Searching for Milky Way Satellite Galaxies with DECam Alex - - PowerPoint PPT Presentation

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Searching for Milky Way Satellite Galaxies with DECam

DPF 2017 July 31, 2017

Alex Drlica-Wagner

David N. Schramm Fellow Fermilab

What are Dwarf Galaxies?

The Milky Way

What are Dwarf Galaxies?

The Milky Way Small Magellanic Cloud The Milky Way

What are Dwarf Galaxies?

The Milky Way Small Magellanic Cloud The Milky Way

Fornax Sculptor Draco

Small Magellanic Cloud

Why are dwarf galaxies important?

Dwarf Galaxies

Wolf et al. (2010)

“Brightness”

Gravitational Mass Visible Mass )

(

Star Clusters

Dwarf galaxies are the most dark- matter-dominated

• bjects knowns

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Smallest Structures Probe Fundamental Characteristics of Dark Matter

Image Credit: Massey & Moustakas

Deviations from Cold Dark Matter could be detected in the abundance and densities of the smallest structures.

S t a n d a r d C D M

D e c a y l i f e t i m e

10 -3 10 -2 10 -1 10 0 10 1 10 2 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1

Dark matter transfer function

1018 1016 1014 1012 1010 108

S t a n d a r d C D M

1 2 k e V s t e r i l e

!

10 -2 10 -1 10 0 10 1 10

Wavenumber k (h/Mpc)

1018 1016 1014 1012 1010 108

Collapse mass (Msun)

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S t a n d a r d C D M

10 -2 10 -1 10 0 10 1 10 2 1018 1016 1014 1012 1010 108

S t e r i l e !

Wavenumber k (h/Mpc)

Super WIMPS Sterile Neutrinos Warm Dark Matter Self-Interacting Dark Matter

Collapse Mass (Msun)

5 Lovell et al. (2012)

Warm Dark Matter Cold Dark Matter

Vogelsberger et al. (2016)

Self-Interacting Dark Matter Cold Dark Matter

Smallest Structures Probe Fundamental Characteristics of Dark Matter

Simulations

Observational Challenges 
 to Cold Dark Matter

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The “Missing Satellites” Problem The “Too Big to Fail” Problem

Garrison-Kimmel et al. (2014)

Observed satellites are under-dense compared to simulations Fewer satellites are

• bserved compared to

simulations

Garrison-Kimmel et al. (2014)

Simulation Observation Simulation Observation

Observational Challenges 
 to Cold Dark Matter

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The “Missing Satellites” Problem The “Too Big to Fail” Problem

Garrison-Kimmel et al. (2014)

Observed satellites are under-dense compared to simulations Fewer satellites are

• bserved compared to

simulations

Garrison-Kimmel et al. (2014)

Simulation Observation Simulation Observation

Observationally Limited!

Alex Drlica-Wagner | Fermilab

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The Milky Way Naked Eye Visible Large Magellanic Cloud (LMC) Small Magellanic Cloud (SMC)

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ESO/DSS2

1.2m Telescope Photographic Plates

Sculptor Dwarf Galaxy

Brighter Color Redder Bluer Fainter Magnitude

Paust et al. (2007) M92

Brighter Color Redder Bluer Fainter Magnitude

Paust et al. (2007) M92 Age Metallicity Distance

NOTE: We can’t measure dark matter content from photometry alone…
 
 Spectroscopy talk by Ting Li

Measure:

• Age
• Metallicity
• Distance

Alex Drlica-Wagner | Fermilab

Dwarf Galaxy Discovery Timeline

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SDSS Begins

Alex Drlica-Wagner | Fermilab

Matched-Filter Searches

12 1 22 20 18 16 14 0.5 1 1.5

−0.5

g − r r

0.5 0.5

−0.5

δ ra (degrees) δ dec (degrees)

−0.5

0.5 0.5

−0.5

δ ra (degrees) δ dec (degrees)

−0.5

0.5 0.5

−0.5

δ ra (degrees) δ dec (degrees)

−0.5

Koposov et al. (2008) Walsh et al. (2009) Willman et al. (2010)

2) Apply a selection in color-magnitude space based on a stellar isochrone 1) Start with a large catalog of stars 3) Convolve with a spatial kernel Stellar Isochrone

Alex Drlica-Wagner | Fermilab

Dwarf Galaxy Discovery Timeline

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SDSS Begins

SDSS Sky Coverage

14 (Belokurov 2013)

Discovered before SDSS
 (classical dwarfs) Discovered with SDSS (ultra-faint dwarfs) Sky Covered by SDSS

SDSS Sky Coverage

14 (Belokurov 2013)

Discovered before SDSS
 (classical dwarfs) Discovered with SDSS (ultra-faint dwarfs) Sky Covered by SDSS

The Dark Energy Survey

570 megapixel Dark Energy Camera (DECam) <20s readout time ~3 deg2 field-of-view Unprecedented 
 sensitivity up to 1µm Mounted on the 4m Blanco
 telescope at CTIO in Chile

+ +

Alex Drlica-Wagner | Fermilab

Maximum-Likelihood Searches

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Spatial Model

this SV field n the ster ing

Survey Sensitivity A likelihood analysis to simultaneously combine spatial and spectral information This technique naturally yields a membership probability for each star; important for spectroscopic targeting

• Stars

) 1 log( log

i i

f p L

• λ

p is the satellite membership probability of each star

• Stars

1

i i

p f

• λ

i i i i

b u u p

• ui = signal probability

bi = background probability λ = number of stars in the dwarf f = observable fraction of stars

• g
• g
• g
• g

Spectral Model

• g
• g
• g
• g

Color Brightness

Alex Drlica-Wagner | Fermilab

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Reticulum II

Bechtol, ADW et al. (2015)

4m Telescope DECam CCD Camera

Alex Drlica-Wagner | Fermilab

Re

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Reticulum II

• 1
• 4
• 4m Telescope

DECam CCD Camera

Bechtol, ADW et al. (2015)

Reticulum II

• Reticulum II

Colors correspond to the membership probability assigned to each star by the likelihood analysis

Alex Drlica-Wagner | Fermilab

Dwarf Galaxy Discovery Timeline

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SDSS Begins DECam Installed DES Year 1 DES Year 2

Alex Drlica-Wagner | Fermilab

Dwarf Galaxy Discovery Timeline

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SDSS Begins DECam Installed

Alex Drlica-Wagner | Fermilab

SDSS + DES Sky Coverage

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Blue - Previously discovered satellites Green - Discovered in 2015 with 
 PanSTARRS, SDSS, etc. Red outline - DES footprint Red circles - DES Y1 satellites Red triangles - DES Y2 satellites

ADW, et al. ApJ 813, 109 (2015)

Alex Drlica-Wagner | Fermilab

SDSS + DES Sky Coverage

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Blue - Previously discovered satellites Green - Discovered in 2015 with 
 PanSTARRS, SDSS, etc. Red outline - DES footprint Red circles - DES Y1 satellites Red triangles - DES Y2 satellites

ADW, et al. ApJ 813, 109 (2015)

Satellites of the Magellanic Clouds?

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• Z

2 New Satellites 15 New Satellites

ADW et al. ApJ 813, 109 (2015)

LMC SMC

b = 2 b = −20

E(NLMC

• bs

) = 10.8 .8 0.21 0.41 0.83 1.7 3.3 6.6 13 27 53

LMC satellites

−60 −40 −20 20 40 60 BMS (deg) −100 −50 50 100 LMS (deg)

Jethwa et al. MNRAS 461, 2 (2016)

There is ~3σ evidence that DES satellites are not isotropically distributed. This anisotropy could be explained by an association with the Magellanic Clouds

Magellanic Satellites Survey

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DECam Program for 12 nights in 2016-2017 PI: Keith Bechtol Deputy PI: ADW Funding through the NASA Guest Investigator Program PI: ADW Collaboration of ~45 members across ~20 institutions

(MagLiteS)

Alex Drlica-Wagner | Fermilab

Magellanic Satellites Survey
 (MagLiteS)

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12 nights ~1300 deg2 3 tilings Roughly comparable in depth to DES Y2 in g and r-bands

Satellites of the Magellanic Clouds?

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~

• =
• 1

<

• <

<

• a

d

• +
• +
• +
• +
• +

t

• +

Z

• +

å

• +
• +
• +
• + 4
• +
• +
• +
• )
• +
• +
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< <

• Simulations predict ~3 dwarf

galaxies for an isotropic distribution and ~10 galaxies for a Magellanic Cloud association. First satellite found in a 1/4th of the MagLiteS data;

• ther candidates being

investigated.

ADW et al. ApJL 833, 5, 2016

Blanco Imaging of the Southern Sky

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Collaboration of ~35 members across ~10 institutions NOAO DECam Program for 12 nights in 2017A Co-PIs: Soares-Santos & ADW 3 Science Drivers:

• Dwarf Galaxy Searches
• Gravitational Wave Follow-up
• Search for Planet 9

Cover ~2000 deg2 in 2017; eventually cover the entire sky in g,r,i,z bands

Gravitational Waves Dwarf Galaxies Planet 9

Alex Drlica-Wagner | Fermilab

Blanco Imaging of the Southern Sky
 (BLISS)

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BLISS also uses all pre-existing DECam Data

g-band r-band i-band z-band

Sum(teff x texp) log-scale from 30s (blue) to 300s (red)

Blanco Imaging of the Southern Sky

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• Most exposures pass

cuts on exposure quality

• 2017A data covers ~2200

deg2 in any single band

Blanco Imaging of the Southern Sky

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• Most exposures pass

cuts on exposure quality

• 2017A data covers ~2200

deg2 in any single band

Alex Drlica-Wagner | Fermilab

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CDM Predictions for Future Dwarf Discoveries

ADW et al. (2015)

ADW et al. (2016) ADW et al.

“Smoothed” 𝚳CDM Prediction Predicted Dwarf
 Discoveries Logarithmic
 Scale

(Hargis et al. 2014)