140 research outputs found
The 8 o'clock Arc: A Serendipitous Discovery of a Strongly Lensed Lyman Break Galaxy in the SDSS DR4 Imaging Data
We report on the serendipitous discovery of the brightest Lyman Break Galaxy
(LBG) currently known, a galaxy at z=2.73 that is being strongly lensed by the
z=0.38 Luminous Red Galaxy (LRG) SDSS J002240.91+143110.4. The arc of this
gravitational lens system, which we have dubbed the "8 o'clock arc" due to its
time of discovery, was initially identified in the imaging data of the Sloan
Digital Sky Survey Data Release 4 (SDSS DR4); followup observations on the
Astrophysical Research Consortium (ARC) 3.5m telescope at Apache Point
Observatory confirmed the lensing nature of this system and led to the
identification of the arc's spectrum as that of an LBG. The arc has a spectrum
and a redshift remarkably similar to those of the previous record-holder for
brightest LBG (MS 1512-cB58, a.k.a "cB58"), but, with an estimated total
magnitude of (g,r,i) = (20.0,19.2,19.0) and surface brightness of
(mu_g,mu_r,mu_i) = (23.3, 22.5, 22.3) mag/arcsec^2, the 8 o'clock arc is thrice
as bright. The 8 o'clock arc, which consists of three lensed images of the LBG,
is 162deg (9.6arcsec) long and has a length-to-width ratio of 6:1. A fourth
image of the LBG -- a counter-image -- can also be identified in the ARC 3.5m
g-band images. A simple lens model for the system assuming a singular
isothermal ellipsoid potential yields an Einstein radius of 2.91+/-0.14 arcsec,
a total mass for the lensing LRG (within the (10.6+/-0.5)/h kpc enclosed by the
lensed images) of 1.04x10^12/h Msun, and a magnification factor for the LBG of
12.3(+15/-3.6). The LBG itself is intrinsically quite luminous (approximately
6L*) and shows indications of massive recent star formation, perhaps as high as
160/h Msun/year.Comment: 4 pages 5 figures, submitted to ApJ Letter
The Sloan Bright Arcs Survey : Six Strongly Lensed Galaxies at z=0.4-1.4
We present new results of our program to systematically search for strongly
lensed galaxies in the Sloan Digital Sky Survey (SDSS) imaging data. In this
study six strong lens systems are presented which we have confirmed with
follow-up spectroscopy and imaging using the 3.5m telescope at the Apache Point
Observatory. Preliminary mass models indicate that the lenses are group-scale
systems with velocity dispersions ranging from 466-878 km s^{-1} at z=0.17-0.45
which are strongly lensing source galaxies at z=0.4-1.4. Galaxy groups are a
relatively new mass scale just beginning to be probed with strong lensing. Our
sample of lenses roughly doubles the confirmed number of group-scale lenses in
the SDSS and complements ongoing strong lens searches in other imaging surveys
such as the CFHTLS (Cabanac et al 2007). As our arcs were discovered in the
SDSS imaging data they are all bright (), making them ideally
suited for detailed follow-up studies.Comment: 13 pages, 3 figures, submitted to ApJL, the Sloan Bright Arcs page is
located here: http://home.fnal.gov/~kubo/brightarcs.htm
The Sloan Bright Arcs Survey: Four Strongly Lensed Galaxies with Redshift >2
We report the discovery of four very bright, strongly-lensed galaxies found
via systematic searches for arcs in Sloan Digital Sky Survey Data Release 5 and
6. These were followed-up with spectroscopy and imaging data from the
Astrophysical Research Consortium 3.5m telescope at Apache Point Observatory
and found to have redshift . With isophotal magnitudes
and 3\arcsec-diameter magnitudes , these systems are some of
the brightest and highest surface brightness lensed galaxies known in this
redshift range. In addition to the magnitudes and redshifts, we present
estimates of the Einstein radii, which range from 5.0 \arcsec to 12.7
\arcsec, and use those to derive the enclosed masses of the lensing galaxies
Rest-Frame Optical Spectra of Three Strongly Lensed Galaxies at z~2
We present Keck II NIRSPEC rest-frame optical spectra for three recently
discovered lensed galaxies: the Cosmic Horseshoe (z = 2.38), the Clone (z =
2.00), and SDSS J090122.37+181432.3 (z = 2.26). The boost in signal-to-noise
ratio (S/N) from gravitational lensing provides an unusually detailed view of
the physical conditions in these objects. A full complement of high S/N
rest-frame optical emission lines is measured, spanning from rest-frame 3600 to
6800AA, including robust detections of fainter lines such as H-gamma,
[SII]6717,6732, and in one instance [NeII]3869. SDSS J090122.37+181432.3 shows
evidence for AGN activity, and therefore we focus our analysis on star-forming
regions in the Cosmic Horseshoe and the Clone. For these two objects, we
estimate a wide range of physical properties, including star-formation rate
(SFR), metallicity, dynamical mass, and dust extinction. In all respects, the
lensed objects appear fairly typical of UV-selected star-forming galaxies at
z~2. The Clone occupies a position on the emission-line diagnostic diagram of
[OIII]/H-beta vs. [NII]/H-alpha that is offset from the locations of z~0
galaxies. Our new NIRSPEC measurements may provide quantitative insights into
why high-redshift objects display such properties. From the [SII] line ratio,
high electron densities (~1000 cm^(-3)) are inferred compared to local
galaxies, and [OIII]/[OII] line ratios indicate higher ionization parameters
compared to the local population. Building on previous similar results at z~2,
these measurements provide further evidence (at high S/N) that star-forming
regions are significantly different in high-redshift galaxies, compared to
their local counterparts (abridged).Comment: 16 pages, 8 figures. Accepted for publication in the Astrophysical
Journa
Discovery of A Very Bright, Strongly-Lensed z=2 Galaxy in the SDSS DR5
We report on the discovery of a very bright z = 2.00 star-forming galaxy that
is strongly lensed by a foreground z=0.422 luminous red galaxy (LRG). This
system was found in a systematic search for bright arcs lensed by LRGs and
brightest cluster galaxies in the Sloan Digital Sky Survey Data Release 5
sample. Follow-up observations on the Subaru 8.2m telescope on Mauna Kea and
the Astrophysical Research Consortium 3.5m telescope at Apache Point
Observatory confirmed the lensing nature of this system. A simple lens model
for the system, assuming a singular isothermal ellipsoid mass distribution,
yields an Einstein radius of 3.82 +/- 0.03 arcsec or 14.8 +/- 0.1 kpc/h at the
lens redshift. The total projected mass enclosed within the Einstein radius is
2.10 +/- 0.03 x 10^12 M_sun/h, and the magnification factor for the source
galaxy is 27 +/- 1. Combining the lens model with our gVriz photometry, we find
an (unlensed) star formation rate for the source galaxy of 32 M_sun/h / yr,
adopting a fiducial constant star formation rate model with an age of 100 Myr
and E(B-V) = 0.25. With an apparent magnitude of r = 19.9, this system is among
the very brightest lensed z >= 2 galaxies, and provides an excellent
opportunity to pursue detailed studies of the physical properties of an
individual high-redshift star-forming galaxy.Comment: 31 pages, 12 figures, 4 tables, submitted to Ap
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Discovery of A Very Bright, Strongly-Lensed z=2 Galaxy in the SDSS DR5
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