NGC 1553
Encyclopedia
NGC 1553 is a prototypical lenticular galaxy
in the constellation
Dorado. It is the second brightest member of the Dorado Group
of galaxies. British astronomer John Herschel
discovered NGC 1553 on December 5, 1834 using an 18.7 inch reflector
.
together with elliptical
NGC 1549 which lies 11′.8 away from it in the sky. Their interaction appears to be in the early stage and can be seen in optical wavelengths by faint but distinct irregular shells of emission and a curious jet on the northwest side. Together, these two galaxies comprise the center of the Dorado group.
but has an H I mass to B-band luminosity ratio (MHI/LB) of less than 0.01. NGC 1553's ultraviolet
spectrum shows weak flux under the main-sequence turn off at around 2,400 A°
. This is characteristic of old intermediate populations of quiescent
lenticular galaxies.
NGC 1553 has an especially well developed lens (~36″) component of nearly constant surface brightness that is found between the bulge and the exponential disk. Its lens is similar to what is found in NGC 3945 and its inner parts are very hot.
NGC 1553 has associated with itself cool gas and dust. It can also be seen in infrared
and is a weak radio source
. Hubble
observations in 2000 revealed an inner torus-like
dust lane about 3″ across at the galaxy's center.
Chandra X-ray
imaging of NGC 1553 show diffuse hot gas making up 70% of the emissions, dotted with many point-like sources (low-mass X-ray binaries) making up the rest. Similarly to NGC 4697
and Messier 60
, these bright spots are due to binary star systems of black hole
s and neutron star
s most of which are located in globular clusters and reflect this old galaxy's very active past. In these systems, material pulled off a regular star is heated and gives off X-rays as it falls toward the accompanying black hole or neutron star. The brightest of the point sources is coincident with the galaxy's optical nucleus. Its luminosity and spectrum suggest its being an obscured central active galactic nucleus
(AGN). This source is visible in the center of the X-ray image of NGC 1553 shown above.
s have been resolved in the galaxy by the Hubble Space Telescope. There are an estimated 600 globulars in NGC 1553. Like Messier 87
, there is a central deficit of globulars with respect to the underlying luminosity.
Lenticular galaxy
A lenticular galaxy is a type of galaxy which is intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. Lenticular galaxies are disk galaxies which have used up or lost most of their interstellar matter and therefore have very little ongoing...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Dorado. It is the second brightest member of the Dorado Group
Dorado Group
The Dorado Group is a loose concentration of galaxies containing both spirals and ellipticals. It is generally considered a 'galaxy group' but may approach the size of a 'galaxy cluster'. It lies primarily in the southern constellation Dorado and is one of the richest galaxy groups of the Southern...
of galaxies. British astronomer John Herschel
John Herschel
Sir John Frederick William Herschel, 1st Baronet KH, FRS ,was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work...
discovered NGC 1553 on December 5, 1834 using an 18.7 inch reflector
Reflecting telescope
A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
.
Interacting galaxy
It forms a pair of interacting galaxiesInteracting galaxy
Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy's disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision.-Satellite interaction:A giant...
together with elliptical
Elliptical galaxy
An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...
NGC 1549 which lies 11′.8 away from it in the sky. Their interaction appears to be in the early stage and can be seen in optical wavelengths by faint but distinct irregular shells of emission and a curious jet on the northwest side. Together, these two galaxies comprise the center of the Dorado group.
Characteristics
NGC 1553 is an early type galaxy with a luminosity of 4 L⊙. It has been detected in H IH I region
An H I region is an interstellar cloud composed of neutral atomic hydrogen , in addition to the local abundance of helium and other elements. These regions are non-luminous, save for emission of the 21-cm region spectral line. This line has a very low transition probability, so requires large...
but has an H I mass to B-band luminosity ratio (MHI/LB) of less than 0.01. NGC 1553's ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
spectrum shows weak flux under the main-sequence turn off at around 2,400 A°
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
. This is characteristic of old intermediate populations of quiescent
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
lenticular galaxies.
NGC 1553 has an especially well developed lens (~36″) component of nearly constant surface brightness that is found between the bulge and the exponential disk. Its lens is similar to what is found in NGC 3945 and its inner parts are very hot.
NGC 1553 has associated with itself cool gas and dust. It can also be seen in infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
and is a weak radio source
Radio galaxy
Radio galaxies and their relatives, radio-loud quasars and blazars, are types of active galaxy that are very luminous at radio wavelengths, with luminosities up to 1039 W between 10 MHz and 100 GHz. The radio emission is due to the synchrotron process...
. Hubble
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
observations in 2000 revealed an inner torus-like
Torus
In geometry, a torus is a surface of revolution generated by revolving a circle in three dimensional space about an axis coplanar with the circle...
dust lane about 3″ across at the galaxy's center.
Chandra X-ray
Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
imaging of NGC 1553 show diffuse hot gas making up 70% of the emissions, dotted with many point-like sources (low-mass X-ray binaries) making up the rest. Similarly to NGC 4697
NGC 4697
NGC 4697 is an elliptical galaxy some 40 to 50 million light-years away in the constellation Virgo. It is a member of the NGC 4697 Group, a group of galaxies also containing NGC 4731 and several generally much smaller galaxies This group is about 55 million light-years away; it is one of the...
and Messier 60
Messier 60
Messier 60 is an elliptical galaxy approximately 55 million light-years away in the constellation Virgo.-History:...
, these bright spots are due to binary star systems of black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
s and neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
s most of which are located in globular clusters and reflect this old galaxy's very active past. In these systems, material pulled off a regular star is heated and gives off X-rays as it falls toward the accompanying black hole or neutron star. The brightest of the point sources is coincident with the galaxy's optical nucleus. Its luminosity and spectrum suggest its being an obscured central active galactic nucleus
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
(AGN). This source is visible in the center of the X-ray image of NGC 1553 shown above.
Globular clusters
Globular clusterGlobular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
s have been resolved in the galaxy by the Hubble Space Telescope. There are an estimated 600 globulars in NGC 1553. Like Messier 87
Messier 87
Messier 87 is a supergiant elliptical galaxy. It was discovered in 1781 by the French astronomer Charles Messier, who cataloged it as a nebulous feature. The second brightest galaxy within the northern Virgo Cluster, it is located about 16.4 million parsecs from Earth...
, there is a central deficit of globulars with respect to the underlying luminosity.