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Unformatted text preview: 1/15/12 Galaxies and the Universe - Alternate Approaches and the Redshift Controv A A R (T B C J M F !) AGN
) ( , .T Q SO (
Cont rov ersies, I
Science), H , .T
(Quasars, Redshif t s, and
Seeing Red: Redshif t s, Cosmolog and Academic ,
. T AGN
A (1967 A J 146, 321)
). Q SO .S
( - , ,A 1981 A J 250, 31 T
Q SO Q SO ?T
, , Q SO . F
1971 A J 170, 233). T
NGC 3067/3C 232, NGC 4651/3C 275.1, NGC 4138/3C 268.4,
5832/3C 309.1. B
" - Q SO
S Q SO - ,
.A Q SO , ... ,
I Q SO .
, , .W
" - ' " . As s ociation of gala ie s at dis parate re ds hifts . T
.N , ad hoc
NGC 4319/M 205, Ste phan's Quinte t
c = 5700 - 6700
www.astr.ua.edu/keel/galaxies/arp.html S 'Q , NGC 7603.
NGC 7320 800 /,
1/7 1/15/12 Galaxies and the Universe - Alternate Approaches and the Redshift Controv that of the bright spiral NGC 7331 only abour 1/2 away. NGC 7320 is of larger angular size than the other
members, but only less than a factor 2. NGC 7320 shows a low- surface- brightness tail approximately opposite
the other group members. Detection of even fainter structure is thwarted by especially strong galactic "cirrus"
reflection in this area. Sizes of H II regions have been used to argue for various distances, but as Kennicutt has
shown, linear sizes are unreliable distance indicators. The distribution of H II regions has been considered (Arp
1966 ApJ) as evidence for interaction with the other members, but Hodge showed in a later set of papers that
the brightest H II regions in pairs do not necessarily occur between the galaxies in question. Supernovae and
velocity dispersions are consistent with the redshift distances for the higher- redshift members. A crucial test
would be direct resolution into stars, unless one is willing to invoke some magical mechanism by which the stars
are all made faint in galaxies of anomalous systems so that the galaxies will be completely indistinguishable from
much more distant ones. This has probably been resolved (literally) by HST imaging, such as the WFPC2
mosaic released by ESA and reproduced below, in which the magnitudes of brightest stars are clearly quite
different in NGC 7320 and the other members. M a ka ian 205 was reported by Weedman as a Seyfert nucleus appearing within the arms of the lower- redshift
spiral galaxy NGC 4319. Most of the argument here has centered on whether or not there is a visible connection
between the two. Pictures were published with and without a bridge (Arp once said that he had pictures that
showed no bridge as well, and didn't want to be thought lacking in observational skill). There was some early
discussion of photographic proximity effects creating false bridges between bright objects, but it doesn't go away
with linear detectors. Various reports were given by Arp 1971 (ApLett 9,1), Lynds and Millikan 1972 (ApJLett
176, L5), Stockton et al 1979 (ApJ 231, 673), and Sulentic 1983 (ApJLett 265, L49). Cecil and Stockton
(1985 ApJ 288, 201) used CCD data from Mauna Kea to show that there is definitely some kind of luminous
object between Mkn 205 and NGC 4319, stating that "Arp was correct in his insistence that his broad- band
plates showed luminous intervening material. The opposite conclusions of his critics were - depending on their
degree of qualification - either wrong, misleading, or irrelevant." They go on to say that Mkn 205 itself has a
companion 3.3 arcseconds away, and that a tidal feature attributable to hi interaction probably accounts for
much of the luminous connection. More problematic is the evidence that this connection winds its way all the way
into the nucleus of NGC 4319 (Sulentic 1983). Furthermore, it belongs to the very select set of galaxies with
peculiar, nonstellar ionization of gas throughout the disk (Sulentic and Arp 1987 ApJ 319, 693). I must point out
www.astr.ua.edu/keel/galaxies/arp.html 2/7 1/15/12 Galaxies and the Universe - Alternate Approaches and the Redshift Controv NGC 4319
) H ( H , . NGC 7603
NGC 7603 S .
8700 U , / 17,000 / . S
(1986 A J 302, 245)
. - T ; . 86
VV172. Quas ar-Gala A' Statis tics . T .O
.F ?A , , ?
A U- B ,
( 259, L1)
H Q SO . T
), V K 1982 (A JL :
, A' , - Q SO .A
139, 240). R
", " , .V
1979 A J 229, 496) BAL QSO (B www.astr.ua.edu/keel/galaxies/arp.html , 107.
NGC 3842 (A
. 1996 AJ 112, 2533) G
BL L X- NGC
3/7 1/15/12 Galaxies and the Universe - Alternate Approaches and the Redshift Controv =0.40,0.65 on either side of NGC 4258 (Burbidge 1995 A&A 298, l1; neither of these last two citations is to
the obvious Burbidge). However, the solution of this issue must rest on quantifiable statistics for which it is clear
that large areas of sky with and without bright galaxies have been searched. Arp and Hazard have examined a
few "blank fields" and report interesting structure in the quasar distribution even there. With recent evidence on
large- scale structure in galaxies, perhaps we are falling victim to a facile assumption that the quasar distribution is
much more uniform at moderate redshifts =1- 2 than it really is. Note also that there is a minor literature now on
gravitational- lensing explanations, as to whether objects in galaxy halos can reasonably account for an excess of
the claimed magnitude - see for example Canizares 1981 (Nature 291, 620). Archival variability studies show
that in every case we can check the quasar was there at the turn of the century (Keel 1982) so that this is not
due to lensing by low- mass objects; proper motions would destroy the necessary precise alignment in a few
decades. If Arp's objects turn out to represent a strong excess, there does not appear to be enough mass density
in typical galaxies to do all of it via microlensing (as shown as well for QSOs in the directions of clusters by
Rodrigues- Williams & Hogan 1994 AJ 107, 451). Statistics continue to improve on this issue (see, for example,
the somewhat puzzling results by Thomas et al. 1995 MNRAS 273, 1069, maybe attributable to lensing and
then again maybe not). For some examples of the pairings under discussion, here are two QSO/galaxy pairs from
ESO 3.6m data:
Non-ve locit re ds hifts in gala ie s . There are certain peculiarities, claimed or accepted, that suggest either
strange behavior of redshifts or that we don't know how to measure them as well as we think. These take the
forms of an inescapable asymmetry in redshifts of binary galaxies, and claims that such redshift differences are
quantized and completely disallow a dynamical interpretation.
Re ds hift as mme trie s are found in almost all samples of paired galaxies with precise redshifts, especially
where spirals are involved. The tendency is for the fainter galaxy to have a slightly larger redshift, with a peak in
the distribution at 50- 80 km/s. The form of the distribution suggests that this is independent of background
contamination. Conventional explanations have focussed on problem in measuring redshifts of dusty rotating
disks (for example, if dust is stronger on the inside or outside of arms, the nuclear velocity may be distorted) or,
for small groups, on expansion and perspective effects in unbound groupings (Byrd and Valtonen 1985 APJ
289, 535; 1986 ApJ 303, 523). This problem is not directly related to AGN, but letting one camel's nose into
the Hubble tent might weaken its defenses for other applications. Detailed study of how one measures redshifts
from optical spectra in complicated velocity fields shows that some of this effect comes from the different
weightings of continuum and emission- line radiation (Keel 1996 ApJS 106, 27).
Tifft has claimed that redshift differences in galaxy pairs are quanti e d, with intervals from 12- 72 km/s
depending on sample size (Tiffy 1982 ApJ 257, 442; 257, 442, for example). Such an effect must nullify velocity
Doppler shifts since, under conventional dynamics, they would smear out any other fine structure in the velocity
distribution into invisibility. These distributions have naturally been the subject of vigorous (that's the polite word)
debate. There have been claims that such periodicity could not be found from samples of the sizes used
(Newman et al 1989 ApJ 344, 111), and possibly most damaging, the finding that though different data sets
show similar V distributions, a single pair may move from one peak to another depending on the particular
measurement (Sharp, Trieste proceedings 1985). This last would imply that the periodicities exist in the data but
not in the sky, a depressing though for people who want to do precise redshift surveys. Most recently, Tifft has
concentrated on 21 cm redshifts, identifying several previously ignored sources of low- level error. However,
there is a limit to how precisely one can consider some moment of an H I profile as representing "the" galaxy
redshift - just look at a 21 cm map of M101, for example. The issue then is not one of how precise and
www.astr.ua.edu/keel/galaxies/arp.html 4/7 1/15/12 Galaxies and the Universe - Alternate Approaches and the Redshift Controv ,
.S ,I ""
(1996 A JS 106, 27, ,
). S 1 T 1982 (A J 257, 442, AAS): A ne ph s ics ,
, S .S
- , " ",
- .H ' .F , ,S ,
- H .
- ?I - S .W
.H ' " N ,
. I ,A .O
, ( ,
BL L .F ). A , , , - , , .T - .M - - Q SO
. S ?W
, Gala ie s ,
- AGN ). I
(1992 A J 393, 68) - . Q SO Q SO Q SO
' ( - Q SO
(1+ )4 ,
3C 48). T www.astr.ua.edu/keel/galaxies/arp.html Q SO
5/7 1/15/12 Galaxies and the Universe - Alternate Approaches and the Redshift Controv suggesting that the galaxies have distances related to redshift, and many are certainly galaxies containing stars as
shown by direct spectroscopy.
Gravitational le ns ing will work only if the lens and QSO are at approximately their Hubble- law distances; this
argument has been set out explicitly by Dar 1991 (ApJLett 382, L1). At the least, the QSO must be beyond the
lens galaxy, which already has redshifts of order 0.5. Again, one must invoke quite a coincidence otherwise.
Huchra has admitted orally that his first thought on discovering the Einstein cross was the chilling thought that Arp
might have been right all these years.
Abs orption-line s s te ms again require that the QSO be beyond all the absorbing material unless all the
intervening material has noncosmological redshifts as well. In this case, a strong coincidence is needed to make
the redshift distributions of various kinds of absorber make any sense at all in a conventional model. Shaver has
done an interesting test of QSO pairs at different distances; when absorption is seen at one QSO redshift, it's
always the lower- redshift one against the high- member. Much the same thing is found with associations of
QSOs and low- redshift galaxies, although the absorbing gas seems to be patchy enough that some of the
absorption lines are quite weak and one has to work hard to get a significant detection.
AGN without black hole s ?
Occam's Razor has driven many people to conceive alternate schemes for AGN energy production, though most
end up no less extreme than a massive black hole. Attention has recently focussed on the aftermath of a violent
starburst, when some stars become extreme WR objects with effective temperatures near 105 K (sound
familiar?). Terlevich and Melnick (1985 MNRAS 213, 841) have presented a picture where these so- called
"Warmers" mimic a power- law spectrum and therefore match the ionization level seen in AGN. They suggest a
sequence starburst - Sy 1 - Sy 2 as the supernovae drive broad line emission and die away. Filippenko has in
fact found one supernova that looked for a time much like a Sy 1 nucleus, with narrow forbidden lines and broad
Balmer and Fe II emission. This picture has trouble with jets and rapid variability, but is a useful reminder of why
theories were driven to massive objects in the first place.
In a similar vein, Condon has recently argued that some quasars are intense starbursts confined within small
regions. I am not sure that a starburst with 1012 solar luminosities in a region only 100 pc across is less exotic
than a massive black hole. Besides, how do a bunch of stars manage collimated jets? At least an accretion disk
gives some sort of natural funnel.
Connecting these pictures, Weedman (1983 ApJ 266, 479) notes that the neutron stars left over after a spatially
confined starburst may undergo rapid collapse and give a small configuration mimicking in some respects that of
a single object. Variability and collective effects pose challenges here.
The evidence in favor of the standard picture is hardly compelling (it would be marvellous to actually see an
accretion disk on a larger scale than cataclysmic binary stars). It survives mostly because nothing better has
shown up; the volume restrictions from variability, even when eased by Doppler factors, are formidable for
anything except a relativistically compact object. Limits to the size of the object at the Galactic Center also rule
out some of the exotic ideas other than a black hole, such as degenerate neutrino balls or quark configurations.
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This note was uploaded on 01/15/2012 for the course AY 620 taught by Professor Williamkeel during the Fall '09 term at Alabama.
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