The Galactic disk contains a substantial fraction of the baryonic matter angular momentum and at least two main stellar populations. Therefore, the formation and evolution of the Galactic disk is essential for understanding how our Galaxy was formed and evolved. We used accurate photometric metallicity estimates and Gaia Early Data Release 3 astrometries and two independent techniques (velocity and action space behavior) to select a highly pure sample of stars with [Fe/H] < -0.8 and thick disk-like kinematics. We confirm that the mean rotational velocity of this metal-poor sample lags the canonical thick disk by 30 km/s. Radially our sample has comparable size to the Galactic thick disk’s size but is more extended vertically. Also it has orbital eccentricities distribution that bridges the typical thick disk and halo eccentricities. Finally we use the derived gradients the shape of the eccentricity distribution and theoretical thick disk formation scenarios to discuss the origin of our sample stars. Our results strongly indicate that this sample of stars is an independent disk population which we dub the Atari disk. Our sample shows that the Atari contains 11 stars with [Fe/H] < -3.0 and 261 with <-2.0. Further investigation of literature stars reveals another 18 metal-poor stars oft hat kinematically belong our sample five of which have [Fe/H] < -4.0. This suggests that the Atari disk may harbor a significant portion of the most metal-poor stars. The existence of such metal-poor stars as well as the other observed properties of the Atari disk suggest an accretion origin in which a dwarf galaxy radially plunged into the early Galactic disk at early times.
BIO
Dr. Mohammad Mardini is a highly accomplished researcher in the field of Galactic Archaeology, with a strong academic background and extensive experience in the study of our Milky Way galaxy's formation and evolution. Dr. Mardini obtained his Ph.D. from the National Astronomical Observatories of China (NAOC), where he conducted groundbreaking research on understanding the chemical composition, dynamics, and stellar populations within our galaxy. His doctoral thesis involved utilizing information from large astronomical surveys like Gaia and LAMOST to extract valuable information about the formation and evolution of the Milky Way. For his valuable asset in unraveling the mysteries of our cosmic home, he received the prestigious "excellent international PhD student" award for the 2019 year.
Currently, Dr. Mardini holds a prestigious postdoctoral position at the Institute for the Physics and Mathematics of the Universe (IPMU). In this role, he is utilizing machine learning algorithms to investigate various aspects related to Galactic Archaeology to ultimately deciphering the history of chemical enrichment processes and dynamical properties within the Milky Way. He have also developed innovative theoretical time-dependent gravitational potential, derived from Milky Way analogues selected from the Illustris-TNG simulation, that help in obtaining a less idealized and more realistic kinematic history of ancient metl-poor stars. Beyond their research accomplishments, Dr. Mardini is passionate about science communication and outreach activities, aiming to inspire and educate young minds in the field of astronomy and astrophysics.
