Radio Galaxy Zoo Talk

Quasars with unusual spectra

  • WizardHowl by WizardHowl

    I am asking specifically about http://radiotalk.galaxyzoo.org/#/subjects/ARG000116e here, although I have asked before what constitutes 'unusual' for quasar spectra ( http://radiotalk.galaxyzoo.org/#/boards/BRG0000006/discussions/DRG00003we ).

    I realise that the spectra typically seen for quasars comes from the BOSS survey and that these are broadly in the visual part of the spectrum - thus for quasars the lines seen are those that have been redshifted into this part of the spectrum and typically the most prominent feature is a huge, wide line associated with MgII. Some lines that might ordinary be seen but which are redshifted out of the visual part of the spectrum for very distant objects such as quasars are Halpha and OIII/NII/SII. Therefore, the 'typical' spectrum for a quasar of a particular redshift will revolve around a different set of spectral lines.

    My understanding is, within the lines potentially observable, for a quasar these are broadened due to 'rotational broadening' as they arise from material in close orbit of the supermassive black hole. Where my understanding has problems is with what sort of galaxy is host to the quasar and what features from it, if any, are expected to be detectable in the spectrum. This is why I have to ask the question: 'is this odd/interesting/important' when I see other features present (note that these might not all originate in the host galaxy - absorption from the IGM in between us and the quasar can occur and has been observed in some objects). In the case of http://radiotalk.galaxyzoo.org/#/subjects/ARG000116e the host galaxy appears to be a QSO at Z_sp=0.925 and it shows emission lines of OII/III and Hbeta that I normally associate with star-forming galaxies, such as disk galaxies at low Z. Is this assessment reasonable and, if so, does it make this object particularly odd/interesting/important?

    Posted

  • Kevin by Kevin scientist, admin

    Hey can you link me to the spectrum? I'll take a look at it.

    Broad lines originate from near the black hole, whereas narrow lines like [OIII] come from the host galaxy. In fact, you can't really produce [OIII] near the black hole because the conditions don't allow for the transition to happen. That's why you never really see broad [OIII]

    Posted

  • WizardHowl by WizardHowl in response to Kevin's comment.

    The spectrum of the object (SDSS J103848.25+421856.6) is found at

    http://dr10.sdss3.org/spectrumDetail?plateid=4632&mjd=55644&fiber=150

    My understanding has been moving on gradually and I realise now this might not be so unexpected for the narrow-line part of AGN emission, however the continuum is very flat for this object, compared to most QSOs that have a strong slope bluewards. The OIII line is also very much stronger than for the MgII but I'm not familiar with spectra enough to know what constitutes an unusual strength ratio between any pair of spectral lines.

    Thanks for responding!

    Posted