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High-Velocity Clouds (HVCs), those assemblies of gas around galaxies that do not follow the galactic rotation, have been enigmatic since their discovery almost 60 years ago. Recent observational and theoretical advances have clarified their properties and importance to galaxy formation and evolution. To explore this topic further, a Green Bank Workshop on “Galactic and Extragalactic High-Velocity Clouds” will be held June 26-29, 2022. It will bring together scientists with diverse interests for lively discussions of the latest observations, computational models, and theoretical considerations.

The Workshop will be held at the Green Bank Observatory, where the great natural beauty and intimate setting produce meetings characterized by a high level of interaction. Because of logistical considerations, attendance will be limited to 45 participants.

Lodging

Lodging will be at the Observatory or nearby locations. All meals will be served in the Observatory Cafeteria. A $550 per participant fee will cover all local expenses, including lodging and meals. It may be possible to waive this cost for some of the participants.

Accommodations for accompanying persons and child care will be available.

Travel Information

The easiest way to get here is to follow the directions on our “Getting Here” page. Please note that some GPS systems do not always give the best route to the Green Bank Observatory, and nothing beats the good old-fashioned paper map for navigation.

We will attempt to coordinate ride-sharing from airports if there is interest.

Workshop Schedule

Date	Start Time	Duration	Topic/Title
26-June 2022 Sunday			People arrive throughout the afternoon and evening
	17:30	1:00	Dinner in the Cafeteria
	18:30		Informal Reception in the Drake Lounge
27-June  Monday	7:45	1:00	Breakfast in the cafeteria
Session 1 — Overview	8:45	0:15	Welcome: Jim Jackson  and LOC
Chair: Bob Benjamin	9:00	0:45	M. Putman: High Velocity Clouds
	9:45	0:45	J. Werk: HVCs and the Circumgalactic Medium
	10:30	0:20	Coffee
	10:50	0:30	N. Lehner:  Discovery and Properties of HVCs Through Absorption Spectroscopy
	11:20	0:45	A. Fox: Magellanic HVCs
	12:05	0:20	Y. Zheng: The Mocky Way: Investigating Biases in Observing HVCs in the Milky Way
End of session 1	12:25
	12:30	0:45	Lunch in Cafeteria
Session 2 — GBT Tour	13:15	2:15	GBT Tour
	15:30	0:00
Session 3 —  Origins and measurements	15:30	0:30	F. Fraternali: How to make HVCs via fountain-driven condensation (remote)
Chair: Will Armentrout	16:00	0:30	A. Marasco:  Collimated outflows and diffuse inflows traced by ionised HVCs and IVCs at the disc-halo interface
	16:30	0:15	Coffee and group photo
	16:45	0:25	E. Di Teodoro: HVCs in the nuclear wind of the Milky Way
	17:10	0:25	B. Wakker: Metalicities of HVCs
	17:35	0:25	T. Tripp: The High-Velocity Clouds Above the Disk of the Outer Milky Way: Misty Precipitating Gas in a Region Roiled by Stellar Streams
	18:00	0:00
	18:00
End of session 3	18:00
	18:00	1:00	Drinks and Dinner in the Science Center
Session 4: Panel Discussion	19:00	1:30	Evening Panel in Science Center Auditorium: The Origin of HVCs — Ionized and Neutral
			Ashley, Howk, Marasco, Tripp
	20:30		Retire to the Drake Lounge for continued Discussion
28 June Tuesday	7:45	0:45	Breakfast in the cafeteria
Session 5 — The Magellenic Streams	8:30	0:25	S. Lucchini: A new orbital history for the Magellanic Clouds
	8:55	0:20	E. Chwalik: Mapping the Edge of the Magellanic Stream
	9:15	0:20	K. Barger: The LMC’s Galactic Feedback
	9:35	0:20	D. Nidever: Recent Star Formation in the Magellanic Stream Leading Arm
	9:55	0:20	F.J. Lockman: The Smith Cloud
End of session 5	10:15	0:20	Coffee Break
Session 6 — Theoretical Issues	10:35	0:40	A. Gronnow: The effect of magnetic fields on High-Velocity Clouds
	11:15	0:20	P. Oh: Thermal Instability and Mixing Layers
	11:35	0:20	B. Tan: Radiative Turbulent Mixing Layers in Cold Clouds
	11:55	0:20	G. Bryan: The structure of turbulent radiative mixing layers and the cloud/CGM interaction
	12:15	0:15
	12:30
	12:30	0:45	Lunch in the Cafeteria
	13:15	0:20	L. Armilotta: The impact of cosmic rays on the dynamics of the extra-planar gas
	13:35	0:20	R. Shelton: Simulations of dark-matter Rich HVCs
End of session 6	13:55	0:20	F. Heitsch:Metallicity Estimates of HVCs: Insights from Simulations
	14:15	0:20	Coffee Break
Session 7	14:35	0:20	L. Jung: Search for magnetic field associated with high-velocity clouds using Faraday rotation
	14:55	0:20	A. Hill: Polarized radio emission from the anti-centre shell: Interaction between an HVC and the Galactic magnetic field
	15:15	0:20	D. French: A FUSE  HI survey of the Galactic Halo
	15:35	0:30	Poster viewing session
	16:05	0:20	B. Benjamin: Complexity in the Outer Galaxy
	16:25	0:20	T. Minter: No OH in the Smith Cloud (remote)
	16:45	0:20	A. Smith: Intermediate Velocity Molecular Clouds
	17:05	0:25
End of session 7	17:30
	17:30	0:30	Drinks in the Lounge
	18:00	1:00	Dinner in the cafeteria
Session 8	19:00	1:30	Panel in the Jansky Lab — Theoretical issues in HVCs:
			Armillotta, Byon, Gronnow, Oh
	20:30		Discussion continues in the Drake Lounge
29-June Wednesday	7:45	1:00	Breakfast in the Cafeteria
Session 9 — HVCs from the nuclear wind	0:30	R. Bordoloi: The UV perspective on the nuclear wind
	9:15	0:20	T. Ashley: Metallicities of Outflowing Fermi Bubble Clouds
	9:35	0:20	D. Krishnarao: Anomalous Velocity Gas near Galactic Center
	9:55	0:20	F. Cashman: Molecular Gas within the Milky Way’s Nuclear Wind
Session 10 — Extragalactic HVCs	10:15	0:20	J.C. Howk: Project AMIGA: H I in a Sea of H II in Andromeda’s Halo
	10:35	0:20	Coffee Break
	10:55	0:25	DJ Pisano: The HI Clouds surrounding M31
	11:20	0:25	H. Gim: Anomalous HI clouds in M100
Session 11: Panel	11:45	0:45	HVCs: The Path Forward
Workshop End	12:30		Lunch in the Cafeteria

Topics to be considered include:

• The origin of HVCs
• New observations
• Magnetic, ionized, metal, and dark matter components
• The Magellanic Stream
• HVCs in other galaxies
• HVCs effect on our Galaxy and its CGM
• HVCs as probes of their environments
• The fates of HVCs
• The connection between nuclear winds and HVCs
• Intermediate Velocity Clouds and their Connections to HVCs

Scientific Organizing Committee

• Kat Barger (TCU)
• Joss Bland-Hawthorn (Univ. Sydney)
• Andy Fox (STScI)
• Filippo Fraternali (Univ. Groningen)
• Jay Lockman (Green Bank Observatory)
• Naomi McClure-Griffiths (Australian National Univ.)
• Mary Putman (Columbia Univ.)
• Robin Shelton (Univ. Georgia)

Registered Participants

Will Armentrout	Green Bank Observatory
Lucia Armillotta	Princeton University
Dr. Trisha Ashley	Space Telescope Science Institute
Kat Barger	Texas Christian University
Bob Benjamin	University of Wisconsin
Rongmon Bordoloi	North Carolina State University
Greg Bryan	Columbia University
Francie Cashman	Space Telescope Science Institute
Erica Chwalik	Montana State University
Enrico Di Teodoro	Johns Hopkins University
Andy Fox	STScI
David M. French	STScI
Hansung Gim	Montana State University
Eric Goetz	University of Georgia
Asger Gronnow	Kapteyn Institute, University of Groningen
Fabian Heitsch	UNC Chapel Hill
Alex S. Hill	UBC Okanagan / DRAO
Chris Howk	University of Notre Dame
Jim Jackson	Green Bank Observatory
Lyla Jung	Australian National University
Dhanesh Krishnarao (DK)	Johns Hopkins University / Colorado College
Glen Langston	National Science Foundation
Nicolas Lehner	University of Notre Dame
Jay Lockman	Green Bank Observatory
Scott Lucchini	University of Wisconsin – Madison
Antonino Marasco	INAF – Padova Observatory
Jennifer Donovan Meyer	NRAO
Toney Minter	Green Bank Observatory
David Nidever	Montana State University
Peng Oh	UCSB
D.J. Pisano	UCT/WVU
Mary Putman	Columbia University
Evan Schneider	University of Pittsburgh
Nigel Sharp	National Science Foundation
Dr. Robin Shelton	University of Georgia
Allison Smith	Arecibo Observatory
Brent Tan	UCSB
Todd Tripp	University of Massachusetts – Amherst
Ananya Tuli	PhD candidate at the University of Notre Dame
Jo Vazquez	Texas Christian University
Bart Wakker	University of Wisconsin-Madison
Chen Wang	University of Georgia
Jessica Werk	University of Washington
Ellie White	Green Bank Observatory
Yong Zheng	UC Berkeley

Local Organizing Committee

• Brenne Gregory
• Sue Ann Heatherly
• Jay Lockman
• Pedro Salas
• Ellie White

Receiver	Band	Frequency Range (GHz)	Focus	Polarization	Beams	Polarizations per Beam
Prime Focus 1	342 MHz 450 MHz* 600 MHz* 800MHz	.290-.395 .385-.520 .510-.690 .680-.920	Prime	Linear/Circular	1	2
Prime Focus 2*	—	.910-1.23	Prime	Linear/Circular	1	2
L-Band	—	1.15-1.73	Gregorian	Linear/Circular	1	2
S-Band	—	1.73-2.60	Gregorian	Linear/Circular	1	2
C-Band	—	3.95-7.8	Gregorian	Linear/Circular	1	2
X-Band	—	7.80-11.6	Gregorian	Circular	1	2
Ku-Band	—	12.0-15.4	Gregorian	Circular	2	2
KPFA	—	18.0-27.5	Gregorian	Circular	7	2
Ka-Band	MM-F1 MM-F2 MM-F3	26.0-31.0 30.5-37.0 36.0-39.5	Gregorian	Linear	2	1
Q-Band	—-	39.2-50.5	Gregorian	Circular	2	2
W-Band 4mm	MM-F1 MM-F2 MM-F3 MM-F3	67-74 73-80 79-86 85-93	Gregorian	Circular	2	2
MUSTANG2	—	80-100	Gregorian	—		—
Argus	—	74-116	Gregorian	Linear	16	1

Receiver	Band	Beam Separation	FWHM	Gain (K/Jy)	Aperture Efficiency	Maximum Instantaneous Bandwidth (MHz)
Prime Focus 1	342 MHz 450 MHz* 600 MHz* 800MHz	—	36′ 27′ 21′ 15′	2.0	72%	240
Prime Focus 2*	—	—	12′	2.0	72%	240
L-Band	—	—	9′	2.0	72%	650
S-Band	—	—	2.8′	2.0	72%	970
C-Band	—	—	1.4′	2.0	72%	3800
X-Band	—	—	54″	2.0	71%	2400
Ku-Band	—	330″	32″	1.9	70%	3500
KPFA	—	96″	Greg.	1.9	68%	1800, 8000
Ka-Band	MM-F1 MM-F2 MM-F3	26.0-31.0 30.5-37.0 36.0-39.5	26.8″ 22.6″ 19.5″	1.8	63-67%	4000
Q-Band	—	39.2-50.5	16″	1.7	58-64%	4000
W-Band 4mm	MM-F1 MM-F2 MM-F3 MM-F3	286″	10″	1.0	30-48%	6000 4000 4000 4000
MUSTANG2	—	—	10″	—	35%	20000
Argus	—	30.4″	8″	—	20-35%	1500