These images are available under the terms of the Creative Commons Deed (version 2.0), unless it is noted otherwise. What this means is spelled out here. Basically it prevents unauthorized use of these images in commercial works. What the public has paid for once, it'd shouldn't have to pay for again. Of course, getting authorization to use these images commercially is a simple as just asking.
Non-commercial use of the images requires no prior authorization - so enjoy! If you're using these images on a web page or in a powerpoint/keynote/impress/KPresenter presentation, I'd certainly appreciate it if you'd attribute images to Dave Strickland (http://proteus.pha.jhu.edu/~dks).
To view or save any of these images at full resolution right click on the image.
Messier 82 (M82) is the archetype of starburst galaxy, and of a galaxy with a starburst-driven superwind. The image of the left presents a false-color view of M82 is the optical waveband (a composite of HST ACS broad-band imaging and ground-based narrowband imaging), in which the stellar disk of the roughly-edge on galaxy appears blue and green and H-alpha and [N II] line emission from warm ionized gas (T~1e4 K), a tracer of the superwind, appears in red. The image on the righ hand side is the same field of view, but now viewed in X-ray emission as observed with the Chandra X-ray Observatory. The stellar disk of the galaxy is now invisible, and a mixture of diffuse X-ray and point-like X-ray emission from accreting binary star systems (most probably high mass binaries with neutron star or black holes as the accretor) is visible. Soft thermal X-ray emission (T~4e6 K, photon energies E=0.3 to1.1 keV), shown in red, emrges perpendicular to the disk of the galaxy and has a similar morphology to the optical H-alpha emission. Note the fainter extended X-ray and H-alpha emission outside the main, bright, region of X-ray and H-alpha emission.
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| M82 (starburst) | NGC 1482 (starburst) | NGC 253 (starburst w/LLAGN) | NGC 3628 (starburst) | NGC 3079 (starburst w/LLAGN) |
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| NGC 4945 (Sy 2 w/starburst) | NGC 4631 (starburst) | NGC 6503 (normal) | NGC 891 (normal) | NGC 4244 (normal) |
All images show a region 20 x 20 kpc in projected size, centered on the
dynamical center of each galaxy.
The intensity scale is square-root in all images and in all bands...
...but the absolute intensities differ from image to image.
Blue is diffuse soft (0.3-2.0 keV energy band)
X-ray emission from the Chandra observations. This has been rather heavily
smoothed, so much of the genuine smaller scale structure in the X-ray data
is not visible in these images.
Green is optical R-band, i.e. emission from stars,
primarily old stars.
Red is continuum subtracted H-alpha, or
H-alpha+[N II] emission, i.e. emission from warm ionized gas with T~10^4 K.
Within the disk of these galaxies you're seeing HII regions,
but the extra-planar H-alpha in the starbursts is warm
ionized gas being dragged out of these
galaxies by the superwind at velocities between 200 and 1000 km/s, depending
which superwind we're interested in.
Note:We did not detect any
extra-planar (|z|> 2kpc) soft X-ray emitting gas
around either NGC 6503 and NGC 4244 (normal, not starburst, galaxies). There
is only weak extra-planar diffuse X-ray emission detected above the nuclear
regions of NGC 4945. The X-ray emission apparent in the top left and bottom
right of the NGC 4945 image, and that outside the optical disk in the image
of NGC 6503, is at the noise level of the X-ray data (we believe it is noise).
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| M82 (starburst) | NGC 1482 (starburst) | NGC 253 (starburst w/LLAGN) | NGC 3628 (starburst) | NGC 3079 (starburst w/LLAGN) |
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| NGC 4945 (Sy 2 w/starburst) | NGC 4631 (starburst) | NGC 6503 (normal) | NGC 891 (normal) | NGC 4244 (normal) |
All images show a region 5 x 5 kpc in projected size, centered on the
dynamical center of each galaxy.
The intensity scale is square-root in all images and in all bands...
...but the absolute intensities differ from image to image.
Blue is diffuse soft (0.3-2.0 keV energy band)
X-ray emission from the Chandra observations. Again, the
X-ray emission has been heavily
smoothed (thoughh not as heavily as in the 20x20 kpc images),
so much of the genuine smaller scale structure in the X-ray data
is not visible in these images.
Green is optical R-band, i.e. emission from stars,
primarily old stars.
Red is continuum subtracted H-alpha, or
H-alpha+[N II] emission, i.e. emission from warm ionized gas with T~10^4 K.
As described above, within the disk of these galaxies you're seeing
HII regions in H-alpha emission, but in
the H-alpha nuclear outflow cones (where present,
e.g. NGC 253, NGC 3079, NGC 4945, probably NGC 3628,
and the larger and more amorphous examples
of M82 and NGC 1482) the H-alpha is warm
ionized gas being dragged out of these
galaxies by the superwind at velocities between 200 and 1000 km/s.
This is coming primarily from the walls of the outflow cavity.
Note: The is only a very weak statistical detection of diffuse
X-ray emission from the disk of NGC 4244, which may due to
the expected population of unresolved X-ray binaries. There is genuine
diffuse X-ray emission in the disk of NGC 6503, although this rendition
of the data is pretty crummy and shows a lot of the noise as well.
Representative color image of the X-ray emission from the central 5 x 5 kpc of M82, from our ACIS-S observation. Soft X-ray emission in the 0.3-1.6 keV energy band is shown in red, 1.6-2.8 keV energy band emission in green and harder 2.8-8.0 keV energy band emission in blue. The soft thermal X-ray emission from the superwind (or more technically, from some form of interaction between the wind and the ambient ISM of M82) is clearly visible in red and green (and combinations thereof), showing thermal emission from gas at a temperature of approximately 5 million degrees K. Point-like X-ray sources (X-ray binaries) show up as white or bluish spots. Diffuse hard X-ray emission is visible in the very central starburst region as a faint blue glow. This is probably non-thermal emission from cosmic rays interaction with IR photons in the starburst, but some small fraction of it may be thermal emission from very hot (T > 30 million K) gas that ultimately drives the superwind. The image has been adaptively smoothed and is shown on a asinh intensity scale.
Soft X-ray emission (0.3-2.0 keV energy band) from our Chandra ACIS-S observation of NGC 3079 is shown in blue, overlaid on optical image of the galaxy (H-alpha emission in red, R-band in green). The X-ray image have been adaptively, but heavily, smoothed to show the 10-kpc scale spurs delineating the X-structure that probably marks the limb-brightened walls of the outflow. X-ray point sources have been left in this rather old image (the brighter compact blue circles). The scale of the region is approximately 25 by 20 kpc. The kpc-scale nuclear "superbubble" is barely visible.
Green: R-band; Red: Continuum-subtracted H-alpha emission.
Square-root intensity scale.
Image size: 1000x750 pixels, approximately 14x10 kpc.
A comparison between the gas density in two simulations of a superwind, 7.5 Myr after the start of the starburst event. The color scale represents the log particle number density, running from -3.5 (purple) to 1 (red). The vertical height of the image represents a distance of 11.7 kpc from the plane of the galaxy. The only substantive difference between the model parameters in the two simulations is the different distribution of the disk ISM. In the left hand image (model tbn_1 of Strickland & Stevens 2000) the disk has a large vertical scale height, which tends to confine the wind more initially, and leads to more entrainment of dense disk ISM into the wind, as compared to the model shown on the right (model mod_3).
Gas density in a higher resolution (cell size 7.3 pc) simulation of a superwind. Right click and "view image" to see the image at full resolution. Compared to the images on the equivalent lower resolution model tbn_1 above there is a clear increase in spatial structure associated with entrained dense ambient gas (this is the material seen as warm ionized and warm neutral gas in superwinds). Theoretical models of winds must strive for high resolution in order to follow gas entrainment accurately.
The LMC superbubble DEM L50, taken from Strickland, Oey, Chu and Garcia-Segura (in preparation). Red is H-alpha emission (ionized gas at T = 10000 degrees K), green is optical R-band (starlight) and blue is X-ray emission from hot gas at T = 2 million degrees (observed with Chandra). The bubble is approximately 100 pc in diameter, and only a few million years old.