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)  S0 1, S0 2, S0 3 – strength of dust absorption, S0 1 has none  SB0 1, SB0 2, SB0 3 – 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)

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

Hubble classification scheme

Ellipticals M89 – E0

Ellipticals M87—E1

Ellipticals M32—E2, dwarf

Ellipticals M49-E4

Ellipticals M59-E5

Lenticulars M84—S0

Lenticulars NGC5866 – S03

Spirals M65--Sa

Spirals M104—Sa Sombrero

Spirals M31 -- Sb Andromeda

Spirals M33--Sc

Spirals -- barred M58--SBb

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)

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

Spirals M83—SAB(s)c

Spirals NGC303—SAB(r)c

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, M B < -21 V – chaotic, small arms, least luminous spirals, usually Sd-Im, M B = > -17 Luminosity class is listed in Revised Shapley Ames Catalog

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

Dwarf Elliptical Optical Near-infrared

Dwarf Spheroidal Leo I

Dwarf Irregular IC 10

Low Surface Brightness Galaxy Malin 1

Interacting Galaxies Arp 295

Interacting Galaxies The Mice NGC 4676

Interacting Galaxies The Tadpole Arp 188 UGC 10214

Overview of Galaxy Properties ES0SaSbScSdIrr ColorRedBlue Stellar Pop. OldOld + Intermediate Old + Intermediate + Young Intermediate + Young SFRzerolowhigherhigh HI (gas) Zero/ low modesthighhighest dustZero/ low Higher highestLower (less metals) Dyn.Bulge/halo dom. Disk dominated, so rotation

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, Total Mass of ~10 11 – M   Depending on how much dark matter there is

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.

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 10 6 in luminosity Masses range from 10 7 M  to M 

The Coma Cluster

Center of the Coma Cluster cD – NGC 4881

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 10 9 to M 

Hubble Deep Field

Hubble Deep Field – zoomed in

Released March 9, days of observing!

Spiral Galaxies at different wavelengths

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 10 8 to M 

Irregular Galaxies at different wavelengths Optical Near-infrared

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

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 for online infowww.ngcic.org Shapley-Ames Catalog (Harvard 1932) Bright galaxies, m pg < 13.2 Whole-sky coverage, fairly homogenous 1246 galaxies, all in NGC/IC Revised by Sandage & Tamman in 1981

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

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, 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

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: