Jet Physics and Matter
Content in Powerful Quasars
Background Information: Quasars are the most powerful,
continually emitting objects in the universe. Powered by the
accretion of matter onto a central, supermassive black hole, in every
band these objects far outshine the giant elliptical galaxies that host
them. Their activity takes many forms, including a hot accretion
disk and corona, a cooler, surrounding torus, and emission line
regions. About 10% of quasars exhibit powerful jets (an example
is shown in the figure at bottom left), which are launched from the
central engine at nearly the speed of light and propagate out for
hundreds of kiloparsecs, well outside the host galaxy and out into the
surrounding cluster that the galaxy resides in.
Despite several decades of work, many subjects are poorly understood
regarding the physics of jets. One of the issues that is poorly
constrained is their matter content (i.e., the relative amounts of
leptons and hadrons in the jet), and how this affects their energy
budget. We have recently written a paper on this subject
(Georganopoulos et al. 2005, Astrophysical Journal, 625, 656-666; see
figure at bottom right) suggesting a new way to trace the matter
content in these jets, namely by using inverse-Comptonization of
photons from the cosmic microwave background -- a mandatory process --
by 'cold' matter within the relativistically flowing jet.
At left, the jet of the quasar PKS 0637-752, in X-rays (false color,
top) and optical (false color, bottom) with radio contours
overplotted. This jet features three bright knots, as well as a
much fainter, 'quiet' part that extends for >50 kpc (165,000
light-years) projected distance. At right, our model predictions
for bulk Comptonization of the CMB in the quiet part of the jet.
The two sets of curves refer to different assumptions for the amount of
power in the jet, specifically (top) where the lepton power in the
bright knots is provided by the cold leptons in the jet, or (bottom)
where the jet provides just the number of
leptons needed in the knots.
The Project: This project
will test this new diagnostic
of jet matter content using observations of two quasar jets with
the Hubble Space Telescope, Chandra X-ray Observatory and Spitzer Space
Telescope. The student will reduce data from HST, CXO and SST and
compare them with models. Additional modeling of the matter
content and/or jet spectrum will be done as needed.
The work would be done primarily
at UMBC, although collaboration with scientists at the Goddard Space
Flight Center is to be expected. The student would be supervised
primarily by Eric Perlman, a Research Associate Professor in the JCA,
in collaboration with other members of the UMBC jet physics group. If a
paper results from this work, you can expect to be a co-author.
The
Student: We would
like the student to have a strong background in physics and an interest
in astronomy, astrophysics and basic research.
Questions?
ask Eric
Perlman or Markos Georganopoulos.