# Galaxies

Objects Nearby: the number of objects returned by a search on http://ned.ipac.caltech.edu, within +/- 750 kpc and +/- 500 km/s.

Key properties of surveyed galaxies
Name RA Dec Redshift Nearby Objects
NGC 0986 02h 33′ 34.349″ −39° 02′ 42.21″ 0.006585 3 (list)
UGCA 168 02h 33′ 34.349″ −39° 02′ 42.21″ 0.003089 26 (list)
NGC1433 03h 42′ 01.5″ -47° 13′ 19″ 0.003589 32 (list)
NGC 1792 5h 14′ 6.7″ −40° 02′ 48″ 0.004039 16 (list)
NGC 2369 07h 16′ 37.7″ -62° 20′ 37″ 0.010807 8 (list)
NGC 2427 07h 36′ 28.2″ -47° 38′ 08″ 0.003242 10 (list)
NGC 3223 10h 21′ 35.1″ -34° 16′ 01″ 0.009644 6 (list)
NGC 5643 14h 32′ 40.7″ -44° 10′ 28″ 0.003999 7 (list)
NGC 6300 17h 16′ 59.5″ -62° 49′ 14″ 0.003699 6 (list)
NGC 7090 21h 36′ 28.865″ −54° 33′ 26.35″ 0.002825 3 (list)
NGC 1350 3h 31′ 8.1″ −33° 37′ 43″ 0.006354 23 (link)
NGC 1291 03h 17′ 18.6″ -41° 06′ 29″ 0.002799 8 (list)
NGC 1543 04h 12′ 43.2″ -57° 44′ 17″ 0.003922 39 (list)
ESO 121- G006 06h 07′ 29.8″ -61° 48′ 27″ 0.004039 3 (list)
ESO 539- G003 03h 50′ 04.65″ -33° 36′ 58.3″ 0.026855 5 (list)
IC 4837A 19h 15′ 16.2″ -54° 07′ 57″ 0.009498 10 (list)
NGC 0360 01h 02′ 51.4″ -65° 36′ 36″ 0.007693 2 (list)

\label{table:nonlin}

## NGC 0986

NGC 0986 is a spiral galaxy located in the Fornax constellation approximately 56 million light years away from earth. A large number of blue stars are found in the swing arms of this galaxy. The bright bar running through the center gives it the characteristic of being a barred spiral galaxy.

The Fornax (Furnace) constellation is located in the southern sky. The Fornax cluster, which lies in the Fornax constellation, is the second richest galaxy cluster within 100 million light years totalling 58 observable galaxies. The brightest member in the cluster is NGC 1316, a lenticular galaxy and is the fourth brightest radio source in the sky.

NGC 0986

## UGCA 168

UGCA 168 is a spiral galaxy found in the constellation of Antlia. The Antlia constellation is found in the second quadrant of the Southern Hemisphere. Antlia belongs to the Lacaille family of constellations and represents an air pump.

UGCA 168, from wikisky.org

UGCA 168, from the SuperCOSMOS Sky Survey

## NGC 1433

NGC 1433 is a spiral galaxy located in the constellation of Horologium. It is 30 million light years away from Earth. The galaxy has an active galactic nuclei and is a Seyfert galaxy.

The Horologium constellation is located in the first quadrant of the southern sky. It is a relatively small, faint constellation and its the 58th constellation in size.

NGC 1433

## NGC 1792

NGC 1792 is a starburst spiral galaxy located in the Columba constellation. It is rich in neutral hydrogen gas, a fuel source for new stars. Because of this NGC 1792 is currently rapidly forming new stars, the reason that it is classified a starburst galaxy.

NGC 1792 is located in the globular cluster of Columba which is roughly 35,000 light years from earth where several other galaxies are present.

NGC 1792

## NGC 2369

NGC 2369 is a spiral galaxy located in the Carina constellation. The Carina constellation is part of the Heavenly Waters family and is in the second quadrant of the southern hemisphere.

NGC 2369, from wikisky.org

## NGC 2427

NGC 2427 is a barred spiral galaxy found in the constellation of Puppis. It is located about 45 million light years away from Earth. It has a diameter of about 65,000 light years.

Puppis is the 20th constellation in the sky and is located in the second quadrant of the southern hemisphere.

NGC 2427, from wikisky.org

## NGC 3223

NGC 3223 is a faint barred galaxy found in the constellation Antlia. It is located 108.8 million light years away from Earth. The Antlia constellation is one of the smaller constellations in size, and occupies the second quadrant in the Southern hemisphere. Antlia only has one star known to have planets.

NGC 3223, from wikisky.org

## NGC 5643

NGC 5643 is located in the Lupus constellation. NGC 5643 is a barred spiral galaxy. The Lupus constellation is located in the third quadrant of the southern hemisphere.

NGC 5643, from wikisky.org

## NGC 6300

NGC 6300 is a Seyfert galaxy that is located in the constellation of Ara. It is a barred spiral galaxy. The galaxy is located 0.051 billion light years away from Earth. The galaxy emits X-rays, and is suspected to have a black hole 300,000 times the size of our sun in the middle of it.

NGC 6300 is located in the Ara constellation. It is a small constellation located in the southern sky and belongs to the Hercules family of constellations. Ara contains part of the Milky Way, therefore it has rich star fields.

NGC 6300

## NGC 7090

NGC 7090 is a spiral galaxy which is 30 million light years from the sun and is located in the southern constellation Indus. In the picture above the red that is visible are clouds of hydrogen gas. The picture also views the galaxy edge on from the earth and the spiral arms present are harder to see.

NGC 7090 is not an H1 deficient galaxy. The red zones in the picture are clouds of hydrogen gas. These structures are the location for new stars to form, this means that NGC 7090 is still actively forming stars. NGC 7090 is located in the Indus constellation, found in the southern sky. In 2015 a superluminous supernova was detected in this region.

NGC 7090

## NGC 1350

NGC 1350 is a spiral galaxy located 87 million light years away in the constellation Fornax and measures 130,000 light years across.

NGC 1350 in on the outskirts of the Fornax cluster of galaxies although the distance from the cluster suggests that it is not actually part of the Fornax cluster. NGC 1350 is slightly larger than the Milky Way galaxy.

NGC 1350

## NGC 1291

NGC 1291 is a ring galaxy located 33 million light years away from earth in the Eridanus constellation. It is composed of an inner bar and a surrounding ring structure. The Eridanus constellation, which NGC 1291 is found in, has a supervoid which is speculated to be caused by quantum entanglement with another universe.

NGC 1291, from wikipedia.org

## NGC 1543

NGC 1543 is a lenticular galaxy located 56 million light years away from Earth. It is located in the constellation of Reticulum. Reticulum is one of the smallest constellations in the sky and is located in the first quadrant of the southern hemisphere.

NGC 1543

## ESO 121 - G006

ESO 121 - G006 is a spiral galaxy located in the Pictor constellation. The pictor constellation is located in the first quadrant of the southern hemisphere. Its neighboring constellations are Caelum, Carina, Columba, Dorado, Puppis and Volans.

ESO 121-G006, from the Hubble Space Telescope
ESO 121 - G006, from the SuperCOSMOS Sky Survey

## ESO 539 - G003

ESO 539-G003 is an intermediate spiral galaxy located in the Eridanus constellation. The Eridanus constellation is located in the first quadrant of the Southern Hemisphere. The constellation contains 7 stars with known planets.

ESO 539 - G003, from the SuperCOSMOS Sky Survey

## IC 4837A

IC 4837A is a spiral galaxy located in the telescopium constellation. The telescopium constellation is located in the fourth quadrant of the southern sky and is in the Lacaille family.

IC 4837A, from wikisky.org

## NGC 0360

NGC 0360 is a barred spiral galaxy found in the Tucana constellation. The Tucana constellation is located in the first quadrant of the southern sky.

NGC 0360, from wikisky.org

# H-1 Deficient Galaxies

Hydrogen is the fuel for galaxies to produce stars. Large amounts of hydrogen gas found in various nebulas and galaxies are compacted and form stars, where nuclear fusion takes place. For a galaxy to produce new stars it must have fuel, and in galaxies where hydrogen is abundant many new stars will continue to form. An example of a hydrogen rich environment is a starburst galaxy where new stars are being formed and is NGC 1792 in the Columba constellation.

However, when galaxies lack the necessary fuel to produce stars they are considered to be H1 deficient. NGC 4921 is an example of an H1 deficient galaxy. Sidney Van den Bergh, the astronomer who discovered the galaxy described it as "anemic" because of the low rate of star formation. When examined, NGC 4921 was found to be strongly H1 deficient.

NGC 4921 (from NASA.org)

NGC 4921 could have had its hydrogen stripped from it through interaction with the intergalactic medium (IGM). IGM is rarefied ionised plasma which surrounds and stretches between galaxies. The stripping of hydrogen gas occurs mostly within clusters of galaxies and there were 73 objects found near (within 750 kpc and 500 km/s) NGC 4921, part of the Coma cluster, which justifies the likeliness of NGC 4921 losing its hydrogen through IGM interaction. Another example is the Virgo Supercluster, where H1 deficiency is widely present.

The Virgo Supercluster apod.nasa.gov

# Angular Momentum

## Momentum

Momentum is the quantity of motion an object has. Momentum can be described by the equation $$p=mv$$, where $$p$$ represents the momentum, $$m$$ is the mass of the object, and $$v$$ is the velocity of the object. This equation shows that the momentum is directly proportionate to the mass and directly proportionate to the velocity of the object.

## Angular Momentum

Angular momentum for a particle is described by the equation $$L=r \times p$$, where $$r$$ is a vector from the center of rotation to the object, and $$p$$ is the linear/translational momentum described in the section above. This vector cross product produces another vector which is perpendicular to both $$r$$ and $$p$$. In the diagram below, $$L$$ points out of the computer screen towards the viewer. If the rotation was clockwise instead, $$L$$ would point away from the viewer. In this way, angular momentum is different to normal momentum as the vector describes the axis that the object is rotating around instead of the direction it is travelling.

## Measuring angular momentum of a galaxy

Galaxies are often very far away, so how is it possible measure how fast a galaxy spins? Astronomers would need to observe a galaxy for a very long time to see it spin. The solar system moves at a staggering 828,000 kilometers per hour, and yet it would still take 230 million years to complete one revolution.

Instead, the doppler effect can be used to obtain the rotation.

Around all galaxies there is a hydrogen cloud. As hydrogen atoms change their energy state, they emit photons with a wavelength of approximately 21cm. Due to the doppler effect, these waves are either stretched or squeezed as they travel back to Earth. On the whole, all objects in space are redshifted, because they are moving away from us because of the expansion of the universe. However, if the galaxy is spinning, then one side will be moving away more than the other. This difference in redshift can be converted into the speed that the galaxy is spinning at.

## Impact on Star Formation

The more angular momentum the gas in the galaxy has, the less it is pulled together by the forces of gravity. Therefore, galaxies with high angular momentum will form stars less easily.

Angular momentum has recently been shown to regulate the amount of atomic hydrogen (http://adsabs.harvard.edu/abs/2016arXiv160504927O). Galaxies that have higher angular momentum will form stars less, and thus will have more atomic hydrogen, making them potentially H1 excess. Galaxies with a lower angular momentum are able to actively form new stars, using up their hydrogen faster and leading to H1 deficiency.

A diagram showing how angular momentum works