Rafelski M.,Infrared Processing and Analysis Center |
Wolfe A.M.,University of California at San Diego |
Prochaska J.X.,University of California at Santa Cruz |
Neeleman M.,University of California at San Diego |
Mendez A.J.,University of California at San Diego
Astrophysical Journal | Year: 2012
We present chemical abundance measurements for 47 damped Lyα (DLA) systems, 30 at z > 4, observed with the Echellette Spectrograph and Imager and the High Resolution Echelle Spectrometer on the Keck telescopes. H I column densities of the DLAs are measured with Voigt profile fits to the Lyα profiles, and we find an increased number of false DLA identifications with Sloan Digital Sky Survey at z > 4 due to the increased density of the Lyα forest. Ionic column densities are determined using the apparent optical depth method, and we combine our new metallicity measurements with 195 from previous surveys to determine the evolution of the cosmic metallicity of neutral gas. We find the metallicity of DLAs decreases with increasing redshift, improving the significance of the trend and extending it to higher redshifts, with a linear fit of -0.22 ± 0.03 dex per unit redshift from z = 0.09-5.06. The metallicity "floor" of 1/600 solar continues out to z 5, despite our sensitivity for finding DLAs with much lower metallicities. However, this floor is not statistically different from a steep tail to the distribution. We also find that the intrinsic scatter of metallicity among DLAs of 0.5 dex continues out to z 5. In addition, the metallicity distribution and the α/Fe ratios of z > 2 DLAs are consistent with being drawn from the same parent population with those of halo stars. It is therefore possible that the halo stars in the Milky Way formed out of gas that commonly exhibits DLA absorption at z > 2. © © 2012. The American Astronomical Society. All rights reserved..
Neeleman M.,University of California at San Diego |
Wolfe A.M.,University of California at San Diego |
Prochaska J.X.,University of California at Santa Cruz |
Rafelski M.,Infrared Processing and Analysis Center
Astrophysical Journal | Year: 2013
Using a sample of 100 H I-selected damped Lyα (DLA) systems, observed with the High Resolution Echelle Spectrometer on the Keck I telescope, we present evidence that the scatter in the well-studied correlation between the redshift and metallicity of a DLA is largely due to the existence of a mass-metallicity relationship at each redshift. To describe the fundamental relations that exist between redshift, metallicity, and mass, we use a fundamental plane description, which is described by the following equation: [M/H] = (- 1.9 ± 0.5) + (0.74 ± 0.21)·log Δv 90-(0.32 ± 0.06)·z. Here, we assert that the velocity width, Δv 90, which is defined as the velocity interval containing 90% of the integrated optical depth, traces the mass of the underlying dark matter halo. This description provides two significant improvements over the individual descriptions of the mass-metallicity correlation and metallicity-redshift correlation. Firstly, the fundamental equation reduces the scatter around both relationships by about 20%, providing a more stringent constraint on numerical simulations modeling DLAs. Secondly, it confirms that the dark matter halos that host DLAs satisfy a mass-metallicity relationship at each redshift between redshifts 2 through 5. © 2013. The American Astronomical Society. All rights reserved.
This artistic rendering provided by California Institute of Technology shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Scientists reported Wednesday, Jan. 20, 2016, they finally have "good evidence" for Planet X, a true ninth planet on the fringes of our solar system. (R. Hurt/Infrared Processing and Analysis Center/Courtesy of California Institute of Technology via AP) More CAPE CANAVERAL, Fla. (AP) — The solar system may have a ninth planet after all. This one is 5,000 times bigger than outcast Pluto and billions of miles farther away, say scientists who presented "good evidence" for a long-hypothesized Planet X on Wednesday. The gas giant is thought to be almost as big as its nearest planetary neighbor Neptune, quite possibly with rings and moons. It's so distant that it would take a mind-blowing 10,000 to 20,000 years to circle the sun. Planet 9, as the pair of California Institute of Technology researchers calls it, hasn't been spotted yet. They base their prediction on mathematical and computer modeling, and anticipate its discovery via telescope within five years or less. The two reported their research Wednesday in the Astronomical Journal because they want people to help them look for it. "We could have stayed quiet and quietly spent the next five years searching the skies ourselves and hoping to find it. But I would rather somebody find it sooner, than me find it later," astronomer Mike Brown told The Associated Press. "I want to see it. I want to see what it looks like. I want to understand where it is, and I think this will help." Brown and planetary scientist Konstantin Batygin feel certain about their prediction, which at first seemed unbelievable to even them. "For the first time in more than 150 years, there's good evidence that the planetary census of the solar system is incomplete," Batygin said, referring to Neptune's discovery as Planet 8. Once it's detected, Brown insists there will be no Pluto-style planetary debate. Brown ought to know; he's the so-called Pluto killer who helped lead the charge against Pluto's planetary status in 2006. (Once Planet 9, Pluto is now officially considered a dwarf planet.) "THIS is what we mean when we say the word 'planet,' " Brown said. Brown and Batygin believe it's big — 10 times more massive than Earth — and unlike Pluto, dominates its cosmic neighborhood. Pluto is a gravitational slave to Neptune, they pointed out. Another scientist, Alan Stern, said he's withholding judgment on the planet prediction. He is the principal scientist for NASA's New Horizons spacecraft, which buzzed Pluto last summer in the first-ever visit from Planet Earth. He still sees Pluto as a real planet — not a second-class dwarf. "This kind of thing comes around every few years. To date, none of those predicts have been borne out by discoveries," Stern said in an email Wednesday. "I'd be very happy if the Brown-Batygin were the exception to the rule, but we'll have to wait and see. Prediction is not discovery." Brown and Batygin shaped their calculation on the fact that six objects in the icy Kuiper Belt, or Twilight Zone on the far reaches of the solar system, appear to have orbits influenced by only one thing: a real planet. The vast, mysterious Kuiper Belt is home to Pluto as well. Brown actually discovered one of these six objects more than a decade ago, Sedna, a large minor planet. "What we have found is a gravitational signature of Planet 9 lurking in the outskirts of the solar system,' Batygin said. The actual discovery, he noted, will be "era-defining." Added Brown: "We have felt a great disturbance in the force." Scott Sheppard of the Carnegie Institution for Science in Washington said Brown and Batygin's effort takes his own findings to "the next level." Two years ago, he and a colleague suggested a possible giant planet. "I find this new work very exciting," Sheppard said in an email. "It makes the distant Super-Earth planet in our solar system much more real. I would say the odds just went from 50 percent to 75 percent that this distant massive planet is real." Depending on where this Planet 9 is in its egg-shaped orbit, a space telescope may be needed to confirm its presence, the researchers said. Or good backyard telescopes may spot it, they noted, if the planet is relatively closer to us in its swing around the sun. It's an estimated 20 billion to 100 billion miles away. The Caltech researchers prefer calling it Planet 9, versus the historical term Planet X. The latter smacks of "aliens and the imminent destruction of the Earth," according to Brown.
When some speedy, massive stars plow through space, they can cause material to stack up in front of them in the same way that water piles up ahead of a ship. Called bow shocks, these dramatic, arc-shaped features in space are leading researchers to uncover massive, so-called runaway stars. "Some stars get the boot when their companion star explodes in a supernova, and others can get kicked out of crowded star clusters," said astronomer William Chick from the University of Wyoming in Laramie, who presented his team's new results at the American Astronomical Society meeting in Kissimmee, Florida. "The gravitational boost increases a star's speed relative to other stars." Our own sun is strolling through our Milky Way galaxy at a moderate pace. It is not clear whether our sun creates a bow shock. By comparison, a massive star with a stunning bow shock, called Zeta Ophiuchi (or Zeta Oph), is traveling around the galaxy faster than our sun, at 54,000 mph (24 kilometers per second) relative to its surroundings. Zeta Oph's giant bow shock can be seen in this image from the WISE mission: Both the speed of stars moving through space and their mass contribute to the size and shapes of bow shocks. The more massive a star, the more material it sheds in high-speed winds. Zeta Oph, which is about 20 times as massive as our sun, has supersonic winds that slam into the material in front of it. The result is a pile-up of material that glows. The arc-shaped material heats up and shines with infrared light. That infrared light is assigned the color red in the many pictures of bow shocks captured by Spitzer and WISE. Chick and his team turned to archival infrared data from Spitzer and WISE to identify new bow shocks, including more distant ones that are harder to find. Their initial search turned up more than 200 images of fuzzy red arcs. They then used the Wyoming Infrared Observatory, near Laramie, to follow up on 80 of these candidates and identify the sources behind the suspected bow shocks. Most turned out to be massive stars. The findings suggest that many of the bow shocks are the result of speedy runaways that were given a gravitational kick by other stars. However, in a few cases, the arc-shaped features could turn out to be something else, such as dust from stars and birth clouds of newborn stars. The team plans more observations to confirm the presence of bow shocks. "We are using the bow shocks to find massive and/or runaway stars," said astronomer Henry "Chip" Kobulnicky, also from the University of Wyoming. "The bow shocks are new laboratories for studying massive stars and answering questions about the fate and evolution of these stars." Another group of researchers, led by Cintia Peri of the Argentine Institute of Radio Astronomy, is also using Spitzer and WISE data to find new bow shocks in space. Only instead of searching for the arcs at the onset, they start by hunting down known speedy stars, and then they scan them for bow shocks. "WISE and Spitzer have given us the best images of bow shocks so far," said Peri. "In many cases, bow shocks that looked very diffuse before, can now be resolved, and, moreover, we can see some new details of the structures." Some of the first bow shocks from runaway stars were identified in the 1980s by David Van Buren of NASA's Jet Propulsion Laboratory in Pasadena, California. He and his colleagues found them using infrared data from the Infrared Astronomical Satellite (IRAS), a predecessor to WISE that scanned the whole infrared sky in 1983. Kobulnicky and Chick belong to a larger team of researchers and students studying bow shocks and massive stars, including Matt Povich from the California State Polytechnic University, Pomona. The National Science Foundation funds their research. Images from Spitzer, WISE and IRAS are archived at the NASA Infrared Science Archive housed at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.
The vacuum chamber at NASA's Jet Propulsion Laboratory in Pasadena, California, used for testing WFIRST and other coronagraphs. A star is simulated inside the chamber using light brought in by an optical fiber, and the light of this "star" is suppressed in the testbed by coronagraph masks and deformable mirrors. WFIRST is managed at Goddard, with participation by NASA's Jet Propulsion Laboratory in Pasadena, California, the Space Telescope Science Institute in Baltimore, the Infrared Processing and Analysis Center, also in Pasadena, and a science team comprised of members from U.S. research institutions across the country. Credit: NASA We humans might not be the only ones to ponder our place in the universe. If intelligent aliens do roam the cosmos, they too might ask a question that has gripped humans for centuries: Are we alone? These aliens might even have giant space telescopes dedicated to studying distant planets and searching for life. Should one of those telescopes capture an image of our blue marble of a planet, evidence of forests and plentiful creatures would jump out as simple chemicals: oxygen, ozone, water and methane. Many earthlings at NASA are hoping to capture similar chemical clues for Earth-like planets beyond our solar system, also known as exo-Earths, where "exo" is Greek for "external." Researchers are developing new technologies with the goal of building space missions that can capture not only images of these exo-Earths, but also detailed chemical portraits called spectra. Spectra separate light into its component colors in order to reveal secrets of planets' atmospheres, climates and potential habitability. "Evidence for life is not going to look like little green people—it's going to reveal itself in a spectrum," said Nick Siegler, the chief technologist for NASA's Exoplanet Exploration Program Office at the agency's Jet Propulsion Laboratory in Pasadena, California. The program is helping to develop NASA's plans for future exo-Earth imaging missions. On the road to this goal, NASA is actively developing coronagraph technology in various laboratories, including JPL. Coronagraphs are instruments introduced in the early 20th century to study our sun. They use special masks to block out light from the circular disk of the sun, so that scientists can study its outer atmosphere, or corona. Now NASA is developing more sophisticated coronagraphs to block the glaring light of other stars and reveal faint planets that might be orbiting them. Stars far outshine their planets; for example, our sun is 10 billion times brighter than Earth. That's similar to the flood of football stadium lights next to a tiny candle. "The search for Earth-like planets begins with the suppression of starlight," said Rhonda Morgan of JPL, a coronagraph technologist for the Exoplanet Exploration Program Office. "It's like blocking the sun with a sun visor while driving in order to see the road." Telescopes on the ground have already used coronagraphs to take pictures of planets, but those planets are easier to photograph because they are large, bright, and orbit far from their host stars. To take a picture of Earth-size planets lying in the habitable zone of sun-like stars—the region where temperatures are just right for possible liquid oceans and lakes—will require a telescope in space. Out in space, the blurring effects of our blustery atmosphere can be avoided. Several types of coronagraphs are under development for proposed space missions. One mission, led by NASA's Goddard Space Flight Center, Greenbelt, Maryland, is known as WFIRST. WFIRST stands for Wide-Field Infrared Survey Telescope. The WFIRST mission would be able to identify chemicals in the atmospheres of exoplanets as small as super-Earths, which are like Earth's bigger cousins, such as Kepler-452b, a recent discovery by NASA's Kepler mission. This would pave the way for future studies of the smaller exo-Earths. The WFIRST mission would also investigate other cosmic mysteries such as dark matter and dark energy. Engineers and scientists at JPL are busily tinkering with different coronagraph technologies for WFIRST. Ilya Poberezhskiy, who manages the testbeds at JPL, explained two primary coronagraph designs while holding in his hand the tiny, starlight-blocking masks. One of them, the "shaped pupil" mask, is a few centimeters across, while the "hybrid Lyot" mask is a pinprick of a dot, barely visible at only one-tenth of a millimeter in size. Both technologies will fly together on the WFIRST mission as a part of one instrument—the occulting mask coronagraph. "A wheel-like mechanism will rotate to switch different masks inside the instrument and convert the coronagraph from one mode to another," said Poberezhskiy. The main challenge for coronagraphs is controlling starlight, which has a tendency to stray. Just putting a circular mask in front of the star doesn't obstruct the light completely; starlight bends around the mask like ocean waves curving around islands in a process called diffraction. Each coronagraph type deals with this challenge differently by using multiple masks as well as mirrors that can deform to sequentially suppress starlight in various stages. An animation explaining how the hybrid Lyot coronagraph works can be seen online at: exoplanets.jpl.nasa.gov/resources/1061/ "The starlight likes to walk all over the place, and into the area where you want to image the planet," said Wes Traub, the JPL project scientist for WFIRST. "The goal now is to get more practical with the kind of telescope we will use for WFIRST." Another challenge in designing coronagraphs is adjusting for a space telescope's tiny vibrations, or jitter. The team at JPL is assessing how their coronagraphs handle jitter by simulating the effects in a vacuum chamber. They built a table-top-size telescope simulator for the tests. "In space, telescopes experience warping and vibrations that need to be measured and reduced inside the coronagraph," said Poberezhskiy. "Our mock telescope will let us test the WFIRST coronagraph under realistic, space-like conditions." As WFIRST development moves forward, mission planners are already thinking about a possible next step: a space telescope designed to image true Earth analogs. Such a mission may be more than a decade away, but development of the nuts and bolts of the technology is underway at a feverish pace. "It's an exciting time for exoplanet research," said Gary Blackwood, manager of the Exoplanet Exploration Program. "This is history in the making." WFIRST is managed at NASA's Goddard, with participation by JPL, the Space Telescope Science Institute in Baltimore, the Infrared Processing and Analysis Center, also in Pasadena, and a science team comprised of members from U.S. research institutions across the country.