HI in the Interacting Pair
NGC 4618/4625
Stephanie J. Bush
Case Western Reserve University
What's so exciting?
● Why do we care ● Why neutral
about NGC hydrogen?
4618/4625? – we can observe it!
– intermediate masses – often more extended
– lopsided galaxies and possibly more
massive distributions
– Interactions
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 http:///burro.cwru.edu/Academics/Astr222/Galaxy/Structure/gas.html
sum
So how about some
data?
A quick optical glimpse...
Sloan Digital Sky Survey
Total HI distribution
NGC 4618
Spatial Analysis
● Intensity vs. radius plots
● Adopting 6 Mpc distance and
effective radii (Odewahn 1991)
we find... NGC 4625
– 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
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