Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/research/WALLABY/Wallaby2010/TWestmeier-Wallaby2010.pdf Дата изменения: Wed Dec 8 04:33:01 2010 Дата индексирования: Fri Feb 11 23:22:17 2011 Кодировка: Поисковые слова: m 106

ICRAR is a partnership between The University of Western Australia and Curtin University of Technology

Gas and Dark Matter in the Sculptor Group
Tobias Westmeier (ICRAR / UWA)

2 December 2010

H surveys with ASKAP and MeerKAT

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Pilot Observations of the Sculptor Group

2 December 2010

H surveys with ASKAP and MeerKAT

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Pilot Observations
Pilot Observations


ATCA H I observations of the Sculptor Group NGC 300 N GC 5 5

NGC 55

NGC 300

Image: ESO

Image: ESO

2 December 2010

H surveys with ASKAP and MeerKAT

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Pilot Observations
ATCA H Observations of NGC 55 / 300


Frequency: Array configurations: Covered area: Number of pointings: Total integration time: Angular resolution: Velocity resolution: 5 H sensitivity:

1420 MHz EW 352/367 2° в 2° 32 96 h 9 0 в 1 8 0 0.8 в 1.6 kpc 4 km s
-1 2 Australia Telescope Compact Array



1019 cm- 1 05 M

2 December 2010

H surveys with ASKAP and MeerKAT

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H I Observations of NGC 300

2 December 2010

H surveys with ASKAP and MeerKAT

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NGC 300
DSS Image of NGC 300

Westmeier, Braun & Koribalski 2010, MNRAS, in press

2 December 2010

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NGC 300
Lowest H contour: 5 в 1020 cm-2

Westmeier, Braun & Koribalski 2010, MNRAS, in press

2 December 2010

H surveys with ASKAP and MeerKAT

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NGC 300
Lowest H contour: 1 в 1019 cm-2 Very extended outer disc with different orientation angle.

VLA, Puche et al. (1990)

Westmeier, Braun & Koribalski 2010, MNRAS, in press

2 December 2010

H surveys with ASKAP and MeerKAT

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NGC 300
Velocity Model Residual





Distortion of gas disc obvious from the velocity field. Fitting of tilted-ring model to velocity field to characterise disc structure. Radial velocity: vrad(x,y) = vsys + vrot sin(i) cos(), = f(x,y,).

2 December 2010

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NGC 300
Westmeier, Braun & Koribalski (2010) Rotation curve Westmeier, Braun & Koribalski (2010) Position angle





Rotation curve traced out to R 20 kpc, almost twice as far out as VLA data by Puche et al. (1990). Rotation curve decreases beyond R 10 kpc. 2 2 2 2 Mass modelling: v rot r = f gas v gas r f stars v stars r v DM r
Gas Stars DM 10

2 December 2010

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NGC 300
t ot al DM

g as

stars

Westmeier, Braun & Koribalski (2010)

2 December 2010

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NGC 300

Westmeier, Braun & Koribalski (2010)

2 December 2010

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NGC 300
pl at eau exponential

Westmeier, Braun & Koribalski (2010)



Strong asymmetries in the H disc of NGC 300. South-eastern edge sharp and smooth. North-western edge broad and ragged. Possible explanation: ram-pressure interaction while NGC 300 is moving through intergalactic medium.
H surveys with ASKAP and MeerKAT 13

2 December 2010


NGC 300
Ram-pressure Stripping
Ram pressure:
P
ram

=

IGM

v

2

Gravitational pressure: P

grav

r = ga s r z





gravitational pressure
max

Westmeier, Braun & Koribalski (2010)

ram pressure of IGM wind

Face-on situation, but valid for inclination angles of up to 60° (Rdiger et al. 2005).

2 December 2010

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NGC 300
vrel = 200 km/s vrel = 150 km/s

gravity dominates ram pressure dominates
Westmeier, Braun & Koribalski (2010)

Ram-pressure stripping does occur in galaxy groups (not only in clusters) at reasonable assumptions on the IGM density (10-4 to 5 в 10-6 cm-3) and relative velocities (100 to 300 km/s). It affects the faint outer gas discs of galaxies and possibly contributes to the warping observed in many galaxies (U-shaped warps?). A systematic study of ram-pressure stripping + simulations can be used as a probe to constrain the density of the IGM in galaxy groups.
2 December 2010 H surveys with ASKAP and MeerKAT 15


NGC 300
vrel = 200 km/s vrel = 150 km/s

Ram-pressure stripping does occur in galaxy groups (not only in clusters) at reasonable assumptions on the IGM density (10-4 to 5 в 10-6 cm-3) and relative velocities (100 to 300 km/s). It affects the faint outer gas discs of galaxies and possibly contributes to the warping observed in many galaxies (U-shaped warps?). A systematic study of ram-pressure stripping + simulations can be used as a probe to constrain the density of the IGM in galaxy groups.
2 December 2010 H surveys with ASKAP and MeerKAT 16

! rnoon fte s aWestmeier, Braun & Koribal ram pressure dominates hi alk t t kki's e nji B e ee K S
gravity dominates

ski (2010)


NGC 300





High dispersion of 20 kms-1 along boundary between inner and outer disc of NGC 300. Double-peak profile indicates sudden transition from inner to outer disc within beam size of 1 kpc.
H surveys with ASKAP and MeerKAT 17

2 December 2010

Westmeier et al. (2010)


NGC 300
Comparison with Stellar Disc




Optical observations of outer disc by Bland-Hawthorn et al. (2005) with the Gemini South 8-m telescope. Stellar disc of NGC 300 detected out to 14 kpc in two targeted fields. Stellar disc exponential across entire radial extent without deviation or break.

Bland-Hawthorn et al. (2005) Bland-Hawthorn et al. (2005)

2 December 2010

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NGC 300
Comparison with Stellar Disc






Strong radial metallicity gradient (Vlaji et al. 2009) with break near boundary between inner and outer H I disc. Possible explanations: Star formation activity only in the inner disc, but radial mixing of stars in the disc. Star formation activity slowly progressing outwards. Outer gas disc does not play significant role, consistent with old age of stars ( 1 Ga).

Bland-Hawthorn et al. (2005)

Vlaji et al. (2009)

2 December 2010

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H I Observations of NGC 55

2 December 2010

H surveys with ASKAP and MeerKAT

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NGC 55
DSS Image of NGC 55

Westmeier et al., in prep.

2 December 2010

H surveys with ASKAP and MeerKAT

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NGC 55
Lowest H contour: 5 в 1020 cm-2

Westmeier et al., in prep.

VLA image, Puche et al. (1991)

2 December 2010

H surveys with ASKAP and MeerKAT

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NGC 55
Lowest H contour: 1 в 1019 cm-2 H image of NGC 55 looks very distorted. Extended regions of extraplanar gas as well as isolated gas clouds or HVCs of a few times 106 M.

Westmeier et al., in prep.

VLA image, Puche et al. (1991)

2 December 2010

H surveys with ASKAP and MeerKAT

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NGC 55
Velocity Field


Complex velocity field with s-shaped isotachs: Extended disc most likely due to warp, not outflows or extra-planar gas. Velocities of isolated gas clouds different from disc gas.

2 December 2010

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NGC 55

N W E S



Strong asymmetry in N


H I

profile:



East: Exponential with a = -0.18. West: Steeper than exponential. Asymmetry also along minor axis. Integrated spectrum asymmetric too.

2 December 2010

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NGC 55

HVCs

MS

HVCs



Several isolated H I clouds all around NGC 55. H I masses typically 5 в 106 M. Velocity dispersions of 10...20 km/s.
H surveys with ASKAP and MeerKAT 26



2 December 2010


NGC 55
NGC 55 or Foreground?
T wo Cl Cl or possibilities: ouds are at the distance of NGC 55. ouds are foreground from Milky Way Magellanic Stream.
HIPASS

I C 161 3



Virial mass: H mass: Mass ratio:

M M

vir H

v 2 R d Fint d 2 d
vir HI

247 2 253



M M

d

-1

30 0

55

2 December 2010

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Ma ge lla nic Str ea m

Virial mass vs. H mass

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NGC 55
Virial-to-H I mass ratio Mvir / MH

Westmeier et al., in prep.

Westmeier et al., in prep.

Values of = 50 to 100 for six clouds, but well below 10 for remaining two.

2 December 2010

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NGC 55
Origin of the Gas Clouds


M31





Origin of NGC 55 clouds currently unknown. Similar populations observed around other galaxies, including M31 (Thilker at al. 2004, Westmeier et al. 2005, 2009) M83 (Miller et al. 2009) MW high-velocity clouds Possibly combination of different origins, including Gaseous satellites Outflows Tidal stripping

Westmeier, Braun & Thilker (2005) Westmeier, BrЭns & Kerp (2009)

2 December 2010

H surveys with ASKAP and MeerKAT

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Summary
H I Observations of NGC 55 / 300




NGC 300 Extended, warped H I disc with decreasing rotation curve. Evidence of ram-pressure stripping by the IGM in the Sculptor group. Low metallicities in the outer disc indicate lack of star formation. NGC 55 Extended, asymmetric H I disc, presumably the result of warping.


Population of circumgalactic H I clouds with MH I 106 M.





Questions arising Origin of warp? Origin of circum-galactic gas clouds? Role of ram-pressure stripping in groups? WALLABY will enable us to study these questions with the help of a large sample of galaxies.
H surveys with ASKAP and MeerKAT 30

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Summary
Weather Forecast for the Sculptor Group
"Mainly sunny throughout most of the Sculptor group with a few clouds near NGC 55. Strong winds of up to 4 x 105 knots in central parts of the Sculptor group."

2 December 2010

H surveys with ASKAP and MeerKAT

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