CHUN-HAO TO PRO
I am a cosmologist!
*chto@uchicago.edu
Arxiv: 2509.20458
First Weak Lensing Detection of Spectroscopically Confirmed Dwarf Galaxies
Chun-Hao To*,
Chihway Chang, Dhayaa Anbajagane, Risa H. Wechsler, Alex Drlica-Wagner, and DELVE collaboration
First Weak Lensing Detection of Spectroscopically Confirmed Dwarf Galaxies
Chun-Hao To*,
*chto@uchicago.edu
Chihway Chang, Dhayaa Anbajagane, Risa H. Wechsler, Alex Drlica-Wagner, and DELVE collaboration
Arxiv: 2509.20458
Dwarf galaxy lensing with Decade
Chun-Hao To*, and others
*chto@uchicago.edu
What I usually work on
Cosmology
Baryon feedback
Cosmological simulations
To+ 21ab,22,25ab
To+ 24, Dalal,To+25
To+ 23 https://chunhaoto.com/cardinalsim/
What I will talk today
5 arcmin
Galaxy-halo connection probes many astrophysics
To+ 2020 (CL)
Lin+04, Wechsler&Tinker+18, Behroozi+18, Kravtsov+18, To+20, Manwadkar+21, Kravstov+22 .... many others
AGN
AGN
AGN
Supernovae
Supernovae
Stellar winds
Weak lensing measures the total matter profiles
Weak lensing measures the total matter profiles
Weak lensing measures the total matter profiles
Weak lensing measures the total matter profiles
Weak lensing measures the total matter profiles
Halo Mass
Weak lensing measures the total matter profiles
Satellite fraction
Weak lensing measures the total matter profiles
Satellite fraction
Halo Mass
-
But weak lensing is weak.
-
S/N ~2% for
-
Weaker for low-mass objects.
-
\sigma_v \simeq 120~\rm{km}~{\rm{sec}}^{-1}
Needs lots of lens and source galaxies!
Dwarf galaxy detection are hard
Mao+24
DECADE + DESI*
*https://data.desi.lbl.gov/doc/releases/dr1/vac/extragalactic-dwarfs/, Manwadkar, Wechsler+ in prep.
DECADE + DESI*
*https://data.desi.lbl.gov/doc/releases/dr1/vac/extragalactic-dwarfs/, Manwadkar, Wechsler+ in prep.
DECADE + DESI*
*https://data.desi.lbl.gov/doc/releases/dr1/vac/extragalactic-dwarfs/, Manwadkar, Wechsler+ in prep.
DECADE + DESI*
*https://data.desi.lbl.gov/doc/releases/dr1/vac/extragalactic-dwarfs/, Manwadkar, Wechsler+ in prep.
DECADE + DESI*
*https://data.desi.lbl.gov/doc/releases/dr1/vac/extragalactic-dwarfs/, Manwadkar, Wechsler+ in prep.
DECADE + DESI*
*https://data.desi.lbl.gov/doc/releases/dr1/vac/extragalactic-dwarfs/, Manwadkar, Wechsler+ in prep.
Lens galaxy selection
To+25
Mass profile around dwarfs
\red{S/N=12.4}
\red{S/N=5.6}
To+25
Mass profile around dwarfs
Systematics?
Measurement systematics
Photometry
Shredding
Blanton+05, Mao+21, many others
Measurement systematics
Stellar mass estimation
de los Reyes+25, Zou+24,...
Photometry
Shredding
Blanton+05, Mao+21, many others
Measurement systematics
Stellar mass estimation
de los Reyes+25, Zou+24,...
Robust to stellar mass estimation
To+25
Photometry Shredding
Fracflux: fraction of flux from other sources
Fiducial analysis: Fracflux<0.2
Robust to photometry shredding
To+25
Fiber incompleteness
3 arcmin
~= 150 kpc @ z=0.04
Fiber incompleteness
Less likely to all get fiber assigned
More likely to all get fiber assigned
240 kpc for
Satellite galaxies
Isolated galaxies
M=10^{11} M_\odot
Fiber incompleteness impacts the measurement
To+25
Fiber incompleteness impacts the measurement
To+25
Fiber incompleteness correction
In every observation, DESI logs the total count of potential objects that might have received fibers.
Individual inverse probability weight (IIP)
= \frac{1}{\rm Number\ of\ potential\ objects}
Bianchi+ 18, Lange+ 24, Ross+ 25, Lasker+ 25
Title Text
Lange+ 24IIP weights correct the fiber incompleteness issue
To+25
Data shows similar trend to sims
Inferences: a simulation based model
Inferences: a simulation based model
P(\log M_* | \log M_{\rm peak}) = \\ \mathcal{N}\left(\log \textcolor{teal}{M_{11}}+\textcolor{teal}{\alpha}(\log M_{\rm peak}-11), \textcolor{teal}{\sigma_{\log M}}\right)
\textcolor{teal}{f_{\rm{sat},l}}, \textcolor{teal}{f_{\rm{sat},h}}
control satellite fraction in each stellar mass bin
Inferences: a simulation based model
P(\log M_* | \log M_{\rm peak}) = \\ \mathcal{N}\left(\log \textcolor{teal}{M_{11}}+\textcolor{teal}{\alpha}(\log M_{\rm peak}-11), \textcolor{teal}{\sigma_{\log M}}\right)
\textcolor{teal}{f_{\rm{sat},l}}, \textcolor{teal}{f_{\rm{sat},h}}
control satellite fraction in each stellar mass bin
Inferences: a simulation based model
MCMC
P(\log M_* | \log M_{\rm peak}) = \\ \mathcal{N}\left(\log \textcolor{teal}{M_{11}}+\textcolor{teal}{\alpha}(\log M_{\rm peak}-11), \textcolor{teal}{\sigma_{\log M}}\right)
\textcolor{teal}{f_{\rm{sat},l}}, \textcolor{teal}{f_{\rm{sat},h}}
control satellite fraction in each stellar mass bin
Inferences: a simulation based model
MCMC
P(\log M_* | \log M_{\rm peak}) = \\ \mathcal{N}\left(\log \textcolor{teal}{M_{11}}+\textcolor{teal}{\alpha}(\log M_{\rm peak}-11), \textcolor{teal}{\sigma_{\log M}}\right)
\textcolor{teal}{f_{\rm{sat},l}}, \textcolor{teal}{f_{\rm{sat},h}}
control satellite fraction in each stellar mass bin
20% priors on galaxy number density according to DESI SMF (Xu+25)
Weak lensing measures the total matter profiles
Satellite fraction
Halo Mass
Weak lensing measures the total matter profiles
Satellite fraction
Halo Mass
Stellar mass–Halo mass relation
Stellar mass–Halo mass relation
Stellar mass–Halo mass relation
Weak lensing measures the total matter profiles
Satellite fraction
Halo Mass
Satellite fraction
Satellite fraction
Satellite fraction
Satellite fraction
Satellite fraction
Satellite fraction
S/N=12.4, 5.6
Arxiv: 2509.20458
dwarf_NW_20250925
By CHUN-HAO TO
