1. HI in galaxies from z = 0.002 to z = 0.2 Thijs van der Hulst
Kapteyn Astronomical Institute
University of Groningen
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Kapteyn astronomical
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2. Open Questions When and how quickly did the gas settle in the
dark matter potential wells
- Where and how did gas get converted into stars
When and how did the merging process develop
What is the importance of gas accretion versus merging
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Radiotelescopes can trace the neutral gas extremely well
( to go beyond z = 0.2 we need SKA )

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4. COLD GAS HI observations local universe
- Extended HI disks with outer spiral structure
- Large majority of disks WARPED and LOPSIDED
- Large reservoirs extra-planar gas
- Lumpy HI structures (clouds, tails, filaments)
around galaxies
Result of recent minor mergers and accretion?
Sancisi et al. A&A Rev., 2008

5. WSRT 1976
HI VLA
WARPS
LOPSIDEDNESS
HI WSRT

6. HI masses
in outer structures Mʘ
3x108 Mʘ

7. EXTENDED HI (note the spiral structure)
optical NGC neutral hydrogen WSRT
same scale
Battaglia et al. 2005

8. EXTENDED HI (spiral arms)
NGC neutral hydrogen WSRT
GALEX
same scale
Battaglia et al. 2005

9. NGC 6946
optical neutral hydrogen
WSRT
same scale
Boomsma et al. 2007

10. NGC 6946 Deep B-band neutral hydrogen WSRT same scale
Some star formation also in outer disk
NGC 6946
Deep B-band
neutral hydrogen
WSRT
same scale
A. Ferguson 2007
Boomsma et al. 2007

11. HIGH VELOCITY
CLOUDS
( total amount
~3 x 108 Mʘ )

12. NGC 6946
Accretion?
HI map WSRT
Boomsma et al. 2007

13. NGC 2403 HI VLA Anomalous gas 3x108 Mʘ Fraternali et al. 2001 model
thin disk
Fraternali
et al.
2001

15. NGC 891
Anomalous HI
~ 1 x 108 Mʘ
Fraternali, 2007

16. Extra-planar HI MILKY WAY, NGC 891, NGC 2403 M 31, NGC 4559, NGC 253,
UGC 7321, NGC 5775, NGC 6946

17. Emerging picture: HI disk Extra-planar HI (high velocity clouds)
extended with outer spiral structure
warped
lopsided
porous
Extra-planar HI (high velocity clouds)
ACCRETION?

18. Local Universe HI detection limits: Column densities 1 x 1019 cm-2
Masses x 106 Mʘ
Accreted HI Mʘ
Time scales yrs
Galaxy fraction %
Accretion rate Mʘ / yr

19. SUMMARY 1. Spiral structure and star formation
in outer HI disks
2. Most galaxies warped and lopsided
3. Large reservoirs of extra-planar HI
4. Cold gas lumpy accretion at a mean
rate of 0.1 – 0.5 Mʘ / yr
25 – 50 % of all galaxies accrete lumps of gas of Mʘ

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21. 3.8 x 108 Mʘ HI near the center of the Virgo cluster
NGC 4388
Oosterloo & van Gorkom, 2005, A&A 437, 19

22. The Amazing NGC 7426 - ‘Normal Elliptical
>300 h-1 kpc
- ‘Normal Elliptical
- Two tails, 185, 125 h-1 kpc in length!
- 4 x 109 h-2 Mʘ
- NHI (min) = 1019 cm-2
- Tails aligned with Pisces-Perseus
super cluster structure
Schiminovich, van Gorkom et al.

23. Present state of the art: imaging HI emission out to z = 0.2
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240 hour integration with WSRT
Verheijen, van Gorkom et al. 2007

24. SKA goals for deep fields:
get to MHI* galaxies out to z = 2
detect HVC mass objects to z = 0.2
detect dwarf galaxies to z = 0.5

25. Number of galaxies detectable as a function of redshift per square degree
lookback
time
HI mass limit (Msun)
# detections
Gyr
t = 360 h
t = 1000 h
0.5 – 1.0
5.0 – 7.7
5.0 x 108
1.6 x 106
3.0 x 108
2.4 x 106
1.0 – 1.5
7.7 – 9.3
1.3 x 109
1.8 x 106
7.9 x 108
2.7 x 106
1.5 – 2.0
9.3 – 10.3
2.7 x 109
1.9 x 106
1.6 x 109
2.0 – 2.5
10.3 – 11.0
4.8 x 109
1.7 x 106
2.9 x 109
2.5 x 106
2.5 – 3.0
11.0 – 11.5
7.8 x 109
4.7 x 109
2.3 x 106
3.0 – 3.5
11.5 – 11.8
1.2 x 1010
1.4 x 106
7.3 x 109
2.0 x 106
3.5 – 4.0
11.8 – 12.1
1.8 x 1010
1.2 x 106
1.1 x 1010
4.0 – 4.5
12.1 – 12.3
2.7 x 1010
1.0 x 106
1.6 x 1010
1.5 x 106

26. Phase-1 SKA: Number of galaxies / sq. deg. as a function of redshift
lookback
time
HI mass limit (Msun)
# detections
Gyr
t = 360 h
t = 1000 h
0.5 – 1.0
5.0 – 7.7
3.6 x 109
3.8 x 105
2.1 x 109
5.6 x 105
1.0 – 1.5
7.7 – 9.3
9.3 x 109
4.5 x 105
5.6 x 109
6.5 x 105
1.5 – 2.0
9.3 – 10.3
1.9 x 1010
4.3 x 105
1.1 x 1010
6.4 x 105
2.0 – 2.5
10.3 – 11.0
3.4 x 1010
4.0 x 105
2.0 x 1010
5.8 x 105
2.5 – 3.0
11.0 – 11.5
5.5 x 1010
3.6 x 105
3.3 x 1010
5.2 x 105

28. Detection limits for SKA for t = 12 hours
Redshif t
Frequenc y
Tsys
Angular Resolutio n
Linear Resolutio n
SB - dimming
Luminosit y Distance
Lookbac k time
HI mass limit
MHz K
arcsec
kpc
Gpc
Gyr
Msun
0.2
50.4
0.52
1.7
0.796
0.972
2.41
6.1x108
0.5
946.94
51.4
0.65
4.0
1.486
2.825
5.02
8.7x108
2.0
710.20
53.8
0.87
7.0
3.026
6.640
7.73
2.7x109
2.5
568.16
57.5
1.09
9.3
4.000
11.02
9.32
7.2x109
473.47
62.7
1.31
11.1
4.796
15.75
10.32
1.5x1010
405.83
69.6
1.52
12.5
5.469
20.72
11.00
2.6x1010
3.0
355.10
78.3
1.74
13.6
6.052
25.87
11.48
4.3x1010
3.5
315.64
89.3
1.96
14.6
6.566
31.15
11.83
6.7x1010
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29. Phase-1 SKA Detection limits for t = 12 hours
Redshif t
Frequenc y
Tsys
Angular Resolutio n
Linear Resolutio n
SB - dimming
Luminosit y Distance
Lookbac k time
HI mass limit
MHz K
arcsec
kpc
Gpc
Gyr
Msun
1.0
710.20
53.8
0.87
7.0
3.026
6.640
7.73
1.9x1010
1.5
568.16
57.5
1.09
9.3
4.000
11.02
9.32
5.1x1010
2.0
473.47
62.7
1.31
11.1
4.796
15.75
10.32
1.0x1011
2.5
405.83
69.6
1.52
12.5
5.469
20.72
11.00
1.8x1011
3.0
355.10
78.3
1.74
13.6
6.052
25.87
11.48
3.0x1011
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