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GalaxiesA2290-16 1GalaxiesRelativity and AstrophysicsLecture 16Terry HerterA2290-16 Galaxies 2Outline Discovering Galaxies Classifying Galaxies Hubble (morphological) classification Different types of galaxies Note:  Most galaxy photos from Astronomy Picture of the Day (APOD) on the web – you can find them (and credits for images) by searching the name of the object.GalaxiesA2290-16 2A2290-16 Galaxies 3Galaxies A galaxy is a collection of stars, gas and dust along w/ associated starlight, magnetic fields and cosmic rays. Four broad categories based on morphology (appearance): E elliptical S spiral (normal & barred) S0 lenticular I irregularA2290-16 Galaxies 4Ellipticals Galaxies Range from spherical to highly flattened with designations E0 to E7 Contain old stars (Pop II) Very little gas and dust 1-200 kpc in diameter Mostly found in clusters of galaxies Average spectral type: K 106to 1013MsunNGC 4636 (E0/S01)NGC 3377 (E5-6) NGC 3115 (E7/S01)NGC 4406 (E3)NGC 4278 (E1)GalaxiesA2290-16 3M87Giant Elliptical GalaxyA2290-16 Galaxies 6Spiral Galaxies Flattened systems which have a thin disk Display spiral structure Divided into barred (SB) and unbarred (S) spirals Further subdivided into classes a, b, and c; e.g. SBb, Sc, ... where  a  large nuclear bulge & tightly wound spiral arms c  small nuclear bulge & loosely wound spiral arms Young (Pop I) and old (Pop II) stars Copious amounts of gas and dust 5-50 kpc in diameter Found mostly in the “field” (outside clusters of galaxies) Average spectral type: A, F, G, K 109to 1011MsunM33 - ScGalaxiesA2290-16 4Sc: Whirlpool (M51) SABc: Southern Pinwheel (M83)Spiral Galaxy ImagesSBc: M109Sa: M65A2290-16 Galaxies 8Lenticulars (S0 Galaxies) Like spiral galaxies in shape and color but no spiral arms Flattened systems which are morphologically between ellipticals and spirals.M85NGC 5866GalaxiesA2290-16 5A2290-16 Galaxies 9Irregulars By definition, irregular in shape Mostly young stars (Pop I) Lots of gas and dust 1-10 kpc in diameter Found in the field (outside clusters) Average spectral type: A, F 108to 1010MsunM82A2290-16 Galaxies 10Hubble Tuning Fork – For classifying galaxiesEllipticalsE0E7S0Normal SpiralsBarred SpiralsSaSBaSbSBbScSBc The classification scheme is strictly morphological and does not necessarily imply an evolutionary sequence.GalaxiesA2290-16 6Thumbnail Version of Hubble Tuning ForkSource:M65, M77, M84, M101: IPAC Multiwavelength gallery; M49, M89, M91, M109: NOAO Image Gallery;M95: Nial R. Tanvir (through SEDS)M101, ScM77, SbM65, SaM49, E4M84, S0 (E1?)M89, E0M109, SBcM91, SBbM95, SBa/bA2290-16 Galaxies 12Other Types of Galaxies Dwarfs 106to 108stars Peculiar Exploding, Rings, Disrupted Seyfert Very Bright Nucleus Interacting Tidal Effects, Tails (pairs) QSO Collapsed Nuclei?GalaxiesA2290-16 7Dwarf GalaxiesLeo INGC 1313Interacting GalaxiesCartwheel GalaxyThe Antennae (NGC 4038 and NGC 4039)GalaxiesA2290-16 8Interacting GalaxiesArp 104 – NGC 5216 (top right) and NGC 5218Arp 273A2290-16 Galaxies 16The Local Group100 kpcLMCSMCMilky WayM33M31GalaxiesA2290-16 9SMC(Dwarf)50kpcNearby galaxies – SMC47 TucGlobularClusterLMC(Dwarf)50kpcNearby galaxies – LMCGalaxiesA2290-16 10M31(Sb)700kpcNearby galaxies – M31Great galaxy in AndromedaNGC205 (dE5) = M110M32 (cE2)=NGC 221A2290-16 Galaxies 20Notes on Classifying Galaxies Classifying of galaxies by their morphology is a bit problematic Appearance can depend on exposure time, wavelength, and angular resolution. Thus can change with redshift – even if no intrinsic evolution Classification Requirements Homogeneous data set Unique classification Flexible and unambiguous notation Unfortunately these requirements are often violated Can get ambiguities and inconsistencies Some examples of how galaxy morphology can change with exposure time and wavelength are given in the next slide.GalaxiesA2290-16 11A2290-16 Galaxies 21Cen A: Two Different ScalesThe image of the peculiar galaxy Cen A (NGC 5128) but with different image display scales. How would YOU classify this galaxy? The same effect could be achieved with different exposure times. [Image is IIIaJ, 4680A from the Digital Sky Survey (DSS) via NASA Extragalactic Database (NED).]Cen A: Two Different WavelengthsThe image of Cen A (NGC 5128) but with a two different wavelengths. Both images are from APOD (Astronomy Picture of the Day) Left image: antwrp.gsfc.nasa.gov/apod/ap030806.html Right image: antwrp.gsfc.nasa.gov/apod/ap040624.htmlGalaxiesA2290-16 12Centaurus A (Peculiar Galaxy)Nearest Radio GalaxyCentaurus A (Peculiar Galaxy)In the InfraredGalaxiesA2290-16 13HI + cont.8.0 um3.6 umB Color visualM81 at different wavelengths0.23 um (yellow), 0.16 um (blue)24 um70 um160 umM81: H-alpha emissionV image from NED H-alpha in blue, V in red + greenGalaxiesA2290-16 14M81: Blue lightColor enhanced image using B & V bands. Color mix is V=red, B=green, B/V=blue.Ratio of B to V imagesA2290-16 Galaxies 28Galaxy Classification Systems Hubble System (of Classification) Introduced in by Edwin Hubble in 1936 book, The Realm of the Nebulae Definitive expose by Alan Sandage in 1961, The Hubble Atlas of Galaxies A number of other classification systems exist  De Vaucouleurs’ Extension of the Hubble System, 1959 Yerkes System (W. W. Morgon 1958, 1959, 1970) David Dunlap Observatory (DDO) System (S. van den Bergh 1960, 1976) Note – these system are based on visual


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CORNELL ASTRO 290 - Galaxies

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