Milky Way Satellite Galaxies with DES Alex Drlica-Wagner kadrlica@fnal.gov! DES Milky Way Working Group Coordinator! January 11, 2015
Milky Way Satellite Galaxies Segue 1 The Milky Way is surrounded by small satellite galaxies Close to Earth (25 kpc to 250 kpc) M. Geha Luminosities range from 10 7 L to 10 3 L Astrophysically simple Fornax Most dark matter dominated objects known Birth of near-field cosmology D. Malin (Bullock, Geha, Powell) 30 kpc 2
Walker et al. 2007 Dark Matter Dominated The stars in dwarf galaxies are moving too fast to be explained by visible mass alone Dwarf Galaxies Moore (2009) Globular Clusters Wolf et al. 2010 3
Finding Milky Way Satellite Galaxies 4
Finding Milky Way Satellite Galaxies Shapley (1938) Johnson & Sandage (1956) Brightness M3 Sculptor Redness 5
Sculptor ESO/DSS2 6
Segue 1 Geha 7
Segue 1 Geha 8
Finding Milky Way Satellite Galaxies 4 14 14 14 16 14 16 14 r 18 20 kpc 16 22 16 20 Select Stars with a 22 Characteristic 0 r 18 g r Age and Metallicity 20 14 100 kpc 20 kpc 4 Advances in Astronomy (a) 1 1.5 r 18 16 r 18 r 18 20 20 22 Advances i 0 g r 1.5 1 (b) 20 16 14 r 18 100 kpc 16 16 20 22 r18 0 20 Koposov et al. (2008) Walsh et14al. (2009) Willman et al. (2010) g r 1 (c) 1.5 22 0 r 18 1.5 1 g r (d) 20 Convolve with Spatial Kernel Figure 1: A color-magnitude (CM) filter used to suppress the noise from foreground stars while preserving the signal from dwarf galaxy stars at a specific distance. (a) and (c) CM filters for an old and metal-poor stellar population at a distance modulus of 16.5 and 20.0, respectively. The solid lines show Girardi isochrones for 8 and 14 Gyr populations with [Fe/H] = 1.5 and 2.3. (b) and (d) These CM filters overplotted 22 the character of the foreground contamination 22 22 are from SDSS as a function of dwarf distance. Data on stars from a 1 deg2 field to illustrate 1.5 1.5 1.5 0 1 0 1 0 0 1 DR7. g r g r g g r (a) (b) (c) (d) δ dec (degrees) δ dec (degrees) δ dec (degrees) Figure 1: A color-magnitude (CM) filter used to suppress the noise from foreground stars while preserving the signal from dw at a specific distance. (a) and (c) CM filters for an old and metal-poor stellar population at a distance modulus of 16.5 and 20. The solid lines show 0 Girardi isochrones for 8 and 14 Gyr 0 2.3. (b) and (d) These CM filte 0 populations with [Fe/H] = 1.5 and 2 onfield stars from a 1 deg field to illustrate the character of the foreground contamination as a function of dwarf distance. Data a Stellar DR7. 0 δ ra (degrees) 0 δ ra (degrees) 0 δ ra (degrees) 9
Discovery Timeline
Discovery Timeline SDSS Begins
Discovery Timeline DES Year 2 DECam Installed DES Year 1 SDSS Begins
SDSS DR10 + DES Y2 Blue - Previously discovered satellites Green - Discovered in 2015 with PanSTARRS/SDSS Red outline - DES footprint Red circles - DES Y1 satellites Red triangles - DES Y2 satellites 13
Open Questions 14
Missing Satellites 15 10
Missing Satellites Galaxies inhabit dark matter halos Simulations predict that the Milky Way halo should contain thousands of dark matter subhalos We only see dark matter halo that are traced by baryons, and we only know of several dozen dwarf galaxies. Where are the missing satellites? What can we learn about galaxy formation and the nature of dark matter?! Combine large photometric surveys (DES, SDSS, Pan-STARRs, etc.) Opportunities to work with Big Data, data mining, and statistics! James Bullock Understand the galaxies that we *don t see*. 16
Galaxy Formation 17
Galaxy Formation The Milky Way satellites found in DES are not distributed uniformly Is the observed distribution of satellites consistent with LCDM? Biases from the Solar position? Accretion as satellites of the Magellanic Clouds? Accretion along the same filament as the Magellanic Clouds? A plane of satellites? Need larger photometric coverage to test these various hypotheses (new Magellanic Satellites Survey) Need spectroscopy and proper motions to determine the dynamics of satellite systems. Lots of opportunities to do photometry and spectroscopy! 18
Origin of Heavy Elements Rapid absorption of free neutrons during explosive event Possible sites: core-collapse SNe, neutron star mergers Observed excess of r-process elements in Ret II relative to other ultra-faint dwarfs (by factor >100) suggests enrichment by a single (rare) event Consistent with neutron star merger hypothesis??? 19
Origin of Heavy Elements Heavy elements are formed in extreme conditions through (r)apid and (s)low neutron capture processes Satellite galaxies are nearby relics of the early universe Are r-process elements created continuously by core-collapse supernova or in rare events like neutron star mergers? Ret II Stars enriched in Eu r-process s-process Ji et al. 2015 (1512.01558) 20
Origin of Heavy Elements Magellan/M2FS Gemini/GMOS VLT/GIRAFFE AAT/AAOmega 21
Nature of Dark Matter Dark Matter Distribution Particle Propagation Particle Detection Dark Matter Annihilation DM DM? SM SM Neutral Particles (γ, ν) Charged Particles (e ±, p ±, etc.) 22
Nature of Dark Matter iduals Galactic Substructure: Lower statistics Lower background Galactic Center: Larger signal Larger background Residual Map: 1-3 GeV Credit: Tim Linden 23
Nature of Dark Matter ) 24
Shorter Term Projects 24 17 J2204-4626 DES 1 J2339.9-5424 3 Filtered Stars J2356-5935 J0002-6051 Gru I J2251.2-5836 J2337-6316 2 16 2000 (deg) DES J2356-5935 1 Tucana SMC 0 18 Tucana group of satellites (Magellan observing this semester) 1 20 22 2 DES J0002-6051 24 3 3 2 1 0 1 2 3 projection of the density of stars observed in both g- and r-bands with g < 2 (deg) 2 he DES Y2Q1 footprint ( 5000 deg ). Globular clusters arestars marked with + Tidal tails around Tucana III RR Lyrae in DES Y2 dwarfs (deeper photometry) (SOAR observing this semester) 6, 2010 edition), two faint outer halo clusters are marked with symbo uque et al. 2015), Local Group galaxies known prior to DES are marked wit 25 Satellites and stream around in Y1 DES data are marke nnachie 2012), dwarf galaxy candidates discovered - 0 1 1.5 2000 Fig. 9. Color-Magnitude diagram of stars within 2rh of the center of Hydra II (1 The red star indicates the location of the RR Lyrae star 35.6516. For reference w stars confirmed with radial velocities as members of Hydra II (Kirby et al. 201 cyan circles, while radial velocity non-members are indicated with green circles. magenta squares show the location of variable stars that could not be classified. dotted lines correspond to a 13 Gyr old, metal-poor ([Fe/H]= 2.0) isochrone (Br 2012) shifted to 151 and 134 kpc, respectively. Fornax & Sculptor (Y3 DES data)
Scientific Skills These projects will develop a wide range of skills. Observing Experience Photometry: DECam, SOAR, Gemini Spectroscopy: Magellan, VLT, AAT Astronomical Tools Photometry of large survey data sets (DES, SDSS, DECaLs, Pan-STARRs, ) Medium resolution spectroscopy for velocity determination High resolution spectroscopy and spectral synthesis for elemental abundances Computational Tools Parallelized processing of big data Machine learning and data mining Statistical modeling with frequentist and bayesian techniques 26
Working in DES The DES Collaboration provides an extensive support structure. Opportunities to meet and interact with scientists around the world. Opportunities in other science areas, public outreach, etc. Milky Way science is undersubscribed in DES DES provides a large audience, a lot of support, and little competition.! Chicago is at the heart of DES Josh Frieman (FNAL/UChicago) Rich Kron (UChicago) Brian Yanny (FNAL) Scott Dodelson (FNAL/UChicago) and many other faculty, staff, post-docs and students! 27
Even More Questions Optimized searches for low-luminosity dwarf galaxies beyond the MW virial radius. Satellite systems of nearby galaxies Understanding the structure of the Milky Way halo using various stellar tracers (i.e., MSTO stars, HB stars, etc.) High resolution spectroscopy of Carbon-enhanced metal poor (CEMP) stars. Identifying high proper motion stars in DES (white dwarfs?) Using internal proper motions to understand the dark matter distribution of Milky Way satellite galaxies. many, many more 28