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The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to occur from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model in general agreement with observed phenomena is the Lambda-CDM model—that is, that clustering and merging allows galaxies to accumulate mass, determining both their shape and structure. Hydrodynamics simulation, which simulates both baryons and dark matter, is widely used to study galaxy formation and evolution.
A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars, all orbiting in a stable, compact formation. Globular clusters are similar in form to dwarf spheroidal galaxies, and the distinction between the two is not always clear. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".
A quasar is an extremely luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Quasars are usually categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation. The opposite change, a decrease in wavelength and simultaneous increase in frequency and energy, is known as a blueshift, or negative redshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. The main causes of electromagnetic redshift in astronomy and cosmology are the relative motions of radiation sources, which give rise to the relativistic Doppler effect, and gravitational potentials, which gravitationally redshift escaping radiation. All sufficiently distant light sources show cosmological redshift corresponding to recession speeds proportional to their distances from Earth, a fact known as Hubble's law that implies the universe is expanding.
In cosmology and physics, cold dark matter (CDM) is a hypothetical type of dark matter. According to the current standard model of cosmology, Lambda-CDM model, approximately 27% of the universe is dark matter and 68% is dark energy, with only a small fraction being the ordinary baryonic matter that composes stars, planets, and living organisms. Cold refers to the fact that the dark matter moves slowly compared to the speed of light, giving it a vanishing equation of state. Dark indicates that it interacts very weakly with ordinary matter and electromagnetic radiation. Proposed candidates for CDM include weakly interacting massive particles, primordial black holes, and axions.
In the fields of Big Bang theory and cosmology, reionization is the process that caused electrically neutral atoms in the universe to reionize after the lapse of the "dark ages".
Halton Christian "Chip" Arp was an American astronomer. He was known for his 1966 Atlas of Peculiar Galaxies, which catalogues many examples of interacting and merging galaxies, though Arp disputed the idea, claiming apparent associations were prime examples of ejections. Arp published Seeing Red: Redshift, Cosmology and Academic Science in 1998. Arp was also known as a critic of the Big Bang theory and for advocating a non-standard cosmology incorporating intrinsic redshift.
Redshift quantization, also referred to as redshift periodicity, redshift discretization, preferred redshifts and redshift-magnitude bands, is the hypothesis that the redshifts of cosmologically distant objects tend to cluster around multiples of some particular value.
IC 1101 is a class S0 supergiant (cD) lenticular galaxy at the center of the Abell 2029 galaxy cluster. It has an isophotal diameter at about 123.65 to 169.61 kiloparsecs. It possesses a diffuse core which is the largest known core of any galaxy to date, and also hosts a supermassive black hole that is one of the largest black holes known. The galaxy is located at 354.0 megaparsecs from Earth. The galaxy was discovered on 19 June 1790, by the British astronomer William Herschel.
Galaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies involved. The exact effects of such mergers depend on a wide variety of parameters such as collision angles, speeds, and relative size/composition, and are currently an extremely active area of research. Galaxy mergers are important because the merger rate is a fundamental measurement of galaxy evolution. The merger rate also provides astronomers with clues about how galaxies bulked up over time.
The Dark Energy Survey (DES) is an astronomical survey designed to constrain the properties of dark energy. It uses images taken in the near-ultraviolet, visible, and near-infrared to measure the expansion of the universe using Type Ia supernovae, baryon acoustic oscillations, the number of galaxy clusters, and weak gravitational lensing. The collaboration is composed of research institutions and universities from the United States, Australia, Brazil, the United Kingdom, Germany, Spain, and Switzerland. The collaboration is divided into several scientific working groups. The director of DES is Josh Frieman.
A Lyman-alpha emitter (LAE) is a type of distant galaxy that emits Lyman-alpha radiation from neutral hydrogen.
NGC 4319 is a face-on barred spiral galaxy located about 77 million light years away in the constellation Draco. The morphological classification is SB(r)ab, which indicates it is a barred spiral with an inner ring structure and moderate to tightly wound arms. It is situated in physical proximity to the galaxies NGC 4291 and NGC 4386, with X-ray emissions from the intervening gap indicating NGC 4319 and NGC 4291 may be interacting. NGC 4319 has a much higher proportion of ionized hydrogen compared to the Milky Way galaxy.
While the presence of any mass bends the path of light passing near it, this effect rarely produces the giant arcs and multiple images associated with strong gravitational lensing. Most lines of sight in the universe are thoroughly in the weak lensing regime, in which the deflection is impossible to detect in a single background source. However, even in these cases, the presence of the foreground mass can be detected, by way of a systematic alignment of background sources around the lensing mass. Weak gravitational lensing is thus an intrinsically statistical measurement, but it provides a way to measure the masses of astronomical objects without requiring assumptions about their composition or dynamical state.
The Butcher–Oemler Effect is a scientific hypothesis suggesting the cores of galaxy clusters at intermediate redshift contain a larger fraction of blue galaxies than do the cores of low redshift clusters. The claim was first put forward by Harvey Butcher and Augustus Oemler in a 1978 Astrophysical Journal paper.
The thick disk is one of the structural components of about 2/3 of all disk galaxies, including the Milky Way. It was discovered first in external edge-on galaxies. Soon after, it was proposed as a distinct galactic structure in the Milky Way, different from the thin disk and the halo in the 1983 article by Gilmore & Reid. It is supposed to dominate the stellar number density between 1 and 5 kiloparsecs above the galactic plane and, in the solar neighborhood, is composed almost exclusively of older stars. Its stellar chemistry and stellar kinematics are also said to set it apart from the thin disk. Compared to the thin disk, thick disk stars typically have significantly lower levels of metals—that is, the abundance of elements other than hydrogen and helium.
Haro 11 (H11) is a small galaxy at a distance of 300,000,000 light-years (redshift z=0.020598). It is situated in the southern constellation of Sculptor. Visually, it appears to be an irregular galaxy, as the ESO image to the right shows. H11 is named after Guillermo Haro, a Mexican astronomer who first included it in a study published in 1956 about blue galaxies. H11 is a starburst galaxy that has 'super star clusters' within it and is one of nine galaxies in the local universe known to emit Lyman continuum photons (LyC).
References
- 1 2 Colless, Matthew; Ellis, Richard S.; Broadhurst, T. J.; Taylor, Keith; Peterson, Bruce A. (March 1993). "Faint blue galaxies – High or low redshift?". Monthly Notices of the Royal Astronomical Society. 261: 19–38. Bibcode:1993MNRAS.261...19C. doi: 10.1093/mnras/261.1.19 .
- 1 2 Carlberg, R. G. (November 1992). "Merging and fast galaxy evolution". Astrophysical Journal Letters. 399 (1): L31–L34. Bibcode:1992ApJ...399L..31C. doi:10.1086/186599.
- 1 2 Carlberg, R. G.; Charlot, Stephane (September 1992). "Faint galaxy evolution via interactions". Astrophysical Journal. 397 (1): 5–13. Bibcode:1992ApJ...397....5C. doi: 10.1086/171759 .
- ↑ Kron, Robert G. (1978). Photometry of a Complete Sample of Faint Galaxies (Ph.D. thesis). Berkeley, California: University of California. Bibcode:1978PhDT........13K.
- ↑ Peterson, B. A.; Ellis, R. S.; Kibblewhite, E. J.; Bridgeland, M. T.; Hooley, T.; Horne, D. (1 November 1979). "Number magnitude counts of faint galaxies". Astrophysical Journal Letters. 233: L109–L113. Bibcode:1979ApJ...233L.109P. doi: 10.1086/183087 .
- ↑ Tyson, J. A.; Jarvis, J. F. (15 June 1979). "Evolution of galaxies – Automated faint object counts to 24th magnitude". Astrophysical Journal Letters. 230: L153–L156. Bibcode:1979ApJ...230L.153T. doi:10.1086/182982.
- ↑ Yoshii, Yuzuru; Takahara, Fumio (1 November 1989). "On the redshift-volume measurement of the cosmological density parameter". Astrophysical Journal. 346: 28–33. Bibcode:1989ApJ...346...28Y. doi:10.1086/167983.
- ↑ David C., Koo (21–23 June 1989). "The evolution of field galaxies – Is Omega = 1?". Evolution of the universe of galaxies; Proceedings of the Edwin Hubble Centennial Symposium. Berkeley, California: Astronomical Society of the Pacific. pp. 268–285. Bibcode:1990ASPC...10..268K.
- ↑ Broadhurst, T. J.; Ellis, R. S.; Shanks, T. (1 December 1988). "The Durham/Anglo-Australian Telescope faint galaxy redshift survey". Monthly Notices of the Royal Astronomical Society . 235 (3): 827–856. Bibcode:1988MNRAS.235..827B. doi:10.1093/mnras/235.3.827.
