ASTR 622
Observational Cosmology
Problem Set 2
Due in class Thursday 4 March 2010

  1. Radiation Domination
    Consider the epoch of radiation domination where the energy density is dominated by photons with ρ = aT4 (where a is the radiation constant and T is their temperature) and the equation of state is P = ρ/3.
    Justify any assumptions you need to make.

  2. Inflation

  3. Age-Redshift Relation

  4. H0 and the Distance to Virgo
    Professor Fink returns excited from an observing run because he has discovered a nova in a galaxy in the Virgo cluster, a key step in the distance scale. He knows that novae can be used as standard candles since they obey a luminosity--fade-time relation
    MVpeak = -10.7 + 2.3 log(t2)
    where t2 is the time in days that it takes for a nova to fade 2 magnitudes from its peak. (That's a base ten logarithm, as is conventional in astronomy.) Professor Fink hands you the data in the graph, and asks you to determine The Answer.

    Was Fink's initial excitement justified?
    (Keep in mind that the modern goal is to measure H0 to better than 10%.)

    Light curve of nova in the Virgo cluster.

    Postscript version of plot

  5. The Tully-Fisher distance to the Ursa Major cluster

    Use the data of Verheijen 2001, ApJ, 563, 694 to determine the distance to the UMa cluster of galaxies using the I-band and K-band calibration of the HST Key Project (Sakai et al. 2000, ApJ, 529, 698). Be sure to include a plot of the data with calibration lines overlaid.

    Assuming the recession velocity of the Ursa Major cluster is 1088 km/s, what Hubble constant(s) do you find? How does this compare to the value given by Sakai et al.?

    * Note that Verheijen gives absolute magnitudes for a presumed distance of 15.5 Mpc. Also note that ascii versions of the tables, convenient for plotting, can be downloaded from the journal website.

    ** For the K'-band data, use the H-band calibrations assuming H-K = 0.25.