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Adrian Price-WhelanFlatiron Institute (NYC, USA)@adrianprw
David Nidever
Yumi Choi, Rachael Beaton, Eddie Schlafly, Tim Morton,Sergey Koposov, Vasily Belokurov
Discovery & Characterization of a Recent Star Formation Event Far into the Milky Way’s Halo
The Milky Way over O'ahu i.e., from within the Galactic disk
credit: /u/Hyper_Hummingbird808 ; reddit
Tom and Gail Haynes/Adam Block/Mount Lemmon SkyCenter/University of Arizona
A Milky Way look-alike (NGC 3953)
Where the Sun would be
The HIPPARCOS mission (1989–1993) measured precise stellar "proper motions" within here
Where the Sun would be
~800 lightyears
Tom and Gail Haynes/Adam Block/Mount Lemmon SkyCenter/University of Arizona
Tom and Gail Haynes/Adam Block/Mount Lemmon SkyCenter/University of Arizona
The equivalent volume for the ESA Gaia mission (2013–present)
~100,000 lightyears
Gaia Data Release 2 (April 2018): 1.7 billion parallaxes, proper motions, and stellar colors
Idea: Use the many new sky motions and stellar colors to search for star clusters around the Milky Way
How?
Mining Gaia Data Release 2
Stars in known stellar clusters
points = individual stars, colors = different star clusters
Young Star Clusters ~40–1000 Million Years Located in the Galactic disk
Blue/Hot Red/Cool
Brighter
Fainter
Figures from Babusiaux et al. 2018
How to Find a Star Cluster: The Power of Gaia
Sky positions of stars:
All stars in a sky region
Sky positions of stars:
Only blue stars
How to Find a Star Cluster: The Power of Gaia
Sky positions of stars:
Gaia "proper motion"
How to Find a Star Cluster: The Power of Gaia
Sky positions of stars:
Blue & Co-moving
How to Find a Star Cluster: The Power of Gaia
Discovery with Gaia
Blue Red
Brighter
FainterSky positions
Cluster stars
Foreground/background
Discovery and Characterization
Summary info. for "Price-Whelan 1" (PW 1) Age: 116 million years Total mass: 1200 solar massesDistance (from us): 94,000 light yearsMetallicity: 6% of the Sun'sSize: 1.5º on the sky, 1600 light years
Comparable to the Pleaides
but 200 times farther away!
and 100 times bigger!
PW 1 is far from the Milky Way disk, in the relatively devoid region around the Galaxy: the "Halo"
The Magellanic Clouds
Credit: ESO/Y. Beletsky
Falling in to the Milky WayClose to 1/10 the mass of the Milky WayWill be important drivers of the fate of the Galaxy (i.e., star formation, appearance)
Most Hydrogen gas in the Galactic Halo is associated with the Magellanic Clouds
Location of the cluster
Credit: D. Nidever 2010
"Leading arm"
Trailing stream
PW 1
Figure from S. Lucchini, E. D'Onghia, S. Pardy
100,000
200,000
300,000
400,000
Position along the Magellanic Stream
500,000
Distance(light years)
Simulations of the Magellanic Clouds & StreamPredicted distance to gas in the Magellanic stream
LMC / SMC
70 65 60 55 50 45 40LMS
0
100
200
300
400V L
SR0.10 1.0 10.
−13<BMS<−8 GASS HI Gaussians
LA II
LMS [deg]
V LSR
[km
s−1 ]
The missing link: Line-of-sight velocity of the cluster
Unknown high-velocity gas
Magellanic stream
Milky Way disk
Position along the Magellanic Stream
GasLine of sight
Velocity
Location of PW 1
1. We found a young star cluster (PW 1) far from the Milky Way disk (where all other young star clusters are found)
2. Likely formed in the gas stream originating from the Magellanic Clouds
3. But, need line-of-sight velocities to confirm that the stars are associated with the gaseous Magellanic Stream
4. These would be the only known stars in the Stream, and allow us to measure the first precise distance to the stream
Summary (part 1)
Adrian Price-Whelan [email protected]@adrianprw
David Nidever [email protected]
Price-Whelan, Nidever et al. 2019 Nidever, Price-Whelan et al. 2019 (The Astrophysical Journal)
