QUASAR

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QUASARS

• Improving selection Methods

Kenechukwu C. Obi, Dr Julia Kennefick.
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What are quasars?

• Quasars are the active nuclei of young galaxies.
• Extremely bright distant
• Powered by accretion of matter into black holes
• Discovered in the 1960s

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How do astronomers classify Objects?

• Magnitude
• Tells us about brightness of an object
• Dimmer objects have higher magnitudes and vice
  versa
• Color
• Color is the ratio of the magnitude of flux
  coming in from one bandwidth to another
  bandwidth.
• Useful for comparing objects based upon the
  amount of EM waves they emit.

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How do astronomers classify Objects?

• Morphology
• Shape and size of objects
• Formation of objects
• Spectroscopy
• Chemical Composition of objects
• Redshift Distance
• Temperature
• Information about intervening material

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How do astronomers identify quasars?

• They make use of graphs called color diagrams
• Color diagrams are x-y plots of two colors, one
  against the other
• When objects are plotted on this diagrams, they
  separate out because of their different
  properties
• Stars form a neat stellar locus pattern, while
  quasars lie on the borders of this locus without
  any definite pattern.

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Here is an example of a color diagram.

• The comet like shape is the stellar locus
• The dots around the edges are the possible quasars

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What kind of quasars are we interested in?

• In this project we decided to look for quasars of
  redshift between 2-3.
• Quasars of the given redshift are the most
  abundant in the sky.
• However, these same quasars have similar optical
  colors with most stars, i.e. they are the most
  star like in their colors.
• Thus they are very hard to distinguish between
  stars and these quasars.

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The graph that shows abundance of quasars based
on their redshift
This graph shows the inefficiency in quasar
detection versus redshift.
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How do we get around this problems?

• In previous work, color diagrams have been done
  with only optical colors.
• We will introduce infrared color diagrams,
  whereby we plot one optical versus one infrared
  color.
• We believe that there will be a better
  distinction between stars and quasars in the
  infrared than in the optical.

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How do we test our assumption?

• The blue and black squares are known quasars of
  redshift 2-3.
• J-K is the infrared color while g-J is the
  optical color.
• Notice that in this plot our candidates (the
  small squares) lie roughly in the same region as
  the these known quasars.
• Note how far away our candidates and known
  quasars lie from the stellar locus (black dots).

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We also did some computer programming.

• Programs were written using Fortran language.
• The aim of these programs are to calculate the
  distances of these quasars from us based on their
  brightness and redshift.
• Another purpose of the program was to calculate
  the absolute luminosity of an object based on its
  redshift and apparent luminosity.
• How bright an object appears depends on its
  redshift.

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We also did some computer programming.

• Two objects may appear equally bright, but this
  is deceptive because one might be farther away.
• The program takes these facts into consideration
  and deduces the correct brightness and distances.

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• This graph shows the variation of absolute
  magnitudes with redshift for a given apparent
  magnitude
• This graph shows the variation of distances with
  redshift for a given apparent magnitude.

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Future work.

• Our work will be incomplete until we have taken
  spectra of our candidates to verify that they are
  indeed quasars.
• Fortunately, we have been given time in September
  at the Kitt Peak National Observatory in Tucson,
  Arizona.
• We will spend about a week looking at the spectra
  of these candidates.
• Keep your fingers crossed for us!!!!

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Acknowledgements.

• I want to take this opportunity to thank the
  following institutions and people.
• My mentor, Dr. Julia Kennefick, for her kind
  instruction.
• My Colleagues, Ashley Stewart Shelly Bursick,
  for their assistance and support.
• The University of Arkansas Space center, and NSF
  for funding this program.
• And lastly, SDSS, 2MASS, and Kitt Peak for
  letting us use their data and equipment.