Archivi tag: surveys

Gas, Dust, and Star Formation in Galaxies from the Local to the Far Universe

Spitzer, Herschel, and Planck allowed us to make an important step forward in our understanding of the nature of galaxies. On one hand, the extensive surveys of nearby galaxies performed by Herschel studied with unprecedented details the distribution and the properties of dust, and provided key insights on the processes of dust heating and star formation in these objects. On the other hand, the deep infrared and sub-millimeter surveys revealed a large population of massive, gas-rich, intensely star-forming galaxies, which have no local analogues. Continua a leggere Gas, Dust, and Star Formation in Galaxies from the Local to the Far Universe

The Role of Hydrogen in the Evolution of Galaxies

As the most abundant element in the Universe, hydrogen is an ubiquitous tracer of structures at various scales and plays a fundamental role in galaxy formation. Accretion of hydrogen from the intergalactic medium (IGM) feeds galaxies with the raw material necessary for the formation of stars. Continua a leggere The Role of Hydrogen in the Evolution of Galaxies

Supernovae in the Local Universe: Celebrating 10,000 Days of Supernova 1987A

Supernovae are a core element of modern astrophysics, providing fundamental insights into stellar evolution, the interstellar medium, astroparticle physics, nucleosynthesis and cosmology. While astronomers now routinely detect enormous number of supernovae every year at increasingly large distances, wide-field surveys and all-sky monitoring are now providing an important new element to such studies: there are a growing number of new supernovae being discovered very close to home. Continua a leggere Supernovae in the Local Universe: Celebrating 10,000 Days of Supernova 1987A

Exploring the properties of the Universe by Doppler lensing

Sappiamo che l’Universo contiene centinaia di miliardi di galassie, basti guardare le spettacolari immagini che ci ha fornito il telescopio spaziale Hubble. Ce ne sono tante di diverse forme e dimensioni, ma quali sono in definitiva quelle più grandi? E poi, quali sono quelle più vicine alla nostra galassia che sembrano apparentemente più grandi delle altre? Naturalmente, non è possibile rispondere a queste domande analizzando semplicemente le immagini astronomiche poichè, di fatto, è necessario conoscere le distanze a cui si trovano le galassie in modo tale da ricavare una stima delle loro dimensioni reali.

Astronomers have their ways to measure a distance to a galaxy which allows them to solve this conundrum. One of the most popular methods, and in most cases, the only method that can be used to measure a distance to a remote galaxy, is to analyse its electromagnetic spectrum which includes the visible light that enables us to see it. Since the Universe is expanding, all distant galaxies are moving away from us. Because of this motion the spectrum of a galaxy is shifting towards its red part, the redshift as it is known to astronomers. The redshift phenomenon is a manifestation of the Doppler effect, the faster the motion, the larger the shift of the frequency. Therefore, the larger the redshift, the greater the distance to the observed galaxy. The exact relation between the redshift and distance follows from the cosmological model of the Universe. So if astronomers can measure a distance in some other way, then by comparing the observed distance and redshift with a prediction, they can measure the properties of our Universe such as for example the amount of dark matter and dark energy. There is, however, one problem here.

If a galaxy is moving on the top of the global expansion of the Universe, then this motion, via the Doppler effect, contributes to the observed redshift. And galaxies move all the time, just as molecules of the air, or bees within a swarm. The contribution from this local motion is not big if compared to a motion that follows from the expansion of the Universe. Still this additional redshift introduces noise to our measurements. This noise then distorts our estimation of the distance, and therefore our estimation of the real size of the observed galaxy. This is what is called the Doppler lensing, “Doppler” because of the Doppler effect involved, and “lensing” because this effect distorts the inferred size, just as the observed size of an object is distorted when observed through an optical lens. How then can we tell what is the real size of a galaxy? If all galaxies are moving and if their motion distorts our measurements then that sounds like a real mess. However, this “mess” or to be precise the amount of “messiness” can give us a very good insight into what our Universe is made of. Astronomers are now in a situation similar to radar operators who during World War II complained about “noise” in returned echoes due to rain, snow, and sleet. Back then it was a nuisance, now we actually look for this “noise” in order to predict weather. Similarly, if astronomers could measure apparent sizes of a very large number of galaxies, and correlations between them, then they could estimate an average amplitude of the “noise”. Using the technique based on the Doppler lensing effect, they can measure properties of our Universe and estimate how much dark matter and dark energy it contains.

With large galaxy surveys such as Dark Energy Survey (DES) and the contribution from the Australian OzDES we will be able to measure this effect. Further, much larger surveys will follow after completion of the Square Kilometre Array (SKA) telescope, currently being built partly in Western Australia and partly in South Africa, and utilise the Doppler lensing effect to get a better insight into properties and mysteries of our Universe. The calculations and the method itself were recently developed by a group of astronomers from Australia, South Africa, and United Kingdom. The method shows how by measuring correlations in the distortion of sizes of galaxies we can learn about the properties of our Universe (such as amount of dark matter and dark energy). This method and predictions that follow from this method will be presented today at the 8th Workshop of the Australian National Institute for Theoretical Astrophysics (ANITA) hosted by the Sydney Institute for Astronomy (SIfA) at the University of Sydney.

The Conversation: The measure of the universe through doppler lensing

arXiv: Cosmology with Doppler Lensing

Tracing the cosmic Web

Large galaxy redshift surveys have revealed that the Universe has a striking weblike structure. On these scales, galaxies and matter in the universe are arranged in a complex network of dense compact clusters, elongated filaments, two-dimensional sheets, and huge near-empty voids. The Cosmic Web is one of the most intriguing and striking patterns found in nature, rendering its analysis and characterization far from trivial. The absence of an objective and quantitative procedure for identifying and isolating clusters, filaments and voids in the cosmic matter distribution has been a major obstacle in investigating the structure and dynamics of the Cosmic Web. The overwhelming complexity of the individual structures and their connectivity, the huge range of densities and the intrinsic multiscale nature prevent the use of simple tools that may be sufficient in less demanding problems. One aspect that the workshop will focus on strongly is the analysis and identification of the Cosmic Web and its various components. Progress on the study of the weblike geometry of the Megaparsec  and sub-Megaparsec matter distribution and of the relation between the large scale weblike environment and the galaxies populating its constituents has been hampered by the absence of a well-defined, commonly accepted language for quantifying its structure and topology. Quantities as basic and general as the mass and volume content of clusters, filaments, walls and voids are still not firmly established or defined.  Since there is not yet a common framework to objectively define filaments and walls, the comparison of results of different studies concerning properties of the filamentary network — such as their internal structure and dynamics, evolution in time, and connectivity properties — is usually rendered cumbersome and/or difficult. Over the years, a variety of heuristic measures were forwarded to analyze specific aspects of the spatial patterns in the large scale Universe. In recent years we have seen the development of more solid and well-defined machineries for the description, characterization and quantitative analysis of the intricate and complex spatial patterns of the Cosmic Web. They address the full range of weblike features simultaneously, instead of focusing just on voids, or filaments in their own right.  For a successful identification and characterization of the Cosmic Web we also need sophisticated reconstructions of the cosmic density field on the basis of the observed galaxy distribution.

During the course of the workshop, we will discuss and assess the different identification and reconstruction techniques, and contrast them with an aim towards developing a consensus among experts in the field. Amongst the specific issues that will be addressed are the following ones:

  • to increase our understanding of dynamics and evolution of the Cosmic Web, and the relation between the dark matter, gaseous
  • and galaxy distribution.
  • to obtain a handle on the way in which the web environment affects the formation and evolution of galaxies.
  • to obtain a representative census of the various methods to dissect the Cosmic Web and to identify its various components.
  • to assess and explore the fundamental differences between the different web analysis techniques.
  • to adapt techniques used for idealized theoretical and numerical circumstances to a range of observational data and surveys. Compare
  • the performance of the instruments for analysis of computer simulations with those used for the analysis of observational data and surveys.
  • to provide participants (before the meeting) with a z = 0 simulation snapshot and to compile comparative analyses of the simulation during the workshop. This comparison is intended to be published in a peer-reviewed journal.

GREAT3 Mid-challenge Meeting

The third GRavitational lEnsing Accuracy Testing challenge, or GREAT3, is a blind data analysis competition held by the world-wide weak lensing community to test weak lensing measurement algorithms. With several major astronomical surveys beginning to make large-scale cosmological weak lensing measurements in 2013 in order to better understand our cosmological model (including the mysterious dark matter and dark energy), this challenge will play an important role in identifying promising measurement algorithms and quantifying their performance.

The meeting will include a description of the GREAT3 challenge, guides to the simulated data, information on how to participate in GREAT3, and information about the public tools provided to make this easier. Throughout there will also be invited and contributed talks, and discussion, on cutting edge topics in weak gravitational lensing, inference, and image analysis for cosmology.

Multiwavelength AGN Surveys and Studies

AGN surveys are the source for the most interesting objects in the extragalactic Universe: QSOs, Seyfert galaxies, blazars, radio galaxies, LINERs, etc. They are important for understanding the variety of extragalactic sources and their interrelationship, as well as understanding the evolution of the Universe. Recent ground-based and space missions give vast amount of new multiwavelength (MW) data, which are being put together to discover many new AGN. Virtual Observatories (VOs) help in accomplishment of complex research programs using all these data. A combined study of these data also gives the overall picture of the AGN and answers some of the most important questions:

i) understanding the possible evolutionary and/or physical connection between the different classes of AGN, i.e. their consistency with the unification model,

ii) the relation of AGN to their host galaxies,

iii) understanding the true fraction of heavily obscured AGN in order to determine the true AGN luminosity function and its variation with redshift.

The Symposium will provide a good opportunity to elaborate a strategy, based on the acquired experience, to plan future surveys best fitted to fulfill the needs, and to coordinate follow-up observations with the new large ground-based and space telescopes.

The restless nature of AGNs

bh_artistIt is widely accepted that variability provides important information on the nature of the emission mechanisms and the geometry of the central source in Active Galactic Nuclei. This is an exciting time in the field of AGN variability, due to the wealth of new results produced in the last few years. This conference intends to focus on radio-quiet sources, discussing our current understanding of the central source variability across the IR, optical, and UV regimes up to hard X-rays, and the clues that variability provides about the physics and structure of the AGN phenomena. The contributions are intended to address the problem of AGN variability both from the observational and theoretical point of view, on short and long time scales, presenting results and expectations from wide-field/deep surveys, pointed observations, ground-based and space observatories.

Topics:

•X-ray flux and spectral variability

•Outflows and SED variability

•The UV-X ray connection

•Variability on the optical band: reverberation, the continuum and the full sky surveys

•AGN variability analysis methods

•Variability in MHD simulations of accretion flows

Brown Dwarfs come of Age

An international conference on Brown Dwarfs will be held next May in the sunny island of Fuerteventura, exactly 11 years after the first IAU Symposium devoted to these once elusive objects and 18 years after the definitive observational confirmation of their existence. Much work has been done in the last two decades, both from the theoretical and observational point of view. Time is ripe now to have a conference to provide a comprehensive overview of this very active field of research. Some of the most relevant work on Brown Dwarfs has been done in the Canarian Observatories, making Canary Islands an ideal location to host this conference. Fuerteventura is the easternmost island of the Canaries, rich of unique natural spaces and impressive landscapes. It is well connected by direct flights with many European cities and offers many possibilities of affordable and comfortable accommodation. This island is working to preserve its dark night sky and become a Starlight Reserve.

Wide-area surveys such as DENIS, SDSS and 2MASS have played a major role in the discoveries of some of the first brown dwarfs and the definition of the spectral classes L and T. Recently completed and ongoing surveys such as IPHAS, PANSTARS, UKIDSS and WISE are shedding new light on the field. An even cooler spectral class, the Y dwarfs, has been revealed. Detailed studies of brown dwarfs have uncovered surprising behaviours such as ultra-fast rotation rates, the presence of clouds, polarization and strong radio emission. Observations of dust in disks around very low-mass primaries with the Spitzer and Herschel satellites have provided information on the conditions of planet formation. Brown dwarfs have become prime interest targets for searches for habitable planets due to their small masses and radii, and the presence of a habitable regions very close to them for extended periods of time. Brown dwarfs populate the natural bridge between stars and planets. As such, they are connected with both types of objects. One of the main focus of this international conference will be to examine whether the fundamental properties of brown dwarfs represent a smooth continuity from stars to planets or not. Brown dwarfs and their extension into planetary masses represent the low-mass end of the stellar IMF. Deep observations of young open clusters and star-forming regions and microlensing surveys have found a population of very low-mass brown dwarfs or free-floating planets.

Our conference will provide a comprehensive update of the status of this active field of research. Here is a list of the scientific topics that will be treated:

  • Formation and early evolution of brown dwarfs
  • Angular momentum and disk evolution in very low mass systems
  • Large scale surveys
  • Deep surveys
  • Brown dwarfs in binary systems
  • The lower end of the IMF
  • Planets around brown dwarfs
  • Ultracool atmospheres
  • Spectroscopy of brown dwarfs
  • Time domain phenomena in brown dwarfs: activity and weather
  • Oncoming and future projects in the substellar world
  • The brown dwarfs-exoplanet connection