Check out the Tutorial for some illustrations
Objects
Galaxy
Any galaxy under study, ranging from small dwarf galaxies to massive ellipticals.
Region of interest
A region of interest which is clearly in the background compared to the main galaxies of interest.
LSB structures
Shells
Shells are arcs of circles centered on the galaxy. There can be several concentric shells of
arbitary numbers. Shells can be very fine or thick. They can be recognised by their
sharp outer edge.
Plumes
Plumes are tidal tails that do not have the usual elongated, antennae-like structure. They can be rounded, fuzzier.
Tidal Tails
Tidal tails are composed of stars and gas stripped away from a galaxy during interactions or mergers with
similar-mass galaxies, due to tidal forces. They are still attached to the galaxy, and they eventually
fall down on it under gravity, making a twisted shape.
Tidal tails can contain young stars and dwarf galaxies that were created by the compression of gas in the tail.
Streams
Streams are similar to tidal tails, but they were created out of dwarf galaxies rather than the main
merging galaxy. Therefore, they contain materials and stars that are older than in a tidal tail, making them redder. They often
have a S shape. The dwarf galaxy that was disrupted into a stream (i.e. the progenitor) is sometimes
visible with both branches of the S on either side. Sometimes, the progenitor is hidden or completely destroyed, and only the stream remains.
Internal Structures
Nucleus
Central concentration of stars (nuclear star cluster) in the center of a dwarf galaxy.
Bar
A bright, roughly rectangular bar, in the center of the galaxy.
Rings
The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because
of the young, hot OB stars that inhabit them.
Spiral Arms
The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because
of the young, hot OB stars that inhabit them.
Dust Lanes
A dust lane is a relatively dense obscuring band of interstellar dust, observed as a dark swath against
the background of a brighter object, especially a galaxy. These dust lanes can usually be seen in spiral galaxies.
Inner Structure
A part near the galaxy center that displays some features. It can for instance encompass the light of the galaxy
as seen in shallow surveys, incluing the spiral arms for spirals or the extended round component for
ellipticals.
Artifacts
Instrument
Any artifact coming from the instrument, such as CCD gaps.
Ghosted Halo
Imaging artifact that is due to reflections of light inside the telescope and CCD. They are centered on all the
bright objects of the image.
The ghost halos have a fix size that depends on the telescope. They are usually the same colour but they
are not correctly centered on the bright object: in some parts of the image they are a bit up, in others a bit down, etc.
Cirrus
A cirrus is a dust cloud in our Galaxy, scattering the optical light. They can be recognised because they usually
occupy a large part of a very large image - it is therefore best to zoom out to verify a suspicion of cirrus.
They have a filamentary texture with consistent orientation throughout the image.
High Background
regions in deep images, with background levels higher than the blank sky values, not clearly identified
as structured cirrus. These regions may trace dust illuminated by bright objects. They are not flat field
defects but are really due to higher foreground emissions in these regions. High background regions make
tidal features identification difficult.
Satellite Trail
A trail left by a satellite passing in the field-of-view.
Other
Not Sure
When you are unsure that your annotation does not resemble any of the above.