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Measuring the Gas in Galaxies in the Distant Past Philip Lah
Too late. Here comes the SKA.


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


Atmospheric Transmission
optical
gamma rays, X-rays & ultravio let infrared radio

Atmospheric Opacity

100 % 50 %
0% 1 nm 1 m 1 mm 1m 1 km

Wavelength Frequency


Hydrogen Gas in the Universe


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


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


Atmospheric Transmission
optical
gamma rays, X-rays & ultravio let infrared radio

Atmospheric Opacity

100 % 50 %
0% 1 nm 1 m 1 mm 1m 1 km

Wavelength Frequency

2 1 cm


HI 21-cm Emission From Galaxies


Galaxy M33: optical


Galaxy M33: HI 21-cm emission


Galaxy M33: optical and HI


Galaxy M33: optical


Why Study Neutral Atomic Hydrogen Gas?


HI Gas and Star Formation

neutral atomic hydrogen gas cloud (HI)

molecular gas cloud (H2)

star formation


Redshift, Observing the Past



The Expanding Universe


Hubble`s Law redshift velocity related to distance distance related to age (due to light travel time)


Hubble`s Law redshift velocity related to distance distance related to age (due to light travel time)


Atmospheric Transmission
optical
gamma rays, X-rays & ultravio let infrared radio

Atmospheric Opacity

100 % 50 %
0% 1 nm 1 m 1 mm

redshifted

1m

1 km

Wavelength Frequency

2 1 cm


The History of Star Formation in the Universe


Star Formation Rate Density


Star Formation Rate Density

~10 times current rate


The Amount of HI Gas in the Universe


HI Gas Density


HI Gas Density

~2 times current density


HI Gas Density


HI Gas Density

region where I have been working


Current Observations


Giant Metrewave Radio Telescope


Giant Metrewave Radio Telescope


Coadding HI signals


Coadding HI signals
Radio Data Cube

DEC

RA


Coadding HI signals
Radio Data Cube

DEC
positions of optical galaxies

RA


Coadding HI signals

flux

frequency


z1

Coadding HI signals

z2

flux

z3

frequency

z1, z2 & z3 optical redshifts of galaxies


Coadding HI signals
z1

z2

flux

z3

velocity

z1, z2 & z3 optical redshifts of galaxies


Coadding HI signals
z1

z2

Coadded HI signal

flux

z3

velocity z1, z2 & z3 optical redshifts of galaxies

velocity


My Current Best Observation


HI blue outside x-ray gas blue

galaxies surrounding the core of a large galaxy cluster

galaxies observed as they were 4 billion years ago

coadding signal from 94 galaxies


HI blue outside x-ray gas blue

galaxies surrounding the core of a large galaxy cluster

galaxies observed as they were 4 billion years ago

coadding signal from 94 galaxies


Future Observations


The SKA and Me
· SKA`s collecting area 20GMRT`s collecting area · SKA better receivers · SKA larger field of view · SKA better RFI environment


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


The SKA pathfinders


MeerKAT

South African SKA pathfinder

· 13.5 m diameter dishes
· 64 dishes · finished 2014 (2018)


ASKAP
· 12 m diameter dishes · 30 dishes · focal plane array · finished 2013