Discovery of a bright quasar ...

The journal article ``Discovery of a bright quasar without a massive host galaxy'' in Nature 437, 381-384 (15 September 2005) describes observations of the object HE0450-2958 made with the Hubble Space Telescope (HST) and the Very Large Telescope (VLT). The article is available on-line through the University subscription to Nature following the link on the class web site at http://www.physics.louisville.edu/astro/students/590. A pdf version for your use is on our computer system in the directory /home/data/bright_quasar along with image files you will need.

After you have read the article and we have discussed it in class, answer the questions that follow. A few points to keep in mind:

• The increase in the wavelength of spectral lines from distant galaxies (and quasars) due to the expansion of the universe is given by the Hubble Law
  
  $$v = H d$$
  
  
  where $v$ is the velocity of recession and $d$ is the distance of the galaxy. $H$ is the Hubble Constant, taken in this article to be 65 km/s-Mpc. Distance is measured in parsecs, the distance at which the parallax of an object would be 1 second of arc. A parsec is also the distance at which 1 astronomical unit, the mean distance of the Earth from the Sun, would subtend an angle of 1 second of arc. The velocity of recession is measured in km/s. An Mpc is a ``megaparsec'', $10^6$ parsecs.
• The velocity of recession implies a shift of wavelengths to the red due to the Doppler effect. This change in wavelength is given exactly by
  
  $$\frac{\lambda_{observed}}{\lambda_{emitted}} = 1 + z$$
  
  
  
  
  $$\frac{\lambda_{observed}}{\lambda_{emitted}} = \sqrt{\frac{c + v}{c - v}}$$
  
  
  In the limit that $v/c$ is small, this becomes
  
  $$\frac{\Delta\lambda}{\lambda}= \frac{v}{c}$$
  
  
  where $v$ is positive when the galaxy is moving away from us.
• Absolute magnitude $M$ is the magnitude an object would have if it were 10 parsecs away. It is related to the apparent magnitude $m$ by
  
  $$m - M = 5\log d - 5$$
  
  
  which follows from the definition of the magnitude scale and the inverse square law for light flux.