Transcript Rubber sheet analogy to GR Einstein’s view of orbits The closer the light beam passes to the deflector, the greater.

Rubber sheet analogy to GR
Einstein’s view of orbits
The closer the light beam passes to the deflector, the greater is the
deflection; for large impact parameters the image location IS the
source location. In general, the source location is not observable.
Lensing can create multiple images
“SOURCE”
Fritz Zwicky & Coma
QSO 0957+561
lens z = 0.36, source z = 1.41, separation = 6.1’’ (huge!!)
The very first known lens (Walsh, Weyman & Carswell 1979)
Einstein Cross/Huchra’s Lens
MACHO-96-BLG5 (candidate microlensing event in the bulge)
Can’t resolve the two stellar images but
can measure the increase in brightness
accurately using differential photometry
Genuine lensing events should follow the
predicted amplification curve, never
repeat, and be achromatic (except for
limb darkening effects)
Sample MACHO light curves
Complications with interpretations: don’t know the distance to the dark object, so don’t know its tangential velocity, so don’t
know the mass accurately. Most “MACHOs” were seen towards the bulge and most were consistent with star-star lensing.
Giant Arc in Abell 370
cluster z = 0.374, arc z = 0.725
One of the first giant arcs to be discovered (Lynds & Petrosian 1986)
arc length = 21”, mean thickness = 2”, radius of curvature = 15”
Giant arc in cluster Cl2244-02
One of the first arcs to be discovered (Lynds & Petrosian 1986)
Existence of SINGLE
giant arcs proves the
cluster mass distribution
cannot be spherical
Note: HST FWPC2 FOV=3sq.
arcmin. (= most cluster images
prior to ACS are single pointings
= only the central regions of
most clusters)
Galaxy clusters make great lenses (massive & centrallycondensed)
Cl0024+16, with multiple
images of the same galaxy
Abell 2218 - the “Poster Child” of cluster lenses
Cluster lens discovered in the SDSS
Note: ACS
FOV = 2x
WFPC2
First known 5-image QSO
Galaxy Lens Candidates (HST Medium Deep Survey; Griffths, Ratnatunga et al.)
Galaxy Lenses (most are ellipticals!)
PG115+080
one of the first “Einstein rings” to be discovered
ring is lensed image of the QSO host galaxy
“Einstein rings” made by galaxy lenses (SLACS Team; SDSS galaxies)
“Double” Einstein Ring (galaxy lens)
Cluster lenses magnify very distant galaxies! (Zwicky was right.)
The recordholder in 1997
Lens is
Cl1358+62
(z=0.33)
Source is
galaxy at
z=4.92 (and the
arc is not the
only image of
it!)
XXX
“SCUBA” sources first discovered via cluster lensing using JCMT (Blain et al. 1997)
Top: 850 micron maps
Bottom: 450 micron maps
Left: A370
Right: Cl2244
Sub-mm galaxies at z=2
to z=3 that are undergoing
massive amounts of star
formation and are highly
dust enshrouded; redshifts
mostly come from radio
counterparts
A z=10 galaxy lensed by A1853 (?); Pello et al. (2004)
Pello et al. have a 4-5 sigma detection of a single line in the spectrum; if
that line is Lyman alpha, then the galaxy is at z=10
Star formation rate is ~60 solar
masses per year (uncorrected for
lensing)
Stellar mass is ~8x108 solar masses
Luminosity is ~2x1010 solar
luminosities
Lensing magnification is ~25 to 100
Graham et al. (2005) failed to detect the galaxy with long Keck integrations, Spitzer
observations, and a re-reduction of Pello et al.’s original data (from VLT archive)
Confirmed z=7 galaxy seen through A2218 (Kneib et al. 2006)
In principle, high-z galaxies seen
through lenses should form an
unbiased sample (but they are
rare to find)