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The HI gas content of galaxies around Abell 370,
a galaxy cluster at z = 0.37
International SKA Forum 2010
Philip Lah
A New Golden Age for Radio Astronomy
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Collaborators: Frank Briggs (ANU)
Michael Pracy (Swinburne) Jayaram Chengalur (NCRA)
Matthew Colless (AAO)Roberto De Propris (CTIO)
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Method: Coadding the HI signals from
distant galaxies using the galaxies’ known
optical positions and redshifts
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Giant Metrewave Radio Telescope
Anglo-Australian Telescope
India Australia
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Nearby Galaxy Clusters Are Deficient
in HI Gas
The Coma Cluster
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So why target moderate redshift clusters
for HI gas?
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The Butcher-Oemler Effect
Redshift, z
Blu
e Fr
actio
n, f B
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The Butcher-Oemler Effect
Redshift, z
Blu
e Fr
actio
n, f B
Abell 370
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Abell 370 a galaxy cluster at z = 0.37
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Abell 370, a galaxy cluster at z = 0.37
Abell 370 cluster core, ESO VLT image
large galaxy cluster of order same size as Coma
similar cluster velocity dispersion and X-ray gas
temperature
GMRT ~34 hours on cluster
optical imaging ANU 40 inch telescope
spectroscopic follow-up with the AAT
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redshift histogram
324 useful redshifts
from AAT observations
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redshift histogram
GMRT sideband frequency
limits
324 useful redshifts
from AAT observations
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Abell 370 galaxy cluster
324 galaxies
105 blue (B-V 0.57)
219 red (B-V > 0.57)
Abell 370 galaxy cluster
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Abell 370 galaxy clusterAbell 370 galaxy cluster
3σ extent of X-ray gas
R200 radius at which cluster
200 times denser than the
general field
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Coadded HI Mass
Measurements
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HI mass324 galaxies
219 galaxies
105 galaxies
94 galaxies
168 galaxies
156 galaxies
110 galaxies
214 galaxies
Inner Regions Outer Regions
The galaxies around Abell 370 are a mixture of early and late types in a variety of environments.
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HI mass324 galaxies
219 galaxies
105 galaxies
94 galaxies
168 galaxies
156 galaxies
110 galaxies
214 galaxies
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HI mass324 galaxies
219 galaxies
105 galaxies
94 galaxies
168 galaxies
156 galaxies
110 galaxies
214 galaxies
11 blue galaxies within intra-cluster hot x-ray gas appear HI deficient
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HI mass324 galaxies
219 galaxies
105 galaxies
94 galaxies
168 galaxies
156 galaxies
110 galaxies
214 galaxies
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HI mass324 galaxies
219 galaxies
105 galaxies
94 galaxies
168 galaxies
156 galaxies
110 galaxies
214 galaxies
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HI Density Comparisons
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cluster redshift
Distribution of galaxies around Abell 370com
plete GM
RT redshift range
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Inner Cluster Region
Outer Cluster Region
HI density
Whole Redshift Region
z = 0.35 to 0.39
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cluster redshift
Distribution of galaxies around Abell 370
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Distribution of galaxies around Abell 370
cluster redshift
8 Mpc radius region
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Inner Cluster Region
HI density
Outer Cluster Region
Whole Redshift Region
z = 0.35 to 0.39
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cluster redshift
Distribution of galaxies around Abell 370
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cluster redshift
Distribution of galaxies around Abell 370
within R200
region
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HI density
Outer Cluster Region
Inner Cluster Region
Whole Redshift Region
z = 0.35 to 0.39
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HI Mass to Light Ratios
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HI Mass to Light RatiosHI mass to
optical B band luminosity for
Abell 370 galaxies
Uppsala General Catalog
Local Super Cluster
(Roberts & Haynes 1994)
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HI Mass to Light RatiosHI mass to
optical B band luminosity for
Abell 370 galaxies
Uppsala General Catalog
Local Super Cluster
(Roberts & Haynes 1994)
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Galaxy HI mass vs
Star Formation Rate
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Galaxy HI Mass vs Star Formation Rate
HIPASS&
IRASdataz ~ 0
Doyle & Drinkwater
2006
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HI Mass vs Star Formation Rate in Abell 370all 168 [OII]
emission galaxies
line from Doyle &
Drinkwater 2006
Average
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HI Mass vs Star Formation Rate in Abell 370
81 blue [OII]
emission galaxies
line from Doyle &
Drinkwater 200687 red [OII]
emission galaxies
Average
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Star Formation Rate from
[OII] Emissionand
Radio Continuum Emission
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Radio Continuum vs. [OII] Star Formation Rate
all 168 [OII]
emission galaxies
line fromBell 2003
Average
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Radio Continuum vs. [OII] Star Formation Rate
line fromBell 2003
81 blue [OII]
emission galaxies
87 red [OII] emission galaxies
Average
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Conclusion
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• Abell 370, a galaxy cluster at redshift z = 0.37 (~4 billion years ago) contains significantly more HI gas than observed in similar nearby clusters
• however the galaxies in regions of higher density within Abell 370 have less gas than galaxies located in regions of lower density, the same trend seen in nearby galaxy clusters
• despite their high HI mass the galaxies around Abell 370 appear normal; they have HI Mass to Light Ratio and a Star Formation Rate to HI Gas correlation similar to that seen in nearby galaxies
Paper: Lah et al. 2009 MNRAS.399.1447L
Conclusion
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• Abell 370, a galaxy cluster at redshift z = 0.37 (~4 billion years ago) contains significantly more HI gas than observed in similar nearby clusters
• however the galaxies in regions of higher density within Abell 370 have less gas than galaxies located in regions of lower density, the same trend seen in nearby galaxy clusters
• despite their high HI mass the galaxies around Abell 370 appear normal; they have HI Mass to Light Ratio and a Star Formation Rate to HI Gas correlation similar to that seen in nearby galaxies
Paper: Lah et al. 2009 MNRAS.399.1447L
Conclusion
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• Abell 370, a galaxy cluster at redshift z = 0.37 (~4 billion years ago) contains significantly more HI gas than observed in similar nearby clusters
• however the galaxies in regions of higher density within Abell 370 have less gas than galaxies located in regions of lower density, the same trend seen in nearby galaxy clusters
• despite their high HI mass the galaxies around Abell 370 appear normal; they have HI Mass to Light Ratio and a Star Formation Rate to HI Gas correlation similar to that seen in nearby galaxies
Paper: Lah et al. 2009 MNRAS.399.1447L
Conclusion
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Additional Slides
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SKA pathfindersFor the Future
The SKA pathfinders ASKAP and MeerKAT can measure the HI 21-cm emission from galaxies out to redshift z = 1.0 using the coadding technique with existing optical redshift surveys.
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Colour – Mag Diagrams -all
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Colour – Mag Diagrams -inner
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WFI selection
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Abell 370 – R band imagesThumbnails
10’’ sq
324 galaxies with useful
redshifts (z~0.37)
Ordered by observed
R band magnitudes
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HI all spectrumall Abell 370 galaxies
neutral hydrogen gas measurement
using 324 redshifts – large smoothing
MHI = (6.6 ± 3.5) ×109 M
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HI Flux – All Galaxies
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HI blue outside x-ray gasblue galaxies outside of x-ray gas measurement of neutral hydrogen
gas content
using 94 redshifts – large smoothing
MHI = (23.0 ± 7.7) ×109 M
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HI Flux – Blue Galaxies Outside X-ray Gas
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HI 21cm emission at z > 0.1Telescope Redshift Obs
TimeNumber and HI Mass of galaxies
Who and When
WSRT z = 0.18 Abell 2218
200 hours 1 galaxy 4.8 109 M
Zwaan et al. 2001
VLA z = 0.19 Abell 2192
~80 hours 1 galaxy 7.0 109 M
Verheijen et al. 2004
WSRT two clusters at z = 0.19 &
z = 0.21420 hours
42 galaxies5109 to 41010 M
Verheijen et al. 2007
Arecibo z = 0.17 to 0.25
2 to 6 hours per
galaxy
26 galaxies(2 to 6) 1010 M
Catinella et al. 2007
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Average HI Mass
Comparisons with Coma
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Abell 370 and Coma Comparison
214 galaxies
324 galaxies
110 galaxies
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Abell 370 and Coma Comparison
214 galaxies
324 galaxies
110 galaxies
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Abell 370 and Coma Comparison
214 galaxies
324 galaxies
110 galaxies
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Why target moderate redshift clusters?
• the cluster core to the cluster outskirts are within the field of view of a radio telescope at moderate redshifts
• the number density of galaxies around a cluster is significantly higher than a typical field pointing
• the Butcher-Oemler effect
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Why target moderate redshift clusters?
• the cluster core to the cluster outskirts are within the field of view of a radio telescope at moderate redshifts
• the number density of galaxies around a cluster is significantly higher than a typical field pointing
• the Butcher-Oemler effect
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Why target moderate redshift clusters?
• the cluster core to the cluster outskirts are within the field of view of a radio telescope at moderate redshifts
• the number density of galaxies around a cluster is significantly higher than a typical field pointing
• the Butcher-Oemler effect