by Ann » Tue Jul 23, 2013 7:52 pm
Thanks for processing the Hubble data for this image, geckzilla.
NGC 3185 is an interesting galaxy (but then, all galaxies are). NGC 3185 is deceptive. With its impressive dust ring, full of light and dark patches, it appears to be full of hot bright young stars and flamboyant emission nebulae. Yet it isn't.
The B-V index of NGC 3185 is 0.82. That isn't strikingly red, but it isn't blue, either. We may compare NGC 3185 with
NGC 4725 and
M90. Neither of these galaxies is very blue, and neither has a lot of star formation, but both are bluer than NGC 3185. NGC 4725 and M90 both have a B-V index of 0.72. Admittedly both appear to be slightly less dusty than NGC 3185. NGC 3185 is half a magnitude brighter in far infrared than in blue light, but M90 is 0.2 magnitudes
fainter and NGC 4725 a full magnitude fainter in far infrared than in blue light. This suggests, but doesn't prove, that NGC 3185 will form more stars than NGC 4725 and M90 in the future.
This is an ultraviolet image of the NGC 3190 group. We can see that
NGC 3190 (yellow galaxy cut by a dust lane) looks completely non-blue in the ultraviolet image, a clear sign that this galaxy lacks a significant population even of stars as modest as spectral class A, similar to Sirius and Vega. But we can clearly see the (light) blue ring of NGC 3185 (at five o'clock). The light blue color means that there are plenty of stars like Sirius and Vega here, at least, but there may be few or no stars like Rigel or Eta Carina.
This SDSS image gives us a clue. The ring is blue, but not strikingly so, and it contains no bright blue or green spots. In SDSS images, green spots mean red emission nebulae. None can be seen in NGC 3185. Neighbouring galaxy NGC 3187, however, a starforming galaxy with a B-V index of 0.47, looks very different in the
SDSS palette. NGC 3187, unlike NGC 3185, is clearly blue and contains bright blue knots, some with a greenish tinge. These are sites of large emission nebulae.
We may look at NGC 4725 in ultraviolet and in the SDSS palette, too.
In ultraviolet, the ring of NGC 4725 is bright and clearly patterned.
In the SDSS palette, NGC 4725 is mostly yellow, but its ring looks relatively blue. It is subtly but obviously bluer than NGC 3185.
So to summarize: NGC 3185 in impostor, a yellowish galaxy in a blue galaxy's morphology.
Ann
Thanks for processing the Hubble data for this image, geckzilla.
NGC 3185 is an interesting galaxy (but then, all galaxies are). NGC 3185 is deceptive. With its impressive dust ring, full of light and dark patches, it appears to be full of hot bright young stars and flamboyant emission nebulae. Yet it isn't.
The B-V index of NGC 3185 is 0.82. That isn't strikingly red, but it isn't blue, either. We may compare NGC 3185 with [url=http://en.spaceengine.org/_fr/15/5864153.jpg]NGC 4725[/url] and [url=http://www.dudeman.net/spacedog/gn/m90.jpg]M90[/url]. Neither of these galaxies is very blue, and neither has a lot of star formation, but both are bluer than NGC 3185. NGC 4725 and M90 both have a B-V index of 0.72. Admittedly both appear to be slightly less dusty than NGC 3185. NGC 3185 is half a magnitude brighter in far infrared than in blue light, but M90 is 0.2 magnitudes [i]fainter[/i] and NGC 4725 a full magnitude fainter in far infrared than in blue light. This suggests, but doesn't prove, that NGC 3185 will form more stars than NGC 4725 and M90 in the future.
[float=left][img2]http://www.popsci.com/files/imagecache/article_image_large/articles/NGC3190-NGC3187-NGC3189GALEX.jpg[/img2][c][size=85]Photo: GALEX[/size][/c][/float] This is an ultraviolet image of the NGC 3190 group. We can see that [url=http://www.robgendlerastropics.com/NGC3190-HST-GendlerSS.jpg]NGC 3190[/url] (yellow galaxy cut by a dust lane) looks completely non-blue in the ultraviolet image, a clear sign that this galaxy lacks a significant population even of stars as modest as spectral class A, similar to Sirius and Vega. But we can clearly see the (light) blue ring of NGC 3185 (at five o'clock). The light blue color means that there are plenty of stars like Sirius and Vega here, at least, but there may be few or no stars like Rigel or Eta Carina.
[float=right][img]http://casjobs.sdss.org/ImgCutoutDR7/getjpeg.aspx?ra=154.41067794&dec=21.68824744&scale=0.39612&width=512&height=512&opt=&query=[/img][/float] This SDSS image gives us a clue. The ring is blue, but not strikingly so, and it contains no bright blue or green spots. In SDSS images, green spots mean red emission nebulae. None can be seen in NGC 3185. Neighbouring galaxy NGC 3187, however, a starforming galaxy with a B-V index of 0.47, looks very different in the [url=http://cseligman.com/text/atlas/ngc3187.jpg]SDSS palette[/url]. NGC 3187, unlike NGC 3185, is clearly blue and contains bright blue knots, some with a greenish tinge. These are sites of large emission nebulae.
We may look at NGC 4725 in ultraviolet and in the SDSS palette, too. [url=http://upload.wikimedia.org/wikipedia/commons/5/55/NGC_4725_4747_4712_GALEX_WikiSky.jpg]In ultraviolet, the ring of NGC 4725 is bright and clearly patterned[/url]. [url=http://casjobs.sdss.org/ImgCutoutDR6/getjpeg.aspx?ra=192.61083&dec=25.50083&scale=1.584508&width=512&height=512&opt=&query=]In the SDSS palette, NGC 4725 is mostly yellow[/url], but its ring looks relatively blue. It is subtly but obviously bluer than NGC 3185.
So to summarize: NGC 3185 in impostor, a yellowish galaxy in a blue galaxy's morphology.
Ann