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TOPIC: Distant Galaxies


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Hubble Reveals Observable Universe Contains 10 Times More Galaxies Than Previously Thought

The universe suddenly looks a lot more crowded, thanks to a deep-sky census assembled from surveys taken by NASA's Hubble Space Telescope and other observatories.
Astronomers came to the surprising conclusion that there are at least 10 times more galaxies in the observable universe than previously thought. This places the universe's estimated population at, minimally, 2 trillion galaxies.

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Title: Galaxy Zoo: Morphological Classifications for 120,000 Galaxies in HST Legacy Imaging
Author: Kyle W. Willett, Melanie A. Galloway, Steven P. Bamford, Chris J. Lintott, Karen L. Masters, Claudia Scarlata, B.D. Simmons, Melanie Beck, Carolin N. Cardamone, Edmond Cheung, Edward M. Edmondson, Lucy F. Fortson, Roger L. Griffith, Boris Haeussler, Anna Han, Ross Hart, Thomas Melvin, Michael Parrish, Kevin Schawinski, R.J. Smethurst, Arfon M. Smith

We present the data release paper for the Galaxy Zoo: Hubble (GZH) project. This is the third phase in a large effort to measure reliable, detailed morphologies of galaxies by using crowdsourced visual classifications of colour composite images. Images in GZH were selected from various publicly-released Hubble Space Telescope Legacy programs conducted with the Advanced Camera for Surveys, with filters that probe the rest- frame optical emission from galaxies out to z ~ 1.

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Title: Galaxy Zoo: Quantitative Visual Morphological Classifications for 48,000 galaxies from CANDELS
Author: B. D. Simmons, Chris Lintott, Kyle W. Willett, Karen L. Masters, Jeyhan S. Kartaltepe, Boris Häubler, Sugata Kaviraj, Coleman Krawczyk, S. J. Kruk, Daniel H. McIntosh, R. J. Smethurst, Robert C. Nichol, Claudia Scarlata, Kevin Schawinski, Christopher J. Conselice, Omar Almaini, Henry C. Ferguson, Lucy Fortson, William Hartley, Dale Kocevski, Anton M. Koekemoer, Alice Mortlock, Jeffrey A. Newman, Steven P. Bamford, N. A. Grogin, Ray A. Lucas, Nimish P. Hathi, Elizabeth McGrath, Michael Peth, Janine Pforr, Zachary Rizer, Stijn Wuyts, Guillermo Barro, Eric F. Bell, Marco Castellano, Tomas Dahlen, Avishai Dekel Jamie Ownsworth, Sandra M. Faber, Steven L. Finkelstein, Adriano Fontana, Audrey Galametz, Ruth Grützbauch, David Koo, Jennifer Lotz, Bahram Mobasher, Mark Mozena, Mara Salvato, et al. (1 additional author not shown)

We present quantified visual morphologies of approximately 48,000 galaxies observed in three Hubble Space Telescope legacy fields by the Cosmic And Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and classified by participants in the Galaxy Zoo project. 90% of galaxies have z < 3 and are observed in rest-frame optical wavelengths by CANDELS. Each galaxy received an average of 40 independent classifications, which we combine into detailed morphological information on galaxy features such as clumpiness, bar instabilities, spiral structure, and merger and tidal signatures. We apply a consensus-based classifier weighting method that preserves classifier independence while effectively down-weighting significantly outlying classifications. After analysing the effect of varying image depth on reported classifications, we also provide depth-corrected classifications which both preserve the information in the deepest observations and also enable the use of classifications at comparable depths across the full survey. Comparing the Galaxy Zoo classifications to previous classifications of the same galaxies shows very good agreement; for some applications the high number of independent classifications provided by Galaxy Zoo provides an advantage in selecting galaxies with a particular morphological profile, while in others the combination of Galaxy Zoo with other classifications is a more promising approach than using any one method alone. We combine the Galaxy Zoo classifications of "smooth" galaxies with parametric morphologies to select a sample of featureless disks at 1 < z < 3, which may represent a dynamically warmer progenitor population to the settled disk galaxies seen at later epochs.

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Title: The Impossibly Early Galaxy Problem
Author: Charles L. Steinhardt, Peter Capak, Dan Masters, Josh S. Speagle

The current hierarchical merging paradigm and LambdaCDM predict that the z~4-8 universe should be a time in which the most massive galaxies are transitioning from their initial halo assembly to the later baryonic evolution seen in star-forming galaxies and quasars. However, no evidence of this transition has been found in many high redshift galaxy surveys including CFHTLS, CANDELS and SPLASH, the first studies to probe the high-mass end at these redshifts. Indeed, if halo mass to stellar mass ratios estimated at lower-redshift continue to z~6-8, CANDELS and SPLASH report several orders of magnitude more M~1012-13 solar mass halos than are possible to have formed by those redshifts, implying these massive galaxies formed impossibly early. We consider various systematics in the stellar synthesis models used to estimate physical parameters and possible galaxy formation scenarios in an effort to reconcile observation with theory. Although known uncertainties can greatly reduce the disparity between recent observations and cold dark matter merger simulations, even taking the most conservative view of the observations, there remains considerable tension with current theory.

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Catching a 'Wave' of Galaxies Ending the Dark Ages

Through a project dubbed SURFS UP, NASA's Spitzer Space Telescope and Hubble Space Telescope are catching sight of a "wave" of galaxies that emerged in the early universe. Starlight from these primordial galaxies is reckoned to have cleared a fog of hydrogen gas that shrouded the cosmos during a mysterious period known as the Dark Ages.
Spitzer has revealed that the stars shining in two of the young SURFS UP galaxies, discovered by Hubble, look surprisingly mature. The finding suggests these stars formed earlier than expected, and thus began lifting the cosmic fog sooner than previously thought.

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Some galaxies in the early universe grew up quickly

Some galaxies grew up in a hurry. Most of the galaxies that have been observed from the early days of the universe were young and actively forming stars. Now, an international team of astronomers, including Carnegie's Eric Persson and Andy Monson, have discovered galaxies that were already mature and massive in the early days. Fifteen mature galaxies were found at a record-breaking average distance of 12 billion light years, when the universe was just 1.6 billion years old. Their existence at such an early time raises new questions about what forced them to grow up so quickly. The finding is published by The Astrophysical Journal Letters.
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Quasar host galaxies
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Title: Quasar host galaxies in the SDSS Stripe 82
Authors: Jari Kotilainen. Renato Falomo, Daniela Bettoni, Kalle Karhunen, Michela Uslenghi

We present first results from our study of the properties of ~400 low redshift (z < 0.5) quasars, based on a large homogeneous dataset derived from the Stripe 82 area of the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). For this sky region, deep (r~22.4) u,g,r,i,z images are available, up to ~2 mag deeper than standard SDSS images, allowing us to study both the host galaxies and the Mpc-scale environments of the quasars. This sample greatly outnumbers previous studies of low redshift quasar hosts, from the ground or from space. Here we report the preliminary results for the quasar host galaxies. We are able to resolve the host galaxy in ~80 % of the quasars. The quasar hosts are luminous and large, the majority of them in the range between M*-1 and M*-2, and with ~10 kpc galaxy scale-lengths. Almost half of the host galaxies are best fit with an exponential disk, while the rest are spheroid-dominated. There is a reasonable relation between the central black hole mass and the host galaxy luminosity.

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Astronomers find most distant galaxy to date

With the help of NASAs Hubble and Spitzer Space Telescopes, a team of astronomers led by Hopkins Wei Zheng has discovered the most distant - and, hence, the youngest - galaxy ever observed with high confidence.
The telescopes captured light from that galaxy when the universe, now 13.7 billion years old, was just 500 million years of age. The light travelled about 13.2 billion light years before reaching the telescopes.

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Seeing the Birth of the Universe in an Atom of Hydrogen

An international team of scientists led by researchers at Tel Aviv University have developed a method for detecting galaxies of stars that formed when the universe was in its infancy, during the first 180 million years of its existence. The method is able to observe stars that were previously believed too old to find, says Prof. Rennan Barkana of TAU's School of Physics and Astronomy.
Published in the journal Nature, the researchers' method uses radio telescopes to seek out radio waves emitted by hydrogen atoms, which were abundant in the early days of the universe. Emitting waves measuring about eight inches (21 centimetres) long, the atoms reflect the radiation of the stars, making their emission detectable by radio telescopes, explains Prof. Barkana. This development opens the way to learning more about the universe's oldest galaxies.

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Title: Stars throw their weight in old galaxies
Authors: Nate Bastian

The observation that old, massive galaxies have a larger fraction of low-mass stars than their younger, lower-mass counterparts adds to mounting evidence that star formation may have been different in the early Universe.

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