Hubble image o compac dwa galaxy SBS 1415+437.
B idging Simula ions and Obse a ions:
Towa ds Nex -Gene a ion S udies o
Dwa Galaxy S uc u e wi h LSST
LSST@Eu ope7 2025/09/15
Ga e h Ma in*,Aa on Wa kins, Yohan Dubois, Suga a Ka i aj, Duho
Kim, Ka a ina K ajic, Ilin Laza , F aze Pea ce, Sebas ien Pei ani,
Ch is ophe Pichon, Sukyoung Yi, Julien De iend , Ad ianne Slyz
*Uni e si y o No ingham ([email p o ec ed])
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Laza +(2024 a,b)
Low-mass galaxies as Labo a o ies o Galaxy E olu ion
• Dwa s do no appea o be solely an
ex ension o high-mass popula ions
• Some mo phological ea u es p esen in he
high-mass egime ex end o dwa galaxies
• Bu we also obse e dwa s wi h
mo phologies and s uc u al p ope ies
only ound in he low-mass egime
(Laza +2024a, 2024b)
• Cosmological simula ions a e uned o
ep oduce high mass galaxy popula ions,
bu no he low mass Uni e se, which is
obse a ionally incomple e
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Low-mass galaxies as Labo a o ies o Galaxy E olu ion
Wa kins+2025
• Dwa s do no appea o be solely an
ex ension o high-mass popula ions
• Some mo phological ea u es p esen in he
high-mass egime ex end o dwa galaxies
• Bu we also obse e dwa s wi h
mo phologies and s uc u al p ope ies
only ound in he low-mass egime
(Laza +2024a, 2024b)
• Cosmological simula ions a e uned o
ep oduce high mass galaxy popula ions,
bu no he low mass Uni e se, which is
obse a ionally incomple e
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Low-mass galaxies as Labo a o ies o Galaxy E olu ion
• Deep-wide imaging e eals ha p e ious wide-a ea
su eys (e.g. SDSS) missed many low-mass galaxies
due o su ace b igh ness limi s.
• e.g. “Ul a-di use galaxies” ( an Dokkum+2015)
highligh signi ican selec ion biases in pas
obse a ions.
• Biased owa ds he mos s a - o ming objec s
(Ka i aj+2025)
• Dwa galaxies a e e y sensi i e o eedback and
en i onmen al p ocesses due o shallow po en ial
wells
• S ella eedback
• Indica ion ha AGN play some ole (e.g.
Reines+2013,Ka i aj+2019,Bichang'a+2024)
• In e ac ions wi h en i onmen
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
A New E a o Obse a ions and Simula ions
C edi : P ince on Uni e si y/HSC P ojec
• Nex -gene a ion su eys (Rubin, Euclid,
JWST) a e e olu ionizing ou iew o low-
mass galaxies wi h unp eceden ed dep h.
• The COSMOS ield (HSC-SSP) p o ides
one o he deepes cu en da ase s o
s udying ain dwa s (μi(3σ, 10″×10″) > 31
mag a csec-2).
• Cosmological simula ions (e.g.
NewHo izon, TNG50, FIREbox) now
esol e low-mass galaxies o e ela i ely
la ge olumes.
• Fo wa d modelling allows di ec
compa ison be ween eal and simula ed
galaxies.
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
A New E a o Obse a ions and Simula ions
C edi : Y. Dubois, H. Choi
• Nex -gene a ion su eys (Rubin, Euclid,
JWST) a e e olu ionizing ou iew o low-
mass galaxies wi h unp eceden ed dep h.
• The COSMOS ield (HSC-SSP) p o ides
one o he deepes cu en da ase s o
s udying ain dwa s (μi(3σ, 10″×10″) > 31
mag a csec-2).
• Cosmological simula ions (e.g.
NewHo izon, TNG50, FIREbox) now
esol e low-mass galaxies o e ela i ely
la ge olumes.
• Fo wa d modelling allows di ec
compa ison be ween eal and simula ed
galaxies.
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Simula ions
NewHo izon (Dubois+2021)
TNG50 (Nelson+2019, Pillepich+2019)
Code
RAMSES (AMR)
AREPO (mo ing mesh)
Volume
Zoom-in o 20 Mpc sphe ical
egion om Ho izon-AGN
50 Mpc box
Resolu ion
~1.3×10⁴ M☉(s a s), ~34 pc
(spa ial)
~8.5×10⁴ M☉(s a s/gas), 100–140 pc
(spa ial)
En i onmen
Co e age
Field and g oup (max halo
~10¹³ M☉)
Field, g oup & poo clus e s (~10¹⁴ M☉)
S a Fo ma ion
Tu bulence- egula ed
Schmid law
ISM Physics
Mul iphase ISM
Idealised wo-phase model
SN Feedback
Mechanical eedback om SN
Type II (Kimm & Cen 2014)
Di ec hea ing + delayed kine ic winds
(Sp ingel & He nquis 2003)
Ex as
MHD
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Obse a ions
We use da a om he COSMOS ield, suppo ed by deep Hype Sup ime-
Cam (HSC) imaging:
•COSMOS2020 (Wea e +2021)
• P o ides s ella masses, edshi s, and es - ame p ope ies ia comp ehensi e (40-
band) mul iwa eleng h pho ome y.
• Pho ome ic edshi s each <1% p ecision o b igh sou ces.
•HSC-SSP Imaging (Aiha a+2019)
• Deep i-band imaging (μ ≈ 31 mag a csec⁻²) o e he cen al 1.5° o COSMOS.
• We use he DR2 deepCoadd images o p ese e ex ended lux.
• COSMOS p obes ela i ely a e age en i onmen s, wi h a galaxy numbe densi y
simila o TNG50 and NewHo izon olumes a 0.05 < z < 0.3.
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Connec ing Obse a ions and Theo y
• Galaxy mo phology encodes key in o ma ion abou o ma ion his o y,
eedback, and en i onmen .
• Mo phological compa isons be ween obse a ions and simula ions help es
physical p esc ip ions.
• In his wo k, we:
• Gene a e ealis ic syn he ic HSC-like images om TNG50 and
NewHo izon.
• Measu e s uc u al p ope ies o COSMOS dwa galaxies.
• Compa e s uc u al di e si y ac oss obse ed and simula ed samples.
• Ou aim: o assess how well cu en simula ions ep oduce he di e si y o
dwa galaxy s uc u e, and wha his e eals abou eedback and ISM
physics.
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Mass E olu ion T ends Di e
• A high mass end (~109.5 M☉), simula ions begin o con e ge
owa d obse ed alues bu s ill di e sys ema ically
•TNG50:
• S ong inc ease in concen a ion and Sé sic index wi h
mass. La ge disc epancy wi h bo h NewHo izon and
COSMOS
•NewHo izon:
• Remains somewha oo di use e en a highe masses
•COSMOS dwa s:
• Weak ends wi h mass — s uc u al p ope ies a e
ela i ely s able
• Much be e ag eemen has been shown a highe masses (e.g.
Dubois 2021, Wang & Lilly 2023)
•Highligh s limi a ions in how eedback and s a o ma ion scale
in simula ions.
Ma in e al 2025, NRAS 541 1831
Feedback & ISM Physics D i e Di e gence
•TNG50:
• Smoo h ISM, con inuous s a o ma ion, SN eedback, and MHD p ocesses → e en ion o low AM
gas
• P omo es cen al gas accumula ion → compac , concen a ed s uc u es
• Insu icien angula momen um edis ibu ion leads o o e ly compac galaxies
•NewHo izon:
• Mul iphase ISM, bu s y s a o ma ion, local SN eedback → low angula momen um gas ejec ed
om cen al egions
• E icien edis ibu ion o gas esul s in mo e di use, i egula galaxies
•Impac o Feedback:
•NewHo izon’s bu s y SF leads o i egula mo phologies and less compac s uc u es
•TNG50’s con inuous SF esul s in smoo he , mo e compac galaxies. Di e ences also in luenced
by esolu ion, PSF biases, and en i onmen
•Feedback and ISM models, no esolu ion o obse a ional bias, a e p ima y d i e s.
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Summa y
Ma in e al 2025, NRAS 541 1831
•S uc u al Di e ences:
•Low-mass galaxies a e highly sensi i e o ISM, s a o ma ion, and eedback implemen a ions
• Rep oducing global obse ables (e.g. s ella mass unc ions) isn' su icien — esol ed mo phology
adds c ucial cons ain s especially gi en apa en degene acies be ween models in ep oducing
in eg a ed p ope ies like s ella mass (W igh +2024).
•NewHo izon: P oduces di use, ex ended galaxies wi h low concen a ion,bu s ie s a o ma ion
•TNG50: P oduces compac , concen a ed galaxies wi h high cen al densi y,smoo he s a o ma ion
•Feedback and ISM Physics:
•NewHo izon: Bu s ie SF, dynamic ISM leads o mo e asymme ic and less compac galaxies as low AM
gas ejec ed e icien ly
•TNG50: Con inuous SF wi h eedback uncoupled om he cen al pa s o galaxies, smoo h ISM esul s in
mo e compac , concen a ed s uc u es
•Disc epancy wi h Obse a ions:
• Bo h simula ions show di e gen ends compa ed o obse ed COSMOS dwa galaxies, wi h nei he ully
cap u ing he obse ed s uc u al di e si y
• S uc u al misma ch in dwa s is a powe ul diagnos ic o sub-g id physics in simula ions
•Fu u e Insigh s:
•Nex -gene a ion su eys like LSST and Euclid will p o ide la ge , deepe and highe - esolu ion da ase s
o cons ain and e ine simula ions and be e unde s and he physical mechanisms d i ing dwa galaxy
e olu ion.
ga e h.ma in@no ingham.ac.uk
Summa y
•S uc u al Di e ences:
•Low-mass galaxies a e highly sensi i e o ISM, s a o ma ion, and eedback implemen a ions
• Rep oducing global obse ables (e.g. s ella mass unc ions) isn' su icien — esol ed mo phology
adds c ucial cons ain s especially gi en apa en degene acies be ween models in ep oducing
in eg a ed p ope ies like s ella mass (W igh +2024).
•NewHo izon: P oduces di use, ex ended galaxies wi h low concen a ion,bu s ie s a o ma ion
•TNG50: P oduces compac , concen a ed galaxies wi h high cen al densi y,smoo he s a o ma ion
•Feedback and ISM Physics:
•NewHo izon: Bu s ie SF, dynamic ISM leads o mo e asymme ic and less compac galaxies as low AM
gas ejec ed e icien ly
•TNG50: Con inuous SF wi h eedback uncoupled om he cen al pa s o galaxies, smoo h ISM esul s in
mo e compac , concen a ed s uc u es
•Disc epancy wi h Obse a ions:
• Bo h simula ions show di e gen ends compa ed o obse ed COSMOS dwa galaxies, wi h nei he ully
cap u ing he obse ed s uc u al di e si y
• S uc u al misma ch in dwa s is a powe ul diagnos ic o sub-g id physics in simula ions
•Fu u e Insigh s:
• This pilo s udy is e y limi ed by su ey a ea. LSST will p o ide a wide da ase s down o simila dep h o
cons ain and e ine simula ions and be e unde s and he physical mechanisms d i ing dwa galaxy
e olu ion.
Ma in e al 2025, NRAS 541 1831 ga e h.ma in@no ingham.ac.uk
Addi ional slides
Pa ame e ize galaxy s a o ma ion his o y acco ding o hei o ma ion
ime and le el o bu s iness
NewHo izon galaxies ha e mo e bu s y SFHs and o med ea lie
No e olu ion in SFH obse ed as a unc ion o mass o TNG-50 dwa
galaxies
Bu s y SF
Cons an SF
Fo med ea ly
Fo med la e
S a o ma ion his o y
Pa ame e ize galaxy s a o ma ion his o y acco ding o hei o ma ion
ime and le el o bu s iness
NewHo izon galaxies ha e mo e bu s y SFHs and o med ea lie
No e olu ion in SFH obse ed as a unc ion o mass o TNG-50 dwa
galaxies
We can measu e he le el o co ela ion be ween SFH and isual
simila i y
S a o ma ion his o y
Pa ial co ela ions
Co ela ion be ween he isual appea ance o simula ed galaxies and
hei s a - o ma ion his o ies is seen, e en con olling o mass and
en i onmen .
Unde s anding his link is key o unde s anding he di e ing dwa
galaxy p ope ies be ween he wo simula ions
Obse e gene al co ela ion be ween mo e isually simila galaxies a e
mo e likely ha e simila s a - o ma ion his o ies
When con olling o en i onmen only TNG-50 shows a dec ease in
s eng h o co ela ion
Co ela ion o mo phology and SFH wi h local densi y disappea s when
es ic ed o less dense en i onmen s – domina ed by in e nal
p ocesses in he ield
S a o ma ion his o y s isual simila i y
