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

και εξέλιξη των γαλαξιών

Topography ofTopography of the the Local Group of GalaxiesLocal Group of Galaxies

35 galaxies35 galaxies Size 1.2 MpcSize 1.2 Mpc

Grebel 1999

Sparke & Gallagher 2007

Sparke & Gallagher 2007

Sparke & Gallagher 2007

rhombs

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

Gallery of Local Group Galaxies: SpiralsGallery of Local Group Galaxies: Spirals

M33M33 M31M31

Milky WayMilky Way

Range of Masses: 10 Million to 1 trillion solar massesRange of Masses: 10 Million to 1 trillion solar masses

U B 24μdust

HaHI

CO

Bulge 30-40% of Ltot

The nucleus of M31 HST

Gallery of Local Group Galaxies: IrregularsGallery of Local Group Galaxies: Irregulars

LMCLMC SMCSMC

NGC 6822NGC 6822 Most Irrs are Most Irrs are gas richgas rich Most show Most show currentcurrent star star

formation at a significant levelformation at a significant level Most Most dwarfdwarf Irrs are Irrs are remoteremote

objectsobjects

IC 5152IC 5152

Magellanic Clouds

HI map

HI

Ha

optical

Dust (24μ)

Gallery of Local Group Galaxies: Gallery of Local Group Galaxies: Dwarf ellipticals and spheroidalsDwarf ellipticals and spheroidals

Dwarf Spheroidal Leo IDwarf Spheroidal Leo IDwarf Elliptical Dwarf Elliptical

(nucleated) NGC 205(nucleated) NGC 205

The least massive members of the LG (5 orders of The least massive members of the LG (5 orders of magnitude less massive than the MW)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 spiralsMost 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 The least massive members of the LG (5 orders of magnitude less massive than the MW)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 spiralsMost 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 (?)

Sagittarius Dwarf GalaxySagittarius Dwarf Galaxy

Comparison between DSph, GCs, nuclear cluster, ωCen

Sparke & Gallagher 2007

Dwarf distance from primary versus HI mass

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

Approximate age-indicatorsApproximate age-indicators

The observed Hertzsprung-Russell Diagram of an old The observed Hertzsprung-Russell Diagram of an old coeval stellar populationcoeval stellar population

Measu

re o

f M

easu

re o

f ste

llar

lum

inosit

yste

llar

lum

inosit

y

Measure of surface effective Measure of surface effective temperaturetemperature

MS turnoffMS turnoff AGEAGE

Red Giant Branch Red Giant Branch Metallicity +ageMetallicity +age

RR-Lyrae variablesRR-Lyrae variables Distance (+Z)Distance (+Z)

How the population synthesis modeling worksHow the population synthesis modeling works

Initial mass Initial mass functionfunction

Stellar evolution Stellar evolution theory: isochronestheory: isochrones Assumed SFR(t)Assumed SFR(t)

(Assumed?) Chemical (Assumed?) Chemical evolutionevolution

Synthetic color-Synthetic color-magnitude diagrammagnitude diagram

+errors+errors

How the population synthesis How the population synthesis modeling worksmodeling works

Models for Models for different coeval different coeval

populationspopulations

Observed diagram: Observed diagram: areas of number areas of number comparisonscomparisons

Final Adopted Final Adopted modelmodel

The effect of distance on the c-m diagramThe effect of distance on the c-m diagram

The simpler systems:The simpler systems:Star Formation History of Star Formation History of dwarf spheroidaldwarf spheroidal galaxy Leo galaxy Leo

II

Adopted model color-Adopted model color-magnitude diagrammagnitude diagram

Observed Color magnitude diagramObserved Color magnitude diagram

SFR(t)SFR(t)

Carina Dwarf SpheroidalCarina Dwarf Spheroidal

What caused this uniquely (?) What caused this uniquely (?) erratic star formation activity erratic star formation activity in Carina?in Carina?

1515

Bu

rst

str

en

gth

Bu

rst

str

en

gth

Age (Gyr)Age (Gyr)

Star Formation History Boxes for 15 Local Group Star Formation History Boxes for 15 Local Group Dwarf Spheroidal GalaxiesDwarf Spheroidal Galaxies

X-axis: t(Gyr)Y-Axis: SFRZ-Axis: [Fe/H]

X-axis: t(Gyr)Y-Axis: SFRZ-Axis: [Fe/H]

Star Formation History Boxes for 15 Local Group Star Formation History Boxes for 15 Local Group Irregular GalaxiesIrregular Galaxies X-axis: t(Gyr)

Y-Axis: SFRZ-Axis: [Fe/H]Distances from LG barycenter

X-axis: t(Gyr)Y-Axis: SFRZ-Axis: [Fe/H]Distances from LG barycenter

Direct Evidence of Environmental Influence to Galactic Direct Evidence of Environmental Influence to Galactic Evolution in the Local GroupEvolution in the Local Group

• Morphological type segregationMorphological 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 : SagittariusPossible 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 ago2-3 Gyr ago

• Morphological type segregationMorphological 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 : SagittariusPossible 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 ago2-3 Gyr ago

Dark Matter in Local Group GalaxiesDark Matter in Local Group Galaxies

Galaxy Type DM M/LGalaxy Type DM M/L Type of evidenceType of evidence ((MMoo//LLoo))

Spirals - disks yes 1-3 HI rotation curvesSpirals - disks yes 1-3 HI rotation curves

Spirals - bulges yes 10-20 stellar kinematicsSpirals - bulges yes 10-20 stellar kinematics

Spirals – halos yes >20 stellar kinematics Spirals – halos yes >20 stellar kinematics (microlensing)(microlensing)

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

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

STAR FORMATION HISTORIES OF LG DWARFS SHOW HUGE STAR FORMATION HISTORIES OF LG DWARFS SHOW HUGE VARIETYVARIETY

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

mergersmergers The problem of unknown orbitsThe problem of unknown orbits

• UV radiation from giant spiral can delay cooling and SF in close-by UV radiation from giant spiral can delay cooling and SF in close-by dwarfdwarf

• role of dark matter halos in modifying SF activity (helping retain role of dark matter halos in modifying SF activity (helping retain escaping gas?)escaping gas?)

Possib

le f

acto

rsP

ossib

le f

acto

rs

Galactic Chemical evolution:Galactic Chemical evolution:A function of galactic massA function of galactic mass

Total visible mass seems to be the decisive parameter that determines the Total visible mass seems to be the decisive parameter that determines the overall chemical evolution of a galaxyoverall chemical evolution of a galaxy

Epoch of highest Star Formation Rate: Epoch of highest Star Formation Rate: A function of galactic mass?A function of galactic mass?

Or ofOr of Environment?Environment?

Total visible mass is an important parameter that determines the general Total visible mass is an important parameter that determines the general characteristics of the Star Formation History of a galaxy!!characteristics of the Star Formation History of a galaxy!!

Closing remarksClosing remarks

• Common epoch of early SFCommon epoch of early SF

• No two LG galaxies have identicalNo two LG galaxies have identical SF historiesSF 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 mattertotal 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 galaxythe 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 contentMass, interactions, dark matter content

ΑσκήσειςΑσκήσεις

• 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