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M. Cirasuolo

Publications and source records attributed to M. Cirasuolo.

95 records · Page 6Linked to original sources
arXiv2004

Faint radio-loud quasars: clues to their evolution

The quasar sample selected by cross-correlating the FIRST and the 2dF Quasar Redshift Surveys allows us to explore, for the first time, the faint end of the radio and optical luminosity functions up to z = 2.2. We find indications (~3 σ) of a negative evolution for these faint sources at z > 1.8, both in radio and optical bands. This corresponds to a decrement in the space density of faint quasars of about a factor 2 at z=2.2 and confirms the presence of a differential evolution for the population of radio-active quasars. The faint end of both luminosity functions flattens and the comparison with the (optical) number density of the whole quasar population supports a dependence of the fraction of radio detected quasars on the optical luminosity. A progressive decrease in the fraction of quasars in the whole radio source population can be consistently accounted for within the `receding torus' scenario. The population of low luminosity quasars, which the FIRST-2dF detects, appears to depart from the `classical' scheme for radio-loud quasars.

astro-ph↗
arXiv2004

From First Galaxies to QSOs: feeding the baby monsters

We present a physical model for the coevolution of massive spheroidal galaxies and active nuclei at their centers. Supernova heating is increasingly effective in slowing down the star formation and in driving gas outflows in smaller and smaller dark matter halos. Thus the more massive protogalaxies virializing at early times are the sites of faster star formation. The correspondingly higher radiation drag causes a faster angular momentum loss by the gas and induces a larger accretion rate onto the central black hole. In turn, the kinetic energy of the outflows powered by the active nuclei can unbind the residual gas in a time shorter for larger halos. The model accounts for a broad variety of dynamical, photometric and metallicity properties of early-type galaxies, for the M_BH -- σrelation and for the local supermassive black-hole mass function.

astro-ph↗
arXiv2003

Unveiling Radio Loudness in Quasars

We present a new approach to tackle the issue of radio loudness in quasars. We constrain a (simple) prescription for the intrinsic distribution of radio-to-optical ratios by comparing properties of Monte Carlo simulated samples with those of observed optically selected quasars. We find strong evidence for a dependence of the radio luminosity on the optical one, even though with a large scatter. The intrinsic distribution of the radio-to-optical ratios shows a peak at R*{1.4} ~ 0.3, with only ~5 per cent of objects being included in a high R*{1.4} tail which identifies the radio loud regime.

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arXiv2003

Is there a Dichotomy in the Radio Loudness Distribution of Quasars?

We present a new approach to tackle the issue of radio loudness in quasars. We constrain a (simple) prescription for the intrinsic distribution of radio-to-optical ratios by comparing properties of Monte Carlo simulated samples with those of observed optically selected quasars. We find strong evidence for a dependence of the radio luminosity on the optical one, even though with a large scatter. The dependence of the fraction of radio loud quasars on apparent and absolute optical magnitudes results in a selection effect related to the radio and optical limits of current surveys. The intrinsic distribution of the radio-to-optical ratios shows a peak at $R^*_{1.4} \sim 0.3$, with only $\simlt 5$ per cent of objects being included in a high $R^*_{1.4}$ tail which identifies the radio loud regime. No lack or deficit of sources -- but only a steep transition region -- is present between the radio loud and radio quiet populations at any $R^*_{1.4}$. We briefly discuss possible origins for this behaviour (e.g. absence of jets in radio quiet sources, large range of radiative radio efficiency, different life-times for the accretion and jet ejection phenomena, ...).

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arXiv2003

The Radio Loud / Radio Quiet dichotomy: news from the 2dF QSO Redshift Survey

We present a detailed analysis of a sample of radio-detected quasars, obtained by matching together objects from the FIRST and 2dF Quasar Redshift Surveys. The dataset consists of 113 sources, spanning a redshift range 0.3 < z < 2.2, with optical magnitudes 18.25 < b_J < 20.85 and radio fluxes S_{1.4 GHz} < 1 mJy. These objects exhibit properties such as redshift and colour distribution in full agreement with those derived for the whole quasar population, suggestive of an independence of the mechanism(s) controlling the birth and life-time of quasars of their level of radio emission. The long debated question of radio-loud (RL)/radio-quiet (RQ) dichotomy is then investigated for the combined FIRST-2dF and FIRST-LBQS sample, since they present similar selection criteria. We find the fraction of radio detections to increase with magnitude from < 3% at the faintest levels up to 20% for the brightest sources. The classical RL/RQ dichotomy, in which the distribution of radio-to-optical ratios and/or radio luminosities shows a lack of sources, is ruled out by our analysis. We also find no tight relationship between optical and radio luminosities for sources in the considered sample, result that tends to exclude the mass of the quasar black hole as the physical quantity associated to the level of radio emission.

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