FLASHy galaxies in cosmological simulations
PHISCC 2025
Emily Kerrison
with Samuel Ward & Stephanie Tonnesen
University of Sydney/CSIRO Space & Astronomy
CCA Predoctoral Fellow (Spring 2025)
Credit: NOIRLab/NSF/AURA/M.
First results 2: FLASH detections dominated by young, compact radio galaxies
The ASKAP-FLASH Survey @ PHISCC 2025 | Elizabeth Mahony + Hyein Yoon
Image: Emily Kerrison
z=0.55
z=0.73
z=0.58
z=0.81
z=0.67
Redshift
OFFICIAL
OFFICIAL
First results 2: FLASH detections dominated by young, compact radio galaxies
The ASKAP-FLASH Survey @ PHISCC 2025 | Elizabeth Mahony + Hyein Yoon
Image: Emily Kerrison
z=0.55
z=0.73
z=0.58
z=0.81
z=0.67
Redshift
OFFICIAL
OFFICIAL
PS sources with RadioSED (Kerrison+2024)
4
Data at low and high frequencies to capture a (sometimes) complex Spectral Energy Distribution (SED)
PS sources with RadioSED (Kerrison+2024)
Data at low and high frequencies to capture a (sometimes) complex Spectral Energy Distribution (SED)
5
RadioSED provides automated SEDs using 23 wide area radio surveys (76MHz - 200GHz)
Bayesian model inference and comparison to identify different SED classes
~300,000 sources across the southern sky!
PS sources with RadioSED (Kerrison+2024)
Thanks to well documented sensitivities (and Bayesian statistics) – we can incorporate upper limits to discover more PS sources!
6
Stripe 82 – a test case (Kerrison+ submitted)
Stripe 82 with RadioSED
~300 deg2 equatorial field (20h-4h)
2,760 fittable radio sources (S888MHz ≥ 10mJy)
7
Radio sources (2,760)
Stripe 82 – a test case (Kerrison+ submitted)
Stripe 82 with RadioSED
~300 deg2 equatorial field (20h-4h)
2,760 fittable radio sources (S888MHz ≥ 10mJy)
8
Radio sources (2,760)
Known PS sources (12)
Stripe 82 – a test case (Kerrison+ submitted)
Stripe 82 with RadioSED
~300 deg2 equatorial field (20h-4h)
2,760 fittable radio sources (S888MHz ≥ 10mJy)
9
Radio sources (2,760)
Known PS sources (12)
New PS sources (359)
Stripe 82 – a test case (Kerrison+ submitted)
Stripe 82 with RadioSED
~300 deg2 equatorial field (20h-4h)
2,760 fittable radio sources (S888MHz ≥ 10mJy)
10
Radio sources (2,760)
Known PS sources (12)
New PS sources (359)
~13% of an untargeted field are PS
Stripe 82 – a test case (Kerrison+ submitted)
Stripe 82 with RadioSED
~300 deg2 equatorial field (20h-4h)
2,760 fittable radio sources (S888MHz ≥ 10mJy)
11
Radio sources (2,760)
Known PS sources (12)
New PS sources (359)
~13% of an untargeted field are PS
What about FLASH?
A specific population
12
Frequency
Flux
Frequency
Flux
Compact
Breakout
A specific population
21/30 FLASH detections are towards compact radio jets (≲ 1kpc) (from broadband SED shape)
≫ 70% of radio galaxies are extended on these scales (O’Dea 1998, Callingham+17, Kerrison+subm.)
13
Frequency
Flux
Frequency
Flux
Compact
Breakout
A specific population
21/30 FLASH detections are towards compact radio jets (≲ 1kpc) (from broadband SED shape)
≫ 70% of radio galaxies are extended on these scales (O’Dea 1998, Callingham+17, Kerrison+subm.)
14
Frequency
Flux
Frequency
Flux
Compact
Breakout
Why are most detections in an untargeted survey towards compact sources?
jet-ISM interactions (Morganti+23) OR selection effects
Why are most detections in an untargeted survey towards compact sources?
jet-ISM interactions (Morganti+23) OR selection effects
A cool view of radio AGN - simulations
We know exactly:
Why are most detections in an untargeted survey towards compact sources?
jet-ISM interactions (Morganti+23) OR selection effects
A cool view of radio AGN - simulations
We know exactly:
Why are most detections in an untargeted survey towards compact sources?
jet-ISM interactions (Morganti+23) OR selection effects
So we can find out what matters amongst:
Galaxy orientation
Radio luminosity
Jet morphology
The project: A cool view of radio AGN in cosmological simulations
Galaxy orientation
Radio luminosity
Jet morphology
The right tool for the job
Cosmological simulations
CAMELS collaboration, Thomas+21
The right tool for the job
Cosmological simulations
SIMBA (Dave+19)
CAMELS collaboration, Thomas+21
– Observations
+ Simulations (low jet power)
– Observations
+ Simulations (high jet power)
Finding the right galaxies
Observationally-motivated snapshot choice (z=0.4)
HI-rich galaxies → focus on gas distribution rather than presence/absence
Finding the right galaxies
Observationally-motivated snapshot choice (z=0.4)
HI-rich galaxies → focus on gas distribution rather than presence/absence
AGN jet hosts (Thomas+21)
For experts:
Ṁ > 0
0 < fEdd < 0.02
The range of galaxies
100 kpc
More disky
More complex
The range of galaxies
100 kpc
More disky
More complex
Plus 250 more!
“Observing” SIMBA radio galaxies I - radio flux
We add to SIMBA:
“Observing” SIMBA radio galaxies I - radio flux
We add to SIMBA:
Static jets
“Observing” SIMBA radio galaxies I - radio flux
We add to SIMBA:
Static jets
Discretised flux
“Observing” SIMBA radio galaxies I - radio flux
We add to SIMBA:
Static jets
Discretised flux
3D ray tracing through gas particles
“Observing” SIMBA radio galaxies I - radio flux
With physical parameters:
We add to SIMBA:
Static jets
Discretised flux
3D ray tracing through gas particles
“Observing” SIMBA radio galaxies I - radio flux
With physical parameters:
We add to SIMBA:
Static jets
Discretised flux
3D ray tracing through gas particles
Radiative transfer!
“Observing” SIMBA radio galaxies I - radio flux
With physical parameters:
FR0
(confined)
FRI
FRII
(breakout)
We add to SIMBA:
Static jets
Discretised flux
3D ray tracing through gas particles
Radiative transfer!
“Observing” SIMBA radio galaxies I - radio flux
With physical parameters:
FR0
(confined)
FRI
FRII
(breakout)
We add to SIMBA:
Static jets
Discretised flux
3D ray tracing through gas particles
Radiative transfer!
“Observing” SIMBA radio galaxies I - radio flux
With physical parameters:
FR0
(confined)
FRI
FRII
(breakout)
We add to SIMBA:
Static jets
Discretised flux
3D ray tracing through gas particles
Why are most detections in an untargeted survey towards compact sources?
jet-ISM interactions (Morganti+23) OR selection effects
Radiative transfer!
“Observing” SIMBA radio galaxies II - instrument effects
Simulated Absorption of Neutral Gas for Radio Astronomy
(SANGRiA - Ward, Kerrison & Tonnesen in prep.)
Jet
FR0
FRII
“Observing” SIMBA radio galaxies II - instrument effects
Simulated Absorption of Neutral Gas for Radio Astronomy
(SANGRiA - Ward, Kerrison & Tonnesen in prep.)
Jet
Pixelate
FR0
FRII
“Observing” SIMBA radio galaxies II - instrument effects
Simulated Absorption of Neutral Gas for Radio Astronomy
(SANGRiA - Ward, Kerrison & Tonnesen in prep.)
Jet
Pixelate
Convolve
FR0
FRII
“Observing” SIMBA radio galaxies II - instrument effects
Simulated Absorption of Neutral Gas for Radio Astronomy
(SANGRiA - Ward, Kerrison & Tonnesen in prep.)
Jet
Pixelate
Convolve
FR0
FRII
“Observing” SIMBA radio galaxies II - instrument effects
Simulated Absorption of Neutral Gas for Radio Astronomy
(SANGRiA - Ward, Kerrison & Tonnesen in prep.)
Simulated!
FLASH
“Observing” SIMBA radio galaxies II - instrument effects
Simulated Absorption of Neutral Gas for Radio Astronomy
(SANGRiA - Ward, Kerrison & Tonnesen in prep.)
Simulated!
FLASH
Using the same Bayesian FLASHfinder to identify detections (Allison+2012)
where do we see HI?
Where would we see FLASH detections?
Galaxy orientation matters
Compact radio source (FR0) → significant changes to line profile from galaxy
orientation alone
Galaxy orientation matters
Compact radio source (FR0) → significant changes to line profile from galaxy
orientation alone
Galaxy orientation matters
Compact radio source (FR0) → significant changes to line profile from galaxy
orientation alone
Edge-on
deepest line (highest NHI)
Face-on
shallow line, blueshifted outflow (AGN feedback!)
Radio luminosity also matters
0o
60o
90o
Radio luminosity also matters
0o
60o
90o
L ~ 5 x 1026 W Hz-1
L ~ 325 W Hz-1
L ~ 3 x 1026 W Hz-1
Radio luminosity also matters … across one galaxy
Radio luminosity also matters … across one galaxy
100 kpc
More disky
More complex
Plus 250 more!
Radio luminosity also matters … across all galaxies
1e20
LAGN [W Hz-1]
NHI [cm-2]
Detection fraction
1e21
1e22
1e23
1e24
l
l
l
l
l
1e24
1e25
1e26
1e27
l
l
l
l
Radio luminosity also matters … across all galaxies
1e20
LAGN [W Hz-1]
NHI [cm-2]
Detection fraction
1e21
1e22
1e23
1e24
l
l
l
l
l
1e24
1e25
1e26
1e27
l
l
l
l
It’s easy to see HI with:
high NHI
high LAGN
Does radio morphology matter?
1e20
LAGN [W Hz-1]
NHI [cm-2]
Detection fraction
1e21
1e22
1e23
1e24
l
l
l
l
l
1e24
1e25
1e26
1e27
l
l
l
l
FR0 / confined
0.5 kpc
FRII / breakout
10 kpc
Does radio morphology matter?
1e20
LAGN [W Hz-1]
NHI [cm-2]
Detection fraction
1e21
1e22
1e23
1e24
l
l
l
l
l
1e24
1e25
1e26
1e27
l
l
l
l
FR0 / confined
0.5 kpc
FRII / breakout
10 kpc
Does radio morphology matter?
1e20
LAGN [W Hz-1]
NHI [cm-2]
Detection fraction
1e21
1e22
1e23
1e24
l
l
l
l
l
1e24
1e25
1e26
1e27
l
l
l
l
FR0 / confined
0.5 kpc
FRII / breakout
10 kpc
Does radio morphology matter?
1e20
LAGN [W Hz-1]
NHI [cm-2]
Detection fraction
1e21
1e22
1e23
1e24
l
l
l
l
l
1e24
1e25
1e26
1e27
l
l
l
l
FR0 / confined
0.5 kpc
FRII / breakout
10 kpc
Not detected!
Conclusions & Future work
FLASH is more likely to detect HI when:
Conclusions & Future work
FLASH is more likely to detect HI when:
Future work:
Conclusions & Future work
FLASH is more likely to detect HI when:
Future work:
Questions? Get in touch emily.kerrison@sydney.edu.au
Conclusions & Future work
FLASH is more likely to detect HI when:
Future work:
Questions? Get in touch emily.kerrison@sydney.edu.au
… or hire me! :)
More info: Mock observations
ASKAP beam : 30’’
pixel scale : 5’’
Noise: 5mJy/beam after conv.
Spectra : brightest pixel
(SIMBA spatial res. ~1kpc
<< FLASH angular res.)
Line identification: Bayesian FLASHfinder (Allison+12) using Multinest
lnB >= 30 for secure detections (FLASH)
More info: luminosity distributions
But FLASH detections are intrinsically very luminous
We can apply the Thomas+21 prescription to SIMBA galaxies to determine radio luminosities
And it is well matched to observations of the general radio population
What about realistic samples?
From our uniform grid
What about realistic samples?
From our uniform grid
With a suitable target distribution
What about realistic samples?
From our uniform grid
With a suitable target distribution
We can obtain a realistic distribution with importance resampling
What about realistic samples?
From uniform inputs
What about realistic samples?
From uniform inputs
To matched outputs!
Does radio morphology matter?
LAGN [W Hz-1]
NHI [cm-2]
FR0 / confined
0.5 kpc
FRII / breakout
10 kpc
Does radio morphology matter?
LAGN [W Hz-1]
NHI [cm-2]
FR0 / confined
0.5 kpc
FRII / breakout
10 kpc
Expert easter egg: confined vs. breakout statistics
Number of observations does suggest the difference is significant!
FR0 / confined
FRII / breakout
The ASKAP-FLASH survey
First Large Absorption Survey in HI (Allison+2022):
Image credit: Hyein Yoon
30,000 deg2, Dec < +15o
(excluding galactic plane)
The ASKAP-FLASH survey
First Large Absorption Survey in HI (Allison+2022):
~20’’ spatial, ~10km/s spectral resolution
0.4 < z < 1 HI absorption
in sources > 40mJy
Image credit: Hyein Yoon
20’’
30,000 deg2, Dec < +15o
(excluding galactic plane)