COSMOS-3D: Two obscured X-ray AGNs with hot dust and He I$λ$10830 absorption at z~3

TL;DR

This study reports the discovery of two z~3 broad-line X-ray AGNs, cid_414 and cid_947, exhibiting He I λ10830 emission and absorption with hot dust signatures from JWST COSMOS-3D. Through JWST NIRCam/MIRI imaging, grism spectroscopy, and extensive multiwavelength ancillary data, the authors characterize dense circumnuclear gas at BLR-like scales, its connection to the dusty torus, and its role in obscuration and black hole growth. Photoionization modeling and SED fitting reveal distinct evolutionary states: cid_414 in a blowout, high-λ_Edd phase with strong AGN feedback, and cid_947 in a more obscured, lower-λ_Edd phase; together they imply dense gas near the nucleus regulates accretion and co-evolution at high redshift. A preliminary high-z luminosity function suggests such absorption-line AGNs are rare but detectable with JWST, highlighting the importance of dense circumnuclear gas in shaping AGN demographics and evolution in the early universe.

Abstract

We report the discovery of two broad-line X-ray AGNs cid_414 and cid_947 at z~3 that exhibit prominent He I$λ$10830+ Pa$γ$ emission and absorption, identified from the JWST Cycle 3 large GO treasury program COSMOS-3D using NIRCam F444W grism spectroscopy. Additional UV/optical line measurements (e.g., Ly$α$, Si IV, C IV) come from complementary COSMOS-field spectroscopy. Both sources are robustly detected in the mid-infrared, with detections in MIRI F1000W for both AGNs and an additional detection in MIRI F2100W for cid_414, indicating the presence of hot dust emission. The source cid_947 shows a higher He I$λ$10830 absorption column density and X-ray-inferred $N_{\rm H}$, and displays strong outflow signatures in He I, Si IV, and C IV with velocity offsets exceeding 5000 km/s. The source cid_414 shows a narrow Ly$α$ emission line with luminosity $\log L_{\rm Lyα}=42.49\pm0.01~\mathrm{erg~s^{-1}}$ and a higher intrinsic 2-10 keV X-ray luminosity. Host-galaxy decomposition and multi-component SED fitting indicate that cid_947 hosts a more massive black hole but lower star formation rate than cid_414. From simplified photoionization modeling, we infer that the dense absorbing gas has a characteristic size comparable to the nuclear broad-line region and is likely kinematically coupled to the obscuration associated with the dust torus. He I$λ$1083 absorption has also been identified in several compact little red dots at similar redshifts. Together with the two AGNs reported here, these findings suggest that dense circumnuclear gas are plausibly prevalent at high redshift and plays an important role in regulating AGN obscuration and black hole--host co-evolution.

Figures (9)

• Figure 1: The JWST 2D and 1D grism F444W spectra of cid_414 (left) and cid_947 (right) from C3D. The Gaussian fits to the He i$\lambda$10830–Pa $\rm \gamma$ complex are shown as red solid curves. The broad and narrow components of the fits are plotted as red dashed curves.
• Figure 2: Multiwavelength images and SED fitting results of cid_414 (left) and cid_947 (right). We present the SED fitting from two tools, AGNfitter (blue lines) and CIGALE (black lines), respectively. The dashed lines represent the best-fit AGN emission. Red dots with error bars indicate the observed photometry, while black arrows show the upper limits. For cid_414, the green, blue, and black points show the model photometry from the two Sérsic components, as plotted in Figure \ref{['fig:galfits']}. The details of the host galaxy decomposition are presented in Section \ref{['sec:decomposition']}.
• Figure 3: Left: Host galaxy star formation rate (SFR) and stellar mass ($M_*$) from SED fitting (squares: cid_414; circles: cid_947). The pink shaded region indicates the star-forming main sequence from whitaker12. Right: Stellar mass versus black hole mass. The local relations from kormendy13 and zhuang23 are shown as blue and black dashed lines, with their corresponding 1$\sigma$ shaded regions. The black arrows indicate the two black hole–host galaxy growth pathways proposed in zhuang23. Blue symbols mark high-luminosity quasars at $z\sim6$ from galfits, including sources from ASPIRE (PID #2078, PI: F. Wang), EIGER (PID #1243, PI: S. Lilly), and the Subaru High-redshift Exploration of Low-luminosity Quasars survey. The squares represent the JWST AGN compilation jones25, with LRDs in orange and non-LRDs in red. Three additional AGNs with He i$\lambda$10830 absorption from the literature are also shown: RUBIES 40579 kocevski25, W25 wang25, and J25 juodzbalis24.
• Figure 4: X-ray–inferred hydrogen column density versus Eddington ratio. The dashed and dash-dotted curves show the effective Eddington limits for the single-scattering case fabian09 and for models including IR radiation trapping ishibashi18, respectively. The blue shaded region marks the obscured regime, while the green shaded region indicates unobscured AGNs. The white region represents the blowout phase where AGN radiative feedback is expelling the surrounding dusty gas.
• Figure 5: The column density of He i ($\log N_{\rm HeI}$) in the metastable level as a function of gas volume density from the CLOUDY modeling. The left panel shows cid_414 and the right panel shows cid_947, each modeled with a different stopping criterion in $N_{\rm H}$. Solid lines represent models with solar metallicity and the dashed lines represent models with $\log(Z/Z_{\odot})=-1$. Colors indicate the value of $\log U$. The horizontal blue line marks the observed $\log N_{\rm HeI}$ for each source.