Virgo A

[Checker]

Is Vir A really weak at 1420 MHz ?

73,

Dan

[Jim Abshier]

It depends on what you call weak. It has a flux density of 198 Jy at
1420 MHz.

Jim Abshier

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[Checker]

Hi Jim, I apologize for my slow brain activity :-)) when i compared my plots from Vir A, Cas A and Cyg i noticed a big drop in Vir A..... after reading your reply i pulled up the " Info Windows " for each one in the Radio Eyes Program and found that at 1420 MHz Vir A is 200 Jy, Cyg A is 1500 Jy and Cas A 2400 Jy. So looking at the plots again i see that. Attached are 3 screen shots for each one.

73,

Dan

[Jim Abshier]

Hi Dan, It appears that you are plotting the hydrogen line in the
direction of these sources. The flux density values that you got from
Radio Eyes are for continuum radiation. Both Cyg A and Cas A are on or
near the galactic plane, and the hydrogen line signal would likely be
strong in those directions. Virgo A is not on the galactic plane, and
the hydrogen signal would likely be weaker in that direction.

 Jim Abshier

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[Lamar Owen]

A minor point: M87, as a full-on galaxy, DOES have HI emission away from the nucleus and jet.  We had a grad student do some research here and make HI observations on M87 a couple of years ago, and got results.  I'll have to look for the graphs.

[fasleitung3]

Hi,

First let me say that as Jim has pointed out you are observing the hydrogen emission in direction towards the mentioned sources, but not the sources themselves. This is a common misunderstanding. Indeed, if you would record the spectrum in these directions the outcome would be more or less the same for small dishes if the sources were not present at all.

Furthermore, let me comment on the flux of CAS A. I have seen this 2400 Jy in several places, but this is definitely wrong as of today.

A good reference for the flux of various sources is the paper by Baars et al. http://adsabs.harvard.edu/pdf/1977A%26A....61...99B . In this paper, the flux of CAS A at 1415 MHz is given as 2369 Jy as of the data of publication back in 1977.

The special thing about CAS A is that, beeing a supernova remnant, it is declining over time. Baars et al. have made a prediction how it would decline and based on this projection CAS A would be weaker than CYG A by now. However, the decline over this 45 years has been somewhat less. We did a measurement in 2017 and at that time the flux density from CAS A was 1671 Jy. So if you take roughly 1650 as of today that should be about right.

Cheers,

Wolfgang

[Checker]

Thanks Lamar, yes please i would like to see those graphs.

73,

Dan

[Checker]

Thank You Jim and Wolfgang,

Yes i understand i am observing the HI, it is convenient to give the name of an object passing across the antenna since i use the various objects as reference points.

And Thank You Wolfgang for the link.

73,

Dan

[Lamar Owen]

Well, I should have re-read the report prior to commenting; the student
was observing several extragalactic sources and looking for HI emission;
M87, thanks to its high energy profile likely is a prime analog
ionization source, meaning that there should be little to no neutral
hydrogen, and the data showed that.  So M87 should have no HI; if it
were to have HI emissions, those should be centered around 1.41435 GHz
thanks to the redshift.  He DID see one observation of 3C273 with HI
(centered at 1.22623 GHz thanks to redshift) but was unable to repeat
that, so that observation is considered unreliable.

He did get HI spectra from M81 and M86, both of which are blue-shifted. 
I've attached the M86 graph, taken with a 5-minute integration time.

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Pisgah Astronomical Research Institute
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[fasleitung3]

Hi Lamar,
Unfortunately the spectrum you have shown cannot be from M86: It is
only a few km/sec wide. Spectra from galaxies however are typically a
few hundred km/s wide, and in some cases if you happen to look
perpendicular to its plane maybe a few 10 km/s. So the sepctrum shown
is far to narrow to come from a galaxy.
Hydrogen emission from M86 was detected as part of the ALFALFA survey
by the Arecibo telescope with fairly low SNR only. So one cannot expect
to see something with a 85 foot dish within 5 minutes of integration
time.
There are other galaxies which are well within the range of
possibilities for a 85 foot dish, such as NGC2366, NGC2304, UGC4305,
NGC4449, NGC5055 (M63), NGC5457 (M101), NGC6946. You could try some of
these.
Cheers,
Wolfgang