Galaxy Zoo Talk

AGZ000eli8 - bulge-less spiral

  • Peter_Dzwig by Peter_Dzwig

    DR9 says "Starburst". Don't know that it is, but find the lack of a central bulge, but WITH presence of a bar fascinating. Any thoughts on why? I know galaxies with bulges don't necessarily have SMBHs, but NO bulge at all that we can see, What does that mean? Was there one once that has shut down? was there never one? is it just very small? what mechanisms are likely?

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  • zoob1172 by zoob1172

    1237667736112070869 1237667783901380691 1237667736649138379

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  • Budgieye by Budgieye moderator

    "Starburst" means that many blue stars have formed and died in short period of time.

    2.2 Nucleus, nuclear bulge, and bulgeless, X-shaped bulges , nuclear rings https://talk.galaxyzoo.org/#/boards/BGZ0000001/discussions/DGZ0000wrb?page=2

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  • Peter_Dzwig by Peter_Dzwig in response to Budgieye's comment.

    Hi Budgieye, I think that I could have put it a little better. I understand what a Starburst galaxy is supposed to be. I was wondering why DR9 calls it such. It appears to me to be a blue object that is interacting. It may or may not be creating stars and they are possibly young. I think that it might be creating stars as a result of the interaction, not necessarily that the galaxy itself is creating stars independently of the interaction, which is somewhat different. Is DR9 using a fairly broad definition of starburst?

    Link at 2.2 seems broken and/or self-referential.It just takes me back to the same page. In any case my question was more what is the current position on why some galaxies don't have bulges. Does it imply lack of an SMBH and accretion disk? Kevin?

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  • Peter_Dzwig by Peter_Dzwig in response to zoob1172's comment.

    Can you clarify both this and your comment on the image please. Thanks.

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  • zoob1172 by zoob1172

    There are other objects in the area at the same red shift. You can compare spectra. It might answer your question about new stars.
    This is a paper about MTGs https://arxiv.org/abs/1506.00648

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  • Peter_Dzwig by Peter_Dzwig in response to zoob1172's comment.

    Thanks. MTGs?

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  • vrooje by vrooje admin, scientist

    One of my favorite papers discussing the challenge that bulgeless galaxies present to the overall picture of galaxy evolution is Kormendy et al. (2010). The basic (bit oversimplified, but not bad) picture is that "classical" bulges form in substantial mergers, so a bulgeless galaxy can't have had a merger big enough to create a bulge, and in a Universe where mergers drive the growth of galaxies (and black holes) that we see many of them is a bit odd. We do see them with growing SMBHs; that was a GZ paper we published in 2013. Some of those bulgeless galaxies do have bars.

    One way to solve this is to say that bulgeless galaxies are all really low mass, i.e. they just haven't really grown much, so it's not inconsistent for them to be merger-free. The dwarf galaxy attached to this thread might satisfy that, but we also do see bulgeless galaxies that are much more massive (actually, we think the Milky Way may be a bulgeless galaxy).

    Another solution is to just say that mergers don't drive as much of galaxy growth as we thought. Simulations show that, actually, the calm/smooth/"cold" accretion of gas onto galaxies from the surrounding intergalactic medium (IGM) can account for a lot of galaxy growth, and that would likely not drive bulge formation. I don't know that anyone has used those simulations to make predictions about how many bulgeless galaxies we should see and what they should look like.

    The slight wrench in this is the existence of "pseudo"bulges, which Kormendy et al. above discuss. Those look like bulges on images, at least visually, but they're different in terms of light concentration (usually) and orbits (by definition). Their orbits are more rotational, like the disks they're found in, and they're thought to be merger-free creations. Bars seem in simulations to naturally lead to the growth of pseudobulges, so actually seeing a bar in a bulgeless galaxy is interesting from that perspective too.

    Hope that helps.

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  • Peter_Dzwig by Peter_Dzwig in response to vrooje's comment.

    ...so youre saying that in bulgeless and psuedobulgeless galaxies we see low velocity dispersion and no evidence of BHs - SM or otherwise?

    I'll gp back to Kormendy et al

    Peter

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