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The Top 12 of 2012

10.(Tie with 9) Stellar and Dark Matter Mass tell Galaxies When to Stop Forming stars

Why it is important: The observed bimodal color distribution of galaxies– either blue and star forming like our own spiral Milky Way galaxy, or ‘red and dead‘ (usually) like ellipticals– leads us to believe that something causes galaxies to evolve from gas-rich to gas-poor. Here, the authors look for trends in large galaxy samples to catch this evolution in the act.

In this paper, the time when a galaxy reaches its peak star formation efficiency is defined as the ‘pivot’ (After this, star formation declines). The authors find that a galaxy’s pivot dark matter halo mass (x-axis) decreases toward lower redshifts, indicating that the star formation is quenched first in massive systems (downsizing). However, the pivot ratio of stellar to dark-matter halo mass (y-axis) is unchanged with redshift, which suggests that quenching really ‘turns on’ when a galaxy hits this special ratio. (Adapted from Figure 18 of Leauthaud et al.)

Next: (#9) Stars in Old Galaxies–They are NOT Just Like Us: The Masses of Stars at Birth May Depend on Environment

Previous: (# 11) Dark Matter core, nothing more! How to Mess With the Dark Matter in Dwarf Galaxies

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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

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6 Responses to “The Top 12 of 2012”

  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"


    Posted by Dave Coulter | February 20, 2013, 5:14 pm
  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.

    Posted by Donald D Clayton | February 20, 2013, 7:39 pm
  3. Hi, I think the mass-to-light ratio of a low-mass star is higher than that of a high-mass star. In addition, the Salpeter IMF has more low-mass stars than the Kroupa and Chabrier IMFs.

    I think that the article in astrobites has more detail introduction:

    Posted by Song, Wang | February 20, 2013, 9:05 pm

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