M82A Study of the galaxies starburst nature

and composition

Credit: NASA, ESA and the Hubble Heritage Team STScI/AURA). Acknowledgment: J. Gallagher (University of Wisconsin), M. Mountain (STScI) and P. Puxley (NSF).

Basic Information

M82, located in Ursa Major, was first discovered by Johann Elert Bode in 1774.

Its classified as a prototype Starburst Galaxy of the second type, famous for its heavy star formation due to its close encounter with its neighbouring galaxy M81.

M82 is five times as bright as the entire milky way galaxy, and 100 times as bright as the Mily Way’s center, although only about a quarter of its size.

Basic Information

Distance to Object: 11.5 +- 0.8 Mly Size :

› 10.47’ x 4.365’ (Angular Size) › (Physical Size)

Apparent Magnitude : 9.3 Position:

› (J200) RA: 09h 55m 52.2s D: +69° 40′ 47″

How to locate M82 First locate the big dipper. The next step is to draw an

imaginary line from gamma Ursae Majoris to alpha Ursae Majoris, then double its length in the same direction.

Doing this alone, you will most probably locate M81 as a very faint patch of light. M82 is located close by and is generally harder to locate as it has a low magnitude. This method may be summarized by the following diagram.

Backyard Astro. 2009. Deepsky Top-100 (10): M 81 & M82. http://www.backyard-astro.com/deepsky/top100/10.html

Observing the Galaxy at different wavelengths

In X-ray Chandra Telescope. Credit 

NASA/SAO/G.Fabbiano et al. Scale  Image is 5 arcmin

across. Release Date  June 05, 2001 Red = low energy, green

intermediate, and blue high-energy X-rays. White and yellow sources emit both low- and high-energy X-rays

Observation Time  13 hours Observation Dates 

September 20, 1999

The bright spots in the center are Supernova remnants or X-ray binaries. Observing M82 in the Infrared spectrum, it is the brightest galaxy in the sky.

Frommert H, Kronberg C. 1998. The Messier Catalogue. http://seds.lpl.arizona.edu/Messier/more/m082_cxo.html

Spitzer Telescope Image (Infrared)

Scale: 7.9 arcmins ac ross

Telescope : Spitzer Telescope

Image Credit: NASA/JPL-Caltech/C. Engelbracht (University of Arizona)

Instrument: IRAC

Wavelength: Infrared: Red

Exposure Date: May 6, May 8, and May 9 2005

Exposure Time: 4 minutes per point, 1 hour for full image

Field of View: 12.6 x 12.6 arcminutes

Orientation: North is 57.7 deg counter clockwise from up

Release Date: 16 March 2006

Chandrea X-ray Observatory. 2008. http://chandra.harvard.edu/photo/2006/m82/more.html

ASTRO-1 UIT – UV spectrum

This picture was taken with a combination of telescopes: the VLA in New Mexico, and the MERLIN in the UK

The reason behind the three distinct maxima is most widely described by the presence of UV-absorbing dust covering its nucleus.

Frommert H, Kronberg C. 1998. The Messier Catalogue. http://www.seds.org/messier/more/m082_uit.html

Astro-1 UIT - Visible The image is

in false colour The dust

covering the galaxies core is still visible, however, not as prominent as with the UV image taken with the same telescope Frommert H, Kronberg C. 1998. The Messier

Catalogue. http://www.seds.org/messier/more/m082_uit.html

Multi-Wavelength Distribution

Credit:   X-ray: NASA/CXC/JHU/D.Strickland; Optical: NASA/ESA/STScI/AURA/The Hubble Heritage Team; IR: NASA/JPL-Caltech/Univ. of AZ/C. Engelbracht

Scale: Image is 7.9 arcmin across

Observation Dates:  June 18, 2002

Observation Time:   5 hours Color Code  Energy : (X-

ray: Blue; Optical: Green & Orange; Infrared: Red)

Instrument : ACIS Release Date:  April 24,

2006

Chandrea X-ray Observatory. 2008. http://chandra.harvard.edu/photo/2006/m82/more.html

Research Topic : Starburst Regions

A starburst galaxy is a galaxy in which there is an abnormal amount of star creation.

Two main types of Starburst Galaxies:› Blue Compact Galaxies

Contain low amounts of mass, metallicity, and dust, and contain a large amount of hot young stars.

Radiate in the UV spectrum› Ultra-luminous Infrared Galaxies

Generally extremely dusty. Seen in the infrared. The UV light emitted from the hot

young stars is absorbed and reemitted as infrared by the dust flooding the galaxy.

The center of a ULIRG can be seen in the X-ray spectrum.

Starburst Galaxies

In order to create a Starburst Galaxy, there must be present a large supply of gas to form large amounts of new stars. This large amount of gas must undergo compression through tidal forces triggered by a close encounter or collision with another nearby galaxy

M82’s high level of star formation is due to a close encounter with its neighbouring galaxy M81. The interaction is evident through discovery of large streams of neutral hydrogen connecting the two galaxies seen in the radio spectrum.

“What can be understood upon observing M82’s UV radiation?”

Far-UV imaging of the starburst galaxy M82 One of the maxima is interpreted to be a reflection

nebula, and the other two due to massive stars in gas and dust poor locations in the outer disk.

They used two telescopes, › SCAP with a diameter of 13 cm› FOCA with a diameter of 40 cm.

M82 was observed using FOCA, which was mounted to a balloon that rose to 40 km altitude and is sensitive to wavelengths between 195 nm and 210 nm. They took 8 exposures of 150s each covering a field of view of 2.3 degrees, centered on 9h 58m 57.0 s, +69 degrees 01’ 41”.

“What can be understood upon observing M82’s UV radiation?”

The central region was found to have a minimum connecting the two maxima (in the form of a saddle point in the 2D image).

The central region is therefore not a maximum of UV emission, as expected

They conclude that the regions of high UV emission have an absence of IR, and therefore gas and dust poor.

One possible explanation for the UV emission is the presence of very hot burning stars in dust and gas poor regions .

The presence of two distinct regions may either mean that there exists two distinct emission regions or that absorbing matter is located infront of the plane in the central regions

Taking the images and Processing our Data

The telescope used to take our images was the 40 cm Evan’s reflecting telescope at the Glenlea Observatory in Winnipeg Manitoba.

An apogee AP-47 CCD camera was used for capturing the images.

We used ImageJ for processing our images and developing a final processed image of the galaxy M82

Master Bias Convert the images to 32 bit. Measure the mean value of the over scan region for

each Bias Frame image used via analyze>Set Measurements>”check mean grey values”, then Analyze>Measure.

This is a region of size 6 x 512 pixels along the left hand side of each image.

Remember to open each group of images as a Stack and to use to ROI Manager to manage each image in the stack.

Subtract this mean pixel value from each of the bias frames, then crop each image to 520 x 512.

The Master Bias frame is the average of 10 bias frames, and can be created with the use of the ROI manager and Z project

Master Bias Raw Data:

› Date: Feb. 08, 2007› Time: 7:16 – 7:18

PM› Temperature: -29 °C› CloudCover: Clear› Moon: Wanning

Gibbous› Visibility: 22.7 km › Equipment: The 40

cm Evans' reflecting telescope

› Size : 520 x 512

Master Dark To Create a Master Dark, subtract the

over scan region and crop as done with the Master Bias region. Further, subtract the Master Bias frame from each Dark Frame via Process>Math>Subtract. (Remember everything must be in 32 bit format)

Z stack the Dark frames to create the final Master Dark frame.

Master Dark Raw Data

› Date: Feb. 08, 2007› Time: 7:25 – 7:51 PM› Temperature: -29 °C› CloudCover: Clear› Moon: Waning Gibbous› Visibility: 22.7 km › Equipment: The 40 cm

Evans' reflecting telescope

› Size : 520 x 512› Exposure time: 300s

Dark Sky Flats To create the Master Flat frame (in our case

Dark Sky Flats), first convert the images to 32 bit format, subtract the over scan region, crop to 520 x 512 pixel size, and subtract both the Master bias frame and Master Dark frame from each image.

Because the stars appear in different locations from image to image, we may make use of the plug-in called “Background Extractor” which will normalize the sky frames and create the final Master Flat image. ( Normalize each image by Mean, and Combine stack by Median)

Dark sky flats Raw Data:

› Date: Feb. 08-09, 2007› Time: 11:39 – 12:03 PM› Temperature: -29 °C› CloudCover: Clear› Moon: Wanning Gibbous› Visibility: 22.7 km › Equipment: The 40 cm

Evans' reflecting telescope

› Size : 520 x 512› Exposure time: 300 s › Comments; The dust

halos are quite evident.

The final dark-subtracted, flat-fielded and co-added but otherwise unmanipulated image. We must first convert the images to 32-bit

format, subtract the overscan region from each image, crop each image to 520 x 512 pixel size, subtract the master bias frame from each image, subtract the master dark frame from each image, and finally divide each image by the master flat.

Select the usable frames, and register and combine them via the set of plug ins “TurboReg” and “StackReg” to register and aligned the frames,

We now have the final image of our Galaxy!

Our image of M82 Raw data

› Date: Feb. 08 2007› Time: 10:58 – 11:31 PM› Temperature: -29 °C› CloudCover: Clear› Moon: Wanning Gibbous› Visibility: 22.7 km › Equipment: The 40 cm

Evans' reflecting telescope

› Size : 520 x 512› Exposure time: 300s

each

Finding the field of view of our images

To find the field of view for our images, we may use an image of the “double double” star Eplison Lyrae.

Plotting a Profile across both stars will lead us to a separation in pixels between the two stars, and knowing the true distance between them can allow us to develop a scale by which we may calculate the angular field of view for our images.

Field of View

We find:

Pixel Counts of certain regions of our image:

Background Sky: › Three value average:› 1856.26, 1982.14, 1914.34› Average : 1917.58

Pixel Counts of certain regions of our image:

Faintest observable region of the object› Outer extension of

M82 to the left:› 2467.82,

2334.34, 2300.34› Average:

2367.5 +- 80.0› Outer

extension of M82 to the right:

› 2309.34, 2359.56, 2488.45

› Average: 2385.79 +- 90.00

Pixel Counts of certain regions of our image:

Brightest region of the object: the galaxies core› Plotting the

pixel profile of a 10 pixel radius around the core, we find that its peak pixel value is : 14479.12

Stellar Magnitudes For Stellar bodies, I

used the circle tool to analyze our image. The circle has a radius of 8 pixels (the size of the largest star).

Peak pixel value of faintest stellar object› The peak value for

the faintest star : 2222.737

Peak pixel value of the brightest unsaturated stellar object

Peak pixel value of the brightest unsaturated stellar object: 64203.707 (note : this is now closely approaching the saturation limit)

Stellar Magnitudes The stellar body is actually a cluster of millions of stars

associated with M82. I used the circle tool to determine the flux through a circle of 8 pixel radius for each stellar body.

For the brightest stellar region, › IntDen : 5710094.058

For the faintest stellar region,› IntDen: 403256.245

The ratio of these values is :› 14.160

To estimate the magnitude of the faint star, we can use the following equation:

Where m is the magnitude of the faint star.

The faint star therefore can be estimated to have a magnitude of m = 12.88.

Best Image for observing faint objects

Best image using linear scaling to easily observe faint regions of image.

This image was inverted via image>look up tables>Invert LUT

The image’s brightness and contrast was also altered

The surrounding dim stars may be more easily seen this way.

Best Image for observing faint objects

Using :› Image>look up

tables>royal› Image>look up

tables >invert LUT The following

image can be determined.

In this image, the brightest parts of the core of the galaxy may be seen in more detail.

Another method by which the bright regions of M82 can seen:

Using:› Image>look up

tables>phase In this image, the

regions closely surrounding the nuclear regions are detailed. One can clearly see the edges of this region. This image is of false colour.

A logarithmically scaled image:

Changing the transfer function to a logarithmic one will reduce saturation as well as increase the detail of the brighter regions of our galaxy.

The image was obtained by Process>Math>Log in ImageJ

Contour Mapping A Contour

mapping of the image will show associations between different regions.

These are the pixel values by which the boundaries may be calibrated.

We used the following settings:

The associated Contour Map of M82

I set the outer green boundary to a pixel value, 2300 , within error of the values found earlier for the outer edge of the visible galaxy.

Orange : the boundary in which the bright white region which makes up the body of the galaxy

Red: the apparent multi-core nature of the galaxy in the visible spectrum

Blue: the brightest of these ‘cores’ (the true nucleus).

Plotting Pixel Profile across certain regions of our image

Dimmest Stellar Body has a typical Gaussian shaped distribution curve

Across Galaxy From this plot, the large

amount of enveloping dust and gas around M82’s core is most evident. It may be associated with the large dips in the luminosity distribution.

This profile plot cannot be associated with a Gaussian curve.

Due to perhaps the large amount of dust covering its center, a large dip in the profile may be seen.

Some other M82 profile plots

Examining the apparently multi-cored nature at M82’s center

Examining the bridge between the apparent core and the associated bright region to the left of the nucleus, one can more clearly see the distinction between the two peak brightness values, and perhaps the presence of dust and gas covering one single bright region.

Then it was scaled to ten times larger. Also, it was : image>Look up Tables>Phase. Finnaly it was sharpened.

Estimating the Angular size of our Galaxy

We may use our calculated field of view and the boundary defined through our contour mapping to determine the angular size of our galaxy. Measured across and length wise:› Its length is: 19.1 +- 0.1 cm› Its width is: 5.5 +- 0.1 cm

The width of the whole image is: 23.4 +- 0.2 cm (error double because measured by moving ruler once)› The estimated angular length is : (19.1 +- 0.1 cm / 23.4 +- 0.2

cm) x = (5.66 +- 0.30 arcmins)› The estimated angular width is : (5.4 +- 0.1 cm / 23.4 +- 0.2 cm)

x = (1.60 +- 030 arcmins) The expected angular size: 10.47’ x 4.365’ Deviation due to the definition of our galaxies outer

boundary.

Image used for this determination

Estimating Physical Size Estimating our Physical size, we know:

› (Distance to object) x tan (angular size) = (physical size of object)

Length : (11.5 +- 0.8 Mly) x tan ((5.66 +- 0.30) / (60) deg) = 18933.93 +- 2000.00 ly

Width: ((11.5 +- 0.8 Mly) x tan ((1.60 +- 0.30) / (60) deg)) = 5352.34 +- 1000.00 ly› As expected, these values are mathematically

inconsistent with the known values of : Actual size: (Physical Size)

This again has to do with the boundaries by which the size of the galaxy is defined.

Images from SLOAN digital sky survey

The spectral classification of each image is described by the following chart:

Top Left : UTop Right: GMiddle : R

Bottom Left: IBottom Right: Z

SLOAN images

As expected, the dust and gas covering the center of the Galaxy grows less visible as the wavelength of light used to observe M82 increases.

Because the dust and gas absorbs the UV radiation emitted by the hot young stars from the Starburst regions of the galaxy, the dust is more visible upon viewing of the galaxy at smaller wavelengths (closer associated with the UV spectrum ) . Remember that the dust is represented by an absence of emission in the UV spectrum. (dark clouds)

Conclusion: The galaxy I researched was M82, a prototype Starburst

Galaxy famous for heavy star formation due to its close encounter with M81.

Through the use of several image processing techniques including general image reduction with the use of the› Master Bias,› Master Dark,› Master Flat

And the use of several more advanced processing techniques including › using look up tables>(invert LUT, royal, phase)› logarithmic image scaling› image sharpening› manipulation of the brightness and contrast,

Through these methods we could more easily analyze our image.

Conclusion

We found that in correlation to past research in the UV emission spectrum, the dust was more visible (an absence of emission) as dark clouds surrounding the center of the galaxy. Wilson and Petipas were able to determine that the double peaked nature could also be due to the result of two individually separated clumps of molecular gas collecting on a inner Lindblad resonance (ILR) and not an edge on molecular torus.

We determined a physical and angular size of our galaxy, however our results were not consistent with the expected ones

References

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Backyard Astro. 2009. Deepsky Top-100 (10): M 81 & M82. http://www.backyard-astro.com/deepsky/top100/10.html

Cotton WD, Condon JJ, Arbizzani E. 1999. Arcsecond positions of UGC galaxies. Astrophys J 125:409

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Frommert H, Kronberg C. 1998. The Messier Catalogue. http://www.seds.org/messier/more/m082_uit.html

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