With all the great NGC 253 images exhibited recently I decided to revisit my own image and reprocess it.
Reading about the halo around NGC 253 gave me the idea of processing the bright NGC 253 as a faint dwarf galaxy in order to bring out the halo.
Quote:
Context. Outskirts of large galaxies contain important information about galaxy formation and assembly. Resolved star count studies
can probe the extremely low surface brightness of the outer halos.
Aims. NGC 253 is a nearly edge-on disk galaxy in the Sculptor group where we resolved the halo stars from ground-based images,
with the aim of studying its stellar population content, the structure and the overall extent of the halo.
Methods. We use Z and J-band images from the VIRCAM camera mounted on the VISTA telescope to construct the spatially resolved
J vs. Z-J colour-magnitude diagrams (CMDs). The very deep photometry and the wide area covered allows us to trace the red giant
branch (RGB) and asymptotic giant branch (AGB) stars that belong to the halo of NGC 253 out to 50 kpc along the galaxy minor
axis.
Results. We confirm the existence of an extra planar stellar component of the disk, with a very prominent southern shelf and a
symmetrical feature on the north side. The only additional visible sub-structure is an overdensity in the north-west part of the halo
∼ 28 kpc distant from the plane and extending over 20 kpc parallel with the disk. We measure the transition from the disk to the halo
at a radial distance of about 25 kpc with a clear break in the number density profile. The isodensity contours show that the inner halo
is a flattened structure that blends with a more extended, diffuse, rounder outer halo. Such external structure can be traced to the very
edge of our image out to 50 kpc from the disk plane. The number density profile of the stars in the stellar halo follows a power law
with index −1.6, as function of radius. The CMD shows a very homogeneous stellar population across the field; by comparing with
isochrones we conclude that the RGB stars are ∼ 8 Gyr old or more, while the AGB stars trace a population of about 2 × 108 M
formed from ∼ 0.5 to a few Gyr ago. Surprisingly, part of this latter population appears scattered over a wide area. We explore several
ideas to explain the origin of this relatively young component in the inner halo of NGC 253.
Key words. Galaxies: spiral – Galaxies: Individual: NGC 253 – Galaxies: star clusters[
In fairly deep data (in particular, an image by Mike Sidonio and one of mine) I have seen an obvious lobe of halo to the South that extends as far as TYC6421-01351-1. Perhaps you need more data to pick that up?
This is really good juicy stuff. I like the science and what you are attempting. The article seems to show that there is no outer "edge", just as the sun's 'atmosphere' effectively extends to Pluto and beyond, just getting thinner and thinner. So the job becomes showing that at some given distance, the image is statistically significantly brighter than the background. That means getting a really good image of the background.
That in turn means a really cold chip, really good flats (that's where I fall down!), and an incredibly dark sky, so no thin cirrus, no moon, and photographing high above the horizon out of the mirk and skyglow.
Avoiding these sources of artifact might be even more important than long subs and a deep stack.
This is really good juicy stuff. I like the science and what you are attempting. The article seems to show that there is no outer "edge", just as the sun's 'atmosphere' effectively extends to Pluto and beyond, just getting thinner and thinner. So the job becomes showing that at some given distance, the image is statistically significantly brighter than the background. That means getting a really good image of the background.
That in turn means a really cold chip, really good flats (that's where I fall down!), and an incredibly dark sky, so no thin cirrus, no moon, and photographing high above the horizon out of the mirk and skyglow.
Avoiding these sources of artifact might be even more important than long subs and a deep stack.
Good project and well worth doing.
Best,
Mike
Thanks Mike.
Since I prefer to image the more obscure and fainter object, the background plays a very important role in processing for me.
Quote:
Originally Posted by RickS
An interesting experiment, Steven.
In fairly deep data (in particular, an image by Mike Sidonio and one of mine) I have seen an obvious lobe of halo to the South that extends as far as TYC6421-01351-1. Perhaps you need more data to pick that up?
Cheers,
Rick.
Thanks Rick.
I had a look at your fine image.
Then it dawned on me I had used the wrong process, a legacy I suppose of processing an image a 4.00am.
