by Ann » Thu Nov 03, 2016 7:08 am
While it is true that NGC 253 is a starburst galaxy, the starburst itself is confined to the nuclear region, and in spite of the numerous (and comparatively small) pink emission nebulas, the disk of NGC 253 is not very rich in young stars. James D Wray, who in the 1980s
photographed about a thousand galaxies or so through ultraviolet, blue and yellow-green filters, showed that the disk of NGC 253 doesn't emit a lot of UV light.
To appreciate the small size of the nuclear starburst of NGC 253, consider the image at left, taken through infrared filters J, H and K. Even though infrared light is often able to penetrate dust, the dust hiding the starburst of NGC 253 is so thick that not even this infrared image can completely reveal the starburst underneath. The Hubble telescope, whose infrared capabilities aren't stellar, also had trouble
seeing through the dust.
And while the nucleus of NGC 253 is undergoing a starburst, the disk of NGC 253 isn't particularly rich in young stars. The colors of the galaxy are relatively red, too, with a B-V of 0.850 and an U-B of 0.380. Of course, the galaxy is very dusty and therefore dust-reddened, too. The far infrared magnitude of NGC 253 is two and a half magnitudes brighter than its B magnitude, which is a clear signature of dust.
M82. Photo: Jason Jennings.
An even more extreme case of a nuclear starburst and a "dead" disk is M82. The central outflow from the nuclear region of M82 is tremendous, the B-V index of M82 is a little redder than that of NGC 253 (0.890 vs 0.850), the U-B index is a little bluer (0.310 vs 0.380), the dust content of M82 may be even higher than that of NGC 253 (the far infrared magnitude is three and a half magnitudes brighter than its B magnitude), and no obvious sites of star formation can be spotted in the disk at all.
It is almost as if a really runaway nuclear starburst may blow the entire galaxy free of gas, dampening or even destroying the galaxy's future starforming ability.
Ann
While it is true that NGC 253 is a starburst galaxy, the starburst itself is confined to the nuclear region, and in spite of the numerous (and comparatively small) pink emission nebulas, the disk of NGC 253 is not very rich in young stars. James D Wray, who in the 1980s [url=https://images-na.ssl-images-amazon.com/images/I/11BZ08Z3TQL._BO1,204,203,200_.jpg]photographed about a thousand galaxies or so[/url] through ultraviolet, blue and yellow-green filters, showed that the disk of NGC 253 doesn't emit a lot of UV light.
[float=left][img2]http://www.gemini.edu/images/pio/News/2015/wf2015_12/fig1.jpg[/img2][c][size=85]Infrared image of the nuclear starburst of NGC 253.
Source: http://www.gemini.edu/node/12441[/size][/c][/float] To appreciate the small size of the nuclear starburst of NGC 253, consider the image at left, taken through infrared filters J, H and K. Even though infrared light is often able to penetrate dust, the dust hiding the starburst of NGC 253 is so thick that not even this infrared image can completely reveal the starburst underneath. The Hubble telescope, whose infrared capabilities aren't stellar, also had trouble [url=https://cdn.spacetelescope.org/archives/images/screen/opo9510c.jpg]seeing through the dust[/url].
And while the nucleus of NGC 253 is undergoing a starburst, the disk of NGC 253 isn't particularly rich in young stars. The colors of the galaxy are relatively red, too, with a B-V of 0.850 and an U-B of 0.380. Of course, the galaxy is very dusty and therefore dust-reddened, too. The far infrared magnitude of NGC 253 is two and a half magnitudes brighter than its B magnitude, which is a clear signature of dust.
[float=right][img2]http://cosmicphotos.com/gallery/displayimage.php?fld_image_id=174&fld_album_id=12&fld_resol=1[/img2][c][size=85]M82. Photo: Jason Jennings.[/size][/c][/float]
An even more extreme case of a nuclear starburst and a "dead" disk is M82. The central outflow from the nuclear region of M82 is tremendous, the B-V index of M82 is a little redder than that of NGC 253 (0.890 vs 0.850), the U-B index is a little bluer (0.310 vs 0.380), the dust content of M82 may be even higher than that of NGC 253 (the far infrared magnitude is three and a half magnitudes brighter than its B magnitude), and no obvious sites of star formation can be spotted in the disk at all.
It is almost as if a really runaway nuclear starburst may blow the entire galaxy free of gas, dampening or even destroying the galaxy's future starforming ability.
Ann