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PixInsight => Gallery => Topic started by: jeffweiss9 on 2013 March 05 17:35:18

Title: M81 + IFN
Post by: jeffweiss9 on 2013 March 05 17:35:18
Here's a recent 6.3hr LRGB of M81 that managed to pull out some of the IFN.
It could use more data and Ha but helpful processing comments greatly appreciated:


Title: Re: M81 + IFN
Post by: Lex on 2013 March 06 09:55:26
Hi Jeff,

Really nice image, you managed to reveil nice flux! Also nice details are visible  8)
The only "negative" point is, IMHO the levels of blue/green are not anymore in the natural scale?
Is there narrowband data processed within?


and congrats on the lovely detailed pic!
Title: Re: M81 + IFN
Post by: jeffweiss9 on 2013 March 06 19:38:35
Hi, Lex-
   Thanks very much for your comments.
   Yes, the blue color (I think more cyan as SCNR should have removed the green) is a mystery to me but all of my galaxies now show the same color using the PI ColorCalibration process for galaxies. I've grown to like it as different but it definitely is out of the range of what probably most people consider 'natural color'.  I do note, however, that if you go to the PI home page,


you will see that all of the galaxies posted there from CAHA (m51,m74,ngc7331,m81/82) processed by our PTeam leaders, and many other galaxies posted there have the very same cyan cast to them. So I've attributed this to the PI galaxy color calibration method up to now.
   The only other causes that I can think of in my processing are either the particular set of LRGB Astrondon Series I Gen2 filters that I use or perhaps the fact that I get most or all of my saturation increase in my PI processing (all target types) from lowering the Saturation setting in the LRGBCombination tool from the default 0.5.  I've found that getting most of the color saturation from LRGBCombination gives me very colorful stars that I strive very much to obtain in my images (being very keen on getting a lot of color in my images).  I should probably do some reprocessing testing without method to confirm it  is the cause of the cyan color of all my galaxies but that is my current assumption. 
   Further thoughts on the matter would be appreciated, but as I said, I have grown to like this PI-galaxy color, if can generalize to say that.
   Clear skies,
Title: Re: M81 + IFN
Post by: jeffweiss9 on 2013 March 21 21:37:14
I've added a bunch more data, including Ha, to turn this into a 12.7 hour HaLRGB. It still has the cyan colored of all my galaxies (discussed above), but that is still what I get with the ColorCalibration process and most galaxies.


Feedback definitely appreciated on this one.
Clear skies,
Title: Re: M81 + IFN
Post by: Geoff on 2013 March 21 23:19:39
Hi Jeff
Just wondering about the strange horizontal stripe- like feature at the top of the brown centre bit. Any idea about what causes these? I'm sure they are real features of the galaxy, but they do look a bit odd.
I wish I could get more of that blue colour in my pics.
Title: Re: M81 + IFN
Post by: jeffweiss9 on 2013 March 22 08:22:52
Hi, Geoff-
 That's a really interesting question. There are 3 or 4 of those linear dust bands that you wouldn't think could be generated by 'normal' density waves in spiral galaxies.  I could guess that maybe they are remnants of another galaxy swallowed by m81 long ago except that usually is seen as star streams, not dust bands, so that's almost certainly wrong.   Maybe some of the astronomer / imagers who might be reading this could answer.
 Anyway, here's a crop and reframe of the image that shows the galaxy in more detail (although loosing a bunch of faint fuzzies in the original):


Clear skies,
Title: Re: M81 + IFN
Post by: pfile on 2013 March 22 08:42:35
i read a PPT presentation about the IFN which implied (probably only because it's just the slides for a talk, not that the author didn't know) that those streaks are actually the IFN obscuring the galaxy. or perhaps they meant it was M82's own IFN, not sure. but they were discussing IFN in the vicinity of M82, so i suppose it would be 'ours'.
Title: Re: M81 + IFN
Post by: jeffweiss9 on 2013 March 22 16:37:04
Sounds plausible, Rob-
There's a lot of IFN in that region and, if between us and m81, its contrast may be specially enhanced against a background of the bright galaxy center (the brown bit).

(Still could use some suggestions on improving the image, if anyone has any.)
Title: Re: M81 + IFN
Post by: jeffweiss9 on 2013 March 24 09:44:07
Geoff, Rob, et al.-

It looks the identification of the 'many dust features overlapping the field of view of M81' is that they are likely part of Arp's Loop and caused by Milky Way galactic cirrus clouds (i.e., what Mandel called Integrated Flux Nebula or IFN).  That would make them a lot closer to us than to M81 but they do leave some doubt in the following excerpt:

"Our optical images revealed this peculiar ring has a filamentary structure characterized by many dust features overlapping the field of view of M81 (NGC3031). The ratios of far-infrared flux and the estimated dust-to-gas ratios indicate the infrared emission of Arp’s loop is dominated by cold dust that is most likely from Galactic cirrus that lies above the Milky Way.

Although our observations cannot exclude the presence of some material stripped from the disk of M81 (NGC3031) and/or M82 (NGC3034) that is chance located in our line of sight to and far behind this intruiging structure, our findings suggest that Arp's Loop is situated between the observer and M81 (NGC3031) and represents an optically (relatively) bright concentration of Milky Way galactic cirrus."

Full source at:


Here's another reference by one of the authors (Jay GaBany):

"Until very recently, galactic cirrus was also misidentified as evidence of galactic interaction between M 81 and M 82. Seen as dark vertical lines to the right of the M 81's central region, these curious linear features remained a mystery until they were recognized to be a portion of galactic cirrus back lit by the iconic northern galaxy. Recent research revealed they are part of Arps loop , a cirrus structure that appears next to M 81 but actually located close to the Milky Way and along our line of sight to the more distant galaxy by chance alignment. "

with full source at:


Clear skies,
Title: Re: M81 + IFN
Post by: pfile on 2013 May 02 11:25:26
thanks for digging that stuff out. i somehow missed your post until today. i'll read the links.