1 / 12

Spiral arms in the milky way galaxy and cosmic rays

Spiral arms in the milky way galaxy and cosmic rays. Smadar Levi The Hebr e w University of Jerusalem International School of Cosmic Ray Astrophysics July 2004. Work in progress in collaboration with Nir Shaviv. A typical galaxy. ~15Kpc. ~0.5Kpc. The disk. The Central Bulge.

ermin
Download Presentation

Spiral arms in the milky way galaxy and cosmic rays

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Spiral arms in the milky waygalaxy and cosmic rays Smadar Levi The Hebrew University of Jerusalem International School of Cosmic Ray Astrophysics July 2004 Work in progress in collaboration with Nir Shaviv

  2. A typical galaxy ~15Kpc ~0.5Kpc The disk The Central Bulge The disk is characterized with stars that move in nearly circular orbits around the galactic center. The Central Bulge is characterized with stars with large random motions. Therefore its distribution is ellipsoidal. The star in the disk has a differential velocity, meaning the star nearer to the center has a shorter period of motion.

  3. Density WavesThe Lin Shu Hypothesis • Spiral structure is: Quasi – steady density wave. • The arms are a region where the star density is the highest. • The Star velocity is different than the arms velocity. • The spiral arms represent the places where the stars spend more time than in an equivalent area of space elsewhere in the galaxy.

  4. t1 t2 t3 Direction of movement Spiral wave – the moving traffic jam Stars=cars spiral arm=jam

  5. We denote as the circular velocity of the stars. And is the circular velocity of the arms, which we call: pattern speed . is the measured angle At first we simplify the analysis by assuming that the orbits are circular. Hence: Finding the arms velocity We wish to work in a frame of reference which rotates with the arms.

  6. Analysis • Open clusters. From Loktin & Dias catalogs. • Fitting the data to a logarithmic arm with 500pc thickness. • 3 parameters to find. • a – the slope. • b – the interjection point with the r axis. • - the pattern speed

  7. Analysis

  8. Analysis • Fitting 500pc logarithmic arm to the data points: Finding a minimum to a weight function. • Bootstrap: Replacing ~37% random data points by ~37% different random points. • Extracting the significant minima's and finding the errors. Bootstrap: The term derives from the phrase to pull oneself up by one's bootstraps (Adventures of Baron Munchausen, by Rudolph Erich Raspe).

  9. Looking for minimum Two sets of arms!!

  10. Every ~125 million years higher CR flux Nir Shaviv [2003] ice age ? Improving the position limits Density profile In The Milky Way .... Two sets of arms!! future work:

More Related