To τοπικό σύστημα γαλαξιών: oι νάνοι γαλαξίες – ο ρόλος...

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

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  • Topography of the Local Group of Galaxies35 galaxiesSize 1.2 MpcGrebel 1999

  • Sparke & Gallagher 2007

  • Sparke & Gallagher 2007

  • Sparke & Gallagher 2007rhombs

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

  • Gallery of Local Group Galaxies: Spirals M33

    M31

    Milky WayRange of Masses: 10 Million to 1 trillion solar masses

  • UB24dustHaHICOBulge 30-40% of Ltot

  • The nucleus of M31 HST

  • Gallery of Local Group Galaxies: Irregulars LMC

    SMC NGC 6822

    Most Irrs are gas rich Most show current star formation at a significant level Most dwarf Irrs are remote objects

    IC 5152

  • Magellanic CloudsHI map

  • HIHaopticalDust (24)

  • 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)Most of the LG galaxies belong to this category. Most are close to the giant spiralsMost contain little or no gas Evidence of dark matter halos (?)

  • Sagittarius Dwarf Galaxy

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

  • Comparison between DSph, GCs, nuclear cluster, CenSparke & Gallagher 2007

  • Morphological segregation in Local GroupMost dwarf spheroidals/ellipticals are located close to giant spiral

    Gas-loss ?

  • Dwarf distance from primary versus HI mass

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

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

  • Approximate age-indicators

  • The observed Hertzsprung-Russell Diagram of an old coeval stellar populationMeasure of stellar luminosityMeasure of surface effective temperatureMS turnoff AGERed Giant Branch Metallicity +ageRR-Lyrae variables Distance (+Z)

  • How the population synthesis modeling worksInitial mass functionStellar evolution theory: isochronesAssumed SFR(t)(Assumed?) Chemical evolutionSynthetic color-magnitude diagram+errors

  • How the population synthesis modeling works Models for different coeval populations Observed diagram: areas of number comparisons

    Final Adopted model

  • The effect of distance on the c-m diagram

  • The simpler systems:Star Formation History of dwarf spheroidal galaxy Leo IAdopted model color-magnitude diagramObserved Color magnitude diagramSFR(t)

  • Carina Dwarf Spheroidal What caused this uniquely (?) erratic star formation activity in Carina?15Burst strengthAge (Gyr)

  • Star Formation History Boxes for 15 Local Group Dwarf Spheroidal GalaxiesX-axis: t(Gyr)Y-Axis: SFRZ-Axis: [Fe/H]

  • Star Formation History Boxes for 15 Local Group Irregular GalaxiesX-axis: t(Gyr)Y-Axis: SFRZ-Axis: [Fe/H]Distances from LG barycenter

  • Direct Evidence of Environmental Influence to Galactic Evolution in the Local Group Morphological type segregation

    Tidal tails and bridges found in - Magellanic System - Saggitarius - Carina dsph

    Possible merger : Sagittarius

    Interactions triggered Star Formation: - Magellanic Bridge - Burst of star cluster formation in LMC 2-3 Gyr ago

  • Dark Matter in Local Group GalaxiesGalaxy Type DM M/L Type of evidence (Mo/Lo)

    Spirals - disks yes 1-3 HI rotation curves

    Spirals - bulges yes 10-20 stellar kinematics

    Spirals halos yes >20 stellar kinematics (microlensing)

    Dwarfs yes 1-80 (?) stellar kinemtics survival of Sgr ?problem with tides

    Compact HVC yes 10-50(?) HI rotation curves

  • STAR FORMATION HISTORIES OF LG DWARFS SHOW HUGE VARIETY

    Stochasticity of SF in low mass galaxies (no central control) highly variable SFR changes in gas content which can result from: mass (and metal) loss via galactic winds gas accretion or gas loss via galactic interactions gas infall from outer regions of galaxy changes in internal dynamics (due to interactions, Bar formation) - mergers The problem of unknown orbits

    UV 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?)

    Possible factors

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

  • 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!!

  • Closing remarksCommon epoch of early SFNo two LG galaxies have identical SF historiesThe smaller a galaxy the more intermittent its SF historyGas poor, low mass, old galaxies mostly near giant spiralsGas rich star forming galaxies mostly isolatedMinor mergers and tidal interactions currently happeningTriggering of SF in tidal tails observed total amount of current visible matter seems to be an important parameter for the overall chemical evolution of a galaxy and 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

  • Sparke & Gallagher 2.15,2.16,2.18,2.19,2.20,4.2,4.3,4.5

    / 4.1.4 Sparke & Gallagher

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    The LG is a small group of galaxies around the MW and M31.For a spherical potential the zero-velocity surface of the LG is at 1.2Mpc.35 galaxies have been found within this radius. It is not clear if the most remote of those are actually bound to the LG

    The LG comprises galaxies with a variety of different morphological types, a range of masses (about 5 decades, from 10^7 to few 10^12 Mo), (mean) ages and metallicities (from 2.2 to +0.5, about 2.5 orders of magnitude) and different degrees of isolation. Their proximity makes them ideal targets for studying their detailed SF history and galactic evolution in general, from their resolved populationsThe MW and M31 are giant spirals with masses of the order of 10^12 Mo.They have the most complex SF histories.Different subpopulations can be distinguished by their ages, metallicities and kinematics.At least the MW and M31 appear to have a supermassive black hole (of a few 10^6Mo) in their center.M(HI) of the order of 10^9 MoMtot of the order of 10^9-10^10Mo

    Dwarf ellipticals have masses of the order of 10^9Mo or less and contain some HI (less than 10^8Mo). 2 (NGC205, M32) of the 4 dEs they are all companions to M31) are nucleated. M32 is known to have a central black hole and follows the scaling laws of giant ellipticals.Dwarf spheroidals are the least massive (about 10^7Mo) and have very little or no gas detected (less than 10^5Mo)Detailed kinematical studies yield information on DM content and its distribution. Ideal sites!However tidal effects also seem to play an important role in shaping these galaxies, and one has to take themProperly into accountNote also the existence of compact HVC (with large HI masses, infall to LG barycenter) masses about 10^7Mo,No stars (?) Large M/L. Failed galaxies?Hierarchical CDM models predict 10 times more dark matter halos than the number of known LG satellites.But note that a lot of the low surface brightness galaxies in the LG were found only recently. There may well be more lingering around. Compact high velocity clouds seem to be DM dominated and with total masses of a few 10^8 Mo may well be the missing halosThis is a powerful method but it has shortcomings. It depends on the IMF and on stellar evolution modelsVery strongly as well as on the assumed age-metallicity relation, which is unknown for most LG galaxies.And this is very impoartant as for relatively old populations age and metallicity are pretty much degenerate.When predicting a certain SF history you should also be able to properly predict the age-metallicity relationAnd the elemental ratios that are connected to SN explosions (and are related to the type of SF you have and henceThe IMF )

    One of the few examples of late formation of the bulk of the stellar populationCarina experienced three significant episodes of star formationat 15, 7, and 3 Gyr. Contrary to the generic picture of galaxy evolution, however, the bulk of star formation, at least50%, occurred during the episode 7 Gyr ago, which may have lasted as long as 2 Gyr. For unknown reasons, Carinaformed only 10%20% of its stars at an ancient epoch and then remained quiescent for more than 4 Gyr. The remainder ( 30%) formed relatively recently , only 3 Gyr ago

    Did it loose all its gas? But then how did the last formation episode occur? Maybe DM halo plays an important role?Also very little enrichment. This is consistent with having lost hot gas due to burst of SF, thus stopping further SF.Where did it get unenriched gas for the next episodes?Most show declining SF rate(especially the smaller ones) and differing enrichment histories.There are three cases of late formers Fornax and the Leos, and one case of a completely bursty SF history(Carina). The first type are mostly close to the MW. But Tucana is very similar and is pretty much isolated!!So environment isnt the only cause!!!!! Other problem: we do not know the orbits but only the current positions and radial velocities (proper motions are still very poorly known even for the nearest systems)

    Generally more continuous than in dwarf spheroidalsThere are some cases of pretty young galaxies.First era of astration: Oldest first populations: Oldest MW,M31, M32, LMC, Fornax, Draco, UM,Carina and LeoII, Tucana Younger by a few Gyr: SMC, WLM, LeoA, DDO210 IC10? IC5152? CHVC?Rotation curves flat 2-3 times beyond the optical extent of the galaxySome dwarfs may have formed in remnant DM halos, so will contain DMOther dwarfs may have formed in tidal tails (e.g. Antenae-type interactions, as seen in this system and in numerical simulations). These should not have DM. So we may have two types of dwarfs.All dsphs with DM seem to have DM halos of the order of 2x10^7MoStudy of Sgr shows DM halo that is not centrally concentrated!! Despite the fact that the parameters affecting the history of evolution of any one galaxy are too many and in many cases ill-defined there are some underlying general trends that are revealed by the data. Scatter is expectedly very large as other parameters become important, e.g. proximity to a giant galaxy.However there is a remarkable trend that shows that the lowest mass galaxies at least in the LG made most of theirStars in old times. This is probably only due to a selection effect in a way, as the lowest mass objects are closeTo giant spirals and probably they were not left to make any stars after the first generation due to the effectOf the giant (UV, gas loss?)