[Paper Review] GN-z11: The environment of an AGN at $z=$10.603

Jan Scholtz, Callum Witten+24 more|arXiv (Cornell University)|Jun 15, 2023

Galaxies: Formation, Evolution, Phenomena15 references14 citations

TL;DR

JWST/NIRSpec IFU reveals extended Lyα halo around GN-z11 hosting an AGN at z=10.603, with nearby Lyα blobs and a candidate protocluster core in an overdense region.

ABSTRACT

Recent observations with the extit{James Webb} Space Telescope (JWST) have further refined the spectroscopic redshift of GN-z11, one of the most distant galaxies identified with the extit{Hubble} Space Telescope (HST) at $z=10.603$. The presence of extremely dense gas ($>10^{10}$ cm$^{-3}$), the detection of high-ionisation lines and of CII*1335 emission, as well as the presence of an ionisation cone, indicate that GN-z11 also hosts an Active Galactic Nucleus (AGN). Further photometric and spectroscopic follow-up demonstrates that it lies in a large-scale, overdense structure with possible signatures of Population III (PopIII) stars in its halo. Surprisingly, Ly$α$ has also been detected despite the expected largely neutral inter-galactic medium at such a redshift. We exploit recent JWST/NIRSpec IFU observations to demonstrate that the Ly$α$ emission in GN-z11 is part of an extended halo with a minimum size of 0.8--3.2 kpc, depending on the definition used to derive the halo size. The surface brightness of the Ly$α$ halo around GN-z11 appears consistent with Ly$α$ halos observed around $z\sim6$ quasars. At the wavelength of Ly$α$ at $z\sim$10.6, we identify three other emission line candidates within the IFU Field-of-View with no UV rest-frame counterpart visible in deep images from the JWST/NIRCam. If confirmed, this could be the first evidence that the local region of GN-z11 represents a candidate protocluster core, forming just 400 Myr after the Big Bang. We give a first estimate of the dark matter halo mass of this structure ($M_h$=2.96$^{+0.44}_{-0.39} imes$10$^{10}$ M$_{\odot}$), consistent with a Coma-like cluster progenitor.

Motivation & Objective

• Investigate the spatially resolved Lyα emission around GN-z11 and its halo morphology.
• Characterize the kinematics of Lyα relative to GN-z11 and identify velocity offsets.
• Search for companion galaxies and Lyα-emitting blobs in the GN-z11 vicinity.
• Assess the environment and overdensity to evaluate a protocluster core at z≈10.6.

Proposed method

• Use JWST/NIRSpec IFU data from the G140M/F100LP and G235M/F170LP configurations to map emission lines.
• Construct Lyα maps by background subtraction and continuum-corrected channel collapsing within ±400 km/s of the Lyα peak.
• Extract spectra from defined regions and fit with Gaussian profiles to obtain fluxes, FWHMs, and velocity offsets.
• Compare Lyα halo size and surface brightness to simulations and to Lyα halos around z≈6 quasars and star-forming galaxies.
• Identify and analyze Lyα blobs and potential companion emission lines (e.g., CIV, HeII) within the IFU field.
• Estimate the dark matter halo mass of the surrounding structure using abundance-based methods.

Figure 1: Left column: JWST/NIRCAM F277W continuum image with Ly $\alpha$ emission map overlaid as red dashed contours (2,3,4 and 5 $\sigma$ levels). For each row, we also plot the mask used to extract the spectrum on the right as blue solid lines. These regions were selected to estimate the total L

Experimental results

Research questions

• RQ1 What is the extent and surface brightness profile of the Lyα halo around GN-z11 at z=10.603?
• RQ2 What are the velocity offsets of Lyα relative to GN-z11’s systemic redshift in different halo regions?
• RQ3 Do companion Lyα-emitting blobs indicate a protocluster environment around GN-z11?
• RQ4 How does the GN-z11 region compare with simulations and with Lyα halos around quasars vs. star-forming galaxies at high redshift?
• RQ5 What is the inferred dark matter halo mass of the surrounding structure and its consistency with a Coma-like progenitor?

Key findings

• The Lyα halo around GN-z11 extends with a radius between 0.8 and 3.2 kpc under two definitions.
• Centroid Lyα velocity offsets are 520+66-55 km/s for the central region and 915+86-85 km/s for the NE extension.
• The Lyα halo surface brightness and size are consistent with halos around z~6 quasars rather than star-forming galaxies.
• A Lyα-emitting blob is detected ~0.4'' NE of GN-z11, with a tentative CIV] detection suggesting a highly ionising source.
• A second Lyα-emitting blob is detected 2.1'' east, indicating multiple companions and an overdense environment.
• Preliminary protocluster analysis yields a dark matter halo mass of ~2.96(+0.44,-0.39)×10^10 M☉, compatible with a Coma-like cluster progenitor at z≈10.6.

Figure 2: Comparison of the Ly $\alpha$ halo surface brightness of GN-z11 to the profiles of Ly $\alpha$ halos around star-forming galaxies at z=5.0-6.0 (red shaded region Wisotzki et al., 2018 ) and quasars z=5.7-6.6 (yellow and orange shaded region Farina et al., 2019 ) . For the quasars from Fari