* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Milky Way and Its Neighbors
History of Solar System formation and evolution hypotheses wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Physical cosmology wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Outer space wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Corona Australis wikipedia , lookup
Dark matter wikipedia , lookup
Gamma-ray burst wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Aries (constellation) wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Space Interferometry Mission wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Stellar evolution wikipedia , lookup
Observable universe wikipedia , lookup
Lambda-CDM model wikipedia , lookup
Malmquist bias wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Open cluster wikipedia , lookup
Andromeda Galaxy wikipedia , lookup
Globular cluster wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Observational astronomy wikipedia , lookup
Structure formation wikipedia , lookup
Stellar kinematics wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Future of an expanding universe wikipedia , lookup
Star formation wikipedia , lookup
Galaxy Morphology The Tuning Fork that Blossomed into a Lemon Lance Simms MASS Talk 9/8/08 Hubble’s Tuning Fork Tuning Fork Diagram used by Hubble from 1925-1935 Irregular class was later added to right hand side Hubble originally thought evolution was from left to right Irregulars would fall over here Lenticulars S0 galaxies with large central bulge No spiral arms, gas, or dust Flattened disc of stars Ellipticals – En n=10(1-b/a) b: semi-minor axis a: semi-major axis Bulge/Disc Ratio Loose Arms Gas and Dust Lemon Classification of Vaucouleurs A=‘Normal’ B=‘Barred’ Image: Mod. Phys Rev, G. De Vucouleurs, Large-Scale Structure and Direction of Rotation in Galaxies Rotational Velocity Curves • • • • Differential rotation can be observed through spectra Useful for Spiral Galaxies that are viewed edge-on Difficult to use for Ellipticals Overall shift in spectral lines gives velocity and with Hubble Law, approximate distance away Away from us Towards us Note: Galaxy should be edge-on Image for illustrative purposes N II-658.53 nm (in rest frame) Hα-656.28 nm (in rest frame) Velocity Dispersions • Profile width gives velocity dispersion σ – Spectral fitting methods vary • Mass is obtained via the virial theorem • Very useful for elliptical galaxies Virial Theorem 2K U 0 K – Kinetic Energy U – Potential Energy Rv 2 M G α – Constant that depends on distribution of mass within galaxy Increasing dispersion Irregular Galaxies • • • • Small percentage of known galaxies are irregulars (~3%) Galaxies that do not show spiral or elliptical structure • No nuclear bulge • No spiral arms Divided into two main types • Irr-I : some structure • Irr-II : chaotic mess Some are Starburst Galaxies • Very high rate of star formation IC 1613 – Cetus Mass range: Size range: Magnitudes: Composition: Color: 108 −1010 solar masses 1 − >10 kiloparsecs −13 to −20 in B bandpass Varied Young Stars HII regions Varied, toward blue IC 10 - Cassiopea Spiral Galaxies We think about 66% of galaxies are spirals Most have active Star Formation (SF) occurring in spiral arms Appearance depends on angle relative to our line of sight Consist of 4 Distinct Components 4 MAIN COMPONENTS OF SPIRAL 1) Flattened, rotating disc of stars and 1 4 2 3 gas − Arms are in plane of disc 2) Central bulge with mainly old stars − Brightest component of galaxy 3) Nearly spherical halo of stars − Globular Clusters − Dark Matter 4) Supermassive black hole at Spiral Galaxies: A Slice of the Lemon A – Normal spiral -- no bar r – internal ring around nucleus -- spiral arms begin on ring s – no internal ring -- spiral arms begin directly at nucleus B – Barred Spiral Spiral Galaxies Mass range: Size range: Magnitudes: Composition: 109 −1012 solar masses 5 − >100 kiloparsecs −16 to −23 in B bandpass Young and Old Stars Active Star Formation (SF) occurring in spiral arms is very bright in UV Young stars emit towards UV Several types shown below Spiral Galaxies Mapping the Milky Way Our Spiral – The Milky Way In past, mostly done with 2 methods: 1)Mapping HI regions with radio observations - 21 cm line measurements 2)Mapping HII regions via Hα emission lines - HII regions trace active star formation Old data showed that there were 4 arms New data from Spitzer indicates that there are only 2 major spiral arms: -Scutum and Perseus Arms 10,000 ly Our Sun Elliptical Galaxies Ellipticals appear to have very little gas or dust Approximately 10% of known galaxies are elliptical Stars orbit the galaxy center in all different planes Circular orbital velocity measurements do not work very well Sometimes a preferred direction of very slow rotation Luminosity decreases quickly from center so measurements are always made within 10 kpc. Detailed kinematic observations ( σ(r) and Vsys(r) ) only exist for some 10s of galaxies Usually limited to σo and Vsys at center Before 1977 Theorists thought they understood ellipticals well in 1970s = axially symmetric isothermal ensembles = increasingly flattened the more rapidly they rotate about center M32 After 1977 Observations proved them wrong = Spectroscopic data (stellar absorption lines) showed that ellipticals do not rotate globally = Not isothermal = Velocity dispersion is anisotropic = Now strong evidence that they are triaxial ellipsoids http://www.astr.ua.edu/ Elliptical Galaxies Mass range: Size range: Smallest: Composition: Color: 107 −1013 solar masses 0.1 − >100 kiloparsecs Dwarf Ellipticals Mostly old, red stars Towards the red end Luminosity Profiles: Hubble’s Law (1930) I /Io [(r /a) 1]2 I is intensity emitted per unit area at r from center a is core radius; Io is intensity per unit area at center De Vaucouleurs’s Law (1948) log( I /Ie ) 3.33[(r /re )1/ 4 1] M87 –Largest Galaxy in Virgo Cluster re is radius containing half of total luminosity Ie is intensity at a distance re from center Dwarf Spheroidal Galaxies • Low luminosity galaxies • More spherical than elliptical • Companions to Milky Way or other galaxies such as M31 • Little or no gas or dust • No recent star formation • Approximately spheroidal in shape NGC 147 – Dwarf Spheroidal in Local Group Spheroids: A spheroid is basically an ellipsoid with to of its axes equal Saturn is an oblate spheroid, flattened near equator Equation in 3-d: Oblate Spheroid Globular Clusters Large, gravitationally bound groups of stars 10,000 – 1,000,000 stars Not galaxies; considered a part of our galaxy Orbit center of our galaxy in elliptical orbits Some orbits are highly extended Some contain “Tidal Tails” Highly concentrated in Galactic Longitude (337°) NGC 5466 Tidal Tails When globulars pass by bulge of Milky Way, gravity is strong enough to rip stars away Trail of stars left behind is called a Tidal Tail Dwarf Spheroidal or Globular Cluster? • Distinction between globulars (GCs) and Dwarf Spheroidal Galaxies (dSphs) is ambiguous – Globular clusters are generally more compact, but some dwarf galaxies are also – Small galaxies have about same mass as globulars – Galaxies are more “isolated”, but there are intergalactic ‘tramp’ globulars – Color Magnitude Diagrams (CMD) look similar • As of 2003, there were – ~150 GCs – ~9 dSphs • Now, there are ~20 dSphs Globulars and DSphs • There is significant overlap in i) Mass iii) Luminosity iii) Size ii) Mass-to-light ratio iv) Spread in Metallicity • Apparently, ellipticity may be a distinguishing factor • only 20 galaxies in plot, 1.4 data points per plot point Taken from van den Bergh Dwarf Spheroidal or Globular? • Carina Low Surface Brightness (LSB) dSph Dwarf Spheroidal or Globular? NGC 288 Globular Cluster