S0 Galaxies Bipolar

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S0 Galaxies - Bipolar ??
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Properties of Galaxies

• Intrinsic
• Luminosity
• Morphological type
• Size
• Shape
• Mass
• Stellar content (3D)
• Gas content (3D)
• Spectrum I? (?)
• Color(s)
• Rotation profile
• Light profile I(r,?, z)
• Age

• Extrinsic
• Position on the sky
• Distance
• Apparent brightness
• Angular size
• Radial velocity
• Proper motion
• Orientation

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Stellar Magnitudes and Luminosities
Light from any source fades as the distance
squared - referred to as geometric dilution

• Luminosity, L energy emitted per unit time
  units ergs/s, W.
• Flux, F ergs/s/cm2 is the energy passing
  through area ? to the line-of-sight per unit
  time.
• Flux measurements depend on luminosity AND
  distance.
• To determine a stars true luminosity, both its
  apparent brightness and distance must be measured.

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Stellar brightness is defined in terms of ?
magnitudes ?
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Magnitudes

• ? An archaic system to quantify the intensity of
  EM
• radiation emitted by or received from
  celestial sources
• ? Brighter objects have numerically smaller
  magnitudes
• ? Magnitudes are logarithmic quantities. A
  difference of 1
• magnitude a difference of 2.512 in
  luminosity.
• ? A difference of 5 magnitudes a factor of 100
  difference in
• luminosity
• ? Magnitudes can be negative.
• ? Sun ?26.8 Full Moon ?12.5 faintest
  star visible to
• the eye 6 HST limit 30

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Apparent magnitude brightness of an object as
seen
from Earth Absolute magnitude the brightness
of an object if seen
from a distance of 10 parsecs
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Magnitudes and Fluxes

• Definition
• Difference in magnitude
• The magnitude scale based on comparison with
  standard stars.
• ? Lyra (Vega) is defined as m 0

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The Distance Scale

• Determination of intrinsic galaxian parameters
• requires a measure of their distances
• Multiple methods are employed to estimate
  distances
• to celestial objects, collectively termed
  the distance
• scale
• The most accurate, fundamental method involves
• measure of trigonometric parallaxes
• Distances are expressed in parsecs 3.26 Ly

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Distances to Galaxies

• Many techniques in use of varying accuracy
• Calibrating the galactic distance scale is a
  major effort in astronomy
• Easiest distance estimator uses a galaxys
  recessional velocity.
• Distance and velocity are related via Hubbles Law

D (Mpc) cz / H0

• H0 Hubbles constant, a (until recently) very
  controversial number

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Magnitudes and Distance
Apparent and absolute magnitudes are related via
the distance to a celestial source
? d must be expressed in parsecs
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The color of stars is a measure of the stars
surface temperature. Stellar colors can be
easily measured by taking images through
different filters. Colors of stars are most
often expressed as a blue visual color,
(B V) (B V) 1 is a red star
(B V) 0 is a blue star
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Color Index

• A color (index) is defined as the difference,
  expressed
• in magnitudes, between the observed (or
  intrinsic) flux
• of an object between two segments of its
  spectrum
• The Johnson color system is the most commonly
  used
• system in the optical near-IR spectrum
• Johnson bands are labeled UBVRI JHK

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Size Axial Ratio
Angular size Expressed as the distance (in
angular units) where the surface brightness falls
to a value of 25 mags/? D25 Also referred to
as the major axis, a Axial ratio Ratio of major
to minor axis b/a
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A galaxy with b/a 0.15. This system appears
almost edge-on to our view
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Galaxy Classification

• Galaxies are classed according to Hubble type, a
  system devised by Edwin Hubble, and modified by
  deVaucouleurs and Sandage
• The Hubble sequence is based on (1) the presence
  of a disk, (2) the bulge-to-disk light ratio, (3)
  structure in the spiral arms arm openness, and
  arm prominence.
• More quantitative classification criteria have
  been proposed, but none adopted as standard.
• Most commonly used quantitative morphological are
  the concentration index and asymmetry index
• deVaucouleurs devised a simple single-valued
  scale for Hubble type, called the T-value, which
  ranges from -5 for ellipticals to 10 for
  irregulars

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