normal-galaxies

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Unformatted text preview: " 30% of your grade Ident can bring in a single 8.5” X 11” sheet of paper with Weather is still not cooperating for observing—we will continue to monitor the forecast. _ Astronomy Open Night this Friday, 7:30pm in E88 001 (counts as -. m. extra credit). Exam extra credit assignment-will- be handed out nextciasseeit will be due in recitation on Fri. May 13‘“. NASA, NOAO, ESAand The Hubble Heritage Team (STScl/ Normal Galaxies (Kulner, Ch. 17; also Bennett el al. Ch. 20, Shu Ch. 12) AST 203 (Spring 2011) radio continuum (408 Mljz)‘ atomic hydrogen rad-lo continuum 5' éfizj molecular hidr'o‘g'eln, infrared mid‘im‘rared near infrared :- a. .n on V5 5" 5 RI V1 9 "3 § 5 5 optical x-r‘uy . : r‘,f:':i“i‘i‘¥"*‘ Milky’Way Last Time The velocity of an orbit around the galactic center depends only on the distance and the enclosed mass (spherically symmetric): mv2(R) : GM(7“)m 02(R)R R R2 : MR): 0 Mapping H | clouds and molecular clouds gave the Galactic rotation curve. Note: it flattens out— evidence for dark matter. ROTATION SPEED (KM S") a m R A D 1 u s ( K P c ) m rm.” N m Wmmm Mum“ mt. Wm“ m mm mm. m. M W Wm M a.) w M. «u mewmma. AST 203 (Spring 2011) (Clemens 1985) Flat Rotation Curve What does it mean for the velocity curve to be flat? If we assume that the material is spherically distributed, then dM(T) d7“ 1; r F dM(r) _ U2 dr — E = p(r)47rr2 Now, we know that M(r) = and that v = const. so Equating these, we have The density drops off as 1/1”2 . AsT 203 (Spring 2011 :1 “Island Universes” or “Spiral Nebula”? AST 203 (Spring 2011) “lslad Univeres” o “iral Neua”? Dust and the NGC 7771 Group AST 203 (Spring 2011) Cred“ & Copyright Ken Cram“ (Ranmo Del Sol Observatory) http://antwrp.gsfc.nasa.gov/apod/ap100121.html The Great Debate (Bennett et al. Ch. 20, Carroll and Ostlie, Ch. 23) By 1920, a lot of spiral “nebula” identified (including Andromeda) Are these gas clouds in our galaxy or entire galaxies outside of our own? Great Debate between Shapley and Curtis: Shapley argued that these nebula were in the Milky Way lfAndromeda were a Galaxy, it would be very far away—this distance was larger than any known distances at the time Cited some (wrong!) data that the rotation of M101 could be directly observed Curtis said that they were separate galaxies Nova observed in spiral nebula must be far away to match brightness of Galactic novae. Observed Doppler shifts were much large than anything Galactic. AST 203 (Spring 2011) Normal Galaxies Hubble observed Cepheids in spiral “nebula” showed they are outside of our Galaxy. Hubble went on to classify galaxies based on their shape. Originally thought to be an evolutionary sequence. Spirals classified according to whether there is a bar AST 203 (Spring 2011) (\Mkipedia, author: \fille Koistinen) Ellipticals Within the elliptical classification, E0 are spherical shaped and E7 have large eccentricities. Dwarf galaxies are the most common type of ellipticals R ~ few kpc M ~ few x 106 M 0 Giant ellipticals are the largest R ~ 100 kpc M ~ 1012— 1013 M O AST 203 (Spring 2011) Giant Ellipticals MGIaAiElliplltaIGflawHessian?!” ‘ I NGC 4881 Coma Cluster HST - WFPC2 EFH PFflfirfl'l - ET 51:1 DFD - January 1555 -w, Baum (u WA), NASA 1127.95 zgl M87 (Canada-France-Hawaii Telescope, J.-C. Cuillandre (CFHT), Coelum) AST 203 (Spring 2011) Dwarf Ellipticals M32, a satellite of Andromeda (1.1 Meter Hall Telescope, Lowell Observatory, Bill Keel(U. Alabama» M110, a satellite of Andromeda (Johannes Schedler (Panther Observatory» Dwarf ellipticals look like smaller versions of the giant ellipticals. AST 203 (Spring 2011) Ellipticals Ellipticals have very little gas and dust Most of the gas is very hot and emits in X-rays ISM is < 1% of the mass of the stars we see Small amount of dust and gas —> ellipticals do not collapse into disks and become spirals (i.e. no evolutionary sequence). Spirals have much more dust and gas Stars are evolved—no O or B stars are present No active star formation Metalicities can be quite high though Rotating only very slowly—most of the motion is random Could collapse w/o forming a disk? AST 203 (Spring 2011) Ellipticals Observe an elliptical in 2—d sky. Define surface luminosity (luminosity/unit surface area) Ellipticals are described well by a power law behavior of the surface luminosity [(r) 1/4 l(0)e’WT0) l(0) doesn't vary much between ellipticals, but rodoes. 14 t NGC 3379 \ \ [6 18 24 26 28 30 32 ‘ 1 2 3 4 5 6 7 (Carroll and Osllie; from de Vaucouleurs and Capaccioli) AST 203 (Spring 2011 :i Spirals Spirals make up ~ 2/3 of the large galaxies in the Universe Spirals are classified according to how tightly wound the arms are and how prominent the bulge is. Sa spirals have large bulge and tightly wound arms Sc have the smallest bulge and loosely wound arms Some spirals have a central bar—classified SBa, SBb,... Grand design spirals have a very well defined spiral pattern Flocculent spirals do not. AST 203 (Spring 2011) Spirals ' - NGC 7217, an Sa spiral (Mischa Schinner . (ING) and Gilles Bergond (IAA, Granada» NGC 4622, an Sab spiral (NASA and The Hubble Heritage Team (STScI/AURA)) ' " ' ' ' NGC 1232, M31—the Andromeda galaxy, an an Sc Spiral Sb spiral (John Lanouelleipedia) (ESANLT) AST 203 (Spring 2011) Barred Spirals NGC 1530, an SBb spiral (Adam Block/NOAOIAURAINSF) NGC 1365, an SEC spiral (FORS Team, 8.2-melerVLT Anlu, ESO) As we mentioned last time, there is evidence that our galaxy has a bar at the center. AST 203 (Spring 2011) Grand Design Vs. Flocculent M81, a grand design Sb spiral (NASA/JPL-CallechlSST) NGC 6744 (Southern African Large Telescope (SALT)) AST 203 (Spring 2011) Spirals Sometimes we see spirals edge on, but we still know that they are spirals because of the dark dust lanes. NGC 4565, an Sb spiral M104, the Sombrro Galaxy, an Sab spiral (NASA and The Hubble Heritage Team (STScl/AURA)) 1;!“ use 4555 i"- , V Sub AST 203 (Spring 2011) Spirals The type of a spiral is not really correlated with the luminosity. A separate luminosity class is assigned, l = brightest, V = faintest Masses range from 107 to 1011 M O Spirals show strong dust features and have lots of gas Spirals bluer than ellipticals—young, massive stars are present. Star formation is taking place Spirals also follow a luminosity radius relation, L(r) : Loe’T/D Typical value of D is ~ 5 kpc AST 203 (Spring 2011) Colliding Galaxies Sometimes we see colliding galaxies NGC 4676A (right) / NGC 4676B (left) (NASA/ESA) The stars will not physically collide, but the gas will, and it will compress. Tidal features distort the shape of these galaxies. AST 203 (Spring 2011) Colliding Galaxies When the gas collides, star formation is triggered. interacting CAL-1w System NCC. 6745 Hubble l {aritage NASA andThe Hubble HeritageTefim [STSDHALIRAI Hubble szcoTBIeicopa WFPCZ - STSCI-PRCDD-Sfl AST 203 (Spring 2011) Colliding Galaxies These galaxies will merge and likely become an elliptical galaxy. The Antenna Galaxies (SDSS) AST 203 (Spring 2011) Tidal Forces Close encounters between galaxies eject stars/gas. Tidal interactions: nearby stars/gas experience a larger gravitational force than the further part. Large galaxies can continue to eat smaller ones—galactic cannibalism. Giant ellipticals may form this way (Stelios Kazantzidis) AST 203 (Spring 2011) Clusters Virgo cluster: Over 100 galaxies Spans > 5 degrees on the sky , _ . A '_ _ ' I MBJ‘ Our local group is moving n It ' _ - toward this cluster. . '- . r A. 4425 “11 - 4:36 MW A The Virgo Cluster (MauBenDaniei) 4 Close up of M86, M84, and NGCs 4387 and AST 203 (Spring 2011) 4388 (Jean-Charles Cuillandre (CFHT), Hawaiian Starlight, CFHT) Clusters About 80% of galaxies in clusters are ellipticals Outside of clusters, ~ 80% of galaxies are spirals Spirals sometimes form groups—loose collections (like our own local group) AST 203 (Spring 2011) Others... Irregular galaxies are small galaxies with no distinct shape—these account for a few percent of all galaxies. They appear more common the further we look back in time/distance. The Large Magellanic Cloud, a satellite to our own galaxy (Wei-Hao Wang (lfA, U. Hawaii» AST 203 (Spring 2011) Others... SO galaxies are in between spirals and ellipticals—the disk is about the same size as the bulge. NGC 5866, also called M102, an SO galaxy (NASA/STScI) AST 203 (Spring 2011) Others... Finally, some galaxies have some unusual structure—we call these peculiar galaxies. This can result from tidal interactions with neaby galaxies or recent bursts of star formation. M82 (HST/NASAIESA) AST 203 (Spring 2011) Star Formation in Galaxies (Kulner Ch. 17) Questions about star formation in spirals: What is the large-scale distribution of star-forming material? Is the ISM concentrated into the spiral arms? How do the sizes of molecular clouds compare to those in our galaxy? AST 203 (Spring 2011) Star Formation in Galaxies In the visible light, we see a reddish bulge and blue arms. The red clumps in the spiral arms are H II regions. There are also clearly visible dark dust lanes along the spiral arms. Optical (R. Gendler) (Adapted from Multiwavelength Astronomy/Cool Cosmos/NASA) AST 203 (Spl ing 2011) Star Formation in Galaxies Near IR: un-obscured light from cool stars. At longer wavelengths, we are seeing the dust— note that the spiral arms are clearly visible in IR. Campufilte 35-24 microns \ 3 5 microns Spiral Galaxy MB’I Spitzer Space Telescope ' MIPS ' IRAC inst ' visible ii h NDAD (Adapted from Mulliwavelenglh Astronomy/Cool Cosmo ‘ 9 “i i AST 203 (Spring 2011) NASA JFLCaltech K. Gordon [University of Arizona], 5. Willner [Hurvai‘dSmithsunian CFA] 55520037081 Star Formation in Galaxies 21 cm: tracing out neutral H Notice that neutral H is abundant in the full length of the spiral arms, but very little is found in the bulge. radio/21 cm line (VLA) (Adapted from Mulliwavelenglh Astronomy/Cool Cosmos/NASA) AST 203 (Spring 2011) Star Formation in Galaxies In the UV and X-ray we see hot gas. ‘ ' Spiral arms in UV are traced by hot stars. X-rays show that the galaxy core is the brightest. Other point sources are a background UV(ASTR01> object and a recent supernova (SN1993J). (Adapted from Mulliwavelenglh Astronomy/Cool Cosmos/NASA) AST 203 (Spring 2011) x_ray (ROSA-r) Star Formation in Galaxies We see the same behavior in other spirals. If we put this information together, we learn that molecular clouds are coincident with the inside of the spiral arms. H II regions trace out spiral arms Atomic gas is more prevalent in the outer regions of the disk. nr M1ryl.|rld.Hl m: mama/rm Rut; CFAl (Kulner) AST 203 (Spring 2011) Spiral Structure lf material were frozen into the spiral arms, then the arms would wind up. Period is shorter closer to the center of the galaxy Alternate explanation: spiral density waves move through the galaxy Regions of slightly higher than average density Material entering the wave is compressed—triggers star formation Standard analogy: think about traffic behind a slow moving car. Cars slow down as the approach. But they continuously pass by the slow car. Pattern moves at a different speed than individual cars. AST 203 (Spring 2011) Wind-up problem Initial rotation curve (v(R) vs. R) —> AST Spiral Structu re Eacharmisasail-sustainingpanim than average inside the density wave 9 is higher there The wave does not move matter (just like a water wave does not). Find and ynlimv law-ms; 512 V. Iongnr lives and populate tra Imagine "my survive in many a Dople mom mmn EflJchM,flMSlsl‘il\n as mm wwslay (Bennett el al.) AST 203 (Spring 2011) Spiral Structure Dar/v patches on mne/ Edge 0/ Splta/ arm s/mw Where gas C/Uudt an? par/1mg Inger/16: and compress/arr Ufthese Glands triggers slar furmalimz In my mm v 5/119 speaks in 9 young srars rhar Int-mud m Um 5mm! am: Her] hatches a! e ram/anal) nova/30 around the hattesr, young/1252 Sta/57 ' Flow of gas: and stars jhrpugh spiral Irm‘ Cow me 2003 Pearson Educauon me numsmng as Pearson Addisourwesley (Bennett el al.) AST 203 (Spring 2011) Spiral Structure Figure from Hohl, 1971 ' Pm. I.~U L ' ed I u'nn I fliei 'I.in.lly bahnmd uniSormly mtau‘ng disk of 100030 stalk AST 203 (Spring 2011) m “m bagging“, Vfim‘; mini”. 5;” by Toomm’s :riterian. Spiral Structure This explains the distribution _, —p of molecular clouds and star :5 formation in the spiral arms. '5 9 Prediction of spiral density ' J .. wave theory: molecular _pe,—y_p 032B clouds should only exist in mm: mm [litsimtiim spiral arms. _m (‘ln‘ud u'lth nr Wltllllul. H" Small Molecular R . _ Eglllnh Clouds Scenariu for molecular clouds tracing spiral arms. If the gas is circulating faster than the spiral pattern. as with the density wave picturetthe gas can overtake the spiral arms [ram behind. Before reaching the arms. the gas is in the form of low density HI cIu-ud. passiny containing some small molecular clouds.The entry Into the arm slows- the HI clouds down and :DrnprEsSés them. It may also gather tugether small molecular clouds. In any Event. giant molecular clouds form These clquds gm: birth m 0 and B stars {as well as to all the other types}.The radiatinn From the O and B stars disrupts the Clouds. _ (Kutner) AST 203 (Spi mg 2011) Dark Matter MW rotation curve flattens out at large distances from the center This is true for other galaxies too. This was first discovered by Vera Rubin. A number of different possibilities have been proposed to explain this dark matter, MACHOs, WIMPs, neutrino mass,... is) m co 0 o i f NGC 7541 Mac 1 UGC 2885 = ~ ~ “W 50 g 200 A / NGC 2998 > . E 100 .5 5 l | l r 50 100 150 zoo distance from center (thousands of lighlryears) Rotation curves for 4 galaxies showing the same characteristic flattening out (from Bennett etalt) AST 203 (Spring 2011) cupmi e mm a.” mum mm.“ 5- Wu mum Aside: Active Galactic Nuclei AST 203 (Spring 2011) Active Galactic Nuclei (Bennett el al. Ch. 21) Some galaxies show extreme activity in their nuclei thought to be a short lived phase—early in a galaxy's history driven by central supermassive black hole Quasar appear star-like: quasi-stellar radio source nucleus luminosity ~ 1012 Le center of very distant galaxy radiate from radio to gamma-rays Quasar 3C 273 Credit: NOAO/AURNNSF AST 203 (Spring 2011) Active Galactic Nuclei “This Hubble picture provides evidence for a merger between a quasar and a companion galaxy. The bright central object is the quasar itself, located several billion light-years away. The two wisps on the left of the central object are remnants of a bright galaxy that have been disrupted by the mutual gravitational attraction between the quasar and the companion galaxy." http:/Ihubblesile.orgln ewscenlerlamhive/releasesl1 995/04] AST 203 (Spring 2011) Quasar PKS 2349 HST - WFPC2 ST Sal 0P0 - January 1995 - J. Eahcali (Princeton), NASA Active Galactic Nuclei “Streaming out from the center of the galaxy M87 like a cosmic searchlight is one of nature's most amazing phenomena, a black-hole-powered jet of electrons and other sub-atomic particles traveling at nearly the speed of light. In this Hubble telescope image, the blue jet contrasts with the yellow glow from the combined light of billions of unseen stars and the yellow, point-like clusters of stars that make up this galaxy. Lying at the center of M87, the monstrous black hole has swallowed up matter equal to 2 billion times our Sun's mass. M87 is 50 million light-years from Earth. “ http:/Ihubblesile.org/newscenlerlarchivelreleaseleOOO/ZOI AST 203 (Spring 2011) Active Galactic Nuclei (Bennett el al. Ch. 21) Powered by massive black holes luminosity can double in hours—emitting region is small power source: accretion disk surrounding BH eventually run out of gas—activity ceases. AST 203 (Spring 2011) ...
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