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Ice in the Galactic Center

Adam Ginsburg
University of Florida, Gainesville
Savannah Gramze, Nazar Budaiev, Brandt Gaches, Ash Barnes, Cara Battersby Alyssa Bulatek, Jonny Henshaw, Desmond Jeff, Xing "Walker" Lu, Betsy Mills, Dan Walker, Matt Ashby
Supported by the NSF: 2008101, 2206511, CAREER 2142300, STSCI grants 1905, 2221
Context: We use dust and molecular gas emission and absorption to infer mass.

Problem: What do dust and molecules really tell us about hydrogen?
Important for many questions: SFR vs gas, density of hadrons to collide, etc.
Battersby+2025: 3D-CMZ Paper I
There is a Galactic metallicity gradient, but the inner ~3 kpc are poorly constrained
The Brick is icy
Ginsburg+ 2023
https://cosmicds.github.io/minids/jwst-brick/
F466N F405N
The Brick is icy
Ginsburg+ 2023
https://cosmicds.github.io/minids/jwst-brick/
F466N F405N
Compare to a foreground cloud:
The dust ridge: Cloud B/C/D
... and a foreground cloud in front
We measure ice via stellar absorption
There are clear environmental differences
  • Smith+ 2025: 27 data points

Standard assumed carbon breakdown, roughly.
Standard assumed carbon breakdown, roughly.
Standard assumed carbon breakdown, roughly.
Standard assumed carbon breakdown, roughly.
The Smith+ 2025 measurements hint at nearly 100% of CO in ice
With measured GC CO ice column, the fraction of carbon in CO ice becomes uncomfortably large...
With measured GC CO ice column, the fraction of carbon in CO ice becomes uncomfortably large...
or even exceeds the total budget


With measured GC CO ice column, the fraction of carbon in CO ice becomes uncomfortably large...
or even exceeds the total budget
If $Z_{GC} = 2.5 Z_\odot$, the CO ice fraction goes back to normal ($\sim10-20$%).
(but some lines-of-sight still have $\sim$double that CO ice...)
There is more CO ice in the inner galaxy
(and two points make a line...)
CO ice abundance is correlated with metallicity
I have added to the problem:
  • What does CO tell us when it's 100% frozen out but we see it in the gas?
  • What does dust tell us if Z=2.5 Z$_\odot$?
    (probably gas-to-dust is lower by 2.5x 😬)
No solutions today, just a cautionary note.
The CMZ...
The CMZ by ACES...
The CMZ by ACES, with JWST today...
The CMZ by ACES, with JWST today
and later this year (legacy survey!)
The CMZ by ACES, with JWST today
and later this year (legacy survey!)
and Roman
The CMZ by ACES, with JWST today
and later this year (legacy survey!)
and Roman
The CMZ by ACES, with JWST today
and later this year (legacy survey!)
and Roman
  • The CMZ is icy.
  • Ice $\propto$ metal.
  • CMZ gas is metal rich (Z$\sim2.5$).
  • Ice varies (Savannah Gramze poster).
  • ACES is here!
  • JWST Legacy Survey coming!
  • Roman is coming!
  • Ask about the MUBLO and Sgr B2...
  • ... but first, lunch!
Papers:

The CMZ

$\sim10^8$ M$_\odot$ of gas in $\sim200$ pc, 10% of Galactic star formation
Image: NRAO, Ginsburg
Ginsburg+ 2018a
$>\frac{1}{3}$ of CMZ SF is in bound clusters (3-8$\times$ local)
$\sim$50% of CMZ SF occurs in the Sgr B2 cloud.

The Central Molecular Zone of the Galaxy represents one extreme of star forming conditions in the Galaxy

PPVII review: Henshaw, Barnes, Battersby, Ginsburg, Sormani, Walker
Sgr B2 with JWST/ NIRCam MIRI on MEERKAT: Ionized gas shows layers of the cloud
Budaiev+ 2025
MIRI reveals deeply embedded, feedback-heated gas
Budaiev+ 2025
MIRI 25 micron shows the outflow:
first IR light from within Sgr B2 N
Budaiev+ 2025
Sgr B2 N Accretion + Outflow: the most deeply embedded protocluster
Budaiev+ 2025: H$_2$O masers & SiO outflow
Schwörer+ 2019: Accretion along filaments: \(\sim0.1~\mathrm{M}_\odot \mathrm{yr}^{-1}\)
JWST found new HII regions:
the SFR is higher than estimated from radio
(remember Sgr B2 already accounts for $\sim$50% of the CMZ SFR)
R=770
G=(480-[410-405])
B=Brα
■ New HII regions
Budaiev+ 2025
There is an overall asymmetry in the star formation seen both in JWST (HII regions) and ALMA (embedded YSOs)
JWST shows the transition is sharp
What ALMA sees, JWST doesn't: 3/700 point source matches
(HII regions, outflow cavities do match)
What does this mean in context?
TBD, but it hints at an ongoing compression event
Budaiev+ 2025

The CMZ: ACES

The first complete survey of the CMZ with 2.4" resolution between ~2 microns and 10 cm. (previous best was ~15")
https://sites.google.com/view/aces-cmz/home
First five data papers submitted July 2025, refereed, resub in Nov 2025.
Six early result papers out: https://sites.google.com/view/aces-cmz/publications
Ask if you want to know more about the MUBLO