1. To τοπικό σύστημα γαλαξιών: oι νάνοι γαλαξίες – ο ρόλος τους στην διαμόρφωση και εξέλιξη των γαλαξιών

2. Topography ofthe Local Group of Galaxies Topography of the Local Group of Galaxies 35 galaxies Size 1.2 Mpc Grebel 1999

3. Sparke & Gallagher 2007

5. rhombs

7. Sparke & Gallagher 2007 The LG is a “typical” galactic environment: It is not very dense like Virgo, but it is dense enough to bind the galaxies together

8. Gallery of Local Group Galaxies: Spirals M33 M31 Milky Way Range of Masses: 10 Million to 1 trillion solar masses

9. U B24μ dust Ha HI CO Bulge 30-40% of L tot

10. The nucleus of M31 HST

11. Gallery of Local Group Galaxies: Irregulars LMC SMC NGC 6822 Most Irrs are gas rich Most show current star Most show current star formation at a significant level formation at a significant level Most dwarf Irrs are remote Most dwarf Irrs are remote objects objects IC 5152

12. Magellanic Clouds HI map

13. HI Ha optical Dust (24μ)

14. Gallery of Local Group Galaxies: Dwarf ellipticals and spheroidals Dwarf Spheroidal Leo I Dwarf Elliptical (nucleated) NGC 205 The least massive members of the LG (5 orders of magnitude less massive than the MW) The least massive members of the LG (5 orders of magnitude less massive than the MW) Most of the LG galaxies belong to this category. Most of the LG galaxies belong to this category. Most are close to the giant spirals Most are close to the giant spirals Most contain little or no gas Most contain little or no gas Evidence of dark matter halos (?) Evidence of dark matter halos (?) The least massive members of the LG (5 orders of magnitude less massive than the MW) The least massive members of the LG (5 orders of magnitude less massive than the MW) Most of the LG galaxies belong to this category. Most of the LG galaxies belong to this category. Most are close to the giant spirals Most are close to the giant spirals Most contain little or no gas Most contain little or no gas Evidence of dark matter halos (?) Evidence of dark matter halos (?)

15. Sagittarius Dwarf Galaxy

16. Sagittarius dwarf Irregular galaxy: an instance of galactic cannibalism The closest dwarf galaxy to the Milky Way (16 kpc) The closest dwarf galaxy to the Milky Way (16 kpc) Tidally distorted – merging into the MW Tidally distorted – merging into the MW Its survival up to now is consistent with a flat Its survival up to now is consistent with a flat rather than a centrally concentrated dark matter halo rather than a centrally concentrated dark matter halo The closest dwarf galaxy to the Milky Way (16 kpc) The closest dwarf galaxy to the Milky Way (16 kpc) Tidally distorted – merging into the MW Tidally distorted – merging into the MW Its survival up to now is consistent with a flat Its survival up to now is consistent with a flat rather than a centrally concentrated dark matter halo rather than a centrally concentrated dark matter halo

17. Comparison between DSph, GCs, nuclear cluster, ωCen Sparke & Gallagher 2007

18. Morphological segregation in Local Group Most dwarf spheroidals/ ellipticals are located close to giant spiral Gas-loss ?

19. Dwarf distance from primary versus HI mass

20. The luminosity function of the Local Group of Galaxies The Missing Dwarf Problem : too few by a factor of 10! (according to hierarchical CDM models) (according to hierarchical CDM models)

21. For each LG galaxy we want to derive a three dimensional picture showing the SFR and chemical enrichment as a function of time

22. Approximate age-indicators

23. The observed Hertzsprung-Russell Diagram of an old coeval stellar population Measure of stellar luminosity Measure of surface effective temperature MS turnoff AGE AGE Red Giant Branch Metallicity +age Metallicity +age RR-Lyrae variables Distance (+Z) Distance (+Z)

24. How the population synthesis modeling works Initial mass function Stellar evolution theory: isochrones Assumed SFR(t) (Assumed?) Chemical evolution Synthetic color- magnitude diagram +errors

25. How the population synthesis modeling works Models for different coeval populations populations Observed diagram: areas of number comparisons Final Adopted model

26. The effect of distance on the c-m diagram

27. The simpler systems: Star Formation History of dwarf spheroidal galaxy Leo I Adopted model color- magnitude diagram Observed Color magnitude diagram SFR(t)

28. Carina Dwarf Spheroidal What caused this uniquely (?) erratic star formation activity in Carina? What caused this uniquely (?) erratic star formation activity in Carina? 15 Burst strength Age (Gyr)

29. Star Formation History Boxes for 15 Local Group Dwarf Spheroidal Galaxies X-axis: t(Gyr) Y-Axis: SFR Z-Axis: [Fe/H]

30. Star Formation History Boxes for 15 Local Group Irregular Galaxies X-axis: t(Gyr) Y-Axis: SFR Z-Axis: [Fe/H] Distances from LG barycenter

34. Direct Evidence of Environmental Influence to Galactic Evolution in the Local Group Morphological type segregation Morphological type segregation Tidal tails and bridges found in Tidal tails and bridges found in - Magellanic System - Magellanic System - Saggitarius - Saggitarius - Carina dsph - Carina dsph Possible merger : Sagittarius Possible merger : Sagittarius Interactions – triggered Star Formation: Interactions – triggered Star Formation: - Magellanic Bridge - Magellanic Bridge - Burst of star cluster formation in LMC - Burst of star cluster formation in LMC 2-3 Gyr ago 2-3 Gyr ago Morphological type segregation Morphological type segregation Tidal tails and bridges found in Tidal tails and bridges found in - Magellanic System - Magellanic System - Saggitarius - Saggitarius - Carina dsph - Carina dsph Possible merger : Sagittarius Possible merger : Sagittarius Interactions – triggered Star Formation: Interactions – triggered Star Formation: - Magellanic Bridge - Magellanic Bridge - Burst of star cluster formation in LMC - Burst of star cluster formation in LMC 2-3 Gyr ago 2-3 Gyr ago

35. Dark Matter in Local Group Galaxies Galaxy Type DM M/L Type of evidence ( M o / L o ) ( M o / L o ) Spirals - disks yes 1-3 HI rotation curves Spirals - bulges yes 10-20 stellar kinematics Spirals – halos yes >20 stellar kinematics (microlensing) (microlensing) Dwarfs yes 1-80 (?) stellar kinemtics survival of Sgr survival of Sgr ?problem with tides ?problem with tides Compact HVC yes 10-50(?) HI rotation curves

36. STAR FORMATION HISTORIES OF LG DWARFS SHOW HUGE VARIETY Stochasticity of SF in low mass galaxies (no central control)Stochasticity of SF in low mass galaxies (no central control) highly variable SFR highly variable SFR changes in gas content which can result from:changes in gas content which can result from: mass (and metal) loss via galactic winds mass (and metal) loss via galactic winds gas accretion or gas loss via galactic interactions gas accretion or gas loss via galactic interactions gas infall from outer regions of galaxy gas infall from outer regions of galaxy changes in internal dynamics (due to interactions, Bar formation) - mergerschanges in internal dynamics (due to interactions, Bar formation) - mergers The problem of unknown orbits The problem of unknown orbits UV radiation from giant spiral can delay cooling and SF in close-by dwarfUV radiation from giant spiral can delay cooling and SF in close-by dwarf role of dark matter halos in modifying SF activity (helping retain escaping gas?)role of dark matter halos in modifying SF activity (helping retain escaping gas?) Possible factors

37. Galactic Chemical evolution: A function of galactic mass Total visible mass seems to be the decisive parameter that determines the overall chemical evolution of a galaxy

38. Epoch of highest Star Formation Rate: A function of galactic mass? Or of Environment? Total visible mass is an important parameter that determines the general characteristics of the Star Formation History of a galaxy!!

39. Closing remarks Common epoch of early SFCommon epoch of early SF No two LG galaxies have identicalSF historiesNo two LG galaxies have identical SF histories The smaller a galaxy the more intermittent its SF historyThe smaller a galaxy the more intermittent its SF history Gas poor, low mass, old galaxies mostly near giant spiralsGas poor, low mass, old galaxies mostly near giant spirals Gas rich star forming galaxies mostly isolatedGas rich star forming galaxies mostly isolated Minor mergers and tidal interactions currently happeningMinor mergers and tidal interactions currently happening Triggering of SF in tidal tails observedTriggering of SF in tidal tails observed total amount of current visible matter total amount of current visible matter seems to be an important parameter for seems to be an important parameter for the overall chemical evolution of a galaxy and the overall chemical evolution of a galaxy and the epoch when the SFR was highest in a particular galaxy the epoch when the SFR was highest in a particular galaxy BUT offset between dIrr and dSph. Were the latter much more massive once? BUT, offset true for ancient pops as well. Nature rather than nurture? Mass, interactions, dark matter content

40. Ασκήσεις Να λυθούν οι ακόλουθες ασκήσεις από το βιβλίο των Sparke & Gallagher 2.15,2.16,2.18,2.19,2.20,4.2,4.3,4.5 Να γίνει μελέτη/παρουσίαση του κεφαλαίου 4.1.4 των Sparke & Gallagher Παράδοση Παρασκευή 21/12 Την Τρίτη 18/12 θα γίνει η εργαστηριακή άσκηση