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Post Info TOPIC: Ly-alpha Blobs
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RE: Ly-alpha Blobs
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Title: A New Population of High Redshift, Dusty Lyman-Alpha Emitters and Blobs Discovered by WISE
Authors: Carrie R. Bridge, Andrew Blain, Colin J.K. Borys, Sara Petty, Dominic Benford, Peter Eisenhardt, Duncan Farrah, Roger L. Griffith, Tom Jarrett, S. Adam Stanford, Daniel Stern, Chao-Wei Tsai, Edward L. Wright, Jingwen Wu

We report a new technique to select 1.6<z<4.6 dusty Lyman-alpha emitters (LAEs), over a third of which are 'blobs' (LABs) with emission extended on scales of 30-100kpc. Combining data from the NASA Wide-field Infrared Survey Explorer (WISE) mission with optical spectroscopy from the W.M. Keck telescope, we present a colour criteria that yields a 78% success rate in identifying rare, dusty LAEs of which at least 37% are LABs. The objects have a surface density of only ~0.1 per square degree, making them rare enough that they have been largely missed in narrow surveys. We measured spectroscopic redshifts for 92 of these WISE-selected, typically radio-quiet galaxies and find that the LAEs (LABs) have a median redshift of 2.3 (2.5). The WISE photometry coupled with data from Herschel reveals that these galaxies have extreme far-infrared luminosities (L_IR>10^{13-14}L_sun) and warm colours, typically larger than submillimetre-selected galaxies (SMGs) and dust-obscured galaxies (DOGs). These traits are commonly associated with the dust being energised by intense AGN activity. We hypothesise that the combination of spatially extended Lyman-alpha, large amounts of warm IR-luminous dust, and rarity (implying a short-lived phase) can be explained if the galaxies are undergoing strong 'feedback' transforming them from an extreme dusty starburst to a QSO.

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Blobrana


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Lyman-Alpha Nebulae
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Title: A Successful Broad-band Survey for Giant Lya Nebulae I: Survey Design and Candidate Selection
Authors: Moire K. M. Prescott (1 and 2), Arjun Dey (3), Buell T. Jannuzi (3) ((1) UC Santa Barbara, (2) Steward Observatory, (3) NOAO)

Giant Lya nebulae (or Lya "blobs") are likely sites of ongoing massive galaxy formation, but the rarity of these powerful sources has made it difficult to form a coherent picture of their properties, ionisation mechanisms, and space density. Systematic narrow-band Lya nebula surveys are ongoing, but the small redshift range covered and the observational expense limit the comoving volume that can be probed by even the largest of these surveys, posing a significant problem when searching for such rare sources. We have developed a systematic search technique designed to find large Lya nebulae at 2<z<3 within deep broad-band imaging and have carried out a survey of the 9.4 square degree NOAO Deep Wide-Field Survey (NDWFS) Bootes field, corresponding to a total survey comoving volume of ~10^8 h^-3_70 Mpc^3, the largest volume survey for Lya nebulae ever undertaken. In this first paper in the series, we present the details of the survey design and the selected sample of 80 candidates, which includes one previously discovered Lya nebula.

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Blobrana


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Lyman-alpha emitters
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Title: Lyman-alpha emitters as tracers of the transitioning Universe
Authors: Nilsson, Kim K.; Møller, Palle

Of the many ways of detecting high redshift galaxies, the selection of objects due to their redshifted Ly-alpha emission has become one of the most successful. But what types of galaxies are selected in this way? Until recently, Ly-alpha emitters were understood to be small star-forming galaxies, possible building-blocks of larger galaxies. But with increased number of observations of Ly-alpha emitters at lower redshifts, a new picture emerges. Ly-alpha emitters display strong evolution in their properties from higher to lower redshift. It has previously been shown that the fraction of ultra-luminous infrared galaxies (ULIRGs) among the Ly-alpha emitters increases dramatically between redshift three and two. Here, the fraction of AGN among the LAEs is shown to follow a similar evolutionary path. We argue that Ly-alpha emitters are not a homogeneous class of objects, and that the objects selected with this method reflect the general star forming and active galaxy populations at that redshift. Ly-alpha emitters should hence be excellent tracers of galaxy evolution in future simulations and modelling.

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Blobrana


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RE: Ly-alpha Blobs
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Black holes, dead stars and other objects so dense that not even light can escape them might seem like the most inwardly focused denizens of the universe. Space and time have effectively closed around them, leaving no exit.
But astronomers have found growing evidence that black holes can be extroverts, reaching out across millions of light-years and controlling the destinies of galaxies and even clusters of galaxies. The ultimate control freaks, the black holes seem to be able to regulate other objects' cosmic growth by a fiery feedback of light and other radiation from material on its way to oblivion.

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Blobrana


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Mysterious space blobs aren't infant galaxies as astronomers once thought. Scientists say they mostly consist of galaxies going through puberty, all hot and bothered.
A new study using NASA's Chandra X-Ray Observatory and other space and ground telescopes comes up with an explanation for these high-energy glowing blobs that have been observed for about a decade. Astronomers looked at 29 of these gaseous blobs in one distant area of the universe, dating back to more than 11 billion years ago.

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Blobrana


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Lyman-alpha blobs
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A deep study of 29 gigantic blobs of hydrogen gas has been carried out with NASA's Chandra X-ray Observatory to identify the source of immense energy required to illuminate these structures. These mysterious blobs -- called "Lyman-alpha blobs" by astronomers because of the light they emit -- are several hundred thousand light years across and are seen when the Universe is only about two billion years old, or about 15% of its current age.

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Blobrana


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RE: Ly-alpha Blobs
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In astronomy, a Lyman-alpha blob (LAB) is a huge concentration of a gas emitting the Lyman-alpha emission line. The Lyman-alpha emission line is produced by recombination of electrons with ionised hydrogen atoms. LABs are some of the largest known individual objects in the Universe. Some of these gaseous structures are more than 400,000 light years across. So far they have only been found in the high-redshift universe because of the ultraviolet nature of the Lyman-alpha emission line. Since the Earth's atmosphere is very effective at filtering out UV photons, the Lyman-alpha photons must be redshifted in order to be transmitted through the atmosphere.
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Blobrana


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Posts: 131433
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Lyman-alpha blobs
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Lyman Alpha BlobsCredit: Left panel: X-ray (NASA/CXC/Durham Univ./D.Alexander et al.); Optical (NASA/ESA/STScI/IoA/S.Chapman et al.); Lyman-alpha Optical (NAOJ/Subaru/Tohoku Univ./T.Hayashino et al.); Infrared (NASA/JPL-Caltech/Durham Univ./J.Geach et al.); Right, Illustration: NASA/CXC/M.Weiss


A deep study of 29 gigantic blobs of hydrogen gas has been carried out with NASA's Chandra X-ray Observatory to identify the source of immense energy required to illuminate these structures. These mysterious blobs - called "Lyman-alpha blobs" by astronomers because of the light they emit - are several hundred thousand light years across and are seen when the Universe is only about two billion years old, or about 15% of its current age.
The composite image on the left shows one of the largest blobs observed in this study. Glowing hydrogen gas in the blob is shown by a Lyman-alpha optical image (coloured yellow) from the National Astronomy Observatory of Japan's Subaru telescope. A galaxy located in the blob is visible in a broadband optical image (white) from the Hubble Space Telescope and an infrared image from the Spitzer Space Telescope (red). Finally, the Chandra X-ray Observatory image in blue shows evidence for a growing supermassive black hole in the center of the galaxy. Radiation and outflows from this active black hole are powerful enough to light up and heat the gas in the blob. Radiation and winds from rapid star formation occurring in the galaxy is believed to have similar effects. Clear evidence for four other active black holes in blobs is also seen.

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Blobrana


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Posts: 131433
Date:
Mysterious space blobs
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Mysterious space blobs aren't infant galaxies as astronomers once thought. Scientists say they are galaxies going through puberty, all hot and bothered.
A new study using NASA's Chandra X-Ray Observatory comes up with an explanation for these high-energy glowing blobs that have been observed for about a decade.
One theory was that they were young galaxies cooling off. But the new research says they are hot and chaotic with gas halos and growing supermassive black holes and about to stabilise.
Study lead author James Geach (Geech) of Durham University in England said it is almost as if the adolescent galaxies are having a final tantrum before growing up.

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Blobrana


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SSA 22 protocluster
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Star formation: Lyman-alpha emitters in the SSA 22 protocluster

Many different populations of young star-forming galaxies in the early Universe are known, but the relationships between them and the cosmic large-scale structure are still not well understood. One group, the Lyman-alpha emitters, are thought to be young, low-mass galaxies with ages of around 108 years. An overdensity of them in one region of the sky is believed to mark a forming protocluster. Galaxies that are bright at submillimetre wavelengths are undergoing violent episodes of star formation, so the question of whether they are also associated with the protocluster naturally arises. Tamura et al. report an enhancement of submillimetre galaxies near the core of the SSA 22 protocluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-alpha emitters, suggesting synchronous formation of the two very different types of star-forming galaxies within the same structure at high redshift.

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