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Morphological Classification

Morphological Classification. Hubble proposed a scheme for classifying galaxies in his 1936 book, The Realm of the Nebulae Four types of galaxies – Ellipticals (E): En, there n=10[1 –(b/a)], so E0 is round and E7 is most flattened Lenticulars (SO or SB0)

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Morphological Classification

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  1. Morphological Classification • Hubble proposed a scheme for classifying galaxies in his 1936 book, The Realm of the Nebulae • Four types of galaxies– • Ellipticals (E): En, there n=10[1 –(b/a)], so E0 is round and E7 is most flattened • Lenticulars (SO or SB0) • S01, S02, S03 – strength of dust absorption, S01 has none • SB01, SB02, SB03 – prominence of bar • Spirals – normal (S) or barred (SB) • Sa – Sc depending on bulge/disk ratio, tightness of spiral arms, and gas content • Irregulars (does not fit into above category)

  2. Hubble’s original tuning fork Hubble thought this was an evolutionary sequence, so ellipticals are “early-type” and spirals are “late-type”

  3. Hubble classification scheme

  4. Ellipticals M89 – E0

  5. Ellipticals M87—E1

  6. Ellipticals M32—E2, dwarf

  7. Ellipticals M49-E4

  8. Ellipticals M59-E5

  9. Lenticulars M84—S0

  10. Lenticulars NGC5866 – S03

  11. Spirals M65--Sa

  12. Spirals M104—Sa Sombrero

  13. Spirals M31 -- Sb Andromeda

  14. Spirals M33--Sc

  15. Spirals -- barred M58--SBb

  16. Extensions to the Hubble Sequence • De Vaucouleurs (1959) added three new classes: Sd, Sm (e.g., Large Magellanic Cloud is an SBm), Im (e.g., Small Magellanic Cloud)

  17. Extensions to the Hubble Sequence • De Vaucouleurs also introduces: • Notation SA for unbarred galaxy (to match SB for barred) • Notation SAB for intermediate, weakly barred systems • Symbols (r) and (s) to indicate systems with and without rings • In Second (and Third) Reference Catalog, also uses T-type ranging from –5 to 10: • E = -5, E/S0 = -3, S0 = -2, S0/a = 0 • Sa = 1, Sab=2, Sb=3, Sbc = 4, Scd =6 • Sdm=8, Im=10

  18. Spirals M83—SAB(s)c

  19. Spirals NGC303—SAB(r)c

  20. Extensions to the Hubble Sequence • Van den Bergh (1960) added luminosity classes based on arm quality/length (DDO System) • I – strong, well-defined arms, most luminous galaxies, MB < -21 • V – chaotic, small arms, least luminous spirals, usually Sd-Im, MB = > -17 • Luminosity class is listed in Revised Shapley Ames Catalog

  21. What is missing from the Hubble Sequence? • Dwarf galaxies • Faint, M > -18, • Dwarf Ellipticals, dwarf spheroidals, dwarf irregulars • There are probably lots of these, in the Local Group there are >30! • Low Surface brightness galaxies • Very difficult to detect! • Need dedicated surveys • Probably lots of these too! • Peculiar Galaxies • In particular, interacting galaxies • Many cataloged by Arp in 1966

  22. Dwarf Elliptical Optical Near-infrared

  23. Dwarf Spheroidal Leo I

  24. Dwarf Irregular IC 10

  25. Low Surface Brightness Galaxy Malin 1

  26. Interacting Galaxies Arp 295

  27. Interacting Galaxies The Mice NGC 4676

  28. Interacting Galaxies The Tadpole Arp 188 UGC 10214

  29. Overview of Galaxy Properties

  30. Overview of Galaxy Properties • As a fiducial, the Milky Way • Radial Scale Length of 3-4 kpc • Blue Luminosity of ~ 1.5 x 10 L • Absolute blue magnitude, -20.7 • Total Mass of ~1011 – 1012 M  • Depending on how much dark matter there is

  31. Overview of Elliptical Galaxies • About 20% of field galaxies are ellipticals • Most ellipticals are found in clusters! • There are a number of different types of ellipticals • E’s (normal ellipticals) • cD’s (massive bright ellipticals at the centers of galaxy clusters) • dE’s (dwarf ellipticals) • dSph’s (dwarf spheroidals) • Note that these do not form a continuous sequence, they are structurally, kinematically, and physically different objects.

  32. Overview of Elliptical Galaxies • Measure the size of ellipticals by its effective radius – radius which encloses half the light • For comparison the effective radius in an exponential disk is 1.7 x the scale length • Sizes range from few tenths of a kpc (dE’s) to tens of kpc (cD’s) • Absolute magnitudes range from –10 (dSph’s) to –25 (cD’s), a factor of 106 in luminosity • Masses range from 107 M to 1013 - 1014 M

  33. The Coma Cluster

  34. Center of the Coma Cluster cD – NGC 4881

  35. Overview of Spiral Galaxies • About ¾ of galaxies in the field are spirals • Most spirals are found in the field (in groups) • Spiral galaxy scale lengths run from ~1 kpc (dwarfs) to ~50 kpc • Absolute magnitudes ranging from –16 to –23, that’s a factor of ~1000 in luminosity! • Masses ranging from 109 to 1012 M

  36. Hubble Deep Field

  37. Hubble Deep Field – zoomed in

  38. Released March 9, 2004 11.3 days of observing!

  39. Spiral Galaxies at different wavelengths

  40. Spiral Galaxies at different wavelengths

  41. Overview of Irregular Galaxies • Make up a few % of the field galaxy population • Generally smaller, sizes of a few kpc • Absolute magnitudes of –13 to –20 • Masses of 108 to 1010 M

  42. Irregular Galaxies at different wavelengths Near-infrared Optical

  43. Catalogs and Atlases of Galaxies • In late 1700’s, Messier made a catalog of 109 nebulae so that comet hunters wouldn’t mistake them for comets! • ~40 of these were galaxies, e.g., M31, M51, M101. • Most are gaseous nebulae within the Milky Way, e.g., M42, the Orion Nebula • Some are stellar clusters, e.g., M45, the Pleiades

  44. Catalogs and Atlases of Galaxies • New General Catalogue (Dreyer 1888) • Based on lists of Herschel (5079 objects) • Plus some more for total of 7840 • ~50% are galaxies, catalog includes any non-stellar object • Index Catalogue (IC) – (Dreyer 1895, 1898) • Additions to the NGC, 6900 more objects • See www.ngcic.org for online info • Shapley-Ames Catalog (Harvard 1932) • Bright galaxies, mpg < 13.2 • Whole-sky coverage, fairly homogenous • 1246 galaxies, all in NGC/IC • Revised by Sandage & Tamman in 1981

  45. Catalogs and Atlases of Galaxies • Uppsala General Catalog (UGC --Nilson 1973) • Based on Palomar Observatory Sky Survey (POSS) • Size limited, a > 1 arcmin • 13000 objects • ESO (European Southern Observatory) Catalog • Similar to UGC in southern sky,  < 30 • 18000 objects • Morphological Catalog of Galaxies (MCG, Vorontsov-Vel’yaminov et al) • Based on POSS plates • 32000 objects, -2 <  <-18

  46. Catalogs and Atlases of Galaxies • Hubble Atlas (Sandage 1961) • Present plates used by Hubble in developing classification system plus explanation of system • Atlas of Galaxies Useful for measuring the Cosmological Distance Scale (Sandage & Bedke 1988) • Nearby Galaxies Atlas & Catalog (Tully 1988) • V < 3000 km/s • Reference Catalog of Bright Galaxies (RC3, deVaucoleurs et al 1991) • B < 15.5, 23022 galaxies • Also, RC1 (1964, 2599 galaxies) and RC2 (1976, 4364 galaxies) • Carnegie Atlas (Sandage & Bedke 1994) – Images of galaxies in the Revised Shapley Ames Catalog

  47. Catalogs and Atlases of Galaxies • Catalogs of sources in x-ray, radio, infrared, etc. • More recent galaxy surveys – APM survey, CfA Redshift Survey, 2dF redshift survey, Sloan Digital Sky Survey (SDSS) • The list is fairly endless! • The NASA/IPAC Extragalactic Database (NED) is a good source of information on galaxies, plus has many galaxy catalogs on-line: http://nedwww.ipac.caltech.edu/

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