by Ann » Tue Jan 01, 2013 2:55 pm
This is a very interesting image.
It's not for me to argue, but NGC 5011B doesn't look like a spiral galaxy to me. Instead it looks like a lenticular galaxy, with a disk but no arms. The galaxy has a huge halo and what looks like a pretty high surface brightness inner halo and disk. The galaxy is completely monocolored, at least at this resolution, which suggests that it's made up of an entirely old population. I would guess that its B-V index may be around +0.9 or possibly even 0.95.
NGC 5011C fairly screams "dwarf galaxy"! It has a very low surface brightness, it is "large and spread out", it is easily resolved into stars by Hubble, and its color - to the extent that its color can be judged by exposures through an orange and and infrared filter - suggests a mostly old and relatively metal-poor population. In all probability, this galaxy hasn't been through many major star forming episodes through its lifetime. However, there is some suggestion that this galaxy has in fact formed a few stars within the last few million years. Tiny groups or very small associations of bluish stars can be seen in the inner part of the galaxy. Its outer halo is redder, and no stars may have formed here for at least a few hundred million years. I would guess that its color index is somewhere between 0.6 and 0.8.
My software erroneously places NGC 5011B and 5011C at the same distance, so it's a good thing that Hubble has cleared up that misunderstanding!
Ann
This is a very interesting image.
It's not for me to argue, but NGC 5011B doesn't look like a spiral galaxy to me. Instead it looks like a lenticular galaxy, with a disk but no arms. The galaxy has a huge halo and what looks like a pretty high surface brightness inner halo and disk. The galaxy is completely monocolored, at least at this resolution, which suggests that it's made up of an entirely old population. I would guess that its B-V index may be around +0.9 or possibly even 0.95.
NGC 5011C fairly screams "dwarf galaxy"! It has a very low surface brightness, it is "large and spread out", it is easily resolved into stars by Hubble, and its color - to the extent that its color can be judged by exposures through an orange and and infrared filter - suggests a mostly old and relatively metal-poor population. In all probability, this galaxy hasn't been through many major star forming episodes through its lifetime. However, there is some suggestion that this galaxy has in fact formed a few stars within the last few million years. Tiny groups or very small associations of bluish stars can be seen in the inner part of the galaxy. Its outer halo is redder, and no stars may have formed here for at least a few hundred million years. I would guess that its color index is somewhere between 0.6 and 0.8.
My software erroneously places NGC 5011B and 5011C at the same distance, so it's a good thing that Hubble has cleared up that misunderstanding!
Ann