Galaxy formation and evolution

Abstract:

The period between z ∼ 3-6 (`cosmic morning'), a key transformational phase in galaxy evolution preceding `cosmic noon' (z ∼ 1-3), is very poorly explored in terms of feedback from active galactic nuclei (AGN) acting through gas outflows driven by energetic radiation. In this work, we study the properties of outflows in AGN (mostly X-ray-selected) from the GOODS-S field, exploiting JWST NIRSpec IFU observations as part of the Galaxy Assembly with NIRSpec IFS (GA-NIFS) GTO survey. Together with its twin subsample from the COSMOS field reported in a previous GA-NIFS work, this constitutes the largest spatially resolved sample of AGN outflows at these redshifts to date, comprising 16 targets with outflows (out of a total of 19 AGN), and probes the unexplored regime of AGN at z ∼ 3-6 with bolometric luminosities of łbol ∼ 10^ 45-46 We mapped the rest-frame optical ionised gas emission lines (e.g. at sub-kiloparsec scales and spectrally isolated the broad wings that trace fast outflows from the gas at rest in the host galaxies. The incidence of ionised outflows in the GOODS-S + COSMOS GA-NIFS sample is high (>75%), among the highest at any redshift; however, a more homogeneous outflow detection method and sample selection would be required to draw firm conclusions on the redshift evolution of the outflow incidence. We inferred outflow velocities between ∼600--2000 ̨ms, maximum radii of łesssim1 up to ∼4 kpc, and ionised gas mass outflow rates of ∼0.1 up to ≳100 which in some cases can exceed the host galaxy star formation rate (SFR). The assumed electron density of 1000 cm -3 is conservative; lower values, as measured in some outflow studies and suggested by theory, would imply inversely proportionally higher mass outflow rates. We find that the outflow properties inferred for the GOODS-S + COSMOS GA-NIFS AGN sample and their relations to łbol and SFR generally align with those observed for other spatially resolved literature samples of AGN outflows across different redshifts and AGN luminosities. Nonetheless, after accounting for any luminosity bias, our analysis suggests a cosmic evolution of the outflow properties, with higher median mass outflow rates (and possibly also mass loading factors) at higher redshifts, especially at z>3, which indicates that AGN outflows were stronger in the early Universe than at later times, and thus potentially more capable of affecting their host galaxy.

Abstract:

Abstract JWST has revealed a large population of massive black holes (BHs) in the early Universe with unusual properties which mark them as distinct from low-redshift active galactic nuclei. Such findings have prompted the development of new models of BH formation and growth, and of their co-evolution with host galaxies. Linking the gas-phase metallicity of BH environments to seed masses is key to understanding which evolutionary pathways could explain the population of JWST-discovered BHs. We present new high-resolution JWST NIRSpec/IFU observations covering the rest-frame optical emission lines of a Little Red Dot (LRD) at z = 3.55, known as The Cliff, from the ‘Red Unknowns: Bright Infrared Extragalactic Survey’ (RUBIES). We find evidence for low metallicity (Z = 0.016 ± 0.003 Z⊙) based on the low narrow-line [O iii]λ5007/Hβ ratio, supported by the non-detection of low-ionisation emission lines such as [O ii]λλ3727,3729 and [N ii]λλ6548,6583. We find that the observed properties of The Cliff, including its overmassive BH, can be reproduced by some simulations of black hole growth and evolution down to z ∼ 3.5. However, such outcomes require high seed masses (104 − 105 M⊙) and appear rarely within a simulation volume comparable to the 3 < z < 4 RUBIES volume, highlighting the unusual nature of The Cliff. Future simulations and numerical models will help to uncover how such a metal-poor system managed to develop a massive black hole and persist to such low redshift.