Quasars...

[Nereid]

starbiter, the closest that TPOD comes to answering the question ("what (to EU theorists and Thunderbolts Forum members) is the (or an) observational definition of a 'quasar'?") is, it seems, this:

His most recent tactic has been to look at the objects called ULX's (the quasar above is one of them). ULX stands for Ultra Luminous X-ray sources, which are tiny concentrations of x-rays in or very near an active galaxy. The x-ray concentration is stronger than any known astronomical object, even a supernova, can produce. Over the last two years, Arp has shown that at least 20 of these objects are quasars, with redshifts much higher than the galaxy they are associated with.

Assume, for now, that Arp is not an EU theorist (he isn't a Thunderbolts Forum member, as far as I can tell). This part of the TPOD seems to be saying that at least some objects can be called quasars if:
a) they are ULXs (per the definition in the TPOD), AND
b) Arp states that they are quasars.

Or am I missing something?

It is not the case that I, Solar, have coined an "observational definition" of a Quasar, QSO, AGN etc - but that this (and many other terms quantified and qualified by their particulars) is what has been provided by those who work in that field.

Thanks Solar.

If (all) the EU theorists agree with you, then there would be a basis for challenging what these EU theorists have written about the Hubble redshift-distance relationship as it applies to quasars.

For example, to take starbiter's post (and assuming my understanding is correct), then we can simply read all Arp's papers and compile a list of objects he says are quasars; conversely, if an object is not mentioned in any of Arp's papers (as being a quasar, or not), then we must not include it in any analysis we might think of doing, into the Hubble redshift-distance relationship as it applies to quasars (say) ... no matter how closely, in every observed aspect, that object resembles a quasar (in one of his papers).

It seems, though, that there might be a problem with the approach you outline (I'll read up on how the SDSS pipeline assigns "QSO" to objects which are given SDSS ObjIDs), when it comes to beginning to research the Hubble redshift-distance relationship as it applies to quasars, from the EU perspective. What to do, for example, if SDSS assigns the classification "QSO" to an object which Arp (say) says is not a QSO?

starbiter, the TPOD says "And yet the galaxy is opaque". However, the Galianni et al. paper it quotes as (the sole?) source, does not use the word "opaque" (nor "dust", "clouds" ("cloud" occurs just once), "bright triangular jet", "fat end", "disturbed", ...). As the TPOD is unsigned, we can have no clue as to whether its author (or at least one of its authors) is an EU theorist or a Thunberbolts Forum member. That makes it rather challenging to conclude anything firm about this object and this galaxy, with respect to the Hubble redshift-distance relationship as it applies to quasars from the EU perspective, wouldn't you say?

[davesmith_au]

starbiter, the closest that TPOD comes to answering the question ("what (to EU theorists and Thunderbolts Forum members) is the (or an) observational definition of a 'quasar'?") is, it seems, this:

His most recent tactic has been to look at the objects called ULX's (the quasar above is one of them). ULX stands for Ultra Luminous X-ray sources, which are tiny concentrations of x-rays in or very near an active galaxy. The x-ray concentration is stronger than any known astronomical object, even a supernova, can produce. Over the last two years, Arp has shown that at least 20 of these objects are quasars, with redshifts much higher than the galaxy they are associated with.

Assume, for now, that Arp is not an EU theorist (he isn't a Thunderbolts Forum member, as far as I can tell). This part of the TPOD seems to be saying that at least some objects can be called quasars if:
a) they are ULXs (per the definition in the TPOD), AND
b) Arp states that they are quasars.

Or am I missing something?

Yes you are missing the point. There is a huge difference between "Arp states that they are quasars" and that Arp SHOWS that they are quasars.

It is not the case that I, Solar, have coined an "observational definition" of a Quasar, QSO, AGN etc - but that this (and many other terms quantified and qualified by their particulars) is what has been provided by those who work in that field.

Thanks Solar.

If (all) the EU theorists agree with you, then there would be a basis for challenging what these EU theorists have written about the Hubble redshift-distance relationship as it applies to quasars.

For example, to take starbiter's post (and assuming my understanding is correct), then we can simply read all Arp's papers and compile a list of objects he says are quasars; conversely, if an object is not mentioned in any of Arp's papers (as being a quasar, or not), then we must not include it in any analysis we might think of doing, into the Hubble redshift-distance relationship as it applies to quasars (say) ... no matter how closely, in every observed aspect, that object resembles a quasar (in one of his papers).

It seems, though, that there might be a problem with the approach you outline (I'll read up on how the SDSS pipeline assigns "QSO" to objects which are given SDSS ObjIDs), when it comes to beginning to research the Hubble redshift-distance relationship as it applies to quasars, from the EU perspective. What to do, for example, if SDSS assigns the classification "QSO" to an object which Arp (say) says is not a QSO?

Nereid you are being simplistic to the point of ridicule. It's (again) not a matter of what Arp (or anyone else for that matter) "says" but what has been shown in the relevant, peer-reviewed literature.

starbiter, the TPOD says "And yet the galaxy is opaque". However, the Galianni et al. paper it quotes as (the sole?) source, does not use the word "opaque" (nor "dust", "clouds" ("cloud" occurs just once), "bright triangular jet", "fat end", "disturbed", ...). As the TPOD is unsigned, we can have no clue as to whether its author (or at least one of its authors) is an EU theorist or a Thunberbolts Forum member. That makes it rather challenging to conclude anything firm about this object and this galaxy, with respect to the Hubble redshift-distance relationship as it applies to quasars from the EU perspective, wouldn't you say?

And here you go with even more obfuscation tactics. So how about we take a quick look at the actual peer-reviewed paper:

THE DISCOVERY OF A HIGH-REDSHIFT X-RAY-EMITTING QSO VERY CLOSE TO THE NUCLEUS OF NGC 7319 - Pasquale Galianni et al.
(Pasquale Galianni, E. M. Burbidge, H. Arp, V. Junkkarinen, G. Burbidge, and Stefano Zibetti)
as published in The Astrophysical Journal, 620:88-94, 2005 February 10.

Firstly, let's look at some of the terms you hasten to point out that the "source" (of the TPOD) does not use.

OPAQUE:

As was pointed out by the referee, this anisotropy is expected if NGC 7319 is typical of a Seyfert 2 system with an obscuring torus, if we accept the unified model of AGNs that was developed following the discovery of an obscuring torus in NGC 1068
(Antonucci & Miller 1985).

There are no signs of background objects showing through the disk in our HST picture of the inner regions of NGC 7319 (Fig. 1).

Is it not reasonable to use the term "opaque" if paraphrasing the paper?


DUST, CLOUDS:

Pedantry. Again, when paraphrasing the paper for a general audience, such terms do not appear to be out of order.


BRIGHT TRIANGULAR JET, FAT END, DISTURBED:

Jet/Filament

"V" shaped jet

Couldn't the "top" or open part of the "V" be considered the "fat end"?


Also in Section 4.4 you will find "luminous connection" and "wake" in reference to the same feature, and throughout the paper the term "outflow" used extensively to describe the same feature (Section 4.2 once, Section 4.3 five times, and once in Section 7), and in Section 7 "V-shaped feature" appears twice.

The terms "disturbance" and "disrupted" appear in Sections 4.4 and 5.1 respectively, so what could possibly be your objection to the term "disturbed"?

I suggest you read through the paper rather than search for terms used elsewhere, and see if you can come to an understanding of what the paper is getting at. Here's a hint:

We have clearly demonstrated that the ULX lying 8" from the nucleus of NGC 7319 is a high-redshift QSO. This is to be added to a list of more than 20 ULX candidates that have all turned out to be genuine QSOs (cf. Burbidge et al. 2003; Arp et al. 2004). Since all of these objects lie within a few arcminutes or less from the centers of these galaxies, the probability that any of them are QSOs at cosmological distance, observed through the disk of the galaxy, is negligibly small. Thus, this is further direct evidence that high-redshift QSOs are generated and ejected in low-redshift active galaxies. The case described here is particularly interesting, since there is a considerable amount of observational evidence that the QSO is interacting with the gas in the main body of the galaxy, although we have pointed out that there are difficulties in understanding it in detail.

Cheers, Dave.

[Nereid]

Let's look at how 'quasar' is defined, in SDSS; I'll work from Schneider et al. (2003) - "The Sloan Digital Sky Survey Quasar Catalog II. First Data Release" (link is to the arXiv preprint abstract).

First, though, I'll refresh our memories of one of Arp's papers, "Quasars near companion galaxies", published in 1981. In this paper Arp proposes a physical association (this is an oversimplification for the sake of brevity) between a number of large, bright galaxies ("main galaxies", in Table 1), some 'companion' galaxies, and some (34) quasars. The main galaxies have redshifts listed as from 95 to 5429 km/s (i.e. a z of 0.0003 to 0.0181); the companions from 147 to 21,300 km/s (0.0005 to 0.071); the quasars from 0.027 to 2.40. In this paper, Arp explicitly refers to a 1970 paper of his for the definition of quasar he uses in the 1981 paper; here it is:

The definition of a quasi-stellar object is clearly then: an object which appears stellar on photographs (diameter <1") and which has a large redshift (relative to normal stars in our own Galaxy).

Schneider et al. (2003) begins as follows:

Over the past two decades the number of quasars produced by an individual survey has increased by about two orders of magnitude. One of the most intensively studied quasar data sets, the Bright Quasar Survey of Schmidt & Green (1983), contains approximately 100 quasars. In the 1990s the Large Bright Quasar Survey (LBQS; Hewett, Foltz, & Chaffee 1995, 2001) presented more than 1,000 quasars, and recent results from the 2dF Quasar Survey (Croom et al. 2001) have pushed quasar survey sample sizes past the 10,000 object milestone.

The third paragraph begins as follows:

The catalog in the present paper consists of the 16,713 objects in the SDSS First Data Release (DR1; Abazajian et al. 2003) that have a luminosity larger than Mi = −22.0 (calculated assuming an H0 = 70 km s−1 Mpc−1, ΩM = 0.3, ΩΛ = 0.7 cosmology, which will be used throughout this paper), and whose SDSS spectra contain at least one broad emission line (velocity FWHM larger than ~ 1000 km s−1). The quasars range in redshift from 0.08 to 5.41, and 15,786 (94%) were discovered by the SDSS.

The start of the fourth para is: "The DR1 catalog does not include classes of Active Galactic Nuclei (AGN) such as Type II quasars and BL Lacertae objects".

There is a section (3.3) devoted to "Luminosity and Line Width Criteria"; it begins as follows:

Quasars have historically been defined as the high-luminosity branch of Active Galactic Nuclei (AGN); the (somewhat arbitrary) luminosity division between quasars and Seyfert galaxies has a consensus value of MB = −23 for an H0 = 50 km s−1 Mpc−1, ΩM = 1, ΩΛ = 0 cosmology (e.g., Schmidt and Green 1983).

There are, to state the blindly obvious, significant differences between the observational/operational definition of 'quasar' used in SDSS (or at least DR1) and what an EU theorist and/or Thunderbolts Forum member would use. For example, the luminosity criterion is surely meaningless (to EU theorists).

There is a huge difference between "Arp states that they are quasars" and that Arp SHOWS that they are quasars.
[...]
Nereid you are being simplistic to the point of ridicule. It's (again) not a matter of what Arp (or anyone else for that matter) "says" but what has been shown in the relevant, peer-reviewed literature.

Leave aside, for now, the question of the independent verifiability of reports of objects observed by Arp, or anyone else (this is most certainly not pedantry, nor trivial!).

Can you now see, Dave, how an object may be (or may have been) classified by Arp as a "quasar", but may be classified as something else - a Seyfert galaxy perhaps - in published catalogues such as the SDSS DR1 one?

Interestingly, a topic mentioned in the abstract of Arp's 1970 paper has an echo in Schneider et al. (2003).

Arp: "Photographs show that the supposed quasi-stellar objects B264 and Ton 256 have apparent diameters of 6" and 9", respectively. Current definitions require these to be called compact galaxies." Section 2.2 of Schneider et al. (2003) - "Target Selection" can be read as addressing the 'quasar/compact galaxy' distinction (and the possibly biases it introduces, in terms of survey completeness).

[davesmith_au]

Let's look at ...

<snip obfuscation>

No, let's not.

You don't get to lead me around by the nose like a bull at the show.

Address the matters in my post.

If you cannot admit that you were obfuscating, trivializing and being pedantic when I have shown clear evidence that you have, then perhaps you would be more comfortable on a forum where such tactics are commonplace.

I trust I don't have to "define" every word of my above paragraphs to you, and that you will get the point.

Dave.

[Lloyd]

Nereid said: starbiter, the TPOD says "And yet the galaxy is opaque". However, the Galianni et al. paper it quotes as (the sole?) source, does not use the word "opaque" (nor "dust", "clouds" ("cloud" occurs just once), "bright triangular jet", "fat end", "disturbed", ...). As the TPOD is unsigned, we can have no clue as to whether its author (or at least one of its authors) is an EU theorist or a Thunberbolts Forum member. That makes it rather challenging to conclude anything firm about this object and this galaxy, with respect to the Hubble redshift-distance relationship as it applies to quasars from the EU perspective, wouldn't you say?

* Nereid, do you have reason to believe the image is not that of NGC 7319 and a quasar in front of it or within it? I haven't been able to find a name or number for the quasar, but it seems to be generally acknowledged that the blob in front of NGC 7319 has high redshift, as other quasars do. Do you need an official astronomer to tell you that the object is in front of or within the galaxy? Here's the image.

[davesmith_au]

*sound of crickets*



...



*sound of crickets*

[Nereid]

This is my sixth, and last permissible, post for today. I am responding to davesmith_au's post, rather than any other that contains direct questions to me, because I consider his posts the most important.

Introduction
My last post in the thread (date&time stamped Thu Jan 20, 2011 7:28 pm) was primarily a response to an earlier one by Solar, and a making-good of my promise:

It is not the case that I, Solar, have coined an "observational definition" of a Quasar, QSO, AGN etc - but that this (and many other terms quantified and qualified by their particulars) is what has been provided by those who work in that field. The same applies with the "citizen scientist" participating in the Galaxy Zoo project (yes, I have an account there as well). Their 'observational definition' of a Quasar is what the naming convention of the genre says it is.

Note that the original Galaxy Zoo used SDSS images, classifications, etc (those in DR6, I think).

It seems, though, that there might be a problem with the approach you outline (I'll read up on how the SDSS pipeline assigns "QSO" to objects which are given SDSS ObjIDs), when it comes to beginning to research the Hubble redshift-distance relationship as it applies to quasars, from the EU perspective.

It was also a partial response to an earlier one of davesmith_au's.

In not clearly identifying exactly what my post was (principally) in response to, I seem to have created a big misunderstanding Dave. The fault for creating that misunderstanding is entirely mine, and I apologise.

Dave's post, point by point (Note, I will take them somewhat out of order)

DUST, CLOUDS:

Pedantry. Again, when paraphrasing the paper for a general audience, such terms do not appear to be out of order.

BRIGHT TRIANGULAR JET, FAT END, DISTURBED:

Jet/Filament

"V" shaped jet

Couldn't the "top" or open part of the "V" be considered the "fat end"?

Also in Section 4.4 you will find "luminous connection" and "wake" in reference to the same feature, and throughout the paper the term "outflow" used extensively to describe the same feature (Section 4.2 once, Section 4.3 five times, and once in Section 7), and in Section 7 "V-shaped feature" appears twice.

The terms "disturbance" and "disrupted" appear in Sections 4.4 and 5.1 respectively, so what could possibly be your objection to the term "disturbed"?

In my post I put the terms "dust" etc in parentheses. My intended meaning was to emphasise the apparent lack of provinence, etc; as such they are entirely secondary and, in hindsight, I should not have included them (and would retract them if I could).

I suggest you read through the paper rather than search for terms used elsewhere, and see if you can come to an understanding of what the paper is getting at. Here's a hint:

We have clearly demonstrated that the ULX lying 8" from the nucleus of NGC 7319 is a high-redshift QSO. This is to be added to a list of more than 20 ULX candidates that have all turned out to be genuine QSOs (cf. Burbidge et al. 2003; Arp et al. 2004). Since all of these objects lie within a few arcminutes or less from the centers of these galaxies, the probability that any of them are QSOs at cosmological distance, observed through the disk of the galaxy, is negligibly small. Thus, this is further direct evidence that high-redshift QSOs are generated and ejected in low-redshift active galaxies. The case described here is particularly interesting, since there is a considerable amount of observational evidence that the QSO is interacting with the gas in the main body of the galaxy, although we have pointed out that there are difficulties in understanding it in detail.

Cheers, Dave.

What I am trying to do - apparently quite unsuccessfully so far - is to find out how EU theorists and Thunderbolts Forum members address the 'bolted in and can't be removed' Hubble redshift-distance relationship embedded in the contemporary definition of 'quasar', as the material on how quasars are classified in SDSS makes clear (see above; my original question: what (to EU theorists and Thunderbolts Forum members) is the (or an) observational definition of a 'quasar'?).

The Galianni et al. paper and, especially, conclusions are certainly interesting, and I would be more than happy to have a discussion on it (and them); however, my main interest is in learning what (to EU theorists and Thunderbolts Forum members) is the (or an) observational definition of a 'quasar' (assuming 'QSO' is an exact synonym, which it often is). In that regard, CXOU J223603.6+335825 (to give the object its name, per the Trinchieri et al. (2003) x-ray observations), meets the second SDSS criterion ("spectra contain at least one broad emission line (velocity FWHM larger than ~ 1000 km s−1)"), and would likely meet the first ("have a luminosity larger than Mi = −22.0 (calculated assuming an [] cosmology") if it were at a distance from us inferred from the Hubble relationship (and the stated cosmological parameters) ... but, per Galianni et al., it's not.

Firstly, let's look at some of the terms you hasten to point out that the "source" (of the TPOD) does not use.

OPAQUE:

As was pointed out by the referee, this anisotropy is expected if NGC 7319 is typical of a Seyfert 2 system with an obscuring torus, if we accept the unified model of AGNs that was developed following the discovery of an obscuring torus in NGC 1068 (Antonucci & Miller 1985).

There are no signs of background objects showing through the disk in our HST picture of the inner regions of NGC 7319 (Fig. 1).

Is it not reasonable to use the term "opaque" if paraphrasing the paper?

No, it is not.

In "the unified model of AGNs", obscuring tori subtend angles of ~milli-arcseconds, as seen from Earth; in fact in the Antonucci & Miller (1985) paper, the NGC 1068 dust torus is estimated to be ~10 milli-arcsec ("and this corresponds to an optically thick dust cloud of angular size ~10 milli-arcsec. This would not be in conflict with any other observation.")

The reasons why it is not reasonable to use the term opaque to paraphrase the Section 5 sentence are both interesting and rather technical. As it is you, Dave, who is asking about this, I shall explain them in my next posts to this forum. For now, consider Dwingeloo 1 (source: Loan et al. (1996)).

[Solar]

Let's look at how 'quasar' is defined, in SDSS; I'll work from Schneider et al. (2003) - "The Sloan Digital Sky Survey Quasar Catalog II. First Data Release" (link is to the arXiv preprint abstract).

First, though, I'll refresh our memories of one of Arp's papers, "Quasars near companion galaxies", published in 1981. In this paper Arp proposes a physical association (this is an oversimplification for the sake of brevity) between a number of large, bright galaxies ("main galaxies", in Table 1), some 'companion' galaxies, and some (34) quasars. The main galaxies have redshifts listed as from 95 to 5429 km/s (i.e. a z of 0.0003 to 0.0181); the companions from 147 to 21,300 km/s (0.0005 to 0.071); the quasars from 0.027 to 2.40. In this paper, Arp explicitly refers to a 1970 paper of his for the definition of quasar he uses in the 1981 paper; here it is:

The definition of a quasi-stellar object is clearly then: an object which appears stellar on photographs (diameter <1") and which has a large redshift (relative to normal stars in our own Galaxy).

Schneider et al. (2003) begins as follows:

Over the past two decades the number of quasars produced by an individual survey has increased by about two orders of magnitude. One of the most intensively studied quasar data sets, the Bright Quasar Survey of Schmidt & Green (1983), contains approximately 100 quasars. In the 1990s the Large Bright Quasar Survey (LBQS; Hewett, Foltz, & Chaffee 1995, 2001) presented more than 1,000 quasars, and recent results from the 2dF Quasar Survey (Croom et al. 2001) have pushed quasar survey sample sizes past the 10,000 object milestone.

The third paragraph begins as follows:

The catalog in the present paper consists of the 16,713 objects in the SDSS First Data Release (DR1; Abazajian et al. 2003) that have a luminosity larger than Mi = −22.0 (calculated assuming an H0 = 70 km s−1 Mpc−1, ΩM = 0.3, ΩΛ = 0.7 cosmology, which will be used throughout this paper), and whose SDSS spectra contain at least one broad emission line (velocity FWHM larger than ~ 1000 km s−1). The quasars range in redshift from 0.08 to 5.41, and 15,786 (94%) were discovered by the SDSS.

The start of the fourth para is: "The DR1 catalog does not include classes of Active Galactic Nuclei (AGN) such as Type II quasars and BL Lacertae objects".

There is a section (3.3) devoted to "Luminosity and Line Width Criteria"; it begins as follows:

Quasars have historically been defined as the high-luminosity branch of Active Galactic Nuclei (AGN); the (somewhat arbitrary) luminosity division between quasars and Seyfert galaxies has a consensus value of MB = −23 for an H0 = 50 km s−1 Mpc−1, ΩM = 1, ΩΛ = 0 cosmology (e.g., Schmidt and Green 1983).

There are, to state the blindly obvious, significant differences between the observational/operational definition of 'quasar' used in SDSS (or at least DR1) and what an EU theorist and/or Thunderbolts Forum member would use. For example, the luminosity criterion is surely meaningless (to EU theorists).

Thank you for your efforts with this Nereid - and thank you for understanding what may have been my somewhat confusingly expressed quandary with regard to the parameters used to identify/classify quasars. There is quite a bit in there what with assumptions and consensus concerning global cosmological parameters and all. Do I gather then that with the tighter constraints fed into the SDSS pipeline via algorithm(s) in conjunction with the 'definition' you've attributed to Arp that said 'definition' (at that time) may have been a bit broad in comparison to today's standards?

[Nereid]

The unreasonableness of "the galaxy is opaque", part I - too bright to see through

As promised, in this post I shall begin to address the question of whether it is "not reasonable to use the term "opaque" if paraphrasing the paper?" in reference to this sentence in the Galianni et al. (2005) paper: "There are no signs of background objects showing through the disk in our HST picture of the inner regions of NGC 7319 (Fig. 1)." I'll address this question in two parts, which I'll call 'too bright to see through' opaque, and 'obscuring dust' opaque; in this post I'll deal with the first.

Go out when the Sun is well and truly up, and nary a cloud is in the sky, and look in the direction of the Moon (assume it too is up in the sky, well away from the horizon, and not near the Sun). While pale, the Moon is clearly visible (OK, perhaps I should add the assumption that you're at at one of the places amateur astronomers really like, a 'dark site'; i.e. well away from smog, thick haze, etc).

Now look in the direction of Venus (assume that it too is ...). You may be lucky, and can just make it out; with the aid of a typical amateur astronomer's telescope, it should be fairly easy to see.

Repeat, for a bright star, Alpha Centuri, say, or Vega.

Repeat for a star that's about as faint as you could see, on a dark moonless night from this site.

And so on.

At some point, you'll fail; at some brightness, it will no longer be possible for you to see a star (of this brightness), even with the most powerful telescope (at wavelengths you can 'see' with your eyes, and with your eyes).

Is the daytime sky opaque because it's too bright to see through?

YMMV (your mileage may vary), but that's not how I use the word "opaque", and in fairness, neither does the author of the Oct 01, 2004 TPOD, per the first (of only two) times she uses that word: "The tiny white spot is a quasar either silhouetted in front of the opaque gas clouds or embedded in the topmost layers of the dust."

However, there's a more subtle aspect, to do with surface brightness, that's relevant to the Galianni et al. sentence; namely, that surface brightness is independent of distance (barring intervening absorption or a geometry of space that is not flat, Euclidean).

At first sight, this seems wrong; after all, surely the Sun as seen from Pluto, say, is fainter than as seen from Mercury!?

To our eyes, even with the aid of telescopes, the sky is flat, and even the Moon is so far away that we see no parallax; we can treat it as a 2D surface (for this exercise).

Further, we can 'resolve' the Sun; it's bigger than a point, so we could measure the brightness within a small bit of its surface, a square arcminute, say. If we were to travel to Mercury, or Venus, the Sun would be seen to have the same surface brightness; a square arcminute of its surface would be the same (OK, we need to be above any atmosphere; that's obviously 'intervening absorption'). However, at Pluto, the Sun would be smaller than an arcmin in diameter, so a square arcmin of sky, centered on the Sun, would include lots of not-Sun, and we'd have to switch to a smaller unit to see that surface brightness is independent of distance, a square arcsec perhaps.

Of course, our eyes can't resolve things as small as an arcsec, so we can't judge (measure) surface brightness below the resolution limit; we can only talk about apparent surface brightness.

Fast forward to NGC 7319, and an image of it.

If an object - whether foreground, ground, or background, there's no parallax - has an apparent surface brightness well below the apparent surface brightness of the disk, then we couldn't see it (in the image at least) ... you can often see Mercury, clearly, in the daytime sky, with a telescope, but you can't see it with your unaided eyes (DON'T TRY THIS BY YOURSELF, unless you an experienced amateur astronomer, or have one handy to help you!). CXOU J223603.6+335825's apparent surface brightness, in the Hubble image, is considerably greater than the apparent surface brightness of the NGC 7319 disk nearby, and there are several other objects in the image.

How did Galianni, the Burbidges, Arp, Junkkarinen, and Zibetti conclude that none of these 'elevated surface brightness objects' were background objects? From reading the paper itself, we don't know, because they didn't say.

(to be continued)

[flyingcloud]

sounds like the gas/dust cloud* is glowing quite brightly then

* dusty gas, or gassy dust

[flyingcloud]

Is the daytime sky opaque because it's too bright to see through?

wow, and actually yes would have to be the answer.
take away the atmosphere
do your same situation on the moon
the atmosphere is too opaque as it scatters light
that's why the sky is blue

[Nereid]

The unreasonableness of "the galaxy is opaque", part I - too bright to see through (continued)

There are two 'direct' images of NGC 7319, or part of it, in Galianni et al. (2005), Figures 1 and 4.

The captions read, respectively:
"Fig. 1. - Multicolor HST image of the central region of NGC 7319 showing the optical ULX candidate 8" south of the nucleus. (For orientation, the brightest stellar image at the right-hand edge of the picture is at the northwest edge of the figure.)"
and
"Fig. 4. - Enhanced HST image showing a filament or "wake" moving down from the center of NGC 7319 to within ~3".4 of the QSO. The orientation is the same as in Fig. 1. Processed photograph reproduced courtesy Coelum Astronomia (Italy)."

The two figures are referred to, in the text, in Section 2 ("In Figure 1 we show that there are only two optical objects in the field around the nucleus of NGC 7319. Both are to the south; one resembles a luminous gas cloud and the other appears to be stellar."), Section 4 ("In obtaining the spectrum, the candidate QSO was placed at the center of a 0".7 slit that was oriented at a position angle of P.A. = 205o on the sky (see Fig. 4)."), ("For ~8" along the slit we see the strongest emission lines fromthe galaxy (these regions are shown in Fig. 4)"), ("However, the major emission lines from NGC 7319 are found to be coming from the bright disklike region of the galaxy just south of the nucleus, as shown in Figures 1 and 4."), Section 4.1 ("This is about twice the extent of the galaxy emission lines in the red, and it indicates that the line comes from a different, larger region. In fact, it essentially samples the full extent of the inner disk as pictured in Figure 4."), Section 4.4 ("Figure 4 gives pictorial evidence in support of a model in which the QSO has been ejected from the nucleus of the Seyfert galaxy NGC 7319. It is seen that there is a luminous connection reaching from the nucleus ( just at the top of the picture frame) down in the direction of the ULX/QSO, stopping ~3" from it. It is also apparent that this connection or wake is bluer than the body of NGC 7319."), Section 5 ("There are no signs of background objects showing through the disk in our HST picture of the inner regions of NGC 7319 (Fig. 1)."), and Section 7 ("In Figures 2 and 4 we have independently seen the "V-shaped feature" of Aoki et al. (1999) and concluded that it represented a luminous extension or wake trailing the QSO."). Here is Aoki et al. (1999) (arXiv preprint abstract).

I have bolded the ones directly relevant to this post.

I have not yet been able to access the relevant issue of Coelum Astronomia, so I cannot really comment on Figure 4 (the right hand image in the Oct 01, 2004 Quasar in Front of Galaxy TPOD may be a processed version of this); the source of Figure 1 is given simply as "Multicolor HST". A bit of sleuthing turned up a set of 2001 Hubblesite images that seems to match that in the paper; oddly (to me anyway), Galianni et al. seem to have downloaded one of the JPEG for their image analysis. In 2009, another set of Hubblesite images of NGC 7319 became available. Comparing the two sets of JPEG images (from Hubblesite, 2001 and 2009), the effect of the resolution limit on the visibility of (and so number of) 'elevated surface brightness objects' is obvious; where Galianni et al. note only two optical objects in the field around the nucleus of NGC 7319, I can make out well over a dozen in the 2009 4894 X 5840 JPEG (the cameras used are WFPC2 and WFC3, respectively). Further, in the 2009 image there are plenty of signs of background objects showing through the disk (at least, to me there are)! I'll go over this point in more detail in the second part, where I comment on 'opaque, as in obscured by dust'.

In my last post, I wrote that "if an object - whether foreground, ground, or background, there's no parallax - has an apparent surface brightness well below the apparent surface brightness of the disk, then we couldn't see it (in the image at least)". There is, in fact, a way to 'see' such faint objects, at least in some cases. Consider, for example, the M87 optical jet. Here is an image of that jet, including parts that are well 'below' the brightness of the galaxy itself ... and there's no sign of the elliptical galaxy at all! Sparks et al. (1996) ("The Jet of M87 at Tenth-Arcsecond Resolution: Optical, Ultraviolet, and Radio Observations*") explain how; basically a digital model of the light from the galaxy is subtracted from the digital image from the HST (there's actually rather a lot more image processing involved, but that's the key step). In fact, amateur astronomers regularly use a similar technique to 'go deeper than the sky' (i.e. display, in a processed image, objects whose apparent surface brightness is much less than that of the sky).

If processing of this kind had been applied to the Galianni et al.'s Figure 1, would there be signs of background objects? By casual inspection of the 2009 WFC3 Hubble JPEG image, it's hard to conclude anything other than yes, there would be signs of background objects.

So, to conclude part I: in the case of the Figure 1 HST image of NGC 7319, it is unreasonable to conclude that the relevant part of the disk is too bright to see through.

Next: The unreasonableness of "the galaxy is opaque", part II - opaque gas clouds/dust.

[Nereid]

Is the daytime sky opaque because it's too bright to see through?

wow, and actually yes would have to be the answer.
take away the atmosphere
do your same situation on the moon
the atmosphere is too opaque as it scatters light
that's why the sky is blue

I'm going to break my promise, just this once ... because it's central to my post (the one flyingcloud quotes from).

Here, here, here, and here are webpages where amateur astronomers (mostly) discuss daytime observations, mostly of Mercury, but also of other objects.

The daytime sky is not opaque because it's too bright to see through ... and you, flyingcloud, can verify this for yourself, by following the advice in the above webpages (for example).

[solrey]

Not sure where you're going with this whole opacity fishing expidition. The atmosphere is too bright to see objects beyond the atmosphere that are less than a certain magnitude, because the atmosphere is opaque at many electromagnetic wavelengths.

Opacity

The words "opacity" and "opaque" are often used as colloquial terms for objects or media with the properties described above. However, there is also a specific, quantitative definition of "opacity", used in astronomy, plasma physics, and other fields, given here.

In this use, "opacity" is another term for the mass attenuation coefficient (or, depending on context, mass absorption coefficient, the difference is described here). κν at a particular frequency ν of electromagnetic radiation.

More specifically, if a beam of light with frequency ν travels through a medium with opacity κν and mass density ρ, both constant, then the intensity will be reduced with distance x according to the formula

When flyingcloud said
"the atmosphere is too opaque as it scatters light
that's why the sky is blue"

he was pretty much right. The atmosphere is opaque at certain wavelengths, including several in the visible band. Good thing it's opaque to x-ray's, eh?

cheers

[flyingcloud]

I will concede that the earth's atmosphere is not opaque to some visible frequencies
It is opaque to infrared just beyond visible on the side thats important
found that a bit curious