Spiral arms in theSpiral arms in the milky way milky way

galaxy and cosmic raysgalaxy and cosmic rays

Spiral arms in theSpiral arms in the milky way milky way

galaxy and cosmic raysgalaxy and cosmic rays

Smadar LeviSmadar LeviThe HebrThe Hebreew University of Jerusalemw University of Jerusalem

International School of CosmicInternational School of CosmicRay AstrophysicsRay Astrophysics

July 2004July 2004

Smadar LeviSmadar LeviThe HebrThe Hebreew University of Jerusalemw University of Jerusalem

International School of CosmicInternational School of CosmicRay AstrophysicsRay Astrophysics

July 2004July 2004Work in progress in collaboration with Nir Shaviv

A typical galaxy

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.

~15Kpc

The diskThe Central

Bulge

~0.5Kpc

Density WavesDensity Waves The Lin Shu HypothesisThe Lin Shu Hypothesis

• Spiral structure is: Quasi – steady density Spiral structure is: Quasi – steady density wave.wave.

• The arms are a region where the star The arms are a region where the star density is the density is the highest.highest.

• The Star velocity is different than the arms The Star velocity is different than the arms velocity.velocity.

• The spiral arms represent the places The spiral arms represent the places where the stars spend more time than in where the stars spend more time than in an equivalent area of space elsewhere in an equivalent area of space elsewhere in the galaxy.the galaxy.

Spiral wave – the moving traffic Spiral wave – the moving traffic jamjam

Direction of movement

t3

t1

t2

Stars=cars spiral arm=jam

Finding the arms velocity We wish to work in a frame of reference which rotates with the arms.

We denote as the circular velocity of the stars.And is the circular velocity of the arms, which we call: pattern speed. P

tr Pbirth Pr tr P

is the measured angle

At first we simplify the analysis by assuming that the orbitsare circular. Hence : rrbirth

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

baarm

birther

P

Analysis

Analysis

• Fitting 500pc logarithmic arm to the data points: Finding a minimum to a weight function.

• Bootstrap:Bootstrap: Replacing ~37% random data points by ~37% different random points.

• Extracting the significant minima's and finding the errors.

Bootstrap:Bootstrap:

The term derives from the phrase to pull oneself up by one's bootstraps (Adventures of Baron Munchausen, by Rudolph Erich Raspe).

rr

dpcr armarm

11500~

Looking for minimum

Two sets of Two sets of armsarms!!!!

In The Milky Way....

Two sets of arms!!

kpc

kmP

sec

7.02.14kpc

kmP

sec

5.04.30

sec2405.8:

kmVkpcrfor

kpc

kmP

sec

7.02.14

Every ~125 million years

higher CR flux

future work:

Nir Shaviv [2003] ice ageice age

Density profile

Improving the position limits?