The nature of LINER galaxies: Ubiquitous hot old stars and rare accreting black holes

Context. Galaxies, which often contain ionised gas, sometimes also exhibit a so-called low-ionisation nuclear emission line region (LINER). For 30 years, this was attributed to a central mass-accreting supermassive black hole (more commonly known as active galactic nucleus, AGN) of low luminosity, making LINER galaxies the largest AGN sub-population, which dominate in numbers over higher luminosity Seyfert galaxies and quasars. This, however, poses a serious problem. While the inferred energy balance is plausible, many LINERs clearly do not contain any other independent signatures of an AGN. Aims. Using integral field spectroscopic data from the CALIFA survey, we compare the observed radial surface brightness profiles with what is expected from illumination by an AGN. Methods. Essential for this analysis is a proper extraction of emission lines, especially weak lines, such as Balmer H beta lines, which are superposed on an absorption trough. To accomplish this, we use the GANDALF code, which simultaneously fits the underlying stellar continuum and emission lines. Results. For 48 galaxies with LINER-like emission, we show that the radial emission-line surface brightness profiles are inconsistent with ionisation by a central point-source and hence cannot be due to an AGN alone. Conclusions. The most probable explanation for the excess LINER-like emission is ionisation by evolved stars during the short but very hot and energetic phase known as post-AGB. This leads us to an entirely new interpretation. Post-AGB stars are ubiquitous and their ionising effect should be potentially observable in every galaxy with the gas present and with stars older than ~1 Gyr unless a stronger radiation field from young hot stars or an AGN outshines them. This means that galaxies with LINER-like emission are not a class defined by a property but rather by the absence of a property. It also explains why LINER emission is observed mostly in massive galaxies with old stars and little star formation.

Los orígenes de las reivindicaciones autonomistas catalanas y sardas a través de la prensa periódica del siglo XIX (1840-1890)

The purpose of the thesis for obtaining this PhD diploma is a comparative research between the origin of the Catalonian national movement and the Sardinian national one through the analysis of the 19th century periodicals as well as through a bibliography obtained by extracting them from consulted newspapers and magazines. Not only are both realities compared because of the Aragonese-Catalan influence over the Sardinian culture during its conquer but also because both movements had their origin during the 1840s and developed concurrently along that century presenting some differences, though. The political and cultural scene in Sardinia in those years was characterized by the spread of a discomfort feeling among the population after the acceptance of the “ Fusione perfetta” in 1848 and the following rollout of the “Statuto Albertino” in the island, representing this last regulation an attempt to unify the different Italian provinces in an administrative and legislative way, together with the previous “Feliciano” code from 1827. Therefore, this is how it began to be defined the set of political, economic, and cultural theme that forms the central point of the “questione sarda” (this term and its whole connotation were used for the first time in 1867 in an article published in the Cagliaritano weekly-publication La Cronaca). The singularity of this Sardinian nationalistic movement is related to the origin of the first regional demands expressed during those same years in some European regions and, more specifically, in Catalonia. Actually in this region, in those same years, we find the origin of a cultural movement called RenaixenÇa whose initial claim was the linguistic and cultural Catalonian renaissance and which adopted a more political meaning along the 19th century...

An X-ray study of the SNR G344.7-0.1 and the central object CXOU J170357.8-414302

Aims. We report results of an X-ray study of the supernova remnant (SNR) G344.7-0.1 and the point-like X-ray source located at the geometrical center of the SNR radio structure. Methods. The morphology and spectral properties of the remnant and the central X-ray point-like source were studied using data from the XMM-Newton and Chandra satellites. Archival radio data and infrared Spitzer observations at 8 and 24 mu m were used to compare and study its multi-band properties at different wavelengths. Results. The XMM-Newton and Chandra observations reveal that the overall X-ray emission of G344.7-0.1 is extended and correlates very well with regions of bright radio and infrared emission. The X-ray spectrum is dominated by prominent atomic emission lines. These characteristics suggest that the X-ray emission originated in a thin thermal plasma, whose radiation is represented well by a plane-parallel shock plasma model (PSHOCK). Our study favors the scenario in which G344.7-0.1 is a 6 x 10^3 year old SNR expanding in a medium with a high density gradient and is most likely encountering a molecular cloud on the western side. In addition, we report the discovery of a soft point-like X-ray source located at the geometrical center of the radio SNR structure. The object presents some characteristics of the so-called compact central objects (CCO). However, its neutral hydrogen absorption column (N_H) is inconsistent with that of the SNR. Coincident with the position of the source, we found infrared and optical objects with typical early-K star characteristics. The X-ray source may be a foreground star or the CCO associated with the SNR. If this latter possibility were confirmed, the point-like source would be the farthest CCO detected so far and the eighth member of the new population of isolated and weakly magnetized neutron stars.