[naturenews] from [nature.com]
[naturenews]
Published online 24 December 2009 | Nature | doi:10.1038/news.2009.1165
News
Researchers claim most distant galaxies yet
Deep-field image from Hubble triggers competing reports.
Lizzie Buchen
Astronomers have caught a glimpse of galaxies that existed a mere 500 million years after the Big Bang, more than 13 billion years ago.
In August, NASA's Hubble Space Telescope made the deepest image ever of the Universe in near-infrared wavelengths using its new set of eyes, the Wide Field Camera 3 (WFC3) installed by astronauts in May. In the near infrared astronomers can detect galaxies that are so distant, and receding so quickly, that their light is stretched longer — or redder — than visible light. The more distant an object, the more its light is shifted red and the higher its 'redshift'.
For the past few months, researchers have been poring over this new data set — a sliver of sky about one-twelfth the diameter of the full Moon, viewed for 173,000 seconds over four days — searching for ancient galaxies that might deepen understanding of how the Universe evolved. The current record-holder for distance is a gamma ray burst, discovered in April, with a redshift of 8.2.
Now, astronomer Garth Illingworth at the University of California, Santa Cruz, and his colleagues have found tentative evidence of three galaxies with redshifts of around 10. These would have existed when the Universe was just 3-4% of its current age, and would be among the oldest objects ever seen. The findings have been posted on the preprint server arXiv.org1.
"Even though it's not really unexpected, finding galaxies at such early times is hugely exciting," says Illingworth, who also helped to create the publicly available Hubble image and data set. "There's no smoking gun, but we're confident that this is what we're really seeing."
Older than thou
The team's report of galaxies with a redshift of 10 isn't the first. For instance, Rogier Windhorst at Arizona State University in Tempe and his colleagues have reported finding 20 galaxies with a redshift near 10 in the same data set, although this 20 did not include Illingworth's three. Windhorst and his colleagues posted their findings on arXiv.org in October2.
The various teams disagree over how exactly to define these distant galaxies, and what constitutes a definitive detection. Illingworth argues that Windhorst's standards were not stringent enough, and that some of the galaxies the other team detected were close to large, bright galaxies that could have contaminated the results. "That could have confused their software and caused them to get a lot of objects that just were not real high-redshift galaxies," he says.
Illingworth also notes that 20 galaxies of redshift 10 in such a small region of space indicates a higher rate of star formation than has been predicted for that time. "It doesn't accord with what we would expect theoretically or logically," he says.
Windhorst acknowledges that his group "may have overshot", but adds that Illingworth's group was "overly conservative". Even so, Windhorst noted that two of the galaxies detected by Illingworth's team did not meet his team's criteria as high-redshift, and the third was not detected after the data were processed. "Being conservative is good, but I think they haven't reduced the data as good as they could have," Windhorst says.
Let there be light
But Illingworth's team "appears to have done a more careful job than Windhorst's", says astronomer Richard Ellis at the California Institute of Technology in Pasadena, who in 2007 reported candidate galaxies with redshifts between 8 and 10 using the Keck telescope in Hawaii. He added that Illingworth's team "goes to great lengths to justify their candidates", although he is cautious because the camera detects high-redshift objects only in one filter, and because many such claims, including his, have been revisited by other groups with mixed results.
"The history of claims for finding redshift-10 galaxies is a chequered one, but it's exciting," he says. "Ultimately, we will still have to verify these claims. It's going to be very hard, as it has turned out to be with [other] candidates."
The lack of many bright galaxies at redshift 10 offers clues to what kicked off the Universe's "reionization epoch" — a period between 500 million and 1 billion years after the Big Bang during which luminous objects such as galaxies and quasars ionized the intergalactic medium. The lack of bright galaxies at the start of this timespan suggests that they did not initiate the reionization process, Windhorst says.
"There are still a lot of questions to address," says Illingworth. "This is very tantalizing, but we need to understand the properties of those galaxies. That's where the real scientific interest is."
References
1. Bouwens, R. J. et al. http://arxiv.org/abs/0912.4263 (2009).
2. Yan, H. et al. http://arxiv.org/abs/0910.0077 (2009).
[naturenews]
Published online 24 December 2009 | Nature | doi:10.1038/news.2009.1164
News
Why it's hot in the city
Heat wave in Baltimore made worse by hot air from Washington DC.
Katharine Sanderson
{{Hot air blowing in from neighbouring metropolises may make some cities hotter during heat waves.}
Punchstock}
While most of Europe and much of North America are currently in the middle of a cold snap, researchers trying to understand a heatwave that hit the northeastern United States in 2007 have found that Baltimore's sweltering temperatures were exacerbated by the presence of its neighbours, Washington DC and Columbia.
Meteorologist Da-Lin Zhang at the University of Maryland in College Park and his colleagues used a three-dimensional meteorological model to investigate how weather and temperature change over time across the Baltimore and Washington DC region. Baltimore sits about 100 kilometres northeast of Washington, with Columbia about halfway between them.
Zhang wanted to look at the urban heat-island effect, a well-known phenomenon where built-up areas become much hotter than surrounding rural areas in warm weather. His models included data showing what the land in this large area was used for. The roughness of the surface — whether it is covered by trees or water or buildings — affects the weather at the surface and he was able to put detail down to 500 metres into the model.
Then, using data for 7–10 July 2007, when the area was hit by a heatwave, Zhang ran the models to simulate the weather at that time.
This heatwave was "horribly hot, dangerously hot," according to Russell Dickerson, an atmospheric chemist and a co-author of the paper, which is published in Geophysical Research Letters1.
Stagnant heat
The models confirmed that it had been hotter in Baltimore than in Washington — Baltimore reached 37.5 °C while Washington basked in a relatively balmy 36.5 °C — and that the air quality over Baltimore was also much worse, with ozone levels of 125 parts per billion (ppb) compared with 85 ppb over Washington. The US Environmental Protection Agency recommended maximum for ozone at ground level is 75 ppb. The amounts of small particulate pollutants over Baltimore were also higher than over Washington.
"The heat-island effect was worse in Baltimore than in Washington DC," says Dickerson, and this can't be explained simply by the physics of the buildings and road surfaces in Baltimore, he adds. The effect has to be a consequence of the weather dynamics in the area.
The prevailing winds over the region in July 2007 were southwesterlies. There was also an easterly breeze coming off Chesapeake Bay to the east of Baltimore. The model showed that the hot air from the two heat islands of Washington and Columbia was moved up to Baltimore by the prevailing wind, where it stagnated because of the incoming bay breeze, making temperatures soar and pollution stay put over the city, which was also subject to its own heat-island effect.
When Zhang and his team ran a model in which Washington was bulldozed and replaced by trees, things got cooler in Baltimore. The heat-island effect there was reduced by 25%, and the city was cooler by 1.25 °C.
"The urban heat island is a well-known phenomenon, but was thought to be quite local," says Gabriele Curci, who studies air quality and pollution transport at the University of L'Aquila in Italy. He suggests that this work will help to decide where best to place air-quality monitoring balloons.
"It's good to know that [the urban heat island] is not only a local effect," says Susanne Grossman-Clarke at the Global Institute of Sustainability, Arizona State University in Tempe. "Urban planners only think about the local aspect of the heat island," she adds. "The city is in the context of other cities."
Dickerson agrees that in the light of this work, planners should pay more attention to outside influences on urban heat islands. And they might — the research was supported in part by Maryland's Department of the Environment to determine how planting trees might help to improve air quality, Dickerson says. Zhang is currently working in China to advise on that country's heat-island problems.
"A little state like Maryland can't do much to help global climate change, but there are things you can do to mitigate the adverse impacts of climate locally," says Dickerson.
References
1. Zhang, D.-L. et al. Geophys. Res. Lett. 36, L24401 (2009).
[naturenews]
Published online 24 December 2009 | Nature | doi:10.1038/news.2009.1165
News
Researchers claim most distant galaxies yet
Deep-field image from Hubble triggers competing reports.
Lizzie Buchen
Astronomers have caught a glimpse of galaxies that existed a mere 500 million years after the Big Bang, more than 13 billion years ago.
In August, NASA's Hubble Space Telescope made the deepest image ever of the Universe in near-infrared wavelengths using its new set of eyes, the Wide Field Camera 3 (WFC3) installed by astronauts in May. In the near infrared astronomers can detect galaxies that are so distant, and receding so quickly, that their light is stretched longer — or redder — than visible light. The more distant an object, the more its light is shifted red and the higher its 'redshift'.
For the past few months, researchers have been poring over this new data set — a sliver of sky about one-twelfth the diameter of the full Moon, viewed for 173,000 seconds over four days — searching for ancient galaxies that might deepen understanding of how the Universe evolved. The current record-holder for distance is a gamma ray burst, discovered in April, with a redshift of 8.2.
Now, astronomer Garth Illingworth at the University of California, Santa Cruz, and his colleagues have found tentative evidence of three galaxies with redshifts of around 10. These would have existed when the Universe was just 3-4% of its current age, and would be among the oldest objects ever seen. The findings have been posted on the preprint server arXiv.org1.
"Even though it's not really unexpected, finding galaxies at such early times is hugely exciting," says Illingworth, who also helped to create the publicly available Hubble image and data set. "There's no smoking gun, but we're confident that this is what we're really seeing."
Older than thou
The team's report of galaxies with a redshift of 10 isn't the first. For instance, Rogier Windhorst at Arizona State University in Tempe and his colleagues have reported finding 20 galaxies with a redshift near 10 in the same data set, although this 20 did not include Illingworth's three. Windhorst and his colleagues posted their findings on arXiv.org in October2.
The various teams disagree over how exactly to define these distant galaxies, and what constitutes a definitive detection. Illingworth argues that Windhorst's standards were not stringent enough, and that some of the galaxies the other team detected were close to large, bright galaxies that could have contaminated the results. "That could have confused their software and caused them to get a lot of objects that just were not real high-redshift galaxies," he says.
Illingworth also notes that 20 galaxies of redshift 10 in such a small region of space indicates a higher rate of star formation than has been predicted for that time. "It doesn't accord with what we would expect theoretically or logically," he says.
Windhorst acknowledges that his group "may have overshot", but adds that Illingworth's group was "overly conservative". Even so, Windhorst noted that two of the galaxies detected by Illingworth's team did not meet his team's criteria as high-redshift, and the third was not detected after the data were processed. "Being conservative is good, but I think they haven't reduced the data as good as they could have," Windhorst says.
Let there be light
But Illingworth's team "appears to have done a more careful job than Windhorst's", says astronomer Richard Ellis at the California Institute of Technology in Pasadena, who in 2007 reported candidate galaxies with redshifts between 8 and 10 using the Keck telescope in Hawaii. He added that Illingworth's team "goes to great lengths to justify their candidates", although he is cautious because the camera detects high-redshift objects only in one filter, and because many such claims, including his, have been revisited by other groups with mixed results.
"The history of claims for finding redshift-10 galaxies is a chequered one, but it's exciting," he says. "Ultimately, we will still have to verify these claims. It's going to be very hard, as it has turned out to be with [other] candidates."
The lack of many bright galaxies at redshift 10 offers clues to what kicked off the Universe's "reionization epoch" — a period between 500 million and 1 billion years after the Big Bang during which luminous objects such as galaxies and quasars ionized the intergalactic medium. The lack of bright galaxies at the start of this timespan suggests that they did not initiate the reionization process, Windhorst says.
"There are still a lot of questions to address," says Illingworth. "This is very tantalizing, but we need to understand the properties of those galaxies. That's where the real scientific interest is."
References
1. Bouwens, R. J. et al. http://arxiv.org/abs/0912.4263 (2009).
2. Yan, H. et al. http://arxiv.org/abs/0910.0077 (2009).
[naturenews]
Published online 24 December 2009 | Nature | doi:10.1038/news.2009.1164
News
Why it's hot in the city
Heat wave in Baltimore made worse by hot air from Washington DC.
Katharine Sanderson
{{Hot air blowing in from neighbouring metropolises may make some cities hotter during heat waves.}
Punchstock}
While most of Europe and much of North America are currently in the middle of a cold snap, researchers trying to understand a heatwave that hit the northeastern United States in 2007 have found that Baltimore's sweltering temperatures were exacerbated by the presence of its neighbours, Washington DC and Columbia.
Meteorologist Da-Lin Zhang at the University of Maryland in College Park and his colleagues used a three-dimensional meteorological model to investigate how weather and temperature change over time across the Baltimore and Washington DC region. Baltimore sits about 100 kilometres northeast of Washington, with Columbia about halfway between them.
Zhang wanted to look at the urban heat-island effect, a well-known phenomenon where built-up areas become much hotter than surrounding rural areas in warm weather. His models included data showing what the land in this large area was used for. The roughness of the surface — whether it is covered by trees or water or buildings — affects the weather at the surface and he was able to put detail down to 500 metres into the model.
Then, using data for 7–10 July 2007, when the area was hit by a heatwave, Zhang ran the models to simulate the weather at that time.
This heatwave was "horribly hot, dangerously hot," according to Russell Dickerson, an atmospheric chemist and a co-author of the paper, which is published in Geophysical Research Letters1.
Stagnant heat
The models confirmed that it had been hotter in Baltimore than in Washington — Baltimore reached 37.5 °C while Washington basked in a relatively balmy 36.5 °C — and that the air quality over Baltimore was also much worse, with ozone levels of 125 parts per billion (ppb) compared with 85 ppb over Washington. The US Environmental Protection Agency recommended maximum for ozone at ground level is 75 ppb. The amounts of small particulate pollutants over Baltimore were also higher than over Washington.
"The heat-island effect was worse in Baltimore than in Washington DC," says Dickerson, and this can't be explained simply by the physics of the buildings and road surfaces in Baltimore, he adds. The effect has to be a consequence of the weather dynamics in the area.
The prevailing winds over the region in July 2007 were southwesterlies. There was also an easterly breeze coming off Chesapeake Bay to the east of Baltimore. The model showed that the hot air from the two heat islands of Washington and Columbia was moved up to Baltimore by the prevailing wind, where it stagnated because of the incoming bay breeze, making temperatures soar and pollution stay put over the city, which was also subject to its own heat-island effect.
When Zhang and his team ran a model in which Washington was bulldozed and replaced by trees, things got cooler in Baltimore. The heat-island effect there was reduced by 25%, and the city was cooler by 1.25 °C.
"The urban heat island is a well-known phenomenon, but was thought to be quite local," says Gabriele Curci, who studies air quality and pollution transport at the University of L'Aquila in Italy. He suggests that this work will help to decide where best to place air-quality monitoring balloons.
"It's good to know that [the urban heat island] is not only a local effect," says Susanne Grossman-Clarke at the Global Institute of Sustainability, Arizona State University in Tempe. "Urban planners only think about the local aspect of the heat island," she adds. "The city is in the context of other cities."
Dickerson agrees that in the light of this work, planners should pay more attention to outside influences on urban heat islands. And they might — the research was supported in part by Maryland's Department of the Environment to determine how planting trees might help to improve air quality, Dickerson says. Zhang is currently working in China to advise on that country's heat-island problems.
"A little state like Maryland can't do much to help global climate change, but there are things you can do to mitigate the adverse impacts of climate locally," says Dickerson.
References
1. Zhang, D.-L. et al. Geophys. Res. Lett. 36, L24401 (2009).
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