JWST IFU observations uncover host galaxy continua in extremely red and obscured quasars

Yu-Ching Chen, Nadia L. Zakamska, Andrey Vayner, Jack M. M. Neustadt, Dominika Wylezalek, David S. N. Rupke, Sylvain Veilleux, Caroline Bertemes, Yuzo Ishikawa, Marie Wingyee Lau, Weizhe Liu, Marshall D. Perrin

First listed 2025-06-13 | Last updated 2025-06-13

Abstract

Uncovering bright quasars' host galaxies at cosmic noon is challenging because of the high contrast between the quasar and its host and redshifted light, making them primarily visible in the infrared. We present JWST NIRSpec integral field unit (IFU) observations of six extremely red quasars (ERQs) at $z=2.4-2.9$ and two dust-obscured quasars at lower redshifts. Using image decomposition across the spectral range, we successfully separate quasar and host galaxy continuum emission, model host morphologies, and extract spectra. The ERQs and obscured quasars have compact host galaxies with half-light radii of 1.4$-$2.9 kpc and stellar masses of 10$^{10.6-10.9}$ $M_{\odot}$. Their stellar masses are consistent with the average stellar mass of quasar hosts as expected from abundance matching and clustering analysis. Most of the quasars in our sample exhibit significant spatial offsets (0.4$-$1.3 kpc) between the quasar and host galaxy, potentially caused by post-merger dynamics or non-uniform dust obscuration. The ERQs reside 0.5$-$2 dex above the local black hole-stellar mass relation, similar to other heavily obscured populations such as HotDOGs, optically selected quasars at cosmic noon, and high-redshift SMBH candidates identified with JWST. However, this "over-massive" feature might be attributed to selection bias. Compared to HST-based studies, our JWST measurements reveal more compact host galaxies, smaller Sersic indices, and lower stellar masses, likely because of improved resolution, more accurate modeling, and minimal line contamination. These findings highlight the unique capabilities of JWST IFU in revealing quasar host galaxy properties and potential evolutionary stages of obscured quasars at cosmic noon.

Short digest

JWST/NIRSpec IFU datacubes of six extremely red quasars at z=2.4–2.9 plus two lower‑z dust‑obscured quasars are decomposed across wavelength to isolate host‑galaxy continua and morphologies. The hosts are compact (Re = 1.4–2.9 kpc) with stellar masses 10^10.6–10.9 Msun, and many targets show quasar–host centroid offsets of 0.4–1.3 kpc suggestive of post‑merger dynamics or patchy obscuration. ERQs sit 0.5–2 dex above the local MBH–M* relation and appear more compact, lower‑n, and lower‑mass than HST‑based inferences, underscoring the leverage of IFU‑based continuum separation. The authors note that the apparent over‑massive black holes may reflect selection bias.

Key figures to inspect

• Figure 1: Verify that MSA‑leakage correction removes stripe‑like artifacts in PSF‑subtracted cubes; this demonstrates that detected continuum structures are not reduction residuals.
• Figure 2: Use the total spectra and wavelength‑averaged, PSF‑subtracted images to read off per‑target morphology and measure quasar–host centroid offsets (green star vs. host light).
• Figure 3: Inspect GALFIT Sersic models and residuals to see which hosts are well constrained; note that J0832+1615, J1217+0234, and F2M1106 are poorly constrained, while successful fits illustrate the compact Re and low n values.
• Figure 4: Examine pPXF fits to the host spectra from forced photometry—identify absorption features and continuum windows that anchor the stellar‑mass estimates and check emission‑line masking quality.