The Effect of Gas Bulk Rotation on the Lyman Alpha Line

Talk given at EWASS (European Week of Astronomy and Space Science) 2014

Transcript

1. The effect of rotation on the morphology of the Lyman alpha line. Juan Nicolás Garavito-Camargo¹. Jaime e. Forero-Romero¹. Mark Dijkstra². ¹Universidad de los Andes. ²Oslo University. EWASS 2014 Geneva, Switzerland 1
2. Motivation: l 2 Rotation is an intrinsic characteristic of galaxies. Does rotation have any impact in the morphology of the Lyman alpha line? Make a systematic study of the impact of rotation in the Lyman-alpha line morphology. If it does, what morphological Features are affected?
3. Rotation in Galaxies: 3 Rotation curves of galaxies: Solid body Rotation:
4. Models: 24 Models in total l The gas is Homogeneous in density and temperature. 4 Viewing Angle: Ө k out k
5. Initialization: 1. Frequency {x in }: 2. Direction of propagation {k}: Random 3. Dust Model: Albedo (A): A = ½ x in = v·k in /v th → Homogeneous Distribution 5
6. 1. Unaffected quantities due to rotation and L.O.S. 2. Affected quantities under rotation and L.O.S. 3. Analytical Solution. Results: 6
7. 7 Vmax = 0 km s-1 , τ H = 105 Vmax = 100 km s-1 , τ H = 105 Viewing Angle effects:
8. Line profiles changes with rotation: Vmax: 0 km/s 100 km/s 200 km/s 300 km/s τ H = 105 For all this models We choose: Θ = π/2 8 τ H = 106 τ H = 107
9. Total flux is invariant with the viewing angle & velocity Are the total flux the same for all LoS and for all the velocities? We define the total flux as: 9
10. Line width increases towards the equatorial region: 10
11. Width – velocity relation 11 How it is the dependency of the FWHM with Vmax? FWHM 0 = FWHM (at Vmax=0 km s-1) FWHM2 = FWHM 0 2 + (Vmax / λ)2
12. From double peaks to a single peak 12
13. Invariant number of scatterings 13 Numero de scatterings vs rotacion
14. Invariant escape fraction f esc = Nγ Emit / Nγ Init Invariant under viewing angle 14
15. Analytical Solution: 15
16. Analytical Solution: 16
17. Conclusions: • Rotation has an impact in the Lyα line morphology; the width and the relative intensity of the peaks and the center of the lines are affected. For high velocities the line becomes single peaked. • The width of the line (FWHM) increases with rotational velocity. FWHM2 = FWHM 0 2 + (Vmax/γ)2 • Rotation induces an anisotropy for different viewing angles, viewing angles close to the pole the line are double peaked and the line makes a transition to single peaked for viewing angles along the equator. • We derive an approximate expression for the spectra, assuming a functional form for the surface brightness profiles I(μ). This solution agrees with our simulated models. 17