* Astronomy

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RE: Distant Galaxies

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Space telescope spots 'invisible' galaxies

Five distant galaxies so choked with dust that they are completely invisible at optical wavelengths have been spotted at submillimetre wavelengths by the European Space Agency's Herschel telescope. Because the dust is generated by young stars, such galaxies could open a new window on the universe's most active star-formation period.
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Title: A Large Number of z > 6 Galaxies around a QSO at z = 6.43: Evidence for a Protocluster?
Authors: Yousuke Utsumi (1, 2), Tomotsugu Goto (3, 4), Nobunari Kashikawa, Satoshi Miyazaki, Yutaka Komiyama (1, 2), Hisanori Furusawa (2), Roderik Overzier (5) ((1) The Graduate University for Advanced Studies (2) National Astronomical Observatory of Japan (3) Institute for Astronomy, University of Hawaii (4) Subaru Telescope (5) Max-Planck Institute für Astrophysik )

QSOs have been thought to be important for tracing highly biased regions in the early universe, from which the present-day massive galaxies and galaxy clusters formed. While overdensities of star-forming galaxies have been found around QSOs at 2<5, the case for excess galaxy clustering around QSOs at z>6 is less clear. Previous studies with HST have reported the detection of small excesses of faint dropout galaxies in some QSO fields, but these surveys probed a relatively small region surrounding the QSOs. To overcome this problem, we have observed the most distant QSO at z=6.4 using the large field of view of the Suprime-Cam (34' x 27'). Newly-installed CCDs allowed us to select Lyman break galaxies (LBG) at z~6.4 more efficiently. We found seven LBGs in the QSO field, whereas only one exists in a comparison field. The significance of this apparent excess is difficult to quantify without spectroscopic confirmation and additional control fields. The Poisson probability to find seven objects when one expects four is ~10%, while the probability to find seven objects in one field and only one in the other is less than 0.4%, suggesting that the QSO field is significantly overdense relative to the control field. We find some evidence that the LBGs are distributed in a ring-like shape centred on the QSO with a radius of ~3 Mpc. There are no candidate LBGs within 2 Mpc from the QSO, i.e., galaxies are clustered around the QSO but appear to avoid the very center. These results suggest that the QSO is embedded in an overdense region when defined on a sufficiently large scale. This suggests that the QSO was indeed born in a massive halo. The central deficit of galaxies may indicate that (1) the strong UV radiation from the QSO suppressed galaxy formation in its vicinity, or (2) that star-formation closest to the QSO occurs mostly in an obscured mode that is missed by our UV selection.

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Bright galaxies like to stick together

Astronomers using the European Space Agency's Herschel telescope have discovered that the brightest galaxies tend to be in the busiest parts of the Universe. This crucial piece of information will enable theorists to fix up their theories of galaxy formation.
For over a decade, astronomers have been puzzled by some strange, bright galaxies in the distant Universe which appear to be forming stars at phenomenal rates, making them very hard to explain with conventional theories of galaxy formation. One important question has been the environments in which they are located, such as how close together they are. The Herschel Space Observatory, with its ability for very sensitive mapping over wide areas, has been able to see thousands of these galaxies and identify their location, showing for the first time that they are packed closely together in the centre of large galaxy clusters.
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The false-colour background image is composed from images taken with the Subaru telescope's Suprime-Cam instrument (B and z' images for the blue and green channels, respectively) and WIRCAM on the Canada-France-Hawaii telescope (Ks filter for the red channel). The field size is 6 arc-minutes by 4 arc-minutes. The small square is centred on the target galaxy which is at a distance of 10 billion light years. The spectra taken with MOIRCS on Subaru is shown on the background. A two-dimensional spectrum is shown above and a one dimensional spectrum is shown with a grey line. The heavy black line represents the smoothed grey line. Red line represents a model spectrum, which is in good agreement with the observed spectrum. Strong absorption lines detected and used to measure the line broadenings are indicated with black arrows which come from Hydrogen, Calcium, and CH radicals (noted as "G-band"). Masks have been added to the brightest stars in the background images.

The central wavelength of B, z', and Ks filters are 440 nm, 900 nm, and 2200 nm, respectively.

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Title: A z=1.82 Analogy of Local Ultra-massive Elliptical Galaxies
Authors: M. Onodera, E. Daddi, R. Gobat, M. Cappellari, N. Arimoto, A. Renzini, Y. Yamada, H. J. McCracken, C. Mancini, P. Capak, M. Carollo, A. Cimatti, M. Giavalisco, O. Ilbert, X. Kong, S. Lilly, K. Motohara, K. Ohta, D. B. Sanders, N. Scoville, N. Tamura, Y. Taniguchi

We present observations of a very massive galaxy at z=1.82 which show that its morphology, size, velocity dispersion and stellar population properties that are fully consistent with those expected for passively evolving progenitors of today's giant ellipticals. These findings are based on a deep optical rest-frame spectrum obtained with the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) on the Subaru telescope of a high-z passive galaxy candidate (pBzK) from the COSMOS field, for which we accurately measure its redshift of z=1.8230 and obtain an upper limit on its velocity dispersion sigma_star<326 km/s. By detailed stellar population modelling of both the galaxy broad-band SED and the rest-frame optical spectrum we derive a star-formation-weighted age and formation redshift of t_sf~1-2 Gyr and z_form~2.5-4, and a stellar mass of M_star~(3-4)x10^{11} M_sun. This is in agreement with a virial mass limit of M_vir<7x10^{11}M_sun, derived from the measured sigma_star value and stellar half-light radius, as well as with the dynamical mass limit based on the Jeans equations. In contrast with previously reported super-dense passive galaxies at z~2, the present galaxy at z=1.82 appears to have both size and velocity dispersion similar to early-type galaxies in the local Universe with similar stellar mass. This suggests that z~2 massive and passive galaxies may exhibit a wide range of properties, then possibly following quite different evolutionary histories from z~2 to z=0.

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It seems, early on its life, our Universe was a place of extremes.
That's the conclusion scientists are drawing from new infrared observations of a very distant, unusually bright and massive elliptical galaxy.
This galaxy was spotted 10 billion light years away, and gives us a glimpse of what the Universe looked like when it was only about one-quarter of its current age.
Measurements show that the galaxy is as large and equally dense as elliptical galaxies that can be found much closer to us. Coupled with recent observations by a different research team - which found a very compact and extremely dense elliptical galaxy in the early Universe - the findings deepen the puzzle over how 'fully grown' galaxies can exist alongside seemingly 'immature' compact galaxies in the young Universe.
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Distant cluster of galaxies

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RE: Distant Galaxies

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Explained: Why many surveys of distant galaxies miss 90% of their targets

Astronomers have long known that in many surveys of the very distant Universe, a large fraction of the total intrinsic light was not being observed. Now, thanks to an extremely deep survey using two of the four giant 8.2-metre telescopes that make up ESO's Very Large Telescope (VLT) and a unique custom-built filter, astronomers have determined that a large fraction of galaxies whose light took 10 billion years to reach us have gone undiscovered. The survey also helped uncover some of the faintest galaxies ever found at this early stage of the Universe.
Astronomers frequently use the strong, characteristic "fingerprint" of light emitted by hydrogen known as the Lyman-alpha line, to probe the amount of stars formed in the very distant Universe [1]. Yet there have long been suspicions that many distant galaxies go unnoticed in these surveys. A new VLT survey demonstrates for the first time that this is exactly what is happening. Most of the Lyman-alpha light is trapped within the galaxy that emits it, and 90% of galaxies do not show up in Lyman-alpha surveys.
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