Upload
others
View
9
Download
0
Embed Size (px)
Citation preview
28.05.2017
1
Starburst Dwarf Galaxies
1 SS 2017
2
The star-formation
history does in
general not show a
continuous evolution
but preferably an
episoidal behaviour.
Starburst Dwarf Galaxies
SS 2017
28.05.2017
2
4
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
SS 2017
5
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
SS 2017
28.05.2017
3
6
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)
SS 2017
7 Martin et al. (2002) ApJ 574
Abundances in the galactic wind from
X-ray spectra
SS 2017
28.05.2017
4
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
28.05.2017
5
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)
12 SS 2017
28.05.2017
6
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
15 SS 2017
28.05.2017
7
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
28.05.2017
8
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
28.05.2017
9
(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)
21 SS 2017
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
22 SS 2017
28.05.2017
10
What triggers the high star-formation rates?
Gas Infall?
Consider the effects of external gas infall!
23 SS 2017
24
What triggers the
high star-formation rates?
Consider the effects of
external gas infall!
Gas Infall to DGs
SS 2017
28.05.2017
11
25
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)
SS 2017
NGC 1569 Gas Infall confirmed!
see Muehle et al. (2005)
and in many other SBDGs!
Stil & Isreal (2002)
H
HI
26 SS 2017
28.05.2017
12
NGC 4449 a triggered starburst
(Hunter et al. 1995) 27 SS 2017
II Zw 40 (van Zee et al. 1997) 28 SS 2017
28.05.2017
13
I Zw 18 - a perturbed dIrr with gas infall?
(Östlin & Kunth 2000)
(van Zee et al. 1997) 29 SS 2017
30
van Zee et al. (1998)
8.8.7. Associated HI Clouds I Zw 18 is associated with a
kinematically disjunct HI
complex.
SS 2017
28.05.2017
14
BCD NGC 1705
31 SS 2017
32
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
SS 2017
28.05.2017
15
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
34 SS 2017
28.05.2017
16
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
28.05.2017
17
Can Gas Infall explain
a chemical rejuvenation of dIrrs and their abundance peculiarities ?
37 SS 2017
38
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!
SS 2017
28.05.2017
18
39
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