Astr212 Galaxy Projects, Spring 2007

NGC 3115, George Vander Tuig

Intro
The galaxy NGC 3115 is classified as a Spindle Galaxy (SO galaxy). It is a lenticular, meaning that it has a disk shape with a large bulge, but without the spiral arm structures. It is an intermediate type of galaxy that falls between ellipticals and spirals. We view this galaxy from almost completely on its side. We see the disk as simply a straight line with a large bulge in the center.
It has a distance of 14 Mpc or ~ 45,000 kly. It has a linear size of about 10 kpc (that is 1/5 size of the Milky Way). NGC 3115 has a black hole that is 1 billion times more massive than our sun.
 
Color
NGC 3115 has a bland yellow color that tells us that it is made up primarily of old stars. There is a also slight bluish tint indicating that newly formed stars are present as well. The is no significant dust to speak of in this galaxy.

Light Profile
The light profile comparing radius to brightness shows the change in brightness as you follow the major axis out from the bulge of the galaxy. It shows at what rate the brightness decreases as you move out from the center of the galaxy. In the case of NGC 3115, there is a very large bulge. The bulge begins almost 1 kpc from the center

.

In finding the best fit for the light profile I found that it is not just a simple logarithmic fit, as an elliptical galaxy would be. Rather, it is broken up into 3 distinct sections. After plotting the profile on a logarithmic scale I found that the graph has 3 sections having perfect linear fits. One guess is that these sections represent the parts of the bulge and the disk. These findings confirm that this galaxy is neither an elliptical nor a spiral, but it is in fact an intermediate form.

Spiral Fit

For further study of my galaxy I tried to fit the profile as if it were a spiral galaxy,with a disk that decreases exponentially in brightness. I found that there is a linear correlation at a radius of 1.75 kpc and beyond. From this it could be concluded that the bulge begins as far away as 1.75 kpc from the center. This is a depiction of the massive size of this galaxy.

This image is taken by the 2MASS telescope, taken in the near infrared.This image is not drastically different from the color combined image, though it does have a nicely defined circular bulge.

This is the rotation curve graph for NGC 3115. The rotation curve shows us the orbital velocity of the galaxy based on its distance from the center. Using this we can see the distribution of mass in the galaxy. We see that the graph levels out for the majority of the time indicating that there is more mass out there that is not generating any light that we could have picked up in the light profile. This illustrates the effects of dark matter. Also by using this graph we can visibly see the distance of the bulge from the center in kpc. It does seem to confirm that the bulge begins in the vicinity of 1.75 kpc.

References:
Images of Black Hole Galaxies

The Spindle Galaxy-NGC 3115

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

GMOS Spectroscopy of the SO Galaxy NGC 3115

Description of Data Reduction

The image has a gamma level of 0.3, a minimum of 35 and a maximum of 10000.