All you want to know about M82

Introduction

M82 is probably the second most studied galaxy, only the Milky Way being studied in more detail. It is home to a variety of interesting phenomena, but the one reason why it attracts so much attention is because it is the nearest galaxy hosting a starburst nucleus. On the one hand, M82 is used as a template to understand the starburst occuring in more distant galaxies, while on the other hand, it is the favorite first light target for many science instruments. In fact, M82 is the brightest galaxy in the sky in the K-band. The avalanche of information makes it difficult to search for the required information on this galaxy. With this in mind, we have prepared this page, wherein the potential researcher can learn everything that is known about M82 without having to search amongst more than 1000 research papers, spread over half a decade. We hope that the page will be equally useful to a researcher who wants to contribute something new to M82, as well as all those who want to use M82 results in their area of research. A subject index, citing notable work on M82 is listed at the end, along with key references. There exist already excellent pages dedicated to some aspect of M82. A link to these pages is also given at the very end of this document.

Morphological description

M82 is the prototype of the Irr II class of galaxies. Galaxies in this class are characterized by an amorphous distribution of light. The optical view of this nearly edge-on galaxy is dominated by a network of dust filaments. However, in the near infrared, especially in the K-band, the intensity distribution is smooth and reveals a bar of 1 arcmin (1 kpc) length, running roughly along the major axis of the galaxy. The following table summarizes the observed and derived properties of the galaxy. For a complete table click NED

Morphological type Irr II/Amorphous Sandage & Brucato (1979)
mB(mag) 9.30 NED
mK(mag) 4.67 NED
fFIR (W/m2) 5.84E-11 NED
Diameter (Holmberg) 13.4'x8.5' Appleton et al. (1981)
Velocity 175 km/s (CO)
183 km/s (HI)		 Young & Scoville (1984)
Appleton et al. (1981)
Distance 3.63 Mpc Freedman et al. (1994)
Rotation curve Keplerian Sofue (1998)
Mass 6x109 Sofue (1998)
LFIR 3x1010 IRAS
SFR 10 Mo/yr
Inclination angle 77o Mayya (2005)
Position angle 62o Mayya (2005)
Disk scalelength 825 pc (K-band) Mayya (2005)
Bar length 1 kpc Telesco et al. (1991)
Spiral pitch angle 14o Mayya (2005)
HI mass 2.9x109 Crutcher et al. (1978)
Molecular gas mass 2.9x108 Young & Scoville (1984)
Tidal Tails - HI/CO Yun, Ho, & Lo

The following set of images summarizes most of the observed morphological characteristics.

Multi-band images of M82 (North is up and East to the left in all images)

KHJ (OAGH) - The disk and bar
KHJ (disk subtracted)- Spiral Arms
KVB - The dust filaments

HaRB (Subaru) - superwind cone
Disk, Spiral and superwind cone
UV (Galex) - superwind cone

Comparison of M82 images in different bands

Multi-band images of M82
M82 Look-alikes

The HST view of the Starburst nucleus


Composite color image of IVB HST images.
Wide-field view of M81 and M82

FUV/NUV - Galex | Optical - KPNO | Palomar Sky Survey1
Simulation of the interaction, where M82 is represented in yellow
Velocity cube

Identification of prominent regions in M82 (O'Connell & Mangano (1978).

Schematic view of the superwind cone (Ohyama et al. 2002)

  1. The Structural properties

    2. The disk

    The intensity distribution of the disk obeys an exponential profile. The K-band scalelength is 47 arcsec (or 825 pc).

    The newly discovered spiral arms

    The spiral arms are seen only when the exponential disk is subtracted. The resulting arms have a maximum contrast of 1.6 in the K-band and are bluer relative to the disk at the same radius. The arms are found to emerge from the tips of the bar, with a pitch angle of 14o.

    The bar

    The bar has a length of 1 arcmin (1 kpc), and is oriented almost along the major axis of the galaxy. The intensity along the bar is almost constant, whereas parpendicular to it, it falls exponentially.

    The Nucleus

    The nucleus is extremely bright in the K-band, and is barely seen in the optical because of high visual extinction. The high flux is due to the on-going starburst activity in the central 15 arcsec radius. The properties of the starburst are described in a later section.

    The nuclear ring/hotspots

    Midway through the nucleus and the end of the bar, there are a couple of knots in the near infrared (NIR) band images. These knots would have resembled hotspots/circum-nuclear rings, if the galaxy was seen at a lesser inclination angle. High visual extinction does not allow a clear view of this region in the optical bands.

    The Halo

    M82 images clearly illustrate considerable structure at all wavelengths along the minor axis. These structures could be due to the presence of a thick disk, or could be due to the emission inside the superwind cone, or may be simply disk light scatterred by the dust particles in the halo.

    Simulated galactic sub-components

    Exponential disk
    Spiral arm
    The bar
    The ring/hostspot

    Model: Face-on view
    Model: Inclined
    Inclined and Noisy
    Observed K-band
    Matching to the observed K-band image

    Disk subtracted (Observed K image)
    Disk subtracted (Noise-free Simulated)
    Major and minor axis intensity cuts

    Under construction here onwards

  2. The interstellar Medium

  3. As a prototype Starburst

  4. As a member of the M81 Group

  5. New morphological classification

  6. Subject Index

References

Cottrell, G. A. 1978, \mnras, 184, 259
de Vaucouleurs, G. 1959, Classification and Morphology of External Galaxies, Handbuch der Physik, 53, 275 Second reference catalogue of bright galaxies, 1959, Austin: University of Texas Press.
Elmegreen, B. G. \& Elmegreen, D. M. 1984, \apjs, 54, 127
Freedman, W. L., Hughes, S. M., Madore, B. F., Mould, J. R. et al. 1994, \apj, 427, 628
Freeman, K. C. 1970, \apj, 160, 811
Gottesman, S. T., \& Weliachew, L. 1977, \apj, 211, 47
Greve, A., Wills, N., Neininger, N. \& Pedlar, A. 2002, A&A, 383, 56
Greeve, A. 2004, A&A, 416, 67
Holmberg, E. 1958, Lund Medd. Astron. Obs. Ser. II, 136, 1
Hunt, L. K., Mannucci, F., Testi, L., Migliorini, S., Stanga, R. M., et al. 1998, \aj, 115, 2594 %Baffa, C.; Lisi, F.; Vanzi, L.
Ichikawa, T., Yanagisawa, K., Itoh, N., Tarusawa, K., van Driel, W., \& Ueno, M. 1995, \aj, 109, 2038
Johnson, H. L. 1966, \apj, 143, 187
Kaaret, P., Prestwich, A. H., Zezas, A. Murray, S.S. et al., 2001, \mnras, 321, L29
Krienke, O. K., \& Hodge, P. W. 1974, \aj, 79, 1242
Kronberg, P. P., Biermann, P., \& Schwab, F. R. 1985, \apj, 291, 693
Lehnert, M, D., Heckman, T. M., \& Weaver, K. A. 1999, \apj, 523, 575
Marcum, P. M., O'Connell, R. W., Fanelli, M. N., Cornett, R. H., Waller, W. H. et al. 2001, \apjs, 132, 129
Mayya, Y.D., Carrasco, L., \& Luna, A. 2005, ApJL submitted
O'Connell, R. W., Gallagher, J. S., Hunter, D. A. \& Colley, W. N. 1995, \apjl, 446, L1
O'Connell, R. W., \& Mangano, J. J. 1978, \apj, 221, 62
Ohyama, Y. et al. 2002, PASJ, 54, 891 ADS
Rieke, G. H., Lebofsky, M. J., Thompson, R. I., Low, F. J., \& Tokunaga, A. T. 1980, \apj, 238, 24
Sandage A. (1961) The Hubble atlas of galaxies (Washington: Carnegie Institution)
Sandage, A., \& Brucato, R. 1979, \aj, 84, 472
Shen, J., \& Lo, K. Y. 1995, \apjl, 445, L99
Sofue, Y. 1998, \pasj, 50, 227
Telesco, C. M., Joy, M., Dietz, K., Decher, R., \& Campins, H. 1991, \apj, 369, 135
Toomre, A. \& Toomre, J. 1972, \apj, 178, 623
Walter, F., Weiss, A., \& Scoville, N. 2002, \apjl, 580, L21
Yun, Min S., Ho, Paul T. P., \& Lo, K. Y. 1993, \apj, 411, 17
Yun, Min S., Ho, Paul T. P., \& Lo, K. Y. 1994, Nature, 372. 530

Internet Links

Cigar Galaxy
The M81 group
Multispectral Image Collection of M82
Galaxy Wars: M81 Versus M82
A Superwind from the Cigar Galaxy
M82 in Astronomy Picture of the Day
M82 - Exploding or Starburst Galaxy?
Information about this page:
Authors: Y. D. Mayya, L. Carrasco, A. Luna
The extensive literature survey that we have carried out before reporting the discovery of spiral arms in M82, is the motivation behind developing this page. If you find this page useful or if you have any suggestions, comments or complaints, please write to ydm @ inaoep.mx
Home Last updated June 13, 2005 (ydm @ inaoep.mx)