952 research outputs found
Observations of GW170817 by DESGW and the DECam GW-EM Collaboration
On August 17, 2017 LIGO/Virgo detected a binary neutron star via gravitational waves. We observed 70 sq-degrees in the LIGO/Virgo spatial localization with the DECam on the 4m Blanco telescope covering 80% of the final map. Our group independently discovered an optical counterpart in NGC 4993. We searched our entire imaged region: the object in NGC 4993 was the only viable candidate. Our observations of NGC4993 show complicated morphology but simple star formation history. Our x-ray and radio observations indicate an off-axis jet as afterglow. Our high-cadence optical and infrared spectra show a source that must be described by at least two components, one of which is dominated by the r-process nucleosynthesis elements characteristic of a kilonova. Our modeling of the light curve demonstrates such a model in which 0.05 MO of material is ejected from the system. Finally, we discuss the first standard siren measurement of H0
Snowmass2021 Cosmic Frontier: Report of the CF04 Topical Group on Dark Energy and Cosmic Acceleration in the Modern Universe
Cosmological observations in the new millennium have dramatically increased
our understanding of the Universe, but several fundamental questions remain
unanswered. This topical group report describes the best opportunities to
address these questions over the coming decades by extending observations to
the universe. The greatest opportunity to revolutionize our understanding
of cosmic acceleration both in the modern universe and the inflationary epoch
would be provided by a new Stage V Spectroscopic Facility (Spec-S5) which would
combine a large telescope aperture, wide field of view, and high multiplexing.
Such a facility could simultaneously provide a dense sample of galaxies at
lower redshifts to provide robust measurements of the growth of structure at
small scales, as well as a sample at redshifts to measure cosmic
structure at the largest scales, spanning a sufficient volume to probe
primordial non-Gaussianity from inflation, to search for features in the
inflationary power spectrum on a broad range of scales, to test dark energy
models in poorly-explored regimes, and to determine the total neutrino mass and
effective number of light relics. A number of compelling opportunities at
smaller scales should also be pursued alongside Spec-S5. The science
collaborations analyzing DESI and LSST data will need funding for a variety of
activities, including cross-survey simulations and combined analyses. The
results from these experiments can be greatly improved by smaller programs to
obtain complementary data, including follow-up studies of supernovae and
spectroscopy to improve photometric redshift measurements. The best future use
of the Vera C. Rubin Observatory should be evaluated later this decade after
the first LSST analyses have been done. Finally, investments in pathfinder
projects could enable powerful new probes of cosmology to come online in future
decades.Comment: Topical Group Report for CF04 (Dark Energy and Cosmic Acceleration in
the Modern Universe) for Snowmass 202
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
Cosmology with Gravitational Waves in des and LSST
Motivated by the prospect of the wealth of data arising from the inauguration of the era of gravitational wave detection by ground-based interferometers the DES collaboration, in partnership with members of the LIGO collaboration and members of the astronomical community at large, have established a research program to search for their optical counterparts and to explore their use as cosmological probes. In this talk we present the status of our program and discuss prospects for establishing this new probe as part of the portfolio of the Dark Energy research program in the future, in particular for the next generation survey, LSST
- …