Review: On the Origin of the Salpeter Slope for the Initial Mass Function

It was back to science this week for the astronomy twitter journal club, with a discussion of the origin of the steep slope in the stellar initial mass function based on this paper.

There’s some background to the topic in our background post and over at astrobites. The full tweet transcript of the meeting is also available here.

Why was the paper chosen?

Suggested this paper because it is a very simple idea & ‘natural explanation’ of the slope, coming from a simple -2 slope. – @MarcelAstroph

had this for journal club in Hawai`i, seems a good model but a lot of the interesting physics is at the lower mass end – @nialldeacon

How original is the model put forward?

Is it a new idea? Or have people been focusing on more complicated explanations? – @astronomyjc

Igimf is not new at all, I think realizing that the imf itself is an igimf is new. – @MarcelAstroph

(Igimf = Integrated galaxy initial mass function – @astronomyjc)

Some more details on the model might help

I wonder why they don’t show their imfs, I bet they aren’t clean single power laws, as I showed in

They don’t show very much at all. There doesn’t seem to be very much info on their model even – @astronomyjc

indeed, it usually uses an input imf being salpeter-like, these people take a -2 input and find salpeter back. – @MarcelAstroph

Other models rely on turbulence to get Salpeter slope then interesting physics (variable m_Jeans, accretion) happens at lower mass – @nialldeacon

What about the most massive stars?

I also think their sampling method is extreme in biasing against high mass stars and not physically motivated. Any thoughts? – @MarcelAstroph

It does seem rather like a toy model (as far as I know) – @astronomyjc

I don’t think a model with this amount of simplicity should be used to constrain complicated physics… – @MarcelAstroph

But is it interesting if even a toy model does match slope solely from built-in mass selection? – @NGC3314

yes, but as I showed in my paper, you can get out any shape by choosing the input mass functions and limits right, – @MarcelAstroph

Overall we liked it

It is, imho, nice to see that papers with just a very simple idea, that is not even fully new gets published and attention! – @MarcelAstroph

Completely agree with that. It’s good to see people playing around with simple ideas which could develop in future – @astronomyjc

And finally…

#astrojc today reminds me of a chat at JCMT: what’s more complex physics, dN(M)/dM of rocks on HP summit or stellar IMF? We thought rocks… – @StephenSerjeant

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