The Host-galaxy Properties of Type 1 versus Type 2 Active Galactic Nuclei

Fan Zou, Guang Yang, William N. Brandt, Yongquan Xue

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

The unified model of active galactic nuclei (AGNs) proposes that different AGN optical spectral types are caused by different viewing angles with respect to an obscuring "torus." Therefore, this model predicts that type 1 and type 2 AGNs should have similar host-galaxy properties. We investigate this prediction with 2463 X-ray-selected AGNs in the COSMOS field. We divide our sample into type 1 and type 2 AGNs based on their spectra, morphologies, and variability. We derive their host-galaxy stellar masses (M ) through spectral energy distribution (SED) fitting, and we find that the hosts M of type 1 AGNs tend to be slightly smaller than those of type 2 AGNs by Δlog;M ≈ 0.2 dex (≈4σ significance). Besides deriving star formation rates (SFRs) from SED fitting, we also utilize far-infrared (FIR) photometry and a stacking method to obtain FIR-based SFRs. We find that the SFRs of type 1 and type 2 sources are similar once their redshifts and X-ray luminosities are controlled. We also investigate the cosmic environment, and we find that the surface number densities (sub-Mpc) and cosmic-web environments (≈1-10 Mpc) are similar for both populations. In summary, our analyses show that the host galaxies of type 1 and type 2 AGNs have similar SFRs and cosmic environments in general, but the former tend to have a lower M than the latter. The difference in M indicates that the AGN unification model is not strictly correct, and both host galaxy and torus may contribute to the optical obscuration of AGNs.

Original languageEnglish (US)
Article number11
JournalAstrophysical Journal
Volume878
Issue number1
DOIs
StatePublished - Jun 10 2019

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active galactic nuclei
galaxies
star formation rate
stacking
energy
spectral energy distribution
rate
prediction
infrared photometry
occultation
stellar mass
x rays
luminosity
distribution
predictions

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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title = "The Host-galaxy Properties of Type 1 versus Type 2 Active Galactic Nuclei",
abstract = "The unified model of active galactic nuclei (AGNs) proposes that different AGN optical spectral types are caused by different viewing angles with respect to an obscuring {"}torus.{"} Therefore, this model predicts that type 1 and type 2 AGNs should have similar host-galaxy properties. We investigate this prediction with 2463 X-ray-selected AGNs in the COSMOS field. We divide our sample into type 1 and type 2 AGNs based on their spectra, morphologies, and variability. We derive their host-galaxy stellar masses (M ∗) through spectral energy distribution (SED) fitting, and we find that the hosts M ∗ of type 1 AGNs tend to be slightly smaller than those of type 2 AGNs by Δlog;M∗ ≈ 0.2 dex (≈4σ significance). Besides deriving star formation rates (SFRs) from SED fitting, we also utilize far-infrared (FIR) photometry and a stacking method to obtain FIR-based SFRs. We find that the SFRs of type 1 and type 2 sources are similar once their redshifts and X-ray luminosities are controlled. We also investigate the cosmic environment, and we find that the surface number densities (sub-Mpc) and cosmic-web environments (≈1-10 Mpc) are similar for both populations. In summary, our analyses show that the host galaxies of type 1 and type 2 AGNs have similar SFRs and cosmic environments in general, but the former tend to have a lower M ∗ than the latter. The difference in M ∗ indicates that the AGN unification model is not strictly correct, and both host galaxy and torus may contribute to the optical obscuration of AGNs.",
author = "Fan Zou and Guang Yang and Brandt, {William N.} and Yongquan Xue",
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The Host-galaxy Properties of Type 1 versus Type 2 Active Galactic Nuclei. / Zou, Fan; Yang, Guang; Brandt, William N.; Xue, Yongquan.

In: Astrophysical Journal, Vol. 878, No. 1, 11, 10.06.2019.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The Host-galaxy Properties of Type 1 versus Type 2 Active Galactic Nuclei

AU - Zou, Fan

AU - Yang, Guang

AU - Brandt, William N.

AU - Xue, Yongquan

PY - 2019/6/10

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N2 - The unified model of active galactic nuclei (AGNs) proposes that different AGN optical spectral types are caused by different viewing angles with respect to an obscuring "torus." Therefore, this model predicts that type 1 and type 2 AGNs should have similar host-galaxy properties. We investigate this prediction with 2463 X-ray-selected AGNs in the COSMOS field. We divide our sample into type 1 and type 2 AGNs based on their spectra, morphologies, and variability. We derive their host-galaxy stellar masses (M ∗) through spectral energy distribution (SED) fitting, and we find that the hosts M ∗ of type 1 AGNs tend to be slightly smaller than those of type 2 AGNs by Δlog;M∗ ≈ 0.2 dex (≈4σ significance). Besides deriving star formation rates (SFRs) from SED fitting, we also utilize far-infrared (FIR) photometry and a stacking method to obtain FIR-based SFRs. We find that the SFRs of type 1 and type 2 sources are similar once their redshifts and X-ray luminosities are controlled. We also investigate the cosmic environment, and we find that the surface number densities (sub-Mpc) and cosmic-web environments (≈1-10 Mpc) are similar for both populations. In summary, our analyses show that the host galaxies of type 1 and type 2 AGNs have similar SFRs and cosmic environments in general, but the former tend to have a lower M ∗ than the latter. The difference in M ∗ indicates that the AGN unification model is not strictly correct, and both host galaxy and torus may contribute to the optical obscuration of AGNs.

AB - The unified model of active galactic nuclei (AGNs) proposes that different AGN optical spectral types are caused by different viewing angles with respect to an obscuring "torus." Therefore, this model predicts that type 1 and type 2 AGNs should have similar host-galaxy properties. We investigate this prediction with 2463 X-ray-selected AGNs in the COSMOS field. We divide our sample into type 1 and type 2 AGNs based on their spectra, morphologies, and variability. We derive their host-galaxy stellar masses (M ∗) through spectral energy distribution (SED) fitting, and we find that the hosts M ∗ of type 1 AGNs tend to be slightly smaller than those of type 2 AGNs by Δlog;M∗ ≈ 0.2 dex (≈4σ significance). Besides deriving star formation rates (SFRs) from SED fitting, we also utilize far-infrared (FIR) photometry and a stacking method to obtain FIR-based SFRs. We find that the SFRs of type 1 and type 2 sources are similar once their redshifts and X-ray luminosities are controlled. We also investigate the cosmic environment, and we find that the surface number densities (sub-Mpc) and cosmic-web environments (≈1-10 Mpc) are similar for both populations. In summary, our analyses show that the host galaxies of type 1 and type 2 AGNs have similar SFRs and cosmic environments in general, but the former tend to have a lower M ∗ than the latter. The difference in M ∗ indicates that the AGN unification model is not strictly correct, and both host galaxy and torus may contribute to the optical obscuration of AGNs.

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