The Top 12 of 2012

9. The Masses of Stars at Birth May Depend on Environment

Why it is important: When stars are born, there appear to always be many more low-mass stars than massive stars. However, if this ratio or ‘Initial Mass Function‘ (IMF) varies, it can change the way more extreme systems like high-redshift galaxies evolve.

Observations of early-type galaxies (circles; colors indicate the velocity dispersion, which increases with galaxy mass) show systematic differences in their stellar mass to light ratios (x-axis) compared to that expected for a standard Salpeter IMF (y-axis). Other comparison IMFs are shown as constant horizontal lines. Since the mass to light ratio decreases for more massive stars, an IMF with relatively fewer high-mass stars like Salpeter will have a higher mass-to-light ratio. No constant IMF fits all of these galaxies, and this trend is independent of the assumed fraction of Dark Matter in these galaxies. Read more about it in this astrobite!  (Adapted from Figure 2 of Cappellari et al.)

Next: (#8) Gravitational Lenses as a Cosmic Bathroom Scale: Weighing the Dark Matter in Galaxy Clusters with Hubble

Previous: (#10) A Magic Ratio to Quench Star Formation? Stellar and Dark Matter Mass tell Galaxies When to Stop Forming stars

About Betsy Mills

I am a 22nd-grader at UCLA, working with Mark Morris and spending the year at the MPIA in Heidelberg finishing my thesis. I like molecules in space, radio telescopes, the extreme center of our galaxy, getting to look at things no-one else has ever seen before, solving puzzles, and finding creative ways to survive graduate school


  1. Hi Betsy:

    Just a note– it looks like the arXiv link that you have on the first page of this article does not link to the title you provide.

    The link looks like it goes here:

    “How supernova feedback turns dark matter cusps into cores”

    instead of here:

    “Keck Spectroscopy of Faint 3<z<8 Lyman Break Galaxies:- Evidence for a Declining Fraction of Emission Line Sources In the Redshift Range 6<z<8"


    • Ah, actually the links are just switched–


      • Thanks Dave! The links are now fixed.

  2. Fascinating articles! But counting citations seriously distorts what astronomy is about. Because most young astronomers today work in observational cosmology, 10/12 papers are on that topic, the most glamorous frontier. But 10/12 of the most significant new papers of 2012 (selected some other way) paint a certainly much broader canvas, and reflect the amazing scope of astronomical research!
    Only the search for new planets (another glamour topic) and new calculations of the evolution of rotating stars in the HR diagram (a classic issue in stellar astronomy) penetrated the top twelve. So much more was missing!
    Nonetheless, an interesting citation poll.

    • Yes, I had the mass-to-light ratio section entirely backward; this is now corrected (and consistent with the linked astrobite). Thank you!!


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