gas cycles in characteristics of dwarf irregulars galaxies dirrs - … · 2007. 4. 19. · ngc 4449...
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Gas Gas Mixing Mixing + Gas + Gas CyclesCycles in in
DwarfDwarf IrregularsIrregulars GalaxiesGalaxies
Gerhard Hensler(University of Kiel)
Joachim Köppen, Jan Pflamm, Andreas Rieschick
Content:I. Characteristics of dIrrsII. Perturbed HI envelopesIII. Effect of Gas Infall on star formation?IV. OutflowsV. Gas mixing of outflow with the gaseous envelopeVI. Chemical preference for Gas Infall
� low masses� gas rich - HI disky
envelopes� low chemical abundances
Examples:
CharacteristicsCharacteristics of of dIrrsdIrrs
X-ray
HI: λ21cm
optical
LMCLMCLMC NGC 1569NGC 1569A
Prototypical Starburst
Dwarf Galaxy
Stil & Isreal (2002)
���� Hαααα���� X ���� HI
Martin et al. (2002))
HI ≈1.3•108 M�
Hα ����Yun et al. 1994
ChemChemicalical AbundanceAbundances:s:dIrrsdIrrs vs. vs. Cosmological objectsCosmological objects
N/O-O relation
-2,50
-2,00
-1,50
-1,00
-0,50
0,00
5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 10,0
12+lo g(O/H)
solarQuasarsQ0000-2619Q2348-147HS 1700+6416,z=1.15HS 1700+6416,z=0.86NGC 4449He 2-10NGC 1569UGC 4483I Zw 18Peg DIGNGC 5253NGC 4214SBS 0355-052II Zw 40VII Zw 403II Zw 70UGCA 292LG dIrrsLMCCNELGsGCsPettini et al.(02)
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Characteristics of dIrr Galaxies
Characteristics of Characteristics of dIrrdIrr GalaxiesGalaxies
� dIrrs are gas rich
� small masses: 107...1010 M�
� mostlylow star formation (10-3...10-1 M
�yr-1)
patchy star-formation distribution
various epochs of enhanced star-formation
� some with very bright, blue, compact SFcenters:
Starbursts?
� low chemical abundances (10-2...<1 Z�)
� but: alwaysat least oneold stellar populationexists, widely distributed: I(r) ~ exp{-r/r0)
} Are they young?
No!
Tosi 2002
I Zw 18 - a perturbed dIrr
with gas infall?
II ZwZw 1818 -- a a perturbed dIrrperturbed dIrr
withwith gas infall?gas infall?
(Östlin & Kunth 2000)
(van Zee et al. 1997)
Similarities Similarities to to local Dwarf Galaxieslocal Dwarf Galaxies??
Gas in dSph‘s:almost gas free or infall!
Carignan (1995)
HI gas outside Sculptor dSph? Welsh et al. (1998)
Gas infall in NGC 205 enhances SF
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with courtesy from Eva Grebel Fe/H has to increase in simple chem. evolution!
Characteristics of dIrr GalaxiesCharacteristics ofCharacteristics of dIrrdIrr GalaxiesGalaxies
� dIrrs are gas rich
� small masses: 107...1010 M�
� mostlylow star formation: (10-3...10-1 M
�yr-1)
patchy star-formation distributionvarious epochs of enhanced star-formation
� some with very bright, blue, compact SFcenters:
Starbursts?but: always old stellar populationexisting
widely distributed: I(r) ~ exp{-r/r0)
� low chemical abundances (10-2...<1 Z�)
but: no closed-box models fit, low eff. yield
abundance peculiarities
� gaseous envelopes: infall?
� low gravitation� SF self-regulation strongly
affected by energetic events(e.g.stellar energy release, external perturbations,etc.)
� trigger mechanism?� infall
� Are they young?No!No!
� outflows of metal-rich gas?
� infall of low-metallicity gas?
� gas-phase mixing
�� dIrrsdIrrs are ideal laboratories of astrophysical processesare ideal laboratories of astrophysical processes
TheThe rolerole of of hugehuge HHII gas gas reservoirs around dIrrsreservoirs around dIrrs? ?
--Gas infallGas infall from from
perturbedperturbed HHII envelopesenvelopes??
CasesCases of of peculiarpeculiar HHIIkinematicskinematics::
I Zw 18 - a perturbed dIrr
with gas infall?
II ZwZw 1818 -- a a perturbed dIrrperturbed dIrr
withwith gas infall?gas infall?
(Östlin & Kunth 2000)
(van Zee et al. 1997)
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NGC 4449a triggered starburst
NGC 4449a triggered starburst
(Hunter et al. 1995)
NGC 1569Gas Infall
confirmed!?
NGC 1569Gas InfallGas Infall
confirmedconfirmed!?!?
(Stil & Isreal, 2002)
Hαααα
HI
1.1. questionquestion::What triggers the high star-formation rates?Gas Infall?Gas Infall?
Consider the effects Consider the effects of of externalexternal gas infall!gas infall!
hot gas
clouds
stars
remnants
gas energy
cloud energy
Star-formation rate
Analytical InvestigationsAnalytical Investigations of Gas Infallof Gas Infall
}exp{),( KTcCTc cn
nc410
331) AA, (1998, G.H. Theis, Köppen,in astreatment
−=Ψ
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solar vicinity;
units in Myrs, M�, pc
Star-formation is inherently self-regulated
Köppen, Theis, G.H. 1995, AA, 296
Köppen, Theis, G.H. 1998, AA, 331
SelfSelf--regulated evolution regulated evolution without without gas infallgas infall
Infall of a Infall of a cloud with cloud with Jeans Jeans mass mass ofof
• 105 M�
(curves from left to right): 400, 100, 50,10, 1 km/s
• 104 M�
(curves from left to right): 100,10, 1 km/s
Starburst
Pflamm (2003) thesis
Pflamm, G.H. (2003) in prep.
• How many metals from SNeII are stored in the hot ISM?• How much metals can be lost from a galaxy by galactic winds?• How efficiently is hot halo gas removed by gas stripping?• Are outflows facilitated or hampered by cluster environments?
2. 2. questionquestion::What consequences What consequences of of high starhigh star--formation ratesformation rates??
SNeSNeIIII ⇒⇒⇒⇒⇒⇒⇒⇒ superbubbles superbubbles ⇒⇒⇒⇒⇒⇒⇒⇒ outflowsoutflows, , galactic windsgalactic winds!!!!
GalacticGalactic wind in M82wind in M82
Yun et al. (1994)
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Garnett (2002)
Effective yields of dIrrs smaller than solar!Outflow of SNII gas reduces O and yeff
MacLow & Ferrara (1999)Ferrara & Tolstoy (2000)
Galactic blowGalactic blow--away is almost away is almost impossible impossible !!
pressure of external gasand DM gravitational potentialmostly hamper galactic winds
Proofs:• many objects reveal
Hα loops and arcs:e.g. NGC 1705, I Zw 18
• Cluster DGs more evolved
NGC 1705
• Single SSCformed:
age ≈ 10 Myrs, Mvir ≈ 105 M�
• SSC embedded in HI disk: MHI ≈ 108 M�
• X-ray maxima surrounded byHα loops,representing tips of asuperbubble, expanding vertically to the HI disk, but confined
X-ray contours Hαoverlaid on HI
Hα(Hensler et al. 1998) 2 kpc
Meurer et al. (1998)
10 kpc
But: super star cluster is not formed in the center !!
3. 3. questionquestion::Can outflows explain abundance Can outflows explain abundance peculiaritiespeculiarities??
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N/O production: • O is produced in massive stars and
released by supernovae II (hot gas);• N is mainly produced in intermediate-
mass stars (warm gas);
• Massive stars live shorter than IMS;
• (N also produced and released by massive stars as primary and secondary element)
N/O signatures:• HII regions in gSs along second.-N
production track;• outer HII regions resemble dIrrs scatter;
• dIrrs show low N/O (~ -1.6) at low O!• radial abundance homogeneity in dIrrs ⇒
global homogenisation
Pagel, B.N.P. (1985) ESO Workshop“ ... C,N,O Elements”
Henry, R.B.C. & Worthey, G. (1999)
the N/O problemthe N/O problem
solutions:• dIrrs are very young like DLAs: no!• O loss by galactic winds: O/H-N/O�
• Starbursts produce fresh O: O/H-N/O �
• Infall of pristine gas: O/H-N/O �
N/O N/O evolution modelsevolution models
Garnett (1990)
Pilyugin(1992)
Henry, Edmunds, Köppen, (1999)
early evolution: track through DLA regime
at later epochs:models settle at secondary N-line,
But: no no returnreturn to to dIrr regimedIrr regime !!
Gas InfallGas Infall can explain can explain
the chemical evolution the chemical evolution ((rejuvenationrejuvenation) )
and and abundance peculiaritiesabundance peculiarities
Gas Infall and its Effect on AbundancesGas Infall and its Effect on Abundances
Model assumptions:� Yieldssame as in Henry,
Edmunds, Köppen (2000): van der Hoek & Groenewegen (1997), Maeder (1992)
� Galaxy models evolvefor 13 Gyrs with different yeff of 0.1 ... 1⇒ different locations in (N/O)-(O/H) diagram
� Infall of clouds with primordial abund. and masses of 106... 108 M
�
� Extension of tracks depends on yeff
� (N/O) scatter reproduc-ible by age differences of start models
Köppen, G.H. (2003) in prep.
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Main Main issuesissues::� Gas infall can explain the most significant
observational signatures of gaseous galaxies both 1. Modes of star formation 2. Chemical refreshment
� Gas infall is the main driver of star formation
Further comparisonsFurther comparisons4. 4. questionquestion::
On On what timescales are released what timescales are released metals incorporated into the metals incorporated into the cool cool ISM? ISM?
What can What can chemochemo--dynamical models dynamical models teach usteach us??
low-mass stars0.1-1 Mo
massive stars,10-100 Mo
star formation
remnants
dissipation
evaporationcondensation
SNeII
SNeIa
WNM, WIM M ≈≈≈≈ 105-107 Mo T ≈≈≈≈ 102 -104 K
ChemodynamicalChemodynamical TreatmentTreatmentCNM
M<104 MoT≤≤≤≤100 K
HIM T≥≥≥≥105 K
.M.E
Lyc, stellar winds
O,Si...Fe
Fe
C,N
WD NS BH
cooling
cooling
coolingGerhard Hensler, Univ. Kiel
Lyc
Clouds:formation
collisions
intermediate-mass stars 1-10 Mo
planetary
nebulae
all chemodynamical processes given bytheor. + empirical results from literaturefree parameters: initial cond., IMF
initial conditions:starting from the recombination timemass: Mg = 109 M� Ms=0DM: 1010 M� (Burkert 1995)
rini = 20 kpc
ρρρρ(r), L/M(r)
evolution:� collapse sets in due to dissip. + cooling
� ISM phases approach equlibrium
� different evolutionary phases
ChemoChemo--dynamicaldynamical dIrrdIrr ModelModel
2 kpc
Chemo-dynamical treatment:Theis, Burkert, G.H. (1992) AA, 265, 465Samland, G.H., Theis (1997) ApJ, 476,544
Rieschick, G.H. (2003) AA subm.
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Brightness of Stellar ComponentsBrightness of Stellar Componentsmassive stars
low-mass stars5. 5. questionquestion::
What isWhat is thethe effecteffect of of heatheatconductionconduction??
Evaporation vs. Evaporation vs. Condensation Condensation in in the the wind wind phase phase of of chemochemo--dynamical dynamical dir dir modelmodel
Local Gas Mixing vs. Local Gas Mixing vs. LargeLarge--scale Circulationscale Circulation
ρρρρcond - ρρρρevap (Hensler et al. , 1999, ASP Conf. Ser. 187)
parameter ββββ = ---------------ρρρρcond + ρρρρevap
collapse phase (left), wind phase (half left); wind phase:(for red β=1, blue β= -1.) CM (half rigth),OCM (right) distributions
problems:• Abundances determined from HII regions: Abundances of which component?• SNII explosions release metals to the hot ISM. • What is the mixing time to the cool ISM?• No DGs with pristine gas observed. Self-enriched or ICM polluted?
Gas mixing and cycles: metal self-enrichment
Gas mGas mixingixing and and cyclescycles: : metal metal selfself--enrichmentenrichment
� star formation and resulting SNII explosions: ⇒ evaporationof local CM, mass-loaded flows
� condensationand sweep up of local gas in superbubble shells: ⇒ local self-enrichmentof star-forming regions by 25%
� outflow of hot SN-enriched gas: ⇒ gradual mixing by condensationon slowly infalling(primordial) clouds (few km/s)
� enrichment timescales:
⇒ 2 mixing cycles:
•for instantaneous recycling (locally 25%) = few 10 Myrs;
•for fall back (from > 3 kpc) > 1 Gyr
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Chemodynamical Abundance Evolution Chemodynamical Abundance Evolution of a 10of a 1099 MM�������� dIrrsdIrrs
N/O-O relation
-2,50
-2,00
-1,50
-1,00
-0,50
0,00
5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 10,0
12+lo g(O/H)
solarQuasarsQ0000-2619Q2348-147HS 1700+6416,z=1.15HS 1700+6416,z=0.86NGC 4449He 2-10NGC 1569UGC 4483I Zw 18Peg DIGNGC 5253NGC 4214SBS 0355-052II Zw 40VII Zw 403II Zw 70UGCA 292LG dIrrsLMCCNELGsGCsPettini et al.(02)
Large-scale streaming and gas-phase mixingLargeLarge--scale streaming scale streaming and gasand gas--phase mixingphase mixing
Hot-gas outflow mixes with infalling HI� Cloud evaporation leads to mass-loaded flows
(with N) and outflow; � Condensation of expanding + cooling hot gas on
infalling clouds leads to cloud enrichment;� ISM is homogenized on scales up to 1 kpc
(NGC 1569: Kobulnicki & Skillman 97, I Zw 18: Izotov 99);
� Slow fall back of metal-enriched clouds;� Remaining part: blowout, blowaway, stripping:
What metal fraction goes to ICM?
Timescales of return� cooling of blow-out hot gas and fall back: ~ Gyrs (TT 1986)� turbulent mixing: ~ 20 Myrs (Recchi et al. 2001) [Poster 259]� cloud evap. enhances bubble cooling; HII gas studies: Recchi, G.H., et al. (in prep.)
Recchi et al., MN 322 (2001)
Moving Cloud Models Moving Cloud Models
Th=5.6 106K, nh=6.6 10-4 cm-3,vrel=0.3 Ma
Results
� heat conduction stabilizesclouds against KH instability
� mass accretion by condensation almost compensates mass loss
� accreted material (metals!) mixed by internal turbulence
without and with heat conduction
at 25, 50, 75 Myrs
Vieser & Hensler (2002a) AA subm.Conclusions for theConclusions for the dIrrdIrr evolutionevolution
Present ISM abundances not observable in HII regions
Galactic winds possible but HI envelopes/ICM pressure
Blown-up material can be stripped
gas-phase mixing due to evap./cond.+large-scale dynamics� metals are only partly expelled ⇒ chemical abundances change � gas cycles from instantaneous (10 Myrs) to .... several 100 Myrs� abundance homogenisation
gas infall triggers star formation and produces starbursts + chemical peculiarities� rejuvenation of BCDGs� environmental effects determine evolution of dIrrs
�Requirements for Observations:gas infall, Z of single stars and gaseous envelopes of dIrrs, IG clouds, metal content of hot gas, ...
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Problems in Understanding DG EvolutionProblems in Understanding DG Evolution
because of lower gravitation DG evolution is strongly affected by other forms of energetic events:
stellar energy, gas infall, tidal fields etc. lead to� large-scale streaming motions� long cooling timescales� gas-phase mixing processes� star-gas interactions� metals are lost ⇒ chemical abundances change
DGs are ideal laboratories of astrophysical processes
chemical, dynamical, energetical, materialistic processes are coupled + environmental effects
� chemo-dynamical treatment is required combining� Astrophysics (stellar evol., gravitation, yields, etc.)� Dynamics (2 gas phases, stars)� Plasmaphysics (cooling, heating, etc.)