Instituto de Astrofísica de Canarias visitor talks

Cristina Martínez Lombilla (postdoc): “Measuring the disk growth in Milky Way-like galaxies" // The hierarchical model of galaxy formation suggests that galaxies are continuously growing. But can we actually measure the ongoing growth of present-day galaxies? In this talk, we show for the first time a quantification of disc growth in two Milky Way-like galaxies (NGC 4565 and NGC 5907) which we derive from the position of their truncations. The truncation is a low surface brightness feature of the disc, located on their outskirts, and whose location is thought to change dynamically. We measure this change by exploring the position of the truncation at different heights above the galactic disc plane (0<z<8 kpc) and at different wavelengths (from NUV to 3.6 μm). Our results are compatible with an upper limit to the growth rate of 0.5 kpc/Gyr. We will discuss the relevance of our findings within a cosmological context and we will debate whether such a growth rate is compatible with a deceleration of the growth of galaxies at the present cosmic epoch. ///// Felipe Jiménez Ibarra (PhD student): “The vertical structure of the accretion disk in LMXBs" // Low-mass X-ray binaries (LMXB) are binary systems harbouring a neutron star or a black hole accreting mass from a companion star less massive than the Sun. They provide us a unique scenario to study in great detail both the accretion process and geometry, and the fundamental properties of the compact objects. Its optical counterparts are typically faint and highly variable sources: ~20th. mag in quiescence, varying on time scales from milliseconds to years. Therefore, very detailed optical studies of these objects are only at the reach of large telescopes. We will present GTC-10.4m spectroscopy of the optical counterpart of the neutron star transient system Aquila X-1 during three consecutive outburst in 2011, 2013 and 2016. We observed strong high excitation emission lines arising from reprocessing on the donor star. We carried out Doppler mapping in order to determine the radial velocity of these features (Kem). Since this velocity traces the motion of the irradiated, inner side of the companion, Kem is smaller than the radial velocity of its centre of mass (K2). We determine the so-called K-correction, by combining Kem with K2 (previously obtained by our group from VLT-8.2m infrared spectroscopy; Mata Sanchez et al. 2017). The K-correction is closely related with fundamental parameters of the system and can be expressed as function of the mass ratio of components and the accretion disc flaring angle. For first time, we placed strong constraints to the accretion disc vertical size (opening angle) using direct measurements and detailed modelling (Jimenez-Ibarra et al. 2018, MNRAS). Our results are consistent with theoretical predictions for highly irradiated accretion discs.