Galaxy Zoo Starburst Talk

"VESPA" population models

  • mlpeck by mlpeck

    A recent GZ related paper by Tojeiro et al. (2013) made some use of a database of stellar population models described in Tojeiro et al. (2009) and publicly available online at http://www-wfau.roe.ac.uk/vespa/index.html. These models differ a little from some others that are available through SDSS in that they did full spectral fitting rather than fitting to broadband colors or line indices. Also, the database includes star formation histories binned by lookback time at ~0.2 dex resolution.

    I downloaded "run 2" of their main galaxy sample database, which is based on commonly used SSP models of Bruzual & Charlot (2003) with Chabrier IMF and a 2 component dust model. These are the ones most directly comparable to the MPA-JHU pipeline. 1046 of the Quench sample subset 2 and 1100 control sample (subset 2, v2) are in the database.

    So far I've just looked at the distribution of mass fractions in a few very broad time bins, focussing on a more or less arbitrarily defined "intermediate age" bin spanning lookback times from 70 Myr - 1 Gyr. Here are the distributions broken down by BPT type for the quench sample, followed by the controls.

    This plot by the way is called a box plot or sometimes box and whisker plot. The box marks the 25th and 75th percentiles and the median. I've also shown confidence intervals on the medians estimated by bootstrapping. Those are the red points with error bars inside the boxes.

    In the quench sample plot ignore the leftmost bin. There are only 5 objects with "no emission" and at least two of those are misclassified.

    enter image description here

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    So there's a fairly striking difference between the QS and control sample in that all groups have a non-trivial mass fraction in intermediate age stars in the quench sample, with AGNs (including LINERs and what I labelled "weak emission" line galaxies, which I think are probably mostly the low excitation limit of LINERs) appearing to be strongly post-starburst systems.

    One slight twist here is that starforming galaxies also have a modest mass fraction in intermediate age stars in the median, compared to a median mass fraction of 0 in the control sample. This suggests that perhaps the QS starforming group are "star burstier" than their counterparts in the controls.

    All of this seems consistent with other lines of evidence, and I'm not sure it's worth spending a lot more time on. Thoughts anyone?

    Posted