Interstellar Medium GALGAS code CR propagation γ -ray maps Interstellar gas in 3D, implications for CR propagation and gamma-ray emission Gudlaugur Johannesson gudlaugu@hi.is 35 th ICRC in Busan, July 18, 2017 Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Interstellar Matter Components by mass Provides targets for production of secondary CR particles and energy losses. Dust (1%) Split into dust and gas phase with a gas-to-dust ratio of ∼ 100 Gas provides most of the mass. Gas (99%) Interstellar gas is mostly hydrogen ( ∼ 70% of mass) and helium ( ∼ 28% of mass). Metals (1.5%) Helium is really difficult to observe. Assumed to follow the same distribution as hydrogen. He (28%) H (70%) Use 21-cm line emission of H i and 2.6-cm line of CO to constrain the distribution. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Example distribution of H i in external galaxies Image courtesy of NRAO/AUI and Fabian Walter, Max Planck Institute for Astronomy Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Observed distribution of H i in the Milky-Way HI4PI survey (Ben Bekhti, N. et al. 2016, A&A 594) Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Obtaining 3D information Under the assumption that the gas is Figure showing V LSR in the in spherical rotation around the Galactic plane for a fixed Galactic center we can easily turn rotation curve. velocity into distance � R ⊙ � V LSR = sin l cos b R Θ( R ) − Θ( R ⊙ ) where Θ( R ) is the Galactic rotation curve, R ⊙ is the radius of the sun and l and b are Galactic longitude and latitude, respectively. Lines of sight with sin l ≈ 0 V LSR is the velocity measured with provide no distance respect to the local standard of rest information. that is moving in a circular orbit around the Galactic center. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps 3D distributions using kinematic distances H i from Nakanashi & Sofue 2015. CO from Pohl et al. 2008. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Example distribution of H i in external galaxies Image courtesy of NRAO/AUI and Fabian Walter, Max Planck Institute for Astronomy Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Our Approach - Forward Folding Model Parameterized model that is integrated along lines-of-sight to create emission profiles that can be directly compared to data. GALGAS code handles the integration and comparison. Model built from simple geometrical components. Has several advantages: Automatic interpolation over longitude ranges around l = 0 ◦ and l = 180 ◦ . Smoothness of model enforced, no fingers of god. Complexity of model controlled, effects of individual components on CR propagation can be studied. Easier to explore complex models for gas rotation. And some disadvantages: Need a lot of components to capture the complex structure of the interstellar gas. The number of model parameters quickly grows and model tuning becomes very time consuming. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps New 3D distributions for interstellar gas Our results using a model with warped disk, flaring in outer Galaxy, spiral arms, and a bulge. H i on left (tuned to LAB) and CO on right (tuned to DHT). Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Quality of new distributions The model captures many of the data features but is still not complex enough to fully explain the data. The likelihood chosen was designed to do this so more complex features would show as positive residuals. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Comparison with current GALPROP gas distributions Current distributions are 2D axisymmetric collected from the literature. Azimuthally averaged density in the plane are similar in the new and old distributions. Density of new models slightly underestimated in the outer Galaxy because of the warp. Simplified radial functions capture main features of older models. Total mass of models in the new H i distribution is factor of ∼ 2 larger compared to the old while the mass in the CO distributions is similar. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Effects on CR propagation GALPROP code used to calculate the CR propagation and resulting diffuse emissions. (see talk by I. Moskalenko on July 17th) Same 2D source model used for both models and Z h fixed. γ -ray emission from gas re-normalized to same gasmaps. Compare results from the old GALPROP 2D gas distributions to the new 3D distributions. Tune the propagation parameters Needed to have apples to apples comparison. New gas distribution result in reduction of both v A and D 0 , xx by a factor ∼ 2. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Effects on γ -ray emission Ratio new/old for total γ -ray emission at 1 GeV. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Effects on γ -ray emission Effect only due to variations in emissivity calculations because models are renormalized IC ratio at 1 GeV to gasmaps. Local and inner Galaxy emission slightly enhanced for pi0-decay and bremsstrahlung. More secondary production in the inner Galaxy and slight variations between the local spectrum of CRs. π 0 -decay ratio at 1 Opposite seen for IC emission because changes in propagation result in more CR flux in the GeV outer Galaxy. These changes are relatively small but well within the statistical range of the Fermi -LAT instrument. Expect larger effects when CR properties are 3D, see talk by T. Porter on July 13th. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Comparison with Fermi -LAT results Clear correlations with residual maps from Ackermann et al. 2012. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
Interstellar Medium GALGAS code CR propagation γ -ray maps Summary Better models for the structure of the Galaxy are needed to fully utilize the precision measurements currently available. Gudlaugur Johannesson gudlaugu@hi.is HI & NORDITA Interstellar gas in 3D, implications for CR propagation and gamma-ray emission
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