by Ann » Tue Jul 16, 2013 9:16 pm
It is an interesting picture and an interesting galaxy. There is a hint of a peanut-shaped bulge, suggesting a bar, and the "brightness profile" of the galaxy in my software suggests the same thing. However, my software classifies NGC 4866 as an S0-a galaxy, not an SB0-a one. In other words, according to my software, NGC 4866 isn't a barred galaxy. And
other pictures of this galaxy suggest the same thing, namely, it is an unbarred galaxy.
The colors of NGC 4866 are unremarkable. Its total B-V index is 0.920 and its total U-B index is 0.490. Its effective B-V index is 0.995 and its effective u-B index is 0.560. That's definitely redder than an average spiral galaxy, whose B-V and U-B indexes may be around 0.70 and 0.10. But that is because the average spiral galaxy contains a moderate to large amount of star formation, whereas lenticulars are more or less barren.
On the other hand, our large neighbour, the Andromeda Galaxy,
definitely contains young blue stars and star formation, but M31 is nevertheless marginally redder than NGC 4866. The total B-V of M31 is 0.920, just like NGC 4866, but its U-B index is as red as 0.500. And the effective B-V index of M31 is as red as 1.010.
So how can M31, a starforming spiral of Hubble class Sb, be so red? I'd say it's because M31 contains such
a fantastic profusion of old red stars in its bright bulge. Visually,
the bulge of M31 is bright, but the outer blue parts of the galaxy are faint.
Thanks to its bright yellow bulge, M31 is very bright overall. According to my software, it is about three times brighter than the Milky Way. We have every reason to think that the Milky Way contains at least as many young blue stars as Andromeda, so the difference in brightness between our galaxy and M31 must be due to the profusion of old red stars in Andromeda.
NGC 4866 almost certainly contains far fewer blue stars than the Andromeda Galaxy. I would guess that the dust lanes of NGC 4866 contain a few moderately young stars of spectral classes A and F, but unlike M31, they probably hold extremely few (if any) B stars and no O-type stars at all. My guess is that the dust lanes of NGC 4866 would have shown up slightly blue if the galaxy had been imaged by the now defunct GALEX ultraviolet telescope. I would say that a blue population is there in NGC 4688,
but it obviously contains far fewer stars than the blue population of M31. On the other hand, NGC 4866 clearly contains far fewer red stars than M31, too. According to my software, NGC 4966 is about equally bright as the Milky Way, whereas M31 is three times brighter.
So the ratio between red and blue stars appears to be the same in M31 and in NGC 4866. M31 just has more of everything, more blue
and red stars.
Ann
It is an interesting picture and an interesting galaxy. There is a hint of a peanut-shaped bulge, suggesting a bar, and the "brightness profile" of the galaxy in my software suggests the same thing. However, my software classifies NGC 4866 as an S0-a galaxy, not an SB0-a one. In other words, according to my software, NGC 4866 isn't a barred galaxy. And [url=http://cosmo.nyu.edu/hogg/rc3/NGC_4866_UGC_8102_irg_clean.jpg]other pictures[/url] [url=http://www.spacetelescope.org/static/archives/vote/ht2012/927.jpg]of this galaxy[/url] suggest the same thing, namely, it is an unbarred galaxy.
The colors of NGC 4866 are unremarkable. Its total B-V index is 0.920 and its total U-B index is 0.490. Its effective B-V index is 0.995 and its effective u-B index is 0.560. That's definitely redder than an average spiral galaxy, whose B-V and U-B indexes may be around 0.70 and 0.10. But that is because the average spiral galaxy contains a moderate to large amount of star formation, whereas lenticulars are more or less barren.
On the other hand, our large neighbour, the Andromeda Galaxy, [url=http://arnholm.org/astro/deepsky/ngc206/ngc206_20071109_rgb_70pst_2.jpg]definitely contains young blue stars and star formation[/url], but M31 is nevertheless marginally redder than NGC 4866. The total B-V of M31 is 0.920, just like NGC 4866, but its U-B index is as red as 0.500. And the effective B-V index of M31 is as red as 1.010.
So how can M31, a starforming spiral of Hubble class Sb, be so red? I'd say it's because M31 contains such [url=http://www2011.mpe.mpg.de/News/PR20110120/M31_wikisky.jpg]a fantastic profusion of old red stars in its bright bulge[/url]. Visually, [url=http://www.universetoday.com/wp-content/uploads/2011/08/Andromeda-Galaxy-by-Brandon-Powers-580x386.jpg]the bulge of M31 is bright, but the outer blue parts of the galaxy are faint.[/url]
Thanks to its bright yellow bulge, M31 is very bright overall. According to my software, it is about three times brighter than the Milky Way. We have every reason to think that the Milky Way contains at least as many young blue stars as Andromeda, so the difference in brightness between our galaxy and M31 must be due to the profusion of old red stars in Andromeda.
NGC 4866 almost certainly contains far fewer blue stars than the Andromeda Galaxy. I would guess that the dust lanes of NGC 4866 contain a few moderately young stars of spectral classes A and F, but unlike M31, they probably hold extremely few (if any) B stars and no O-type stars at all. My guess is that the dust lanes of NGC 4866 would have shown up slightly blue if the galaxy had been imaged by the now defunct GALEX ultraviolet telescope. I would say that a blue population is there in NGC 4688, [url=http://spacefellowship.com/wp-content/uploads/2009/09/386913main_Swift_M31_large_UV.jpg]but it obviously contains far fewer stars than the blue population of M31[/url]. On the other hand, NGC 4866 clearly contains far fewer red stars than M31, too. According to my software, NGC 4966 is about equally bright as the Milky Way, whereas M31 is three times brighter.
So the ratio between red and blue stars appears to be the same in M31 and in NGC 4866. M31 just has more of everything, more blue [i]and[/i] red stars.
Ann