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