HI in the Interacting Pair NGC 4618/4625
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Transcript of HI in the Interacting Pair NGC 4618/4625
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