Interstellar gas in 3D, implications for CR propagation and - - PowerPoint PPT Presentation

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 35th 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

Provides targets for production of secondary CR particles and energy losses. Split into dust and gas phase with a gas-to-dust ratio of ∼ 100

Gas provides most of the mass.

Interstellar gas is mostly hydrogen (∼ 70% of mass) and helium (∼ 28% of mass). Helium is really difficult to observe.

Assumed to follow the same distribution as hydrogen.

Use 21-cm line emission of H i and 2.6-cm line

• f CO to constrain the distribution.

Components by mass

Gas (99%) Dust (1%) H (70%) He (28%) Metals (1.5%)

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 in spherical rotation around the Galactic center we can easily turn velocity into distance VLSR = sin l cos b R⊙ 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. VLSR is the velocity measured with respect to the local standard of rest that is moving in a circular orbit around the Galactic center. Figure showing VLSR in the Galactic plane for a fixed rotation curve. Lines of sight with sin l ≈ 0 provide no distance information.

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

CO from Pohl et al. 2008. H i from Nakanashi & Sofue 2015.

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 Zh 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

• f both vA and D0,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 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.

Opposite seen for IC emission because changes in propagation result in more CR flux in the

• uter 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.

IC ratio at 1 GeV π0-decay ratio 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

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