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Centre National de la Recherche Scientifique / French National Centre for Scientific Research
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Papers by ivan Almeida
arXiv (Cornell University), Feb 10, 2021
Most active supermassive black holes (SMBH) in present-day galaxies are underfed and consist of l... more Most active supermassive black holes (SMBH) in present-day galaxies are underfed and consist of low-luminosity active galactic nuclei (LLAGN). They have multiwavelength broadband spectral energy distributions (SED) dominated by non-thermal processes which are quite different from those of the brighter, more distant quasars. Modelling the observed SEDs of LLAGNs is currently challenging, given the large computational expenses required. In this work, we used machine learning (ML) methods to generate model SEDs and fit sparse observations of LLAGNs. Our ML model consisted of a neural network and reproduced with excellent precision the radio-to-X-rays emission from a radiatively inefficient accretion flow around a SMBH and a relativistic jet, at a small fraction of the computational cost. The ML method performs the fit 4 × 10 5 times faster than previous semianalytic models. As a proofof-concept, we used the ML model to reproduce the SEDs of the LLAGNs M87, NGC 315 and NGC 4261.
Monthly Notices of the Royal Astronomical Society, 2018
NGC 3115 is the nearest galaxy hosting a billion solar mass black hole and is also a lowluminosit... more NGC 3115 is the nearest galaxy hosting a billion solar mass black hole and is also a lowluminosity active galactic nucleus (LLAGN). X-ray observations of this LLAGN are able to spatially resolve the hot gas within the sphere of gravitational influence of the supermassive black hole. These observations make NGC 3115 an important test bed for black hole accretion theory in galactic nuclei since they constrain the outer boundary conditions of the hot accretion flow. We present a compilation of the multiwavelength spectral energy distribution (SED) of the nucleus of NGC 3115 from radio to X-rays. We report the results from modelling the observed SED with radiatively inefficient accretion flow (RIAF) models. The radio emission can be wellexplained by synchrotron emission from the RIAF without the need for contribution from a relativistic jet. We obtain a tight constraint on the RIAF density profile, ρ(r) ∝ r −0.73 +0.01 −0.02 , implying that mass-loss through subrelativistic outflows from the RIAF is significant. The lower frequency radio observation requires the synchrotron emission from a non-thermal electron population in the RIAF, similarly to Sgr A*.
arXiv (Cornell University), Feb 10, 2021
Most active supermassive black holes (SMBH) in present-day galaxies are underfed and consist of l... more Most active supermassive black holes (SMBH) in present-day galaxies are underfed and consist of low-luminosity active galactic nuclei (LLAGN). They have multiwavelength broadband spectral energy distributions (SED) dominated by non-thermal processes which are quite different from those of the brighter, more distant quasars. Modelling the observed SEDs of LLAGNs is currently challenging, given the large computational expenses required. In this work, we used machine learning (ML) methods to generate model SEDs and fit sparse observations of LLAGNs. Our ML model consisted of a neural network and reproduced with excellent precision the radio-to-X-rays emission from a radiatively inefficient accretion flow around a SMBH and a relativistic jet, at a small fraction of the computational cost. The ML method performs the fit 4 × 10 5 times faster than previous semianalytic models. As a proofof-concept, we used the ML model to reproduce the SEDs of the LLAGNs M87, NGC 315 and NGC 4261.
Monthly Notices of the Royal Astronomical Society, 2018
NGC 3115 is the nearest galaxy hosting a billion solar mass black hole and is also a lowluminosit... more NGC 3115 is the nearest galaxy hosting a billion solar mass black hole and is also a lowluminosity active galactic nucleus (LLAGN). X-ray observations of this LLAGN are able to spatially resolve the hot gas within the sphere of gravitational influence of the supermassive black hole. These observations make NGC 3115 an important test bed for black hole accretion theory in galactic nuclei since they constrain the outer boundary conditions of the hot accretion flow. We present a compilation of the multiwavelength spectral energy distribution (SED) of the nucleus of NGC 3115 from radio to X-rays. We report the results from modelling the observed SED with radiatively inefficient accretion flow (RIAF) models. The radio emission can be wellexplained by synchrotron emission from the RIAF without the need for contribution from a relativistic jet. We obtain a tight constraint on the RIAF density profile, ρ(r) ∝ r −0.73 +0.01 −0.02 , implying that mass-loss through subrelativistic outflows from the RIAF is significant. The lower frequency radio observation requires the synchrotron emission from a non-thermal electron population in the RIAF, similarly to Sgr A*.