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HI in the Interacting Pair NGC 4618/4625. Stephanie J. Bush Case Western Reserve University. Why neutral hydrogen? we can observe it! often more extended and possibly more massive distributions than stars more sensitive to interactions. What's so exciting?. - PowerPoint PPT Presentation
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HI in the Interacting Pair NGC 4618/4625
Stephanie J. BushCase Western Reserve University
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
Objectives● We hope to calculate:
– spatial distribution– masses– rotation curves– Interaction history
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/Structure/gas.html
So how about some data?
A quick optical glimpse...
Sloan Digital Sky Survey
Total HI distribution
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 M
sun
● 4625: (3.9 +/- 0.6) x 108 Msun
NGC 4618
NGC 4625
Dynamical Analysis:Velocity Field
Dynamical Analysis:Rotation Curve for
NGC 4618
Preliminary Dynamical Mass: 4.1 x 109 M sun
Dynamical Analysis:Rotation Curve for NGC 4625
Preliminary dynamical mass: 8.2 x 108 Msun
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.
References
● Odewahn, S. C. 1991, AJ, 101, 829.
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