The largest gravitational lens: MACS J0717.5+3745 (z = 0.546)

The Astrophysical Journal (Impact Factor: 5.99). 07/2009; 707(1). DOI: 10.1088/0004-637X/707/1/L102
Source: arXiv


We identify 13 sets of multiply-lensed galaxies around MACS J0717.5+3745
($z=0.546$), outlining a very large tangential critical curve of major axis
$\sim2.8\arcmin$, filling the field of HST/ACS. The equivalent circular
Einstein radius is $\theta_{e}= 55 \pm 3\arcsec$ (at an estimated source
redshift of $z_{s}\sim2.5$), corresponding to $r_e\simeq 350\pm 20 kpc$ at the
cluster redshift, nearly three times greater than that of A1689 ($r_e\simeq 140
kpc$ for $z_{s}=2.5$). The mass enclosed by this critical curve is very large,
$7.4\pm 0.5 \times 10^{14}M_{\odot}$ and only weakly model dependent, with a
relatively shallow mass profile within $r<250 kpc$, reflecting the unrelaxed
appearance of this cluster. This shallow profile generates a much higher level
of magnification than the well known relaxed lensing clusters of higher
concentration, so that the area of sky exceeding a magnification of
$>10\times$, is $\simeq 3.5\sq\arcmin$ for sources with $z\simeq 8$, making
MACS J0717.5+3745 a compelling target for accessing faint objects at high
redshift. We calculate that only one such cluster, with $\theta_{e}\ge
55\arcsec$, is predicted within $\sim 10^7$ Universes with $z\ge 0.55$,
corresponding to a virial mass $\ge 3\times 10^{15} M_{\odot}$, for the
standard $\Lambda CDM$ (WMAP5 parameters with $2\sigma$ uncertainties).

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    • "The area at redshift 12 corresponds to a magnification of 200. For comparison, the gravitational lens with the greatest known Einstein radius (MACS J0717.5+3745 at z=0.546, [14]) has a magnification of 100-300 (average 160) in an area of 0.3 square arcmin at redshift 6-20 (see [15]). While this is in the right ballpark to allow 300 M ⊙ population III stars to be detected, this requires that a number of desperately unlikely conditions are met, as we discuss below. "
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    ABSTRACT: Isolated population III stars are postulated to exist at approximately z=10-30 and may attain masses up to a few hundred solar masses. The James Webb Space telescope (JWST) is the next large space based infrared telescope and is scheduled for launch in 2014. Using a 6.5 meter primary mirror, it will probably be able to detect some of the first galaxies forming in the early Universe. A natural question is whether it will also be able to see any isolated population III stars. Here, we calculate the apparent broadband AB-magnitudes for 300 solar masses population III stars in JWST filters at z=10-20. Our calculations are based on realistic stellar atmospheres and take into account the potential flux contribution from the surrounding HII region. The gravitational magnification boost achieved when pointing JWST through a foreground galaxy cluster is also considered. Using this machinery, we derive the conditions required for JWST to be able to detect population III stars in isolation. We find that a detection of individual population III stars with JWST is unlikely at these redshifts. However, the main problem is not necessarily that these stars are too faint, once gravitational lensing is taken into account, but that their surface number densities are too low.
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    ABSTRACT: We identify the largest known lensed images of a single spiral galaxy, lying close to the centre of the distant cluster MACS J1149.5+2223 ($z=0.544$). These images cover a total area of $\simeq 150 \Box\arcsec$ and are magnified $\simeq 200$ times. Unusually, there is very little image distortion implying the central mass distribution is almost uniform over a wide area ($r\simeq200 kpc$) with a surface density equal to the critical density for lensing, corresponding to maximal lens magnification. Many fainter multiply-lensed galaxies are also uncovered by our model, outlining a very large tangential critical curve, of radius $r\simeq 170 kpc$, posing a potential challenge for the standard LCDM-Cosmology. Because of the uniform central mass distribution a particularly clean measurement of the mass of the brightest cluster galaxy is possible here, for which we infer stars contribute most of the mass within a limiting radius of $\simeq 30 kpc$, with a mass-to-light ratio of $M/L_{B}\simeq 4.5(M/L)_{\odot}$. This cluster with its uniform and central mass distribution acts analogously to a regular magnifying glass, converging light without distorting the images, resulting in the most powerful lens yet discovered for accessing the faint high-$z$ Universe. Comment: 5 pages, 5 figures, accepted to ApJ letters - minor changes made. High resolution figures available at
    The Astrophysical Journal 06/2009; 703(2). DOI:10.1088/0004-637X/703/2/L132 · 5.99 Impact Factor
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    ABSTRACT: We present a strong lensing analysis of the galaxy cluster Abell 370 (z=0.375) based on the recent multicolor ACS images obtained as part of the Early Release Observation (ERO) that followed the Hubble Service Mission #4. Back in 1987, the giant gravitational arc (z=0.725) in Abell 370 was one of the first pieces of evidence that massive clusters are dense enough to act as strong gravitational lenses. The new observations reveal in detail its disklike morphology, and we show that it can be interpreted as a complex five-image configuration, with a total magnification factor of 32+/-4. Moreover, the high resolution multicolor information allowed us to identify 10 multiply imaged background galaxies. We derive a mean Einstein radius of RE=39+/-2" for a source redshift at z=2, corresponding to a mass of M(<RE) = 2.82+/-0.15 1e14 Msol and M(<250 kpc)=3.8+/-0.2 1e14 Msol, in good agreement with Subaru weak-lensing measurements. The typical mass model error is smaller than 5%, a factor 3 of improvement compared to the previous lensing analysis. Abell 370 mass distribution is confirmed to be bi-modal with very small offset between the dark matter, the X-ray gas and the stellar mass. Combining this information with the velocity distribution reveals that Abell 370 is likely the merging of two equally massive clusters along the line of sight, explaining the very high mass density necessary to efficiently produce strong lensing. These new observations stress the importance of multicolor imaging for the identification of multiple images which is key to determining an accurate mass model. The very large Einstein radius makes Abell 370 one of the best clusters to search for high redshift galaxies through strong magnification in the central region. Comment: 6 pages, 2 figures, accepted to MNRAS letters, replaced with accepted version
    Monthly Notices of the Royal Astronomical Society 10/2009; 402(1). DOI:10.1111/j.1745-3933.2009.00796.x · 5.11 Impact Factor
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