Abstract Details

Name: Anshuman Acharya
Affiliation: Indian Institute of Science Education and Research (IISER) - Mohali
Conference ID: ASI2021_175
Title : How Robust are the Inferred Density and Metallicity of the Circumgalactic Medium?
Authors and Co-Authors : Anshuman Acharya (Indian Institute of Science Education and Research (IISER) - Mohali), Vikram Khaire (Indian Institute of Space science and Technology (IIST) - Trivandrum).
Abstract Type : Poster
Abstract Category : Stars, ISM and Galaxy
Abstract : It has been suggested that studying the circumgalactic medium (CGM) of galaxies will lead to a better understanding of galaxy evolution and feedback mechanism. The quantitative estimates of the basic properties of CGM, such as the density and metallicity that are directly related to the size and mass of CGM gas, depend on the spectrum of incident UV background radiation. The models of UV background are known to have large variations, mainly because they are synthesized using poorly constrained parameters, which introduces variations in the inferred properties of the CGM. With rigorous analysis, we quantify such a variation in the inferred density and metallicity of the CGM gas for the first time. For that, we use a large set of new UV background models (Haardt & Madau 2012, seven models from Khaire & Srianand 2019, Puchwein et al. 2019, and Faucher-Giguere 2020) with physically motivated toy models of the metal-enriched CGM gas and Bayesian analysis to recover the densities and metallicities. We find that on average, the density and metallicity of the photoionized CGM gas vary by a factor of 4 and 2.5 (i.e. 0.6 and 0.4 dex), respectively. In the case of collisionally ionized warm-hot gas, we find that the inferred metallicities do not show any significant variation, but the density shows a similar variation of a factor of 4. These estimates are independent of the redshift (for z<1), and the number and species of metals used for the inference. Such a considerable variation in density and metallicity may severely limit the studies of CGM and demand more constraining observations of the input parameters used in synthesizing the UV background models.