Measuring the Gas in Galaxies in the Distant Past
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Transcript of Measuring the Gas in Galaxies in the Distant Past
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Measuring the Gas in Galaxies in the Distant Past
Philip Lah
Too late. Here comes
the SKA.
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Who am I?
• I am astronomer with a joint appointment at the:
National Centre for Radio Astrophysics,
Tata Institute of Fundamental Research, India
and the
Research School of Astronomy & Astrophysics,
Mount Stromlo Observatory,
Australian National University
• I use both radio and optical telescopes for my research
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Atmospheric TransmissionA
tmos
pher
ic O
paci
ty
0 %
50 %
100 %
1 nm 1 μm 1 mm 1 m 1 km
Wavelength →← Frequency
radio
optical
infraredgamma rays, X-rays
& ultraviolet
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Hydrogen Gasin the
Universe
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Hydrogen Gas in the Universe
Hydrogen 76% by mass of the baryons – normal matter
(that is not the weird stuff – Dark Matter)
Neutral Atomic
Hydrogen Gas
produces emission at a wavelength of 21 cm
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Hydrogen Gas in the Universe
Hydrogen 76% by mass of the baryons – normal matter
(that is not the weird stuff – Dark Matter)
Neutral Atomic
Hydrogen Gas (HI)
produces emission at a wavelength of 21 cm
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21 cm
Atmospheric TransmissionA
tmos
pher
ic O
paci
ty
0 %
50 %
100 %
1 nm 1 μm 1 mm 1 m 1 km
Wavelength →← Frequency
radio
optical
infraredgamma rays, X-rays
& ultraviolet
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HI 21-cm Emission From Galaxies
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Galaxy M33: optical
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Galaxy M33: HI 21-cm emission
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Galaxy M33: optical and HI
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Galaxy M33: optical
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Why Study Neutral Atomic Hydrogen Gas?
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HI Gas and Star Formation
neutral atomic hydrogen gas
cloud (HI)
molecular gas cloud (H
2)
star formation
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Redshift, Observing the Past
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The Expanding Universe
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Hubble`s Lawredshift velocity related to distance
distance related to age(due to light travel time)
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Hubble`s Lawredshift velocity related to distance
distance related to age(due to light travel time)
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21 cm
Atmospheric TransmissionA
tmos
pher
ic O
paci
ty
0 %
50 %
100 %
1 nm 1 μm 1 mm 1 m 1 km
Wavelength →← Frequency
radio
optical
infraredgamma rays, X-rays
& ultraviolet
redshifted
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The History of
Star Formation in the Universe
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Star Formation Rate Density
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Star Formation Rate Density
~10 times current rate
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The Amount of
HI Gas in the Universe
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HI Gas Density
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HI Gas Density
~2 times current density
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HI Gas Density
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HI Gas Density
region where I have been
working
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Current Observations
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Giant Metrewave Radio Telescope
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Giant Metrewave Radio Telescope
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Coadding HI signals
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Coadding HI signals
RA
DEC
Radio Data Cube
Frequen
cy
HI red
shift
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Coadding HI signals
RA
DEC
Radio Data Cube
Frequen
cy
HI red
shift
positions of optical galaxies
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Coadding HI signals
frequency
flux
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Coadding HI signals
frequency
flux
z2
z1
z3
z1, z2 & z3 optical redshifts
of galaxies
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Coadding HI signals
velocity
z1
z2
z3
flux
z1, z2 & z3 optical redshifts
of galaxies
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Coadding HI signals
velocity
z1
z2
z3
flux
velocity
Coadded HI signal
z1, z2 & z3 optical redshifts
of galaxies
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My Current Best Observation
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HI blue outside x-ray gasblue galaxies surrounding the core of a large galaxy cluster
galaxies observed as they were 4 billion years
ago
coadding signal from 94 galaxies
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HI blue outside x-ray gasblue galaxies surrounding the core of a large galaxy cluster
galaxies observed as they were 4 billion years
ago
coadding signal from 94 galaxies
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Future Observations
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The SKA and Me
• SKA`s collecting area 20GMRT`s collecting area
• SKA better receivers
• SKA larger field of view
• SKA better RFI environment
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The SKA and Me• my current research looking at galaxies 3 to 4 billion years ago –
SKA directly detect HI signal
• originally SKA proposed to detect HI gas from 8 billion years ago
• stacking with SKA ~12.7 billion years ago, the era of first galaxies
SKA
fully operational
2024
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The SKA pathfinders
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MeerKAT
South African SKA pathfinder
• 13.5 m diameter dishes
• 64 dishes
• finished 2014 (2018)
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ASKAP• 12 m diameter dishes
• 30 dishes
• focal plane array
• finished 2013