Radio Galaxy Zoo Talk

Comparing narrow and broad-line AGNs, in a new diagnostic diagram for emission-line galaxies based on WISE data

  • JeanTate by JeanTate

    by R. Coziol, J. P. Torres-Papaqui, H. Andernach (the last a name we RGZ zooites know well, eh?); arXiv:1504.01127:

    Using a new color-color diagnostic diagram in the mid infrared built from WISE data, the MIRDD, we compare narrow emission-line galaxies (NELGs) that exhibit different activity types (star-forming galaxies, SFGs, and AGNs, i.e.,LINERs, Sy2s and TOs), with broad-line AGNs (QSOs and Sy1s) and BL Lac objects at low redshift (z≤0.25). We show that the BL Lac objects occupy in the MIRDD the same region as the LINERs, whereas the QSOs and Sy1s occupy an intermediate region, between the LINERs and the Sy2s.In the MIRDD these galaxies trace a sequence that can be reproduced by a power law, Fν=να, where the spectral index, α, varies from 0 to −2, which is similar to what is observed in the optical-ultraviolet part of the spectra of AGNs with different luminosities.
    For the NELGs, we perform a stellar population synthesis analysis, demonstrating that the W2−W3 color is tightly correlated with the level of star formation in their host galaxies. A comparison of their MIR colors with the colors yielded by energy distributions (SEDs) of galaxies with different activity types, shows that the SED of the LINERs is similar to the SEDs of the QSOs and Sy1s, consistent with AGN galaxies with mild star formation, whereas the SEDs of the Sy2s and TOs are consistent with AGN galaxies with strong star formation components. For the BL Lac objects, we can only fit a SED that has no star formation component, consistent with AGNs in elliptical-type galaxies.
    From their similarities in MIR colors and SEDs, we infer that, in the nearby universe, the level of star formation activity most probably increases in the host galaxies of emission-line galaxies with different activity types along the sequence BL Lac→LINER→QSO/Sy1→Sy2→TO→SFG.

    Figures 3, 4, 5, 21, and 24 are particularly interesting (though I found them hard to get used to, and some combined plots - clearly distinguishing the various centroids - would have been most helpful).

    Posted

  • ivywong by ivywong scientist, admin

    Yes, this is the very HAndernach that you know in RGZ 😃

    Thanks @JeanTate for posting this. Do note that the use of W3 & W4 is only applicable to low-z galaxies and that many strong radio sources reside at redshifts beyond 0.25.

    Posted