The most extreme electromagnetic radiation that can be observed is known as very high energy gamma rays (VHE, E>100 GeV). It is the last window open to the Universe, thanks to the development of the Cherenkov telescopes. The extragalactic VHE sky is still nowadays vastly unexplored, only composed of around 80 known sources. The great majority of them are classified as blazars, a type of Active Galactic Nuclei (AGN) whose relativistic jets point in the direction of the Earth boosting their emission. While the observation of the gamma-ray emission is crucial to understand the extreme physical mechanisms taking place at the relativistic jets from blazars, the optical characterization of their host galaxies plays a key role in the study of this extreme cosmological sources. There are mainly three aspects for which optical spectroscopic observations are key. The first one is the distance (redshift) of the target, that can only be derived confidently from the optical emission/absorption spectral features. Gamma rays are absorbed when interacting with the low energy diffuse photon fields (Extragalactic Background Light) in their way to the Earth. Such absorption strongly depends on the distance of the source, and therefore the redshift is key to infer the intrinsic gamma-ray emission. The second item is related to the characteristics of the optical emission lines, as they are a proxy to characterize the Broad Line Region (BLR), which photon field can induce gamma-ray absorption. The last important item is that extreme blazars emission peaks at higher energies, unveiling the host galaxy emission. Therefore, their optical spectrum allow us to probe the stellar population which is typically hidden due to the strong emission from their relativistic jets. In this work, the distance for three VHE gamma-ray blazars have been estimated firmly for the first time. The spectroscopic campaign during different flux states on S4 0954+65 was key to detect the weak emission lines. The continuum emission from the jet typically outshines the host galaxy, making very challenging the detection of spectral features. Therefore, the observation during the jet low flux states is important for the detection of weak spectral features. The stellar population has been also investigated for the VHE blazars TXS 1515−273 and RX J0812.0+0237, in both cases present an old and metallic stellar population, characteristics of giant elliptical galaxies.
It may interest you
Esta semana, la junta directiva del Istituto Nazionale di Astrofisica de Italia ha visitado el Instituto de Astrofísica de Canarias para ver in situ, entre otros, el avance de la instalación de la red de telescopios ASTRI. Este proyecto mejora considerablemente las capacidades actuales de captación de eventos de alta energía del universo e incluye elementos innovadores para reducir su impacto medioambiental y mejorar la eficiencia energética del observatorio. A delegation of the board of directors of the Italian Istituto Nazionale di Astrofisica (INAF), including its president, viceAdvertised on
An international scientific collaboration, in which the Instituto de Astrofísica de Canarias (IAC) participates, has discovered two new super-Earths orbiting a bright red dwarf star only 33 light-years away. Both objects are among the closest-known rocky planets yet found outside our solar system. The results are presented today at the American Astronomical Society (AAS) meeting in Pasadena (California, USA). Two new exoplanets, HD 260655 b and HD 260655 c, have been detected using NASA's Transiting Exoplanet Survey Satellite (TESS), a space telescope designed to look for planets in orbitAdvertised on
Researchers at the Instituto de Astrofísica de Canarias (IAC) have participated in the development of NIRPS, an instrument recently installed on the 3.6m telescope at the European Southern Observatory (ESO), which is now hunting for exoplanets around the coolest stars in the Milky Way from the La Silla Observatory, in Chile. The Near InfraRed Planet Searcher (NIRPS) has successfully carried out its first observations. “This remarkable infrared instrument will help us to find the nearest habitable worlds to our Solar System” states René Doyon, the Director of the Institute for ExoplanetaryAdvertised on