THE INTERNAL DYNAMICS OF DWARF SPHEROIDAL GALAXIES: AN OBSERVATIONAL POINT OF VIEW MICHELLE COLLINS - HUBBLE FELLOW @ YALE INTRODUCING THE DWARF SPHEROIDALS OF THE MILKY WAY! 25 +8/9ish ~36/7ish! Bechtol+ 2015; Koposov+ 2015 (predicted by E. Tollerud+2008!) Image from SkyMapper collaboration Triangulum II - Laevens+2015 Hydra II - Martin+2015 Pegasus III - Kim+2015 EXPLAINING THE ‘ISH’ Not all new candidates will be galaxies Zone of Need (chemo)dynamics! CONFUSION Globular clusters Dwarf galaxies MV rhalf (pc) DWARF GALAXIES LIVE IN DARK MATTER HALOS 1st measurement of Draco velocity dispersion from 3 stars in 1983: -1 σv>6.5 kms , M/L≈31 Msun/Lsun Today: -1 σv= 9.1+/-1.2 kms , M/L≈34 Msun/Lsun Draco as viewed by SDSS, composite created by Robert Lupton C stars in Draco, Aaronson 1983 ‘IDEAL' LABORATORIES FOR STUDYING DARK MATTER Milky Way M31 ) sun (M half M Lhalf (Lsun) Collins+(2015) HMMM….. Concerns about the ultra-faints Hercules - MV=-6.6 Plus CVn II & LeoV Willman 1 - MV=-2 (Sand+12) Willman+2011 Sand+09, Roderick+15 PROBLEM FOR MASS MODELING • How to interpret ‘mean’ velocity dispersions • Makes applying normal models tricky (not in dynamical equilibrium) • May not be best objects for indirect dark matter detection experiments BUT COULD ALSO TELL US SOMETHING Cusped and cored galaxies disrupt differently More circular orbit Cusped Cored From hydro sims: expect brighter systems to be cored, fainter to be cusped More radial orbit Peñarrubia+10, Brooks+14, Errani+15 CATAGORISING STRIPPED POPULATION WILL BE INFORMATIVE! Which dSphs are undergoing tidal interactions/ disruption? Are their orbits ‘special’? How does that compare to predictions from simulations? INTRODUCING THE DWARF SPHEROIDALS OF ANDROMEDA! First M31 dwarfs - And I-III (and non-dwarf IV) van den Bergh 1972 Cas III Per I And VII POSS I/II SDSS M31 PAndAS And XXVIII, PS1 Lac I And VI, XXIX van den bergh+72, Armandroff+98,99 M33 Karantchentsev+99,Zucker+04,05, Majewski+,Martin+06,09,13ab,,Ibata+07, Irwin+08,McConnachie+08,Richardon+10 SPECTROSCOPY PAndAS SPLASH SPLASHing PAndAS M31 M33 Collins+(2013,2015), Tollerud+(2012, 2013), Ho+(2012, 2014), Martin+(2014) ALSO DARK MATTER DOMINATED Milky Way M31 ) sun (M half M Lhalf (Lsun) Collins+(2015) R. Michael Rich, DEIMOS 2014B U052B Tip of the red giant branch And XIX Figure 1: Left: Circular velocities (Vc) for dSphs vs. half light radius. Rotation curves from subhalos of different masses within the Aquarius simulations that span the mass range of those predicted by ⇤CDM are overplotted. While 10 subhalos 1 with masses 40 kms− (red curve) are expected around Milky Way sized systems, few are observed in the real Universe ≥ that have high enough Vc (and hence, masses) within their half-light radii to be consistent with this curve. Also a number of 1 systems (including And XIX) have circular velocities that fall below the 10 kms− curve (cyan), which is a lower mass limit beneath which subhalos should not form stars. Some process must have lowered their mass over time, such as tidal stripping. Right: Color magnitude diagram for all stars within 1 half light radius of And XIX. Red lines show magnitude limits to which spectra of S:N of 8, 5 and 3 can be taken within 1 hour. Higher S:N will be possible for our longer 2 hour exposures, allowing ALSO SOME UNUSUALaccurate metallicities to be measured for the brightestOBJECTS… stars. Bate et al. 2013 Stream Figure 2: Number density map of all stars bright enough to observe with DEIMOS in And XIX and the nearby stream (both labeled). Our proposed targeting strategy to map out both features is shown with black rectangles, which represent the DEIMOS field of view. And XIX And XXI 3 And XXV Collins+14 ANDROMEDA XXI 5 • Luminosity ~ 4x10 Lsun • Half-light radii ~ 1kpc • Velocities for ~100 stars Collins+in prep 1ST STEP: VELOCITY DISPERSION PROFILE A Milky Way example 15 10 5 1 rhalf 2 rhalf 500 1000 1500 Velocity dispersion (km/s) Velocity Radius (pc) Walker et al. 2007 AND XXI And XXI ~ 20 stars/bin 1 rhalf More And 21 stars Velocity dispersion (km/s) dispersion Velocity Radius (pc) What’s going Collins et al. in prep on here..? WHAT ABOUT ITS VELOCITY PROFILE? Not in dynamical equilibrium? ‘Wobble’ (km/s) systemic V dispersion (km/s) dispersion radius (arcmin) Collins et al. in prep TIDAL INTERACTION WITH M31? 135 kpc And XXI Or a merger? And II - Amorisco+14 Could explain ‘weird’ kinematics? R. Michael Rich, DEIMOS 2014B U052B Tip of the red giant branch And XIX Figure 1: Left: Circular velocities (Vc) for dSphs vs. half light radius. Rotation curves from subhalos of different masses within the Aquarius simulations that span the mass range of those predicted by ⇤CDM are overplotted. While 10 subhalos 1 with masses 40 kms− (red curve) are expected around Milky Way sized systems, few are observed in the real Universe ≥ that have high enough Vc (and hence, masses) within their half-light radii to be consistent with this curve. Also a number of 1 systems (including And XIX) have circular velocities that fall below the 10 kms− curve (cyan), which is a lower mass limit beneath which subhalos should not form stars. Some process must have lowered their mass over time, such as tidal stripping. A HOST OF DYNAMICALLYRight: Color magnitude diagram for all stars within 1 half light radius of And XIX. Red lines show magnitude limits to which spectra of S:N of 8, 5 and 3 can be taken within 1 hour. Higher S:N will be possible for our longer 2 hour exposures, allowing INTERESTING SYSTEMSaccurate metallicities to be measured for the brightest stars. AndBate et al. 2013XIX And XXI Stream Velocity dispersion (km/s) dispersion Velocity Figure 2: Number density map of all stars bright enough to observe with DEIMOS in And XIX and the nearby stream (both labeled). Our proposed targeting strategy to map out both features is shown with black rectangles, which represent the Radius (pc) DEIMOS field of view. Willman I Hercules 3 SUMMARY • Understanding dynamics not as simple as we’d hoped Messy, complicated dark matter laboratories… • Disrupting objects have interesting things to tell us Unusual orbits? Dark matter halo properties? • More (chemo)dynamics for stars = more information = better understanding MERGER? And II Mv~-12, rh~1000pc, DM31~110 kpc Velocity dispersion (km/s) dispersion Velocity Amorisco et al. 2014 And XXI Mv~-10, rh~1000pc, DM31~130 kpc.