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Preprint
Luminous Mid-IR Selected Type-2 Quasars at Cosmic Noon in SDSS Stripe82 I: Selection, Composite Photometry, and Spectral Energy Distributions
23 Jan 2025
Abstract
We analyze 23 spectroscopically confirmed Type-2 quasars (QSOs) selected from
the WISE 22$\rm \mu$m band in the SDSS Stripe 82 region, focusing on their
multi-band photometry and spectral energy distributions (SEDs). These objects
were selected to be IR-luminous ($\rm flux_{W4} > 5mJy$, i.e., $12.62 < W4 <
14.62 \rm\ AB \, magnitude$), optically faint ($r > 23$) or with red color ($r
- W4 >8.38$). Gemini/GNIRS observations were conducted for all 24 candidates,
and 18/24 were also observed with Keck/LRIS. The observations confirm 23 to be
real Type-2 QSOs in the redshift range $0.88 - 2.99$ (12 are at $z>2$). We
collect multi-band photometry and conduct SED fitting. The composite photometry
probes the wavelength from 0.1$\rm \mu$m to 10$\rm \mu$m at the rest frame. The
IR emission is dominated by dust torus implying an average torus luminosity for
the sample of $L_{\rm torus} 10^{46.84} \rm erg/s$. The origin of the
rest-UV/optical light is not definitive, but we present three possible
scenarios: scattered light, stellar emission, and the reddened accretion disk.
Assuming an obscured:unobscured ratio of approximately 1:1, our targets have
$L_{\rm bol} = 10^{46.28} \rm erg \,s^{-1} - 10^{47.49} \rm erg \,s^{-1}$ and
around SMBH masses $\rm 10^{8.18} M_{\odot} - 10^{9.39} M_{\odot}$, assuming
they accreate at the Eddington limit. Compared to previous Type-2 AGN SEDs, our
targets have a brighter dust torus and redder optical-IR color. By comparing
the SED to the results from JWST `little red dots' (LRDs), we find that these
IR-selected Type-2 QSOs have similar SED shapes to the LRDs. This pilot Type-2
QSO survey demonstrates that mid-IR selection is an efficient way to find
luminous Type-2 QSOs at $z>2$. Finally, the composite photometry and Type-2
QSOs SED model generated by this sample provide a guide for finding more Type-2
QSOs at higher redshift.
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Details
- Title
- Luminous Mid-IR Selected Type-2 Quasars at Cosmic Noon in SDSS Stripe82 I: Selection, Composite Photometry, and Spectral Energy Distributions
- Creators
- Ben WangJoseph F HennawiZheng CaiGordon T RichardsJan-Torge SchindlerNadia L ZakamskaYuzo IshikawaHollis B AkinsZechang Sun
- Resource Type
- Preprint
- Language
- English
- Academic Unit
- Physics
- Other Identifier
- 991022024310104721