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.
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:
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.
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:
Galaxy rotation curves
are plots of
orbital velocity as a function of radius from
galaxy centers.
They are usually only presented for
disk galaxies.
Galaxy rotation curves
and how they strongly suggest the existence of
dark matter
are explicated in the figure below
(local link /
general link: galaxy_rotation.html).
Sub Tasks:
EOF
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.
End of Task