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Contenu archivé le 2024-06-18

Detailed Anatomy of Galaxies

Final Report Summary - DAGAL (Detailed Anatomy of Galaxies)

The Initial Training Network DAGAL, for Detailed Anatomy of GALaxies, ran from April 1st 2012 until March 31st 2016. DAGAL was an ambitious network formed of six research groups in Spain, Germany, Finland, France, and the Netherlands, in collaboration with three private sector partners. The network collaborated very closely with the Spitzer Survey of Stellar Structure in Galaxies (S4G).

We trained eight ESRs (PhD students) and two ERs (postdocs) using a combination of training through high-level astrophysical research and a comprehensive package of complimentary skills training. Our network exploited a unique data set: a combination of very deep mid-infrared imaging of over 2300 local galaxies which we are obtaining with the Spitzer Space Telescope, with ground- and space-based UV, optical, and radio data. The data reach unprecedented levels of surface brightness and radial extent over a very large sample, which is allowing statistical studies of the distribution of old stars, thus stellar mass, young stars, and gas.

Synergising the excellence in different areas of extragalactic research across our network, we tackled fundamental questions concerning the origin and evolution of galaxies. The combination of our Spitzer imaging with a unique set of additional data tracing the distribution and motions of old and young stars, and gas, has allowed us to reveal the interplay between galactic dynamics, current star formation and star formation history. Detailed numerical modelling has been an integral part of our work plan, and has allowed us to relate the present structure and dynamics of galaxies to their cosmological formation and subsequent evolution.

Our eight ESRs and two ERs have received training through this research, and through an ambitious programme of complimentary skills training. The latter includes meeting organisation, presenting, scientific and outreach writing, project management, software use, and language training. This training was delivered to the fellows by their supervisors or team members, by their own universities, or in specific training courses organised by the DAGAL network. For instance, a customised project management course was delivered by our private sector partner Fractal during one of the annual meetings.

Network-wide research training activities were also offered, and included the use of large telescopes (all fellows participated in an observing run on the 2.5m Isaac Newton Telescope on La Palma in the Canary Islands in Spain), training schools on numerical modelling and radio and IFU astronomy, and lectures by invited experts during the annual network meetings. Mobility has been a key aspect of our network approach. All researchers have spent time at different nodes and at meetings. Our training programme has helped prepare the next generation of scientists: Europe’s investment for the future.

From the outset, DAGAL has stimulated public outreach by its team members and fellows. As a result, the project has delivered press releases, radio programmes, and a number of “pretty pictures” of galaxies on its webpage ( The fellows maintained the DAGAL twitter and facebook accounts, with 500 followers, and one fellow won a prize for an outreach article he wrote in his home country. All fellows gave talks to the general public or to school children, in their home countries, place of work, or elsewhere.

The DAGAL network organised three annual meetings, three training schools, a workshop in the Lorentz Center of Leiden University in October 2014, and finally expanded its fourth and final annual meeting into an international scientific conference which achieved the status of Symposium of the International Astronomical Union, and which was organised by DAGAL’s Madrid node in the beautiful city of Toledo.
One of the main products of the DAGAL project is a set of scientific deliverables, which are publicly available ( and They include an advanced search and sample selection tool and links to all reduced S4G Spitzer images, GALEX UV and optical images of most of them, and HI, CO, or Hα kinematic and imaging data for subsets. Also available are an atlas of structures in S4G galaxies (such as bars, lenses, and rings) and a catalogue of gas flows in barred potentials: gas and orbit responses to typical potentials, with varying axial ratio, pattern speed, and bar mass.

To date, over 130 refereed papers are associated with the DAGAL project, of which over 50% have attracted more than three times the median number of citations in our field. Selected highlights of work published by the fellows on the DAGAL network include the identification of a merging dwarf galaxy companion to the galaxy NGC 7742, and the deduction from dynamics, stellar populations and star formation analyses that this is a merger event with a mass ratio similar to the Milky Way - Small Magellanic Cloud pair, with an initial passage some 2 Gyr ago.

We used independent component analysis to separate the 3.6 and 4.5 μm S4G images into emission from old stars and dust emission, which allowed us to derive accurate stellar mass maps (publicly available). These maps were used to derive that interactions increase the star formation rate in galaxies, but only by a factor of around two. We used infrared spectra to extend empirical stellar population models to the mid-IR, vital for the interpretation of star formation histories in galaxies (the models are available on We presented a GALEX/S4G UV−IR colour-colour diagram, from which we deduced that galaxies quickly transition from the so-called GALEX blue to the red sequence, on timescales of order 108 yr.

Galactic bars in the S4G sample were characterised in detail, uncovering possible evidence for the growth of bars from the density amplitudes, lengths, and strengths of bars in galaxies of different morphological types. We also created a catalogue of morphological features in the complete sample of the S4G, reporting among many other parameters the normalised sizes of components like inner rings and lenses. One conclusion is that barlenses indeed form part of the bar. Using the same images from the S4G but combining them with high-quality HI data, we studied the intrinsic scatter in the Tully-Fisher relation, and have uncovered a high sensitivity of the scatter to the internal kinematics of the gas.

Using numerical modelling we discovered how prograde mergers of two galaxies can produce kinematically decoupled cores (KDCs) in the resulting elliptical galaxies, adding another powerful mechanism to form the substantial number of observed KDCs in early-type galaxies. We also studied the imprints of boxy/peanut structures on the kinematics of simulated disk galaxies and explored the effects of modelling a boxy/peanut bulge on the estimates of bar galaxy parameters. We found that failing to allow for a boxy/peanut bulge can induce errors of up to 40% in the forces in the bar region, and significantly impacts the study of a modelled galaxy’s orbital structure, kinematics and morphology.

In summary, our DAGAL initial training network which ran from April 2012 to March 2016 has employed eight ESRs and two ERs, all of whom have made successful steps in their career development and most of whom have most on to coveted follow-up positions. We have made important scientific advances on the topic of galaxy structure and evolution, as described in over 130 refereed publications. We encourage our colleagues to use the DAGAL data products which are publicly available, and which include images as well as catalogues of advanced results.

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