Trail in the IR
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Ptd
There looks, in the IR, to be a trail of material leading in a SE direction away from SDSS J114025.06+221741.5 , half way along it there would appear to be an #Hourglass and at the end of the apparent IR trail is J114024.06+221719.3 but there is no Z listed for the latter so I can't tell if the two galaxies actually have anything to do with each other. Is there a way of measuring Z for the radio sources? Perhaps a naive question but do black holes ever get dragged out of their parent galaxies?
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JeanTate
in response to Ptd's comment.
I think the apparent IR trail is more likely apparent than real ... there are a lot of these sort of faint, quasi-linear features in the WISE images; I suspect that they are a combo of artifacts and unresolved faint sources.
Is there a way of measuring Z for the radio sources?
Using just FIRST data? No; it's taken at a single frequency, and a direct measurement of redshift requires the identification of identifiable 'lines', which means a range of frequencies. Even then, as far as I know, in extra-galactic radio astronomy there's only one 'line', the 21-cm hydrogen line (in the microwave/millimeter region it's a different story), and I rather doubt that anyone would have even tried to detect 21-cm radiation from this source (although it may be possible for LOFAR). When the SKA is 'live', it will be a very different situation ... though I don't know how far north it will go (this source has a Dec of +22) ...
Maybe a radio astronomer will drop by, to correct me and/or add more ...
Hope this helps, and happy hunting! 😃
Ref info:
zph 0.20 SDSS J114025.06+221741.5 ObjId 1237667782830719152
STAR J114024.06+221719.3 ObjId 1237667782830719926Posted
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42jkb
scientist, admin
in response to JeanTate's comment.
JeanTate is correct. There are some other lines in OH and CO that various radio telescopes can observe. However, the key to getting redshift is the identification of the host galaxy of the radio emission.
There are current studies with LOFAR and MWA that are trying to observe the epoch of reionization. However, any HI emission past a redshift of around 0.02 is rather difficult to measure with the current instrumentation.
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JeanTate
in response to 42jkb's comment.
Thanks 42jkb.
There are some other lines in OH and CO that various radio telescopes can observe.
I hadn't realized that these, and some others, have been observed in extra-galactic objects, particularly galaxies beyond the Local Group.
A bit of searching turned up a list of astrophysically most important spectral lines, from the IAU (link).
It starts with the Deuterium counterpart of the 21-cm H line, at 327 MHz, and ends with a Carbon line at 809 GHz, which is well into the mm range. I wonder what the (fuzzy) boundary between radio astronomy and microwave/mm astronomy is? And whether the DI line has been observed in extragalactic sources (time for some more searching)?
The IAU list includes "Suggested minimum bandwidth", and the list as a whole is about parts of the radio spectrum which should be "protected", so that radio astronomy will not be made difficult to impossible by artificial sources. Two of the notes to the table are quite interesting:
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An extension to lower frequencies of the allocation of 1400-1427 MHz is required to allow for the Doppler shifts for HI observed in distant galaxies
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Because these line frequencies are also being used for observing other galaxies, the listed bandwidths include Doppler shifts corresponding to radial velocities of up to 1000 km/s. It should be noted that HI has been observed at frequencies redshifted to 500 MHz, while some lines of the most abundant molecules have been detected in galaxies with velocities up to 50 000 km/s, corresponding to a frequency reduction of up to 17%
And what molecule/species have the second note attached?
OH, CH, H2CO (formaldehyde), C3H2 (cyclopropenylidene, which I'd never heard of!), H2O, NH3, HCN, HCO+, CS, and CO. In several cases, different isotopic species are listed, e.g. 13CO. As above, some fun searching ahead: how many of these have been observed in galaxies beyond the Local Group?
And don't forget that "21-cm" is the same as "1400 MHz". And that FIRST (and NVSS) "observed" at a radio frequency of 1.4GHz! 😃
Oh, and a pet peeve: a discussion forum devoted to radio astronomy, and we can't use sub- or super-scripts?!? 😮
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Ptd
Hi Folks. Many thanks for informative responses, particularly about the issue re getting Z for Radio.
I've now had a look at the WISE link and can see what you mean JeanTate re many similar linear features. A bit worrying if this one is just an artifact, it is brighter than some of the IR sources I've clicked on!
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JeanTate
in response to Ptd's comment.
@Ptd: There are quite a few different kinds of 'linear features' in the WISE images, I reckon.
Perhaps the most obvious, and obviously artifactual (to coin a word), are the diffraction spikes (diffspikes). There are (almost always) four of them, for each bright star they are associated with (though the bright star may be waaaay offstage).
I think a lot of such features are actually made up of real sources, but they become blurred, due to the resolution of the WISE camera, and can look like a quasi-linear feature. So associating some part of such a feature with a host will likely be correct, especially if there's also an obvious galaxy in the corresponding SDSS image, at ~the same place.
Then there's 'noise': random fluctuations in the 'background' can sometimes look like a real source; indeed, unless the noise has very strange properties, this kind of 'apparent but not real' source is inevitable, if rare. It may be that the nature of WISE noise makes quasi-linear 'noise artifacts' more likely than what we might intuitively think.
(no doubt there are other ways a quasi-linear feature can appear in WISE images).
Finally, a linear feature may be due to more than one kind of effect ...
Hope this helps, and happy hunting! 😃
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