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Star formation not primarily quenched by black hole activity in nearby elliptical galaxies

Most galaxies are believed to contain supermassive black holes. Some of these galaxies also have large amounts of dust and gas, which can fall in to the central black hole ("accrete"). As the material falls in, it emits X-rays, so astronomers use X-rays to detect an accreting black hole. Often, a fraction of the accreting dust and gas is blown back out through the galaxy rather than accreting onto the black hole. However, the extra dust and gas in the galaxy that doesn't fall in toward the black hole generates new stars, so active galaxies usually have a lot of star formation as well. As the amount of dust and gas drops, both the star formation rate and the activity drop.

In the past, astronomers have noted that elliptical galaxies in clusters have a lower star formation rate than elliptical galaxies that aren't in clusters ("field" galaxies.) Two new papers indicate that this has more to do with the environment than any intrinsic differences in the galaxies.

Professor Elena Gallo, working with postdoctoral researcher Brendan Miller and former UM undergraduate student Michael Katolik, as well as collaborators at the University of California Santa Barbara, the Seoul National University in the Republic of Korea, and the Max Planck Institute for Astronomy in Heidelberg, Germany, used the Chandra X-ray Observatory to carry out a large systematic survey of nearby elliptical galaxies. The survey included complementary coverage from the Hubble and Spitzer Space Telescopes. This project aims to directly detect low-level activity from the supermassive black holes expected to reside at the centers of these galaxies.

The first part of the survey, led by Gallo, focused on the Virgo cluster, a large collection of gravitationally-bound galaxies. A central X-ray source was discovered in one-third of the targeted ellipticals, confirming the presence of a weakly-accreting supermassive black hole. Since there may be black holes that aren't accreting material and therefore can't be detected, this provides an observational lower limit to the fraction of ellipticals hosting supermassive black holes.

Now, in recent work led by Miller, the team has found that nearby field elliptical galaxies tend toward marginally greater central X-ray luminosities. This suggests that weakly accreting supermassive black holes in the field are slightly more active than those in clusters. While cluster galaxies lose gas as they move through the intra-cluster medium, field galaxies retain a relatively greater amount of cold gas, some of which could plausibly be available for modestly enhanced black hole accretion. These results also indicate that the particularly efficient extinguishing of star formation generally seen within cluster ellipticals (excepting the largest central galaxy) is more closely linked to direct environmental effects, such as gas stripping, rather than to any destructive influence from radiation or outflows driven by the supermassive black hole.

The team will next investigate off-center X-ray sources discovered within many of the Virgo and field galaxies, most of which are likely binary systems characterized by a normal star transferring material to a compact stellar remnant, and assess if the frequency with which such sources are found is likewise dependent upon large-scale environment.

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An Unusual Planetary Disk

V1052 Cen is a young star in Centaurus, about 700 light years away from us. It has a planet forming disk around it, with a very unusual feature.

An international team of Astronomers led Professor Emeritus Charles Cowley imaged the disk using the light from carbon monoxide. Usually, CO is spread throughout the plate-shaped planet-forming disk. However, around V1052 Cen the CO is restricted to a very narrow band, more like a rope than a plate.

"It's exciting because this is the most constrained ring we've ever seen, and it requires an explanation," Cowley said in a U-M News Service story.

This star also has a strong magnetic field, and that may influence the shape of the disk. Or, it may be an indication that planets have already formed, and are "shepherding" the disk particles, much like the shepherd moons of Saturn create the sharp bands in Saturn's rings.

It is an interesting system that raises as many questions as answers.

Read the full U-M News Service story at http://www.ns.umich.edu/new/releases/20169-gaseous-ring-around-young-star-raises-questions

The paper by C. R. Cowley, S. Hubrig, F. Castelli, B. Wolff will be published in Astronomy and Astrophysics Letters under the title "The narrow, inner CO ring around the magnetic Herbig Ae star, HD 101412" and is available at http://arxiv.org/abs/1112.6181

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MOJAVE Recognized by NRAO Program

The National Radio Astronomy Observatory (NRAO) recently designated MOJAVE as one of their prestigious Key Science Projects. NRAO key science projects are intended to recognize projects that "are timely, fundamental, and will have a significant science impact on the wider astronomy and astrophysics communities."

The U-M Radio Astronomy Observatory is a member of the MOJAVE project, which stands for Monitoring Of Jets in Active galactic nuclei with VLBA Experiments. The project is designed to make long term observations in radio frequencies of the high energy jets from active galactic nuclei. These jets are believed to be powered by supermassive black holes at the center of the galaxies. Understanding the evolution of the jets will help astronomers understand the evolution of the galaxies.

You can read more about the Key Science Projects at https://science.nrao.edu/science/key-science-projects

The MOJAVE project description is at http://www.physics.purdue.edu/astro/MOJAVE/project.html

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Most Massive Black Holes Discovered So Far

At the center of every big galaxy is a supermassive black hole. Some astronomers believe you actually need a supermassive black hole to be the seed, around which a galaxy can form, which would make supermassive black holes as common in the universe as galaxies. Our own Milky Way galaxy hosts a black hole more than 2 million times more massive than our Sun at its center. However, astronomers believe it takes a black hole with a mass of 10 billion times our Sun to account for some of the brightest quasars in the early universe. Even after the quasars fade, the supermassive black holes that powered them should remain, and we should be able to find them.

A team of astronomers led by University of California, Berkeley professor Chung-Pei Ma and Nicholas J. McConnell, a graduate student working with Ma published a letter published in the 8 December 2011 issue of Nature, announcing the discovery of two 10-billion-solar-mass black holes. The team included Michigan Astronomy professor Douglas Richstone.

"These two new supermassive black holes are similar in mass to young quasars and may be the missing link between quasars and the supermassive black holes we see today," said Ma.

NGC 3842 is about 320 million light years away in the direction of the constellation Leo. NGC 4889 is about 340 million light years away in the direction of Coma Berenices. Both are giant elliptical galaxies residing in or very near the center of a cluster of galaxies.

Illustration of the stars around a 10-billion-solar-mass black hole300 million light years might sound like a long way off, but for galaxies, that's practically in our backyard. This enabled the team of astronomers to observe the central cores of these galaxies. Using those images, they were able to measure the speed and direction that stars near to core are moving. Then they can determine how much mass is needed to make the stars move that fast. (Illustration at right by Lynette Cook for Gemini Observatory/AURA illustration)

The supermassive black hole at the center of NGC 3842 is around 9.7 billion solar masses. This makes it big enough to be a possible candidate for a former quasar, and would have made it the biggest black hole on record if it weren't for the other galaxy in this paper. That other galaxy, NGC 4889 has a central supermassive black hole of around 20 billion solar masses!

Nicholas J. McConnell, a graduate student working with Ma at UC Berkeley, was lead author on the paper. "These black holes may shed light on how black holes and their surrounding galaxies have nurtured each other since the early universe" he added.

What may be more interesting to astronomers is that both of these black holes are bigger than would be estimated based on the brightness of the galaxy. Most galaxies are much too far away to image their central regions, so in most cases, we can't directly measure the mass of the central black hole. Instead, astronomers trust that there is a relationship between how bright a galaxy appears and how big its central black hole is. They make measurements of nearby galaxies and assume that all galaxies follow the same relationship. These results indicate that giant elliptical galaxies may not follow the same relationship as other galaxies.

The paper "Two ten-billion-solar-mass black holes at the centres of giant elliptical galaxies" by Nicholas J. McConnell, Chung-Pei Ma, Karl Gebhardt, Shelley A. Wright, Jeremy D. Murphy, Tod R. Lauer, James R. Graham & Douglas O. Richstone appears in the 8 Dec. 2011 issue of Nature, http://www.nature.com/nature/journal/v480/n7376/pdf/nature10636.pdf.

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0% Unemployment for Astronomy and Astrophysics Majors

Students have one more reason to major in Astronomy and Astrophysics: a recent survey indicates that the jobless rate for people who majored in astronomy and astrophysics is 0%.

You can read the story "The 10 college majors with the lowest unemployment rates" on yahoo news.

New galaxies Discovered

Multiple models of galaxy formation with dark matter predict very different numbers of dwarf galaxies and at different locations and with different properties within the local group of galaxies. Unfortunately, as their name implies, dwarf galaxies are small and dim, making them hard to detect, and hard to test the predictions of the models. This makes dwarf galaxies a good target for deep sky surveys such as the Sloan Digital Sky survey (SDSS). Using SDSS data, graduate student Colin Slater and Professor Eric Bell found two new dwarf galaxies.

Dwarf galaxies are difficult to detect directly, or tell apart from star clusters within our own galaxy, so astronomers need other techniques. The brightest stars in any galaxy are the giants. While galaxies with a lot of star formation are dominated by blue giants, not all galaxies have a lot of star formation. All galaxies have dying stars however, so astronomers can look for objects with a light signature that indicates an excess of red giant stars.

And XXIXBell and Slater found one such object in the constellation Pegasus. To confirm that it really is a dwarf elliptical galaxy, Bell also imaged it with the Gemini North telescope. The image from Gemini shows this galaxy along with a few foreground stars.

Using the SDSS data, Bell determined that this galaxy is about 2.4 million light years away from us, which puts it at around 675 thousand light years from M31, the Andromeda Galaxy, and makes it a satellite of M31. Because it is a satellite of M31, it is designated Andromeda XXIX (And XXIX). It is oblong in appearance and the light is very red, meaning there is very little star formation, making it a dwarf spheroidal galaxy.

AndXXVIIISlater also found an object in the SDSS data, in the nearby constellation of Pegasus, shown at the right. Again, although it is in the constellation Pegasus, its distance and properties indicate that it is a satellite of M31, so Slater et. al. have identified it, at least for now, as Andromeda XXVIII. It is roughly 2.1 million light years away from us, and 1.2 million light years from M31. If further studies confirm that it is a satellite of M31, this distance would make it one of the most distant satellites of that galaxy. This large distance means it may not have been affected by M31 yet. Dwarf spheroidal galaxies should form from dwarf irregulars when the dwarf irregular interacts with another galaxy, so at this distance, And XXVIII should still be a dwarf irregular and not a dwarf spheroidal galaxy. Unfortunately, the SDSS data is not sufficient to say for certain if this galaxy has much star formation, so Slater can't determine yet which type of dwarf galaxy it is.

The next step for Slater then is to get a more detailed image. Whichever type of galaxy And XXVIII turns out to be, the results will be interesting!

The paper "ANDROMEDA XXIX: A NEW DWARF SPHEROIDAL GALAXY 200 KPC FROM ANDROMEDA" by Bell, Slater and Martin and the paper "ANDROMEDA XXVIII: A DWARF GALAXY MORE THAN 350 KPC FROM ANDROMEDA" by Slate, Bell and Martin appeared in the Astrophysical Journal letters in October 2011. Both are available online, linked from their titles.

Images for this story were provided by Bell. The Gemini image is also available at http://www.gemini.edu/node/11686

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Oceans of Water in a Planet Forming Disk

Several observations indicate that there is water vapor present in planet-forming disks around other stars in the area where terrestrial planets form. However, it is too hot in those areas for the water to condense onto the planets. In order for a planet to have an ocean, the water must come in from farther out, probably carried in on comets. Astronomers can only detect water when it is in vapor form, so it is difficult to detect water in the colder regions of the disk, where comets form.

In the cooler regions of the disk, the water should be in the form of ice frozen onto dust grains. UV light from the young star may liberate a water molecule from the dust for a short time, creating a thin haze of cold water vapor just above (or below) the disk. Since the cool water vapor in Earth's atmosphere would completely block the faint signal from another star system, astronomers must use a space telescope to search for water vapor near planet forming disks. The cool temperatures also mean using an infra-red telescope.

Recently, an international team that includes graduate student Ilsedore Cleeves, Prof. Ted Bergin, and recent graduate Jeffrey Fogel used an instrument on the Herschel Space Telescope to search for water in the planet forming disk around TW Hydrae.

TW Hydrae is a young star, about two-thirds the size of the Sun, and only about 175 light years away. It is one of the closest planet forming disks to us, so it makes a great subject for study. It also has strong emission lines, which are what astronomers use to distinguish light coming from different atoms and molecules.

What they saw was a significant amount of water vapor above the disk. Based on the amount of water vapor they observed, they estimate at least 9x1027 g of water ice in the disk, several thousand times more water than all or Earth's oceans. These results indicate that planets with water may be very common in the galaxy.

Atist's conception of the disk around TW Hydrae and the water spectrum

The paper "Detection of the Water Reservoir in a Forming Planetary System" by Hogerheijde, Bergin, Brinch, Cleeves, Fogel, Blake, Dominik, Lis, Melnick, Neufeld, Panic, Pearson, Kristensen, Yilidz, and van Dishoeck appeared in the October 21 issue of Science and is available online at http://www.sciencemag.org.proxy.lib.umich.edu/content/334/6054/338.full (access required)

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Massive Stars May Have Cleared the Cosmic Fog

The very early universe was filled with a hot, dense, and opaque gas, a kind of cosmic fog. Then something ionized the gas, allowing light to flow freely though the universe, so we can see the light from far distant galaxies, and even the light from that cosmic background.

But what ionized the gas?

Graduate student Jordan Zastrow and Professor Sally Oey might have the answer. They are part of a small team that studied NGC 5253, a nearby, dwarf, starburst galaxy. Starburst galaxies are galaxies undergoing a big bust of star formation, normally concentrated in the center of the galaxy.

UV light coming from young, massive stars ionizes the gas around it. The ionized gas then emits light at very specific wavelengths, rather like an exact shade of a specific color. Astronomers can detect the ionizing UV radiation (which normally can't make it through our atmosphere) by looking for these specific wavelengths instead.

"We are not directly seeing the ultraviolet light. We are seeing its signature in the gas around the galaxy," explained Zastrow

Using a special filter on the Baade telescope at Las Campanas in Chile, the team looked at specific wavelengths of light coming from NGC 5253. What they found is a feature called an ionization cone, a long narrow region where the gas is highly ionized. The image below is a composite of two of the specific wavelengths and a visible light image. The composite highlights the ionized gas, which in this image appears bright red. The ionization cone is visible in this image as the red feature that starts near the center white blob and extends to the lower left, and past the edge of the galaxy.

NGC5253 composit image

"This feature is relatively narrow. The opening that is letting the UV light out is small, which makes this light challenging to detect. We can think of it as a lighthouse. If the lamp is pointed toward you, you can see the light. If it's pointed away from you, you can't see it," Zastrow said. "We believe the orientation of the galaxy is important as to whether we can detect escaping UV radiation."

Although the team could not rule out the possibility that the ionizing radiation could be coming from an active galactic nucleus (AGN), the observations are much more consistent with UV light from young stars. If this is supported by more observations, it shows that young stars can put a huge amount of ionizing radiation out into the universe, well beyond the edge of their galaxies. It also solves one problem astronomers have had with detecting this ionizing radiation. The cone is so small that we have to be nearly perfectly aligned with the galaxy to detect it. Since galaxies are randomly oriented, we can't detect escaping UV radiation from most galaxies.

The paper "An ionization cone in the dwarf starburst galaxy NGC 5253." by Zastrow, Oey, Veilleux, MacDonald, and Martin appeared in the Astrophysical Journal Letters on Oct. 12, 2011 and is available online at http://arxiv.org/abs/1109.6360

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Discovering the origins of Earth's water

During its formation, Earth was a big ball of molten rock, much too hot for any water to exist. Today however, 2/3 of Earth's surface is covered with water. The origin of that water has been a major question for planetary scientists.

"Life could not exist on Earth without liquid water, and so the questions of how and when the oceans got here is a fundamental one," said Prof. Ted Bergin, who is using the Hershel space telescope to study this question. He is coauthor on a study published this week in Nature, which opens new possibilities for the origins of Earth's water.

"It's a big puzzle, and these new findings are an important piece." he said in Agence France Presse news story.

Water is composed of one oxygen atom and two hydrogen atoms. Hydrogen usually just has one proton in the nucleus, but another form of hydrogen, deuterium, also contains a neutron. Deuterium is destroyed at high temperatures, the farther out in the solar nebula the water molecule formed, the more deuterium it contains. Planetary scientists can use the ratio of deuterium to hydrogen, D/H, to determine where Earth's water originated.

When looking for sources of water, Comets seemed good because they contain a lot of water. Most comets in the modern solar system come from a very distant region called the Oort cloud (see image, below). Observations of 6 Oort cloud comets, including such famous members as Halley and Hale-Bop, contained too much deuterium. Less than 10% of Earth's water can come from these Oort cloud comets.

Diagrams showing the orbits of the planets, Kuiper belt, Sedna, and Oort cloud$

The D/H ratio in water from asteroids is a much better match to Earth's water. However, asteroids contain very little water, so it is hard to account for the amount of water on Earth. Still, the asteroid origin hypothesis has been the favored one for several year.

A recent observation using the Hershel Infra-red space telescope may change all that.

Amateur astronomers may remember comet 103P/Hartley 2 as a rather nice comet that passed near Earth in fall 2010. For several weeks, it was a very good target for backyard telescopes, especially with its unusually green color as it passed near several star clusters and red emission nebulae in the northern sky (image by Jaime Fernandez - click for original.)

Hartley2 by Jaime

It also presented a prime opportunity for Hershel to get an up close look at a different type of comet. Hartley 2 appears to come from the Kuiper belt, a region just beyond Neptune, and much closer than the Oort cloud. Astronomers turned Hershel's infrared spectrographs to the comet, to analyze the light actually coming it and measure the D/H ratio. Their observations show Hartley's D/H ratio is nearly identical to the D/H ratio in Earth's oceans. This significantly widens the region in the early solar system where Earth's water could have come from. Objects from both the astroid belt and Kuiper belt are reasonable sources.

The chart below shows the D/H ratio of several solar system objects. The green square represents the carbonaceous asteroids, which is the group whose D/H ratio closely matches Earth's water.

Chart of D/H ratios in the solar system

This work also has implications for our understanding of the formation of the solar system.

Oort cloud comets are believed to have formed near Jupiter and been pushed out of the solar system. Asteroids and Kuiper belt objects are believed to have formed roughly where they are now. However, the similarity of D/H ratio in the Kuiper belt and difference in the Oort cloud comets implies that, rather than remaining relatively constant, there was a great deal of mixing in the early solar system. This model is also supported by recent observations of other solar systems, including observations of very young systems.

Since this is only one data point, the results are still considered preliminary. Observations of other Kuiper belt comets are important to confirming these results.

This work "Ocean-like water in the Jupiter-family comet 103P/Hartley 2" by Paul Hartogh, Dariusz C. Lis, Dominique Bockelée-Morvan, Miguel de Val-Borro, Nicolas Biver, Michael Küppers, Martin Emprechtinger, Edwin A. Bergin, Jacques Crovisier, Miriam Rengel, Raphael Moreno, Slawomira Szutowicz & Geoffrey A. Blake appears as a Letter in the Journal Nature published 05 October 2011. It is available online at http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10519.html

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Black Holes in Distant Dwarf galaxies

In the nearby universe, large galaxies have supermassive black holes in their cores, but dwarf galaxies don't appear to have them.

This may not always have been the case.

Using the Hubble Space Telescope and the Chandra x-ray observatory, a group of astronomers led by Jonathan Trump of UC Santa Cruz and including Prof. Eric Bell looked at distant dwarf galaxies. Their observations indicate that early in the universe, at least some dwarf galaxies did contain massive black holes.

These results raise some interesting questions about these dwarf galaxies. Do the local galaxies actually contain black holes, but not enough gas to make their detection possible? Did the dwarf galaxies with black holes merge to form massive galaxies, leaving only dwarf galaxies without black holes to make it to the modern universe?

With only 28 galaxies in this initial study, these questions will have to wait to be answered.

The paper "A CANDELS WFC3 Grism Study of Emission-Line Galaxies at z~2: A Mix of Nuclear Activity and Low-Metallicity Star Formation" will appear in the ApJ and is available online at http://arxiv.org/abs/1108.6075

Read the press release from UC Santa Cruz at http://news.ucsc.edu/2011/09/black-holes.html

Hubble Space Telescope press release: http://hubblesite.org/newscenter/archive/releases/2011/27/

Dean B. McLaughlin Fellowship Announced

The Department of Astronomy at the University of Michigan is pleased to announce the Dean B. McLaughlin Fellowship, a two-year Prize Fellowship in Astronomy and Astrophysics. This fellowship offers Ph.D. recipients the opportunity to pursue independent lines of research, with access to a wide range of University of Michigan facilities, including the 6.5m Magellan telescopes, the MDM Observatory, and our computer resources. The annual salary is $55,000, with an additional research fund of $6,000 per year, along with an extensive benefits package.

Applicants should send their resume, publication list, and a plan for work to be undertaken at the University of Michigan. The applicant should arrange for three letters of reference to be sent to apply.astro@umich.edu . Applications are due by December 1, 2011, with announcements expected by early January 2012. The University of Michigan is an Affirmative Action/Equal Opportunity Employer. Women and members of minority groups are encouraged to apply.

View the AAS posting at http://jobregister.aas.org/node/40304

Revealing the History of Pandora's Cluster

An international team of astronomers including UM researcher Renato Dupke used several telescopes to capture the collision of 4 galaxy clusters.

Abell 2477 in visible and IR lightThe cluster, officially named Abell 2744, is in the southern hemisphere constellation Sculptor. Astronomers imaged it with several telescopes, including the Hubble Space Telescope (HST), Chandra X-ray observatory, the European Space Agency's Very Large Telescope in Cerro Paranal, Chile (VLT), which can take images in both visible and infra-red light, and Subaru telescope in Hawaii.

The individual galaxies are visible in the visible and infra-red images, like the one to the right. This image is a composite of images from HST and VLT. The galaxies make up less than 5% of the total mass of the cluster, so these images aren't enough.

Abell 2744 with x-ray image overlayBetween the galaxies is a very thin, very hot gas. While the gas is extremely thin, the space between the galaxies is very large, so the total amount of gas is also very large. In fact, it makes up about 20% of the mass of the cluster. This gas glows in x-rays, so it shows up in the images from the Chandra x-ray observatory. The x-rays are shown in pink in this image of the central region, to the left.

Abell 2744 with dark matter map overlayAll together, using IR, visible, and x-ray images, only 25% of the matter in the galaxy cluster can be imaged. The rest of the matter is what astronomers call "dark matter." We can detect it because it has gravity and pulls on the visible matter, but we can't image it directly. Instead, astronomers study the light from more distant galaxies behind the cluster. As the light passes through the cluster, it is bent. How much the light bends and what direction tells astronomers where gravity is strongest, and they use that to make a map of where the dark matter is (shown in the image to the right in blue.)

The team put all this different information together to figure out what happened with this cluster. What they found was an unprecedented collision between a large cluster and three smaller clusters.

Abell 2744, Pandora's cluster, in visible, IR, X-ray and dark matter

"We nicknamed it Pandora's Cluster because so many different and strange phenomena were unleashed by the collision," study author Renato Dupke of the University of Michigan said in a statement. "Some of these phenomena had never been seen before."

Near the core of the cluster is a dense shock wave similar to another cluster called the bullet cluster. However, it looks as if the dark matter passed through this area unaffected.

Stranger still, off to the side is a dense region of dark matter, with almost no gas. It looks as though on of the small clusters passed through the bigger one, had all the gas and galaxies stripped away, but the dark matter continued on unperturbed. In another direction is a cluster of gas and galaxies with almost no dark matter.

Further analysis of these features may tell astronomers more about how dark matter behaves, and that will tell them more about what it could, or could not, be.

A video and explanation of the collision is in Hubblecast 47: Pandora's Cluster, a NASA/ESA podcast, available at http://www.spacetelescope.org/videos/heic1111a/

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Supermassive Black Holes Common in the Early Universe

At the center of every galaxy in the modern universe there lurks a supermassive black hole (SMBH). It is widely believed that the properties of the galaxy depends heavily on the black hole. Professor Marta Volonteri thinks the black hole and galaxy form at the same time from the same cloud of gas, and grow up together. According to her model, super-massive black holes should be common, and should be associated with galaxies very early in the history of the universe.

Illustration of a baby black holeMaking the observations to test this model is very tricky though.

Gas falling into a black hole emits x-rays as it falls in. The first problem faced by observers is that x-rays cannot make it through the earth's atmosphere, so the observations can only be made using a satellite. Additionally, the sources are billions of light years away, so they are extremely faint. It takes very long exposures or stacks of many many images to even detect if there could be an x-ray source. Finally, the light coming from the gas falling into the SMBH tends to be in the lower energy x-ray band astronomers call "soft" x-rays. Soft x-rays are absorbed by the gas the galaxy is made of, so very little of the light can even escape from the young galaxy.

With all these constraints, astronomers have been confined to using very bright objects to study the early universe. Quasars are the brightest objects in the entire universe, and can be hundreds of times brighter than their host galaxies. They are fueled by enormous amounts of gas in a young galaxy falling into a SMBH, so they provide some clues about the relationship between the SMBH and its host galaxy in the early universe. However, they are so huge that they are a very special case, and they don't put very many constraints of smaller galaxies and their SMBHs.

A team lead by Ezequiel Treister of Hawaii decided to try a new technique to learn about normal young galaxies.

The team first used images from the Hubble Space telescope to determine the location of the most distant galaxies known, from when the universe was around 700 million to 950 million years old. Then they stacked together images from the Chandra x-ray observatory of the same locations. By stacking many images together, they were able to detect the faint x-ray sources.

The hubble image and two of the Chandra images showing an x-ray source corresponding to a galaxy

Their results show that between 30% and 100% of young galaxies contain a growing supermassive black hole, supporting the hypothesis that the galaxies and SMBHs form together.

"We had reason to expect that black holes existed in many of the very first galaxies, but they had evaded our searches until now. When I compared Chandra's data to my theoretical models I was stunned by their agreement. It's the dream of any theoretician," said Professor Volonteri.

Professor Volonteri worked with Priya Natarajan of Yale to create models of black hole growth. "Most astronomers think in the present-day universe, black holes and galaxies are somehow symbiotic in how they grow," said Priya Natarajan. "We have shown that this codependent relationship has existed from very early times."

The paper "Black hole growth in the early Universe is self-regulated and largely hidden from view" by # Ezequiel Treister, Kevin Schawinski, Marta Volonteri, Priyamvada Natarajan, & Eric Gawiser appeared in the 16 June 2011 edition of Nature, and is available at http://www.nature.com/nature/journal/v474/n7351/full/nature10103.html

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New Life For Elliptical Galaxies

Regular galaxies come in two major types, ellipticals and spirals. Spiral galaxies are generally bluish, with big clumps of gas and dust and young stars in their spiral arms. Elliptical galaxies are reddish in color and have very little gas. The reddish color comes from a large population of smaller, long-lived stars. Astronomers generally believed this meant that ellipticals couldn't form new stars. However, images taken by Professor Joel Bregman and research scientist Alyson Ford indicate that's not really the case.

Bregman and Ford used the Wide Field Planetary Camera 3 (WFPC3) on the Hubble Space Telescope to image M105, an elliptical galaxy in Leo. The WFPC3 has an exceptionally good resolution, especially at ultra-violet wavelengths where young starts put out most of their light. This special capability allowed Bregman and Ford to resolve small star clusters and even individual massive stars millions of light years away.

"Astronomers previously studied star formation by looking at all of the light from an elliptical galaxy at once, because we usually can't see individual stars," Ford said. "Our trick is to make sensitive ultraviolet images with the Hubble Space Telescope, which allows us to see individual stars."

M105 in Leo, with inset showing several blue starsThey were able to identify several blue stars in M105, as well as several star clusters.

In spirals like the Milky Way, the gas and dust tend to gather together in a disk, and most new stars form there, in clusters. Since elliptical galaxies don't have any structure like a disk, astronomers weren't sure how stars would form. This study seems to indicate that the stars still form in clusters.

"We were confused by some of the colors of objects in our images until we realized that they must be star clusters, so most of the star formation happens in associations," Ford said.

Some of the stars they observed have a mass between 10 and 20 times the Sun's mass. These stars only live for a few tens of millions of years, so they must be relatively young compared to the age of their galaxy. The star formation rate must be fairly low, about one Sun every 10,000 years. In the Milky Way, the rate is a few stars every year.

"This is not just a burst of star formation but a continuous process," said Ford.

They still aren't sure exactly how the process occurs, or where the material to form the new stars in coming from.

"We're at the beginning of a new line of research, which is very exciting, but at times confusing," Bregman said. "We hope to follow up this discovery with new observations that will really give us insight into the process of star formation in these 'dead' galaxies."

Information, quotes and images for this story came from:
"'Dead' galaxies aren't so dead after all, U-M researchers find" UM News Service
"Old galaxies still making new stars" Hindustan Times
 
 
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http://www.universetoday.com/86095/dead-galaxy-dont-think-so/
http://www.astronomy.com/~/link.aspx?_id=1e25ca77-831e-4245-bf5c-3e574e168c01
 
 
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Nathalie Degenaar Joins the Michigan Astronomy Department

Nathalie Degenaar of the University of Amsterdam has been awarded a Hubble Postdoctoral Fellowship. She will join the Department of Astronomy in the Fall of 2011 to continue her work on faint X-ray transients and ultra-compact binary stellar systems.

 

Einstein Fellow Rubens Reis Joins Michigan Astronomy Department

Rubens Reis of Cambridge University has been awarded the Einstein Fellowship and named to the Michigan Society of Fellows. He will be joining the Department of Astronomy in the Fall of 2011 to expand his work on black holes and accretion physics.

For more on the Einstein Fellowship Program, please visit http://cxc.harvard.edu/fellows/.

Lee Hartmann named AAAS Fellow

The National Association for the Advancement of Science elected Michigan Astronomy professor Lee Hartmann as a Fellow.

According to the AAAS website, "AAAS Fellows are elected annually by the AAAS Council for meritorious efforts to advance science or its applications. Fellows have made significant contributions in areas such as research, teaching, technology, services to professional societies, and the communication of science to the public."

Eight other University of Michigan professors were also elected fellows. Read more about them, and the AAAS Fellows at http://ns.umich.edu/htdocs/releases/story.php?id=8192.