The $M_{\rm BH}-M_*$ relation up to $z\sim2$ through decomposition of COSMOS-Web NIRCam images (2401.13742v2)

Abstract: Our knowledge of relations between supermassive black holes and their host galaxies at $z\gtrsim1$ is still limited, even though being actively sought out to $z\sim6$. Here, we use the high resolution and sensitivity of JWST to measure the host galaxy properties for 107 X-ray-selected type-I AGNs at $0.68<z<2.5$ with rest-frame optical/near-infrared imaging from COSMOS-Web and PRIMER. Black hole masses ($\log\left(M_{\rm BH}/M_\odot\right)\sim6.9-9.6$) are available from previous spectroscopic campaigns. We extract the host galaxy components from four NIRCam broadband images and the HST/ACS F814W image by applying a 2D image decomposition technique. We detect the host galaxy for $\sim90\%$ of the sample after subtracting the unresolved AGN emission. With host photometry free of AGN emission, we determine the stellar mass of the host galaxies to be $\log\left(M_/M_\odot\right)\sim9.5-11.6$ through SED fitting and measure the evolution of the mass relation between SMBHs and their host galaxies. Considering selection biases and measurement uncertainties, we find that the $M_\mathrm{ BH}/M_$ ratio evolves as $\left(1+z\right)^{0.48_{-0.62}^{+0.31}}$ thus remains essentially constant or exhibits mild evolution up to $z\sim2.5$. We also see an amount of scatter ($\sigma_{\mu}=0.30^{+0.14}_{-0.13}$), similar to the local relation and consistent with low-$z$ studies, and a non-causal cosmic assembly history where mergers contribute to the statistical averaging towards the local relation is still feasible. We highlight improvements to come with larger samples from JWST and, particularly, Euclid, which will exceed the statistical power of current wide and deep surveys.

• The paper employs high-resolution JWST NIRCam imaging and precise 2D decomposition to separate AGN light from host galaxy emissions.
• It finds minimal evolution in the M_BH-M_* ratio up to z~2.5, aligning with local universe scaling relations.
• The study underscores the role of merger-driven growth in maintaining a stable black hole–galaxy mass relationship over cosmic time.

Overview of the M$_{\text{BH}}$ $-$ M$_{\ast}$ Relation at $z \sim 2$ from COSMOS-Web NIRCam Imaging

This paper addresses the interplay between supermassive black holes (SMBHs) and their host galaxies at high redshifts ($z \sim 2$). Utilizing the advanced capabilities of the James Webb Space Telescope (JWST), the paper aims to decipher the mass relationship between SMBHs and their surrounding galaxies, employing data from the COSMOS-Web and PRIMER surveys, both significantly contributing to the investigation of the co-evolution of galaxies and their central black holes.

Methodology and Data Analysis

The research hinges on high-resolution imaging through JWST's NIRCam and HST/ACS, observing 107 X-ray-selected type-I AGNs within a redshift range of 0.68 to 2.5. The black hole masses, ranging from $\log(M_{\text{BH}}/M_{\odot}) \sim 6.9 - 9.6$, were obtained from prior spectroscopic surveys, and the stellar mass of host galaxies was calculated using Spectral Energy Distribution (SED) fitting, achieving $\log(M_{\ast}/M_{\odot}) \sim 9.5 - 11.6$.

The paper performs meticulous 2D decomposition to separate the host galaxy light from the AGN emission, leveraging multiple PSF reconstruction techniques to mitigate potential biases in morphological parameters. This analytic rigor ensures an extraction of host galaxy components free of AGN contamination.

Findings and Interpretation

A key finding of this paper is the mild evolution of the M$_{\text{BH}}$/M$_{\ast}$ ratio up to $z \sim 2.5$, favouring a scenario where this ratio remains quasi-static with cosmic time, or exhibits minimal change. The scatter, characterized by $\sigma_{\mu} \sim 0.30 - 0.13$, aligns well with local universe studies, underpinning a non-causal accumulation history averring cosmic averaging via mergers. These results nuance our comprehension of black hole-galaxy co-evolution, suggesting that major mergers predominantly drive the observed mass scaling relation.

Implications and Future Directions

This paper contributes substantively to the discourse on SMBH-galaxy co-evolution, highlighting minimal redshift evolution in the relation, implying potentially universal mechanisms regulating the growth of SMBHs vis-à-vis their host galaxies. The research suggests that merger-induced mass relation scatter aligns statistically towards observed local relations. Future investigations can leverage even larger datasets enabled by forthcoming JWST and Euclid observations to refine these projections and further explore the scattering evolution across more significant redshift intervals.

Moreover, the robust approach with multiple PSF constructions emphasizes the need for thorough error estimation and method comparison in observational cosmology, particularly in decomposing AGN-host galaxy structures.

Concluding Remarks

This paper sets a benchmark for high-redshift AGN-galaxy studies by deploying the state-of-the-art JWST capabilities to decrypt the mass interplay of black holes and galactic hosts across cosmic epochs. It invites further inquiry, particularly concerning the role of major mergers and feedback mechanisms in sculpting these colossal galactic centers. The findings situate the M$_{\text{BH}}$/M$_{\ast}$ relation within a broader, temporally invariant framework, pivotal for future interrogations of galactic development and SMBH maturation.

Ultimately, this research enriches our understanding of the cosmic co-evolution of galaxies and their central black holes, providing a robust groundwork for subsequent explorations in the high-redshift universe.