1. HI in the Interacting Pair NGC 4618/4625
Stephanie J. Bush
Case Western Reserve University

2. 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

3. Objectives We hope to calculate: spatial distribution masses
rotation curves
Interaction history

4. 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
So how about some data?

6. A quick optical glimpse...
Sloan Digital Sky Survey

7. Total HI distribution

10. Spatial Analysis Intensity vs. radius plots
NGC 4618
Spatial Analysis
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

11. Dynamical Analysis: Velocity Field

12. Dynamical Analysis: Rotation Curve for NGC 4618
Preliminary Dynamical Mass: 4.1 x 109 M sun

13. Dynamical Analysis: Rotation Curve for NGC 4625
Preliminary dynamical mass: 8.2 x 108 Msun

14. 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 IC 1727) to find trends.

15. References
Odewahn, S. C. 1991, AJ, 101, 829.

16. 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