Types of Galaxies  

In General > s.a. galaxies; galaxy evolution [active galactic nuclei, spiral agalaxies].
* In terms of their shape: Irregular (Irr); Spiral (S0, Sa, Sb, Sc), richer in gas (star formation); Barred spiral (SB0, SBa, SBb, SBc); Elliptic (E0... E7), giants up to 105 pc, 1012 solar masses, denser and hotter; The majority of galaxies are dwarf ellipticals, but most of the large ones are spirals.
* In terms of emission: Quiet and active (Radio, Seyfert, Emission line BL Lacertae objects).
* Questions: How fundamentally different are the various kinds of active galaxies listed, and how many of the differences just depend on our observations? How many differences are a function of time and change with collisions and mergers?
@ By neural network: Lahav et al ap/95; Mähönen & Hakala ApJ(95)ap.
@ Classification systems: Van den Bergh AJ(97)ap; Conselice MNRAS(06)ap; van den Bergh A&A(08)-a0808 [luminosity-diameter relation]; Wijesinghe et al MNRAS-a1001; Forbes & Kroupa PASA(11)-a1101 [definition, galaxy vs star cluster]; Krajnović pw(11)nov-a1604 [using 3D views of galaxies]; Fraix-Burnet et al a1508 [different approaches, rev].
@ Types: Dunlop pw(97)jan [radio]; Bothun SA(97)feb [low surface brightness]; Collins CP(99) [primeval]; Blain in(01)ap/00 [starburst]; van den Bergh AJ(07)-a0706 [in general]; Gadotti a0802-ch [barred]; Kitchin 07; Nair & Abraham ApJL-a1004 [barred spirals, fraction]; Wadadekar a1201-conf [morphology]; Katkov a1403 [isolated lenticular galaxies]; Kalinova et al a1509/MNRAS [dynamical classification system]; > s.a. supermassive black holes [ultracompact dwarf galaxy].
@ Structure: Maciejewski & Sparke ap/98-proc [bars and structure]; Voglis et al MNRAS(06)ap [invariant manifolds and chaotic orbits in spiral galaxies]; Jog & Combes PRP(09) [lopsided spiral galaxies]; van der Kruit a1004-fs, van der Kruit & Freeman a1101/ARAA [disks]; Salo et al ApJL-a1004 [bars and density waves]; Courteau et al RMP(14) [masses].
@ Related topics: Lintott & Land pw(08)sep, Masters a1303-proc [Galaxy Zoo project]; > s.a. astronomical objects [globular clusters]; galaxy distribution [different environments].

Dwarf Galaxies
* Size: Dwarf galaxies go down to 103 pc, 107 MSun.
* Dwarf spheroidals: 2015, Only the dwarf spheroidals around the Milky Way and the Andromeda galaxy are bright enough to study; They are similar enough to their galactic hosts that they could have started to form at the same time; About 60% of Andromeda's dwarf spheroidals occupy a more-or-less spherical halo around their host, while the rest occupy a thin pancake-shaped region that encompasses Andromeda's galactic plane; Studies suggest that Andromeda's on-plane and off-plane dwarfs formed at the same time from the same material, but the prevailing cosmological framework struggles to account for such a starkly bimodal distribution.
@ General references: Beck SA(00)jun [starburst]; Salvadori a1204-conf [cosmological view]; Bellazzini a1210-conf [and globular clusters]; Kormendy a1405-conf [structure and evolution]; Ibata et al a1407 [velocity correlations of satellite galaxies]; Javanmardi et al a1511/A&A [discovery with amateur telescopes]; Read et al a1601/MNRAS [rotation curves]; > s.a. local group.
@ Specific galaxies: Sandoval et al a1506/ApJL [record-breaking compact stellar systems].

Satellites, Pairs, Groups of Galaxies > s.a. galaxy distribution [including clusters]; local group.
* Closest cluster: The closest clustering outside the Local Group is the Antlia-Sextans, at 1.36 Mpc.
@ Pairs of galaxies: Juszkiewicz et al ApJL(99)ap/98 [relative velocity]; Hashimoto et al ApJ(03)ap/02 [orbit evolution]; Azzaro et al ap/03-proc [satellites].
@ Satellites: Cyr-Racine et al a1506 [of distant galaxies]; Welker et al a1512/MNRAS [alignment with the galactic plane].
@ Satellites, velocity dispersion: Zhao et al ApJ(02)ap [theory]; Jing & Börner ApJ(04)ap; Brainerd ap/04/ApJ.
@ Groups and satellites: Sales & Lambas MNRAS(05)ap/04 [statistics]; Macciò et al MNRAS(05)ap/04 [dark energy and local Hubble flow]; Zentner et al ApJ(05)ap [anisotropic distribution]; Agustsson & Brainerd ApJL(06)ap/05, Yang et al MNRAS(06)ap, Kang et al MNRAS(07)ap [alignment]; Moffat & Toth a0708 [and modified gravity, MOG]; Libeskind et al a1503/MNRAS [planes of satellites and the cosmic web].

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