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Universal bolometric corrections for AGN over 7 luminosity decades

F. Duras, A. Bongiorno, F. Ricci, E. Piconcelli, F. Shankar, E. Lusso, S. Bianchi, F. Fiore, R. Maiolino, A. Marconi, F. Onori, E. Sani, R. Schneider, C. Vignali, F. La Franca

TL;DR

This work tackles the longstanding issue of inconsistent AGN bolometric corrections by constructing universal corrections over ~7 dex of luminosity for both type 1 and type 2 AGN. It compiles ~1000 AGN from five diverse samples and performs dedicated SED-fitting to robustly separate nuclear and host emission, deriving reliable $L_{BOL}$ and the bolometric corrections $K_X = L_{BOL}/L_X$ and $K_O = L_{BOL}/L_O$. The hard X-ray correction $K_X(L_{BOL})$ is roughly constant at low $L_{BOL}$ and rises with luminosity, while the optical correction $K_O$ stays near $\,\sim\,5$ across variables, with no significant redshift dependence up to $z\sim3.5$. The authors validate these corrections by predicting AGN bolometric luminosity functions that agree with optical and X-ray LFs within ~0.2 dex, enabling reliable mapping of AGN accretion histories across cosmic time.

Abstract

The AGN bolometric correction is a key element to understand BH demographics and compute accurate BH accretion histories from AGN luminosities. However, current estimates still differ from each other by up to a factor of two to three, and rely on extrapolations at the lowest and highest luminosities. Here we revisit this fundamental issue presenting general hard X-ray ($K_{X}$) and optical ($K_{O}$) bolometric corrections, computed combining several AGN samples spanning the widest (about 7 dex) luminosity range ever used for this kind of studies. We analysed a total of $\sim 1000$ type 1 and type 2 AGN for which a dedicated SED-fitting has been carried out. We provide a bolometric correction separately for type 1 and type 2 AGN; the two bolometric corrections results to be in agreement in the overlapping luminosity range and therefore, for the first time, a universal bolometric correction for the whole AGN sample (both type 1 and type 2) has been computed. We found that $K_{X}$ is fairly constant at $log(L_{BOL}/L_{\odot}) < 11$, while it increases up to about one order of magnitude at $log(L_{BOL}/L_{\odot}) \sim 14.5$. A similar increasing trend has been observed when its dependence on either the Eddington ratio or the BH mass is considered, while no dependence on redshift up to $z\sim3.5$ has been found. On the contrary, the optical bolometric correction appears to be fairly constant (i.e. $K_{O} \sim 5$) whatever is the independent variable. We also verified that our bolometric corrections correctly predict the AGN bolometric luminosity functions. According to this analysis, our bolometric corrections can be applied to the whole AGN population in a wide range of luminosity and redshift.

Universal bolometric corrections for AGN over 7 luminosity decades

TL;DR

This work tackles the longstanding issue of inconsistent AGN bolometric corrections by constructing universal corrections over ~7 dex of luminosity for both type 1 and type 2 AGN. It compiles ~1000 AGN from five diverse samples and performs dedicated SED-fitting to robustly separate nuclear and host emission, deriving reliable and the bolometric corrections and . The hard X-ray correction is roughly constant at low and rises with luminosity, while the optical correction stays near across variables, with no significant redshift dependence up to . The authors validate these corrections by predicting AGN bolometric luminosity functions that agree with optical and X-ray LFs within ~0.2 dex, enabling reliable mapping of AGN accretion histories across cosmic time.

Abstract

The AGN bolometric correction is a key element to understand BH demographics and compute accurate BH accretion histories from AGN luminosities. However, current estimates still differ from each other by up to a factor of two to three, and rely on extrapolations at the lowest and highest luminosities. Here we revisit this fundamental issue presenting general hard X-ray () and optical () bolometric corrections, computed combining several AGN samples spanning the widest (about 7 dex) luminosity range ever used for this kind of studies. We analysed a total of type 1 and type 2 AGN for which a dedicated SED-fitting has been carried out. We provide a bolometric correction separately for type 1 and type 2 AGN; the two bolometric corrections results to be in agreement in the overlapping luminosity range and therefore, for the first time, a universal bolometric correction for the whole AGN sample (both type 1 and type 2) has been computed. We found that is fairly constant at , while it increases up to about one order of magnitude at . A similar increasing trend has been observed when its dependence on either the Eddington ratio or the BH mass is considered, while no dependence on redshift up to has been found. On the contrary, the optical bolometric correction appears to be fairly constant (i.e. ) whatever is the independent variable. We also verified that our bolometric corrections correctly predict the AGN bolometric luminosity functions. According to this analysis, our bolometric corrections can be applied to the whole AGN population in a wide range of luminosity and redshift.

Paper Structure

This paper contains 14 sections, 7 equations, 10 figures, 8 tables.

Table of Contents

  1. Introduction
  2. Data sample
  3. Spectral Energy Distribution
  4. SED-fitting
  5. SED results
  6. Bolometric correction as a function of luminosity
  7. Hard X-ray bolometric correction
  8. Optical bolometric correction
  9. Bolometric correction as a function of redshift
  10. Bolometric correction as a function of Eddington ratio and BH mass
  11. The AGN unobscured bolometric luminosity function
  12. DISCUSSION
  13. Summary and Conclusions
  14. Physical properties of the samples

Figures (10)

  • Figure 1: Intrinsic X-ray luminosity in the 2-10 keV band as a function of the redshift of the SWIFT type 1 (blue filled squares) and type 2 (red filled circles) samples, the X-WISSH sample (blue open squares), the COSMOS type 1 (grey asterisks) and type 2 (lightgrey asterisks) sources, the ASCA type 1 (pink open squares) and type 2 (gold filled circles) objects and the XXL type 1 (cyan open squares) AGN.
  • Figure 2: Examples of UV-to-IR AGN templates with different level of absorption, from Silva2004 and Stalevski2016. The vertical dotted line at $\sim 50 \mu m$ shows the position of the pivotal photometric point derived from the X-ray luminosity, where the AGN templates are very similar.
  • Figure 3: Example of SED fitting results for one type 2 source from the SWIFT sample (left top panel), one type 1 from the X-WISSH sample (right top panel), one type 2 from the ASCA sample (left middle panel), one type 1 from the XXL sample (right middle panel) and one type 2 from the COSMOS sample (bottom panel). The AGN, galaxy, cold dust and excess emission components are shown in different colours and line types (as stated in the legend of the first figure on the upper left panel). Black circles are the photometric points of the source. The virtual AGN pivotal photometric point at 50 $\mu$m, derived from the hard X-ray data, is shown as black pentagon (see text for details).
  • Figure 4: Hard X-ray bolometric correction in the 2-10 keV band as a function of the bolometric luminosity for type 1 (upper panel) and type 2 (central panel) AGN. Symbols are as in legend. Black filled triangles and open circles show the average values for type 1 and type 2 sources respectively (directly compared in the lower panel), in bins of bolometric luminosity. The black solid and dashed lines show our best-fit relations and their extrapolations according to Equation \ref{['eq:rela']}.
  • Figure 5: Intrinsic spread in bins of bolometric luminosity for the X-bolometric correction of type 1, type 2 and the whole AGN sample. Dashed black lines show the average value.
  • ...and 5 more figures