The large total infrared (TIR) luminosities (LTIR ≳ 1012 L⊙) observed in z ∼ 6 quasars are generally converted into high star formation rates (SFR ≳ 102 M⊙ yr−1) of their host galaxies. However, these estimates rely on the assumption that dust heating is dominated by stellar radiation, neglecting the contribution from the central Active Galactic Nuclei (AGN). We test the validity of this assumption by combin- ing cosmological hydrodynamic simulations with radiative transfer calculations. We find that, when AGN radiation is included in the simulations, the mass (luminosity)- weighted dust temperature in the host galaxies increases from T ≈ 50 K (T ≈ 70 K) to T ≈ 80 K (T ≈ 200 K), suggesting that AGN effectively heat the bulk of dust in the host galaxy. We compute the AGN-host galaxy SFR from the synthetic spectral energy distribution by using standard SFR − LTIR relations, and compare the results with the “true” values in the simulations. We find that the SFR is overestimated by a factor of ≈ 3 (≳ 10) for AGN bolometric luminosities of Lbol ≈ 1012 L⊙ (≳ 1013 L⊙), implying that the star formation rates of z ∼ 6 quasars can be overestimated by over an order of magnitude.

Is the star formation rate in z ∼ 6 quasars overestimated?

Fabio Di Mascia
;
Stefano Carniani;Simona Gallerani;Andrea Pallottini;Andrea Ferrara;
2022

Abstract

The large total infrared (TIR) luminosities (LTIR ≳ 1012 L⊙) observed in z ∼ 6 quasars are generally converted into high star formation rates (SFR ≳ 102 M⊙ yr−1) of their host galaxies. However, these estimates rely on the assumption that dust heating is dominated by stellar radiation, neglecting the contribution from the central Active Galactic Nuclei (AGN). We test the validity of this assumption by combin- ing cosmological hydrodynamic simulations with radiative transfer calculations. We find that, when AGN radiation is included in the simulations, the mass (luminosity)- weighted dust temperature in the host galaxies increases from T ≈ 50 K (T ≈ 70 K) to T ≈ 80 K (T ≈ 200 K), suggesting that AGN effectively heat the bulk of dust in the host galaxy. We compute the AGN-host galaxy SFR from the synthetic spectral energy distribution by using standard SFR − LTIR relations, and compare the results with the “true” values in the simulations. We find that the SFR is overestimated by a factor of ≈ 3 (≳ 10) for AGN bolometric luminosities of Lbol ≈ 1012 L⊙ (≳ 1013 L⊙), implying that the star formation rates of z ∼ 6 quasars can be overestimated by over an order of magnitude.
Settore FIS/05 - Astronomia e Astrofisica
File in questo prodotto:
File Dimensione Formato  
stac3306.pdf

accesso aperto

Descrizione: post-print
Tipologia: Accepted version (post-print)
Licenza: Accesso gratuito (sola lettura)
Dimensione 1.22 MB
Formato Adobe PDF
1.22 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11384/125442
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact