Graduate School in Physics and Astrophysics ------------------------------------------- ANNUAL REPORT ------------------------------------------- Fill with a text editor (without TAB or formatting) Repeat fields for each course as necessary. ------------------------------------------- name: Arianna Gallo email: a.gallo@unito.it ciclo: XXXIV year completed (1,2 or 3): 3 supervisor: Luisa Ostorero ------------------------------------------- GRADUATE SCHOOL COURSES (only completed courses, with examination passed in the year) code: 04 title: Dark Matter and Neutrino Physics teacher: Giunti, Taoso hours: 20 (5 CFU) code: 11 title: Big Data Science and Machine Learning teacher: Legger hours: 16 (4 CFU) ------------------------------------------- CONFERENCES, WORKSHOP (only those attended in the current year) title: Kashiwa Dark Matter Symposium 2020 place: Online webpage: http://2020.kashiwa-darkmatter-symposia.org/ days: November 16-19, 2020 talk (Y/N): Y poster (Y/N): N title: Linking the Galactic and Extragalactic place: Online webpage: http://extragalactic-milkyways.org/ days: December 3-4, 2020 talk (Y/N): N poster (Y/N): N title: MW-Gaia Workshop 2021 place: Online webpage: https://zah.uni-heidelberg.de/mw-gaia2021 days: February 10-12, 2021 talk (Y/N): N poster (Y/N): N title: 21st BritGrav meeting place: Online webpage: https://sites.google.com/view/britgrav21/ days: April 12-16, 2021 talk (Y/N): Y poster (Y/N): N title: Current challenges in gravitational physics WORKSHOP place: Online webpage: https://grams-815673.wixsite.com/gravityworkshop days: April 21-28, 2021 talk (Y/N): N poster (Y/N): N --------------------------------------------------- Research activity/Publications in the current year (max characters 2500) In this third year, I finalized the main step of my PhD project. In the framework of preliminary studies for a future astrometric mission, Theia (e.g., [1]), I developed a new method to constrain the shape of the dark matter (DM) halo of the Milky Way (MW) with hypervelocity stars (HVSs) [2]. My method enables to recover the axis ratio of a triaxial DM halo from the latitudinal and azimuthal components of the tangential velocity distribution of a mock sample of ~800 HVSs, with a success rate ≳90%; the unsuccessful cases are off by 0.1, the resolution of our simulations. The sample of available HVS candidates consists of ~90 stars only; in [2] I thus stress the importance of increasing the size of the sample of genuine HVSs by a factor ~10. HVSs are also a powerful tool to discriminate between Newtonian gravity and modified theories of gravity. In [3], we compare HVS velocities simulated in a MW ruled by Newtonian gravity and embedded in a DM halo and those obtained in a MW ruled by Modified Newtonian Dynamics (MOND); we then design a new test to discriminate MOND from Newtonian gravity. We show that in MOND the HVSs within 60 kpc from the Galactic center have azimuthal velocities smaller than a distance-dependent upper limit, not met by Newtonian velocities: detecting even few HVSs with velocities above this limit would thus disprove MOND. A critical issue of both works [2] and [3] is the uncertainty on the HVS velocities used to probe the MW gravitational potential. Currently available velocities from the Gaia Early Data Release 3 (e.g., [4]) are affected by relative uncertainties that can exceed 100%. These errors need to be reduced by at least a factor ~10 to make our gravity test decisive [3], while larger reductions may be necessary to constrain the DM halo shape as in [2]. In [5], I am currently investigating the impact of these uncertainties on the success rate of my method. I find that the HVS proper motions are the main error source on tangential velocities. Determining the precision on the proper motion that future astrometric missions as Theia should achieve to enable significant constraints to the shape of the DM halo is the goal of this last step of my project. Theia is a future, high precision astrometric mission, whose end-of-mission uncertainty on proper motions should be ~100 times smaller than that of Gaia. My PhD work is contributing to the definition of the scientific goals and of the technical requirements of this mission. [1] Malbet et al., 2021, Experimental Astronomy (DOI: 10.1007/s10686-021-09781-1) [2] Gallo, Ostorero, Chakrabarty, Ebagezio, Diaferio, 2021, ready for submission [3] Chakrabarty, Ostorero, Gallo, Ebagezio, Diaferio, 2021, submitted to A&A [4] The Gaia Collaboration, 2021, A&A, 649, A1 [5] Gallo et al., in preparation BE AWARE: visits and stages,research activity and pubs are not evaluated as didactic credits, but are requested to trace the PhD students' career