Elliptical Galaxies II
Dynamics of elliptical galaxies
How do we estimate the mass of an elliptical galaxy?
We use the virial theorem, which can be written
1 d2 I
2 K = U .
I is the moment of inertia of
The colors of a galaxy (the integrated light) can tell us about its stellar population, but we can learn even
more information from its spectrum. Galaxies contain gas and stars; unsurprisingly, the spectrum of a gal
Galaxies are not distributed randomly throughout the universe; they are usually found in associations called
groups or clusters. In both cases, the galaxies are gravitationally bound to each other and orbit the sys
The Stellar Populations of Galaxies
How do we understand the integrated light of galaxies? The colors and spectra of galaxies vary from galaxy
to galaxyhow and why?
Galaxy light comes from stars, so we can understand the evolution
The Luminosity Function
The luminosity function of galaxies
When we count galaxies, we would like to be able to specify the number density of galaxies as a function
of luminosity. This is done with the luminosity function, where
Spiral Galaxies II
The Tully-Fisher relation
Vera Rubins work also showed that the maximum rotational velocity of spiral galaxies depends on the
galaxy type and luminosity: spirals of earlier type have larger vmax , and more lumi
Gas, Dust and Star Formation
In addition to stars, galaxies contain gas and dust, which are both very important to the formation of stars
in galaxies. The gas and dust in galaxies is called the interstellar medium (ISM). The ISM a
Overview of the Universe
Prerequisites and requirements, topics coveredsee syllabus.
Units and scales
Galaxies and cosmology deal with sizes and masses that are both very large and very small.
Distance units: AU,
Kinematics of the Milky Way II
Differential Galactic rotation and Oorts constants
Now well look at rotational motion in other parts of the Galaxy. The basic principles of Galactic rotation
were determined by Jan Oort in 1927. Dif
Types of Galaxies and the Hubble Sequence
Are there other galaxies outside the Milky Way?
A bit of historical perspective: fuzzy things in the sky (called nebulae) had been catalogued, but it wasnt
known whether or not they were
Elliptical Galaxies I
According to the Hubble sequence, elliptical galaxies are classied only by their degree of observed ellipticity. This turns out to be not particularly useful; unlike the properties used to classify spirals, th
Spiral Galaxies I
Goal: understand the 3-d structure of galaxies. How do we get to this from what we can observe?
Easiest to observe: the 2-d surface brightness of a galaxy.
Surface brightness : luminosity per
Contents and Structure of the Milky Way
What is a galaxy?
A collection of stars ( 106 to 1012 , roughly), gas, dust and dark matter, held together by gravity.
Bigger than a star cluster, smaller than a cluster of galaxies. (This
Kinematics of the Milky Way
We usually assign coordinates to astronomical objects using an Earth-based coordinate system (projection
of latitude and longitude onto the sky), which is us