Starburst galaxies in the pairs of galaxies

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Starburst galaxies in the pairs of galaxies

• Mihkel Jõeveer
• Tartu Tuorla seminar 20 21 June 2005, Tõravere

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Starburst galaxies

• Some galaxies show evidence of a recent and
  transient increase in SFR by as much as a factor
  of 50
• The burst may be galaxy-wide or confined to a
  small region about the nucleus
• Many (but by no means all) are associated with
  interacting or merging galaxies
• Tidal interactions do not guarantee enhanced
  activity, they can amplify internal properties
  that would feed such activity (Gallimore Keel,
  1993)

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• We find no correlation between the measured star
  formation rates, and the interacting class,
  suggesting that the enhanced star formation rates
  triggered by the interactions continue throughout
  the whole of merging sequence (Dopita et al.,
  2002)
• Starbursts are strongly represented in samples of
  UV-bright galaxies (the Markarian catalogue)

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Some previous results about Markarian galaxies
in pairs

• 1. Karachentsev (1981, 1987)
• a) Markarian galaxies more often occur in pairs
  (6.1), than as single ones (1.4)
• b) Mean mass-to-luminosity ratio of normal
  galaxies is larger than of Markarian ones
• c) A luminosity of a Markarian galaxy is 50
  larger than normal one
• 2. Keel van Soest (1992)
• The Markarian galaxies are distinguished by
  being systematically the brighter members of
  pairs, by 0.66 magnitude in the mean

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Blue magnitudes of member galaxies in the pairs
Mrk norm Dm mMrk - mnorm
Magnitude of fainter With Seyferts With Seyferts Without Seyferts Without Seyferts
Magnitude of fainter N ltDmgt N ltDmgt
? 14.3 14.4 15.3 15.4 - 15.7 12 10 11 -0.16 ? 0.22 -0.65 ? 0.29 -0.48 ? 0.21 10 9 11 0.02 -0.48 -0.48
? 15.7 33 -0.42 ? 0.13 30 -0.32
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Infrared magnitudes j, h and k of member
galaxies in the pairs Mrk norm (without
Seyferts)Dj jMrk jnorm etc.
Blue magnitude of fainter N ltDjgt ltDhgt ltDkgt
? 14.3 8 0.32 0.35 0.36
14.4 15.3 9 -0.49 -0.51 -0.58
15.4 - 15.7 10 -0.49 -0.58 -0.65
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Selection effects in the catalogue of Markarian
galaxies

• An effect of plate limit
• Zenith distance effect
• Stellar nucleus effect
• Star projection effect
• Image quality effect
• Zenith distance influence on UV-continuum
  estimate
• Observer effect

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An effect of plate limit

• This effect is called by Markarian et al. (1989)
  as most unpleasant selection factor in survey
  works. The objects fainter than 16.m5 are, as a
  rule, worthless for statistical investigation. A
  working sample may include the objects up to
  15.m5 - 15.m7 (the limit of Zwicky catalogue), a
  strict one must contain galaxies brighter than
  15.m0.

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Markarian galaxies in the Catalogue by Zwicky et
al (1961 1968)
mZw NZw NMrk NZw /NMrk
? 14.5 3 672 297 12.4
14.6 15.0 4 217 247 17.1
15.1 - 15.5 10 960 365 30.0
15.6 15.7 8 988 96 93.6
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An example of selection of pairs of galaxies with
Markarian components into the sample
Magnitudes of components
mfainter lt 14.m5 mfainter gt 14.m5
mMrk mnorm 13.0 14.5 all 14.5 13.0 all etc. mMrk mnorm 14.0 15.5 all 15.5 14.0 only some etc.
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Conclusions

• Mean blue and infrared magnitudes of Markarian
  starburst galaxies in the pairs are nearly the
  same as mean magnitudes of normal components.
  Therefore, mean masses of normal components are
  larger in comparison with the masses of Markarian
  components.
• More massive components of pairs are more
  effective triggers of starbursts in companions.
  But this is only the tendency, not a rule.

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