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  • Athena: revealing the Hot and Energetic Universe

    Athena: revealing the Hot and Energetic Universe

  • Where are the hot baryons and how do they evolve?

  • Reveal the causes and effects of cosmic feedback

  • Track obscured accretion through the epoch of galaxy formation

  • Understand the physics of accretion onto compact objects

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NuclearObscuration CRamos CRicci Abstract: "The material surrounding accreting supermassive black holes connects the active galactic nucleus with its host galaxy and, besides being responsible for feeding the black hole, provides important information on the feedback that nuclear activity produces on the galaxy. In this Review, we summarize our current understanding of the close environment of accreting supermassive black holes obtained from studies of local active galactic nuclei carried out in the infrared and X-ray regimes. The structure of this circumnuclear material is complex, clumpy and dynamic, and its covering factor depends on the accretion properties of the active galactic nucleus. In the infrared, this obscuring material is a transition zone between the broad- and narrow-line regions, and, at least in some galaxies, it consists of two structures: an equatorial disk/torus and a polar component. In the X-ray regime, the obscuration is produced by multiple absorbers across various spatial scales, mostly associated with the torus and the broad-line region. In the coming decade, the new generation of infrared and X-ray facilities will greatly contribute to our understanding of the structure and physical properties of nuclear obscuration in active galactic nuclei.

Over the past few decades, several pieces of observational evidence have shown that supermassive black holes (SMBHs; MBH ≈ 106–9.5M) are found at the centre of almost all massive galaxies, and that those SMBHs play an important role in the evolution of their host galaxies during a phase in which they accrete material and are observed as active galactic nuclei (AGNs). Indeed, different modes of AGN feedback are expected to be key processes that shape the environment of SMBHs. In particular, quasar-induced outflows might be capable of regulating black hole and galaxy growth. For instance, they are required by semi-analytical models of galaxy formation for quenching star formation in massive galaxies. However, directly studying the influence of nuclear activity on galaxy evolution is difficult owing to the different timescales involved. Therefore, to probe the AGN–host galaxy connection directly, we must look at the structure and kinematics of the parsec-scale dust and gas that surrounds accreting SMBHs.

AGNs radiate across the entire electromagnetic spectrum, from radio wavelengths up to the gamma-ray regime. A large fraction of this emission is produced in the accretion disk and emitted in the optical and ultraviolet (UV) bands. A significant proportion of these optical/UV photons are reprocessed by: (1) dust located beyond the sublimation radius and re-emitted in the infrared (IR); and (2) a corona of hot electrons close to the accretion disk, which up-scatters them in the X-ray band and illuminates the surrounding material. Thus, studying the IR and X-ray emission and absorption of AGNs is essential for characterizing their nuclear regions."

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Advanced Telescope for High Energy Astrophysics


Athena (Advanced Telescope for High ENergy Astrophysics) is the X-ray observatory mission selected by ESA, within its Cosmic Vision 2015-2025 programme, to address the Hot and Energetic Universe scientific theme. It is the second L(large)-class mission within that programme and is due for launch in 2028.

Athena will study how hot baryons assemble into groups and clusters of galaxies, determine their chemical enrichment across cosmic time, measure their mechanical energy and characterise the missing baryons which are expected to reside in intergalactic filamentary structures. At the same time, it will study the physics of accretion into compact objects, find the earliest accreting supermassive black holes and trace their growth even when in very obscured environment, and show how they influence the evolution of galaxies and clusters through feedback processes. Athena will also have a fast target of opportunity observational capability, enabling studies and usage of GRBs and other transient phenomena. As an observatory, Athena will offer vital information on high-energy phenomena on all classes of astrophysical objects, from solar system bodies to the most distant objects known. See Science chapter for more details.

Athena will consist of a single large-aperture grazing-incidence X-ray telescope, utilizing a novel technology (High-performance Si pore optics) developed in Europe, with 12m focal length and 5 arcsec HEW on-axis angular resolution. The focal plane contains two instruments. One is the Wide Field Imager (WFI) providing sensitive wide field imaging and spectroscopy and high count-rate capability. The other one is the X-ray Integral Field Unit (X-IFU) delivering spatially resolved high-resolution X-ray spectroscopy over a limited field of view. See Mission chapter for more details.

With its unparalleled capabilities, Athena will be a truly transformational observatory, operating in conjunction with other large observatories across the electromagnetic spectrum available in the late 2020s (like ALMA, ELT, JWST, SKA, CTA, etc).