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Astrochemistry as a tool to study Star Formation in the Galaxy

Adam Ginsburg
Associate Professor
Department of Astronomy
University of Florida, Gainesville
  • Postdocs: Miriam Garcia Santa Maria (2024-), Allison Towner (2020-2023)
  • PhD: Desmond Jeff, Theo Richardson, Alyssa Bulatek, Nazar Budaiev, Savannah Gramze, Taehwa Yoo
  • Postbac: Derod Deal, Aden Dawson
  • Supported by NSF 2008101, 2206511, CAREER 2142300, STSCI 1905, 2221, 3523, 5365, 6151, Astropy
Collaborators: John Bally, Ashley Barnes, Cara Battersby, Roberto Galván-Madrid, Jonathan Henshaw, J. M. Diederik Kruijssen, Steven Longmore, Xing Lu, Fanyi Meng, Elisabeth A.C. Mills, Juergen Ott, Justin Otter, Álvaro Sánchez-Monge, Peter Schilke, Daniel Walker, Erik Rosolowsky, Eric Koch, Ciriaco Goddi, Brett McGuire, Dick Plambeck, Melvyn Wright, Johan van der Walt, Henrik Beuther, Kei Tanaka, Yichen Zhang, the ALMA-IMF team (Timea Csengeri, Fabien Louvet, Nichol Cunningham, Frederique Motte, Patricio Sanhueza, Thomas Nony, Yohan Pouteau, Melisse Bonfand, Fernando Olguin, Sylvain Bontemps, and many others), and the ACES team
Slides available at https://keflavich.github.io/talks/colloquium_Oct2024_UGA.html or from my webpage →talks

Star formation drives the evolution of the universe

NASA/WMAP

Star Formation oversimplified

Ṁ
The star formation rate, i.e., how much gas turns to stars
L / M
The light per unit mass, i.e., how stars and stellar populations turn matter into light

High-mass stars produce photons & heavy elements
low-mass stars live practically forever

Point color shows effective temperature, point size shows luminosity (left) and mass (right)
Ekström+ 2012 models, vendian.org colors, www.tinyurl.com/HR-figure

The stellar initial mass function (IMF)

Stars are sampled from this distribution
(but it's not universal)
Hopkins 2018
https://tinyurl.com/IMF-figure
https://tinyurl.com/IMF-figure
https://tinyurl.com/IMF-figure
High-mass stars populate the stellar graveyard

Almost all of the light in star-forming galaxies is produced by high-mass stars

NASA/GALEX via wikipedia

The stars form in and from gas (as traced by dust)

Herschel

Most of what we know of star formation in detail comes from small local clouds

Herschel/Palmeirim+ 2013

Most of what we know of star formation in detail comes from small local clouds

ESO/DSS2, De Martin

Cartoon of isolated low-mass star formation

original cartoon by Cormac Purcell, modified by AG

A molecular cloud collapses and fragments

The core forms a central protostar

The protostar heats its parent core and forms a disk

It drives an outflow and consumes (or runs from or blows out) its core

Eventually, you end with just a star-disk system

Cartoon of isolated low-mass star formation

original cartoon by Cormac Purcell, modified by AG

The isolated cartoon is wrong in several ways

Cores fragment. Massive stars cook their neighbors in hot cores.

Most of what we know of star formation in detail comes from small local clouds

ESO/DSS2, De Martin
Briceño+ 2002
They contain only low-mass stars and do not represent star formation in general

Most stars form in denser regions

HST
NGC 3603 is a high-mass (104 M⊙) cluster
Lada & Lada 2003:
5-10% in bound clusters
in our Galaxy

High-mass clusters have top-heavier IMFs

Hosek+ 2019
https://tinyurl.com/IMF-figure

More stars formed in clusters in the early universe

Mowla+ 2022
Two ALMA large programs probe these conditions:
ALMA-IMF:
  • 15 High-mass protoclusters probing young (few stars) to old (blowing out gas)
  • Two ALMA bands looking at cold gas & dust
  • Data published, analysis ongoing
ACES:
  • The whole Galactic Center, with low-SF and high-SF clouds
  • One ALMA band, biggest mosaic made.
  • Data all delivered, mostly reduced
Are top-heavy IMFs limited to clusters?
NGC 3603 & Westerlund 1
HST
Guarcello+ 2024 EWOCS

SSCs are common in starburst nuclei and drive galactic outflows

NGC 253 protoclusters (Leroy+2018)
NGC 4945 protoclusters (Emig+2020)

Star formation drives the evolution of the universe

Most stars in most galaxies formed long ago
Madau 2014

Galaxies were smaller & denser back then

Conselice 2014
STSCI; Pappovich, Ferguson, Faber, Labbe
...or does the IMF vary with Galactic environment?

Big Questions in Star Formation

I'll highlight incremental progress toward answering some of these
spiced with a few intriguing discoveries

  • How does the IMF vary, and what controls its variation?
  • What controls the star formation rate in galaxies?
  • When and how do planets form?
  • How does stellar clustering affect each of these?
Questions in Star Formation
  1. What initiates star formation?
  2. What Processes Govern Protostellar Evolution and Determine the Stellar Mass and Rotation Rate?
  3. How do Massive Stars Form?
  4. What is Lifetime of Molecular Clouds (and the Duration of Star Formation)?
  5. What Physics Determines the Initial Mass Function?
  6. What Physics Regulates the Rate & Efficiency?
  7. What Role Does Environment Play in Star and Planet Formation?
  8. What Physics Regulates Star Formation in Clusters?
  9. How homogeneous are clusters?
  10. What is the role of feedback (outflow, radiation, wind, etc) in star formation?
  11. What is the role of disks in star and planet formation?
  12. How do multiple systems form?




Goal: Measure number of forming stars at each mass
to answer: How does the IMF form?

Tools: Light emission and absorption by dust and molecules

Our Galaxy

Gaia star colors via ESA

Our Galaxy

2MASS via IPAC

Our Galaxy

Planck + HI4PI via lambda.gsfc.nasa.gov

Our Galaxy

Planck + HI4PI via lambda.gsfc.nasa.gov
Astrochemistry as a tool: what do molecules trace?
Astrochemistry as a tool: what do molecules trace?

Our Galaxy

HI: "Diffuse" gas
HI4PI
Astrochemistry as a tool: what do molecules trace?

Our Galaxy

CO: molecular gas
Planck
Astrochemistry as a tool: what do molecules trace?

Our Galaxy

Dust
Planck

Astronomers' view of Dust

  • It blocks starlight (extinction)
  • It emits in the far-infrared
  • Made of refractory materials (true metals, not astronomer metals)
  • It may come in flavors (carbonaceous, silicate)
  • Sizes from a few atoms (PAHs & nanometer particles) to mm
  • It only grows bigger in protoplanetary systems
  • In cold clouds, dust grains collect ices
  • In cold clouds, all of the refractory materials are in dust:
gas ∝ dust: we use dust to measure total mass

The Galactic Center

The Galactic Center

The Galactic Center

The Galactic Center

Is star formation different in other environments?
In the Galactic Center?

The CMZ

$\sim10^8$ M$_\odot$ of gas in $\sim200$ pc, 10% of Galactic star formation
Image: NRAO, Ginsburg
Ginsburg+ 2018a
Dust, tracing gas

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

The CMZ: ACES

The first complete survey of the CMZ with 2.4" resolution (previous best was ~15")
between ~2 microns and 10 cm.
https://sites.google.com/view/aces-cmz/home
Results forthcoming! Continuum, line data papers, catalogs, kinematic analyses, filament identifications all in prep....
ACES CMZ: HC3N
ACES CMZ: H13CO+
ACES CMZ: SiO

Gas tracers of processes (classic vs reality)

  • SiO: Shock Tracer [shocks destroy dust, release SiO]
    • But, we see SiO everywhere!

  • N2H+: Cold, Dense Gas tracer [CO destroys N2H+; when CO freezes, N2H+ abounds]
    • N2H+ is too abundant in the Galactic Center
  • CH3OH & COMs: dense, ice-processed, reheated gas
    • These are widespread in the Galactic Center
  • "Metal"-bearing molecules are refractory, stuck in dust
    • but there are some in disks
The Brick isn't forming many stars
despite a total mass ~105 M⊙ in <3 pc
Ginsburg+ 2023
https://cosmicds.github.io/minids/jwst-brick/
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

Galactic Center gas: N2H+ coincides w/CO gas

(it shouldn't; gaseous CO should destroy N2H+)
N2H+ contours on CO 3-2
Santa-Maria+ 2021: higher CRIR
Walker+ 2021
Building new tools: Spectral Line Survey of The Brick
Alyssa Bulatek+
in prep
Building new tools: Spectral Line Survey of The Brick
Alyssa Bulatek+
in prep
Building new tools: Spectral Line Survey of The Brick
Alyssa Bulatek+ 2023
A methanol dasar shows dense gas
Alyssa Bulatek: Spectral Line Survey of The Brick
  • Dasar line at 107 GHz
  • CH3OH only in absorption
  • Occurs at density $n<10^6 \mathrm{cm}^{-3}$
Gas-phase metals in disks

the gas & dust where stars form: Orion

Our Galaxy

the gas & dust where stars form

Gas-phase metals in disks

the gas & dust where stars form: Orion

the gas & dust where stars form: Orion

Kong+ 2021, 2019, 2018

the gas & dust where stars form: Orion

The Integral-Shaped filament has $\sim10^4$ M$_\odot$ of gas over $\sim$10 pc Kong+ 2018 CARMA-Orion survey

the gas & dust where stars form: Orion

Bally+ 2015, 2017
The Orion Molecular Cloud is the closest (d$\sim400$ pc) site of high-mass star formation

the gas & dust where stars form: Orion

Bally+ 2015, 2017
BOOM!

Clusters are sites of interactions & collisions


The BN/I/x interaction is the poster case of accretion ended by dynamical interaction.
...even though Orion is only a medium-mass proto-open-cluster

Orion Source I
a disk around a 15 M⊙ YSO

Salt: NaCl
Image: Ginsburg, NRAO

Temperature?

Temperature?

A contrived model

Observing the Keplerian rotation profile of a disk is the most direct way to measure a protostar's mass

(we can only see the disk, not the star itself)

Why do we see salt?

  • Before, NaCl & KCl only in AGB*:
    associated with dust formation
  • Most likely dust destruction here:
    • In the disk?
    • As the outflow is launched?

Where do we see salt?

Only in a disk!

Possible future uses for these lines?

  • Metallicity measurement in deeply embedded star-forming environments? (at least of Na, K, Cl)
  • Disk kinematics of high-mass stars, which are otherwise unobservable (τ>1 at mm wavelengths)
  • Disk kinematic measurements at early stages?
  • Probe dust destruction (and/or formation?) in outflows, disks?
  • Probe radiation environment around HMYSOs?

We do not have a viable model to explain these temperatures

A strong non-blackbody radiation field from 25-40 µm may explain them.
Forsterite (MgSiO4) has some emission bands in that range. Maybe?

Salt is a tool to weigh HMYSOs

Keplerian orbits measure mass

Brine lines measure dynamical mass


NaCl v=1 J=18-17 Stack of v=[0,1] Ju=[18,17]
SrcI

15 M⊙ 30 M⊙ 40 M⊙

More Brinary disks

Ginsburg+ 2023: New sample. Miriam Garcia Santa-Maria is following up

Briny chemistry:

Salts, SiS, SiO, and PN are seen together [but limited spectral coverage]

What have we learned about brinaries?

  • Neither common nor rare: 10 known so far, >23 HMYSO candidates examined
    • Y: SrcI, G17, IRAS16547, NGC6334I, G351.77, W33A
      • Ginsburg+ 2019, Tanaka+ 2020, Ginsburg+ 2023
    • N: I16523, I18089, G11, G5, NGC6334IN, S255IR NIRS3, G333.23-0.06, I18162
      • Ginsburg+ 2023
  • Coincide w/line-poor sources
    • Not hot cores; little mass reservoir?
  • Trace reasonably symmetric disks (in the well-resolved cases)

Compare: G17 vs G11

G17: Brinary
Hot (ionizing) photosphere. Circular disk.
G11: Not-Brinary
Molecule rich, kinematically messy & extended
What's next for salts? (VLA 22A-022, 23A-016)
Deep VLA observations of low-J lines in Orion
We find hot cores here


The Inner Galaxy is where most stars form

We find hot cores here


The Inner Galaxy is where most stars form

ALMA-IMF: 15 high-mass star-forming regions

Orange layer shows ATLASGAL 870$\mu$m dust:
the dense gas where stars form

ALMA-IMF: 15 high-mass star-forming regions

Orange layer shows ATLASGAL 870$\mu$m dust:
the dense gas where stars form ALMA-IMF targets are among the most massive between 2-6 kpc from the sun
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]
1mm Dust
[ALMA]
870 μm Dust
[APEX/ATLASGAL]

ALMA-IMF data highlights

Gas flows in N2H+ filaments (Álvarez-Gutiérrez+ 2024)
N2H+ behaves as expected, tracing dense gas in filaments.

ALMA-IMF: Continuum Data → core catalogs

www.almaimf.com/data.html
Pouteau+ 2022 W43-MM2/3

ALMA-IMF: CMF measurement & YSO counting

www.almaimf.com
(these papers are all now submitted or accepted, but this is a screenshot that includes everyone's photos...)

ALMA-IMF Key Results summary

  • Rich, science-ready data (Ginsburg+ 2022, Cunningham+ 2023)
  • CMF is top-heavy in HMSFRs (Pouteau+ 2022, Louvet+ 2024)
  • Core fragmentation is not 1-to-1 [WIP] (Budaiev+ (CMZ), Yoo+ (W51), Louvet+ (W43), ...)
  • 10% of $M\gtrsim1\mathrm{~M}_\odot$ cores are hot cores (Brouillet+ 2022, Bonfand+ 2024, Wyrowski+)
  • Outflow feedback builds over time, sets initial conditions for many cores (Nony+ 2022, Towner+ 2023)

Hot Cores: L$>10^3 L_\odot$

Hot cores are chemically rich sites of high-mass star formation.
They are only found in the more distant disk & CMZ regions
Ginsburg+ 2017

Hot Cores: L$>10^3 L_\odot$

Hot cores are chemically rich sites of high-mass star formation.
They are only found in the more distant disk & CMZ regions
Ginsburg+ 2017

Hot Cores: L$>10^3 L_\odot$

Hot cores are chemically rich sites of high-mass star formation.
They are only found in the more distant disk & CMZ regions
Hot cores in ALMA-IMF: From rare objects to a population
Cores with line forests
TD>50 K
TG ≳100K
Brouillet+ 2022

Hot core overview:

  • 9 HCs in W43-MM1 (Brouillet+ 2022)
  • ~60-70 HCs in ALMA-IMF sample from CH3OCHO (Bonfand+ 2024; left)
  • ~10% of continuum cores are within hot cores

Hot cores in the Galactic center: Distributed MYSOs

Desmond Jeff+ 2024

Ten hot cores in Sgr B2 DS
outside the massive clusters
TG ~ 200-500 K
M ~ 200 - 2900 M⊙
(proto-O-stars / clusters)
~5% of cores are hot cores
Sgr B2 DS: More massive cores than the Disk
Desmond Jeff+ 2024
Hot Core Line Data: CH3CN, CH3CCH
Temperature measurements with per-pixel rotation diagrams
Desmond Jeff+ 2024 (CH3OH in CMZ), Wyrowski+ in prep (CH3CN in ALMA-IMF)
Temperature measurements show the volumes affected by feedback
Ginsburg+ 2017, Jeff+ 2024
Shocks & Outflows
Bally+ 2022; Sh106
Bally+ 2015; Orion
SiO traces outflows, CS v=0 J=1-0 and v=0 J=2-1 masers may trace a disk
Ginsburg+ 2019
M = 24-10+12M⊙
if the masers trace a disk

CS maser conditions

van der Walt+ 2020
  • Top: CS J=1-0, Bottom: CS J=2-1
  • Red: Consistent w/W51e2e observations
  • Masers do not coexist; require different specific CS column
    (N2-1=1015.6, N1-01016.1 cm-2)
  • Require high abundance (XCS > 10-5)
  • Hot (300-500 K), moderate-density (n~105 cm-3): Disk surface? Or outflow cavity wall?

W51 e2e: Too optically thick at 1mm to measure disk

Goddi+ 2020
Goddi+ 2020
SiO shows messy outflows

The outflow (& disk) around W51 North changed direction by ~50 deg in < 100 years.

ALMA-IMF Line Data: 315 cataloged SiO Outflows
Allison Towner+ 2024
Resolved, structured SiO outflows
5-60% of SiO at low velocities:
Relic outflows?
High velocity cloud-cloud shocks happen in the ISM
Savannah Gramze

Velocity bridge: evidence for collision after overshooting Gramze+ 2023
(these are fully molecular HVCs in the plane of the galaxy - not accreting HI clouds)

How does gas flow into the Galactic Center?

We think the ring-like feature formed in this simulation is a good model for the CMZ
Sormani+ in prep
SiO is spread throughout the clouds before & after collisions

SiO is all over the CMZ

and prevalent throughout Galactic disk clouds.
(Towner+ 2024, Jimenez-Serra 2004, 2008, 2009, 2010)

Models suggest it should precipitate out of gas rapidly (Schilke+ 1997, Gusdorf+ 2008a, 2008b), but low-velocity shocks can keep some as gas if it's in the right part of the dust.

SiO is always present in shocks, and sometimes just there
The MUBLO: Millimeter Ultra Broad-Line Object
Broad-Line: FWHM~160 km s-1
SMA followup detection of H2S
Broad-Line (broader than the CMZ, but only <2")
Weird chemistry (no SiO?!?)
Dusty
...and cold, using SO LTE model
No NIR counterpart
No counterparts!
Hypotheses & Data

Summary

Molecular line emission provides a lot of tools for understanding star formation and the ISM... but we still don't know how all those tools work
  • SiO is everywhere! It's more prevalent in shocks, usually
  • N2H+ is a good tracer of dense gas, but only in limited environments
  • NaCl, KCl, AlO and friends are the first unique disk tracers found


We can still find chemical oddballs - we don't have categories for everything!
  • Gas-phase salt is prominent in disks around high-mass stars - which we'd never seen before
  • There's an extremely broad linewidth, compact source in the Galactic Center with apparently sulfur-rich, everything-else-poor chemistry