Ngc 2500

NGC 2500 is a nearby low surface brightness face on spiral galaxy in central Lynx. NED classifies it as SB(rs)d with HII emission. The NGC project says SAB. The bar is short but obvious. The arms are in disarray causing one source to call it a flocculent galaxy. I just see lots of star clouds that align in semi arm segments. Redshift puts it about 29 million light-years away while non redshift measurements say 33 million, a rather good agreement. Outside the star cloud region is a very faint haze of somewhat blue stars that extends further on the northwest side than the other sides. This gives the galaxy a rather lopsided appearance.

The galaxy was discovered by William Herschel on March 9, 1788. It made the second Herschel 400 list and thus was on my to-do list but at a low priority. Thus I got a few frames of dubious quality last November but was far from getting enough to finish the image. In April with it too far west to use my T-point map I decided to finish it. Since I couldn't work without guiding I had to use a guide star and none were convenient without moving it off center. That meant I couldn't use the older frames without severely cropping it. I ended up retaking it entirely rather than wait yet another year to finish it. Since there had been a request for an image of this galaxy rather than wait to process it with April images I put it back into November where I'm currently working and when the first (unused) frames were taken. A rare exception to my processing order.

Turns out the galaxy is quite isolated with no nearby companions or anything else so I could have cropped it without losing much but a few distant galaxies, quasars and a quasar candidate. But while the new data, being too far west for my best seeing, was still far better than the old data so the complete redo was worth it.

Using the non redshift value of 33 million light-years the galaxy is about 38,000 light-years in diameter. A only slightly smaller than average spiral. But this includes the very faint outlying regions. If limited to the bright portion then it is much smaller at 22,500 light-years. If the redshift distance is used it is slightly smaller yet. It's likely the stars of the galaxy don't suddenly end as the edges of my faint regions but continue on out just too faint for my exposure time so the full size of most all galaxies is likely larger than I can measure it.

NED indicated it had HII emissions and the RGB data showed blue blobs that were likely new blue stars and likely marked the H alpha regions. Just that these new massive stars being so bright they hid the pink of H alpha and beta. It doesn't take much of a cosmological redshift to move the H alpha out of my 6nm bandwidth. But this galaxy was still within my bandwidth. So, with a quarter moon in the sky I took 2 hours of H alpha data. Turned out it was quite weak but a few of the blue clouds did show up. I added the H alpha to the color data (not the luminance) and it made a small difference. The annotated image was made before I took the H alpha data so you can use it to compare to the other images with the H alpha. It was hardly worth the effort but there's nothing else to do on a bright moonlit night. It didn't help that the moon wasn't all that far from the galaxy so I may have lost a bit of contrast to it though I doubt I lost very much as I saw no hint of a gradient from it or anything else in the data.

14" LX200R @ f/10, L=4x10' Ha=4x30' RGB=2x10', STL-11000XM, Paramount ME

Rick

Rick,

I thought that this galaxy was on my list, but didn't find it there. Found a
2002 b/w image though. Unfortunately until recently I have been deleting the
objects that were "done" instead of just marking them as "done". So now I
have a lot of interesting targets missing on my list although a lot of them
would deserve a better image than what I got...

Your image shows the HII regions clearly, which is remarkable for such a
small (well, not small by your standards) galaxy.

Stefan


"WA0CKY" schrieb im Newsbeitrag ...


NGC 2500 is a nearby low surface brightness face on spiral galaxy in
central Lynx. NED classifies it as SB(rs)d with HII emission. The NGC
project says SAB. The bar is short but obvious. The arms are in
disarray causing one source to call it a flocculent galaxy. I just see
lots of star clouds that align in semi arm segments. Redshift puts it
about 29 million light-years away while non redshift measurements say 33
million, a rather good agreement. Outside the star cloud region is a
very faint haze of somewhat blue stars that extends further on the
northwest side than the other sides. This gives the galaxy a rather
lopsided appearance.

The galaxy was discovered by William Herschel on March 9, 1788. It made
the second Herschel 400 list and thus was on my to-do list but at a low
priority. Thus I got a few frames of dubious quality last November but
was far from getting enough to finish the image. In April with it too
far west to use my T-point map I decided to finish it. Since I couldn't
work without guiding I had to use a guide star and none were convenient
without moving it off center. That meant I couldn't use the older
frames without severely cropping it. I ended up retaking it entirely
rather than wait yet another year to finish it. Since there had been a
request for an image of this galaxy rather than wait to process it with
April images I put it back into November where I'm currently working and
when the first (unused) frames were taken. A rare exception to my
processing order.

Turns out the galaxy is quite isolated with no nearby companions or
anything else so I could have cropped it without losing much but a few
distant galaxies, quasars and a quasar candidate. But while the new
data, being too far west for my best seeing, was still far better than
the old data so the complete redo was worth it.

Using the non redshift value of 33 million light-years the galaxy is
about 38,000 light-years in diameter. A only slightly smaller than
average spiral. But this includes the very faint outlying regions. If
limited to the bright portion then it is much smaller at 22,500
light-years. If the redshift distance is used it is slightly smaller
yet. It's likely the stars of the galaxy don't suddenly end as the
edges of my faint regions but continue on out just too faint for my
exposure time so the full size of most all galaxies is likely larger
than I can measure it.

NED indicated it had HII emissions and the RGB data showed blue blobs
that were likely new blue stars and likely marked the H alpha regions.
Just that these new massive stars being so bright they hid the pink of H
alpha and beta. It doesn't take much of a cosmological redshift to move
the H alpha out of my 6nm bandwidth. But this galaxy was still within
my bandwidth. So, with a quarter moon in the sky I took 2 hours of H
alpha data. Turned out it was quite weak but a few of the blue clouds
did show up. I added the H alpha to the color data (not the luminance)
and it made a small difference. The annotated image was made before I
took the H alpha data so you can use it to compare to the other images
with the H alpha. It was hardly worth the effort but there's nothing
else to do on a bright moonlit night. It didn't help that the moon
wasn't all that far from the galaxy so I may have lost a bit of contrast
to it though I doubt I lost very much as I saw no hint of a gradient
from it or anything else in the data.

14" LX200R @ f/10, L=4x10' Ha=4x30' RGB=2x10', STL-11000XM, Paramount ME

Rick


--
WA0CKY