1910.08580
An empirical model of energetic neutral atom imaging of the heliosphere and its implications for future heliospheric missions at great heliocentric distances
Galli, et al
Several concepts for heliospheric missions operating at heliocentric distances far beyond Earth orbit are currently investigated by the scientific community. The mission concept of the Interstellar Probe (McNutt et al. 2018), e.g., aims at reaching a distance of 1000 au away from the Sun within this century. This would allow the coming generation to obtain a global view of our heliosphere from an outside vantage point by measuring the Energetic Neutral Atoms (ENAs) originating from the various plasma regions. It would also allow for direct sampling of unperturbed interstellar medium, and for many observation opportunities beyond heliospheric science, such as visits to Kuiper Belt Objects, a comprehensive view on the interplanetary dust populations, and infrared astronomy free from the foreground emission of the Zodiacal cloud. In this study, we present a simple empirical model of ENAs from the heliosphere and derive basic requirements for ENA instrumentation onboard a spacecraft at great heliocentric distances. We consider the full energy range of heliospheric ENAs from 10 eV to 100 keV because each part of the energy spectrum has its own merits for heliospheric science. To cover the full ENA energy range, two or three different ENA instruments are needed. Thanks to parallax observations, some insights about the nature of the IBEX Ribbon and the dimensions of the heliosphere can already be gained by ENA imaging from a few au heliocentric distance. To directly reveal the global shape of the heliosphere, measurements from outside the heliosphere are, of course, the best option.
An empirical model of energetic neutral atom imaging of the heliosphere and its implications for future heliospheric missions at great heliocentric distances
Galli, et al
Several concepts for heliospheric missions operating at heliocentric distances far beyond Earth orbit are currently investigated by the scientific community. The mission concept of the Interstellar Probe (McNutt et al. 2018), e.g., aims at reaching a distance of 1000 au away from the Sun within this century. This would allow the coming generation to obtain a global view of our heliosphere from an outside vantage point by measuring the Energetic Neutral Atoms (ENAs) originating from the various plasma regions. It would also allow for direct sampling of unperturbed interstellar medium, and for many observation opportunities beyond heliospheric science, such as visits to Kuiper Belt Objects, a comprehensive view on the interplanetary dust populations, and infrared astronomy free from the foreground emission of the Zodiacal cloud. In this study, we present a simple empirical model of ENAs from the heliosphere and derive basic requirements for ENA instrumentation onboard a spacecraft at great heliocentric distances. We consider the full energy range of heliospheric ENAs from 10 eV to 100 keV because each part of the energy spectrum has its own merits for heliospheric science. To cover the full ENA energy range, two or three different ENA instruments are needed. Thanks to parallax observations, some insights about the nature of the IBEX Ribbon and the dimensions of the heliosphere can already be gained by ENA imaging from a few au heliocentric distance. To directly reveal the global shape of the heliosphere, measurements from outside the heliosphere are, of course, the best option.
1910.08588
Improved photometric redshifts with color-constrained galaxy templates for future wide-area surveys
Lee, Chary
Cosmology and galaxy evolution studies with LSST, Euclid, and WFIRST, will require accurate redshifts for the detected galaxies. In this study, we present improved photometric redshift estimates for galaxies using a template library that populates three-color space and is constrained by HST/CANDELS photometry. For the training sample, we use a sample of galaxies which have median photometric redshifts derived by combining the results of different redshift-fitting codes. It allows us to train on a large, unbiased galaxy sample having deep, unconfused photometry at optical-to-mid infrared wavelengths. Galaxies in the training sample are assigned to cubes in three-dimensional color space, V-H, I-J, and z-H. We then derive the best-fit spectral energy distributions (SEDs) of the training sample at the fixed CANDELS median photometric redshifts to construct the new template library for each individual color cube (i.e. color-cube-based template library). We derive photometric redshifts (photo-z) of our target galaxies in the GOODS-S and -N fields using our new color-cube-based template library. We find that our method yields $\sigma_{NMAD}$ of 0.026 and an outlier fraction of 6% using only photometry in the LSST and Euclid/WFIRST bands. This is an improvement of 10% on $\sigma_{NMAD}$ and a reduction in outlier fraction of 13% compared to other techniques. In particular, we improve the photo-z precision by about 30% at 2 < z < 3. We also assess photo-z improvements by including K or mid-infrared bands to the ugrizY JH photometry. Our color-cube-based template library is a powerful tool to constrain photometric redshifts for future large surveys.
1910.09273
Euclid preparation: VII. Forecast validation for Euclid cosmological probes
Euclid Collaboration
The Euclid space telescope will measure the shapes and redshifts of galaxies to reconstruct the expansion history of the Universe and the growth of cosmic structures. Estimation of the expected performance of the experiment, in terms of predicted constraints on cosmological parameters, has so far relied on different methodologies and numerical implementations, developed for different observational probes and for their combination. In this paper we present validated forecasts, that combine both theoretical and observational expertise for different cosmological probes. This is presented to provide the community with reliable numerical codes and methods for Euclid cosmological forecasts. We describe in detail the methodology adopted for Fisher matrix forecasts, applied to galaxy clustering, weak lensing and their combination. We estimate the required accuracy for Euclid forecasts and outline a methodology for their development. We then compare and improve different numerical implementations, reaching uncertainties on the errors of cosmological parameters that are less than the required precision in all cases. Furthermore, we provide details on the validated implementations that can be used by the reader to validate their own codes if required. We present new cosmological forecasts for Euclid. We find that results depend on the specific cosmological model and remaining freedom in each setup, i.e. flat or non-flat spatial cosmologies, or different cuts at nonlinear scales. The validated numerical implementations can now be reliably used for any setup. We present results for an optimistic and a pessimistic choice of such settings. We demonstrate that the impact of cross-correlations is particularly relevant for models beyond a cosmological constant and may allow us to increase the dark energy Figure of Merit by at least a factor of three.
Nature 574, 497–500 (2019)
Identification of strontium in the merger of two neutron stars
Watson, et al
Half of all of the elements in the Universe that are heavier than iron were created by rapid neutron capture. The theory underlying this astrophysical r-process was worked out six decades ago, and requires an enormous neutron flux to make the bulk of the elements. Where this happens is still debated. A key piece of evidence would be the discovery of freshly synthesized r-process elements in an astrophysical site. Existing models and circumstantial evidence point to neutron-star mergers as a probable r-process site; the optical/infrared transient known as a ‘kilonova’ that emerges in the days after a merger is a likely place to detect the spectral signatures of newly created neutron-capture elements. The kilonova AT2017gfo—which was found following the discovery of the neutron-star merger GW170817 by gravitational-wave detectors—was the first kilonova for which detailed spectra were recorded. When these spectra were first reported, it was argued that they were broadly consistent with an outflow of radioactive heavy elements; however, there was no robust identification of any one element. Here we report the identification of the neutron-capture element strontium in a reanalysis of these spectra. The detection of a neutron-capture element associated with the collision of two extreme-density stars establishes the origin of r-process elements in neutron-star mergers, and shows that neutron stars are made of neutron-rich matter.
1910.09582
The matter beyond the ring: the recent evolution of SN 1987A observed by the Hubble Space Telescope
Larsson, et al
The nearby SN 1987A offers a spatially resolved view of the evolution of a young supernova remnant. Here we precent recent Hubble Space Telescope imaging observations of SN 1987A, which we use to study the evolution of the ejecta, the circumstellar equatorial ring (ER) and the increasing emission from material outside the ER. We find that the inner ejecta have been brightening at a gradually slower rate and that the western side has been brighter than the eastern side since ~7000 days. This is expected given that the X-rays from the ER are most likely powering the ejecta emission. At the same time the optical emission from the ER continues to fade linearly with time. The ER is expanding at 680\pm 50 km/s, which reflects the typical velocity of transmitted shocks in the dense hotspots. A dozen spots and a rim of diffuse H-alpha emission have appeared outside the ER since 9500 days. The new spots are more than an order of magnitude fainter than the spots in the ER and also fade faster. We show that the spots and diffuse emission outside the ER may be explained by fast ejecta interacting with high-latitude material that extends from the ER toward the outer rings. Further observations of this emission will make it possible to determine the detailed geometry of the high-latitude material and provide insight into the formation of the rings and the mass-loss history of the progenitor.
Identification of strontium in the merger of two neutron stars
Watson, et al
Half of all of the elements in the Universe that are heavier than iron were created by rapid neutron capture. The theory underlying this astrophysical r-process was worked out six decades ago, and requires an enormous neutron flux to make the bulk of the elements. Where this happens is still debated. A key piece of evidence would be the discovery of freshly synthesized r-process elements in an astrophysical site. Existing models and circumstantial evidence point to neutron-star mergers as a probable r-process site; the optical/infrared transient known as a ‘kilonova’ that emerges in the days after a merger is a likely place to detect the spectral signatures of newly created neutron-capture elements. The kilonova AT2017gfo—which was found following the discovery of the neutron-star merger GW170817 by gravitational-wave detectors—was the first kilonova for which detailed spectra were recorded. When these spectra were first reported, it was argued that they were broadly consistent with an outflow of radioactive heavy elements; however, there was no robust identification of any one element. Here we report the identification of the neutron-capture element strontium in a reanalysis of these spectra. The detection of a neutron-capture element associated with the collision of two extreme-density stars establishes the origin of r-process elements in neutron-star mergers, and shows that neutron stars are made of neutron-rich matter.
1910.09582
The matter beyond the ring: the recent evolution of SN 1987A observed by the Hubble Space Telescope
Larsson, et al
The nearby SN 1987A offers a spatially resolved view of the evolution of a young supernova remnant. Here we precent recent Hubble Space Telescope imaging observations of SN 1987A, which we use to study the evolution of the ejecta, the circumstellar equatorial ring (ER) and the increasing emission from material outside the ER. We find that the inner ejecta have been brightening at a gradually slower rate and that the western side has been brighter than the eastern side since ~7000 days. This is expected given that the X-rays from the ER are most likely powering the ejecta emission. At the same time the optical emission from the ER continues to fade linearly with time. The ER is expanding at 680\pm 50 km/s, which reflects the typical velocity of transmitted shocks in the dense hotspots. A dozen spots and a rim of diffuse H-alpha emission have appeared outside the ER since 9500 days. The new spots are more than an order of magnitude fainter than the spots in the ER and also fade faster. We show that the spots and diffuse emission outside the ER may be explained by fast ejecta interacting with high-latitude material that extends from the ER toward the outer rings. Further observations of this emission will make it possible to determine the detailed geometry of the high-latitude material and provide insight into the formation of the rings and the mass-loss history of the progenitor.
1910.09881
Measuring the Hubble constant from the cooling of the CMB monopole
Abitbol, Hill, Chluba
The cosmic microwave background (CMB) monopole temperature evolves with the inverse of the cosmological scale factor, independent of many cosmological assumptions. With sufficient sensitivity, real-time cosmological observations could thus be used to measure the local expansion rate of the Universe using the cooling of the CMB. We forecast how well a CMB spectrometer could determine the Hubble constant via this method. The primary challenge of such a mission lies in the separation of Galactic and extra-Galactic foreground signals from the CMB at extremely high precision. However, overcoming these obstacles could potentially provide an independent, highly robust method to shed light on the current low-/high-$z$ Hubble tension. We find that a 3\% measurement of the Hubble constant requires an effective sensitivity to the CMB monopole temperature of approximately $60~\mathrm{pK \sqrt{yr}}$ throughout a 10-year mission. This sensitivity would also enable high-precision measurements of the expected $\Lambda$CDM spectral distortions, but remains futuristic at this stage.
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