Letters of Intent received in 2015

LoI 2017-279
Rediscovering our Galaxy

Topics

Short list of topics to be addressed at the Symposium:

• The oldest stars in the Milky Way: Very metal-poor stars, globular clusters, RR Lyrae, White dwarfs
• Halo assembly and building blocks: cosmological simulations, halo assembly and merger history, dark matter, streams, DES Survey
• The Bulge-disk and Bulge-halo interface: disentangling the mixed populations in the central regions of the Galaxy, the bar, the bulge, the central black hole
• New views on the inner Galaxy with OGLE, VVV and APOGEE-North/South
• The Galactic disk and its chemodynamical properties: secular evolution, gas accretion, merger rates, chemistry, ages, and kinematics.
• Galactic archaeology with asteroseismology and spectroscopic surveys: new results from CoRoT, Kepler, K2; preparing for Gaia/LSST/Plato-2
• How well can we calibrate age indicators and constrain star formation histories in the different Milky Way components?
• Establishing advanced models of the Milky Way
• Outlook: upcoming Gaia data releases and new spectroscopic surveys

Rationale

While observations of distant galaxies allow us to probe the times when these systems were formed, it is only our own Galaxy that provides a fossil record detailed enough to unravel its complete formation history. Galaxies are dynamically and chemically inhomogeneous and it is only by using the higher dimensional phase space resulting by combining kinematic and chemical measurements that a full understanding of their constituent parts can be achieved. Deciphering the assembly history of our Galaxy requires a detailed mapping of the structure, dynamics, chemical composition, and age distribution of its stellar populations. The ultimate goal being that of “tagging” individual stars to each of the progenitor building blocks, thus opening up a new era of Galactic astronomy. This requires large-scale ground-based photometric and spectroscopic surveys of the stellar components of the Milky Way and its companion satellite systems. These systems directly complement the ongoing Gaia mission and future LSST providing major new insights on the structure and assembly history of a prototypical (i.e., L∗) galaxy. The DES survey promises a new twist in this topic as recently illustrated by the discovery of several new satellites, almost doubling the number of previously known Milky Way satellites in less than a year.

This IAU Symposium would be a natural step after the IAU Symposium 254, which took place in 2008 soon after the Geneva Copenhagen sample became available, making a jump in the size of available spectroscopic samples at the time (going from a few hundred stars to more than tens of thousand stars). Another radical change has been made by recent surveys not only in number of targets, but also in volume covered. Indeed, since the Copenhagen Symposium, we have stepped out of the volume surveyed by the Hipparcos mission, reaching far out regions of the Milky Way with spectroscopic surveys such as RAVE, SEGUE, APOGEE, LAMOST, and Gaia-ESO. In particular, with the near infrared APOGEE spectrograph, and the photometric ESO-VVV survey we were able to penetrate the dust that obscures significant fractions of the disk and bulge of our Galaxy, seriously complementing our view of the Milky Way. The discovery potential increases further when combining the above information with large time domain photometric surveys such as OGLE, CRTS, Pan-STARRs, SkyMapper and the future LSST. Two illustrative examples are the discovery of a large number of RR Lyrae by OGLE/CRTS and very metal-poor candidates, now also in the Bulge, with SkyMapper. Spectroscopic follow-up of these precious fossil records is already ongoing in several of the 8m-class telescopes, and in two years from now breakthroughs are to be expected.

A further step out of the Hipparcos volume has been made with the use of asteroseismology (from CoRoT and Kepler) combined with the above spectroscopic surveys. This combination also enables drastic improvement in the attainable precision in the masses, radii and ages of giant stars that are as far as ~5 kpc away from us. Further breakthroughs are expected with the K2 mission in the next couple of years (after Kepler's loss of a second spacecraft reaction wheel in May 2013 the original Kepler mission was formally ended, and the K2 mission started with observed fields now located along the ecliptic plane, hence beautifully complementing CoRoT). Several key K2 fields will be completed already one year before the proposed Symposium takes place, in particular with seismic data for stars near the Galactic Center -- a first in the history of Galactic Archaeology.

Finally, another big step forward will be done thanks to the first two Gaia data releases which take place in the summer of 2016 and early 2017 (see www.cosmos.esa.int/web/gaia/release for details on the Gaia data release scenario). The first release will essentially provide only positions and magnitudes, but also provides a major improvement in the proper motion accuracies over the Hipparcos volume. The second release contains Gaia parallaxes and proper motions, complemented by broad-band colours and radial velocities for the brighter stars. The time between the second and third Gaia releases consists also of a sweet spot for RAVE, which overlaps with Tycho-2 and Gaia for around 500000 stars, providing key complementary information, in particular chemistry for several individual elements, which will not yet be available from Gaia at the proposed time of this symposium. This will hence be our first example (in smaller volume) of what we will have in hands at the end of the Gaia mission, and will already certainly lead to breakthroughs in our knowledge of the Milky Way. In this golden era for Galactic archaeology we are thus about to rediscover our Galaxy.

In summary, the field of Galactic Archaeology is quickly transforming. Many of the advances described above are going to take shape in the next 1-2 years. In this sense, the IAU symposium proposed here is timely and should happen even before we are flooded with the Gaia in its full potential. This Symposium goes beyond the topics discussed in the last IAU Symposium dedicated to the Milky Way in 2013, the IAU Symposium 298, as it has an important emphasis on the our new views on the inner Galaxy, and on the new tools brought by Asteroseismology and time-domain fields.

Host Institute role in the field: The host institute has made key contributions to the topic of Galactic Archaeology. It is the PI institute of RAVE, which together with SEGUE were the first two spectroscopic surveys to increase the observed samples for which radial velocities and chemical abundances were measured by an order of magnitude (in the case of RAVE reaching almost half a million stars). The host institution is involved in almost all major ongoing spectroscopic surveys, such as Gaia-ESO, SDSSIII/IV (APOGEE/SEGUE), and RAVE. The host institute is also involved in combining asteroseismology with spectroscopy, which has now become a key topic in Galactic Archaeology (as illustrated by the conference we organized this year -- see https://meetings.aip.de/592-WE-Heraeus-Seminar). The host institute is also the PI institute of 4MOST, a multi-object spectrograph to be built for the VISTA 4m telescope. The main Galactic goal of this instrument is to maximize the scientific return of Gaia, thanks to additional chemical abundance information for stars fainter than ∼14 mag, and radial velocities with 1-2 km/s precision for stars in the 14<V<20 range.

SOC Members: As the 3 SOC chairs are from the same institute, we would like to stress that SOC members from other nationalities will be given a prominent voice in the meeting organization. Below we list the names of those that have already agreed being part of the SOC if this proposal is approved. These are:
• Anthony Brown - Leiden Observatory - The Netherlands [confirmed]
• Joss Hawthorn - The University of Sydney - Australia [confirmed]
• Steve Majewski - University of Virginia - USA [confirmed]
• Andrea Miglio - University of Birmingham- UK [confirmed]
• Julio Navarro - University of Victoria - Canada [confirmed]
• Patricia Whitelock - SAAO and UCT, South Africa [confirmed]
• Beatriz Barbuy - University of Sao Paulo - Brazil [confirmed]
• Vanessa Hill - Observatoire de la Côte d'Azur - France [confirmed]
• Rosemary F. G. Wyse - The Johns Hopkins University - USA [confirmed]
• Andy McWilliam - The Carnegie Observatories - USA [confirmed]
• Francesca Matteucci - University of Trieste - ITALY [confirmed]
• Birgitta Nordstrom - Niels Bohr Institute - Denmark [confirmed]
• Raffaelle Gratton - Osservatorio Astronomico di Padova - INAF - Italy [confirmed]
• Manuela Zoccali - Universidad Católica, Chile [confirmed]
• Gerry Gilmore - Institute of Astronomy Cambridge - UK [TBC]
• Gang Zhao - National Astronomical Observatories - China [TBC]
• Masashi Chiba -- Tohoku University, Japan [TBC]

VENUE:The Symposium would take place at our historical site of Telegrafenberg (The Albert Einstein Science Park), Potsdam Germany (http://www.aip.de/en/institute/locations/transport/telegrafenberg). This is a historic hill in Potsdam that once housed the main Prussian observatories. On it still stand 19th century refractors as well as the famed and architecturally revered "Einstein Tower" designed by E. Mendelsohn. The Telegraphenberg facility can hold up to 400 people, and is equipped with modern audio-visual facilities, includes Wi-Fi and technical support. Next to the lecture theatre there is a large coffee break area where all poster presentations will be on display during the whole duration of the Symposium. Because these facilities are free of charge for our institute, we can keep the conference fee down. Meals: In the same building where the Symposium will take place (upper floor) there is a restaurant where all 300 participants can easily have lunch at affordable prices. Accommodation: We plan to have a shuttle that will take participants from the hotels to conference venue in the morning, and back to the hotels at the end of the day. Hotels are also well connected via the good public transport system. Discounted rates can be obtained in a couple of hotels nearby, for instance: Mercure Hotel Potsdam, Hotel Brandenburger Tor Potsdam, Steigenberger Hotel Sanssouci.