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TOPIC: Distant Galaxies


L

Posts: 131433
Date:
UKIRT
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British astronomers are releasing the first data from the largest and most sensitive survey of the heavens in infrared light to scientists across Europe. The UKIRT Infrared Deep Sky Survey (UKIDSS) has completed the first of seven years of data collection, studying objects that are too faint to see at visible wavelengths, such as very distant or very cool objects. New data on young galaxies is already challenging current thinking on galaxy formation, revealing galaxies that are massive at a much earlier stage of development than expected. These first science results already show how powerful the full survey will be at finding rare objects that hold vital clues to how stars and galaxies in our Universe formed.

UKIDSS will make an atlas of large areas of the sky in the deep infrared. This survey will reveal more cool and faint objects than we have ever been able to see before. It will also detect objects at the very edge of our known universe. UKIDSS is being conducted by UK astronomers working with Japanese and ESO astronomers. The data is being shared with astronomers across Europe through ESO.

"Astronomers across Europe will jump on these exciting new data. We are moving into new territory - our survey is both wide and deep, so we are mapping huge volumes of space. That's how we will locate rare objects - the very nearest and smallest stars, and young galaxies at the edge of the universe" - Andy Lawrence from the University of Edinburgh, UKIDSS Principal Investigator.

The UKIDSS data was collected by the United Kingdom Infrared Telescope situated near the summit of Mauna Kea in Hawaii using the Wide Field Camera (WFCAM) built by the United Kingdom Astronomy Technology Centre (UKATC) in Edinburgh. WFCAM is the most powerful infrared imager in the world. It generates enormous amounts of data - 150 gigabytes per night (equivalent to more than 200 CDs) - and approximately 10.5 Terrabytes in total so far (or 15,000 CDs!!).
A small amount of data was released in January 2006 and already teams led by Omar Almaini at the University of Nottingham and Nigel Hambly of the Institute for Astronomy at the University of Edinburgh are beginning to reveal some of the secrets of star and galaxy formation.
Omar Almaini, Ross McLure and the Ultra Deep Survey team have been looking at distant galaxies by surveying the same region of sky night after night to see deeper and to find these very faint objects. This survey will be one hundred times larger than any similar survey attempted to date and will cover an area four times the size of the full Moon. So far several hundred thousand galaxies have been detected and among the early discoveries, nine remarkable galaxies have been found that appear to be 12 billion light years away. As it has taken 12 billion years for the light to travel from these galaxies to Earth, we are seeing them as they were when they were very young - only a billion years after the Big Bang. The newly discovered galaxies are unusual as they appear to be very massive for their age. This challenges thinking on how galaxies form, since it was thought that large galaxies form gradually over billions of years as smaller components merge together.

"We're surveying an enormous volume of the distant Universe, which allows us to discover rare massive galaxies that were previously almost impossible to find. Understanding how these galaxies form is one of the Holy Grails of modern astronomy, and now we can trace them back to the edge of the known Universe" - Omar Almaini.

Nigel Hambly and Nicolas Lodieu have been using the UKIDSS data to discover more about very cold objects in our Galaxy called brown dwarfs. Brown dwarfs are formed in the same way as stars but typically they have less than 8% of the mass of the Sun (or approximately 80 times the mass of Jupiter). This is not large enough for core nuclear reactions to occur, and so brown dwarfs do not shine like normal stars. Brown dwarfs give off less than one ten thousandth of the radiation of a star like our Sun. This relatively tiny amount of heat can be detected by WFCAM and the UKIDSS survey hopes to find out how many of these 'failed stars' there are in our Galaxy.
Only a few hundred of these enigmatic objects have been found previously but the UKIDSS survey should establish if they are rare or a relatively common phenomenon. This large study of brown dwarfs will reveal the true scale of the link between the smallest normal stars and large gas planets, such as Jupiter.

"There is every reason to suppose that the physical process leading to the formation of stars is continuous across the mass boundary that separates normal hydrogen-fusing stars like the Sun and the so-called failed stars, or brown dwarfs. With UKIDSS, we will find many thousands of brown dwarfs in many different star formation environments within our own Galaxy; furthermore we expect to find even cooler and much dimmer objects than are currently known. This will tell us how significant a role the brown dwarfs have in the overall scheme of Galactic structure and evolution." - Nigel Hambly, of the UKIDSS Galactic Clusters Survey.

Mike Irwin and his team at the Institute of Astronomy, University of Cambridge have automated the processing of the huge amount of data produced by the surveys. More than 2 million images have been analysed so far, with the team tasked with removing instrumental artefacts, cataloguing the thousands of objects visible on each frame and providing quality measures for the 10,000 images produced per night.

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L

Posts: 131433
Date:
Virgo Cluster Dwarf Galaxies
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Title: Colour-Magnitude Diagrams of Resolved Stars in Virgo Cluster Dwarf Galaxies
Authors: Nelson Caldwell (Smithsonian Astrophysical Observatory)

The Advanced Camera for Surveys (ACS) on HST has been used to image two fields in the core of the Virgo cluster that contain a number of dwarf elliptical galaxies. The combined F555W and F814W images have resolved red giant stars in these galaxies, down to 1 mag below the giant branch tip. Two of the galaxies were targeted because of their extremely low central surface brightnesses (Bo > 27.0), thus the successful resolution into stars confirms the existence of such tenuous galaxies. Red giant stars were also found that are not ostensibly associated with any galaxy. Colour-magnitude diagrams in V and I have been derived and used to derive distances and metallicities via the magnitude and mean colour of the red giant branch tip. The mean abundances of stars in the dwarfs range from -1.2 (Fe/H) < -2.4, and fall along the relation between galaxy luminosity and metallicity found for Local Group and M81 group dwarf ellipticals. The mean distance modulus of the six Virgo galaxies is 31.0 ±- 0.05, or 16.1 ± 0.4 Mpc, whereas that for the intracluster stars in those fields is 31.2 ± 0.09 (17.4 ± 0.7 Mpc).

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Posts: 131433
Date:
Blue Compact Dwarf Galaxies
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Title: New southern blue compact dwarf galaxies in the 2dF Galaxy Redshift Survey
Authors: P. Papaderos (1), N.G. Guseva (2), Y.I. Izotov (2), K.G. Noeske (1,3), T.X. Thuan (4), K.J. Fricke (1) ((1) Institute for Astrophysics, University of Goettingen, Germany, (2) Main Astronomical Observatory, Kyiv, Ukraine, (3) University of California, Santa Cruz, USA, (4) University of Virginia, Charlottesville, USA)

Aiming to find new extremely metal-deficient star-forming galaxies researchers extracted from the Two-Degree Field Galaxy Redshift Survey (2dFGRS) 100K Data Release 14 emission-line galaxies with relatively strong [OIII] 4363 emission. Spectroscopic and photometric studies of this sample and, in addition, of 7 Tololo and 2 UM galaxies were performed on the basis of observations with the ESO 3.6m telescope. All sample galaxies qualify with respect to their photometric and spectroscopic properties as blue compact dwarf (BCD) galaxies. Additionally, they show a good overlap with a comparison sample of 100 well-studied emission-line galaxies on the 12+log(O/H) vs. log(Ne/O), log(Ar/O) and log(Fe/O) planes. From the analysis of the 2dFGRS subsample the researchers report the discovery of two new extremely metal-deficient BCDs with an oxygen abundance 12+log(O/H) < 7.6 and of another seven galaxies with 12+log(O/H) < 7.8. Furthermore, they confirm previous oxygen abundance determinations for the BCDs Tol 1304-353, Tol 2146-391, UM 559 and UM 570 to be 12+log(O/H) < 7.8.

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Posts: 131433
Date:
XLSSJ022303.0-043622
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Title: XMM-LSS discovery of a z=1.22 galaxy cluster
Authors: M.N. Bremer, I. Valtchanov, J.P. Willis, B. Altieri, S. Andreon, P.A Duc, F. Fang, C. Jean, C. Lonsdale, F. Pacaud, M. Pierre, J.A. Surace, D.L. Scupe, I. Waddington

Researchers present details of the discovery of XLSSJ022303.0-043622, a z=1.2 cluster of galaxies. This cluster was identified from its X-ray properties and selected as a z>1 candidate from its optical/near-IR characteristics in the XMM Large-Scale Structure Survey (XMM-LSS). It is the most distant system discovered in the survey to date.
The researchers present ground-based optical and near IR observations of the system carried out as part of the XMM-LSS survey. The cluster has a bolometric X-ray luminosity of 1.1 ±0.7 x 10^44 erg/s, fainter than most other known z>1 X-ray selected clusters. In the optical it has a remarkably compact core, with at least a dozen galaxies inside a 125 kpc radius circle centred on the X-ray position. Most of the galaxies within the core, and those spectroscopically confirmed to be cluster members, have stellar masses similar to those of massive cluster galaxies at low redshift. They have colours comparable to those of galaxies in other z>1 clusters, consistent with showing little sign of strong ongoing star formation. The bulk of the star formation within the galaxies appears to have ceased at least 1.5 billion years before the observed epoch.
Their results are consistent with massive cluster galaxies forming at z>1 and passively evolving thereafter. They also show that the system is straightforwardly identified in Spitzer/IRAC 3.6 and 4.5 micron data obtained by the SWIRE survey emphasising the power and utility of joint XMM and Spitzer searches for the most distant clusters.

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Posts: 131433
Date:
XMMXCS 2215-1738
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UK astronomers have discovered the most distant cluster of galaxies ever seen by peering back in time nearly ten billion years. They found hundreds of the "star cities" gathered inside a cloud of gas heated to more than 10 million degrees, it was revealed today.

XMM-XCS 2215-1734

This colour image shows the faint red galaxies of the galaxy cluster XMMXCS 2215-1738 in the center, along with the bluish haze which represents the invisible X-ray emission from the extremely hot gas that exists in between the cluster galaxies.
Credit European Southern Observatory Imaging Survey

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-- Edited by Blobrana at 01:37, 2006-06-08

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Posts: 131433
Date:
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Astronomers have found the most distant cluster of galaxies to date and possibly the most massive one yet seen at such an early era in the universe.

Almost 10 billion light-years from Earth, the cluster, XMMXCS 2215-1738, contains hundreds of galaxies surrounded by superheated X-ray-emitting gas at more than 10 million degrees.
Reporting at the 208th meeting of the American Astronomical Society, members of the XMM Cluster Survey team said they used observations from the European X-ray Multi Mirror Newton satellite to discovery this new cluster and then determined its distance using the 10-meter W. M. Keck telescope in Hawaii.

"I couldn't believe it when I saw that this distant cluster appears to be full of old galaxies. This cluster is a challenge for our models of how massive galaxies formed, and to our understanding of the way such a massive cluster exists at a relatively early era in the Universe" - Adam Stanford, lead research, University of California, Davis, and at Lawrence Livermore National Laboratory.

Co-author Bob Nichol of the University of Portsmouth, England, said the key question associated with the discovery is "What's it doing there? This massive lump of matter is three-quarters the way back to the Big Bang."

Principal investigator Kathy Romer, of the University of Sussex, England, said the cluster actually was not difficult to find. She said the XCS team currently is searching the XMM-Newton archive of observations for more clusters like XMMXCS 2215-1738, using algorithms developed by Robert Mann, of the University of Edinburgh, Scotland.

"This cluster was confirmed on our first good night at Keck, and we have 1000s more to look at. I can't wait to find out how many more clusters like XMMXCS 2215-1738 there are out there" - Kathy Romer.

The real surprise of the XMMXCS 2215-1738 cluster might be its mass. Using the temperature of the X-ray emitting gas, researchers determined the cluster is approximately 500 trillion times the Sun's mass.
Such massive clusters are expected to grow through the amalgamation of many smaller masses, such as groups of galaxies, but this process takes time.

"Such a massive cluster at this early time in the Universe is only expected in a flat universe full of dark energy. It is yet more evidence that we live in a strange Universe" - Pedro Viana, team member and cosmologist at the University of Porto, Portugal.

The team now is embarked on a long-term observing program to find more clusters like XMMXCS 2215-1738 using the 4-meter telescopes of the NOAO at both the Cerro Tololo Inter-American Observatory in Chile and the Kitt Peak National Observatory in Arizona.
That does not mean the team already has forgotten about XMMXCS 2215-1738.

"It's special. We will be studying this cluster using all the tools available to us. We are already getting detailed pictures using the Hubble Space Telescope." - Adam Stanford.

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Posts: 131433
Date:
RE: Distant Galaxies
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A team of astronomers using NASA's Spitzer Space Telescope has discovered a grand total of nearly 300 clusters of galaxies. Almost 100 of these are as far as 8 to 10 billion light-years away, which means they date back to a time when our universe was less than one-third its present age.

DISTANT GALAXIES
Position (2000): RA: 14h32m5.00s Dec: 34d16m48.00s
Image scale: 7 x 7 arcminutes per inset
Credit NASA


Galaxy clusters are the universe's high-density environments, similar to cities on Earth. A single galaxy cluster can contain hundreds of galaxies like our own Milky Way.

"At this distance, we are literally looking at these galaxies as they were over 8 billion years ago. It's like being able to take a picture of Rome during the peak of the Roman Empire" - Dr. Mark Brodwin of NASA's Jet Propulsion Laboratory in Pasadena, Calif., who co-led the discovery.

Brodwin presented the results today at the 208th meeting of the American Astronomical Society in Calgary, Canada.

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Posts: 131433
Date:
Abell2218
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Using massive clusters of galaxies as "cosmic telescopes," a research team led by a Johns Hopkins University astronomer has found what may be infant galaxies born in the first billion years after the beginning of the universe.

If these findings are confirmed, the extra magnification provided by these gargantuan natural telescopes will have given astronomers their best-ever view of galaxies as they formed in the early universe, more than 12 billion years ago.

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Posts: 131433
Date:
NGC1399 Globular Clusters
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Title: Ultra-Compact Stellar Systems in the Fornax Galaxy Cluster
Authors: P. Firth, M. J. Drinkwater, E. A. Evstigneeva, A. Karick, M. D. Gregg, M. Hilker, K. Bekki, J. B. Jones, S. Phillipps

Researchers VLT (FLAMES) observations near NGC1399 investigate the connection between ultra-compact dwarf galaxies (UCDs), NGC1399 globular clusters and intra-cluster globulars.
They have uncovered 30 faint compact stellar systems in the Fornax galaxy cluster, adding to 62 bright UCDs previously reported. The magnitude limit of these stellar systems extends down to the globular cluster domain.
They detect a filament of UCDs and globular clusters stretching across NGC1399 and find weak evidence for its rotation. These compact stellar systems not only congregate around several cluster galaxies but are also widely distributed through intra-cluster space.

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Posts: 131433
Date:
Submillimetre Galaxies
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Title: The Hubble Deep Field North SCUBA Super-map IV - Characterising submillimetre galaxies using deep Spitzer imaging
Authors: Alexandra Pope (1), Douglas Scott (1), Mark Dickinson (2), Ranga-Ram Chary (3), Glenn Morrison (4,5), Colin Borys (6), Anna Sajina (1,3), David M. Alexander (7), Emanuele Daddi (2), David Frayer (3), Emily MacDonald (2), Daniel Stern (8) ((1) UBC, (2) NOAO, (3) SSC, (4)IfA HI, (5) CFHT, (6) Caltech,(7) IoA Cambridge, (8) JPL)

Researchers present SEDs, Spitzer colours, and IR luminosities for 850 micron selected galaxies in the GOODS-N field. Using the deep Spitzer Legacy images and new data and reductions of the VLA-HDF radio data, we find statistically secure counterparts for 60 per cent (21/35) of our submillimetre sample, and identify tentative counterparts for another 12 objects. This is the largest sample of submillimetre galaxies with statistically secure counterparts detected in the radio and with Spitzer. They find that in most cases the 850 micron emission is dominated by a single 24 micron source.
A composite rest-frame SED shows that the submm sources peak at longer wavelengths than those of local ULIRGs of the same luminosity and therefore appear to be cooler. The SEDs of submillimetre galaxies are also different from those of their high redshift neighbours, the near-IR selected BzK galaxies, whose mid-IR to radio SEDs are more like those of local ULIRGs.
Using 24 micron. 850 micron and 1.4 GHz observations, they fit templates that span the mid-IR through radio to derived the integrated IR luminosity of the submm galaxies. By themselves, 24 micron and radio fluxes are able to predict LIR reasonably well because they are relatively insensitive to temperature. However, the submm flux by itself consistently overpredicts LIR when using spectral templates which obey the local ULIRG temperature-luminosity relation.
The shorter Spitzer wavelengths sample the stellar bump at the redshifts of the submm sources, and they find that the Spitzer photometry alone provides a model independent estimate of the redshift. Using X-ray and mid-IR data, only 5 per cent of their secure counterparts show strong evidence for an active galactic nucleus dominating the IR luminosity.

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