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TOPIC: Distant Galaxies


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RE: Distant Galaxies
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A systematic search for the first bright galaxies to form in the early universe has revealed a dramatic jump in the number of such galaxies around 13 billion years ago. These observations of the earliest stages in the evolution of galaxies provide new evidence for the hierarchical theory of galaxy formation -- the idea that large galaxies built up over time as smaller galaxies collided and merged. Astronomers at the University of California, Santa Cruz, used NASA's Hubble Space Telescope to explore the formation of galaxies during the first 900 million years after the Big Bang. They reported their latest findings in the September 14 issue of the journal Nature. Deep observations in three dark patches of sky -- the Hubble Ultra Deep Field and the Great Observatories Origins Deep Survey fields -- gathered the faint light emitted 13 billion years ago by stars in primeval galaxies. Only the brightest galaxies could be detected at such great distances. The researchers observed hundreds of bright galaxies at around 900 million years after the Big Bang. But when they looked deeper, about 200 million years earlier in time, they only found one. Relaxing their search criteria a bit turned up a few more candidates, so there must have been a lot of merging of smaller galaxies during those 200 million years.



This panel shows four candidate galaxies that are likely to have redshifts of 7 and thus have emitted their light when the universe was just 750 million years old. Astronomers can determine when light was emitted from a distant source by its redshift, a measure of how the expansion of the universe stretched the wavelengths of the light as it travelled through space across vast distances.

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Galaxy I0K-1
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Scientists said Wednesday that they have found the most distant galaxy yet, nearly 13 billion light-years away, in a discovery that could help explain how stars were formed at the dawn of time.

The galaxy, named IOK-1, is so far away that the light waves that reached Earth depict it as the system of stars existed shortly after the Big Bang created the universe 13.66 billion years ago.
That period, known to astronomers as the Dark Ages, saw the formation of the first stars and galaxies from elementary particles. Scientists had been unable to directly observe that time period until now.

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Position(2000): RA = 132359.8 Dec = 272456

Astronomers using the Subaru telescope in Hawai'i have looked 60 million years further back in time than any other astronomers, to find the most distant known galaxy in the universe. In doing so, they are upholding Subaru's record for finding the most distant and earliest galaxies known. Their most recent discovery is of a galaxy called I0K-1 that lies so far away that astronomers are seeing it as it appeared 12.88 billion years ago.
This discovery, based on observations made by Masanori Iye of the National Astronomical Observatory of Japan (NAOJ), Kazuaki Ota of the University of Tokyo, Nobunari Kashikawa of NAOJ, and others indicates that galaxies existed only 780 million years after the universe came into existence about 13.66 billion years ago as a hot soup of elementary particles.
To detect the light from this galaxy, the astronomers used Subaru telescope's Suprime-Cam camera outfitted with a special filter to look for candidate distant galaxies. They found 41,533 objects, and from those identified two candidate galaxies for further study using the Faint Object Camera and Spectrograph (FOCAS) on Subaru. They found that IOK-1, the brighter of the two, has a redshift of 6.964, confirming its 12.88 billion-light-year distance.

The discovery challenges astronomers to determine exactly what happened between 780 and 840 million years after the Big Bang. IOK-1 is one of only two galaxies in the new study that could belong to this distant epoch. Given the number of galaxies that have been discovered from 840 million years after the Big Bang, the research team had expected to find as many as six galaxies at this distance. The comparative rarity of objects like IOK-1 means that the universe must have changed over the 60 million years that separate the two epochs.
The most exciting interpretation of what happened is that we are seeing an event known to astronomers as the reionization of the universe. In this case, 780 million years after the Big Bang, the universe still had enough neutral hydrogen to block our view of young galaxies by absorbing the light produced by their hot young stars. Sixty million years later, there were enough hot young stars to ionize the remaining neutral hydrogen, making the universe transparent and allowing us to see their stars.
Another interpretation of the results says that there were fewer big and bright young galaxies 780 million years after the Big Bang than 60 million years later. In this case, most of the reionization would have taken place earlier than 12.88 billion years ago.

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-- Edited by Blobrana at 21:13, 2006-09-13

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RE: Distant Galaxies
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Title: A Spectroscopic Survey of Redshift 1.4<z<3.0 Galaxies in the Goods-North Field: Survey Description, Catalogues, and Properties
Authors: Naveen A. Reddy (NOAO/Caltech), Charles C. Steidel (Caltech), Dawn K. Erb (CfA), Alice E. Shapley (Princeton), Max Pettini (IoA)

We present the results of a spectroscopic survey with the Keck I telescope of more than 280 star-forming galaxies and AGN at redshifts 1.4<z<3.0 in the GOODS-N field. Candidates are selected by their UGR colours using the ``BM/BX'' criteria to target redshift 1.4<z<2.5 galaxies and the LBG criteria to target redshift z~3 galaxies; combined these samples account for ~25-30% of the R and K-band counts to R=25.5 and K(AB)=24.4, respectively. The sample of 212 BM/BX galaxies and 74 LBGs is presently the largest spectroscopic sample of galaxies at z>1.4 in GOODS-N. Extensive multi-wavelength data allow us to investigate the stellar populations, stellar masses, bolometric luminosities (Lbol ), and extinction of z~2 galaxies. Deep Chandra and Spitzer data indicate that the sample includes galaxies with a wide range in Lbol , from 10^10 Lsun to >10^12 Lsun, and covering 4 orders of magnitude in dust obscuration (Lbol/LUV). The sample includes galaxies with a large dynamic range in evolutionary state, from very young galaxies (ages <50 Myr) with small stellar masses (M* ~ 10^9 Msun) to evolved galaxies (ages >2 Gyr) with stellar masses comparable to the most massive galaxies at these redshifts (M* > 10^11 M_sun). Spitzer data indicate that the optical sample includes some fraction of the obscured AGN population at high redshifts: at least 3 of 11 AGN in the z>1.4 sample are undetected in the deep X-ray data but exhibit power-law SEDs longward of ~2 micron (rest-frame) indicative of obscured AGN. The results of our survey indicate that rest-frame UV selection and spectroscopy presently constitute the most time-wise efficient method of culling large samples of high redshift galaxies with a wide range in intrinsic properties, and the data presented here will add significantly to the multi-wavelength legacy of the GOODS survey.

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Type 2 Quasars
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Title: The quest for Type 2 quasars: Chandra observations of luminous obscured quasars in the Sloan Digital Sky Survey
Authors: Authors: C. Vignali (1,2), D.M. Alexander (2), A. Comastri (2) ((1) Dipartimento di Astronomia, Universita` di Bologna, Italy; (2) INAF - Osservatorio Astronomico di Bologna, Italy; (3) Department of Physics, Durham University, UK)

We report on new Chandra exploratory observations of six candidate Type 2 quasars at z=0.49-0.73 selected among the most (OIII) luminous emitters from the Sloan Digital Sky Survey (SDSS). Under the assumption that (OIII) is a proxy for the intrinsic luminosity of the central source, their predicted rest-frame X-ray luminosities are L(2-10keV)~10^45 erg/s. For two of the targets, the photon statistics are good enough to allow for basic X-ray spectral analyses, which indicate the presence of intrinsic absorption (~10^{22-23} cm^-2) and luminous X-ray emission (L_X>10^44 erg/s). Of the remaining four targets, two are detected with only a few (3-6) X-ray counts, and two are undetected by Chandra. If these four sources have the large intrinsic X-ray luminosities predicted by the (OIII) emission, then their nuclei must be heavily obscured (N_H>few 10^23 cm^-2) and some might be Compton thick (N_H>1.5 10^24 cm^-2). We also present the results for two Type 2 quasar candidates serendipitously lying in the fields of the Chandra targets, and provide an up-to-date compilation of the X-ray properties of eight additional SDSS Type 2 quasars from archival Chandra and XMM-Newton observations (five with moderate-quality X-ray data). The combined sample of 16 SDSS Type 2 quasars (10 X-ray detections) provides further evidence that a considerable fraction of optically selected Type 2 quasars are obscured in the X-ray band (at least all the objects with moderate-quality X-ray spectra), lending further support to the findings presented in Vignali, Alexander and Comastri (2004a) and unification schemes of Active Galactic Nuclei, and confirms the reliability of (OIII) emission in predicting the X-ray emission in obscured quasars.

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RE: Distant Galaxies
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Title: Galaxy properties from Voids to Clusters in the SDSS-DR4
Authors: G. Sorrentino (INAF-Naples and INAF-VSTCen, Naples, ITALY), V. Antonuccio-Delogu (INAF-Catania, ITALY), A. Rifatto (INAF-Naples, ITALY)

We investigate the environmental dependence of galaxy population properties in a complete volume-limited sample of 91566 galaxies in the redshift range 0.05 <= z <= 0.095 and with M_r <= -20.0, selected from the Sloan Digital Sky Survey (SDSS) Data Release 4. Our aim is to search for systematic variations in the properties of galaxies with the local galaxy density. In particular, we analyse how the (u - r) color index and the morphological type of galaxies (the latter evaluated through the SDSS Eclass and FracDev parameters) are related to the environment and to the luminosity of galaxies, in order to find hints that can be related to the presence of a ''void'' galaxy population. Void galaxies are identified through a highly selective criterion, which takes also into account redshift and allows us to exclude from the sample all the galaxies that are not really close to the centre of underdense regions. We study the (u - r) colour distribution for galaxies in different luminosity bins, and we look for correlations of colour with the environment, the luminosity, and the morphological type of the galaxies. We find that galaxies in underdense regions (voids) have lower luminosity (M_r > -21) and are bluer than cluster galaxies. The transition from overdense to underdense environments is smooth, the fraction of late-type galaxies decreases while the fraction of early-type galaxies increases smoothly from underdense to dense environments. We do not find any sudden transition in the galaxy properties with density, which, according to a suggestion by Peebles (2001), should mark the transition to a population of "void" galaxies in LCDM models. On the contrary, our results suggest a continuity of galaxy properties, from voids to clusters.

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Galaxy Evolution
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This is the final talk of Symposium 235 on Galaxy Evolution, but there will be much more other things going on tomorrow that are worth writing about.

Downsizing was mentioned frequently during the last days and in the presented survey, red, emission-line-less cluster-galaxies are used to measure the "fossil record" of galaxies, i.e. the old stars. The thousands of spectra are sorted by velocity dispersion (a measure of the total mass) and stacked together to get high quality average spectra with many spectral features that can be analysed to get ages of the stellar population.
They find that the smaller galaxies have smaller ages, i.e. downsizing. The age-spread is much larger at low masses than at the high-mass end. There was no morphological selection but of course it is ellipticals that dominate the sample. The S0-type galaxies are slightly younger than Es with the same sigma, but this trend is weaker than the trend with sigma itself.
Comparisons with the total dynamical mass (also using Sauron-data) there is little room for dark matter (25%).
The ages also correlate with environment, i.e. distance from cluster centre (16% change). Again, this is not a strong trend. Metallicity does not show a trend, but alpha-enhancement does. The tilt of the distribution in a colour-magnitude diagram comes half from ages, half from metallicity.
By calculating backward, how te CMD would have looked for these galaxies at some earlier time, they can be compared to CMDs at some redshift.

Source (IAU Blog)

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Galaxy BzK155043
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SINFONI Discovers Rapidly Forming, Large Proto-Disc Galaxies Three Billion Years After The Big Bang

An international group of astronomers have discovered large disc galaxies akin to our Milky Way that must have formed on a rapid time scale, only 3 billion years after the Big Bang. In one of these systems, the combination of adaptive optics techniques with the new SINFONI spectrograph on ESO's Very Large Telescope (VLT) resulted in a record-breaking resolution of a mere 0.15 arcsecond, giving an unprecedented detailed view of the anatomy of such a distant proto-disc galaxy.

"We have been able, for the first time, to obtain well resolved, two dimensional images of the gas motions in distant star forming galaxies, whose light has travelled more than 11 billion years to the Earth" - Reinhard Genzel, lead author of a paper in this week's issue of Nature in which these results are presented.

BzK155043
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Galaxy BzK155043
Credit SINFONI/VLT

This tells the story how galaxies looked like a mere 3 billion years after the Big Bang.

Over the past decade astronomers have established a global framework of how galaxies formed and evolved when the Universe was only a few billion years old. Gas of ordinary matter cooled and collected in concentrations of the mysterious 'dark' matter (so called dark matter halos). Since that time and up to the present epoch collisions and mergers of galaxies subsequently led to the hierarchical build-up of galaxy mass. This general picture leaves open, however, on what timescales galaxies were assembled and when and how bulges and discs, the primary components of present day galaxies, were formed.
A major study of distant, luminous star forming galaxies at ESO's VLT, the 'SINS' (Spectroscopic Imaging Survey in the Near-Infrared with SINFONI) survey, has now resulted in a major break-through on these questions. This study exploited SINFONI, a novel infrared 'integral field spectrometer' that simultaneously delivers sharp images, with adaptive optics, and highly resolved colour information (spectra) of an object on the sky.
In the case of the galaxy BzK155043 at cosmological redshift 2.4, the SINFONI observations achieved an angular resolution of 0.15 arcsecond, a mere 4000 light years at the distance of this high redshift galaxy. With this superior angular resolution the data reveal the physical and dynamical properties in unprecedented detail. Surprisingly the observations reveal a large and massive rotating proto-disc that is channelling gas toward a growing central stellar bulge. The high gas surface densities, the large star formation rate and the moderately young stellar ages derived from these observations suggest that the system was assembled rapidly, by fragmentation and star formation in an initially very gas rich proto-disc. SINS observations of several other massive, high redshift galaxies give similar results.

The SINFONI data suggest that the proto-discs may have eventually been transformed to dense elliptical galaxies, either by internal processes, such as the spectacular gas inflows observed in BzK15504, or by collisions and mergers with other galaxies, which were frequent in the dense environments in which the high redshift luminous star forming galaxies appear to reside in.
Another important aspect of the work are the very high star formation rates deduced for many of the luminous star forming high redshift galaxies, about one hundred times greater than in the present-day Milky Way.

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RE: Distant Galaxies
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A survey of galaxies observed along the sightlines to quasars and gamma-ray bursts--both extremely luminous, distant objects--has revealed a puzzling inconsistency. Galaxies appear to be four times more common in the direction of gamma-ray bursts than in the direction of quasars.

Quasars are thought to be powered by accretion of material onto supermassive black holes in the centres of distant galaxies. Gamma-ray bursts, the death throes of massive stars, are the most energetic explosions in the universe. But there is no reason to expect galaxies in the foreground to have any association with these background light sources.

"The result contradicts our basic concepts of cosmology, and we are struggling to explain it" - Jason X. Prochaska, associate professor of astronomy and astrophysics at the University of California, Santa Cruz.

Prochaska and graduate student Gabriel Prochter led the survey, which used data from NASA's Swift satellite to obtain observations of the transient, bright afterglows of long-duration gamma-ray bursts (GRBs). They described their findings in a paper accepted for publication in Astrophysical Journal Letters. The paper, which could have strange cosmological implications, has been a source of significant debate among astronomers throughout the world.
The study is based on a fairly straightforward concept. When light from a GRB or a quasar passes through a foreground galaxy, the absorption of certain wavelengths of light by gas associated with the galaxy creates a characteristic signature in the spectrum of light from the distant object. This provides a marker for the presence of a galaxy in front of the object, even if the galaxy itself is too faint to observe directly.
Prochter and Prochaska analysed 15 GRBs in the new study and found strong absorption signatures indicating the presence of galaxies along 14 GRB sightlines. They had previously used data from the Sloan Digital Sky Survey (SDSS) to determine the incidence of galaxies along the sightlines to quasars. Based on the quasar study, they would have predicted only 3.8 galaxies instead of the 14 detected along the GRB sightlines.
The quasar analysis was based on more than 50,000 SDSS observations, so the data for quasars are much more robust statistically than the data for GRBs. Nevertheless, the probability that their results are just a statistical fluke is less than about one in 10,000.
The researchers examined three potential explanations for the inconsistency. The first is obscuration of some quasars by dust in galaxies. The idea is that if a quasar is behind a dusty galaxy it wouldn't be seen, and this could skew the results.

"The counter argument is that with this huge database of quasar observations, the effect of dust has been well characterised and it should be minimal" - Jason Prochaska.

Another possibility is that the absorption lines in the GRB spectra are from gas ejected by the GRBs themselves, rather than from gas in intervening galaxies. But in nearly every case when researchers have taken a closer look in the direction of the GRB, they have in fact found a galaxy at the same position as the gas.
The third idea is that the intervening galaxy may act as a gravitational lens, enhancing the brightness of the background object, and that this effect is somehow different for GRBs than for quasars. Although Prochaska said he prefers this explanation, several factors make strong lensing of the GRBs seem unlikely.

"Those who know more about gravitational lensing than I do tell me it's unlikely to be the answer" - Jason Prochaska.

The paper, a draft of which has been posted on an Internet server for several weeks, has stimulated widespread discussion and at least one new paper proposing a potential explanation. But so far the findings remain perplexing.

"A lot of people have been scratching their heads, and most hope that it goes away. The GRB sample is small, so we would like to triple or quadruple the number in our analysis. That should happen during Swift's extended mission, but it will take time." - Jason X. Prochaska.

In addition to Prochaska and Prochter, the authors of the paper include Hsiao-Wen Chen of the University of Chicago; Joshua Bloom and Ryan Foley of UC Berkeley; Miroslava Dessauges-Zavadsky of the Geneva Observatory; Sebastian Lopez of the University of Chile; Max Pettini of Cambridge University; Andrea Dupree of the Harvard-Smithsonian Centre for Astrophysics; and Puragra GuhaThakurta, professor of astronomy and astrophysics at UC Santa Cruz.
Data used in this study were obtained at the W. M. Keck Observatory, the Gemini Observatory, the Very Large Telescope at the Paranal Observatory, and the Magellan Observatory. Support for this research was provided by the National Science Foundation and NASA.

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Posts: 131433
Date:
Large-scale structures
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A team of astronomers using the Subaru and Keck telescopes on Mauna Kea has discovered giant, three-dimensional filaments of galaxies extending across 200 million light-years of space. These filaments, which formed a mere 2 billion years after the birth of the universe, are the largest-known structures ever discovered. They are studded with more than 30 large concentrations of gas, each up to ten times as massive as our own galaxy. These giant gas clouds are probably the progenitors of the most massive galaxies that exist in the universe today.

This finding is very important because it gives researchers new insight into the large-scale structure of the cosmos. Astronomers expect the universe to look relatively smooth 2 billion years after the birth of the universe.

"Something this large and this dense would have been rare in the early universe. The structure we discovered and others like it are probably the precursors of the largest structures we see today which contain multiple clusters of galaxies" - Astronomer Ryosuke Yamauchi, from Tohoku University.

The research group used the Subaru telescope to make a detailed study of a region of sky 12 billion light-years from Earth that is known to have a large concentration of galaxies. They used Subaru's Suprime-cam camera outfitted with special filters designed to be sensitive to the light from galaxies at that distance. The results showed that this concentration of galaxies is just a small portion of a much larger structure.
The newly found giant structure extends over 200 million light years and has a concentration of galaxies up to four times denser than the universe's average. The only previous known structures with such a high density are much smaller, measuring about 50 million light-years in scale.
Using Subaru's Faint Object Camera and Spectrograph (FOCAS) to study the 3D distribution of galaxies in this filament, the team also discovered at least three overlapping filaments that make up the giant structure.

fig3

Astronomers knew this region contained at least two large concentrations of gas. One of them extends across 400,000 light-years. A comparison with the Andromeda Galaxy, thought to be about the same size as the Milky Way Galaxy, shows the relative immensity of this gas structure.
The researchers found that these large concentrations of gas are located near the overlap regions of the filaments.
The Subaru observations were successful in finding much fainter objects than previously discovered in this region. For example, they found 33 new large concentrations of gas along the filamentary structure extending across 100,000 light-years. This is the first time that so many large concentrations of gas, known to astronomers as Lyman alpha blobs, have been discovered in the distant universe.
Astronomers think that such Lyman alpha blobs, named so since they are seen in the Lyman alpha emission line of hydrogen, are probably related to the births of the largest galaxies. In the "gravitational heating" model, the blobs are regions where gas is collapsing under its own gravity to form a galaxy. The"photoionisation" model attributes emission from the gas to ionisation by ultraviolet light from newborn stars or a massive black hole. The "shock heating" or "galactic superwind" model hypothesises that the glow of the gas is caused by the death of many massive stars born early in the history of the universe, living out short lives, and then dying in supernova explosions that blow out surrounding gas. Team members Yoshiaki Taniguchi and Yasuhiro Shioya (Ehime University) have been advocating for the galactic superwind model.

fig1_e

Observations with the DEIMOS spectrograph at the Keck II telescope revealed that the gas inside the blobs move with speeds greater that 500 kilometres per second. The extent of the gas concentrations and the speed of the material within them suggest that these regions must be up to ten times as massive as the Milky Way Galaxy.
The blobs show a great variety in shape and brightness. For example, some show bubble-like features that match computer simulations of galactic winds such as those by Masao Mori (Senshu University) and Masayuki Umemura (University of Tsukuba). There are also diffuse blobs and those consisting of several galaxies.

m31

"Galaxies of various sizes surround us. The large gas concentrations we found may tell us a lot about how the largest of these came to be" - Yuichi Matsuda of Kyoto University.

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-- Edited by Blobrana at 11:26, 2006-07-27

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L

Posts: 131433
Date:
Infrared Deep Sky Survey
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First data release from UKIRT Infrared Deep Sky Survey

Access to the Data Release 1 is through the WFCAM Science Archive at http://surveys.roe.ac.uk/wsa.

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