Double Lobe and a Star
The IR host in this image seems to be Star J223729.24+024301.7. Would we expect to see radio emissions like this from a Star?
by ivywong scientist, admin
Hi @Gweilouk, the host is not a star but what is known as a Quasi-stellar Object (QSO) or quasar whereby the light from the central active black hole is so bright that it outshines the rest of the galaxy so it appears to look like a star but it's not one. Does this help?
Thanks for the response, and it does indeed help.
I went with Star as the classification as SDSS listed it as a star, assuming I got the right host that is, but you can see I was less than convinced with my own classification by the question. Is the right approach to flag the image with a question if the SDSS optical host description doesn't seem to match what we are seeing in the Radio and IR?
Now for the silly question... are all Active Galactic Neuclei Quasars or are Quasars a specific type of AGN that are luminous across a broad band of electromagnetic radiation?
I went with Star as the classification as SDSS listed it as a star,
That's what I do too. And I add it to my STAR but likely a QSO but don't know it Collection. I also click on the link to NED; often - but not always - there's a reference to either a photometric or spectroscopic redshift estimate.
The only exception is where the STAR has an SDSS spectrum, and it's clearly that of a (z~0) star. There are several examples of such objects, and some of us have been slowly digging into this a bit more (these objects are somewhat of a mystery).
are all Active Galactic Neuclei Quasars or are Quasars a specific type of AGN that are luminous across a broad band of electromagnetic radiation?
That's very far from a silly question! In fact, it's a very pertinent one!! 😄
There was a time, decades ago now, where 'quasar' had a clear, single meaning. And you could unambiguously determine if a star-like object was a quasar. Then it started to get really complicated ... lots of star-like objects with high redshifts were discovered, and they weren't radio sources ('quasar' is an acronym for 'quasi-stellar radio source'). Then some bright, point (star-)like nuclei in otherwise fairly normal-looking galaxies were discovered to have optical spectra very much like that of quasars. And many were found to be radio-bright too. And when deep x-ray and gamma-ray observations were made, it turned out to be even more, um, messy. Ditto IR. And UV.
Fast-forward to today: it is now accepted that all 'quasars' are 'active galactic nuclei' (AGN), but the reverse? Not so much.
Often - but certainly not always! - 'quasar' (or 'QSO', quasi-stellar object) is used for particularly bright AGNs (bright in the optical); sometimes no distinction is made. More confusing is this: I have found that radio astronomers and optical/IR/UV astronomers use the terms differently (and x-ray/gamma-ray ones? likely different again). Ideally, in their papers, the astronomers spell out exactly what they mean; sometimes, sadly, they are not so careful.
What do other zooites/astronomers think?
Hope this helps (and again, ain't astronomy wonderful!) 😃
by ivywong scientist, admin
Thanks @JeanTate. Typically until we obtain a spectrum for the source, it's near-impossible to tell the 2 apart because the images will look identical. However, if the spectrum of the object shows broad strong emission lines, then we can be sure it's not a star since stars typically have absorption lines instead of emission lines...