## 1 Introduction  
[PERSON]'s prediction of black hole radiation in 1974 [1; 2] has been a milestone in our understanding of gravitation, by linking it to quantum field theory, thermodynamics and information theory, with far reaching consequences. The presence of a horizon has two important consequences. First of all, it determines the causal separation of a region of spacetime, containing information that is no longer accessible by observers outside. Moreover, it induces the phenomenon of emission of black-body radiation which has the effect of extracting mass from the black hole leading to evaporation, and therefore to the apparent loss of the information contained inside that region. The production of radiation can be predicted through the tools of quantum field theory in curved spacetime [3; 4; 5; 6], but the description of the evaporation process requires a consistent formulation of semiclassical gravity, in which the degrees of freedom of geometry interact with the quantum degrees of freedom of matter fields. From a geometric point of view, this process entails the shrinking of the radius of the horizon and therefore the raise of the radiation temperature. Furthermore, [PERSON] radiation introduces the so-called transplanckian problem [3; 4; 5; 6], i.e., the fact that low-energy [PERSON] quanta at spatial infinity and late times can be traced back to ultra-high-energy modes close to the horizon. This appears to be a problem of [PERSON]'s derivation as the latter relies on the validity of quantum field theory on curved spacetime which would be obviously untenable at Planck energies. The theory of general relativity is not valid at such scales, and settling this issue would require a knowledge of the ultraviolet completion of the theory, so rising the question about the robustness of [PERSON] radiation with respect to the details of the latter. Unfortunately, we presently do not have the ability of settling these issues experimentally in gravitational systems, as measuring [PERSON] radiation is basically impossible for astrophysical objects. However, [PERSON]'s realization that hydrodynamical systems can be used for simulating black hole spacetimes [7; 8], paved the way for devising more general tabletop experiments in which the propagation of some perturbations on a given background can simulate classical and/or quantum field theory on a curved spacetime. This realization marked the dawn of the so-called Analogue Gravity research field [9]. In particular, in these analogue models the correspondence of their mathematical equations with those of black holes, opens the possibility to reproduce in a lab the analogue of [PERSON] radiation in the presence of a horizon, and so to start addressing long-standing issues such as the aforementioned ones. Indeed, in these systems the robustness of [PERSON] radiation with respect to a well understood ultraviolet completion of the effective spacetime and quantum field theory was soon argued for on theoretical grounds [10; 11; 12], further stimulating the attempt to achieve a direct observation. Bose-Einstein condensates (BEC) have been among the most successful analogue models due to their intrinsic quantum nature, simplicity and experimental realizability [9; 13; 14; 15]. In these systems, Bogoliubov quasi-particles are quantum excitations that propagate following the acoustic metric induced by the wavefunction of the condensate, and the atomic structure provides a natural regularization of the theory at short distances. As such, they have provided an ideal setting for the study of analogue [PERSON] radiation and cosmological particle production [16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27].