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Investigating Local Interstellar Emission through EGRET: Insights from Isabelle Grenier and Jean-Marc Casandjian

This study explores the local interstellar emission using data from the EGRET mission over nine years at a resolution of 0.5°x0.5°. The analysis integrates various models of the interstellar medium (ISM), including NHI and WCO, while accounting for dust extinction and IC emission. Findings indicate significant adjustments are needed in the ISM models due to the exclusion of IC emission, leading to notable increases in 2ln(L) values. The research highlights the complexities and challenges in modeling the local interstellar medium and the influence of high-albedo flux and exposure issues.

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Investigating Local Interstellar Emission through EGRET: Insights from Isabelle Grenier and Jean-Marc Casandjian

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  1. EGRET and the local interstellar emission Isabelle Grenier & Jean-Marc Casandjian Service d’Astrophysique, CEA Saclay

  2. the local interstellar emission • EGRET, 9 years, 0.5°x0.5° • local medium: 5° ≤ |b| ≤ 80°

  3. the local interstellar model

  4. ISM maps • NHI from Hartmann & Burton ’97 and Dickey & Lockman ’90 • WCO from Dame et al. ’01 • dust extinction from Finkbeiner ’99 and Schlegel ‘98 • IC from GALPROP (Strong & Moskalenko)

  5. interstellar fit without IC emission • both models with ISMHI+CO and ISMEGRET badly need IC emission • 2ln(L) increase by ~ 15000 and ~19000 ! ISMHI+CO ISMEGRET

  6. interstellar fit without IC emission HI+CO+EBV 830 HI+CO+I100 1 020 180 HI+CO 270 ISMEGRET+EBV 290 14 530 EBV 19 870 I100 ISMEGRET • NHI+WCO >> ISMEGRET because Xlocal ~ 1.0 ± 0.1 < XGal ~ 1.56 ± 0.05 • warm dust  • total dust  2 ln(L)

  7. interstellar fit with dust • NHI + WCO + EBV + IC + sou + Ibkgd very preliminary! • Xlocal ~ (1.1 ± 0.1) 1020mol. cm-2 K-1 km-1 s • (1.00 ± 0.05)  sources  little bias on the IS model parameters • cold gas associated with cold dust? • or IC emission from FIR dust emission?

  8. 3EG sources |b|> 5° |b|< 5°

  9. exposure and albedo problems • best model residuals albedo contamination? high- exposure problem?

  10. exposure and albedo problems • fraction of exposure at high inclination • with high albedo flux

  11. on-going activities • implementation of HealPix maps • equal area bins even near poles • factor of ~2 fewer bins careful with flux conservation ! • and likelihood analysis • fast convolution (nested) • PSF in spherical harmonics • update EGRET source list off the plane • compute the IC emission from the local dust mm ISRF

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