* Astronomy

Blobrana · L

RE: Galaxy Formation

Blobrana · L

A new theory as to how galaxies were formed in the Universe billions of years ago has been formulated by Hebrew University of Jerusalem cosmologists. The theory takes issue with the prevailing view on how the galaxies came to exist.
The new theory, motivated by advanced astronomical observations and based on state-of-the-art computer simulations, maintains that the galaxies primarily formed as a result of intensive cosmic streams of cold gas (mostly hydrogen) and not, as current theory contends, due primarily to galactic mergers. The researchers show that these mergers had only limited influence on the cosmological makeup of the universe as we know it.

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Blobrana · L

Using a number of telescopes, including the Subaru and Keck observatories on the summit of Mauna Kea, scientists have discovered what they describe as a mysterious space blob 13 billion light years from Earth.
Dubbed Lyman-Alpha blobs, these huge bodies of gas are thought to be precursors to galaxies.

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Blobrana · L

Leo Ring

Blobrana · L

RE: Galaxy Formation

Blobrana · L

A team of astronomers led by Michael Disney of Cardiff University in the U.K. decided to see whether galaxies shared any common characteristics. If they did, the team reasoned, those characteristics could lead to a general rule governing their evolution. So, they surveyed 200 galaxies chosen at random but based on radio emissions from their hydrogen gas clouds, an approach that attempted to remove any visual bias in choosing the candidates, because many galaxies emitting radio waves in the hydrogen band are nearly invisible.
As the team reports in the 23 October issue of Nature, the galaxies differed in almost all of their characteristics--such as luminosity, shape, size, and gas content. But those characteristics all seemed to be regulated by a single, as-yet-undetermined quantity, which the researchers suspect could be mass. They found that if you measure a particular quantity for a galaxy, such as its size, you can infer all of its other main properties, such as luminosity, mass, and gas content.

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Blobrana · L

Astronomers have argued for years over whether massive galaxies form from scratch, or by chunking together smaller galaxies.
Lately, evidence is building for the latter theory, and a new study adds to the growing picture of galaxy formation as a clumpy affair. Using an array of both ground-based and space telescopes, including ESO's Very Large Telescope in Chile and the Hubble Space Telescope, a team of astronomers recently observed groups of huge galaxies in the process of merging, showing that large, established galaxies can still grow bigger.

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Blobrana · L

The universe's hefty black holes are known to devour everything within their reach. Now astrophysicists have found that some of the most massive of these sinkholes use high-energy jets to stomp out nearby star formation.
The finding, presented today here at a meeting of the American Astronomical Society (AAS), solves a long-standing problem in galaxy-formation models.

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Blobrana · L

Title: Unveiling obscured accretion in the Chandra Deep Field South
Authors: F. Fiore, A. Grazian, P. Santini, S. Puccetti, M. Brusa, C. Feruglio, A. Fontana, E. Giallongo, A. Comastri, C. Gruppioni, F. Pozzi, G. Zamorani, C. Vignali

A large population of heavily obscured, Compton Thick AGNs is predicted by models of galaxy formation, models of Cosmic X-ray Background and by the ''relic'' super-massive black-hole mass function measured from local bulges. However, so far only a handful of Compton thick AGNs have been possibly detected using even the deepest Chandra and XMM surveys. Compton-thick AGNs can be recovered thanks to the reprocessing of the AGN UV emission in the infrared by selecting sources with AGN luminosity's in the mid-infrared and faint near-infrared and optical emission. To this purpose, we make use of deep HST, VLT, Spitzer and Chandra data on the Chandra Deep Field South to constrain the number of Compton thick AGN in this field. We show that sources with high 24micron to optical flux ratios and red colours form a distinct source population, and that their infrared luminosity is dominated by AGN emission. Analysis of the X-ray properties of these extreme sources shows that most of them are indeed likely to be highly obscured, Compton thick AGNs. The number of infrared selected, Compton thick AGNs with infrared luminosity higher than 6.3E44 erg/s turns out to be roughly similar to that of X-ray selected, unobscured and moderately obscured AGNs in the redshift bin 1.2-2.6. This ''factor of 2'' source population is exactly what it is needed to solve the discrepancies between model predictions and X-ray AGN selection.

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