dwarf spiral galaxy
kahkašân-e mârpic-e kutulé (#)
Fr.: galaxie spirale naine
A galaxy that belongs to the spiral class but is significantly smaller.
dwarf starburst galaxy
kahkešân-e kutule-ye setâre-belk
Fr.: galaxie naine à flambée d'étoiless
early-type galaxy (ETG)
kahkešân-e gune-ye âqâzin
Fr.: galaxie de type précoce
In the → Hubble classification, galaxies on the left part of the → Hubble sequence. Early-type galaxies tend to have redder colors, higher average surface brightnesses, and lower → neutral hydrogen content than → late-type galaxies. This terminology is based on the obsolete and erroneous idea that → elliptical and → lenticular galaxies might be evolutionary precursors to → spiral and → barred spiral galaxies.
Fr.: galaxie vue par la tranche
kahkašân-e beyzigun (#)
Fr.: galaxie elliptique
A galaxy whose structure is smooth without spiral arms and ellipsoidal in shape. Ellipticals are redder than spirals of similar mass. Giant ellipticals contain over 1012 solar masses, whereas dwarf ellipticals have masses as low as 107 solar masses.
Fr.: galaxie vue de face
Fr.: galaxie de champ
A galaxy that lies in the direction of a → cluster of galaxies, but is not a member of the cluster. Field galaxies are rare, less than about 5% of all galaxies.
flocculent spiral galaxy
kahkešân-e mârpic-e pašmin
Fr.: galaxie spirale floculente
A galaxy that has short segments of patchy spiral structure so that the disk appears like the fleece of a sheep. Examples: NGC 2841 and NGC 5055.
From L. floccus "flock of wool" + -ulent; → spiral galaxy.
Kahkešân, → galaxy; mârpic, → spiral; pašmin "woolly, woollen," from pašm "wool" (Mid.Pers. pašm "wool;" Av. pašna- "eyelash, eyelid;" cp. Skt. páksman- "eyelashes;" Gk. pekos "wool, fleece," pek(t)ein "to comb, pluck;" Lith. pešti "to pluck;" O.N. fax "mane").
1) Generally, a large body of → gas,
→ dust, and → stars
held together by their mutual → gravitational attraction
and ranging in mass from about 106 to
1013 Msun. If a galaxy also contains
→ dark matter its mass will be much larger.
Galaxies are grouped into three main categories: → spiral galaxy,
→ elliptical galaxy, and
→ irregular galaxy
(→ Hubble classification).
From L.L. galaxias "Milky Way," from Gk. galaxis (adj.),
from gala (genitive galaktos) "milk."
Kahkešân, short for (râh-e) kahkešân literally "the (path of the) chaff-draggers" or "trail of chaff," from kah, kâh "chaff, straw, hay" (Mid.Pers. kâh "chaff, straw;" cf. Pali kattha- "a piece of wood;" Skt. kastha- "stick;" Gk. klados "twig;" O.Ir. caill "wood;" Ger. Holz "wood;" E. holt; PIE *kldo-) + kešân pr.p. of kešidan/kašidan "to carry, draw, protract, trail, drag" (Mid.Pers. kešidan "to draw, pull;" Av. karš- "to draw; to plow," karša- "furrow;" cf. Skt. kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base kwels- "to plow"). The term (râh-e) kahkešân may be a popular corruption of Mid. Pers. (râh-i) Kâwôsân "the path of Kâwos" referring to the Persian mythological king Kay Kâwôs, who built an eagle-propelled throne to fly to China, as recounted in the Dênkard and the Shâhnâmé.
Fr.: bimodalité des galaxies
The division of galaxies into a "red sequence" and a "blue sequence" in the → color-magnitude diagrams of galaxies involving large statistical surveys. In both sequences, redder galaxies tend to be brighter. The blue sequence is truncated at the red magnitude ~ -22, while the red sequence extends to brighter magnitudes. The division between the two classes of galaxies is associated with a critical stellar mass ~ 3 × 1010 Msun. Galaxies below the critical mass are typically blue, star forming spirals and reside in the field. Galaxies above the critical mass are dominated by red spheroids of old stars and live in dense environments (Kauffmann et al, 2003, MNRAS 341, 33 & 54).
Fr.: bulbe d'une galaxie
xuše-ye kahkašâni (#)
Fr.: amas de galaxies
An aggregation of galaxies, made up of a few to a few thousand members, which may or may not be held together by its own gravity. Same as → cluster of galaxies.
Fr.: formation de galaxies
Fr.: harcèlement galactique
Frequent, high speed galaxy → encounters within → galaxy clusters. Harassment can disturb the morphologies of the galaxies involved, often inducing a new → burst of star formation. Asymmetrical galaxies, → warps, → bars, and → tidal tails can all be produced through galaxy harassment.
Fr.: galaxie M87
The dominant member of the → Virgo cluster of galaxies, which contains some 2,000 galaxies. Also known as NGC 4486, it has an → apparent visual magnitude 9.6. Discovered in 1781 by Charles Messier, this → elliptical galaxy is located 55 million → light-years away from Earth in the constellation → Virgo. M87 is the home of several thousand billion stars, a → supermassive black hole (SMBH) and a family of roughly 15,000 → globular clusters. For comparison, our → Milky Way galaxy contains only a few hundred billion stars and about 150 globular clusters. M87 is characterized by a prominent kiloparsec scale → relativistic jet emitted by the central SMBH. As gaseous material from the center of the galaxy → accretes onto the black hole, the energy released produces a stream of subatomic particles that are accelerated to velocities near the → speed of light.
galaxy main sequence
rešte-ye farist-e kahkešânhâ
Fr.: séquence principale des galaxies
A scaling relation between the → star formation rate (SFR) in galaxies and the total stellar mass (M*) of the galaxies. This relation, colloquially called the "galaxy main sequence," extends over several orders of magnitudes in M* and out to → high redshifts, with a modest scatter of ~ 0.3 dex which includes both intrinsic scatter and measurement uncertainties. The existence of such tight scatter at all observed epochs suggests that most galaxies assembled their stellar mass fairly steadily rather than predominantly in → starburst episodes, implying that → mergers have a sub-dominant contribution to the global star formation history (Wuyts et al., 2011 ApJ 742, 96).
Fr.: galaxie pauvre en gaz
Fr.: galaxie riche en gaz
A galaxy, usually young, which has a relatively important gas content.
grand design spiral galaxy
kahkešân-e mârpic-e farsâz
Fr.: galaxie spirale parfaite
A galaxy with prominent → arms that are clearly attached to the central → bulge or → bar spiraling continuously outward until they reach the edge of the visible disk. Some examples are: → Whirlpool galaxy (M51), M74 (NGC 628), and NGC 2997.
M.E. graunt, from O.Fr. grant, grand, from L. grandis "big, great," also "full-grown;" design, from M.E. designen, from L. designare "mark out, designate, appoint," from → de- "out" + signare "to mark," from signum→ sign; → spiral; → galaxy.
Green Pea galaxy
kahkešân-e noxod sabz
Fr.: galaxie petit pois
A member of a class of galaxies of relatively small size (→ compact galaxy) having very strong → emission lines especially the → [O III] doublet and an unusually large → equivalent width of up to 1000 Å. They were first noted because of their peculiar bright green color and small size, unresolved in → Sloan Digital Sky Survey imaging. Green Peas are similar to high-→ redshift → Lyman alpha emitting galaxies (LAEs) in many respects (small sizes, low → stellar masses, 108-10 → solar masses (Msun), low metallicities for their stellar masses, high → specific star formation rates (sSFR), and large [O III] λ5007/[O II]λ3727 ratios. Green Peas are relatively luminous and massive galaxies compared to the faint-end → dwarf starburst galaxies and LAEs (See Yang et al, 2017, arxiv/1706.02819, and references therein).