GONE%20WITH%20THE%20WIND

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GONE WITH THE WIND
Galaxy Transformation in Abell 2125
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Galaxy Cluster Abell 2125

• Among richest clusters in Abell catalog
• Redshift z0.25, D3 billion light-years
• 266 confirmed members
• Uniquely rich in radio sources
• Complex structure assembly by infall?
• Underachieving in X-rays for a rich cluster
• Laboratory for active galaxy evolution

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Trail of evidence

• Radio survey shows A2125 as special
• C153 among strongest radio emitters
• Redshift survey identifies cluster components
• Hubble imaging shows unusual structure
• Narrowband imaging reveals O tail
• Spectra show gas and stars move differently
• Chandra shows soft X-ray tail

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Frazer Owen and Mike Ledlow at Kitt Peak
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Abell 2125 is unusual
A2125 X-ray clumps, many radio sources
A2645 just as rich, X-rays smooth, few radio
sources
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Galaxy redshifts show multiple subgroups
C153
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Hubble WFPC2 imagery

• Asymmetric flying fish structure
• Disturbed disk, chaotic dust lanes
• Star-forming blue knots downstream

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Kitt Peak Mosaic images

• Narrow-band filter isolated O II emission
• Long ionized-gas trail stretching 200,000 ly
• Mass greater than 100 million solar masses

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Gemini-N spectra

• Burst of star formation 100 million years ago (as
  galaxy entered cluster core?) involving several
  billion solar masses
• This fits with galaxy being 7 times too bright
  for its gravitational mass
• Stars orbits not strongly disturbed
• Gas and stellar motions are completely different
  which would not result from gravity during a
  tidal interaction

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Gemini spectrum Best-fit model (100 Myr
burst on 10-Gyr basis)
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Chandra X-ray results

• C153 shows a trail in soft X-rays (cooler gas
  than surrounding cluster material)
• Roughly matches optical gas trail

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Galaxies in the eggbeater

• Known since Butcher/Oemler in 1978 that galaxy
  populations in rich clusters change with time
  (especially over last 5 Gyr)
• Hubble images show much of the action is in
  destruction/transformation of spirals
• Usually hard to distinguish roles of multiple
  processes in these busy environments

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Coma - 300 million l.y. (Bothun/McGraw-Hill Obs.)
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Abell 851 5 billion l.y. Hubble
(Dressler/Morrison)
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Coma cluster in X-rays
U. Briel et al, XMM-Newton
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Clusters themselves are dynamic

• Local redshift model implies Virgo growing
• Even rich relaxed clusters (Coma) show X-ray
  and redshift substructure
• Clusters as well as galaxies grow by merger and
  acquisition

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Where have all the spirals gone?

• Most into elliptical and S0 galaxies
• Galaxy collisions/mergers
• Tidal forces from the cluster core
• Cumulative weak tides harassment
• Stripping by ram pressure as galaxies move
  through hot cluster gas
• These would often happen together and are
  difficult to separate

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An ongoing view of stripping

• C153 has an unusually high velocity within A2125
  (at least 2000 km/s)
• It is the only large disk to have passed close to
  the dense gas of the cluster core
• Distinct star/gas responses tell us that its
  transformation is being dominated by gas
  stripping.

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Summary

• We see all the signatures of ongoing stripping of
  gas from a spiral galaxy
• Previous detections have inferred this process
  from its aftermath, or seen more subtle effects
  from a single tracer
• Favorable circumstances of C153 allow this
  process to be seen very clearly
• Is this the Milky Way in 50 billion years?