Scientists Use Quasars to Probe Dark Energy & Measure its Role in the Evolution of the Universe

 

Owner, Baryon Oscillations Spectroscopic Survey, a large volume of dark energy's role in mapping the evolution of the universe estimates. The Sloan Digital Sky Survey III (SDSS III) program, the largest and only mapping techniques, more than 48,000 quasars redshifts based on spectra with 3.5, meaning that light up their first significant results active galaxies 11.5 billion years in the past.

is not being realized, "said principal investigator David boss Schlegel, Lawrence Berkeley National Laboratory, U.S. Department of Energy (Berkeley Lab) of the Physics Division is a star. The accelerating expansion of the universe in our own time is dominated by dark energy. Dark energy affects how slow the rapid transfer of cosmology is one of the most difficult questions. '

Two ways to measure the expansion of the universe

Distribution of galaxies and barely visible in the large-scale variations in the network - as an international collaboration, leading scientists, including many current or former members of Berkeley Lab, baryon acoustic bass education (BAO) oscillations mapping Dark energy from vacuum gas clouds, which appear dark to see a thing impossible. Peaks in the density of matter density variations of the regular Spacing real, cosmic microwave background radiation whose remnants are visible in the air. Spacing calibrating the expansion rate can be measured wherever BAO cosmic ruler provides for.

Sloan Foundation telescope at Apache Point Observatory in New Mexico using, a two-dimensional spectroscopic investigations bass BAO has increased. Bright galaxies with redshifts 0.8 normal first priority is to the survey, seven billion in the past few years, Galaxy, according to the results of a survey of 300,000 galaxies included in the results, to March, 2012 was held in . But soon enough galaxies in the universe at redshifts significantly Map BAO deposited with a 2.5-meter telescopes can not. The goal of this owner: quasars.

Schlegel said, "Quasars brightest objects in the sky, so only reliable spectra measured redshift 2.0 and beyond is a way out,". He said that a hundred times more galaxies with redshifts quasars, but they are too faint to be used for BAO. '

Quasars also directly BAO measurements are sparse, but there is another way BAO at high redshifts is shown. Space such as a quasar's light passes through the gas cloud is on the ground, the spectrum of hydrogen Lyman alpha forest absorption lines is known as a lot of makes. Ideally, "forest" absorption lines in quasar light shows which has been approved by an intervening gas clouds. Like a flashlight seen through a fog individual absorption lines in the spectrum of a single quasar redshifts various prominences and reflect, how the gas density varies with distance along the line.

Coffee quasars, quite close together in the sky with covering a vast difference, interference by clouds of gas distribution will be mapped in three dimensions can. By Patrick McDonald believed already advanced in the early 2000s, the Canadian Institute for theoretical astrophysics and Martin White, both in Berkeley Lab.

"In 2003, when I presented the idea at a conference of cosmologists, they thought it's crazy," White, who at the University of California at Berkeley and a professor of physics and astronomy teams Geological Survey boss chair that is. "Nine years later, the owner has expressed a surprise that this powerful technique. Successful beyond our wildest dreams are."

Much better SDSS III spectrograph, the construction ordered by Berkeley Lab Natalie was fish is much better than the first survey allows coverage and resolution, but Lyman alpha forest still in search of BAO Many reasons was a suggestion of higher risk. Lyman alpha absorption spectrum lines, which are absorbed by Earth's atmosphere are found in the ultraviolet, land, just the right amount redshifted quasars whose spectra are useful. Tag lines only neutral hydrogen, ionized hydrogen in the universe is highest. Among other uncertainties, hydrogen, clouds, or irregular heating of many quasars close together, clustering can distort signals.

Berkeley Lab Nicholas Ross, who led the team, said the target of choice: "A Galaxy poll, compared Lyman alpha forest in search of the BAO is good - high risk, but high reward,". Quasars per square degree of sky, a minimum of 15 to 20 - Boss quasars possible during its five year run of two million individual targets is 10% dedicated enough to capture spectra for quasar clustering on the map. Please goals photometric data (an object glow in different colors) was selected, but the spectra were taken after the team must ensure that the targets were real quasars and stars which were duplicates or other quasar. The owner took a chance.

"We had one thing in our favor," Ross said. It did not matter that this was the type of quasar, as long as it was high redshift.. Finally, we found that all our compilation algorithm has worked well. '

Searching for Signal

Preliminary results Lyman alpha - the first stage of the universe evolution first BAO Map - Space The boss will eventually map is based on only one-third of the volume, and their spectra, confirmed by visual inspection includes 60.369 quasars are. To simplify the search for BAO, many of them were lost.

"BAO data out, we have to model the signal we are looking for is a mess," says Berkeley Lab Bill Carithers. Rejected a broad absorption line class quasars, whose spectra by a fast-moving gas quasar is an active center was dirty. Another class of quasars whose spectra "troughs damped Lyman alpha," that is, Carithers said, are "a lot of gas in the quasar light, a large clump, so it runs in wiping out the forest . "

Removed along with unhelpful spectra, Bass was left with 48.129 quasars. In May of 2011, a Brookhaven National Laboratory under Anže Slosar, Berkeley Lab former team boss only 14,000 quasars using the cosmological distance measure in the space density of hydrogen gas had demonstrated the feasibility - Coffee, Slosar said, "to establish a proof of concept."
Three-dimensional maps and other survey by owner

Until recently, employers and other survey maps the three dimensional distribution of galaxies daily average of just over five and a half billion years ago, were able to measure the back, at a time when the universe's expansion is accelerating already. Now boss of the quasar (red circle, left) vacuum gas distribution measurements by measuring, at a time when the expansion is still under the influence of gravity was slow in the initial investigation of the structure of the universe. quasar with slow data transfer speed of dark energy provides access. Zosia Rostomian, Lawrence Berkeley National Laboratory and NIC Ross, Lyman alpha team boss, Berkeley Lab graph by

"We do not use specific information in a line of sight, we look at correlations between," Carithers said. "This is the first quasars because we have a lot - with very little, you can not see the pattern."

Useful scientific information from raw data to help convert telescopes in addition, Berkeley Lab Stephen Bailey was in charge of obtaining synthetic data sets - the "mocks" - that was based analysis.

"We know where the real quasars and the gas physics that we know, but we do not know where the gas. Positions and redshifts of quasars in our simulations based on real, but fake spectra were different gas with the distribution. analysis in an artificial divide we can see, we should all see it. "

Finally, Berkeley Lab Services group provided by high performance computing Linux cluster of computers to data processing and generation Riemann after mock spectra, more than 48,000 quasars Lyman alpha forest analyze the results of the competition.

Analytical techniques used in this report, Andreu Font boss Ribera and French allies among participating groups has been developed by. Applied real quasar spectra, the density distribution of an image that Bailey said, "We first look at the BAO in the secret places."

Schlegel says, "We have no reliable way of two or more can be measured redshifts BAO., Five years ago it was chancy, but the table is a proposal. Failed in any of several ways: may have been, but nature was good to us. "

White said, matter-dominated universe, he said, we are looking back, when decelerating expansion and dark energy was hard to see. Transition from decelerating expansion to accelerating expansion was faster, and now we live in a universe dominated by dark energy. The biggest puzzle in cosmology is, why now? '

Meanwhile, Lyman alpha forest of ancient Universe is a new approach, BigBOSS as proposed in the future, more powerful survey may prove beneficial with a fully opened.

"Baryon acoustic bass in quasars Lyα forest Oscillations," NG by Busca, Timothée Delubac, James Rich, Stephen Bailey, Andreu Font Ribera, David Kirkby, J.-M. Le Goff, Anže Slosar, Eric Aubourg Julian Bautista, Michael Blomqvist, Bill Carithers, Rupert AC Croft, Kyle S. Dawson, Daniel J. Eisenstein, Hamilton Jean Christophe, Shirley, and Lee Khee GAN, Daniel Margala, Jordi Miralda-Escudé, Pasquier Noterdaeme , Nathalie Palanque Delabrouille, Isabelle Paris, Patrick Petitjean, Matthew M. Pieri, EMMANUEL Rollinde, Nicholas P. Ross, David J. Schlegel, David H. Weinberg, Martin White, and Christophe Yèche, has been submitted Astronomy and Astrophysics and is available at http://arxiv.org/abs/1211.2616 arXiv preprint server.

Source: Paul Preuss, Lawrence Berkeley National Laboratory

Photos: Zosia Rostomian, Lawrence Berkeley National Laboratory, NIC Ross, Lyman alpha team boss, Berkeley Lab, and meaning Springel ET, Virgo Consortium and the Max Planck Institute for Astrophysics, Zosia Rostomian, Lawrence Berkeley National Laboratory and NIC Ross, owner Lyman Alpha Team, Berkeley Lab