THE INTERNAL DYNAMICS OF DWARF SPHEROIDAL : AN OBSERVATIONAL POINT OF VIEW

MICHELLE COLLINS - HUBBLE FELLOW @ YALE INTRODUCING THE DWARF SPHEROIDALS OF THE ! 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 HALOS

1st measurement of Draco velocity dispersion from 3 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 - 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 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? Velocity dispersion (km/s) INTERESTING SYSTEMS A HOSTOFDYNAMICALLY Radius (pc) And XXI pcr fSNo ,5ad3cnb ae ihn1hu.Hge : ilb osbefrorlne orepsrs allowing exposures, hour 2 longer our for possible be will S:N Higher stars. hour. brightest 1 the within for stripping. taken measured tidal be be can as to 3 such metallicities and time, accurate 5 over 8, mass of their S:N lowered of have spectra must process kms Some 10 stars. the form Right: below not fall should that subhalos velocities which circular beneath have XIX) And (including systems by enough predicted high those have of that range mass the masses span with that simulations Aquarius the within Left: 1: Figure 2014B DEIMOS Rich, Michael R. bt aee) u rpsdtreigsrtg ompotbt etrsi hw ihbakrcage,wihrpeetthe represent which rectangles, black with shown is features both out map view. to of field strategy DEIMOS targeting proposed Our labeled). (both 2: Figure oo antd iga o l tr ihn1hl ih aiso n I.Rdlnsso antd iist which to limits magnitude show lines Red XIX. And of radius light half 1 within stars all for diagram magnitude Color ubrdniympo l tr rgteog oosrewt EMSi n I n h erystream nearby the and XIX And in DEIMOS with observe to enough bright stars all of map density Number 40 iclrvlcte ( velocities Circular kms V c 1 adhne ass ihnterhl-ih ai ob ossetwt hscre loanme of number a Also curve. this with consistent be to radii half-light their within masses) hence, (and rdcre r xetdaon ik a ie ytm,fwaeosre ntera Universe real the in observed are few systems, sized Way Milky around expected are curve) (red Willman I Willman V c o Sh s aflgtrdu.Rtto uvsfo uhlso ifrn masses different of subhalos from curves Rotation radius. light half vs. dSphs for ) U052B And XIX And XIX Stream Bate et al. 2013 al. et Bate ⇤ 1 D r vrlte.Wie1 subhalos 10 While overplotted. are CDM uv ca) hc salwrms limit mass lower a is which (cyan), curve Tip of the red giant branch 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