Measuring the Mass of Missing Baryons in the Halo of Andromeda Galaxy with Gamma-Ray Observations

Abstract

One of the biggest mysteries in the modern cosmology and galaxy formation is the hideout of the "missing baryons". The leading theory of galaxy formation predicts that a huge amount of baryons resides around galaxies extending out to their virial radii in the form of diffuse and hot gas of $10^6-10^7$K, which is also known as the major component of the circumgalactic medium (CGM). Studies by various groups via different techniques, however, have not reached a consensus on the role of CGM in accounting for the missing baryons, with the estimated contribution ranging from a minor fraction to enclosing the baryon budget of the galaxy. In this work we attempt to measure the mass of missing baryons in CGM with a novel method based on the gamma-ray observations of the extended halo of the Andromeda Galaxy. Since cosmic-ray particles that are generated inside the galaxy will eventually escape to the CGM, they will produce gamma-ray emission via the proton-proton collision with CGM. Different from some traditional measurements which are sensitive only to gas in certain specific temperature range, the hadronic gamma-ray flux is sensitive to baryonic gases in all phases and does not rely on the metallicity in the halo. Our result suggests that the total baryon mass contained within the virial radius is less than $(1.4-5)\times 10^{10}{M}_{\odot }$ according to the gamma-ray intensity obtained with a model-dependent analysis. It implies that the CGM of Andromeda Galaxy may not account for more than $30\%$ of the missing baryons, but the result is subject to uncertainties from the gamma-ray intensity upper limit, diffusion coefficient of the CRs in the halo as well as the stellar mass and dark matter halo mass of the galaxy. This method will become more constraining provided better understandings on these issues and more sensitive gamma-ray telescopes in the future.

7 pages, 5 figures, 1 table, accepted for publication in ApJ

References in corpus (28)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• The Spectrum and Morphology of the Fermi Bubbles
• Global cosmic-ray related luminosity and energy budget of the Milky Way
• The M31 Velocity Vector. II. Radial Orbit Towards the Milky Way and Implied Local Group Mass
• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
• Cosmic Ray Propagation: Nonlinear Diffusion Parallel and Perpendicular to Mean Magnetic Field
• The long bar as seen by the VVV survey: I. Colour-magnitude diagrams
• Do Hot Haloes Around Galaxies Contain the Missing Baryons?
• The Hestia project: simulations of the Local Group
• Fermi Large Area Telescope observations of Local Group galaxies: Detection of M31 and search for M33
• Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy
• Dark Halos of M31 and the Milky Way
• A Galactic Halo Origin of the Neutrinos Detected by IceCube
• Testing Physical Models for Cosmic Ray Transport Coefficients on Galactic Scales: Self-Confinement and Extrinsic Turbulence at GeV Energies
• The outer halo globular cluster system of M31 - II. Kinematics
• Observations of M31 and M33 with the Fermi Large Area Telescope: a galactic center excess in Andromeda?
• Project AMIGA: The Circumgalactic Medium of Andromeda
• The Circum-Galactic Medium of MASsive Spirals II: Probing the Nature of Hot Gaseous Halo around the Most Massive Isolated Spiral Galaxies
• The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda galaxy
• Balancing mass and momentum in the Local Group
• Dark Matter Interpretation of the Fermi-LAT Observations Toward the Outer Halo of M31
• Detection of missing baryons in galaxy groups with kinetic Sunyaev-Zel'dovich effect
• The sum of the masses of the Milky Way and M31: a likelihood-free inference approach
• Constraining the mass of the Local Group
• Polarization from aligned atoms as a diagnostics of circumstellar, AGN and interstellar magnetic fields: II. Atoms with Hyperfine Structure
• Fluxes of diffuse gamma rays and neutrinos from cosmic-ray interactions with circumgalactic gas
• Examining the secondary product origin of cosmic ray positrons with the latest AMS-02 data
• Gamma-ray and radio background constraints on cosmic rays in Milky Way circumgalactic medium

Cited by in corpus (5)

• Inflow of low-metallicity cool gas in the halo of the Andromeda galaxy
• The rotational kinetic Sunyaev-Zeldovich contribution to the temperature asymmetry toward the M31 halo
• Gamma-rays from the circumgalactic medium of M31
• Implications of the Milky Way Declining Rotation Curve
• The Baryonic Mass Estimates of the Milky Way Halo in the form of High Velocity Clouds