample. We find that 85 per cent of the sources have observed-frame spectral energy distributions that are straight over the frequency range 408–2368 MHz, and that, on average, sources with smaller angular sizes have slightly steeper spectral indices and lower fractional linear polarization. Fractional polarization is anticorrelated with flux density at both 1400 and 2368 MHz. We also use the ATCA data to determine observed-frame Faraday rotation measures for half of the sample.  相似文献   

3.
The Cambridge Low Frequency Synthesis Telescope has been used at 151 MHz to survey three regions centred at RA 10h05m, Dec. 53°54', RA 10h42m, Dec. 57°36' and RA 13h32m, 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.  相似文献   

4.
A new sample of very powerful radio galaxies is defined from the Molonglo Reference Catalogue, according to the criteria S 408 MHz>5 Jy, −30°≤ δ ≤10° and | b |≥10°. The sample is selected to have similar properties to the northern 3CR revised sample, and to be visible to a combination of existing northern telescopes such as the Very Large Array radio interferometer and large southern hemisphere telescope facilities. The sample contains 178 sources, of which spectroscopic redshifts are available in the literature for 128. For the remaining 50 sources, new radio imaging, optical imaging and spectroscopic observations are presented to identify the host galaxies and determine their redshifts. With these new observations the total sample is 100 per cent optically identified and redshifts are available for 174 (98 per cent) of the sources. The sample consists of one starburst galaxy, one Seyfert galaxy, 127 radio galaxies and 49 quasars. Basic properties of the sample, such as the distributions of the quasar and radio-galaxy populations in redshift and their locations on the radio power versus linear size ( P − D ) diagram, show no significant differences from the revised 3CR sample. The equatorial location and the high spectroscopic completeness of this sample make it a valuable resource for detailed studies of the nature and environments of these important objects with the new generation of southern hemisphere telescopes.  相似文献   

5.
We present a final unified catalogue for the 7C survey at 151 MHz with resolution  70 × 70 cosec(δ) arcsec2  . This has been constructed by amalgamating the existing catalogues derived from individual fields imaged at this resolution and eliminating redundancy in regions of mutual overlap. This is a non-trivial procedure because the flux in multiple-component sources may be fitted differently on alternative images, owing, for example, to differences in local noise and beam distortion. The final catalogue lists 43683 sources over an area of about 1.7 sr. Separate final catalogues have been published for the 7C Galactic Plane survey (7CG) and the lower-resolution survey of the low-declination strip  9h < RA < 16h, 20° < Dec < 35°  .  相似文献   

6.
We report the discovery of a pulsar with a Galactic longitude of 304° and a dispersion measure (DM) of 875 cm−3 pc. PSR J1302−63 has the second largest DM of any known pulsar. It is also relatively weak, with a flux density of only 0.2 mJy at 1500 MHz. This is the 13th pulsar with a DM greater than 400 cm−3 pc located more than 50° from the Galactic Centre. It provides further evidence for a significant pulsar population and enhanced electron densities within the major spiral arms.  相似文献   

7.
A method based on Lucy's iterative algorithm is developed to invert the equation of stellar statistics for the Galactic bulge and is then applied to the K -band star counts from the Two-Micron Galactic Survey in a number of off-plane regions (10°>| b |>2°, | l |<15°). The top end of the K -band luminosity function is derived and the morphology of the stellar density function is fitted to triaxial ellipsoids, assuming a non-variable luminosity function within the bulge. The results, which have already been outlined by López-Corredoira et al., are shown in this paper with a full explanation of the steps of the inversion: the luminosity function shows a sharp decrease brighter than M K =−8.0  mag when compared with the disc population; the bulge fits triaxial ellipsoids with the major axis in the Galactic plane at an angle with the line of sight to the Galactic centre of 12° in the first quadrant; the axial ratios are 1:0.54:0.33, and the distance of the Sun from the centre of the triaxial ellipsoid is 7860 pc. The major–minor axial ratio of the ellipsoids is found not to be constant, the best fit to the gradient being K z =(8.4±1.7)×exp(− t /(2000±920) pc), where t is the distance along the major axis of the ellipsoid in parsecs. However, the interpretation of this is controversial. An eccentricity of the true density-ellipsoid gradient and a population gradient are two possible explanations. The best fit for the stellar density, for 1300 pc< t <3000 pc, is calculated for both cases, assuming an ellipsoidal distribution with constant axial ratios, and when K z is allowed to vary. From these, the total number of bulge stars is ∼3×1010 or ∼4×1010, respectively.  相似文献   

8.
We have derived the angular correlation function of a sample of 2096 sources detected in the ROSAT All-Sky Survey (RASS) Bright Source Catalogue, in order to investigate the clustering properties of active galactic nuclei (AGN) in the local Universe. Our sample is constructed by rejecting all known stars, as well as extended X-ray sources. Areas with | b |<30° and declination δ <−30° are also rejected owing to the high or uncertain neutral hydrogen absorption. Cross-correlation of our sample with the Hamburg/RASS optical identification catalogue suggests that the vast majority of our sources are indeed AGN. A 4.1 σ correlation signal between 0° and 8° was detected with w ( θ <8°)=2.5±0.6×10−2. Assuming a two-point correlation function of the form w ( θ )=( θ θ 0)−0.8, we find θ 0=0062. Deprojection on three dimensions, using Limber's equation, yields a spatial correlation length of r 0≈6.0±1.6  h −1 Mpc. This is consistent with the AGN clustering results derived at higher redshifts in optical surveys and suggests a comoving model for the clustering evolution.  相似文献   

9.
Centaurus B (PKS B1343−601) is one of the brightest and closest radio galaxies, with flux density ∼250 Jy at 408 MHz and redshift 0.01215, but it has not been studied much because of its position (i) close to the Galactic plane (it is also known as G309.6+1.7 and Kes 19) and (ii) in the southern sky. It has recently been suggested as the centre of a highly obscured cluster behind the Galactic plane. We present radio observations made with the Australia Telescope Compact Array and Molonglo Observatory Synthesis Telescope to study the jets and lobes. The total intensity and polarization radio images of the FR I jets are used to determine the jet brightness and width variations, magnetic field structure and fractional polarization. The equipartition pressure calculated along the jets declines rapidly over the first 1 arcmin from the galaxy reaching a constant pressure of 10−13  h −4/7 Pa in the lobes blown in the intracluster medium.  相似文献   

10.
We present radio interferometric observations of the Algol-type binary system RZ Cassiopeiae made with the VLA and MERLIN arrays at 6 cm over an incomplete orbital cycle of the system (1.195 d). We detected RZ Cas with both instruments. The images were unresolved in both cases, with angular extents comparable to the synthesized beams. The peak flux density in the VLA image was 1.14 mJy beam−1 and in the MERLIN image it was 0.93 mJy beam−1. The derived brightness temperatures are  4.02 × 108  and  4.35 × 108 K  and the effective electron energies are 0.347 and 0.346 MeV for the MERLIN and VLA data respectively. The radio light curve shows an interesting modulation centred close to the primary eclipse which seems to correlate with ASCA SIS observations of the system. The results can be interpreted as an emitting region on the outer hemisphere of the cool component aligned along the centroid axis of the binary system.  相似文献   

11.
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.  相似文献   

12.
We present a 1.1 mm wavelength imaging survey covering 0.3 deg2 in the COSMOS field. These data, obtained with the AzTEC continuum camera on the James Clerk Maxwell Telescope, were centred on a prominent large-scale structure overdensity which includes a rich X-ray cluster at z ≈ 0.73. A total of 50 mm-galaxy candidates, with a significance ranging from 3.5 to 8.5σ, are extracted from the central 0.15 deg2 area which has a uniform sensitivity of ∼1.3 mJy beam−1. 16 sources are detected with S/N ≥ 4.5, where the expected false-detection rate is zero, of which a surprisingly large number (9) have intrinsic (deboosted) fluxes ≥5 mJy at 1.1 mm. Assuming the emission is dominated by radiation from dust, heated by a massive population of young, optically obscured stars, then these bright AzTEC sources have far-infrared luminosities  >6 × 1012 L⊙  and star formation rates  >1100 M⊙ yr−1  . Two of these nine bright AzTEC sources are found towards the extreme peripheral region of the X-ray cluster, whilst the remainder are distributed across the larger scale overdensity. We describe the AzTEC data reduction pipeline, the source-extraction algorithm, and the characterization of the source catalogue, including the completeness, flux deboosting correction, false-detection rate and the source positional uncertainty, through an extensive set of Monte Carlo simulations. We conclude with a preliminary comparison, via a stacked analysis, of the overlapping MIPS 24-μm data and radio data with this AzTEC map of the COSMOS field.  相似文献   

13.
We present a catalogue of 781 compact radio sources in the declination range 0° ≤ δB1950≤ +20° whose positions have been measured to an rms accuracy of about 14 mas with the Very Large Array (VLA). These sources are primarily intended for use as phase calibration sources for the Jodrell Bank 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.  相似文献   

14.
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.  相似文献   

15.
New images of the supernova remnant (SNR) G351.7+0.8 are presented based on 21-cm H  i -line emission and continuum emission data from the Southern Galactic Plane Survey. SNR G351.7+0.8 has a flux density of 8.4 ± 0.7 Jy at 1420 MHz. Its spectral index is 0.52 ± 0.25 ( S = v −α) between 1420 and 843 MHz, typical of adiabatically expanding shell-like remnants. H  i observations show structures possibly associated with the SNR in the radial velocity range of −10 to −18 km s−1, and suggest a distance of 13.2 kpc and a radius of 30.7 pc. The estimated Sedov age for G351.7+0.8 is less than  6.8×104 yr  . A young radio pulsar PSR J1721−3532 lies close to SNR G351.7+0.8 on the sky. The new distance and age of G351.7+0.8 and recent proper motion measurements of the pulsar strongly argue against an association between SNR G351.7+0.8 and PSR J1721−3532. There is an unidentified, faint X-ray point source 1RXS J172055.3−353937 which is close to G351.7+0.8. This may be a neutron star potentially associated with G351.7+0.8.  相似文献   

16.
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.  相似文献   

17.
We calculate the expected amplitude of the dipole and higher spherical harmonics in the angular distribution of radio galaxies. The median redshift of radio sources in existing catalogues is z  ∼ 1, which allows us to study large-scale structure on scales between those accessible to present optical and infrared surveys, and that of the cosmic microwave background (CMB). The dipole is a result of two effects which turn out to be of comparable magnitude: (i) our motion with respect to the CMB, and (ii) large-scale structure, parametrized here by a family of cold dark matter power-spectra. We make specific predictions for the Green Bank 1987 (87GB) and Parkes–MIT–NRAO (PMN) catalogues, which in our combined catalogue include ∼ 40 000 sources brighter than 50 mJy at 4.85 GHz, over about 70 per cent of the sky. For these relatively sparse catalogues both the motion and large-scale structure dipole effects are expected to be smaller than the Poisson shot noise. However, we detect dipole and higher harmonics in the combined 87GB–PMNraw catalogue which are far larger than expected. We attribute this to a 2 per cent flux mismatch between the two catalogues. Ad hoc corrections made in an effort to match the catalogues may suggest a marginal detection of a dipole. To detect a dipole and higher harmonics unambiguously, a catalogue with full sky coverage and ∼ 106 sources is required. We also investigate the existence and extent of the supergalactic plane in the above catalogues. In a strip of ± 10° of the standard supergalactic equator, we find a 3 σ detection in PMNraw, but only 1 σ in 87 GBraw. We briefly discuss the implications of ongoing surveys such as FIRST and NVSS and follow-up redshift surveys.  相似文献   

18.
We report on the discovery of three new pulsars in the first blind survey of the north Galactic plane  (45° < l < 135°; | b | < 1°)  with the Giant Meterwave Radio telescope (GMRT) at an intermediate frequency of 610 MHz. The survey covered 106 deg2 with a sensitivity of roughly 1 mJy to long-period pulsars (pulsars with period longer than 1 s). The three new pulsars have periods of 318, 933 and 1056 ms. Their timing parameters and flux densities, obtained in follow-up observations with the Lovell Telescope at Jodrell Bank and the GMRT, are presented. We also report on pulse nulling behaviour in one of the newly discovered pulsars, PSR J2208+5500.  相似文献   

19.
We have detected the Sunyaev–Zel'dovich (SZ) increment at 850 μm in two galaxy clusters (Cl 0016+16 and MS 1054.4−0321) using the Submillimetre Common User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope. Fits to the isothermal β model yield a central Compton y parameter of  (2.2 ± 0.7) × 10−4  and a central 850-μm flux of  Δ I 0= 2.2 ± 0.7 mJy beam−1  in Cl 0016. This can be combined with decrement measurements to infer   y = (2.38 ±0.360.34) × 10−4  and   v pec= 400±19001400 km s−1  . In MS 1054 we find a peak 850-μm flux of  Δ I 0= 2.0 ± 1.0 mJy beam−1  and   y = (2.0 ± 1.0) × 10−4  . To be successful such measurements require large chop throws and non-standard data analysis techniques. In particular, the 450-μm data are used to remove atmospheric variations in the 850-μm data. An explicit annular model is fit to the SCUBA difference data in order to extract the radial profile, and separately fit to the model differences to minimize the effect of correlations induced by our scanning strategy. We have demonstrated that with sufficient care, SCUBA can be used to measure the SZ increment in massive, compact galaxy clusters.  相似文献   

20.
We have conducted a submillimetre mapping survey of faint, gravitationally lensed sources, where we have targeted 12 galaxy clusters and additionally the New Technology Telescope (NTT) Deep Field. The total area surveyed is 71.5 arcmin2 in the image plane; correcting for gravitational lensing, the total area surveyed is 40 arcmin2 in the source plane for a typical source redshift z ≈ 2.5. In the deepest maps, an image plane depth of 1σ rms ∼0.8 mJy is reached. This survey is the largest survey to date to reach such depths. In total 59 sources were detected, including three multiply imaged sources. The gravitational lensing makes it possible to detect sources with flux density below the blank field confusion limit. The lensing-corrected fluxes range from 0.11 to 19 mJy. After correcting for multiplicity, there are 10 sources with fluxes <2 mJy of which seven have submJy fluxes, doubling the number of such sources known. Number counts are determined below the confusion limit. At 1 mJy, the integrated number count is  ∼104 deg−2  , and at 0.5 mJy it is  ∼2 × 104 deg−2  . Based on the number counts, at a source plan flux limit of 0.1 mJy, essentially all of the 850-μm background emission has been resolved. The dominant contribution (>50 per cent) to the integrated background arises from sources with fluxes S 850 between 0.4 and 2.5 mJy, while the bright sources S 850 > 6 mJy contribute only 10 per cent.  相似文献   

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