Ancestors

Toot

Written by Michael Porter on 2025-01-18 at 15:09

Question for the cosmologists:

As we look farther out in space, we look farther back in time. I'm under the impression that very distant galaxies show earlier stages of development.

How? Are their metallicities lower? Is it a structural thing? (Can we even resolve that kind of detail)?

[#]Astronomy #Cosmology #BigBangTheory

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Descendants

Written by Evan Mayer on 2025-01-18 at 15:28

@MichaelPorter one thing we see that varies as a function of redshift is the star formation rate, inferred from UV luminosity from bright hot young stars, and IR luminosity, from dust heated by UV photons also from bright hot young stars that may be obscured by the dust.

An overall trend is that star formation reached a peak around a redshift of z=1-2, and then a rapid decline.

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Written by Evan Mayer on 2025-01-18 at 15:31

@MichaelPorter Generally, we think of galaxies as having a sort of “main sequence” like stars, where they have a bunch of hydrogen, stars form, consuming that hydrogen, and then age and die, throwing off dust. There are feedback and bursting effects, but generally that’s what we see, and we can measure that sort of thing by just looking at UV and IR galaxy luminosity, no high resolution required!

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Written by Michael Porter on 2025-01-18 at 15:37

@millijanskys Okay, I guess this is linked to what I heard on Katie Mack and John Green's "Crash Course Pods: The Universe" podcast, that something like 90% of all the stars that will ever be have already formed?

Thanks very much for the info! I'm going to be giving a talk in a month on some of this stuff and it's good to fill in the gaps in my knowledge 😊

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Written by Evan Mayer on 2025-01-18 at 15:44

@MichaelPorter yes, I think it’s linked to that! I can give you some more references if you like, but the “classic plot” seems to be in Madau & Dickinson 2014, Fig. 8 or 9. It’s a bit of a busy plot for a talk if the audience has non-specialists, but would lend itself well to being cartoon-ified 🙂

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Written by Michael Porter on 2025-01-18 at 15:49

@millijanskys I am nothing if not skilled at cartoonifying graphics to suit my audience 😄

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Written by Michael Porter on 2025-01-18 at 17:07

@millijanskys No need for more references - I took a look at the Madau & Dickinson paper and it will do for my needs. This is one of those things that I probably won't talk about, but want to have in my pocket in case anyone asks a good question! Thanks again 😊

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