presentation

The fate of the gas in nearby
irregular dwarf galaxies
Janine van Eymeren
(JBCA, The University of Manchester)
in collaboration with
M. Marcelin (OAMP), B.S. Koribalski (ATNF),
Janine van Eymeren
Strasbourg 05.10.09
1
R.-J. Dettmar (AIRUB),
D.J. Bomans (AIRUB)
NGC 2366
4861
R
Janine van Eymeren
Hα
Strasbourg 05.10.09
2
WIYN 3.5m, Palomar/Las
Calar AltoCampanas
3.5m telescope,
Survey,van
GilEymeren
de Paz etetal.al.(2005)
(2009)
Strategy
• Look at Hα kinematics (3d spectroscopy)
• Compare to HI (reference value) and
measure expansion
• Estimate escape velocity of host galaxies
Fate?
Why dwarf galaxies?
• Outflow (gravitationally
bound)
• Galactic wind (freely
flowing)
⇐ Evolution of galaxies (star
formation), chemical
enrichment of the
intergalactic medium (IGM)
• Low mass
• Low metallicity
• Strong bursts of star
formation
Janine van Eymeren
Strasbourg 05.10.09
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• The expansion of a
superbubble in dwarf
galaxies
Free parameters:
• The galaxy mass
• The energy input
Results:
Increase of mass
Superbubble Model (Mac Low & Ferrara 1999)
• Only a small fraction of
mass gets lost
(increasing with
decreasing mass)
• Metals are almost
Increase of energy
completely blown out
Energy input lasts 50 Myr
into the IGM (especially
State of expansion after 100 Myr
in low
mass
dwarfs)
Janine van Eymeren
Strasbourg 05.10.09
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Observations
Fabry-Perot interferometry
•
•
•
•
•
•
Centred on Hα, scanned through 24
channels (free spectral range of 376
km/s)
Observations in cycles, each channel
exposed for 10s
Photon counting system
Data reduction with ADHOCw (J.
OHP 1.93m telescope equipped
Boulesteix): phase and wavelength calib.
with the Marseille FP
Spectral resolution of 50 km/s
Spatially smoothed to 3'' (seeing)
VLA, http://www.physast.uga.edu/
Radio synthesis observations (VLA)
• NGC 2366: BCD arrays (THINGS,
Walter et al. 2008), 2.6 km/s, 13''x12''
• NGC 4861: CD arrays (Wilcots et al.
1996,
et al. 2004), 5.2
km/s,
JanineThuan
van Eymeren
Strasbourg
05.10.09
31''x30''
5
Results NGC 2366
(van Eymeren et al. 2009a)
Hα:
• Gaussian decomposition
(profiles interactively fitted)
• Red-shifted
outflow: vexp=50
km/s, length of
1.4 kpc
• Blue-shifted
component with
an expansion of
18 km/s
Janine van Eymeren
1 kpc
Strasbourg 05.10.09
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HI:
• HI
intensity
distribution
• HI velocity
field
• HI velocity
dispersion
• HI rotation
curve
• Rotation curve derived from a tilted-ring
analysis (GIPSY task rotcur)
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Strasbourg 05.10.09
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Results NGC 2366
Hα-HI:
Compare HI and Hα:
•
•
•
HI und Hα in good agreement
Red-shifted outflow clearly
stands out
A hint of the blue-shifted
component is visible
1 kpc
Gaussian decomposition of the HI data:
Outflows in HI:
blue
main
red
•
•
Janine van Eymeren
Strasbourg 05.10.09
Red-shifted
outflow: gas
already ionised
Blue-shifted
outflow: HI8
detection
Results NGC 4861
(van Eymeren et al. 2009c)
Hα:
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Strasbourg 05.10.09
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HI:
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Strasbourg 05.10.09
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Results NGC 4861
Hα-HI:
Gaussian decomposition of the HI data:
Janine van Eymeren
Strasbourg 05.10.09
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Outflow or galactic wind?
• Mass decomposition in order to
2 −1
 r 
compare different Dark Matter
ρ ISO = ρ 0 1 +   
halo models (van Eymeren et al.
  rc  


2009b)
⇒ pseudo-isothermal halo (Binney
 rmax  
& Tremaine 1987) describes the
2 

vesc = 2vrot 1 + log

inner kpcs best („cusp-core
 r 

discrepancy“)
rmax = rHI (dashed line)
rmax = 2·rHI (solid line)
NGC 2366
NGC 4861
• Expansion velocities far below
the escape velocity
vesc
vexp
Janine van Eymeren
vrot
⇒ The gas stays gravitationally
bound!
Strasbourg 05.10.09
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Summary
• Outflows in all sample galaxies with expansion velocities
between ~20 und ~70 km/s
• Partially visible in both gas components, partially only in one
• Gas in all galaxies gravitationally bound (in good agreement
with simulations by MacLow & Ferrara 1999, Silich &
Tenorio-Tagle 1998)
Outlook
• Ionisation mechanisms (CLOUDY, MAPPINGS III), star
formation history
• optical spectroscopy (multi-object/integral field spec.)
• high-res. radio continuum observations (e-MERLIN)
• IFS in Echelle mode to study the kinematics of the shell
structures with sufficient spectral res. and sensitivity
• Extending the sample to less massive galaxies
Janine van Eymeren
Strasbourg 05.10.09
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Lopsidedness in WHISP
Galaxies
in collaboration with
Eva Jütte, Yelena Stein, Ralf-Jürgen Dettmar
(AIRUB)
Chanda Jog (Indian Institute of Science, Bangalore)
Motivation
•
•
•
•
Lopsidedness first studied in 1980 by Baldwin et al.
Frequency of lopsidedness quite high
Tidal interactions, mergers, external gas accretion
Lopsidedness more frequent in late-type galaxies
(e.g., Bournaud et al. 2005 and ref. therein)
• However see Angiras et al. (2007): opposite trend
for galaxies of the Eridanus cluster
→ environmental effect?
• Problem: Many studies limited to small radial ranges
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Strasbourg 05.10.09
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Lopsidedness
• Morphological
I.
II.
σ (r , Φ ) = a0 (r ) + ∑ am (r ) cos(mΦ − Φ m (r ))
A1 = a1 / a0
A1 ≥ 0.1
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Strasbourg 05.10.09
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Lopsidedness
• Kinematic
N
vlos (r ) = vsys (r ) + ∑ cm (r ) cos mΨ + sm (r ) sin mΨ
I.
m =1
ε lop
s3 − s1 1 + 2q 2 + 5q 4
=
, q = cos i
4
sin 2ϕ 2 c1 (1 − q )
II. ε = vreceding − vapproaching
lop
2vc
ε lop ≥ 0.05
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Strasbourg 05.10.09
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WHISP
(Westerbork HI Survey
of Spiral and Irregular
Galaxies, Swaters 2002)
•
•
•
•
UGC catalogue
δ > 20°
Dblue > 1.5‘
FHI > 100 mJy (20
mJy)
• Standard data
reduction
• Full res., 30“x30“,
60“x60“
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Strasbourg 05.10.09
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Selection Criteria
• 20° ≤ i ≤ 75°
• dHI/beam ≥ 10
WHISP: 320 galaxies
Selected: 100 galaxies
Worked on: 76 galaxies
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Strasbourg 05.10.09
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Credit: Yelena Stein
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Strasbourg 05.10.09
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Analysis
• Tilted-ring analysis on Hermite velocity
field → rotation curve
• Harmonic decomposition of the HI
intensity distribution and the velocity
field using the parameters derived from
the tilted-ring analysis
• Calculate A1, Φ1, εlop
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Strasbourg 05.10.09
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Examples
• UGC 2455
• UGC 4173
• UGC 4278
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Strasbourg 05.10.09
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Preliminary Results (1)
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Strasbourg 05.10.09
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Preliminary Results (2)
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Strasbourg 05.10.09
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