Gas Accretion and Giant Lyα Nebulae

Abstract

Several decades of observations and discoveries have shown that highredshift AGN and massive galaxies are often surrounded by giant Lyα nebulae extending in some cases up to 500 kpc in size. In this chapter, I review the properties of the such nebulae discovered at z > 2 and their connection with gas flows in and around galaxies and their halos. In particular, I show how current observations are used to constrain the physical properties and origin of the emitting gas in terms of the Lyα photon production processes and kinematical signatures. The emerging picture from these studies suggest that recombination radiation is the most viable scenario to explain the observed Lyα luminosities and Surface Brightness for the large majority of the nebulae and imply that a significant amount of dense (n > 1 cm −3 ), ionized and cold (T ∼ 10 4 K) "clumps" should be present within and around the halos of massive galaxies. Spectroscopic studies suggest that, among the giant Lyα nebulae, the one associated with radio-loud AGN should have kinematics dominated by strong, ionized outflows within at least the inner 30-50 kpc. Radio-quiet nebulae instead present more quiescent kinematics compatible with "stationary" situation and, in some cases, suggestive of rotating structures. However, definitive evidences for accretion onto galaxies of the gas associated with the giant Lyα emission are not unambiguously detected yet. Deep surveys currently ongoing using other bright, non-resonant lines such as Hydrogen Hα and He II 1640 will be crucial to search for clearer signatures of cosmological gas accretion onto galaxies and AGN.

Emission from the circumgalactic medium: from cosmological zoom-in simulations to multiwavelength observables

“…Although this is the case in our models, other works find different solutions for the ionization contributions (e.g. Cantalupo 2017;Oppenheimer et al 2018), suggesting that photoionization is the dominant source for emission from the CGM, rather than collisional ionization.…”

“…It also depends on nearby ionizing continuum objects, such as young stars or AGN (see e.g. Cantalupo 2017). We rather model the effect from the nearby stars separately (see the next section).…”

The large- and small-scale properties of the intergalactic gas in the Slug Ly α nebula revealed by MUSE Heiiemission observations

“…Deep narrow-band imaging campaigns around bright quasars (e.g. Cantalupo et al 2012Cantalupo et al , 2014Martin et al 2014;Hennawi et al 2015;Arrigoni Battaia et al 2016) and, more recently, integral-field spectroscopic campaigns with the Multi Unit Spectroscopic Explorer (MUSE) (e.g., Borisova et al 2016;Arrigoni Battaia et al 2018) and the Palomar/Keck Cosmic Web Imager (P/KCWI) (e.g., Martin et al 2014;Cai et al 2018) are finally revealing giant Lyα nebulae with size exceeding 100 kpc around essentially all bright quasars (at least at z > 3 while at z 2 they seem to be detected more rarely, see e.g., Arrigoni Battaia et al 2016 andCantalupo 2017 for discussion).…”

“…It is characterised by very bright and filamentary Lyα emission extending about 450 projected kpc around the quasar UM287 (see Fig.1). As discussed in Cantalupo et al (2014) and Cantalupo (2017), the high Lyα Surface Brightness (SB) of the Slug would imply either: i) very large densities of cold (T ∼ 10 4 K) and ionised gas (if emission is dominated by hydrogen recombinations) or, ii) very large column densities of neutral hydrogen (if the emission is due to "photon-pumping" or scattering of Lyα photons produced within the quasar broad line region).…”

Are we seeing accretion flows in a 250 kpc Lyα halo at z = 3?

“…The energy sources of Lyα nebulae are poorly constrained (Cantalupo 2017). All processes that excite the Lyα emission depend on the distribution of the emission line gas, the type of objects within the nebula, and on how far away the emission is located from sources of ionizing photons.…”