I started this photo 4 years ago, the winter here has very few nights with affordable seeing and is not always suitable for long focal. In any case, this year I was able to add the HA layer to my rendition of M51 galaxy, with a 5nm filter. That has significantly changed the color rendering of the whole previous version.
That's an impressive M51 with very pleasing colours indeed. The prominent HII regions really add to the view. Top image, and top effort - 4 years in the making!
Many people don't realise just what you go through to get your World class images Leo... but having endured significant imaging hardship for a number of years myself, transporting this setup back and forth on a regular basis (sometimes a few times a week) to my dark site, I know it takes some real tenacity and enthusiasm to keep it up (that pier column alone weighs 50kg btw )...at least I didn't have to contend with 1m of snow!. So... a big salute to your efforts!
This is a fine M51, the arms are particularly impressive showing some very fine details, 4 years well spent
The H-alpha channel adds a lot of interest and additional information to your already very impressive image.
The strong and symmetric two-armed spiral pattern of M51 is, in all likelihood, due to the effects of the encounter with the barred companion of Hubble type S0. The standard physical model of a spiral-shaped wave of increased density occurring in the disk of this galaxy accounts for the symmetric large-scale Two-armed spiral pattern of the prominent HII regions...... which are primarily on the inside of the two main luminous arms.
(in other words, the big HII regions occur where the interstellar gas in M51 is most compressed, and therefore it forms massive O and B stars)
However, the strong two-armed spiral symmetry of the overall pattern of HII regions is strongly disturbed near to the companion!
I am unable to say, from a cursory inspection, whether the gravity of the companion galaxy is pulling the HII regions out from their regular pattern, and/or whether the companion has enough mass to disrupt the underyling mass-dominant stellar population of the disk.
Hi Robert .. thanks for this fantastic explanation ...if you allowed me i add to my web page with credits.
All the best,
Leo
Thats fine with me. Just credit "Madbadgalaxyman, alias Robert Lang". In general, most people on the internet know me as madbadgalaxyman, though when I am away from my home near the centre of NGC 3115, some people call me Robert.
However, you might like to wait until my commentary on your image is completed, as I will be presenting (in this thread) another 5 or 10 images of M51 at various wavelengths, in order to understand the nature and extent of the asymmetry that is evident in the distribution of its HII regions.
Preview of my conclusions :
My tentative conclusion from available imaging of other components of this galaxy (e.g. FUV images showing the OB stars, and infrared imaging showing the warm dust) is that the section of the spiral arm near to the companion galaxyis peculiar, in terms of its unusually high amount of star formation and the unusual distribution of gas in this section of the arm. Also, the abrupt bending of the arm, apparent at some wavelengths, is unusual.
However, the percentage of asymmetry, measured as a fraction of the total integrated light of M51 and/or as a fraction of the total mass of M51, is probably small.
Cheers, Robert
Apart from the overall brilliance of your image, I think that it is the very high degree of prominence of the Ha channel in your presented image that makes your image unique and interesting.
Last edited by madbadgalaxyman; 11-04-2015 at 08:09 AM.
I will move further considerations of the spiral structure of M51 to the IIS Science forum, as I intend to present some ~15 images of this galaxy at many and various wavelengths.
)...at least I didn't have to contend with 1m of snow!. So... a big salute to your efforts! 
in terms of muscle ... but in terms of passion we are equal 
)
