Are quasars signifigantly blue shifted?

[snp.gupta]

For example:



I'm afraid you are simply misunderstanding these references to blueshift. As the above quote makes clear, the so-called "blueshift" is only "with respect to the systemic redshift of the quasars." The so-called "blueshift" is relative to the quasar, not to earth. The C IV emission line is still measured to be redshifted, but just not as much as the other quasar lines. Why the discrepancy? "Wind" from the quasar. Think (solar wind)^100*.

________________
* This number qualitative only.

Authors Basu, D.; Haque-Copilah, S. & Valtonen, M., in their paper titled “Blueshifted Quasars Associated with Nearby Galaxies?” said in their abstract “…may appear quasar-like with a blueshifted spectrum due to the Doppler effect. But quasar spectra are as a rule interpreted as having been redshifted even when there is an equally good or better case for a blueshifted spectrum. Here we study the quasars which are apparently associated with galaxies.” In International Journal of Modern Physics A, Volume 15, Issue 07, pp. 1057-1077 (2000), with Bibliographic Code: 2000IJMPA..15.1057B.

Accordingly I am just checking this Quasar 3C273 for blue shift.

[snp.gupta]

It depends on the specifics. It's quite more complicated than just comparing cosmological and doppler shifting and thinking "it's moving towards me so doppler wins and i'll get a blueshift". It may be moving towards us and we'd still get a redshift, and it may even be moving away from us and we'd get a blueshift.

Can you please explain this further?

.... cosmological redshift by expanding space only works for objects moving with the hubble flow,

How to differentiate this cosmological redshift from local peculiar motion by looking at the quasar spectrum?

[antoniseb]

... How to differentiate this cosmological redshift from local peculiar motion by looking at the quasar spectrum?

We have observed quasars as the centers of galaxies, and those galaxies are in galactic clusters... so the confirmation is not just by looking at the isolated spectrum of one object, but by looking at that object in its context, and the spectra of its surroundings.

[caveman1917]

Can you please explain this further?

You may want to take a look at this paper.

[snp.gupta]

We have observed quasars as the centers of galaxies, and those galaxies are in galactic clusters... so the confirmation is not just by looking at the isolated spectrum of one object, but by looking at that object in its context, and the spectra of its surroundings.

Is such cluster is gravitationally bound? Will you consider gravitation at that distance or only Hubble flow? Any example possible? Will those galaxies in such cluster have uniform red shift and are physically near to each other?

[antoniseb]

Is such cluster is gravitationally bound? Will you consider gravitation at that distance or only Hubble flow? Any example possible? Will those galaxies in such cluster have uniform red shift and are physically near to each other?

Yes, red shifts within a few thousand kilometers per second as expected for elements of a grwvitationally bound system, and confined to a small part of our sky. Gravitational redshift for such a cluster is too small to be an important factor over such distances.

[snp.gupta]

You may want to take a look at this paper.

According to the authors Tamara M. Davis et al., as you have mentioned above in I. INTRODUCTION second para...

“the general expansion of the universe is known as the Hubble flow. A persistent confusion is that galaxies set up at rest with respect to us and then released will start to recede as they pick up the Hubble flow. This confusion mirrors the assumption that, without a force to hold them together, galaxies (and our bodies) would be stretched as the universe expands. The aim of this paper is to clarify the nature of the expansion of the universe, including recession velocities and cosmological redshifts, by looking at the effect of the expansion on objects that are not receding with the Hubble flow…...A small distant galaxy (considered to be a massless test particle) is tethered to an observer in a large galaxy….”

I feel that the general feeling persist in the present day in General relativistic physics is that there is only one force that is causing expansion probably that is dark energy which is totally unknown. The force that is holding the Galaxies together is Gravity, and it is NOT thought over here. Probably gravity is neglected altogether?

I did not understand how a small massless Galaxy was tied to another Galaxy...............

[Strange]

I feel that the general feeling persist in the present day in General relativistic physics is that there is only one force that is causing expansion probably that is dark energy

Dark energy doesn't cause expansion; it causes the acceleration of expansion.

The force that is holding the Galaxies together is Gravity, and it is NOT thought over here.

I don't understand that. Yes, gravity holds galaxies (and clusters) together. But what does "it is NOT thought over here" mean?

Probably gravity is neglected altogether?

No. Of course not.

I did not understand how a small massless Galaxy was tied to another Galaxy

What is a "massless galaxy"?

[snp.gupta]

[QUOTE=Strange;2050524]Dark energy doesn't cause expansion; it causes the acceleration of expansion.

Originally Posted by snp.gupta
I feel that the general feeling persist in the present day in General relativistic physics is that there is only one force that is causing expansion probably that is dark energy

Then what is the cause of expansion?

[primummobile]

[QUOTE=snp.gupta;2055794]

Dark energy doesn't cause expansion; it causes the acceleration of expansion.

Then what is the cause of expansion?

The Big Bang.

[snp.gupta]

[QUOTE=Strange;2050524]

1. I don't understand that. Yes, gravity holds galaxies (and clusters) together. But what does "it is NOT thought over here" mean?
2. What is a "massless galaxy"?

See the paper as quoted by caveman1917, from this I took the portion
http://arxiv.org/abs/astro-ph/0104349/
According to the authors Tamara M. Davis et al., as you have mentioned above in I. INTRODUCTION second para...

“the general expansion of the universe is known as the Hubble flow. A persistent confusion is that galaxies set up at rest with respect to us and then released will start to recede as they pick up the Hubble flow. This confusion mirrors the assumption that, without a force to hold them together, galaxies (and our bodies) would be stretched as the universe expands. The aim of this paper is to clarify the nature of the expansion of the universe, including recession velocities and cosmological redshifts, by looking at the effect of the expansion on objects that are not receding with the Hubble flow…...A small distant galaxy (considered to be a massless test particle) is tethered to an observer in a large galaxy….”

Please see the bolded portions in that paper, I also did not understand, that’s why I asked…

[snp.gupta]

[QUOTE=primummobile;2055796]

Originally Posted by Strange
Dark energy doesn't cause expansion; it causes the acceleration of expansion.

Then what is the cause of expansion?

The Big Bang.

That is an eternal force , is that so? These is no cause for that?

[snp.gupta]

I want to know wave lengths for

Si III]+C III]
Si IV
O IV]
C IV
Al III
Si III]
C III]
Si III]+C III]
Mg II

etc., Where to get them? Can somebody help me?

(These are some of the wavelengths used in red shift determination.)

[antoniseb]

... Where to get them? Can somebody help me?...

Try here:
http://physics.nist.gov/PhysRefData/...lineshelp.html

[primummobile]

[QUOTE=snp.gupta;2055802]

That is an eternal force , is that so? These is no cause for that?

I don't understand your question. The Big Bang isn't a force. It is an event. That's what started the expansion. The cause of the Big Bang is a huge mystery and one we probably can't answer.

[ngc3314]

Here's a line list I got once from Paul Green at the Center for Astrophysics, with lines important in quasars and other active galactic nuclei.

Keep in mind that finding redshifts is more than matching a raw list of wavelengths - some of the ratios of line intensities are consistent between objects, and there are also consistent patterns in line widths (so-called forbidden lines are never as broad as the permitted Balmer, Lyman... lines can be in quasars). This plot shows the spectrum of a Seyfert nucleus with both broad and narrow components to show the distinctions. Lines labelled "abs" appear in absorption either from stars on the host galaxy or due to absorption in its interstellar medium. Some of these listings are actually close doublets which are normally blended in the spectra of these objects ([O II], C IV, Mg II, for example). I added a couple of He II ones that were initially missing.


Line Emitted wavelength (Angstroms)
LyB/OVI 1029.80
Lya 1215.70
NV 1240.10
OI 1305.60
SiIV/OIV 1399.50
CIV 1549.10
He II 1640
CIII 1908.70
CII 2326.60
MgII 2798.70
NeV 3425.90
OII3727 3726.60
NeIII+Heps 3868.80
CaK abs 3933.70
NeIII 3967.50
CaH abs 3968.50
Hdel 4101.70
Gband abs 4304.40
Hgam 4340.50
Fe4570 4570.00
He II 4686
Hbeta 4861.30
OIII4959 4958.90
OIII5007 5006.90
Mg abs 5175.40
CaFe abs 5268.90
Na abs 5892.50
OI 6363.80
NII 6548.10
Ha 6562.80
NII 6583.40
SII 6716.40
SII 6730.80
OII 7319.90
OII 7330.20

[snp.gupta]

Here's a line list I got once from Paul Green at the Center for Astrophysics, with lines important in quasars and other active galactic nuclei.

Keep in mind that finding redshifts is more than matching a raw list of wavelengths - some of the ratios of line intensities are consistent between objects, and there are also consistent patterns in line widths (so-called forbidden lines are never as broad as the permitted Balmer, Lyman... lines can be in quasars). This plot shows the spectrum of a Seyfert nucleus with both broad and narrow components to show the distinctions. Lines labelled "abs" appear in absorption either from stars on the host galaxy or due to absorption in its interstellar medium. Some of these listings are actually close doublets which are normally blended in the spectra of these objects ([O II], C IV, Mg II, for example). I added a couple of He II ones that were initially missing.


Line Emitted wavelength (Angstroms)
LyB/OVI 1029.80
Lya 1215.70
NV 1240.10
OI 1305.60
SiIV/OIV 1399.50
CIV 1549.10
He II 1640
CIII 1908.70
CII 2326.60
MgII 2798.70
NeV 3425.90
OII3727 3726.60
NeIII+Heps 3868.80
CaK abs 3933.70
NeIII 3967.50
CaH abs 3968.50
Hdel 4101.70
Gband abs 4304.40
Hgam 4340.50
Fe4570 4570.00
He II 4686
Hbeta 4861.30
OIII4959 4958.90
OIII5007 5006.90
Mg abs 5175.40
CaFe abs 5268.90
Na abs 5892.50
OI 6363.80
NII 6548.10
Ha 6562.80
NII 6583.40
SII 6716.40
SII 6730.80
OII 7319.90
OII 7330.20

Thank you , you may have to help me a little more...

This list I also got see:

http://www.sdss.org/dr7/algorithms/speclinefits.html

I want to know the values

Si III]+C III]
Si IV
O IV]
C IV
Al III
Si III]
C III]
Si III]+C III]
Mg II

What is the meaning of ']' at the end of C III for example....?

[snp.gupta]

Try here:
http://physics.nist.gov/PhysRefData/...lineshelp.html

Thank you sir, But i need your help a little more....

[ngc3314]

Thank you , you may have to help me a little more...

This list I also got see:

http://www.sdss.org/dr7/algorithms/speclinefits.html

I want to know the values

Si III]+C III]
Si IV
O IV]
C IV
Al III
Si III]
C III]
Si III]+C III]
Mg II

I gave some of those:
SiIV/OIV 1399.50 (about 3 A apart, so close that they are blended at quasar line widths)
CIV 1549.10
CIII 1908.70
CII 2326.60
MgII 2798.70

The strengths of these lines vary greatly - except for quasars with strong absorption troughs, Lyman alpha, C IV, He II, C III], and Mg II are strong, and these other lines listed in the emitted UV are an order of magnitude or more weaker than these.

As best I can tell which lines are in emission, the others are
Si III] 1892 (often blended with much stronger C III])
Al III 1857 (as in the SDSS list)

It sometimes matters that some sources quote wavelengths longer than 2000 A in the "air" convention, almost everyone gives wavelengths shorter than that in vacuum, and SDSS and HST data use vacuum wavelengths consistently. This can make a ~2 A difference. Each observer will be consistent in doing the comparison, folding in vacuum or air wavelengths in their data calibration, but care may be needed in going from one set of published wavelength measures to another unless they specify which convention applies to what data.

What is the meaning of ']' at the end of C III for example....?

There is a classical spectroscopic notation distinguishing so-called permitted and forbidden lines. Permitted lines come from decays of excited states that are very rapid (in the quantum analysis, proceed as electric dipole transitions) so they still appear at very high densities when collisions among electrons and ions are frequent. The best-known of these are the hydrogen Balmer and Lyman series. Then there are forbidden lines, denoted by [] - these have much longer decay lifetimes (happening as electric quadrupole or magnetic dipole transitions), so they are observable only at such low densities that collisions don't change the ion's state before it radiates. Famous examples are [O II]. [O III], and so on. There are a few ions which have transitions whose radiative lifetimes are between typical permitted and forbidden lines; these are called semiforbidden and denoted with a single bracket ]. Some lists get sloppy about including the brackets, which is no help at all.

[snp.gupta]

I gave some of those:
SiIV/OIV 1399.50 (about 3 A apart, so close that they are blended at quasar line widths)
CIV 1549.10
CIII 1908.70
CII 2326.60
MgII 2798.70

Thank you once again.
So these are left with me to find wave lengths...

Si IV
O IV]
C III]
Si III]+C III]

How to get them?

[snp.gupta]

..........
As best I can tell which lines are in emission, the others are
Si III] 1892 (often blended with much stronger C III])
..........

Is Si III]+C III] same as Si III], you mean?

What is the difference between them?

[snp.gupta]

.....
CIII 1908.70
.....

Will this CIII is same as CIII] ? What is the difference?

[snp.gupta]

It sometimes matters that some sources quote wavelengths longer than 2000 A in the "air" convention, almost everyone gives wavelengths shorter than that in vacuum, and SDSS and HST data use vacuum wavelengths consistently. This can make a ~2 A difference. Each observer will be consistent in doing the comparison, folding in vacuum or air wavelengths in their data calibration, but care may be needed in going from one set of published wavelength measures to another unless they specify which convention applies to what data.

Dear ngc3314,

Thank you for explaining lots of questions, but I got some more questions...

You mean your wave lengths will be consistent with SDSS data with ~2 A diff...

[snp.gupta]

... Then there are forbidden lines, denoted by [] - these have much longer decay lifetimes (happening as electric quadrupole or magnetic dipole transitions), so they are observable only at such low densities that collisions don't change the ion's state before it radiates. Famous examples are [O II]. [O III], and so on....

What are actually forbidden lines?

[snp.gupta]

.... There are a few ions which have transitions whose radiative lifetimes are between typical permitted and forbidden lines; these are called semiforbidden and denoted with a single bracket ]. Some lists get sloppy about including the brackets, which is no help at all.

You mean the wave length of emission line with a single bracket ']' is almost same as without?

[Shaula]

What are actually forbidden lines?

http://en.wikipedia.org/wiki/Forbidden_mechanism

Semi-forbidden transitions (resulting in so-called intercombination lines) are electric dipole (E1) transitions for which the selection rule that the spin does not change is violated. This is a result of the failure of LS coupling.

From http://en.wikipedia.org/wiki/Selection_rule

You mean the wave length of emission line with a single bracket ']' is almost same as without?

So no, they refer to different transitions. NGC3314 was talking about lifetimes, or probabilities of occurrence.

[snp.gupta]

http://en.wikipedia.org/wiki/Forbidden_mechanism


From http://en.wikipedia.org/wiki/Selection_rule

Thank you Shaula ...
I checked wiki, found the following values:
Forbidden lines of nitrogen ([N II] at 654.8 and 658.4 nm), sulfur ([S II] at 671.6 and 673.1 nm), and oxygen ([O II] at 372.7 nm, and [O III] at 495.9 and 500.7 nm)

So no, they refer to different transitions. NGC3314 was talking about lifetimes, or probabilities of occurrence.

But still how to get semi forbidden line values

[Shaula]

But still how to get semi forbidden line values

I'd suggest getting the NIST handbook or something like that if you are serious about studying this. Googling NIST spectra will give you access to a DB of spectral lines. It classifies them and gives wavelengths, so you just have to work out the one you are interested in and there you have it.

[ngc3314]

You mean the wave length of emission line with a single bracket ']' is almost same as without?

A transition has a particular decay timescale. Depending on that timescale, which is connected to its decay mode, we describe a transition as permitted, semiforbidden, or forbidden. There are no individual transitions which are more than one. Each transition has a wavelength. Not all listings online are consistent about the brackets. Similarly, one may find wavelengths >2000 A listed in various sources as either air or vacuum wavelengths, and care is needed to make sure which is which if one compares wavelengths between various sources.

[snp.gupta]

A transition has a particular decay timescale. Depending on that timescale, which is connected to its decay mode, we describe a transition as permitted, semiforbidden, or forbidden. There are no individual transitions which are more than one. Each transition has a wavelength. Not all listings online are consistent about the brackets. Similarly, one may find wavelengths >2000 A listed in various sources as either air or vacuum wavelengths, and care is needed to make sure which is which if one compares wavelengths between various sources.

Yes that's true.