22.05.2019 Satellite Galaxies SS2019 1 1. DGs around the Milky Way The Magellanic Clouds: LMC SS2019and SMC 2 1 22.05.2019 1.1. The Magellanic System On the southern sky 2 large diffuse and faint patches are optically visible: SS2019 3 The Magellanic Clouds Small Magellanic Cloud (SMC);SS2019 dIrr; dist.: ~ 58 kpc 4 2 22.05.2019 Large Magellanic Cloud (LMC), dIrr; dist.: ~ 58 kpc SS2019 5 optical : stars + lumin. gas 1.2. The many faces of the LMC Star-forming Regions: H SS2019 6 HI withl21cm 3 22.05.2019 (J. van Loon) SS2019 8 (J. van Loon) SS2019 9 4 22.05.2019 (J. van Loon) SS2019 10 1.3. The LMC, a gas-rich Dwarf Irregular Galaxy (dIrr) SS2019 11 5 22.05.2019 (J. van Loon) SS2019 12 Panchromatic picture (J. van Loon) SS2019 13 6 22.05.2019 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 SS2019 14 Hot Supernova Gas: X-ray (J. van Loon) SS2019 15 7 22.05.2019 SS2019 16 8.8. 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 SS2019 17 Chapt.)] 8 22.05.2019 SS2019 18 1.4. The Magellanic System SS2019 19 9 22.05.2019 Besla et al. (2016) ApJ, 825 SS2019 20 The Magellanic Stream SS2019 21 10 22.05.2019 1.5. Modeling the Magellanic System (2012) ApJ, 421 SS2019 23 Besla et al. (2012) ApJ, 421 SS2019 24 11 22.05.2019 Ram-pressure stripping by the ram-pressure stripping 2 motion through hot halo gas if Pram = IGM·v rel > P0(r) SS2019 25 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! SS2019 26 12 22.05.2019 1.6. Gas-free Dwarf Galaxies: dSphs Fornax dSph D= 138 kpc Mv = -13.5 SS2019 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 SS2019 28 13 22.05.2019 dE‘s in the vicinity of the Milky Way populate the low-mass end and are named Dwarf Spheroidals: Their surface brightness is only slightly larger than the background; almost no gas LeoI SS2019 29 Ursa Minor dSph SS2019 30 14 22.05.2019 Leo I: D = 250 kpc SS2019 32 1.7. Intrinsic properties of dSphs van den Bergh (2008) dSphs are less Mv = 16.2 – 14.26 log Rh concentrated and flatter than dSphs SS2019 33 15 22.05.2019 Correlations of different galaxy types Tolstoy et al. (2010) ARAA, 47 SS2019 34 SS2019 35 16 22.05.2019 SS2019 36 2. The MWG Satellites SS2019 37 17 22.05.2019 SS2019 38 Grebel, 1998 2.1. The 12 major MWG satellites SS2019 40 18 22.05.2019 2.2. Their Location Marla Geha SS2019 42 Spatial Distribution of MW satellites SS2019 43 19 22.05.2019 SS2019 44 Holtzman et al. (2006) ApJS, 166 SS2019 46 20 22.05.2019 2.3. The Population Box SS2019 47 with courtesy by SS2019 48 Eva Grebel SF continues also through the re-ion.epoch 21 22.05.2019 Grebel & Gallagher (2004) ApJ, 610 Most of the star formation in dSphs continued through the era of re- ionization: evidence for ionizationSS2019 inhomogeneity in the Universe!49 2.4. More distant satellites SS2019 50 22 22.05.2019 Gas-poor Dwarf Galaxies in the Local Group SS2019 Antlia51 DG 2.5. 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 SS2019 and dSphs(?). 52 23 22.05.2019 Carina II dIrr SS2019 53 SS2019 54 24 22.05.2019 IC 10, dIrr, Dist.: 1400 SS2019kpc, V = 10.3m 55 Leo A in the solar vicinity SS2019 56 25 22.05.2019 2.6. 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 SS2019 57 (see also Bouchard et al. 2003, 2006) Gas displacement by tidal and ram-pressure effects Carignan 1999 HI gas displaced of Phoenix Welsh et al. (1998) SSGas2019 infall in NGC 205 enhances58 SF 26 22.05.2019 HI Environment? Carignan et al. (1998) Bouchard et al. (2003) AJ, 126 Gas clouds around Sculptor dSphs from expulsion? SS2019 59 The Satellites’ gas content Grcevich & Putman, 09, ApJ, 696 SS2019 60 27 22.05.2019 dIrrs of the MW show stronger and more continuous star formation with an increase of Z. Phoenix is in a stage of morphological transition. SS2019 61 SS2019 62 28 22.05.2019 NGC 147 2MASS 3. 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 SS2019 64 29 22.05.2019 And VII And VI 4. Detection of the Sagittarius Satellite Galaxy If no bright star-forming regions exist, the stellar component of satellite The Sagittarius Dwarf Galaxy SS2019 galaxies is hardly detectible66 at D 24 kpc due to their low brightness. 30 22.05.2019 4.1. Southwards of the MWG center a sample of stars was detected at a distance of 24 kpc due to their collective kinematics: Sgr I Dwarf Galaxy SS2019 67 SS2019 68 31 22.05.2019 SS2019 69 4.2. Satellite Accretion SS2019 70 32 22.05.2019 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! SS2019 71 The tidal stream of Sgr I is detected from enhanced star density. SS2019 72 33 22.05.2019 The tidal stream of Sgr DG is detected from enhanced star density. SS2019 73 SS2019 75 34 22.05.2019 4.3. The Canis Major Satellite Galaxy Canis Major DG discovered recently: 17/11/03, close to the galactic plane at 7.5 kpc distance SS2019 76 The Canis Major tidal Stream SS2019 77 35 22.05.2019 4.4. 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. SS2019 78 Tidal streams around NGC 5907 SS2019 79 36 22.05.2019 4.5. Search for MW tidal streamers SS2019 80 Belokurov et al. (2007) ApJ, 658 SS2019 81 37 22.05.2019 Belokurov et al. (2007) ApJ, 658 SS2019 82 The Aquarius stellar stream SS2019 83 38 22.05.2019 SS2019 84 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 (:=SS 2019tidal radius) 85 that facilitates tidal stripping. 39 22.05.2019 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 approachsSS2019 the MW disk. 86 Metz et al. (2008) ApJ, 680 SS2019 89 40 22.05.2019 5.2. Cosmological implications Satellite galaxies move in the tidal field and the halo gas of mature galaxies. Cosmological models predict numerous satellite galaxies around Hubble types. SS2019 90 SS2019 91 41 22.05.2019 The evolution for 2 Gyrs SS2019 92 Petrov & Hensler (2011) in prep. Interactions of Sat.s important; e.g. Satellites merge; Gas is removed from the Satellites And contributes to the Galactic halo gas: Small subhalos survive, but without gas! Large Satellites are tidally stretched and partly disrupted dSphs merge: Mass spectrum?SS2019 93 42 22.05.2019 5.3. Gas stripping SS2019 95 43 22.05.2019 SS2019 96 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. SS2019 97 44 22.05.2019 4 major questions: 1. Is the Milky Way built-up of dSphs? 2. How did the dSphs evolve? 3. How did the dSphs gained their gas? 4. What does the dSphs distribution tell us? 98 6. Halo Stars by Satellite Accretion 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.