Transcript Document

NGC 1705--Tosi et al WFPC2
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
WLM-dIrr
Luminous GC
MV=-8.8
WFPC2 study
Hodge et al. 1999,
ApJ, 521, 577
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
H1
NGC 147
WIYN V-band
Hodge clusters:
inner & outer
locations
Hodge 1977, AJ, 81,
25
August 28, 2007
H2
J. S. Gallagher
H3
U. Michigan-Dwarfs + GCs
We conclude that---Long ago small galaxies made sufficient
numbers of dense, massive star clusters for
some to survive to the present.
These are found in the range of neabry dwarf
systems from dIrrs to dEs to dSphs in a range
of spatial and kinematic patterns.
Questions:
 How did such small galaxies give birth to
such clusters and what were the impacts?
How does formation connect to chemistry and
kinematics?
 How important are GCs in powering outflows
and reducing baryon content in low mass
galaxies? Does this lead to very gas-poor
galaxies?
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
Observational approach to dwarf
galaxy massive star clusters &
gastrophysics-Nearby dwarf starbursts host young
massive “super star clusters” (SSCs);
structural analogs to globular clusters:
• M ≥ 105 Msun
• R(1/2) < 10 pc
• Age < 30 Myr
SSCs--major power sources of L(Lyc) for
[t<7-8 Myr] and L(mech) [t< 25-30 Myr].
Observe feedback & cluster formation
processes in action.
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
NGC1569 & NGC5253: Two starburst dwarfs
10 Myr, 106Msun
B
A
10
NGC 1569: Gas-Rich Dwarf Starburst Galaxy, MV= -1
P. Anders, U. Goettingen;J.data
HST: ESA/NASA
S. Gallagher
August 28, 2007
U. Michigan-Dwarfs + GCs
Compact massive star cluster development &
feedback: It’s the (re-)radiation!
+ Super molecular cloud core: n>105 cm-3,
Vturb~10 km/s
+ Mm to sub-mm -> dusty molecular ISM
+ Efficient star formation; SF>30%
+ SFR>0.1Msun/yr for T~106 yr; Mcl≥105 Msun
+ Thermal IR & radio; super ultradense HII
+ Widespread photoionization + stellar wind
cavity; supergiant HII region
+ UVOIR -> stars + HII & X-ray-shocked ISM
+ Starburst required for M*≤ 3x108 Msun, MV> -15
After Kelsey Johnson 2002, Science, 297, 776; Johnson & Kobulnicky 2003, ApJ, 597, 923
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
Inevitable Nature of Stellar Energetics
Massive stars->> SNe II
SSCs =>long lived supermassive star
SNe II feedback: main mechanical power at low
metals:
Pmech~ (600km/s)2SN(SFR/dMW/dt)
Mass-loading efficiency & galaxy ISM structure
largely determine possible outflow speeds
SNe key factor in lower mass galaxies with Vesc
< 500 km/s
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
More mechanical luminosity: DISK BLOWOUTS
Halo
Supershells:
Blowouts--vent into
halos from disks.
Hot interior partially
confined by cooler
shell
Generally initial
V(exp) << V(esc);
P(z), n(z) critical
Photoionized surfaces
Different physics
than steady winds!
Weaver et al. 1977,
ApJ and later models
Disk
Effects on HI vs fate of
hot gas?
Mac Low et al. 1989, ApJ, 337, 141
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
NUCLEAR STARBURST
WIND STRUCTURE
Sustained mechanical
energy inputs leads to
galactic wind.
Supersonic gas flow
upstream of a critical
point. Organized
outflow
M82 as a nearby
example--seen in larger
galaxies; matter of
scale?
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
NGC 1569 - NIR with WIYN 3.5-m Telescope;
Natural Seeing: SF Patterns: SSCs Embedded
in Young Star Clouds
NGC 1569--3 SSCs in ~10 Myr-Large jump in L(mech)
associated with SSCs!
SSCs
10
Feedback induced
shift in SF
A
mode likely.
B
Superbubble from SSC A a likely dominant factor
SFR declines as dense ISM exhausted-and
ejected? GMC formation vs. destruction?
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
M. Westmoquette, K. Exter, L. Smith, J. Gallagher--2007 in prep
Local views of NGC 1569-- WIYN & HST: multiple super bubb
WIYN
H +[NII]
WFPC2
H +[NII]
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
NGC1569:
SSCs important
supershell drivers.
HI
Some likely to
escape.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
HI
M. Westmoquette et
al. 2007 in prep
C. Martin 1998, ApJ,
506, 222
Kinematic supershells in NGC 1569
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
High spatial
concentration
of massive stars
powers
hot gas outflow
Martin, Kobulnicky, Heckman
2002, ApJ, 574, 663
V(HII) ~ 100 km/s-Slow optical wind
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
NGC1569 HI: starburst small scale relative to HI
2002, A&A, 392, 473
B A
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
Dwarf dichotomy: gas-rich, slowly
evolving vs. gas free
(e.g. Grebel, Gallagher & Harbeck 2003, AJ, 125, 1926)
Nature vs. Nurture.
NGC5253 - gas deficient starburst
HI/L ‹ 0.1, MV≈-18
Starburst driving gas removal & transition
to NGC205 dE-like structure???
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
NGC5253-ACS
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
Complex multi-phase ISM + persistent
cool ISM in presence of intense star
formation: Dellenbusch Wisconsin PhD
Summers et al 2000
Harris et al. 2004
Kobulnicky & Skillman 1995
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs
SSC D>17 kpc
from NGC3310
starburst:
MV= -11
≈106 Msun
Close to tidal
debris but no
HI
GC formation
mode?
SDSS: Knapp et al.2006, AJ
Tidal debris: Wehner et al.
2006, MNRAS; 2005, ApJL
Globulars & Dwarfs: Now
&Then
• SSC formation --> starbursts:
require Mbary≥108 Msun
Triggers for SSCs??
• SSCs in dwarfs usually
centrally concentrated
(NGC3310!)
• Multiple supershells--inefficient
ISM mass loss. More efficient
bleeding of metals
• Gas poor starbursts with central
clusters (disks)--a final collapse
phase of the ISM. Why & how
(Kate Dellenbusch PhD)??
August 28, 2007
• GC formation REQUIRES
starbursts in small galaxies
• GCs have wide spatial
distribution in dwarfs, not
always centrally concentrated;
ISM energy deposition reduced
• GC formation not strictkly
associated with gas loss--SF
extends past GC era
• Denser IGM surroundings may
choke winds--affect metal
evolution and radiation escape
J. S. Gallagher
U. Michigan-Dwarfs + GCs
August 28, 2007
J. S. Gallagher
U. Michigan-Dwarfs + GCs