Review: Cold flows and the first quasars

The seventh meeting of the astronomy journal twitter club was all about the growth of black holes and galaxies in the early Universe. The paper discussed, Cold Flows and the First Quasars, presents the results from a detailed new simulation which suggests that supermassive black holes can exist at very high redshift if they grow via cold flow accretion. Quasar feedback, thought to be key to heating gas and preventing these cold flows at more moderate redshifts, is not sufficient to stop this either. For further details see the preview post, or the excellent astrobites summary. There’s also a full transcript of the meeting.

The meeting kicked off with praise for the simulation, but criticism of a perceived lack of detail:

I was impressed by the huge number of particles they follow in their simulation, which makes for a decent resolution in a big box. but… I was puzzled by the seeming disconnect between the detail in BH growth and feedback, compared to other important physics. – @MarcelAstroph

I agree. Maybe I missed it but the paper seems to make no mention of other feedback process or star formation – @astronomyjc

The discussion then moved onto the details of the feedback heating in the simulation:

If they heat all neighbors, then at low accr. rates, they neighbors will cool down again in the next time step, doing no feedback. – @MarcelAstroph

If they would have chosen to heat 1 neighbor, then the feedback would be efficient at lower accretion rates (Booth&Schaye 2009) – @MarcelAstroph

So because they required all neighbors to be heated in their sim they end up with less efficient feedback – @astronomyjc

I think, but I might be wrong. Would be good if they show that the number of neighbors heated is not important for the conclusion. – @MarcelAstroph

The details of the simulation also came up:

although maybe not so important for the growing of BHs, do you have any comments on the criteria used to merge 2 BHs? (p3,c1,par2). – @ntejos

The merging criteria seem reasonable. Since 1 of their conclusions is that the gals undergo hardly any mergers though would have been good to see more discussion of how the criteria used affect this – @astronomyjc

Along with the details of the feedback process itself:

Does anybody understand why BHs need to blow gas all out of the halo in order to self-regulate? Why is the small scale unimportant? – @MarcelAstroph

The problem is I don’t think anyone’s sure yet exactly how feedback works – via quasar winds, radio jets or what? – @astronomyjc

I agree, but the feedback recipe could also be key to their result, so not testing the dependence on it is dangerous.- @MarcelAstroph

Overall we liked this paper but reading over the transcript, one thing we’d have liked to see was more discussion about how changing different aspects of the simulation might affect the results.

In general what do you all think of the paper? – @astronomyjc

I thought it was a good paper with a plausible explanation for black hole growth in the early universe – @astronomyjc

Agreed, with the caveat that the feedback mechanism is speculative. – @DrMRFrancis

I love the sim. Too bad they didn’t treat other physics better, not sure about the concl about bus above m-sigma. Nice visuals.- @MarcelAstroph

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4 Responses to Review: Cold flows and the first quasars

  1. Marcel Haas says:

    Is there also a pdf available of this review?

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