Quasar Spectral Energy Distributions in the Rest-Frame EUV: Hubble-COS Spectra of Two Ultra-luminous Quasars
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866915446058385408 |
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| author | Shull, J. Michael Bordoloi, Rongmon Danforth, Charles W. |
| author_facet | Shull, J. Michael Bordoloi, Rongmon Danforth, Charles W. |
| contents | Using the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope with both far-UV (FUV) and near-UV (NUV) gratings, we measure the ionizing spectra of two bright, intermediate-redshift quasars in their rest-frame extreme ultraviolet (EUV). The availability of both NUV and FUV spectra allows us to define the quasar continuum and correct for strong Lyman-limit systems (LLS) that fall in the gap between the FUV and optical. Each AGN has a prominent LLS, but the flux recovery shortward of their Lyman edges allows us to fit and restore the true AGN continuum. In the EUV (450-912 A) these AGN have flux distributions, $F_ν \propto ν^{-α_ν}$, with spectral indices $α_ν = 1.11\pm0.22$ (SBS 1010+535, $z_{\rm AGN} = 1.5086$) and $α_ν = 0.98\pm0.22$ (HS 0747+4259, $z_{\rm AGN} = 1.9006$), both considerably harder than the mean index, $α_ν = 1.41\pm0.15$, in a COS composite spectrum of 159 UV-bright AGN. These two AGN are outliers in the index distribution, perhaps resulting from their extremely high UV luminosity ($10^{48}~{\rm erg~s}^{-1}$), estimated black-hole masses (0.5-1)$\times10^{10} M_{\odot}$, and effects on the inner accretion disk and Comptonized winds. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_10097 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Quasar Spectral Energy Distributions in the Rest-Frame EUV: Hubble-COS Spectra of Two Ultra-luminous Quasars Shull, J. Michael Bordoloi, Rongmon Danforth, Charles W. Astrophysics of Galaxies Using the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope with both far-UV (FUV) and near-UV (NUV) gratings, we measure the ionizing spectra of two bright, intermediate-redshift quasars in their rest-frame extreme ultraviolet (EUV). The availability of both NUV and FUV spectra allows us to define the quasar continuum and correct for strong Lyman-limit systems (LLS) that fall in the gap between the FUV and optical. Each AGN has a prominent LLS, but the flux recovery shortward of their Lyman edges allows us to fit and restore the true AGN continuum. In the EUV (450-912 A) these AGN have flux distributions, $F_ν \propto ν^{-α_ν}$, with spectral indices $α_ν = 1.11\pm0.22$ (SBS 1010+535, $z_{\rm AGN} = 1.5086$) and $α_ν = 0.98\pm0.22$ (HS 0747+4259, $z_{\rm AGN} = 1.9006$), both considerably harder than the mean index, $α_ν = 1.41\pm0.15$, in a COS composite spectrum of 159 UV-bright AGN. These two AGN are outliers in the index distribution, perhaps resulting from their extremely high UV luminosity ($10^{48}~{\rm erg~s}^{-1}$), estimated black-hole masses (0.5-1)$\times10^{10} M_{\odot}$, and effects on the inner accretion disk and Comptonized winds. |
| title | Quasar Spectral Energy Distributions in the Rest-Frame EUV: Hubble-COS Spectra of Two Ultra-luminous Quasars |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2508.10097 |