Is Hanny's Voorwerp voor the wrong werp?
Eric Flesch
I think this posting at least comes close to contravening this newsgroup's
charter's principle that
> * Controversial topics and issues in research can be addressed,
> provided that they are discussed with scientific rigor and
> rationale; `because I say so' speculations will be redirected to
> sci.astro.
However, I'm approving this posting in the interests of (possibly)
sparking interesting discussions. I'd like to ask anyone responding
to please avoid "because I say so" arguments, and instead explain *why*
what you're saying (ok, writing) is true.
-- jt]]
A new preprint is out, arxiv.org/abs/0906.5304v1 , which treats an
interesting new object ("Hanny's Voorwerp") which is visible only in
green (!). This is because it is a highly ionized gas emitting
primarily in O III. The object is at the redshift z=0.05 of the
nearby galaxy IC2497, and looks much like a south-facing spider. The
authors conclude that the ionization is from a quasar at the heart of
the galaxy which has (the authors claim) switched off a mere ~20,000
years ago.
[[Mod. note -- The authors actually refer to the timesacle as
(in latex notation) $\sim 10^5$ years, i.e., on the order of 100,000
years with an implication of a factor of perhaps 3 to 10 uncertainty.
-- jt]]
For all 20 of the the learned authors of this article to arrive at
this conclusion is remarkable, considering there is an obvious
alternative. Firstly, the negative point: the very idea that this
quasar has switched off so crisply that (as the paper presents) the
galaxy's own gaseous shell is no longer ionized, but this nearby
object is still strongly ionized, is absurd. Need I go into the
fortuitous-time arguments, etc, of course I don't.
The positive point is that there is an obvious source of the ionized
gas: the "knot" (see section 3.1) at the SW end. To draw a quick
picture, Hanny's Voorwerp looks like a spider, and at the rear tip of
the abdomen there is an object with different qualities -- it is
bright in i and r, and not in g. The authors basically dismiss it as
a background contaminant -- they did not take a spectrum of it, but
did take spectra of 4 segments of the Voorwerp. using a continuous
slit which points to IC2497. Figure 4 shows the sections covered by
each segment. Apart from the assumption inherent in positioning the
slit thusly, we can critique the authors' conclusions as follows:
The authors map the four segments in three ionization regimes in
figure 10, and write in section 8 that they show "the trend to
increasing ionization with greater distance from IC 2497 is clearly
seen in the data for the Voorwerp". But figure 10 does not show this
at all -- rather, the ionization is just a function of whether the
segment is superposed entirely onto the Voorwerp (as the central 2
segments do), or if background glare is included (for segments 1 and
4).
The failure to take a spectrum of the "knot" is a decisive omission.
The shape of the Voorwerp suggests that the object has oozed out the
the "knot" at its tail. The myterious blank disk (around which the
southward front legs circle) is strongly suggestive of a gravitational
scalar, or highland, which the Voorwerp's gas goes around; indeed, the
article states that the radial velocity of the gas is highest at the
edges of the blank disk (figure 9).
So, in my view, the authors should rework the paper to treat equally
the idea that the "knot" is the origin of the Voorwerp, and should get
a spectrum of it, and run a spectrum slit from the knot as they did
for the galaxy. The knot may in fact be the most interesting and
mysterious object in the picture.
Eric Flesch
Pawel Karwowski
which I think, relates strongly to the publication you are reffering
to
and to your remarks:
"Why have corresponding blueshifted emission lines never been
reported, from
approaching jets? They may be difficult to detect: The knots and heads
of
the (relativistic!) jets are expected to emit their synchrotron
radiation strongly
in forward directions, whereas their (slowlymoving) channel-wall
material should
radiate almost isotropically."
The autor of this paper is prof. Wolfgang Kundt of Argelander
Institute for
Astronomy of Bonn University.
Pawel Karwowski
Jonathan Thornburg [remove -animal to reply]
Schawinski et al,
"The Sudden Death of the Nearest Quasar"
http://arxiv.org/abs/1011.0427
ApJ Letters 724, 30
http://dx.doi.org/10.1088/2041-8205/724/1/L30
Abstract:
Galaxy formation is significantly modulated by energy output from
supermassive black holes at the centers of galaxies which grow in
highly efficient luminous quasar phases. The timescale on which
black holes transition into and out of such phases is, however,
unknown. We present the first measurement of the shutdown timescale
for an individual quasar using X-ray observations of the nearby
galaxy IC 2497, which hosted a luminous quasar no more than 70,000
years ago that is still seen as a light echo in `Hanny's Voorwerp',
but whose present-day radiative output is lower by at least 2 and
more likely by over 4 orders of magnitude. This extremely rapid
shutdown provides new insights into the physics of accretion in
supermassive black holes, and may signal a transition of the accretion
disk to a radiatively inefficient state.
The authors combine archival infrared data and newly acquired Suzaku
and XMM-Newton X-ray observations and argue that Hanny's Vorwerp is
indeed a light-echo of IC 2497 when it was an active quasar within
the last 70,000 years. (IC 2497 currently shows signs of low-luminosity
AGN activity in HST and VLBI radio imaging.)
ciao,
--
-- "Jonathan Thornburg [remove -animal to reply]" <jth...@astro.indiana-zebra.edu>
Dept of Astronomy, Indiana University, Bloomington, Indiana, USA
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam
Eric Flesch
>There's an interesting preprint/paper out,
> http://arxiv.org/abs/1011.0427
As I wrote last year, this "fortuitous time" sort of argument is
absurd. If that's the best we can do, then we are not very good. As
high as is my regard for the authors, so am I disappointed that such a
long line of them sign up to this proposition.
The shape of the Voorwerp is that of plasma flowing around contours --
the velocity profiles of the ionized gas support that . Those
contours, if they be such, show an extra large dimension rippling into
our own. And this suggests that the ionizing source stems from there
-- seen through a warp. The Voorwerp would thus be "voor a warp".
Well-developed models like Kaluza-Klein provide for extra dimensions,
so why is it so neglected in the current literature? I expect it is
because the flat manifold required by the standard model excludes it.
Thus this "fortuitous time" argument is the best we can do with
Hanny's Voorwerp when our hands are tied by the standard model.
Can we untie our hands?
Eric
Eric Flesch
publication on the question of Hanny's Voorwerp; it is arXiv:
1101.2784, titled "a nuclear starburst in IC2497".
The approach taken by this new paper is that there is a low-level AGN
in IC2497 which has a starburst shell around it -- this shell would be
opaque from our line of sight. In this way, the AGN can cause the
ionization seen in Hanny's Voorwerp (along its view along the minor
axis) whilst being shielded to our view. This seems quite a
reasonable scenario, and I think it a big improvement over the
previous scenario that I criticized here.
Eric Flesch