Question

(R1 2.4) Suppose the stars in our galaxy have constant orbital speed, v = 220 km s-1, out to the edge of a spherical dark matter halo at distance R 200 kpc. Estimate a "characteristic" time for collapse as tcollR/v. What is the maximum z at which you would expect to see galaxies comparable in R and v to our own galaxy in the concordance model with ?1n at-1-?? 0.3 and h 0.77

Answer 1

The characteristic time for collapse tcol Rv Here, the distance R 200 kpc 200 x 3.0857 x 1019 m -200 x 3.0857 x 1016 km 617.14 x 1016 km Orbital speed v 220 km/sec; Therefore, t col 617.14 x 1016/220 2.805 x 1016 sec The maximum z where galaxies are comparable in R and v to our own galaxy can be cal culated as z v/c for which the orbital speed, v is much less than c, the velocity of light 3 x 103m/sec Therefore, z-220 x 1000/3x 10 22 x 104/3 x 108 7.33 x 104