Credit/Permission: For text, © David Jeffery. For figures etc., as specified with the figure etc. / Only for reading and use by the instructors and students of the UNLV astronomy laboratory course.
This is a lab exercise without observations.
But for reference, see see Sky map: Las Vegas: current time and weather.
Sections
We touch on the following topics:
Some of the
Tasks can be completed ahead of the lab period.
Doing some of them ahead of lab period would be helpful.
However, you can print a copy ahead of time if you like especially if
want to do some parts ahead of time.
You might have to compensate for updates in this case.
The Lab Exercise itself is NOT printed in the lab ever.
That would be killing forests
and the Lab Exercise is designed to be an active web document.
General remarks about quiz prep are given at
Quiz Preparation: General Instructions.
For DavidJ's lab sections, the quiz prep is doing all the items listed here and self-testing with the
Prep Quizzes and Prep Quiz Keys
if they exist.
However to complement and/or supplement the reading, you should at least
read the intro of a sample of the articles
linked
to the following keywords etc.
so that you can define and/or understand some keywords etc. at the level of our class.
A further list of keywords which you are NOT required to look at---but it would be useful to do so---is:
At our level, it is largely an
empirical classification---meaning NOT
based on or biased by theory.
Of course, ideally, one wants to understand the classification theoretically.
And a lot of progress has been made on that.
But the theory of
galaxy formation and evolution
is a complex business, and so we largely, but NOT entirely, skirt it.
The figure below
(local link /
general link: galaxy_vaucouleurs.html)
illustrates the
de Vaucouleurs system
AND
the dVH tuning fork diagram
(a nonce name for a modified version of
Hubble tuning fork diagram)
named for
Gerard de Vaucouleurs's (1918--1995)
galaxy morphological classification system.
This system seems to be the most popular current system and it is the one we use in this lab.
The
de Vaucouleurs system
is mainly an extension
of the older system the
Hubble sequence.
Sub Tasks:
Sub Tasks:
Many galaxies are
interacting galaxies.
The figure below
(local link /
general link: seyfert_sextet.html)
gives an example of
interacting galaxies
and discusses features that indicate
interacting galaxies.
See the portrait
of Carl Seyfert (1911--1960)
in the figure below
(local link /
general link: carl_seyfert.html).
Sub tasks:
Sub Tasks:
We will be classifying Virgo Cluster
galaxies from images
taken by
Sloan Digital Sky Survey (SDSS).
The SDSS images
are a homogeneous
data set.
The images were---yours truly believes---created using the
SDSS ugriz filters.
The
passbands
(AKA transmission functions, AKA response curves) of these filters
are displayed in the figure below
(local link /
general link: photometry_sdss.html).
Sub Tasks:
Classify the 70
galaxies
given in Table: Some Virgo Cluster Galaxies
(see below)
using the
de Vaucouleurs system.
Note that your instructor
MAY direct to you to classify less than 70.
There is a learning curve to climb in the
classification. You get faster as you go along.
Sub Tasks:
The images are
Sloan Digital Sky Survey (SDSS) images
constructed from
observations using the
SDSS ugriz filters.
Yours truly thinks they are approximately
true color though probably
enhanced to bring out features, but it's always hard to
tell with astrophotography since no one is
ever going to tell you.
You can scroll in and out and around on the images and change to images from
surveys other than SDSS.
Do so as needed.
That should allow you to make a
1st-order classification.
For IPI:
In GalClass, there are 4
folder:
E_S0 class, Sa class, Sb class, and Scd_Irr class
containing images of template
galaxies
of the indicated
Hubble sequence galaxy types.
Note the images of template
galaxies form an inhomogeneous
data set of varying quality.
Do the best you can with them.
You should discuss, debate, argue your classification in your groups. It's fun---trust me.
Unfortunately, Sinbad
does NOT always give a
de Vaucouleurs system
classification.
So probably NED
is the best source for the correct
de Vaucouleurs system
classification.
If you classified a galaxy as
intermediate spiral galaxy
count it as right if
it is any kind of
spiral galaxy.
For example, if a galaxy is an
SAB(r)bc and you call it an SBa, then you are right---if you called it an E0
you are wrong.
Don't worry. You get the same mark whatever your score. Unless your
instructor
says otherwise.
But if you are under 50 %, you really blew it.
As an example of interacting galaxies,
we consider
The Mice (AKA NGC 4676)
are shown in the figure below
(local link /
general link: galaxy_mice.html).
Sub Tasks:
Are the galaxy pairs
listed in the Sub Tasks below
interacting galaxies?
Explain why or why NOT making use of the discussion in figure above
(local link /
general link: galaxy_mice.html).
Zoom out on either image of the pair to see them both.
Sub Tasks:
Stars,
interstellar medium (ISM),
other baryonic dark matter
(which is ordinary matter plus whatever black holes
are thought to be made of),
and dark matter
(some exotic particle)
are all in motion around the
center of mass of
a galaxy.
If they were NOT, they would all fall inward under
collective self-gravity
and their
gravitational potential energy
would get converted into some other form of
energy.
So galaxies
are held up by their motion or, more exactly, their
kinetic energy.
The matter
is some kind of orbits---but
NOT closed orbits.
There
are too many
astronomical perturbations
(especially
gravitational perturbations) for that.
A full discussion of galaxy rotation
is beyond our scope.
But we can investigate a few points.
We note there is a main distinction between rotation in
ellipticals
and spirals.
In ellipticals, all the
matter is in orbit, but the orbits have mostly random orientations.
The result is that the net
angular momentum
is nearly zero.
Unlike ellipticals,
spirals
and other disk galaxies
(i.e., galaxies
with something like a galactic disk),
do have non-zero net angular momentum
at least for their
galactic disks.
Galaxy rotation curves
are plots of
orbital velocity as a function of radius from
galaxy centers.
They are usually only presented for
disk galaxies.
The 3 figures below
(local link /
general link: galaxy_rotation_curve_cartoon.html;
local link /
general link: /galaxy_rotation_curve_m33.html;
local link /
general link: galaxy_rotation.html)
explicate
galaxy rotation curves
and how they strongly suggest the existence of
dark matter.
Sub tasks:
We can't do more: it's an immensely complex subject and it's rapidly evolving at present, and
so there is no fixed story to tell.
Yours truly takes it back.
We'll consider the tidbits
sine die---but maybe on
Greek Kalends
(Augustus (63 BCE -- 14 CE)
quote).
Do the preparation required by your lab
instructor.
Keywords:
Andromeda-Milky Way collision,
barred spiral galaxy,
Coma Cluster,
cosmic distance determination,
dark halo,
de Vaucouleurs system
elliptical galaxy,
galactic bulge,
galactic disk,
galactic halo,
galactic tide,
galaxy,
galaxy cluster,
galaxy formation and evolution,
galaxy morphological classification,
galaxy merger,
Hubble's law,
Hubble sequence,
Hubble tuning fork diagram,
interacting galaxies,
irregular galaxy,
lenticular galaxy,
Local Group,
M87,
Milky Way,
spiral density wave theory,
spiral galaxy,
stellar collision,
stellar collisions
in galaxy collisions,
Virgo Cluster.
Hm.
Task Master:
EOF
Galaxy morphological classification
is a classification of galaxies by shape.
We're going to classify some galaxies in the
Virgo Cluster.
Note
The shown galaxies are the ones you will classify.
The procedure is discussed in the sub tasks below.
IMAGE LINKS:
e.g.,
IC 3476 image
for the image of
IC 3476.
Note that
Internet Explorer
puts (or did put) a big grey bar across the images---it's a
feature---just accept it.
Firefox does NOT
have this feature
and, therefore, is preferred for this
task.
Note
But a
1st-order classification
is NOT usually accurate enough.
1st-order classification.
using images of template galaxies
of the main
de Vaucouleurs types
(which for our purposes are the virtually same as the main
Hubble sequence galaxy types).
2nd-order classification.
For RMI:
By comparing the
Virgo Cluster
images of template galaxies,
decide on a final classification
and enter it in
Table: Some Virgo Cluster Galaxies below.
after you have done the
classification yourself.
You'll have to scroll down a bit to find the
NED classification.
Right/Wrong (R/W)
The Sinbad and
NED
links all work, or so
yours truly thinks.
You are right in your classification if you are approximately right: i.e.,
if you got the main classification right:
elliptical galaxy,
lenticular (S0) galaxy,
unbarred spiral galaxy,
intermediate spiral galaxy,
barred spiral galaxy,
irregular galaxy.
In this section, we consider
interacting galaxies.
First note that
galaxies are
NOT static structures.
Angular momentum
is a measure of rotation that includes a measure of direction of rotation.
In fact, angular momentum
is a vector
with direction, loosely speaking, perpendicular to the plane of rotation.
Since
angular momentum is a
vector, it
adds like a vector.
So equal-in-magnitude angular momentum
vectors
that are opposite in direction add to
zero.
Their rotational
kinetic energy does NOT
add to zero.
Zero net angular momentum
is often referred to as zero net rotation
or something like that which is vague,
but understood in a vague way.
End of Task
We will consider a few tidbits on the subject of
galaxy formation and evolution.
Goodnight all.
Post mortem comments that may often apply specifically to
Lab 11: Galaxies: