In the thread "Plasma redshift, coronal heating, QSOs, CMB, DM halos
etc." I wrote about the Transverse Proximity Effect (TPE) with a
foreground quasar. Steve Willner (May 14) suggested that dust
obscuration and beaming may explain the lack of the expected effect.
Here is my response. For a fuller account of the failure to find the
TPE with a foreground quasar, please refer to:
http://astroneu.com/plasma-redshift-1/#TPE
In the intial thread, I wrote:
The TPE effect is expected according to Big Bang cosmology - the
foreground quasar is believed to lie close to the sightline to a
background quasar and the foreground quasar is predicted to
ionize all neutral H in its vicinity, which should result in an
absence of Lyman alpha absorption in the spectrum of the
background quasar at a wavelength corresponding to the redshift
of the foreground quasar.
1 - The foreground quasar turns on and off - and was off
at the time it would have had to be on to ionize the
neutral H in the sightline to the background quasar.
2 - The foreground quasar's light (UV at least) is beamed
towards us and does not affect the sightline to the
background quasar.
3 - The foreground quasar is surrounded by a cloud which
prevents its light from ionizing the neutral H in the
sightline to the background quasar.
However, a simpler explanation is that the redshift of light
from these quasars happens primarily near them (due to plasma
redshift or some other such process) so firstly the quasars are
closer than usually assumed and secondly the redshift along the
sightline doesn't happen in a linear or easily predictable
fashion. In this explanation, we have no clear idea of the
distances to the quasars. Maybe the so-called "background"
quasar, the one with the higher redshift, is closer than the
lower redshift quasar, but has more of its total redshift
occurring in the region close to it.
Steve Willner wrote:
I haven't studied this in detail, although I did look at the thesis
cited above. I'll just offer a couple of comments.
a) It doesn't take very much dust to absorb all the ionizing photons.
b) In the usual QSO model, the active nucleus is surrounded by a dusty
torus.
c) Optical searches will preferentially select QSO's where the torus
is pole-on to our line of sight and thus edge-on where the line of
sight to a background QSO passes nearest the foreground QSO.
I suspect the issue could be settled by a combination of infrared
observations to detect the dusty toruses and using hard X-ray
selection to pick unbiased samples. Maybe that has already been done
-- as I say, I didn't look very hard -- but I didn't see any treatment
of these issues at first glance.
Of the three papers I cited - Rupert Croft's, Michael Schirber's thesis
and his paper with two other researchers:
http://arxiv.org/abs/astro-ph/0310890 (Rupert Croft)
http://arxiv.org/abs/astro-ph/0307563
http://www.physics.ohio-state.edu/~astro/thesis.pdf
I recall that the strongest rejection of beaming is in Croft's paper.
Here are some quotes:
(p17)
Comparing to the SDSS results in Figure 13 it does not seem that
the lack of a proximity effect in that data can be due to the
beaming from an angle close to that we have used here (90 degree
cone angle). Reproducing Figure 13 with beaming alone would
require a much smaller angle.
(p18, discussing his modelling attempts to reproduce the lack of TPE.)
The anisotropy of quasar emission was investigated in our
simulations using a half-opening angle of 45 degrees. This did
have a noticeable effect on the absorption plotted in the sigma
- pi plane, with shadowing evident of regions at greater angles
from the sightline. The extra absorption in these regions did not
lead to much difference in the angle-averaged mean absorption
around quasars though, and in order to reproduce the observed
results, a very small opening angle would appear to be required.
For example, in the observational sample, there are 5 sightlines
with an impact parameters between 2.5 to 5 h^-1MPc, and these show
no evidence of a proximity effect. The excess absorption over the
mean seen close to quasars is evident out to 10 h^-1MPc, which means
that a maximum half opening angle of ~ 15 degrees is required. As
also calculated by Schirber and Miralda-Escude (2003), this seems
too small to be consistent with expectations of quasar emission.
So they estimate that in order to explain the observations with beaming,
beams of UV ionizing radiation only 30 degrees wide would be needed.
The abstract and the paper itself ends with a discussion of quasars
turning on and off.
Variability of quasars in bursts with timescales 10^4years and
10^6 years could reconcile these two facts.
From Micheal Schirber et al's paper, page 19:
A beam radius as small as 20 degrees for the QSO radiation seems
implausible. In unified models of AGN, the continuum ionizing
radiation is supposed to come from the accretion disk, which may be
absorbed by an obscuring torus near the equator, but typical
half-opening angles are ~ 30 - 45 degrees (Antonucci 1993;
Schmitt etal 2001), and they are thought to increase with luminosity
(Rudge & Raine 2000). A separate possibility is that the QSO has not
ionized the gas in its host halo, and that the ionizing radiation is
able to escape only along a narrow tunnel among clouds. However, the
fact that most QSOs of luminosity similar to the foreground one in
pair 1 do not exhibit intrinsic Lyman limit absorption in their
spectrum implies that this explanation could not account for a narrow
beam of emission in most QSOs.
To summarize, beaming of the ionizing radiation might be one of the
reasons for the absence of the transverse proximity effect in our
three pairs, but if this absence is generally confirmed on a larger
sample of pairs, then beaming alone cannot be the sole explanation.
I just used Google and AdsAbs to search for any references to the
"transverse proximity effect" since I last looked. It seems that the
recent papers are generally based on the notion that this lack of TPE
indicates that quasar lifetimes and/or variablitity. Their focus on
lifetimes is clear in their title, or in the quoted text:
Multiepoch Sky Surveys and the Lifetime of Quasars
Paul Martini, Donald P. Schneider 2003 Sep 23 (ApJ 597 L109-L112)
http://arxiv.org/abs/astro-ph/0309650
Calibrating the Galaxy Halo - Black Hole Relation Based on the
Clustering of Quasars
Stuart Wyithe, Abraham Loeb 2004 Mar 31 (Submitted to ApJ.)
http://arxiv.org/abs/astro-ph/0403714
Preliminary results suggested quasar lifetimes of tq ∼ 10^6 −
10^7 years, consistent with the values determined by other
methods (see Martini 2003 for a review), including the
transverse proximity effect (Jakobsen et al. 2003) . . .
QSO Lifetimes
Paul Martini 2003 Apr 1
http://arxiv.org/abs/astro-ph/0304009
Measuring the Radiative Histories of QSOs with the Transverse
Proximity Effect
Kurt L. Adelberger 2004 May 25 (Accepted ApJ.)
http://arxiv.org/abs/astro-ph/0405505
I found only one new paper mentioning the TPE which doesn't seem to be
following the path of quasar variability or limited lifetimes:
The Mysterious Absence of Neutral Hydrogen within One Mpc of a
Luminous Quasar at Redshift 2.168
Paul J. Francis, Joss Bland-Hawthorn 2004 May 25 (Accepted MNRAS.)
http://arxiv.org/abs/astro-ph/0405506
We showed in 4.1 that if the region surrounding PKS 0424-131 were
typical, we should have expected to have seen the fluorescent Ly
alpha emission from a considerable number of clouds. We should also
have seen internally ionised clouds. Instead, we saw nothing.
Since the quasar-quasar TPE researchers do not seem to contemplate the
possibility that the quasar distances are other than that conventionally
predicted by a Doppler interpretation of their redshift, they have to
choose between the quasar turning on and off, beaming, and dust
obscuration. It seems that in general they have ruled out the latter
two, and so are going with the first - though there are many objections
to that as well.
- Robin
http://astroneu.com