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

Searching for Milky Way Satellite Galaxies with DECam Alex Drlica-Wagner David N. Schramm Fellow Fermilab DPF 2017 July 31, 2017 1

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 are the most dark- matter-dominated Dwarf Galaxies objects knowns Visible Mass ) Gravitational Mass Star Clusters Wolf et al. (2010) ( “Brightness”

Smallest Structures Probe Fundamental Characteristics of Dark Matter Collapse Mass (M sun ) Collapse mass (M sun ) 10 18 10 16 10 14 10 12 10 10 10 8 10 18 10 16 10 14 10 12 10 10 10 8 10 18 10 16 10 14 10 12 10 10 10 8 10 -1 Dark matter transfer function 10 -2 S S S 10 -3 t t t a a a n n n d d d a a a 10 -4 r r r d d d C C C D D D 10 -5 M M M Sterile Neutrinos Self-Interacting S Super WIMPS t e 10 -6 r i Warm Dark Matter l Dark Matter e e m ! i t 10 -7 e f i l 1 y a 2 c e k 10 -8 D e V s t e 10 -9 r i l e ! 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 -2 10 -1 10 0 10 1 2 10 -2 10 -1 10 0 10 1 10 2 10 Wavenumber k ( h /Mpc) Wavenumber k (h/Mpc) Deviations from Cold Dark Matter could be detected in the abundance and densities of the smallest structures. Image Credit: Massey & Moustakas 4

Smallest Structures Probe Fundamental Characteristics of Dark Matter Cold Dark Matter Warm Dark Matter Simulations Lovell et al. (2012) Cold Dark Matter Self-Interacting Dark Matter Vogelsberger et al. (2016) 5

Observational Challenges 
 to Cold Dark Matter The “Missing Satellites” Problem The “Too Big to Fail” Problem Observation Observation Simulation Simulation Garrison-Kimmel et al. (2014) Garrison-Kimmel et al. (2014) Fewer satellites are Observed satellites are observed compared to under-dense compared to simulations simulations 6

Observational Challenges 
 to Cold Dark Matter The “Missing Satellites” Problem The “Too Big to Fail” Problem Observation Observation Simulation Simulation Observationally Limited! Garrison-Kimmel et al. (2014) Garrison-Kimmel et al. (2014) Fewer satellites are Observed satellites are observed compared to under-dense compared to simulations simulations 6

Large Magellanic The Milky Way Cloud (LMC) Small Magellanic Cloud (SMC) Naked Eye Visible Alex Drlica-Wagner | Fermilab 7

Sculptor Dwarf Galaxy ESO/DSS2 1.2m Telescope Photographic Plates 8

Paust et al. (2007) Brighter Magnitude Fainter M92 Color Bluer Redder


 Paust et al. (2007) Measure: Brighter - Age - Metallicity Metallicity - Distance Magnitude Distance NOTE: We can’t measure dark matter content from photometry Age alone… 
 Fainter M92 Spectroscopy talk by Ting Li Color Bluer Redder

Dwarf Galaxy Discovery Timeline SDSS Begins Alex Drlica-Wagner | Fermilab 11

Matched-Filter Searches 14 Stellar Isochrone Koposov et al. (2008) Walsh et al. (2009) 16 Willman et al. (2010) 2) Apply a selection in color-magnitude r 18 space based on a 1) Start with a stellar isochrone large catalog of 20 stars 3) Convolve with a spatial kernel 22 0 1 − 0.5 0 0.5 1 1.5 g − r 0.5 0.5 0.5 δ dec (degrees) δ dec (degrees) δ dec (degrees) 0 0 0 − 0.5 − 0.5 − 0.5 0.5 0 − 0.5 0.5 0 − 0.5 0.5 0 − 0.5 δ ra (degrees) δ ra (degrees) δ ra (degrees) Alex Drlica-Wagner | Fermilab 12

Dwarf Galaxy Discovery Timeline SDSS Begins Alex Drlica-Wagner | Fermilab 13

SDSS Sky Coverage Discovered before SDSS 
 Sky Covered by SDSS (classical dwarfs) Discovered with SDSS (ultra-faint dwarfs) (Belokurov 2013) 14

SDSS Sky Coverage Discovered before SDSS 
 Sky Covered by SDSS (classical dwarfs) Discovered with SDSS (ultra-faint dwarfs) (Belokurov 2013) 14

The Dark Energy Survey 570 megapixel Dark Energy Camera (DECam) ~3 deg 2 field-of-view <20s readout time Unprecedented 
 sensitivity up to 1 µ m Mounted on the 4m Blanco 
 telescope at CTIO in Chile

+ +

Maximum-Likelihood Searches Spatial Model Spectral Model Survey Sensitivity Brightness λ this SV field n the � � � � � � ster ing Color � � g � � u A likelihood analysis to simultaneously � � � � � g g i p � combine spatial and spectral information � i u b � � � i i u i = signal probability 1 b i = background probability � � � p λ = number of stars in the dwarf i f � � � � � Stars f = observable fraction of stars i λ This technique naturally yields a � � � � � � log log( 1 ) L p f membership probability for each star; i � g important for spectroscopic targeting � Alex Drlica-Wagner | Fermilab Stars i � 17 � � � g g � p is the satellite membership probability of each star � � � � � � � � � g � g

Reticulum II 4m Telescope DECam CCD Camera Alex Drlica-Wagner | Fermilab Bechtol, ADW et al. (2015) 18

Re Reticulum II Reticulum II Reticulum II Colors correspond to the membership � � probability � assigned to each star by the likelihood analysis 4m Telescope DECam CCD Camera Alex Drlica-Wagner | Fermilab Bechtol, ADW et al. (2015) 19 � � � � � � � � � � � � � � � � 1 � � � � � � � � � � � � � � � � � � � 4 � � � � � � � � � � � � � � � � � � � � � � � �

Dwarf Galaxy Discovery Timeline DES Year 2 DECam Installed DES Year 1 SDSS Begins Alex Drlica-Wagner | Fermilab 20

Dwarf Galaxy Discovery Timeline DECam Installed SDSS Begins Alex Drlica-Wagner | Fermilab 21

SDSS + DES Sky Coverage Blue - Previously discovered satellites Red outline - DES footprint Green - Discovered in 2015 with 
 Red circles - DES Y1 satellites PanSTARRS, SDSS, etc. Red triangles - DES Y2 satellites Alex Drlica-Wagner | Fermilab ADW, et al. ApJ 813, 109 (2015) 22

SDSS + DES Sky Coverage Blue - Previously discovered satellites Red outline - DES footprint Green - Discovered in 2015 with 
 Red circles - DES Y1 satellites PanSTARRS, SDSS, etc. Red triangles - DES Y2 satellites Alex Drlica-Wagner | Fermilab ADW, et al. ApJ 813, 109 (2015) 22

Satellites of the Magellanic Clouds? There is ~3 σ evidence that DES satellites are not isotropically distributed. 2 New Satellites 15 New Satellites Jethwa et al. MNRAS 461, 2 (2016) LMC SMC LMC satellites . 8 0 . 21 0 . 41 0 . 83 1 . 7 3 . 3 6 . 6 13 27 53 ADW et al. ApJ 813, 109 (2015) 60 b b = − 20 = 2 0 40 E ( N LMC ) = 10 . 8 obs 20 B MS (deg) This anisotropy could be � 0 explained by an � � − 20 � � association with the � � � � � � � � − 40 Magellanic Clouds � � � � � � � � � − 60 � 100 50 0 − 50 − 100 � 23 � L MS (deg) � � � � � Z

Magellanic Satellites Survey (MagLiteS) 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 24

Magellanic Satellites Survey 
 (MagLiteS) 12 nights Roughly comparable ~1300 deg 2 in depth to DES Y2 3 tilings in g and r-bands Alex Drlica-Wagner | Fermilab 25

Satellites of the Magellanic Clouds? Simulations predict ~3 dwarf a d + galaxies for an isotropic - + - + � distribution and ~10 galaxies for - + - + - � a Magellanic Cloud association. - + t - + Z - + å - + - + - + 4 - - + � - + - - + - - - ) + - + - ADW et al. ApJL 833, 5, 2016 + - First satellite found in a � < < � 1/4 th of the MagLiteS data; other candidates being investigated. 26 ~ - � � = � � 1 < � - - < <

Blanco Imaging of the Southern Sky Gravitational Waves NOAO DECam Program for 12 nights in 2017A Co-PIs: Soares-Santos & ADW 3 Science Drivers: Dwarf Galaxies • Dwarf Galaxy Searches • Gravitational Wave Follow-up • Search for Planet 9 Cover ~2000 deg 2 in 2017; eventually cover the entire Planet 9 sky in g,r,i,z bands Collaboration of ~35 members across ~10 institutions 27

Blanco Imaging of the Southern Sky 
 (BLISS) Alex Drlica-Wagner | Fermilab 28

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 • Most exposures pass cuts on exposure quality • 2017A data covers ~2200 deg 2 in any single band 30

Blanco Imaging of the Southern Sky • Most exposures pass cuts on exposure quality • 2017A data covers ~2200 deg 2 in any single band 30

CDM Predictions for Future Dwarf Discoveries (Hargis et al. 2014) Predicted Dwarf 
 ADW et al. (2015) Discoveries ADW et al. (2016) Logarithmic 
 Scale “Smoothed” 𝚳 CDM Prediction ADW et al. Alex Drlica-Wagner | Fermilab 31