what do you think about this one?
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SHLOMI54
special, isn't it?
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JeanTate
in response to SHLOMI54's comment.
It's unusual, certainly. Special? I don't think so. 😮
If you accept that it's a ringed spiral, with a modest bar (and lens), and early-type colors (i.e. it's mostly yellow) then there are thousands like it, in SDSS. The little blob, at ~10 o'clock? Most likely an overlap, but whether foreground or background, hard to say (there are little blobs like it throughout the image).
Happy hunting! 😃
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ElisabethB
moderator
Just one remark : there is no lens in this image ! 😄
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JeanTate
in response to ElisabethB's comment.
Oops, sorry Els. 😦
I'm using the term as Buta (Galaxy Morphology, 2011) does (from Section 6.2, "Inner and Outer Lenses"; this galaxy has an inner lens*):
The value of recognizing lenses as significant morphological components was first emphasized by Kormendy (1979), who suggested a dynamical link between inner lenses, which are often filled by a bar in one dimension, and dissolved or dissolving bars. Kormendy noted that lenses can be of the inner or outer type, in a manner analogous to inner and outer rings. He suggested the notation (l) for inner lenses and (L) for outer lenses to be used in the same position of the classification as inner and outer rings. For example, the galaxy NGC 1543 is type (R)SB(l)0/a while galaxy NGC 2983 is type (L)SB(s)0+.
Of course, there is no (strong) gravitational lens (it's just unfortunate that the same word is used for two quite different things).
Here's an image of NGC 1543 showing the inner lens clearly (and a beautiful outer ring) (source):
*I think so, anyway
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ElisabethB
moderator
A lens is for me (and for GZ) a gravitational lens. So no lens here ! PS : I wasn't even aware that lens could mean anything other than a grav lens. 😄
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JeanTate
in response to ElisabethB's comment.
Yeah, it's kinda ironic really...
Waaaay before anyone had mentioned 'gravitational lenses' (outside a tiny community of theoretical physicists), observational astronomers were busy classifying galaxies by their apparent shape (morphology). Ron Buta - who is 'down the hall' from our very own NGC3314 (Bill Keel) - is, arguably, today's expert on the topic, having worked with the great Gérard de Vaucouleurs (Ron made a guest appearance in the February 8, 2013 GZ blog Live Chat: Galactic Rings, Secular Evolution and The Good Old Days).
Anyway, for whatever reasons, in the GZ the classification tree ignores a key dimension in (spiral, disk) galaxy morphology, the inner ring* (it picks the two others, in Gérard de Vaucouleurs' scheme, stage - Hubble type - and family - apparent bar strength). There are quite a few morphological features that are both far more common and far more obvious than gravitational lenses, such as ansae, lenses, and flocculent (a kind of spiral pattern; pretty much the opposite of grand-design).
Of course, strong gravitational lenses are really exciting, and of great scientific interest, so it's only natural that the design of GZ should seek to focus zooites' attention on them. However, the 'experimental design' of the GZ classification tree certainly biases the results ... for example, the relative presence of rings vs bars could not possibly be determined, from a straight-forward analysis of zooites' clicks, because the question sequence strongly disfavors 'rings', and there's no way - using GZ classifications alone - to characterize this obvious bias.
Like I said, it's unfortunate that a perfectly good, technical term - one that has been in use, among observational astronomers, for decades before the GZ was even a twinkle in any zookeeper's eye - is so little known to zooites, when so many of them set eyes on very good examples of just this feature, rather more often than any of us probably realize.
*well, relegates rings to a minor role, that of a named feature if you choose 'anything odd?'
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SHLOMI54
I am happy to see that my post was justified!!!!! Thanks to you both for your answers, very interesting for me, i learnt many things
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JeanTate
Here's a recent preprint which refers to lenses (of the traditional kind, not gravitational): Milky Way mass galaxies with X-shaped bulges are not rare in the local Universe; here's the abstract:
Boxy/Peanut/X-shaped (B/P/X) bulges are studied using the 3.6 micron images from the Spitzer Survey of Stellar Structure in Galaxies (S4G), and the Ks-band images from the Near-IR S0 galaxy Survey (NIRS0S). They are compared with the properties of barlenses, defined as lens-like structures embedded in bars. Based on observations and recent simulation models we show evidence that barlenses are the more face-on counterparts of B/P/X-shaped bulges. Using unsharp masks 18 new X-shaped structures were identified, covering a large range of galaxy inclinations. The similar masses and red B-3.6 micron colors of the host galaxies, and the fact that the combined axial ratio distribution of the host galaxy disks is flat, supports the interpretation that barlenses and X-shapes are physically the same phenomenon. Our detailed 2D multi-component decompositions for 30 galaxies, fitting the barlens/X-shape with a separate component indicate very small or non-existent classical bulges. Taking into account that the structures we studied have similar parent galaxy masses as the Milky Way (MW), our results imply that MW mass galaxies with no significant classical bulges are common in the nearby Universe.
Maybe if the GZ classification tree had a branch that asked about barlenses (and the 'boxy' bulge question extended to cover 'X-shape'), we'd have lots of classification data to explore what Laurikainen et al. cover in this paper? And the relationship with bulges found to be even more interesting?
Astronomy = fun! 😃
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