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7. Dwarf Galaxies

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7. Dwarf Galaxies 29.04.2018 I. Satellite Galaxies 1 1. DGs around the Milky Way The Magellanic Clouds: LMC and SMC 2 1 29.04.2018 1.1. The Magellanic System On the southern sky 2 large diffuse and faint patches are optically visible: 3 The Magellanic Clouds Small Magellanic Cloud (SMC); dIrr; dist.: ~ 58 kpc 4 2 29.04.2018 Large Magellanic Cloud (LMC), dIrr; dist.: ~ 58 kpc 5 optical : stars + lumin. gas 1.2. The many faces of the LMC Star-forming Regions: H 6 HI withl21cm 3 29.04.2018 (J. van Loon) 4/29/2018 Cosmic Matter Circuit 8 (J. van Loon) 4/29/2018 Cosmic Matter Circuit 9 4 29.04.2018 (J. van Loon) 4/29/2018 Cosmic Matter Circuit 10 1.3. The LMC, an gas-rich Dwarf Irregular Gakaxy (dIrr) 11 5 29.04.2018 (J. van Loon) 4/29/2018 Cosmic Matter Circuit 12 Panchromatic picture (J. van Loon) 4/29/2018 Cosmic Matter Circuit 13 6 29.04.2018 14 15 7 29.04.2018 The Magellanic Clouds Computer model of a small satellite galaxy orbiting a larger (edge-on) disk galaxy. As the satellite orbits, stars are stripped from the satellite and orbit in the halo of the larger galaxy. (Kathryn Johnston, Wesleyan): see the bending and tumbling of the satellite‘s figure axis! 17 8 29.04.2018 Further evidence for ram pressure: at its front-side LMC gas is compressed leading to molecular cloud formation triggered star formation Star-forming regions: H 18 Hot Supernova Gas: X-ray (J. van Loon) 4/29/2018 Cosmic Matter Circuit 19 9 29.04.2018 Small Magellanic Cloud (SMC); dIrr; dist.: ~ 58 kpc 20 1.4. More distant dIrrs 21 10 29.04.2018 Carina II dIrr 22 23 11 29.04.2018 IC 10, dIrr, Dist.: 4200 kly, Local Group Cloud 24 Leo A in the solar vicinity 26 12 29.04.2018 1.5. Gas-free Dwarf Galaxies: dSphs Fornax dSph D= 138 kpc Mv = -13.5 27 Faint dSphs pure stellar systems, no gas, metal-poor: Z< Z, faint end of dwarf Es, m extremely faint: Mv>-8 , very small: ~ few kpc, close to the MWG Leo I with Regulus = Leo 28 13 29.04.2018 Ursa Minor dSph Leo I: D = 250 kpc 32 14 29.04.2018 1.6. Intrinsic properties of dSphs van den Bergh (2008) dSphs are less Mv = 16.2 – 14.26 log Rh concentrated and flatter than dSphs 33 1.7. Spatial Distribution of MW satellites 34 15 29.04.2018 The MW Satellites 35 36 16 29.04.2018 Marla Geha 38 39 Grebel, 1998 17 29.04.2018 40 41 18 29.04.2018 NGC 147 2MASS 2. The M31 system NGC 205 NGC 185 BVR NGC 221 Star-formation regions in NGC 185 and NGC 205 of similar size as in dIrrs M32 NGC 205 43 19 29.04.2018 And VII And VI 3. Stellar populations 45 20 29.04.2018 46 49 21 29.04.2018 50 22 29.04.2018 23 29.04.2018 The chart above demonstrates the previous conclusions by showing the abundances of alpha elements in dSphs versus solar metallicity. The symbols are as follows: blue triangles, Carina blue triangles plus circles, Leo I red triangles, Sculptor red triangles plus circles, Fornax green triangles, Draco, Ursa Minor, and Sextans from SCS01 black crosses, Glactic disk stars open squares, halo data from McWilliam et al. 1995 light blue stars, UVES data from a study of LMC star clusters of different ages 60 light blue crosses, Galactic globular cluster measurements 24 29.04.2018 4.1. SF timescale from element Assumptions: abundances closed box, constant Yields yi O+Fe from SNeII of massive stars, Fe by SN Ia from WD-WD or WD-RG slow evolution fast gas consumption Effects: The ratio of element abundances from particular precursor stars allow the age dating of their lifetimes and the derivation of the gas consumption. 63 SNeII of massive stars produce a constant ratio [O/Fe]0.5, while Fe increases continuously. After the typical formation timescale of SN Ia Fe is further enhanced independently of the O enrichment. Thus, O/Fe decreases. From the age of the disk, the SN Ia timescale must be of the same order. Tolstoy & Venn, 2003 65 25 29.04.2018 4.2. Radial gradients in [Fe/H] EK et al., ApJ, submitted 67/42 Walker et al. 26 29.04.2018 69 , 2004 70 27 29.04.2018 The metallicity distributions of dwarf galaxies evolve with luminosity. EK et al., ApJ Kirby et al. 2008, ApJ,685 28 29.04.2018 Kirby et al. 2008, ApJ,685 4.3. The Population Box 74 29 29.04.2018 with courtesy by Eva Grebel SF continues also through the re-ion.epoch dIrrs of the MW show stronger and more continuous star formation with an increase of Z. Phoenix is in a stage of morphological transition. 76 30 29.04.2018 77 (2009) A&A 500 31 29.04.2018 4.4. Gas in dSph‘s: almost gas free, but gas infall! Carignan et al. (1988) HI gas outside Sculptor dSph, Welsh et al. (1998) flocculent HVCs gas infall in NGC 205 enhances SF (see also Bouchard et al. 2003, 2006) Satellites with gas Sculptur (Carignan 1996) Leo A Dwarf Galaxies (low masses) can easily expel all(?) their gas into their intergalactic environment. Gas is stripped off by tidal and dynamical drag, by this, transforming dIrrs into dEs and dSphs(?). 80 32 29.04.2018 HI Environment? Carignan et al. (1998) Bouchard et al. (2003) AJ, 126 Gas clouds around Sculptor dSphs from expulsion? Grcevich & Putman, 09, ApJ, 696 82 33 29.04.2018 Gas-poor Dwarf Galaxies in the Local Group Antlia83 DG 5. Detection of the Sagittarius Satellite Galaxy If no bright star-forming regions exist, the stellar component of satellite The Sagittarius Dwarf Galaxy galaxies is hardly detectible84 at D 24 kpc due to their low brightness. 34 29.04.2018 Southwards of the MWG center a sample of stars was detected at a dist. of 24 kpc due to their collective kinematics: SagDIG Dwarf Galaxy 85 86 35 29.04.2018 87 88 36 29.04.2018 Belokurov et al. (2007) ApJ, 658 89 Belokurov et al. (2007) ApJ, 658 90 37 29.04.2018 91 Search for tidal streamers. 92 38 29.04.2018 6. Satellite Accretion 93 Computer model of a small satellite galaxy orbiting a larger (edge-on) disk galaxy. As the satellite orbits, stars are stripped from the satellite and orbit in the halo of the larger galaxy. (Kathryn Johnston): see the bending and tumbling of the satellite‘s figure axis! 94 39 29.04.2018 Satellites on elliptical orbits experience 1) stretching along the trajectory on their approach to perigalacticum and crushing along the orbit towards apogalacticum because of velocity differences between leading anf trailing part, 2) radial stretching due to the tidal force of the mature galaxy, 3) by this a revolving gravitational potential along the orbit (due to tidal torque), 4) an oscillating equipotential (:= tidal radius) 95 that facilitates tidal stripping. 6.1. Tidal Force Bodies that are extended over d and located at distance D in the central gravitational field of any mass M experience a Tidal Force d Ftide GM 3 D This results in a mode-2 deformation in radial direction towards and away from the center of mass. The detection of the leading arm confirms the tidal stripping effect. The stripped gas approachs the MW disk. 96 40 29.04.2018 7. The Magellanic Stream Gas bridges between the Magellanic Clouds are formed (Magellanic Stream), showing that this complex is tidally disrupted by the Milky Way. Stripped-off gas drops down to the Galactic disk and feeds the MWG. [Dwarf satellite galaxies are swallowed by larger parent galaxies (see next 97 Chapt.)] 98 41 29.04.2018 The tidal stream of Sgr I is detected from enhanced star density. 99 101 42 29.04.2018 The tidal stream of Sgr DG is detected from enhanced star density. 102 8. The Canis Major Satellite Galaxy Canis Major DG discovered recently: 17/11/03, close to the galactic plane at 7.5 kpc distance 103 43 29.04.2018 The Canis Major tidal Stream 104 8.2. Tidal Streams Recent sensitive observations of galaxy halos have revealed tidal streamers of satellite galaxies under disruption in a few of them. In M31 HVCs accumulate along the tidal path. 105 44 29.04.2018 Tidal streams around NGC 5907 106 Search for tidal streamers. 107 45 29.04.2018 The Aquarius stellar stream CDM models of Galaxy Stellar Halos Cosmological models based on CDM predict many accretion events through lifetime of a big galaxy. Infalling satellites are torn apart by tidal forces. 109 46 29.04.2018 8.3. Are halo stars witnesses of accretion? The accretion of satellite galaxies by host galaxies like the Milky Way are observed by 1. Satellite infall 2. Tidally disrupted stellar streams Most halo stars do not agree with Z of the present-day dSphs, but some could be the remnants of accretion. 110 Tolstoy & Venn, 2004 Koch (2009) Rev. Mod. Astron. Conclusion: dSph stars do not match the MW halo stars!! 47 29.04.2018 Tolstoy et al. (2009) ARAA At low Z dSphs coincide with halo star abundance ratios Tolstoy & Venn, 2004 114 48 29.04.2018 8.4. Gas stripping Ram-pressure stripping by the ram-pressure stripping 2 motion through hot halo gas if Pram = IGM·v rel > P0(r) 116 49 29.04.2018 Gas displacement by tidal and ram-pressure effects Carignan 1999 HI gas displaced of Phoenix Welsh et al.
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