Spectral index properties of milliJansky radio sources

Randall, Kate; Hopkins, A. M.; Norris, R. P.; Zinn, Peter; Middelberg, E.; Mao, Minnie; Sharp, Robert

doi:10.1111/j.1365-2966.2012.20422.x

Cited by 50 publications

(51 citation statements)

References 104 publications

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“…This is in good agreement with the majority of previous work by other authors (e.g. Randall et al 2012;Ibar et al 2009). Since we also find that star-forming galaxies tend to have steeper radio spectra compared to AGN, we can support the current notion that star-forming galaxies become the dominant type of radio sources only at flux densities below 100 μJy since our sample does not reach such low flux densities.…”

Section: Discussionsupporting

confidence: 94%

“…Hence, we find no evidence for a flattening of the spectral index towards the lowest flux densities. This is consistent with the findings by Randall et al (2012) who used three frequencies (840 MHz, 1.4 GHz and 2.3 GHz) for their spectral index calculation and extend their findings to fainter flux limits. Ibar et al (2009) come to the same conclusion, too.…”

Section: Spectral Index Vs Flux Densitysupporting

confidence: 91%

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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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Section: Discussionsupporting

confidence: 94%

Section: Spectral Index Vs Flux Densitysupporting

confidence: 91%

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

Zinn

Middelberg

Norris

et al. 2012

A&A

Self Cite

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“…Laing & Peacock 1980) to 13 -49% for 1 -10 mJy level sources (Randall et al 2012;Ker 2012). This is higher than the fraction we observe in our faint 5.5 GHz sample.…”

Section: Radio Spectral Curvaturementioning

confidence: 99%

The ATLAS 5.5 GHz survey of the extendedChandraDeep Field South: the second data release

Huynh¹,

Bell²,

Hopkins³

et al. 2015

Mon. Not. R. Astron. Soc.

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We present a new image of the 5.5 GHz radio emission from the extended Chandra Deep Field South. Deep radio observations at 5.5 GHz were obtained in 2010 and presented in the first data release. A further 76 hours of integration has since been obtained, nearly doubling the integration time. This paper presents a new analysis of all the data. The new image reaches 8.6 µJy rms, an improvement of about 40% in sensitivity. We present a new catalogue of 5.5 GHz sources, identifying 212 source components, roughly 50% more than were detected in the first data release. Source counts derived from this sample are consistent with those reported in the literature for S 5.5GHz > 0.1 mJy but significantly lower than published values in the lowest flux density bins (S 5.5GHz < 0.1 mJy), where we have more detected sources and improved statistical reliability. The 5.5 GHz radio sources were matched to 1.4 GHz sources in the literature and we find a mean spectral index of −0.35 ± 0.10 for S 5.5GHz > 0.5 mJy, consistent with the flattening of the spectral index observed in 5 GHz sub-mJy samples. The median spectral index of the whole sample is α med = −0.58, indicating that these observations may be starting to probe the star forming population. However, even at the faintest levels (0.05 < S 5.5GHz < 0.1 mJy), 39% of the 5.5 GHz sources have flat or inverted radio spectra. Four flux density measurements from our data, across the full 4.5 to 6.5 GHz bandwidth, are combined with those from literature and we find 10% of sources (S 5.5GHz 0.1 mJy) show significant curvature in their radio spectral energy distribution spanning 1.4 to 9 GHz.

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“…These sources include AGNs and supernovae. The possible range of the sources' spectral index is very large, which could range from ∼ 0 to ∼ 1.5 [33,32,34]. The combination of these sources' contributions would give the final spectral index α CR .…”

Section: Spectral Data Fittingmentioning

confidence: 99%

Fitting dark matter mass with the radio continuum spectral data of the Ophiuchus cluster

Chan

Lee

2019

Physics of the Dark Universe

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Recent gamma-ray and anti-proton analyses suggest that dark matter with mass m = 48 − 67 GeV annihilating via bb channel can explain the Galactic center GeV gamma-ray excess and the anti-proton excess as measured by AMS-02 simultaneously. In this article, by differentiating the contributions of dark matter annihilation and normal diffuse cosmic rays, we show that dark matter with mass m = 40 −50 GeV annihilating via bb channel with the thermal relic annihilation cross section can best explain the radio continuum spectrum of the central radio halo of the Ophiuchus cluster. This mass range, annihilation cross section, and the annihilation channel is completely consistent with the dark matter interpretations of the GeV gamma-ray excess and the anti-proton excess.

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Spectral index properties of milliJansky radio sources

Cited by 50 publications

References 104 publications

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

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

The ATLAS 5.5 GHz survey of the extendedChandraDeep Field South: the second data release

Fitting dark matter mass with the radio continuum spectral data of the Ophiuchus cluster

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