A stringent test of the galaxy formation paradigm: detailed modeling of the dynamics and stellar population of the Milky Way

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics

Abstract

High and low-redshift observations, in combination with numerical simulations, have provided a scenario, over the last 30 years, in which galaxy formation proceeds in a hierarchical fashion, driven by the gravitational collapse of dark matter (DM). Although the scenario explains most of the observations, its strongest and cleanest predictions still have to be confirmed: (i) galaxies are expected to be embedded in massive DM halos, however, remarkably, the very existence of DM is still debated and the possibility that the laws of gravity are not those of Einstein is under discussion. (ii) the hierarchical build up of galaxies is expected to leave behind a very large number of substructures, in both the dark and luminous matter. Although some substructure in nearby galaxies exists, this is not at the expected level. (iii) galaxy formation models make detailed prediction about the age and chemical composition of galactic substructure, but these information are difficult to extract from galaxy observations. Due to its vicinity, our Milky Way constitute a unique laboratory to perform the above stringent observational tests of the galaxy formation paradigm. For our Galaxy in fact individual stars can be easily observed, and position and velocity can in principle be obtained. The stars could be used as tracers of the gravity to accurately detect the presence of DM. The chemical composition of individual stars can also be measured, and could be used, in combination with the stellar kinematics, to uncover stellar subcomponents in the Galaxy. However until now no such data existed. The situation is soon going to change dramatically. A number of ongoing large observational survey from the ground (RAVE, SEGUE) and from space (Gaia) will measure position and velocities for a large fraction of all the stars in our Galaxy. This will provide the biggest improvement in our knowledge of the Galaxy, since Galileo observed it with its telescope, four centuries ago, first realizing that it was actually made of individual stars. The new data have a similar potential to revolutionize our understanding of how galaxies form. The main goal of my proposed project is to perform the above three stringent tests of the galaxy formation paradigm, by constructing a detailed model of the dynamics and the chemical composition of our Milky Way, to be compared with the position, velocity and chemical composition stellar measurements provided by the RAVE, SEGUE and then Gaia survey.

Publications

10 25 50
 
Description Since Edwin Hubble introduced his famous tuning fork diagram more than 70 years ago, spiral galaxies and early-type galaxies have been regarded as being two distinct families. The spirals are characterized by the presence of disks of stars and gas in rapid rotation, while the early-types are gas poor and described as spheroidal systems, with less rotation and often non-axisymmetric shapes. This clear distinction is emphasized in Hubble's tuning-fork diagram, where early-type galaxies (E0-E7 and S0) lie on the handle of the fork, well separated from spiral galaxies (Sa-Sc). The separation is physically relevant as it implies a distinct path of formation for the two classes of objects.

A known issue of Hubble's classification, however, is that it mostly relies on optical images, from which it is nearly impossible to recognize thin face-on disks of stars from much rounder edge-on spheroids. For this reason the fraction of disks-like systems hidden in the early-type category has been a matter of debate for decades.

The solution to the problem comes from observations of the stellar kinematics: the stars in a thin disk rotate much faster than those in a rounder spheroid. This implies that the kinematics makes it possible to recognize a disk from a spheroid at any inclination. However it requires complex and time-consuming observations. To address this question I put together as Co-PI a team of people we called Atlas3D.

Thanks to the major allocation of 40 nights of observations with the SAURON integral-field spectrograph at the William Herschel Telescope, the team derived maps of the stellar motions for all 260 galaxies in a carefully selected volume of the nearby Universe. The results were unexpected and reveal a new paradigm for early-type galaxies. For the first time, it was found that the overwhelming majority of the early-type galaxies in the nearby Universe does not consist of roundish spheroidal objects, but instead has disks and mostly resembles spiral galaxies with the gas and dust removed. Only a tiny fraction of the early-type galaxies - the "slow rotators" - are genuine spheroids. This indicates that Hubble's classic tuning-fork gives a misleading description of galaxy structure. To correct for this fact the team proposed a revised scheme in which the vast majority of early-type galaxies - termed "fast-rotators" - are close relatives of spiral galaxies (Sa-Sc) and for this reason form a parallel sequence to them. The new paradigm highlights a much closer connection between early-type and spiral galaxies than previously thought, and this will need to be considered in future models of how galaxies form.
Exploitation Route Our finding is becoming central to the understanding of galaxy formation. It has contributed to the development of much larger surveys of galaxies using two-dimensional observations of the stellar motions, to be able to recognize how galaxy structure varies as a function of environment and other galaxy properties.
Sectors Aerospace, Defence and Marine,Education,Culture, Heritage, Museums and Collections,Other

URL http://www.skyandtelescope.com/astronomy-news/rethinking-galaxies/
 
Description For millennia humanity has aspired at understanding our place and origins in the Universe. Less than a century ago, we discovered we live in a galaxy like millions of others populating the Universe. For this reason, today finding our origins means studying how galaxies came into existence. My research tries to address the question about our origins.
First Year Of Impact 2010
Sector Aerospace, Defence and Marine,Education,Other
Impact Types Cultural

 
Description Astrophysics at Oxford: 2010-2015
Amount £2,486,342 (GBP)
Funding ID ST/H002456/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Academic/University
Country United Kingdom
Start 04/2010 
End 03/2015
 
Description Atlas3D Project 
Organisation ASTRON Netherlands Institute for Radio Astronomy
Country Netherlands 
Sector Public 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation Claude Bernard University Lyon 1 (UCBL)
Department Astrophysics Research Centre of Lyon (CRAL)
Country France 
Sector Academic/University 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation European Southern Observatory (ESO)
Country Germany 
Sector Charity/Non Profit 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation Gemini Observatory
Country United States 
Sector Academic/University 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation Leiden University
Department Leiden Observatory
Country Netherlands 
Sector Academic/University 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation Max Planck Society
Department Max Planck Institute For Extraterrestrial Physics (MPE)
Country Germany 
Sector Charity/Non Profit 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation Max Planck Society
Department Max Planck Institute for Astrophysics
Country Germany 
Sector Public 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation New Mexico Institute of Mining and Technology
Department Physics Department
Country United States 
Sector Academic/University 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation Paris Diderot University
Country France 
Sector Academic/University 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation University of California, Berkeley
Department Department of Astronomy
Country United States 
Sector Academic/University 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation University of Groningen
Department Kapteyn Astronomical Institute
Country Netherlands 
Sector Academic/University 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation University of Hertfordshire
Department Centre for Astrophysics Research (CAR)
Country United Kingdom 
Sector Academic/University 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Atlas3D Project 
Organisation University of Toronto
Department Dunlap Institute for Astronomy & Astrophysics
Country Canada 
Sector Academic/University 
PI Contribution http://www-astro.physics.ox.ac.uk/atlas3d/
Collaborator Contribution The collaborators have contributed to the science results
Impact As part of this effort we were awarded major observing proposals at various multi-wavelength facilities (WSRT, IRAM 30-m, CARMA, INT, WHT). We submitted 12 refereed papers, of which 8 are already published or in press.
Start Year 2007
 
Description Press release 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact Press releases of the results were published by the University of Oxford UK, the CNRS in France and the Subaru Telescopes in Japan.

The results were later disseminated by about 10 additional popular scientific journals on the web.
Year(s) Of Engagement Activity 2010