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Starburst Dwarf Galaxies

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2

The star-formation

history does in

general not show a

continuous evolution

but preferably an

episoidal behaviour.

Starburst Dwarf Galaxies

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Definition: Starburst

from stellar population synthesis

HI mass

Examples:

at former times: Globular Clusters

Dwarf Ellipticals

giant Ellipticals

at present: giant HII regions > 30 Dor

SBDGs NGC 1569, NGC 4449, NGC 5253

He 2-10, NGC 1705, III Zw 102

M82, NGC 253

nuclear SBs NGC 1808, NGC 2903, Mkr 297

ULIRGs Merger

HubbleGHI

SFR

G

t

M

t

)(

100.....10)(

)(

0

0

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In NGC 1569

2 Super Star Clusters

at the base of the gas

stream are the engines

of the galactic wind due

to their cumulative

supernova II explosions.

Dwarf Galaxies and Galactic Winds

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Model:

• bipolar outflow;

• the S part towards

observer is unobscured;

• disk inclination

known.

X-ray in colors according to hardness

(blue: hard, red: soft)

overlaid with HI contours (white) Martin et al. (2002)

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7 Martin et al. (2002) ApJ 574

Abundances in the galactic wind from

X-ray spectra

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8 Martin et al. (2002) ApJ 574

The mass loss can be determined

from the effective yield yeff of the

HI ISM.

The loss of metals should be

visible in the hot gas outflow.

SS 2017

Galactic winds

MacLow & Ferrara (1999)

• Effective yields of dIrrs < solar!

• Outflow of SNII gas reduces e.g. O, yeff

• but: simple outflow models cannot account for gas mixing + turb. heating

courtesy Simone Recchi

9 SS 2017

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MacLow & Ferrara (1999)

Galactic winds in Dwarf Galaxies?

Continuous

mechanical L

over 50 Myrs

for various

galaxy masses

Mg and gas

densities n:

at t=50 Myrs

No consistent

star formation!

11 SS 2017

t=100 Myrs

MacLow &

Ferrara (1999)

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0,1 1 10

106

0,18 1 1

1 0,99 1

107

3.5e-3 8.4e-3 4.8e-2

1 1 1

108

1.1e-4 3.4e-4 1.3e-3

0,8 1 1

Mass ejection efficiencies

Metal ejection efficiencies

Luminosity (1038 erg s-1)‏

Ma

ss (

M

‏(

Galactic winds in DGs and the fate of metals

MacLow & Ferrara (1999) 14 SS 2017

Testing galactic winds in different gas disks

Recchi & Hensler (2013) A&A, 551

Initial conditions:

• Baryonic mass: Mb = 107 , 108 , 109 M

• Stellar disk by Myamoto-Nagai

potential

• Isothermal gas disk with flattening

b/a = 0.2, 1.0, 5.0

• Gas fraction: 60% (L), 90% (H)

• Spherical DM halo with MDM = 10 Mb

• SFR~2

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Testing galactic winds in different gas disks

(2013) A&A, 551

SN ~ 5%

Blow-away of total gas almost impossible:

Only in lowest-mass DGs and flat, light gas

disks, but then all metals are lost.

Gas disk, mixing, turbulence, external halo

gas, and embedded clouds hamper outflow. 16 SS 2017

Oxygen ejection:

Only lowest-mass DGs with lower

gas fraction lose large O fractions.

Thick gas disk and massive DGs

retain their supernova elements.

Testing galactic winds in different gas disks

Recchi & Hensler (2013) A&A, 551

17 SS 2017

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Testing galactic winds in different gas disks

ISM abundances:

• The thicker the gas disk, the higher the metal enrichment.

• The larger the mass, the larger the metallicity.

• The larger the gas content, the greater the metal enrichment.

Blow-away of total gas almost impossible:

• Only in lowest-mass DGs + flat, light gas disks, lose all metals.

• Gas disk, mixing, turbulence, external halo gas, and embedded

clouds hamper outflow.

‘H’ models

18 SS 2017

(2010) Nature, 463 (2012) MNRAS, 422

Can strong Galactic Winds solve the CDM cusp/core problem? Loss of low-ang.mom. gas!

NO solution when metal. mismatch! 20 SS 2017

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(2006) A&A, 445

In reality:

blowaway almost impossible:

gas halo,

infalling clouds,

turbulence

metals retained

Large-scale outflows + gas-phase mixing

Timescales of gas return cooling of blow-out hot gas and fall back: ~ Gyrs turbulent mixing: ~ 20 Myrs evaporative mixing: 10 … 100 Myrs (Rieschick &

G.H. 2002)

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Refill of Superbubbles

Recchi et al. (2006) A&A, 445

Due to cooling

and buoyancy the

surrounding gas

pressure refills

the superbubble

cave after a few

100 Myrs

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What triggers the high star-formation rates?

Gas Infall?

Consider the effects of external gas infall!

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What triggers the

high star-formation rates?

Consider the effects of

external gas infall!

Gas Infall to DGs

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Gas infall triggers Starburst

The case od NGC 1569:

• HI clouds (each ~106 M

)

fall towards in from a disk

• 2 huge super star clusters

are formed. (2005, AJ, 130)

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NGC 1569 Gas Infall confirmed!

see Muehle et al. (2005)

and in many other SBDGs!

Stil & Isreal (2002)

H

HI

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NGC 4449 a triggered starburst

(Hunter et al. 1995) 27 SS 2017

II Zw 40 (van Zee et al. 1997) 28 SS 2017

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I Zw 18 - a perturbed dIrr with gas infall?

(Östlin & Kunth 2000)

(van Zee et al. 1997) 29 SS 2017

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van Zee et al. (1998)

8.8.7. Associated HI Clouds I Zw 18 is associated with a

kinematically disjunct HI

complex.

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BCD NGC 1705

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NGC 1705 Dwarf Starburst Galaxies are experiencing an epoch of strong Star Formation:

• Massive stars illuminate their surrounding gas;

• Exploding stars release hot, vehemently expanding gas

X-ray contours H

overlaid on HI H

(Hensler et al. 1997) 2 kpc

But: super star cluster not formed in the center

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Although clouds hamper the outflow by evaporated mass-loading,

by this, reducing the metal loss, over-running clouds pierce holes

into the superbubble shell: nozzle-like outflows are facilitated.

Recchi & Hensler (2007) A&A, 477

Galactic outflows and infalling clouds

33 SS 2017

CO

V UV

X

Papaderos et al. (1998) Kobulnicky et al. (1995)

Vacca & Conti (1992)

Hensler et al. (1997)

A dIrr colliding with

an intergalactic

cloud?

He 2-10

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Metal differences between

outflow vs. infall

Metal content of the cool (∼104 K)

circumgalactic medium around

28 HI-selected LLS at z 1 observed in

absorption against background QSOs

35 SS 2017

Star formation is self-regulated!

SF = g_cons = Mg/ Hubble

or

sSFR:= s = /Mgal 0.01 Gyr-1

What triggers high star-formation rates?

Gas Infall?

The effects of external gas infall vs. outflow!

Both act simultaneously: e.g. at high z~2-3: Erb (2008) ApJ, 674

at low z 1: Lehner et al. (2013) ApJ, 770

present: starburst DGs 36 SS 2017

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Can Gas Infall explain

a chemical rejuvenation of dIrrs and their abundance peculiarities ?

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Henry, R.B.C. & Worthey, G. (1999)

The N/O problem of dIrrs/BCDs

N/O production: • O is produced in massive stars

and released by SNeII (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 (~ -1.5) at

low O!

Henry, Edmunds, Köppen, (1999)

Stellar evolution tracks pass dIrr regime too fast!

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Gas Infall: its Effect on Abundances

Koeppen & G.H. (2005) A&A, 434

Model assumptions:

Yields same as in

Henry et al. (2000):

van der Hoek & Groenewegen

(1997), Maeder (1992)

Galaxy models

evolve for 13 Gyrs

with different yeff of

0.1 ... 1

reaching different loc.s

in (N/O)-(O/H) diagram

Infall of clouds with

primordial abund. and

masses of 106... 108 M

produces loops.

SS 2017

Gas Infall and its Effect on Abundances

Extension of tracks depends on yeff

(N/O) scatter repro-ducible by age diff‘s of start models

.

Koeppen & Hensler (2005) A&A, 434

40 SS 2017