Galactic dynamics in the era of Gaia

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1 Galactic dynamics in the era of Gaia Amina Helmi Credits:)ESA/Gaia0CC)BY0SA)3.0)IGO)

2 How did the Galaxy come to be like this? We can observe individual stars and measure their properties Decipher sequence of events of formation of a typical galaxy Distributed in various Galactic components, each with specific characteristics e.g. halo stars are as nearly as old as the Universe The Milky Way is a Rosetta stone

3 Galactic Archaeology Key ingredient of galaxy formation: mergers t = 1 Gyr t = 2 Gyr Were mergers important for galaxies like the Milky Way? How often and when did they happen? What were the building blocks? t = 3 Gyr t = 4.5 Gyr Stars are fossils Motions, ages, chemical composition trace origin Substructures pinpoint to debris from accretion events Probe force field! mass (gravity) t = 8 Gyr t = T now today snapshots:)j.)gardner)

4 Testing the cold dark matter paradigm Is this picture correct? Credit: V. Springel Are galaxies like the Milky Way and its nearest neighbours embedded in dark matter halos like those predicted by the cosmological model?

5 Testing the cold dark matter paradigm Is this picture correct? Are galaxies like the Milky Way and its nearest neighbours embedded in dark matter halos like those predicted by the cosmological model?

6 Testing the cold dark matter paradigm Is this picture correct? Credit: V. Springel Are galaxies like the Milky Way and its nearest neighbours embedded in dark matter halos like those predicted by the cosmological model? How much dark matter is there? how is it distributed? what is the dark matter? Is Gravity correct?

7 The Gaia revolution: starting now! (1 km/s proper motions) Gaia will measure positions and motions of stars for 10 9 stars (10,000x larger than predecessor); over a volume 100,000 larger; up to 1,000x more precisely! transformational

8 Simultaneous astrometry, photometry, spectroscopy Complete to G = 20.7 (V = 20-22), G = 16 for spectroscopy Whole sky already observed! First data release in mid-2016 (positions + G magnitude) DR2 in Jan 2017: full phase-space up to 21 million objects/deg 2 By Jan. 2015, 16 billion photom/astrom transits, 1.6 billion spectroscopic Courtesy of Anthony Brown & Gaia/DPAC

9 Courtesy)A.)Brown))

10 Image of the week Photometry RR Lyrae in the LMC Spectroscopy: RVS Spectro-photometry astrophysical parameters

11 )Gaia)astrometric)data)reduc9on) Disentangling) parallax)and) proper)mo9on) needs)more)than) 1)yr)of)data) Courtesy)U.)Lammers,)T.)PrusA,)A.)Brown)and)DPAC)

12 )Gaia)astrometric)data)reduc9on) Disentangling) parallax)and) proper)mo9on) needs)more)than) 1)yr)of)data) Gaia/AGIS)team) wanted)to) experiment)with) full)5dparameter) solu9ons)as)soon) as)possible) Courtesy)U.)Lammers,)T.)PrusA,)A.)Brown)and)DPAC)

13 )Gaia)astrometric)data)reduc9on) Disentangling) parallax)and) proper)mo9on) needs)more)than) 1)yr)of)data) Gaia/AGIS)team) wanted)to) experiment)with) full)5dparameter) solu9ons)as)soon) as)possible) Combine)with) posi9ons)of)stars) in)tycho)catalog:) pm)and)par)for) 2.5)million)stars) Courtesy)U.)Lammers,)T.)PrusA,)A.)Brown)and)DPAC)

14 (Very))preliminary)results)on)TGAS)parallaxes) Courtesy)U.)Lamers,)T.)PrusA,)A.)Brown)and)DPAC)

15 What)do)we)know)now)about)the) Galaxy?) What)are)some)of)the)open)ques9ons?) Assembly)history)of)the)Milky)Way) The)Galac9c)dark)halo))

16 The)accre9on)history)unveiled)so)far:)) The)Galac9c)halo)from)SDSS/PanStarrs) Belokurov)et)al.)2006)+) North)Galac9c)Cap) Outer)halo:) Clear)evidence)of)substructure) Limited)to)highDsurface)brightness)features) (progenitors/9me)of)events)) Qualita9vely)consistent)with)expecta9ons)from) LCDM)(Helmi)et)al.)2011;)Deason)et)al.)2014)) Slater)et)al.)2014+) Galac9c)An9centre)

17 Kinema9cs)for)large)numbers)of)halo)stars:)crucial)

18 Kinema9cs)for)large)numbers)of)halo)stars:)crucial) 100s of streams predicted near the Sun and possibly hiding How to find these? Gaia! Clustering in conserved quantities Follow-up: SFH and chemical evolution of building blocks energy conserved)quan99es) Helmi)&)de)Zeeuw)2000) " FLAMES, 4MOST & WEAVE angular momentum

19 Streams, orbits and gravitational potentials As satellite galaxy disrupts, stars delineate nearly an orbit Present-day spatial distribution (density, shape, total mass): consistent with CDM? Granularity (critical test of CDM) e.g. Johnston et al. 2002; Yoon et al. 2011; Carlberg 2012/2013 Time-evolution e.g. Peñarrubia et al. 2005; Gomez & Helmi 2010, Buist & Helmi (2015)

20 The)dark)halo) Total)mass:))7)x)10 11 ) )2)x)10 12 )M sun)) (factor)3)uncertainty!) ) Rota9on)curve,)density)profile) )poorly)characterized) Shape)constraints:)) CloseDin:)Pal)5)streams)not)too)flajened)towards)disk)(q)~)0.95,)Kupper)et)al.)2015)) At)large)distance:)possibly)triaxial)at)large)distances)but)based)on)just)1)stream:)Sagijarius;)very)debated) Kupper)et)al.)(2015))

21 The Milky Way's dark halo shape and Sgr stream If halo is spherical, motion is in a plane Deviations, if any, tell us shape in CDM halos are triaxial at large radii PUZZLES from models of Sgr stream in axisymmetric potentials Precession signal (non-spherical halo): clearly favour OBLATE (Johnston et al. 2005) Radial velocities: clearly favour PROLATE (Helmi 2004) Law et al. 2005

22 Vera-Ciro & Helmi, 2013 Solution: A triaxial halo? Model by Law & Majewski (2010) # Positions on the sky (hence precession) and radial velocities However, it is odd nearly oblate shape Symmetry plane: yz, i.e. perpendicular to the disk " not a stable configuration/nor intuitive physically Constraints on inner shape weak: can accommodate an oblate flattened inner halo (Vera-Ciro & Helmi 2013) Why long axis along y? LMC provides additional significant torque " effective potential is sum of contribution of triaxial MW halo + LMC " indistinguishable so far

23 Is this picture correct? Koposov)et)al)2009) Springel)et)al.)2008) Granularity: Hundreds of thousands dark clumps if dark matter particle is cold

24 Summary / Next steps Milky Way: A revolution can be expected with Gaia satellite mission Many streams (soon to be) discovered Modeling of the dark halo shape from Sgr streams accommodates inner oblate and outer triaxial Next: halo s density profile, mass and granularity (missing satellites) as well as time evolution History of formation of the Milky Way Milky Way unique probes of cosmology Provided some of the most stringent tests and flaws/problems of the CDM model There is much more to come!

25 Thank)you)for) your)ajen9on) ESADESO)Galaxy)WG )))))ESADESO)mee9ng,)ESTEC,)10)October)ESADESO)2008) 25)

The Gaia Archive. Center Forum, Heidelberg, June 10-11, 2013. Stefan Jordan. The Gaia Archive, COSADIE Astronomical Data

The Gaia Archive. Center Forum, Heidelberg, June 10-11, 2013. Stefan Jordan. The Gaia Archive, COSADIE Astronomical Data The Gaia Archive Astronomisches Rechen-Institut am Zentrum für Astronomie der Universität Heidelberg http://www.stefan-jordan.de 1 2 Gaia 2013-2018 and beyond Progress with Gaia 3 HIPPARCOS Gaia accuracy