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Fraser
2005-Nov-18, 08:08 PM
SUMMARY: Astronomers have turned up 19 new gravitationally lensed quasars using photographs from the Hubble Space Telescope and the Sloan Digital Sky Survey (SDSS). 8 of these are what are known as "Einstein's Rings", where a nearby galaxy and a more distant quasar are perfectly lined up from our vantage point. The nearby galaxy acts as a lens to gravitationally focus the light from the quasar to magnify our view of it.

View full article (http://www.universetoday.com/am/publish/quadruple_ptical_einstein_rings.html)
What do you think about this story? post your comments below.

galacsi
2005-Nov-18, 09:08 PM
Gravitational rings ? or just special cases of galaxies with ring? Because may pictures of ringed galaxies have been shot recently.


http://antwrp.gsfc.nasa.gov/apod/ap010612.html



http://antwrp.gsfc.nasa.gov/apod/ap010612.html



http://hubblesite.org/newscenter/newsdesk/archive/releases/1998/21/image/a

ngc3314
2005-Nov-18, 09:37 PM
Gravitational rings ? or just special cases of galaxies with ring? Because may pictures of ringed galaxies have been shot recently.


What was special about this sample is that they started from a list of objects in which spectra from the Sloan sky survey showed the combination of lowish-redshift absorption-line spectra, matching an elliptical galaxy, and high-redshift spectra usually with strong absorption lines, as typically seen in the luminous star-forming galaxies most likely to be seen when lensed, so they started already with special information about these systems. Otherwise, as you say, one would have to go measure the spectra to be sure that some of these (especially the one at lower right on the montage) are not resonance-ring galaxies.

edit: I just noticed that I mistyped - the higher-redshift spectra usually have strong emission lines, making it much easier to detect them from a faint conponent.

galacsi
2005-Nov-19, 11:42 AM
merci pour ces précisions

snabald
2005-Nov-19, 05:21 PM
And this is why we need to keep the Hubble Space Telescope in service.

madman
2005-Nov-22, 04:11 AM
the bright arcs are blue/white.

at 2 - 4 billion light years there is little redshifting so the emission is probably ultraviolet.

if you brighten the image a little, you can see a bit more structure...showing in a few cases that there are multiple arcs/rings around the galaxies...and the bright arcs are part of those larger arcs/rings.

so if these galaxies are really lensing distant quasars...then they're doing it with a physical lense and not solely by gravity.

ToSeek
2005-Nov-22, 07:28 PM
A bunch of images with this article:

One Ring Guides Them to Dark Matter and... (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1781&mode=thread&order=0&thold=0)


Astronomers now have combined two powerful astronomical assets, the Sloan Digital Sky Survey (SDSS) and NASA's Hubble Space Telescope, to identify 19 new gravitational lens galaxies, adding significantly to the approximately 100 gravitational lenses previously known. By studying the arcs and rings produced by these lens candidates, the astronomers can precisely measure the mass of the foreground galaxies. Among these 19, they also have found eight new Einstein rings. Only three such rings had previously been seen in visible light.

ngc3314
2005-Nov-22, 07:52 PM
the bright arcs are blue/white.

at 2 - 4 billion light years there is little redshifting so the emission is probably ultraviolet.

if you brighten the image a little, you can see a bit more structure...showing in a few cases that there are multiple arcs/rings around the galaxies...and the bright arcs are part of those larger arcs/rings.

so if these galaxies are really lensing distant quasars...then they're doing it with a physical lense and not solely by gravity.

Since these are real, non-spherically-symmetric galaxies in both the foreground and background, what is the reasoning behind that statement?

iron4
2005-Nov-23, 02:40 AM
Anybody knows which is the greatest Einstein radius known? Perhaps some of these new discovered Einstein rings can break the record

madman
2005-Nov-23, 02:53 AM
"what is the reasoning behind that statement?"

studies in other wavebands are necessary to prove there is no material in the foreground galaxies causing the lensing....and that it is a result of gravity only.

*****************************************

here's an example

http://antwrp.gsfc.nasa.gov/apod/ap021111.html

Gerbil94
2005-Nov-23, 12:49 PM
Anybody knows which is the greatest Einstein radius known? Perhaps some of these new discovered Einstein rings can break the record

You can find a reasonably up-to-date list of individual galaxy lenses at the CASTLES website, here (http://www.cfa.harvard.edu/castles/). The largest listed there has an Einstein radius of roughly 8 arcseconds, and was discovered in the SDSS.

Cluster lenses have much larger Einstein radii, on the order of arcminutes.

Blob
2006-Jul-25, 07:57 AM
Title: A Time Delay for the Largest Gravitationally Lensed Quasar: SDSS J1004+4112
Authors: J. Fohlmeister (1), C. S. Kochanek (2), E. E. Falco (3), J. Wambsganss (1), N. Morgan (2), C. W. Morgan (2 and 4), E. O. Ofek (5), D. Maoz (6), C. R. Keeton (7), J. C. Barentine (8), G. Dalton (9), J. Dembicky (8), W. Ketzeback (8), R. McMillan (8), C.S. Peters (10) ((1) Zentrum fur Astronomie der Universitat Heidelberg, (2) Department of Astronomy, Ohio State University, (3) Smithsonian Astrophysical Observatory, (4) Department of Physics, United States Naval Academy, (5) California Institute of Technology, (6) School of Physics and Astronomy and the Wise Observatory, (7) Department of Physics & Astronomy, Rutgers University, (8) Apache Point Observatory, (9) Department of Physics, University of Oxford, (10) Department of Physics and Astronomy, Dartmouth College)

Researchers present 426 epochs of optical monitoring data spanning 1000 days from December 2003 to June 2006 for the gravitationally lensed quasar SDSS J1004+4112. The time delay between the A and B images is 38.4 ±2.0 days in the expected sense that B leads A and the overall time ordering is C-B-A-D-E. The measured delay invalidates all published models. The models failed because they neglected the perturbations from cluster member galaxies. Models including the galaxies can fit the data well, but strong conclusions about the cluster mass distribution should await the measurement of the longer, and less substructure sensitive, delays of the C and D images. For these images, a CB delay of 681±15 days is plausible but requires confirmation, while CB and AD delays of >560 days and > 800 days are required. The researchers clearly detect microlensing of the A/B images, with the delay-corrected flux ratios changing from B-A=0.44 ±0.01 mag in the first season to 0.29 ±0.01 mag in the second season and 0.32 ±0.01 mag in the third season.

Read more (http://arxiv.org/PS_cache/astro-ph/pdf/0607/0607513.pdf) (306kb, PDF)

Attachment:
The r-band image obtained with Minicam on January 16, 2005. The 3.3 arcmin x 3.5 arcmin field shows the lensed images of SDSS J1004+4112 and the five reference stars S1, S2, S3, S4 and S5 used for the PSF.

See Also:
Title: Recurrence of the blue wing enhancements in the high ionisation lines of SDSS 1004+4112 A
Authors: P. Gomez-Alvarez, E. Mediavilla, J. A. Munoz, S. Arribas, S.F. Sanchez, A. Oscoz, F. Prada, M. Serra-Ricart

Researchers present integral field spectroscopic observations of the quadruple-lensed QSO SDSS 1004+4112 taken with the fiber system INTEGRAL at the William Herschel Telescope on 2004 January 19. In May 2003 a blueward enhancement in the high ionisation lines of SDSS 1004+4112A was detected and then faded.
Their observations are the first to note a second event of similar characteristics less than one year after. Although initially attributed to microlensing, the resemblance among the spectra of both events and the absence of microlensing-induced changes in the continuum of component A are puzzling. The lack of a convincing explanation under the microlensing or intrinsic variability hypotheses makes the observed enhancements particularly relevant, calling for close monitoring of this object.

Read more (http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0605/0605522.pdf) (59kb, PDF)