Galaxy Zoo Starburst Talk

Quenched merging systems redder than non-merging

  • astropixie by astropixie scientist

    I found something interesting while playing with the classification results in tools, so i wanted to share them here to see what you all think!

    i made 4 filtered tables:
    (1) quenched with evidence of merging or tidal tails

    (2) quenched with no merging

    (3) control with evidence of merging or tidal tails

    (4) quenched with no merging

    then i looked at the (u-r) color distributions of the 4 classes and also the color - logMass distributions. this is close to the color-magnitude, but i like to use mass because it is a more physical quantity that i feel like i can wrap my head around!

    the color distributions of the 2 control groups samples, both the merging and non-merging, look identical.
    BUT among the quenched galaxies, the merging galaxies are much redder than the non-merging systems. this means the stars in the merging systems are older - there are no young, blue stars left, so it must have been a while since the last episode of star formation!

    i want to show you the histograms directly, but i dont have a place to load the screenshots online right now. sorry. i will do that as soon as i can!

    so.... here is my dashboard:
    my color distribution dashboard

    what do you think??

    the next things i'd like to do, and please jump in if you want, are the following:

    • look at the Halpha_Flux of the quenched mergers vs non-mergers to see if the color does reflect star formation activity
    • look at the D4000 distributions of the quenched mergers vs non-mergers because higher values of D4000 mean the stars are older.

    exciting!!

    Posted

  • JeanTate by JeanTate in response to astropixie's comment.

    It is exciting! 😃

    I've noticed something similar, for some particular QS objects (I'll see if I can dig up what I wrote). If you look at the spectra, I think you may see why: these objects are chock-a-block full of dust.

    Posted

  • mlpeck by mlpeck in response to astropixie's comment.

    This might also relate to my posts looking at the H-delta vs. D4000 plane. I had started to take a look at whether morphology has anything to do with H-delta line strength and commented:

    Here's a quick cut and past look at H-delta strength against a couple of morphological classes, namely "smooth" and "merging." The one noteworthy thing I see here is that the strong H-delta group has a larger number of objects that show evidence of disturbance (everything but "Neither" in the merging classification).

     > table(ea.quench,class.quench$smooth)

ea.quench Features or disk Smooth Star or artifact
    FALSE              466   1047                4
    TRUE               286   1190                3
> table(ea.quench,class.quench$merging)

ea.quench      Both Merging Neither Tidal debris
    FALSE    0   14      84    1305          110
    TRUE     0   27      88    1118          243

    D4000 and u-r color are pretty strongly correlated, and if you substitute color for D4000 in those plots you get this:

    enter image description here

    The control sample disturbed galaxies are well scattered among the general population. The quench sample disturbed are preferentially in the strong H-delta region, which is usually interpreted as indicating a strong starburst in the not too distant past.

    Posted

  • JeanTate by JeanTate in response to JeanTate's comment.

    I haven't - yet - done an analysis of the 'merging' vs 'non-merging' subsets of the v3 QS and QC catalogs, but for the ~one-third of each which are in the 'dominated by star-forming' part of a BPT diagram, the QS objects are, perhaps, redder because they are dustier than their QC counterparts.

    Details in the How to tell how much dust there is in a QS (or QC) galaxy, from the spectroscopic (or photometric) data in the catalogs? thread.

    Posted