Galaxy Structure and Evolution
ICCUB research in this area includes both galactic and extragalactic astronomy:
Galactic astronomy
Galactic astronomy is the study of the Milky Way, a barred spiral galaxy containing several structural components. A barred bulge is in the central part extending out to 10 thousand light-years, which harbors a 4 million solar mass black hole in the center surrounded by a nuclear star cluster. Outside the bar, the thin disk extends from 10000 to 50000 light-years, and contains most of the stellar and gaseous mass and most of the star formation activity of the Galaxy. The thick disk harbors stars of intermediate ages and its origin is still debated. Around the disk is the halo, a roughly spherical structure extending much further than the disk, which contains very few stars but most of the mass of the Galaxy. The halo also contains about 200 globular clusters, which are bound systems of thousands of stars that are orbiting around the center of the Milky Way, and streams of stars that trace past mergers of dwarf galaxies with the Milky Way. The large mass of the halo is inferred from measurements of velocities of stars and gas; we do not know what this mass is made of, and we call it dark matter. Independent evidence for the existence of dark matter in the Universe comes to us from cosmology. [+]
Our Galaxy is a rich laboratory to explore how galaxies form and evolve. The Cold Dark Matter cosmological theory predicts the formation of large galaxies through the merging of smaller ones. Linking the local solar neighborhood, open clusters, the disk and the halo of our Galaxy to the Universe beyond is the key to our understanding of galaxy evolution and the impact of mergers, from the epoch of the formation of the first stars to the present. Although observations of the most distant galaxies are fundamental to understand how galaxies formed, only our own Galaxy and a few nearby dwarf galaxies in the Local Group can be observed in sufficient detail to provide a fossil record that can unravel a complete formation history. Identifying and studying stellar streams can help determine the way the Galaxy has grown and its present components have come into place. Deciphering the assembly history of our Galaxy requires a detailed mapping of the structure, dynamics, chemical composition, and age distribution of its stellar populations. Ideally one would like to “tag” individual stars to each of the progenitor building blocks, and relate this to the accretion history.
Extragalactic astronomy
Extragalactic astronomy studies the structure and evolution of galaxies and the intergalactic medium beyond the Milky Way. This includes a large array of objects ranging from dwarf galaxies, quasars and clusters of galaxies, and spanning the last 13 billion years of the history of the Universe. Extragalactic astronomy is a fertile research ground where many branches of physics (high energy physics, cosmology, hydrodynamics, radiative processes...) converge.[+]
One century after the discovery that our Universe is made of galaxies similar to the Milky Way, many questions on the formation and evolution of galaxies are still poorly understood and lead to research on the theoretical and observational sides. The galaxy formation process is a highly complex, non-linear phenomenon involving both gravity and hydrodynamics on a wide range of scales, and is greatly influenced by the impact of galaxy winds, ionization and radiative transfer. The confrontation of observations drawn from blind wide angle (all-sky) nearby galaxy surveys with detailed analytical models and high-resolution numerical simulations that mimic the hierarchical assembling of structure is an essential procedure to understand how galaxies form and evolve, as well as pinpoint the most essential driving factors and parameters able to explain the main body of galaxy properties. Much can also be learned from the study of the intergalactic medium over a broad range of redshifts, corresponding to the look-back time to past epochs. Absorption lines in quasar spectra allow us to study how the tenuous intergalactic gas collapsed and formed galaxies, and how heavy elements processed inside stars were expelled in supernovae and other stellar explosions to enrich the gas in galaxies with the atoms that are necessary for life.
ICCUB Contribution
Galactic astronomy
Research in galactic astronomy at the ICCUB includes three main lines of research: galaxy modelling, the study of stellar constituents and stellar luminosity calibration. At present, this research is fully influenced by the scientific exploitation of the Gaia mission data, in which ICCUB researchers are deeply involved (see the GAIA Mission link for more information). [+]
Understanding the Milky Way as a holistic system is one of the key challenges astrophysicists will face in the coming decade. ICCUB’s contribution to galaxy modeling is directed towards a better understanding of the origin and evolution of the large structures in the galactic disk —bar, spirals and warp— and the archaeology of the Milky Way —missing satellites—, through an in-depth investigation of the dynamics and chemistry of the system. This field of research is being revolutionized thanks to the recently published Gaia Data Release 2 (and the future releases) with precise astrometry and photometry for more than 1 billion stars. First results can be found at the science verification papers of Gaia data release 2 here.
On the other hand, the study of the stellar constituents of the Galactic disk and halo focuses on two central aspects: 1) where do the stars form and 2)what are their astrophysical properties. The Gaia mission provides us with a detailed interpretation of the phase space data in terms of specific events that have shaped the Milky Way. ICCUB’s contribution is organized around two central goals: a) to provide new insights into the popular scenario that all stars have formed in clusters, i.e. to investigate cluster formation and evolution (our analysis of the DR2 data has already led to a significant revision of our knowledge of galactic clusters, with additions and removals to the list of known clusters), and b) to capitalize on the opportunities that Gaia brings to the study of variable stars’ data. ICCUB is also involved in spectroscopic surveys from ground --as Gaia-ESO and WEAVE-- to acquire complementary data for Gaia stars.
The Gaia satellite will have a dramatic impact on the definition of the cosmic distance scale, providing the direct measurement, via parallaxes, of the local primary distance indicators and, in turn, a direct re-calibration of the secondary distance indicators. This will significantly improve our estimate of the Hubble constant. At the same time Gaia will offer a unique opportunity to assess the systematics affecting the various indicators contributing to the cosmic distance scale as well as to establish new standard candles. ICCUB is working on stellar luminosity calibration in order to develop the necessary tools to achieve these goals.
Extragalactic astronomy
ICCUB’s interest in galactic astrophysics extends beyond the Milky Way and is concerned, too, with the formation of the first galaxies, which were formed from pristine matter. They comprised population III stars, which reionised the intergalactic medium, polluted it with metals and left behind the seeds of SMBHs. These are processes currently being modeled at ICCUB. [+]
Detailed analytical models and huge numerical simulations are being developed, which make use of the most powerful computational tools presently available. The resulting predictions are confronted with the latest, progressively complete, observations drawn from huge wide angle (all-sky) nearby galaxy surveys (e.g. SDSS, 2dF) as well as very deep, high-redshift, ones (e.g. Hubble Deep Field, GROTH, DEEP2), carried out by means of the new generation of very large ground-based telescopes and sophisticated detectors on board of satellites covering the whole electromagnetic spectrum, from gamma to radio wavelengths.
One of the best methods to probe the intergalactic matter out of which galaxies form is through absorption spectra, where we measure the spectrum of light absorbed by intervening matter from a distant luminous source (usually a quasar, or massive black hole accreting matter and emitting a prodigiously bright light). Using these observations, we have studied the distribution of matter in space and of the clouds of gas called Damped Lyman Alpha systems, to relate them to galaxies of different masses in the process of formation.
Lines of Research
- Structure and dynamics of the Galaxy
- Dark matter in the Galaxy
- Semi-analytical and numerical modelling of galaxy formation and evolution
- Data processing of the Gaia mission
- Data mining systems for the scientific exploitation GAIA
- The intergalactic medium as probed by quasar absortion spectra
Members
