The Galactic Halo as seen by Pan-STARRS1
The Galactic Halo as seen by Pan-STARRS1
The Galactic Halo as seen by Pan-STARRS1
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A <strong>Pan</strong>-<strong>STARRS1</strong> View of<br />
the Sagittarius Stream<br />
Colin Slater<br />
Eric Bell (Michigan)<br />
Eddie Schlafly (Harvard -> MPIA)<br />
Mario Juric (Harvard -> LSST)<br />
Nicol<strong>as</strong> Martin (MPIA -> Str<strong>as</strong>bourg)<br />
Hans-Walter Rix (MPIA)<br />
+ PS1 Collaboration
PS1 Survey<br />
1.8 m telescope on Haleakala, 3º FoV<br />
Covers all sky North of -30º (3π)<br />
~40 sec exposures in grizy, cadence optimized for<br />
moving objects<br />
12 fields targeted for Medium Deep survey
Data Processing<br />
Photometric catalogs produced nightly<br />
Images are not stacked nightly<br />
All current 3π catalogs are merged from single-epoch<br />
data<br />
Stacking is underway but CPU-intensive<br />
Survey is übercalibrated (Schlafly et al. 2012, better than 10mmag)
PS1 Coverage<br />
Main Sequence<br />
Turn-off Stars:<br />
0.0 < (g-r) < 0.4
Sagittarius Map<br />
SDSS<br />
Sgr<br />
PS1
Main Sequence Turn-off<br />
l=90º<br />
l=90º<br />
Anti-<br />
GC<br />
GC<br />
l=270º<br />
l=270º
Distance Me<strong>as</strong>urements<br />
Stream visible in MSTO<br />
MSTO is a relatively poor distance indicator<br />
Red Clump is more precise<br />
Combine both for best me<strong>as</strong>urement
Background Regions<br />
Faint Arm Regions<br />
Bright Arm Regions
Example Region CMD<br />
RC<br />
RC
Bright Arm
Faint Arm
Calibration<br />
Sgr dwarf is in PS1 data<br />
P1,<br />
Use dwarf RC to calibrate distances to the stream<br />
Minimizes effects of stellar population differences and<br />
survey differences
Me<strong>as</strong>ured Distances<br />
Bright Arm<br />
Faint Arm<br />
Faint arm consistently closer
Comparison to Models<br />
● Bright Arm<br />
Faint Arm<br />
■ Cetus<br />
Model from Law & Majewski (2010)<br />
Northern points from Niederste-Ostholt et al. (2011)<br />
Cetus from Newberg et al. (2009)
Summary<br />
Sgr stream is bifurcated in North and South<br />
RC is a useful distance indicator for Sgr<br />
Distance to the stream matches model expectations<br />
Faint arm is consistently closer<br />
Unlikely to be confused with Cetus
Origin of Bifurcation<br />
Multiple wraps: unlikely<br />
Internal rotation: unlikely<br />
(Fellhauer+06, but see Yanny+09)<br />
(Peñarrubia+10, but see Peñarrubia+11)<br />
No evidence of internal rotation<br />
Existing sims disagree with trailing arm<br />
Double accretion Plausible Unknown.<br />
Complex dwarf structure Unknown.
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