On the Spectral Index-Flux Density Relation for Large Samples of Radio Sources

Zhang, Xizhen; Reich, W.; Reich, P.; Wielebinski, R.

doi:10.1088/1009-9271/3/4/347

Cited by 7 publications

(9 citation statements)

References 19 publications

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“…frequencies. A similar flattening trend is also seen at both lower and higher frequencies, e.g., between 74 MHz and 1.4 GHz by Cohen et al (2004) and Tasse et al (2006), between 1.4 GHz and 325 MHz by de Vries et al (2002), between 325 MHz and 1.4 GHz by Zhang et al (2003) and Owen et al (2009), between 610 MHz and 1.4 GHz by Bondi et al (2007), and between 1.4 and 5 GHz by Prandoni et al (2006). Recently, Bornancini et al (2010) found that, for a nearcomplete sample of radio galaxies, there is no evidence for spectral steepening or flattening due to redshifted curved radio spectra.…”

Section: Spectral Indicessupporting

confidence: 69%

Deep low-frequency radio observations of the NOAO Boötes field

Intema

Weeren

Röttgering

et al. 2011

A&A

103

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In this article we present deep, high-resolution radio interferometric observations at 153 MHz to complement the extensively studied NOAO Boötes field. We provide a description of the observations, data reduction and source catalog construction. From our single pointing GMRT observation of ∼12 h we obtain a high-resolution (26 × 22 ) image of ∼11.3 square degrees, fully covering the Boötes field region and beyond. The image has a central noise level of ∼1.0 mJy beam −1 , which rises to 2.0-2.5 mJy beam −1 at the field edge, placing it amongst the deepest ∼150 MHz surveys to date. The catalog of 598 extracted sources is estimated to be ∼92 percent complete for >10 mJy sources, while the estimated contamination with false detections is <1 percent. The low rms position uncertainty of 1.24 facilitates accurate matching against catalogs at optical, infrared and other wavelengths. Differential source counts are determined down to 10 mJy. There is no evidence for flattening of the counts towards lower flux densities as observed in deep radio surveys at higher frequencies, suggesting that our catalog is dominated by the classical radio-loud AGN population that explains the counts at higher flux densities. Combination with available deep 1.4 GHz observations yields an accurate determination of spectral indices for 417 sources down to the lowest 153 MHz flux densities, of which 16 have ultra-steep spectra with spectral indices below −1.3. We confirm that flattening of the median spectral index towards low flux densities also occurs at this frequency. The detection fraction of the radio sources in NIR K S -band is found to drop with radio spectral index, which is in agreement with the known correlation between spectral index and redshift for brighter radio sources.

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Section: Spectral Indicessupporting

confidence: 69%

Deep low-frequency radio observations of the NOAO Boötes field

Intema

Weeren

Röttgering

et al. 2011

A&A

103

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“…The flux densities of point-like sources at λ6 cm were estimated from the extrapolation of the NVSS flux density at 1.4 GHz (Condon et al 1998) using a spectral index either taken from Vollmer et al (2005) or derived from the flux densities at 408 MHz and 1420 MHz from the Canadian Galactic Plane Survey (CGPS) (Taylor et al 2003). If no spectral index is available for a source, we adopted the mean value of α = −0.9 according to Zhang et al (2003) obtained from the NVSS and the WSRT source samples.…”

Section: Resultsmentioning

confidence: 99%

A Sino-Germanλ6 cm polarization survey of the Galactic plane

Gao

Han

Reich

et al. 2011

A&A

Self Cite

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Context.Observations of large supernova remnants (SNRs) at high frequencies are rare, but provide valuable information about their physical properties. Aims. The total intensity and polarization properties of 16 large SNRs in the Galactic plane are investigated based on observations of the Urumqi λ6 cm polarization survey of the Galactic plane with an angular resolution of 9. 5. Methods. We extracted total intensity and linear polarization maps of large SNRs from the Urumqi λ6 cm survey, obtained their integrated flux densities, and derived the radio spectra by using these flux densities together with previously published flux densities at various frequencies. In particular, Effelsberg λ11 cm and λ21 cm survey data were used to calculate integrated flux densities. The λ6 cm polarization data also delineate the magnetic field structures of the SNRs. Results. We present the first total intensity maps at λ6 cm for SNRs G106.3+2.7, G114.3+0.3, G116.5+1.1, G166.0+4.3 (VRO 42.05.01), G205.5+0.5 (Monoceros Nebula), and G206.9+2.3 (PKS 0646+06) and the first polarization measurements at λ6 cm for SNRs G82.2+5.3 (W63), G106.3+2.7, G114.3+0.3, G116.5+1.1, G166.0+4.3 (VRO 42.05.01), G205.5+0.5 (Monoceros Nebula), and G206.9+2.3 (PKS 0646+06). Most of the newly derived integrated radio spectra are consistent with previous results. The new flux densities obtained from the Urumqi λ6 cm, Effelsberg λ11 cm and λ21 cm surveys are crucial to determine the spectra of SNR G65.1+0.6, G69.0+2.7 (CTB 80), G93.7−0.2, and G114.3+0.3. We find that G192.8−1.1 (PKS 0607+17) consists of background sources, H ii regions, and extended diffuse emission of thermal nature, and conclude that G192.8−1.1 is not a SNR.

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“…A flattening of the spectral index with lower flux density levels, as e.g. seen by Zhang et al (2003), was initially suspected by Windhorst et al (1993). A major line of argument is that, at sub-mJy levels, a change in population takes place: at mJy levels, the radio sky is completely dominated by AGN (see e.g.…”

Section: Spectral Index Vs Flux Densitymentioning

confidence: 93%

The Australia Telescope Large Area Survey: 2.3 GHz observations of ELAIS-S1 and CDF-S

Zinn

Middelberg

Norris

et al. 2012

A&A

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Context. The Australia Telescope Large Area Survey (ATLAS) aims to image a 7 deg 2 region centred on the European Large Area ISO Survey -South 1 (ELAIS-S1) field and the Chandra Deep Field South (CDF-S) at 1.4 GHz with high sensitivity (up to σ ∼ 10 μJy) to study the evolution of star-forming galaxies (SFGs) and Active Galactic Nuclei (AGN) over a wide range of cosmic time. Aims. We present here ancillary radio observations at a frequency of 2.3 GHz obtained with the Australia Telescope Compact Array (ATCA). The main goal of this is to study the radio spectra of an unprecedented large sample of sources (∼2000 observed, ∼600 detected in both frequencies). Methods. With this paper, we provide 2.3 GHz source catalogues for both ATLAS fields, with a detection limit of 300 μJy (equivalent to 4.5σ in the ELAIS-S1 field and 4.0σ in the CDF-S). We compute spectral indices between 1.4 GHz and 2.3 GHz using matchedresolution images and investigate various properties of our source sample in dependence of their spectral indices. Results. We find the entire source sample to have a median spectral index α med = −0.74, in good agreement with both the canonical value of −0.7 for optically thin synchrotron radiation and other spectral index studies conducted by various groups. Regarding the radio spectral index as indicator for source type, we find only marginal correlations so that flat or inverted spectrum sources are usually powered by AGN and hence conclude that at least for the faint population the spectral index is not a strong discriminator. We investigate the z-α relation for our source sample and find no such correlation between spectral index and redshift at all. We do find a significant correlation between redshift and radio to near-infrared flux ratio, making this a much stronger tracer of high-z radio sources. We also find no evidence for a dependence of the radio-IR correlation on spectral index.

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On the Spectral Index-Flux Density Relation for Large Samples of Radio Sources

Cited by 7 publications

References 19 publications

Deep low-frequency radio observations of the NOAO Boötes field

Deep low-frequency radio observations of the NOAO Boötes field

A Sino-Germanλ6 cm polarization survey of the Galactic plane

The Australia Telescope Large Area Survey: 2.3 GHz observations of ELAIS-S1 and CDF-S

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