Interpretation of deep counts of radio sources

Danese, L.; Franceschini, A.; Toffolatti, L.; Zotti, G. de

doi:10.1086/184928

Cited by 57 publications

(63 citation statements)

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“…Integrating the radio luminosity functions of spiral galaxies, derived from the Benn et al sample, and elliptical galaxies (Dunlop & Peacock 1990) and testing various models for the evolutionary laws of the spiral luminosity function, they indeed find that ellipticals still contribute about 60 per cent of the integrated counts to a radio limit of 0.1 mJy. Previous models for the interpretation of the sub‐mJy radio counts, based on older luminosity functions and different models for the evolution, predicted a substantially lower fraction of early‐type galaxies in the same flux range (see, for example, Danese et al 1987).…”

Section: Discussionmentioning

confidence: 99%

Optical identifications and spectroscopy of a faint radio source sample: the nature of the sub-mJy population

Gruppioni

Mignoli

Zamorani

1999

Monthly Notices of the Royal Astronomical Society

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Deep imaging and spectroscopy have been carried out for optical counterparts of a sample of 68 faint radio sources (S > 0.2 mJy) in the Marano Field. About 60 per cent of the sources have been optically identified on deep CCD exposures (limit R ≃ 24.0) or ESO 3.6‐m plates (limit bJ≃ 22.5). 34 spectra (50 per cent of the total radio sample) were obtained with the ESO 3.6‐m telescope and 30 redshifts were determined. In addition to a few broad‐line active galactic nuclei, three main spectroscopic classes have been found to dominate the faint radio galaxy population. (1) Early‐type galaxies (without emission lines in their spectra) having 0.1 < z < 0.8 and covering the range of radio fluxes 0.2‐‐30 mJy. (2) Late‐type galaxies (with narrow emission lines in their spectra) at moderate redshift (z < 0.4), with relatively bright magnitudes (B < 22.5) and sub‐mJy radio fluxes. When applicable, the diagnostic diagrams for these sources are consistent with the lines being produced by star‐formation activity. (3) A group of bright high‐redshift (z > 0.8) radio galaxies with moderate‐to‐strong [O ii] emission. All of them have B > 22.5 and most of them have S1.4 GHz > 1 mJy. They have spectra, colours and absolute magnitudes similar to those of the classical bright elliptical radio galaxies found in surveys carried out at higher radio fluxes. Star‐forming galaxies do not constitute the main population of our radio sources identified with galaxies. In fact, even at sub‐mJy level the majority of our radio sources are identified with early‐type galaxies. This apparent discrepancy with previous results is due to the fainter magnitude limit reached in our spectroscopic identifications. Moreover, using mainly the large radio‐to‐optical ratio and the information from the available limits on the optical magnitudes of the unidentified radio sources, we conclude that the great majority of them are likely to be early‐type galaxies, at z > 1. If correct, it would suggest that the evolution of the radio luminosity function of spiral galaxies, including starbursts, might not be as strong as suggested in previous evolutionary models.

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Section: Discussionmentioning

confidence: 99%

Optical identifications and spectroscopy of a faint radio source sample: the nature of the sub-mJy population

Gruppioni

Mignoli

Zamorani

1999

Monthly Notices of the Royal Astronomical Society

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“…Early evolutionary models of radio sources (e.g., Danese et al 1987;Dunlop & Peacock 1990;Toffolatti et al 1998;Jackson & Wall 1999) were able to give remarkable successful fits to the majority of data coming from surveys at ν < ∼ 10 GHz, and down to flux densities of a few mJy. In particular, the model by Toffolatti et al (1998) was capable to give a good fit of ERS number counts of WMAP sources as well, albeit with an offset of a factor of about 0.7 (see, e.g., Bennett et al 2003).…”

Section: Introductionmentioning

confidence: 99%

High-frequency predictions for number counts and spectral properties of extragalactic radio sources. New evidence of a break at mm wavelengths in spectra of bright blazar sources

Tucci

Toffolatti

Zotti

et al. 2011

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103

201

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We present models to predict high-frequency counts of extragalactic radio sources using physically grounded recipes to describe the complex spectral behaviour of blazars that dominate the mm-wave counts at bright flux densities. We show that simple power-law spectra are ruled out by high-frequency (ν ≥ 100 GHz) data. These data also strongly constrain models featuring the spectral breaks predicted by classical physical models for the synchrotron emission produced in jets of blazars. A model dealing with blazars as a single population is, at best, only marginally consistent with data coming from current surveys at high radio frequencies. Our most successful model assumes different distributions of break frequencies, ν M , for BL Lacs and flat-spectrum radio quasars (FSRQs). The former objects have substantially higher values of ν M , implying that the synchrotron emission comes from more compact regions; therefore, a substantial increase of the BL Lac fraction at high radio frequencies and at bright flux densities is predicted. Remarkably, our best model is able to give a very good fit to all the observed data on number counts and on distributions of spectral indices of extragalactic radio sources at frequencies above 5 and up to 220 GHz. Predictions for the forthcoming sub-mm blazar counts from Planck, at the highest HFI frequencies, and from Herschel surveys are also presented.

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“…However, the local density of star‐forming radio sources is too small to explain the turn‐up point and slope of the log N / log S curve. Moreover, evolutionary models of the radio sources that dominate the counts at high flux densities cannot reproduce these features either (Danese et al 1987; Danese, De Zotti & Franceschini 1985). Therefore, models for the source counts invoke strong evolution of either spiral galaxies (Condon 1989; Dunlop & Peacock 1990) or star‐forming IRAS population galaxies (Danese et al 1987; Rowan‐Robinson et al 1993; Hopkins et al 1998).…”

Section: Introductionmentioning

confidence: 99%

The Phoenix Survey: optical and near-infrared observations of faint radio sources

Georgakakis

Mobasher

Cram

et al. 1999

Monthly Notices of the Royal Astronomical Society

105

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Using a deep Australia Telescope Compact Array (ATCA) radio survey covering an area of ≈3 deg2 to a 4σ sensitivity of ≥ 100 μJy at 1.4 GHz, we study the nature of faint radio galaxies. About 50 per cent of the detected radio sources are identified with an optical counterpart revealed by CCD photometry to mR=22.5 mag. Near‐infrared (K‐band) data are also available for a selected sample of the radio sources, while spectroscopic observations have been carried out for about 40 per cent of the optically identified sample. These provide redshifts and information on the stellar content. Emission‐line ratios imply that most of the emission‐line sources are star‐forming galaxies, with a small contribution (≈ 10 per cent) from Sy1/Sy2 type objects. We also find a significant number of absorption‐line systems, likely to be ellipticals. These dominate at high flux densities (>1 mJy) but are also found at sub‐mJy levels. Using the Balmer decrement we find a visual extinction AV=1.0 for the star‐forming faint radio sources. This moderate reddening is consistent with the V‐R and R‐K colours of the optically identified sources. For emission‐line galaxies, there is a correlation between the radio power and the Hα luminosity, in agreement with the result of Benn et al. This suggests that the radio emission of starburst radio galaxies is a good indicator of star formation activity.

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Interpretation of deep counts of radio sources

Cited by 57 publications

References 0 publications

Optical identifications and spectroscopy of a faint radio source sample: the nature of the sub-mJy population

Optical identifications and spectroscopy of a faint radio source sample: the nature of the sub-mJy population

High-frequency predictions for number counts and spectral properties of extragalactic radio sources. New evidence of a break at mm wavelengths in spectra of bright blazar sources

The Phoenix Survey: optical and near-infrared observations of faint radio sources

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