NGC 253 - dw2 anyone?

Hi folks,

I just read an article on the Sky&Telescope website about the photographic discovery of a dwarf galaxy near NGC 253 by an Australian amateur astronomer:

http://www.skyandtelescope.com/astro...axy-010820155/

According to this paper the magnitudes are: red 15.0 +/- 0.5 mag, green 15.9 +/- 0.5 mag; radius 3.24 +/- 0.51 arcmin, visual surface brightness 26.5 +/- 0.7 mag/sqarcsec.

http://arxiv.org/pdf/1512.03816v1.pdf

So the surface brightness is a little brighter than Ursa Minor Dwarf's surface brightness (28.3 mag/sqarcsec).

Has anyone attempted to observe this newly discovered dwarf galaxy visually?


Clear skies

Robin

The pre-print above was based on the discovery by the Magellan Clay 6.5 meter telescope at Las Campanas Observatory.

The pre-print based on the amateur discovery is available at http://arxiv.org/pdf/1512.03815v2.pdf

Dang, wish I'd known about this in early October when I was at my favorite dark sky site! I spent a good amount of time sketching NGC 253 under an excellent sky, but dw2 will have to wait for next year now.

I Looked at the POSS II blue image of it and it looks really faint!

POSS II Blue
Attachment 1961

Yes, this seems as daunting as some of the Andromeda dwarfs. That's a separate subject I want to ask the forum about some day... are they even observable?

At our latitudes, it seems like a formidable challenge.

Clear Skies

Quote:

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Originally Posted by Robin

Hi folks,

I just read an article on the Sky&Telescope website about the photographic discovery of a dwarf galaxy near NGC 253 by an Australian amateur astronomer:

http://www.skyandtelescope.com/astro...axy-010820155/

According to this paper the magnitudes are: red 15.0 +/- 0.5 mag, green 15.9 +/- 0.5 mag; radius 3.24 +/- 0.51 arcmin, visual surface brightness 26.5 +/- 0.7 mag/sqarcsec.

http://arxiv.org/pdf/1512.03816v1.pdf

So the surface brightness is a little brighter than Ursa Minor Dwarf's surface brightness (28.3 mag/sqarcsec).

Has anyone attempted to observe this newly discovered dwarf galaxy visually?


Clear skies

Robin

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Hi Robin,

Just FYI, there is another dwarf galaxy in NGC 253 that is probably much easier to find and view, and as far as I know, it is not often observed. This article...

http://www.asnsw.com/sites/default/f...ngc/bngc5.html

... appeared in the January 1993 issue of The Astronomical Society of New South Wales.

Attachment 1962

I've observed this guy many times over the years, whenever I have one of those 'special' nights with good conditions to the south.

Just checked my sketch - didn't see that dwarf, but it sure looks like I could have!

Looks like there is another, brighter, "companion" on the same side of NGC 253 but slightly further away. It is in the upper left in this APOD

http://apod.nasa.gov/apod/ap091121.html

and the dwarf galaxy mentioned by Paul is also visible to the right of the lower bright star.

The brighter companion that Wouter mentioned is PGC 198196 = 2MASX J00472894-2526263 = MAC 0047-2526 at 00h 47m 29.0s -25° 26' 26" (J2000). It's included in NED as well as LEDA, which lists a B magnitude of 16.03 +/- 0.47.

Using Vizier, the fainter and closer companion mentioned by Paul, is 2MASX J00472496-2521253. It's not included, though, in either the NED or LEDA databases.

Thanks for the designations, Steve. Too bad SCL's going to be too low for the next new moon. Can't wait to try them out.

It might be a nice observing project to put together a list of dwarf galaxies associated with brighter / well-known galaxies. My favorite example is Holmberg IX, but I think that might be the only one I know apart from M31's many satellites, and now NGC 253's. Does anyone have a list / other such objects to recommend? (Also, constraint: must be accessible in smaller telescopes, at least smaller than Jimi's! This is so that we don't run into gazillions of them.)

Clear Skies
Akarsh

Wow, that's really interesting stuff. I just looked it up in Cartes du Ciel. The radial velocity of PGC 198196 is listed as 20883 km/s, while NGC 253's is 251 km/s. I can imagine looking at this through a telescope, with some foreground stars, this is quite some depth of field! :-)

Clear skies,

Robin

How do we know that the dwarf that Paul pointed out is actually a dwarf associated with NGC 253 and not a background galaxy? The radial velocity of PGC 198196 is a give away that it is not a dwarf...