Abstract Details

Name: MANAMI ROY
Affiliation: Raman Research Institute
Conference ID: ASI2021_120
Title : Gamma-Ray and Radio Background Constraints on Cosmic Rays in Milky Way Circumgalactic Medium
Authors and Co-Authors : Manami Roy, Ranita Jana, Biman B. Nath.
Abstract Type : Oral
Abstract Category : Stars, ISM and Galaxy
Abstract : Galaxies have three components: galactic disk, dark matter halo and diffuse gaseous halo which is also known as Cicumgalactic medium (CGM). Conventionally the CGM is thought to be in hydrostatic equillibrium under the influence of gravitational potential of dark matter halo by means of only thermal pressure. This implies that the density of cold (10^4 K) phase to have higher density than hot phase (≥ 10^6 K). However observation suggests that the density of cold phase follows the hot gas density which is contrary to the above expectation. This motivates the introduction of non-thermal pressure components e.g magnetic field, cosmic rays (CR) etc. which can add to the thermal pressure. However the amount of CR population in the CGM is highly debated. Recent simulations with different CR transport prescription suggest η = P_CR /P_th to lie in a wide range, from 1 − 100, which represents the uncertainty in the amount of CR population in CGM. We address this issue in the light of the observations of indirect tracers of CR: isotropic γ-ray background and radio continuum. CR protons undergo hadronic collision with CGM protons, creating neutral pions which in turn produces γ−rays, whereas CR electrons in the Galactic magnetic field produce synchrotron emission in radio band. We incorporate CR component in two widely-studied theoretical models : Isothermal (IT) and precipiation (PP) model. The radio continuum does not put any constrain on CR population in both the models, however the IGRB flux puts an upper limit of η ≤ 3 and η ≤ 230 in case IT and PP model respectively. Although anisotropy consideration rules out any CR population in CGM for IT model, it puts a lower limit of η ≥ 100 in the case of PP model.