Morphological Classification

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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 n101 (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)

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Hubbles original tuning fork
Hubble thought this was an evolutionary sequence,
so ellipticals are early-type and spirals are
late-type
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Hubble classification scheme
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Ellipticals
M89 E0
5
Ellipticals
M87E1
6
Ellipticals
M32E2, dwarf
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Ellipticals
M49-E4
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Ellipticals
M59-E5
9
Lenticulars
M84S0
10
Lenticulars
NGC5866 S03
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Spirals
M65--Sa
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Spirals
M104Sa Sombrero
13
Spirals
M31 -- Sb Andromeda
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Spirals
M33--Sc
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Spirals -- barred
M58--SBb
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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)

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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, Sab2, Sb3, Sbc 4, Scd 6
• Sdm8, Im10

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Spirals
M83SAB(s)c
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Spirals
NGC303SAB(r)c
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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 lt -21
• V chaotic, small arms, least luminous spirals,
  usually Sd-Im, MB gt -17
• Luminosity class is listed in Revised Shapley
  Ames Catalog

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What is missing from the Hubble Sequence?

• Dwarf galaxies
• Faint, M gt -18,
• Dwarf Ellipticals, dwarf spheroidals, dwarf
  irregulars
• There are probably lots of these, in the Local
  Group there are gt30!
• 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

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Dwarf Elliptical
Optical
Near-infrared
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Dwarf Spheroidal
Leo I
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Dwarf Irregular
IC 10
25
Low Surface Brightness Galaxy
Malin 1
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Interacting Galaxies
Arp 295
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Interacting Galaxies
The Mice NGC 4676
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Interacting Galaxies
The Tadpole Arp 188 UGC 10214
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Overview of Galaxy Properties
E S0 Sa Sb Sc Sd Irr
Color Red Blue
Stellar Pop. Old Old Intermediate Old Intermediate Old Intermediate Young Old Intermediate Young Intermediate Young Intermediate Young
SFR zero low low higher higher higher high
HI (gas) Zero/ low low low modest modest high highest
dust Zero/ low Higher Higher highest highest highest Lower (less metals)
Dyn. Bulge/halo dom. Bulge/halo dom. Disk dominated, so rotation Disk dominated, so rotation Disk dominated, so rotation Disk dominated, so rotation
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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

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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
• Es (normal ellipticals)
• cDs (massive bright ellipticals at the centers
  of galaxy clusters)
• dEs (dwarf ellipticals)
• dSphs (dwarf spheroidals)
• Note that these do not form a continuous
  sequence, they are structurally, kinematically,
  and physically different objects.

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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 (dEs) to
  tens of kpc (cDs)
• Absolute magnitudes range from 10 (dSphs) to
  25 (cDs), a factor of 106 in luminosity
• Masses range from 107 M? to 1013 - 1014 M?

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The Coma Cluster
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Center of the Coma Cluster
cD NGC 4881
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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,
  thats a factor of 1000 in luminosity!
• Masses ranging from 109 to 1012 M?

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Hubble Deep Field
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Hubble Deep Field zoomed in
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Released March 9, 2004 11.3 days of observing!
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(No Transcript)
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Spiral Galaxies at different wavelengths
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Spiral Galaxies at different wavelengths
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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?

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Irregular Galaxies at different wavelengths
Near-infrared
Optical
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Catalogs and Atlases of Galaxies

• In late 1700s, Messier made a catalog of 109
  nebulae so that comet hunters wouldnt 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

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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 lt 13.2
• Whole-sky coverage, fairly homogenous
• 1246 galaxies, all in NGC/IC
• Revised by Sandage Tamman in 1981

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Catalogs and Atlases of Galaxies

• Uppsala General Catalog (UGC --Nilson 1973)
• Based on Palomar Observatory Sky Survey (POSS)
• Size limited, a gt 1 arcmin
• 13000 objects
• ESO (European Southern Observatory) Catalog
• Similar to UGC in southern sky, ? lt 30?
• 18000 objects
• Morphological Catalog of Galaxies (MCG,
  Vorontsov-Velyaminov et al)
• Based on POSS plates
• 32000 objects, -2? lt ? lt-18?

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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 lt 3000 km/s
• Reference Catalog of Bright Galaxies (RC3,
  deVaucoleurs et al 1991)
• B lt 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

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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.c
  altech.edu/