* Astronomy

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RE: Messier 82

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NGC 3034 Cigar Galaxy, visible-light compared to infrared view

This movie compares a visible-light view of the "Cigar galaxy" to an infrared view from NASA's Spitzer Space Telescope of the same galaxy. The movie begins with the visible image of the galaxy looking cool as a cucumber, then fades into the infrared image, revealing a smokin' hot "cigar."
The visible-light picture of the Cigar galaxy, also called Messier 82, shows only a bar of light against a dark patch of space. Longer exposures of the galaxy (not pictured here) have revealed cone-shaped clouds of hot gas above and below the galaxy's plane. It took Spitzer's three sensitive instruments to show that the galaxy is also surrounded by a huge, hidden halo of smoky dust (red in infrared image).
The infrared image above was taken by Spitzer's infrared array camera. The dust particles (red) are being blown out into space by the galaxy's hot stars (blue).
Spitzer's infrared spectrograph told astronomers that the dust contains a carbon-containing compound, called polycyclic aromatic hydrocarbon. This smelly molecule can be found on Earth in tailpipes, barbecue pits and other places where combustion reactions have occurred.
Messier 82 is located about 12 million light-years away in the Ursa Major constellation. It is viewed from its side, or edge on, so it appears as a thin cigar-shaped bar. The galaxy is termed a starburst because its core is a fiery hotbed of stellar birth. A larger nearby galaxy, called Messier 81, is gravitationally interacting with Messier 82, prodding it into producing the new stars.
The infrared picture was taken as a part of the Spitzer Infrared Nearby Galaxy Survey. Blue indicates infrared light of 3.6 microns, green corresponds to 4.5 microns, and red to 5.8 and 8.0 microns. The contribution from starlight (measured at 3.6 microns) has been subtracted from the 5.8- and 8-micron images to enhance the visibility of the dust features.
The visible-light picture is from the National Optical Astronomy Observatory, Tucson, Ariz.

Credit: NASA/JPL-Caltech/R. Hurt (SSC)

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NGC 3034 Cigar Galaxy

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Title: A deep X-ray observation of M82 with XMM-Newton
Authors: Piero Ranalli, Andrea Comastri, Livia Origlia, Roberto Maiolino

We report on the analysis of a deep (100 ks) observation of the starburst galaxy M82 with the EPIC and RGS instruments on board the X-ray telescope XMM-Newton. The broad-band (0.5-10 keV) emission is due to at least three spectral components: i) continuum emission from point sources; ii) thermal plasma emission from hot gas; iii) charge exchange emission from neutral metals (Mg and Si). The plasma emission has a double-peaked differential emission measure, with the peaks at ~0.5 keV and ~7 keV. Spatially resolved spectroscopy has shown that the chemical absolute abundances are not uniformly distributed in the outflow, but are larger in the outskirts and smaller close to the galaxy centre. The abundance ratios also show spatial variations. The X-ray derived Oxygen abundance is lower than that measured in the atmospheres of red supergiant stars, leading to the hypothesis that a significant fraction of Oxygen ions have already cooled off and no longer emit at energies > ~0.5 keV.

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Title: New Results on the Ages of Star Clusters in Region B of M82
Authors: I. S. Konstantopoulos (1), N. Bastian (1), L. J. Smith (2,1), G. Trancho (3,4), M. S. Westmoquette (1), J. S. Gallagher III (5) ((1) University College London, (2) STScI and ESA, (3) Universidad de La Laguna, (4) Gemini Observatory, (5) University of Wisconsin-Madison)

The post-starburst region B in M82 and its massive star cluster component have been the focus of multiple studies, with reports that there is a large population of coeval clusters of age ~1 Gyr, which were created with a Gaussian initial mass distribution. This is in disagreement with other studies of young star clusters, which invariably find a featureless power-law mass distribution. Here, we present Gemini-North optical spectra of seven star clusters in M82-B and show that their ages are all between 10 and 300 Myr (a factor of 3-100 younger than previous photometric results) and that their extinctions range between near-zero and 4 mag (Av). Using new HST ACS-HRC U-band observations we age date an additional ~30 clusters whose ages/extinctions agree well with those determined from spectroscopy. Completeness tests show that the reported `turn-over' in the luminosity/mass distributions is most likely an artefact, due to the resolved nature of the clusters. We also show that the radial velocities of the clusters are inconsistent with them belonging to a bound region.

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Title: Spatially Resolved Spitzer-IRS Spectroscopy of the Central Region of M82
Authors: P. Beirão, B. R. Brandl, P. N. Appleton, B. Groves, L. Armus, N. M. Förster Schreiber, J. D. Smith, V. Charmandaris, J. R. Houck

We present high spatial resolution (~ 35 parsec) 5-38 um spectra of the central region of M82, taken with the Spitzer Infrared Spectrograph. From these spectra we determined the fluxes and equivalent widths of key diagnostic features, such as the [NeII]12.8um, [NeIII]15.5um, and H_2 S(1)17.03um lines, and the broad mid-IR polycyclic aromatic hydrocarbon (PAH) emission features in six representative regions and analysed the spatial distribution of these lines and their ratios across the central region. We find a good correlation of the dust extinction with the CO 1-0 emission. The PAH emission follows closely the ionisation structure along the galactic disk. The observed variations of the diagnostic PAH ratios across M82 can be explained by extinction effects, within systematic uncertainties. The 16-18um PAH complex is very prominent, and its equivalent width is enhanced outwards from the galactic plane. We interpret this as a consequence of the variation of the UV radiation field. The EWs of the 11.3um PAH feature and the H_2 S(1) line correlate closely, and we conclude that shocks in the outflow regions have no measurable influence on the H_2 emission. The [NeIII]/[NeII] ratio is on average low at ~0.18, and shows little variations across the plane, indicating that the dominant stellar population is evolved (5 - 6 Myr) and well distributed. There is a slight increase of the ratio with distance from the galactic plane of M82 which we attribute to a decrease in gas density. Our observations indicate that the star formation rate has decreased significantly in the last 5 Myr. The quantities of dust and molecular gas in the central area of the galaxy argue against starvation and for negative feedback processes, observable through the strong extra-planar outflows.

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The Spitzer, Hubble, and Chandra space observatories teamed up to create this multi-wavelength, false-coloured view of the M82 galaxy, 11.7 million light-years away in Ursa Major.

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X-ray data recorded by Chandra appears in blue; infrared light recorded by Spitzer appears in red; Hubble's observations of hydrogen emission appear in orange, and the bluest visible light appears in yellow-green.

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A new infrared image from the Spitzer Space Telescope shows the galaxy Messier 82, whose fiery stars appear to be blowing out giant billows of smoky dust.

Messier 82, or the "Cigar galaxy," was previously known to host a hotbed of young, massive stars. The new Spitzer image reveals, for the first time, the "smoke" surrounding those stellar fires.
The false-coloured view shows the irregular-shaped galaxy positioned on its side, as a diffuse bar of blue light. Fanning out from its top and bottom like the wings of a butterfly are huge red clouds of dust believed to contain a compound similar to car exhaust.
The smelly material, called polycyclic aromatic hydrocarbon, can be found on Earth in exhausts, barbecues and other places where combustion reactions have occurred. In galaxies, the stuff is created by stars, whose winds and radiation blow the material out into space.

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Position (2000): RA: 09h55m52.2s Dec: +69d40m47s
The infrared image was taken by Spitzer's infrared array camera. The dust particles (red) are being blown out into space by the galaxy's hot stars (blue).
Credit: NASA/JPL-Caltech

These hazy clouds are some of the biggest ever seen around a galaxy. They stretch out 20,000 light-years away from the galactic plane in both directions, far beyond where stars are found.
Previous observations of Messier 82 had revealed two cone-shaped clouds of very hot gas projecting outward below and above the centre of galaxy. Spitzer's sensitive infrared vision allowed astronomers to see the galaxy's dust.
Messier 82 is located about 11.7 million light-years away in the Ursa Major constellation. It is undergoing a renaissance of star birth in its middle age, with the most intense bursts of star formation taking place at its core. The galaxy's interaction with its neighbour, a larger galaxy called Messier 81, is the cause.

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Scientists using the Rossi X-ray Timing Explorer have found a star orbiting a medium-sized black hole - a theorised "in-between" category of black hole that has eluded confirmation for more than a decade.

With the discovery of the star and its orbital period, scientists are now one step away from measuring the mass of such a black hole, a step that would help verify its existence. The star's period and location already fit into the main theory of how these black holes could form.
A team led by Prof. Philip Kaaret of the University of Iowa, Iowa City, announced these results today in Science Express. The results will also appear in the January 27, 2006, issue of Science.

"We caught this otherwise ordinary star in a unique stage in its evolution, toward the end of its life when it has bloated into a red giant phase. As a result, gas from the star is spilling into the black hole, causing the whole region to light up. This is a well-studied region of the sky, and we spotted the star with a little luck and a lot of perseverance" - Prof. Philip Kaaret

A black hole is an object so dense and with a gravitational force so intense that nothing, even light, can escape its pull once within its boundary. A black hole region becomes visible when matter falls toward it and heats to high temperatures. This light is emitted before the matter crosses the border, called the event horizon.

Our galaxy is filled with millions of stellar-mass black holes, each with the mass of a few suns. These form from the collapse of very massive stars. Most galaxies possess at their core a supermassive black hole, containing the mass of millions to billions of suns confined to a region no larger than our solar system. Scientists do not know how these form, but it likely entails the collapse of enormous quantities of primordial gas.

"In the past decade, several satellites have found evidence of a new class of black holes, which could be between 100 and 10,000 solar masses. There has been debate about the masses and how these black holes would form. Rossi has provided major new insight" - Dr. Jean Swank, Rossi Explorer project scientist at the Goddard Space Flight Centre.

These suspected mid-mass black holes are called ultra-luminous X-ray objects because they are bright sources of X-rays. In fact, most of these black hole mass estimates have been based solely on a calculation of how strong a gravitational pull is needed to produce light of a given intensity.
Kaaret's group at the University of Iowa, which includes Prof. Cornelia Lang and Melanie Simet, an undergraduate, made a measurement that can be used in the equation to directly calculate mass. Using straightforward Newtonian physics, scientists can calculate an object's mass once they know an orbital period and velocity of smaller objects rotating around it.

"We found a rise and fall in X-ray light every 62 days, likely caused by the orbit of the companion star around the black hole. The velocity will be hard to determine, however, because the star is located in such a dust-obscured area. This makes it hard for optical and infrared telescopes to observe the star and make velocity calculations. Yet for now, knowing just the orbital period is very revealing" - Melanie Simet

The suspected mid-mass black hole, known as M82 X-1, is a well-studied ultra-luminous X-ray object in a nearby star cluster containing about a million stars packed into a region only about 100 light years across. A leading theory proposes that a multitude of star collisions over a short period in a crowded region will create a short-lived gigantic star that collapses into a 1,000-solar-mass black hole.
The cluster near M82 X-1 has a high-enough density to form such a black hole. No normal companion could provide enough fuel to make M82 X-1 shine so brightly. But the 62-day orbital period implies that the companion must have a very low density. This fits the scenario of a bloated super-giant star losing mass at a rate high enough to fuel M82 X-1.

"With this discovery of the orbital period, we now have a consistent picture of the whole evolution of a mid-mass black hole binary. It was formed in a 'super' star cluster; the black hole then captured a companion star; the companion star evolved to the giant stage; and we now see it as an extremely luminous X-ray source because the companion star has expanded and is feeding the black hole" - Prof. Philip Kaaret

Position(2000): RA 09 : 55.8 Dec +69 : 41
The type Ir-II galaxy, M82 (NGC 3034), also known as the Cigar Galaxy (top), shows the results of extreme rates of star birth and death. Supernovae, the death explosions of massive stars, contribute to a violent wind of material expelled from M82's central regions. The burst of star formation was likely triggered a mere 100 million years ago in the latest of a series of bouts with neighbouring large galaxy M81 (at bottom).
The striking irregular and spiral galaxy pair are located only about 10 million light-years away in the northern constellation Ursa Major.

-- Edited by Blobrana at 17:55, 2006-01-11