An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 105 Search : Galaxy
Lyman alpha emitting galaxy (LAEs)
  کهکشان ِ گسیلنده‌ی ِ لایمن-آلفا   
kahkešân-e gosilande-ye Lyman-alpha

Fr.: galaxie émettrice de Lyman alpha   

A galaxy belonging to an important population of low mass → star-forming galaxies at → redshift z > 2. Their number increases with redshift. A large fraction of the → dwarf starburst galaxies during the → reionization epoch may be intrinsic LAEs, but their Lyα photons can be scattered by the → neutral hydrogen (H I) in the → intergalactic medium (IGM), which makes Lyα line a powerful probe of reionization. These high-z LAEs have low → metallicity, low stellar masses, low dust → extinction, and compact sizes. The current best nearby analogs of high-z LAEs are → Green Pea galaxies (Yang et al, 2017, arxiv/1706.02819 and references therein).

Lyman alpha line; → emit; → -ing; → galaxy.

Lyman break galaxy
  کهکشان با بُره‌ی ِ لایمن   
kahkešân bâ bore-ye Lyman

Fr.: galaxie de la coupure de Lyman   

A star-forming galaxy at → high redshift affected by the → Lyman break. Such a galaxy is detected in the red (R, → photometric band) but not in the blue (U and B bands). At those high redshfits (above 2.5), the → Lyman limit at 912 Å is shifted between the U and B bands.

Lyman; → break; → galaxy.

Magellanic spiral galaxy
  کهکشان ِ مارپیچ ِ ماژلانی   
kakhešân-e mârpic-e Mâželâni

Fr.: galaxie spirale magellanique   

A class of low-mass galaxies with relatively rare features. In particular, these galaxies are characterized by a → stellar bar whose center is displaced from that of the disk and a one-armed spiral. The → Large Magellanic Cloud (LMC) is considered the prototype of this class of objects. However, despite a wealth of data, there is still a good deal of uncertainty concerning the nature of the LMC's bar. The majority of the observed Magellanic spirals in the nearby Universe share the LMC's structure, in particular the evidence of an offset bar and a one-armed spiral structure. A good example of these systems is NGC 3906, which shows evidence of the bar offset from the photometric center of the galaxy by 1.2 kpc (Pardy et al., 2016, ApJ 827, 149).

Magellanic; → spiral; → galaxy.

Magellanic type galaxy
  کهکشان ِ گونه‌ی ِ ماژلانی   
kahkešân-e gune-ye Magellani

Fr.: galaxie de type magellanique   

A → metal-poor, → irregular galaxy like the → Large Magellanic Cloud or the → Small Magellanic Cloud. Other examples are: NGC 4449, NGC 4214, and NGC 3109.

Magellanic; → type; → galaxy.

Markarian galaxy
  کهکشان ِ مارکاریان   
kahkešân-e Markarian (#)

Fr.: galaxie de Markarian   

A galaxy with abnormally strong emission in the ultraviolet continuum and broad emission lines arising in a bright, semi-stellar nucleus.

Named after B. E. Markarian (1913-1985), an Armenian astronomer who made a catalog of such galaxies (1967-81); → galaxy.


Fr.: métagalaxie   

An obsolete term which once denoted the entire system of galaxies including the Milky Way.

meta-; → galaxy.

metal-deficient galaxy
  کهکشان ِ کم‌فلز   
kahkešân-e kamfelez

Fr.: galaxie pauvre en métaux   

A galaxy whose → metallicity is smaller than that of the → Milky Way galaxy.

Adj. from → metal deficiency; → galaxy.

metal-poor galaxy
  کهکشان ِ کم‌فلز   
kahkešân-e kamfelez

Fr.: galaxie pauvre en métaux   

Same as → metal-deficient galaxy.

metal; → poor; → galaxy.

Milky Way galaxy
  کهکشان ِ راه ِ شیری   
kahkešân-e râh-e širi (#)

Fr.: Voie lactée   

A → spiral galaxy, of which the → solar system is a small part. It is the second largest in our → Local Group of galaxies. The Milky Way is a disk-shaped system, with a diameter of between 80,000 and 100,000 → light-years and a thickness of about 2,000 light-years, containing more than 1011 stars. The stars are divided into two main categories, → Population II stars and → Population I stars.
The core, or nucleus, of the Galaxy is surrounded by an ellipsoidal central → bulge that measures some 15,000 light-years in diameter and about 6,000 light-years in the direction perpendicular to the plane of the disk. Surrounding the bulge and extending in a near spherical distribution above and below the → Galactic plane is the → Galactic halo. The halo contains about 200 → globular clusters and an extremely thinly scattered population of individual stars.
The Sun is located just over half way out from the center to the edge of the disk at a distance of about 25,000 light-years. In common with other stars, the Sun revolves around the → Galactic Center. Its → orbital velocity is about 220 km s-1 and its → orbital period is about 225 million years. Overall, the Galaxy exhibits → differential rotation, that is stars and gas clouds closer to the center have shorter orbital periods than those that are located further out.
The → spiral arms of the Milky Way lie within its disk, where bright → young stars, → H II regions, and → molecular clouds of gas and dust are concentrated into curved "arms" that appear to radiate from the central bulge in a spiral pattern. The Galaxy's spiral pattern consists of several major arms and a number of shorter segments, one of which, the → Orion arm, contains the Sun and the Orion star-forming region.
Near-infrared observations have shown that the stars in the central bulge are arranged in an elongated → galactic bar, about twice as long as it is wide, that is seen nearly end on from the present location of the solar system. The exact center, or nucleus, of the Galaxy coincides with a strong source of radio emission, called → Sagittarius A, that is less than 15 astronomical units in diameter. Observations of the speeds at which clouds of ionized gas are revolving round the → Galactic center imply that several million solar masses of material are concentrated within a region of about one light-year in radius. Since only about half of this mass can be accounted for by stars, it seems likely that the balance (about 2.5 million solar masses) is contained in a central black hole and that accretion onto this black hole is the underlying source of the energy radiated by Sagittarius A.
The Milky Way also has a → dark matter component. The Galactic → rotation curve indicates that there is a large amount of invisible → non-baryonic surrounding the whole Galaxy.

Milky Way; → galaxy.

parent galaxy
  کهکشان ِ پرمار   
kahkešân-e permâr

Fr.: galaxie parente   

Of a high redshift supernova, the galaxy in which the event has occurred.

parent; → galaxy.

passive galaxy
  کهکشان ِ اکار   
kahkešân-e akâr

Fr.: galaxie passive   

A galaxy lacking optical emission-line activity (e.g., [O II], Hα, [O III]) and showing only stellar absorption lines (e.g., the 4000 Å → calcium break, Mg I, Na I). Also called passively evolving galaxy.

passive; → galaxy.

passively evolving galaxy
  کهکشان با فرگشت ِ اکار   
kahkešân bâ fargašt-e akâr

Fr.: galaxie en évolution passive   

Same as → passive galaxy.

passive; → evolve; → galaxy.

peculiar galaxy
  کهکشان ِ اَفد   
kahkešân-e afd

Fr.: galaxie particulière   

An irregular galaxy that has an abnormal shape (neither elliptical, spiral, nor lenticular) and/or has another unusual characteristic.

peculiar; → galaxy.

power-law elliptical galaxy
  کهکشان ِ بیضی‌گون با قانون ِ توانی   
kahkešân-e beyzigun bâ qânun-e tavâni

Fr.: galaxie elliptique en loi de puissance   

An → elliptical galaxy whose → surface brightness can be approximated by a single → power law at small radii (r ≤ 10-20''). More modern interpretations have emphasized that these profiles can be better understood as the inward continuation of the galaxy's overall → Sersic profile, usually modified by an additional, nuclear-scale stellar component (S. P. Rusli et al., 2013, AJ 146, 160).

power; → law; → galaxy.

primordial galaxy
  کهکشان ِ بن‌آغازین   
kahkešân-e bonâqâzin

Fr.: galaxie primordiale   

A high redshift, metal-deficient galaxy that formed very early in the history of the Universe.

primordial; → galaxy.

progenitor galaxy
  کهکشان ِ زادار   
kahkešân-e zâdâr

Fr.: galaxie mère   

A galaxy which is supposed to be at the origin of a specific event, for example a hypothetical galaxy in which globular clusters might have formed.

progenitor; → galaxy.


Fr.: proto-galaxie   

A huge mass of gas that by contraction and condensation becomes a galaxy of stars. A galaxy during the early phase, before it has developed its present shape and stellar/gas content.

proto-; → galaxy.

radio galaxy
  رادیو-کهکشان، کهکشان ِ رادیویی   
râdio kahkešân, kahkešân-e râdioyi

Fr.: radiogalaxie   

A galaxy that is extremely luminous at radio wavelengths between 10 MHz and 100 GHz. The radio luminosity of a strong radio galaxy (1037-1039 watts) can be up to a million times greater than the radio output of an ordinary galaxy and up to a hundred times greater than the optical luminosity of a galaxy such as the Milky Way. The optical counterparts of radio galaxies are usually an → elliptical galaxy. Radio galaxies often exhibit jet structure from a compact nucleus. They typically display two → radio lobes that are often approximately aligned with the jets observed in the optical and that may extend for millions of → light-years.

radio; → galaxy.

receding galaxy
  کهکشان ِ دورشونده   
kahkašân-e dur šavandé

Fr.: galaxie qui s'éloigne   

A galaxy whose distance increases from other galaxies due to the global expansion of the Universe.

Receding, verbal adj. of recede, M.E., from M.Fr. receder, from L. recedere "to go back, withdraw," from → re- "back" + cedere "to go;" → galaxy.

Kahkašân, → galaxy; dur šavandé "receding," from dur, → far, + šavandé agent noun of šodan "to go, to pass; to become, to be, to be doing;" Mid.Pers. šudan, šaw- "to go;" Av. š(ii)auu-, šiyav- "to move, go," šiyavati "goes," šyaoθna- "activity; action; doing, working;" O.Pers. šiyav- "to go forth, set," ašiyavam "I set forth;" cf. Skt. cyu- "to move to and fro, shake about; to stir," cyávate "stirs himself, goes;" Gk. kinein "to move;" Goth. haitan "call, be called;" O.E. hatan "command, call;" PIE base *kei- "to move to and fro."

regular galaxy
  کهکشان ِ باسامان   
kahkašân-e bâsâmân

Fr.: galaxie régulière   

A galaxy which has a uniformly arranged, symmetrical morphology such as a spiral or elliptical galaxy. Opposite of → irregular galaxy.

regular; → galaxy.

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