HI in the Interacting Pair NGC 46184625

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HI in the Interacting Pair NGC 4618/4625
Stephanie J. Bush Case Western Reserve University
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What's so exciting?

• Why do we care about NGC 4618/4625?
• intermediate masses
• lopsided galaxies
• Interactions

• Why neutral hydrogen?
• we can observe it!
• often more extended and possibly more massive
  distributions than stars
• more sensitive to interactions

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Objectives

• We hope to calculate
• spatial distribution
• masses
• rotation curves
• Interaction history

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HI Detection 101

• HI gives off radio emission with a 21 cm
  wavelength
• Higher column density HI gives off more emission
• Doppler shift gives velocities
• Can display channels as a movie or as a sum

http///burro.cwru.edu/Academics/Astr222/Galaxy/St
ructure/gas.html
So how about some data?
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A quick optical glimpse...
Sloan Digital Sky Survey
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Total HI distribution
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Spatial Analysis
NGC 4618

• Intensity vs. radius plots
• Adopting 6 Mpc distance and effective radii
  (Odewahn 1991) we find...
• Extent
• 4618 4 x effective radii
• 4625 9 x effective radii
• HI mass
• 4618 (5.3 /- 0.6) x 108 Msun
• 4625 (3.9 /- 0.6) x 108 Msun

NGC 4625
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Dynamical AnalysisVelocity Field
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Dynamical AnalysisRotation Curve for NGC 4618
Preliminary Dynamical Mass 4.1 x 109 M sun
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Dynamical AnalysisRotation Curve for NGC 4625
Preliminary dynamical mass 8.2 x 108 Msun
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Future work(Preferably, in the next week...)

• Dynamical masses with more detailed halo models,
  perhaps including a disk model
• Interaction history
• What constraints can we put on the galaxies being
  bound or unbound?
• If they are bound what will the merger remnant
  look like?
• Compare with other pairs of galaxies (perhaps
  NGC 672 - IC 1727) to find trends.

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References

• Odewahn, S. C. 1991, AJ, 101, 829.

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Acknowledgments

• Dr. Eric Wilcots
• Dr. Bob Benjamin
• The first year grad student office (ok, ok, no
  pixels!)
• Kiwi Davis and Adrienne Stilp
• the bug graveyard survivors
• the NSF