1901.08595
Weak lensing effect on CMB in the presence of a dipole anisotropy
Agarwal, et al
Investigate weak lensing effect on CMB in the presence of dipole anisotropy. The approach of fiat-sky approximation is considered. Determine the functions sigma_0^2 and sigma_2^2 that appear in expressions of the lensed CMB power spectrum in the presence of a dipole anisotropy. Determine the correction to B-mode PS which is found to be appreciable at low multipoles. However, the temperature and E-mode power spectrum are not altered significantly.
1901.08605
Investing for discovery and sustainability in Astronomy in the 2020s
Najita
This report, created to aid NAOA in its planning for the 2020 Decadal Survey on A+A, review the outcome of the previous Astro2010; describes the themes that emerged from the 2018 NAOA community planning workshop "NOAO Community needs for Science in the 2020s"; and based on the above, offers thoughts for the coming review. Find that a balanced set of investments in small-to-large-scale initiatives is essential to a sustainable future, based on the experience of previous decades. While large facilities are the "value" investments that are guaranteed to produce compelling science and discoveries, smaller facilities are the "growth stocks" that are likely to deliver the biggest science bang per buck, sometimes with outsize returns. Investments in data-intensive missions also have benefits to society beyond the science they deliver. By training scientists who are well equipped to use their data science skills to solve problems in the public or private sector, astronomy can provide a valuable service to society by contributing to a data-capable workforce.
1901.08679
Fourier series expansion of the dark energy equation of state
Tamayo, Vazquez
The DE component of the universe still remains as a mystery, however, several papers based on observational data have shown that its equation of state may have an oscillatory behavior. In this paper, provide a general description for the DE EoS w(z) in the form of Fourier series. This description generalizes some previous dynamical DE models and is in agreement with the w(z) reconstructions. Make use of a modified version of a simple and fast MCMC code to constrain the model parameters. For the analysis, use data from SN Ia, BAO, H(z) measurements and CMB. Provide a comparison of the proposed model with LCDM, wCDM and the standard Taylor approximation. The Fourier series expansion of w(z) is preferred from LCDM at more than 3 sigma significant level based on the improvement in the fit alone. Use the Akaike criteria to perform the model comparison and found that, even though there are extra parameters, there is a slight preference of the Fourier series compared with the LCDM model. The preferred shape of w(z) found here puts in jeopardy the single scalar field models, as they cannot reproduce the crossing the phantom divide line w=-1.
1901.08681
The Local Perspective on the Hubble Tension: Local structures does not impact measurement of the Hubble Constant
Kenworthy, Scolnic, Riess
Use the largest sample to date of spectro-SN Ia distances and redshifts to look for evidence in the Hubble diagram of LS outflows caused by local voids suggested to exist at z<0.15. The sample combines data from the Pantheon sample with the Foundation survey and the most recent release of light curves from the Carnegie Supernova Project to create a sample of 1295 SNe over a redshift range of 0.01<z<2.26. Make use of an inhomogeneous and isotropic Lemaitre-Tolman-Bondi metric to model a void in the SN Ia distance-z relation. Conclude that the SN luminosity distance-z relation is inconsistent at the 4-5 sigma confidence level with large local under densities (|delta|>20%, where the density contrast delta = Delta-rho/rho) proposed in some galaxy count studies, and find no evidence of a change in the Hubble constant corresponding to a void with a sharp edge in the z range 0.023<z<0.15. Conclude that the distance latter value of H0, with a current precision of sigma H0=2.2%, is not significantly affected by local density contrasts, with an empirical precision of sigma H0~0.60%, in agreement with cosmic variance in the Hubble constant of sigma H0=0.42% predicted from simulations of LSS. Derive a 5 sigma constraint on local density contrasts on scales larger than 69 Mpc/h of |delta|<27%. The presence of local structure does not appear to impede the possibility of measuring the Hubble constant to 1% precision.
1901.08875
Laser communication and coordination control of spacecraft swarms
Kalita, et al
Swamis of small spacecraft offer whole new capabilities in earth observation, global positioning and communications compared to a large monolithic spacecraft. These small spacecrafts can provide bigger apertures that increase gain in communication antennas, increase area coverage of effective resolution of distributed cameras and enable persistent observation of ground or space targets. However, there remain important challenges in operating large number of spacecrafts at once. Current methods would require a large number of ground operators monitor and actively control these spacecrafts which poses challenges in terms of coordination and control which prevents the technology from scaled up in cost-effective manner. Technologies are required to enable one ground operator to manage tens if not hundred os spacecrafts. Propose to utilize laser beams directed from the ground or from a command and control spacecraft to organize and manage a large swarm. Each satellite in the swarm will have a customized "smart skin" containing solar panels, power and control circuitry and an embedded secondary propulsion unit. A secondary propulsion unit may include electrospray propulsion, solar radiation pressure-based system, photonics laser thrusters an Lorentz force thrusters. Solar panels typically occupy the largest surface area on an earth orbiting satellite. A laser beam from another spacecraft or from the ground would interact with solar panels of the spacecraft swarm. The laser beam would be used to select a 'leader' amongst a group of spacecrafts, set parameters for formation-flight, including separation distance, local if-then rules and coordinated changes in attitude and position.
1901.08878
The cosmic spectral energy distribution in the EAGLE simulation
Baes, et al
The cosmic spectral energy distribution (CSED) is the total emissivity as a function of wavelength of galaxies in a given cosmic volume. We compare the observed CSED from the UV to the submm to that computed from the EAGLE cosmological hydrodynamical simulation, post-processed with stellar population synthesis models and including dust radiative transfer using the SKIRT code. The agreement with the data is better than 0.15 dex over the entire wavelength range at redshift $z=0$, except at UV wavelengths where the EAGLE model overestimates the observed CSED by up to a factor 2. Global properties of the CSED as inferred from CIGALE fits, such as the stellar mass density, mean star formation density, and mean dust-to-stellar-mass ratio, agree to within better than 20 per cent. At higher redshift, EAGLE increasingly underestimates the CSED at optical-NIR wavelengths with the FIR/submm emissivity underestimated by more than a factor of 5 by redshift $z=1$. We believe that these differences are due to a combination of incompleteness of the EAGLE-SKIRT database, the small simulation volume and the consequent lack of luminous galaxies, and our lack of knowledge on the evolution of the characteristics of the interstellar dust in galaxies. The impressive agreement between the simulated and observed CSED at lower $z$ confirms that the combination of EAGLE and SKIRT dust processing yields a fairly realistic representation of the local Universe.
We use cosmological hydrodynamic zoom-in simulations to study early structure formation in two dark matter (DM) cosmologies, a standard CDM model, and a warm DM (WDM) model with a particle mass of $m_{\chi}c^{2}=3$ keV. We focus on DM haloes with virial masses $M\sim 10^{10}\ M_{\odot}$. We find that the first star formation activity is delayed by $\sim 200$ Myr in the WDM model, with similar delays for metal enrichment and the formation of the second generation of stars. However, the differences between the two models in globally-averaged properties, such as star formation rate density and mean metallicity, decrease towards lower redshifts ($z\lesssim 10$). Metal enrichment in the WDM cosmology is restricted to dense environments, while low-density gas can also be significantly enriched in the CDM case. We calculate the free-free contribution from early structure formation at redshifts $z>6$ to the cosmic radio background (CRB), and find that it is $3.8_{-1.7}^{+15.8}$% ($10.4_{-4.6}^{+43.3}$%) of the total signal inferred from radio experiments such as ARCADE 2, in the WDM (CDM) model. We find that the direct detection of the $\mathrm{H_{2}}$ emission from early structure formation ($z\gtrsim 7.2$), originating from the low-mass haloes explored here, will be challenging even with the next generation of planned far-infrared space telescopes, unless the signal is magnified by at least a factor of 10 via gravitational lensing. However, more massive haloes with $M\gtrsim 10^{12}\ M_{\odot}$ may be observable for $z\gtrsim 10$, even without lensing, provided that our extrapolation from the scale of our simulated haloes is valid.
We present a large spectroscopic campaign with Keck/MOSFIRE targeting Lyman-alpha emission (Ly$\alpha$) from intrinsically faint Lyman-break Galaxies (LBGs) behind 12 efficient galaxy cluster lenses. Gravitational lensing allows us to probe the more abundant faint galaxy population to sensitive Ly$\alpha$ equivalent width limits. During the campaign we targeted 70 LBG candidates with MOSFIRE Y-band, selected photometrically to cover Ly$\alpha$ over the range $7<z<8.2$. We detect $S/N>5$ emission lines in 2 of these galaxies and find that they are likely Ly$\alpha$ at $z=7.148\pm0.001$ and $z=7.161\pm0.001$. We present new lens models for 4 of the galaxy clusters, using our previously published lens models for the remaining clusters to determine the magnification factors for the source galaxies. Using a Bayesian framework that employs large scale reionization simulations of the intergalactic medium (IGM) as well as realistic properties of the interstellar medium and circumgalactic medium, we infer the volume-averaged neutral hydrogen fraction, $\overline{x}_{\mathrm{HI}}$, in the IGM during reionization to be $\overline{x}_{\mathrm{HI}}=0.88^{+0.05}_{-0.10}$ at $z=7.6\pm0.6$. Our result is consistent with a late and rapid reionization scenario inferred by Planck.
Weak lensing effect on CMB in the presence of a dipole anisotropy
Agarwal, et al
Investigate weak lensing effect on CMB in the presence of dipole anisotropy. The approach of fiat-sky approximation is considered. Determine the functions sigma_0^2 and sigma_2^2 that appear in expressions of the lensed CMB power spectrum in the presence of a dipole anisotropy. Determine the correction to B-mode PS which is found to be appreciable at low multipoles. However, the temperature and E-mode power spectrum are not altered significantly.
1901.08605
Investing for discovery and sustainability in Astronomy in the 2020s
Najita
This report, created to aid NAOA in its planning for the 2020 Decadal Survey on A+A, review the outcome of the previous Astro2010; describes the themes that emerged from the 2018 NAOA community planning workshop "NOAO Community needs for Science in the 2020s"; and based on the above, offers thoughts for the coming review. Find that a balanced set of investments in small-to-large-scale initiatives is essential to a sustainable future, based on the experience of previous decades. While large facilities are the "value" investments that are guaranteed to produce compelling science and discoveries, smaller facilities are the "growth stocks" that are likely to deliver the biggest science bang per buck, sometimes with outsize returns. Investments in data-intensive missions also have benefits to society beyond the science they deliver. By training scientists who are well equipped to use their data science skills to solve problems in the public or private sector, astronomy can provide a valuable service to society by contributing to a data-capable workforce.
1901.08679
Fourier series expansion of the dark energy equation of state
Tamayo, Vazquez
The DE component of the universe still remains as a mystery, however, several papers based on observational data have shown that its equation of state may have an oscillatory behavior. In this paper, provide a general description for the DE EoS w(z) in the form of Fourier series. This description generalizes some previous dynamical DE models and is in agreement with the w(z) reconstructions. Make use of a modified version of a simple and fast MCMC code to constrain the model parameters. For the analysis, use data from SN Ia, BAO, H(z) measurements and CMB. Provide a comparison of the proposed model with LCDM, wCDM and the standard Taylor approximation. The Fourier series expansion of w(z) is preferred from LCDM at more than 3 sigma significant level based on the improvement in the fit alone. Use the Akaike criteria to perform the model comparison and found that, even though there are extra parameters, there is a slight preference of the Fourier series compared with the LCDM model. The preferred shape of w(z) found here puts in jeopardy the single scalar field models, as they cannot reproduce the crossing the phantom divide line w=-1.
1901.08681
The Local Perspective on the Hubble Tension: Local structures does not impact measurement of the Hubble Constant
Kenworthy, Scolnic, Riess
Use the largest sample to date of spectro-SN Ia distances and redshifts to look for evidence in the Hubble diagram of LS outflows caused by local voids suggested to exist at z<0.15. The sample combines data from the Pantheon sample with the Foundation survey and the most recent release of light curves from the Carnegie Supernova Project to create a sample of 1295 SNe over a redshift range of 0.01<z<2.26. Make use of an inhomogeneous and isotropic Lemaitre-Tolman-Bondi metric to model a void in the SN Ia distance-z relation. Conclude that the SN luminosity distance-z relation is inconsistent at the 4-5 sigma confidence level with large local under densities (|delta|>20%, where the density contrast delta = Delta-rho/rho) proposed in some galaxy count studies, and find no evidence of a change in the Hubble constant corresponding to a void with a sharp edge in the z range 0.023<z<0.15. Conclude that the distance latter value of H0, with a current precision of sigma H0=2.2%, is not significantly affected by local density contrasts, with an empirical precision of sigma H0~0.60%, in agreement with cosmic variance in the Hubble constant of sigma H0=0.42% predicted from simulations of LSS. Derive a 5 sigma constraint on local density contrasts on scales larger than 69 Mpc/h of |delta|<27%. The presence of local structure does not appear to impede the possibility of measuring the Hubble constant to 1% precision.
1901.08875
Laser communication and coordination control of spacecraft swarms
Kalita, et al
Swamis of small spacecraft offer whole new capabilities in earth observation, global positioning and communications compared to a large monolithic spacecraft. These small spacecrafts can provide bigger apertures that increase gain in communication antennas, increase area coverage of effective resolution of distributed cameras and enable persistent observation of ground or space targets. However, there remain important challenges in operating large number of spacecrafts at once. Current methods would require a large number of ground operators monitor and actively control these spacecrafts which poses challenges in terms of coordination and control which prevents the technology from scaled up in cost-effective manner. Technologies are required to enable one ground operator to manage tens if not hundred os spacecrafts. Propose to utilize laser beams directed from the ground or from a command and control spacecraft to organize and manage a large swarm. Each satellite in the swarm will have a customized "smart skin" containing solar panels, power and control circuitry and an embedded secondary propulsion unit. A secondary propulsion unit may include electrospray propulsion, solar radiation pressure-based system, photonics laser thrusters an Lorentz force thrusters. Solar panels typically occupy the largest surface area on an earth orbiting satellite. A laser beam from another spacecraft or from the ground would interact with solar panels of the spacecraft swarm. The laser beam would be used to select a 'leader' amongst a group of spacecrafts, set parameters for formation-flight, including separation distance, local if-then rules and coordinated changes in attitude and position.
1901.08878
The cosmic spectral energy distribution in the EAGLE simulation
Baes, et al
The cosmic spectral energy distribution (CSED) is the total emissivity as a function of wavelength of galaxies in a given cosmic volume. We compare the observed CSED from the UV to the submm to that computed from the EAGLE cosmological hydrodynamical simulation, post-processed with stellar population synthesis models and including dust radiative transfer using the SKIRT code. The agreement with the data is better than 0.15 dex over the entire wavelength range at redshift $z=0$, except at UV wavelengths where the EAGLE model overestimates the observed CSED by up to a factor 2. Global properties of the CSED as inferred from CIGALE fits, such as the stellar mass density, mean star formation density, and mean dust-to-stellar-mass ratio, agree to within better than 20 per cent. At higher redshift, EAGLE increasingly underestimates the CSED at optical-NIR wavelengths with the FIR/submm emissivity underestimated by more than a factor of 5 by redshift $z=1$. We believe that these differences are due to a combination of incompleteness of the EAGLE-SKIRT database, the small simulation volume and the consequent lack of luminous galaxies, and our lack of knowledge on the evolution of the characteristics of the interstellar dust in galaxies. The impressive agreement between the simulated and observed CSED at lower $z$ confirms that the combination of EAGLE and SKIRT dust processing yields a fairly realistic representation of the local Universe.
1901.08885
Modeling the large-scale power deficit
Vitenti, Peter, Valentini
We investigate a set of cosmological models for which the primordial power spectrum has a large-scale power deficit. The standard power-law spectrum is subject to long-wavelength modifications described by some new parameters, resulting in corrections to the anisotropies in the cosmic microwave background. The new parameters are fitted to different data sets: temperature only, temperature and polarization, the low-redshift determination of $H_0$, and baryonic acoustic oscillations. We discuss the statistical significance of the modified spectra, from both frequentist and Bayesian perspectives. Our analysis suggests motivations for considering models that break scalar-tensor consistency, or models with negligible power in the far super-Hubble limit. We present what appears to be substantial evidence for a new scale around 350 Mpc above which the primordial (scalar) power spectrum is sharply reduced by about 20%.
1901.08994
Global radiation signature from early structure formation
Liu, et al
We use cosmological hydrodynamic zoom-in simulations to study early structure formation in two dark matter (DM) cosmologies, a standard CDM model, and a warm DM (WDM) model with a particle mass of $m_{\chi}c^{2}=3$ keV. We focus on DM haloes with virial masses $M\sim 10^{10}\ M_{\odot}$. We find that the first star formation activity is delayed by $\sim 200$ Myr in the WDM model, with similar delays for metal enrichment and the formation of the second generation of stars. However, the differences between the two models in globally-averaged properties, such as star formation rate density and mean metallicity, decrease towards lower redshifts ($z\lesssim 10$). Metal enrichment in the WDM cosmology is restricted to dense environments, while low-density gas can also be significantly enriched in the CDM case. We calculate the free-free contribution from early structure formation at redshifts $z>6$ to the cosmic radio background (CRB), and find that it is $3.8_{-1.7}^{+15.8}$% ($10.4_{-4.6}^{+43.3}$%) of the total signal inferred from radio experiments such as ARCADE 2, in the WDM (CDM) model. We find that the direct detection of the $\mathrm{H_{2}}$ emission from early structure formation ($z\gtrsim 7.2$), originating from the low-mass haloes explored here, will be challenging even with the next generation of planned far-infrared space telescopes, unless the signal is magnified by at least a factor of 10 via gravitational lensing. However, more massive haloes with $M\gtrsim 10^{12}\ M_{\odot}$ may be observable for $z\gtrsim 10$, even without lensing, provided that our extrapolation from the scale of our simulated haloes is valid.
1901.09001
Constraining the neutral fraction of hydrogen in the IGM at redshift 7.5
Hoag, Bradac, et al
1901.09039
The galaxy - halo connection in low mass haloes
Feldmann, et al
Properties of galaxies vary systematically with the mass of their parent dark matter halos. This basic galaxy - halo connection shows a fair amount of scatter whose origin is not fully understood. Here, we study how differences in the halo assembly history affect central galaxies in low mass (M_halo < 10^12 M_sun) halos at z=2-6 with the help of the MassiveFIRE suite of cosmological simulations. In contrast to previous works that tie galaxy properties to halo concentration and halo formation redshift, we focus on halo growth rate as a measure of assembly history. We find that, at fixed halo mass, faster growing halos tend to have lower stellar masses and higher SFRs per unit stellar mass but similar overall SFRs. We provide a simple explanation for these findings with the help of an analytic model that captures approximately the behavior of our hydrodynamical simulations. Specifically, among halos of a given current mass, quickly growing halos have lower stellar masses (and thus higher sSFRs) because they were less massive and had comparably lower cold gas masses and SFRs in the past than slowly growing halos. By combining these findings with estimates for the scatter of the halo growth rate, we show that variations in growth rate at fixed halo mass may largely explain the scatter of the stellar mass - halo mass relation. In contrast, halo growth variations likely play only a minor role in the scatter of the star forming sequence in low mass galaxies.
1901.09041
The occurrence of compact groups of galaxies through cosmic time
Wiens, et al
We use the outputs of a semi-analytical model of galaxy formation run on the Millennium Simulation to investigate the prevalence of three-dimensional compact groups (CGs) of galaxies from $z = 11$ to 0. Our publicly available code identifies CGs using the 3D galaxy number density, the mass ratio of secondary+tertiary to the primary member, mass density in a surrounding shell, the relative velocities of candidate CG members, and a minimum CG membership of three. We adopt "default" values for the first three criteria, representing the observed population of Hickson CGs at $z = 0$. The percentage of non-dwarf galaxies ($M > 5 \times 10^{8}h^{-1}\ M_{\odot}$) in CGs peaks near $z \sim 2$ for the default set, and between $z \sim 1 - 3$ for other parameter sets. This percentage declines rapidly at higher redshifts ($z \gtrsim 4$), consistent with the galaxy population as a whole being dominated by low-mass galaxies excluded from this analysis. According to the most liberal criteria, $\lesssim 3\%$ of non-dwarf galaxies are members of CGs at the redshift where the CG population peaks. Our default criteria result in a population of CGs at $z < 0.03$ with number densities and sizes consistent with Hickson CGs. Tracking identified CG galaxies and merger products to $z = 0$, we find that $\lesssim 16\%$ of non-dwarf galaxies have been CG members at some point in their history. Intriguingly, the great majority ($96\%$) of $z = 2$ CGs have merged to a single galaxy by $z= 0$. There is a discrepancy in the velocity dispersions of Millennium Simulation CGs compared to those in observed CGs, which remains unresolved.
1901.09083
What the sudden death of solar cycles can tell us about the nature of the solar interior
McIntosh, et al
We observe the abrupt end of solar activity cycles at the Sun's equator by combining almost 140 years of observations from ground and space. These "terminator" events appear to be very closely related to the onset of magnetic activity belonging to the next sunspot cycle at mid-latitudes and the polar-reversal process at high-latitudes. Using multi-scale tracers of solar activity we examine the timing of these events in relation to the excitation of new activity and find that the time taken for the solar plasma to communicate this transition is of the order of one solar rotation, but could be shorter. Utilizing uniquely comprehensive solar observations from the Solar Terrestrial Relations Observatory (STEREO), and Solar Dynamics Observatory (SDO) we see that this transitional event is strongly longitudinal in nature. Combined, these characteristics imply that magnetic information is communicated through the solar interior rapidly. A range of possibilities exist to explain such behavior: the presence of magnetic reconnection in the deep interior, internal gravity waves on the solar tachocline, or that the magnetic fields present in the Sun's convection zone could be very large, with a poloidal field strengths reaching 50k - considerably larger than conventional explorations of solar and stellar dynamos estimate. Regardless of mechanism responsible, the rapid timescales demonstrated by the Sun's global magnetic field reconfiguration present strong constraints on first-principles numerical simulations of the solar interior and, by extension, other stars.
1901.09144
Probing cosmic acceleration by strong gravitational lensing systems
Tu, Hu, Wang
Recently, some divergent conclusions about cosmic acceleration were obtained using type Ia supernovae (SNe Ia), with opposite assumptions on the intrinsic luminosity evolution. In this paper, we use strong gravitational lensing systems to probe the cosmic acceleration. Since the theory of strong gravitational lensing is established certainly, and the Einstein radius is determined by stable cosmic geometry. We study two cosmological models, $\Lambda$CDM and power-law models, through 152 strong gravitational lensing systems, incorporating with 30 Hubble parameters $H(z)$ and 11 baryon acoustic oscillation (BAO) measurements. Bayesian evidence are introduced to make a one-on-one comparison between cosmological models. Basing on Bayes factors $\ln B$ of flat $\Lambda$CDM versus power-law and $R_{h}=ct$ models are $\ln B>5$, we find that the flat $\Lambda$CDM is strongly supported by the combination of the datasets. Namely, an accelerating cosmology with non power-law expansion is preferred by our numeration.
1901.09488
Mock galaxy shape catalogs in the Subaru Hyper Suprime-Cam Survey
Shirasaki, Hamana, Takada, Takahashi, Miyatake
We use the full-sky ray-tracing weak lensing simulations to generate 2268 mock catalogs for the Subaru Hyper Suprime-Cam (HSC) survey first-year shear catalog in Mandelbaum et al. (2018). Our mock catalogs take into account various effects as in the real data: the survey footprints, inhomogeneous angular distribution of source galaxies, statistical uncertainties in photometric redshift (photo-z) estimate, variations in the lensing weight due to observational conditions and galaxy's properties, and the statistical noise in galaxy shape measurements due to both intrinsic shapes and the measurement errors. We then utilize our mock catalogs to evaluate statistical uncertainties expected in measurements of cosmic shear two-point correlations $\xi_{\pm}$ with tomographic redshift information for the HSC survey. First we develop a quasi-analytical formula for the Gaussian sample variance properly taking into account the number of source pairs in the survey footprints. The standard Gaussian formula significantly overestimates or underestimates the mock results by 50\% level. Secondly we show that different photo-z catalogs or the six disconnected fields, rather than a consecutive geometry for the same area, cause variations in the covariance by ~5\%. Thirdly, we study the chi-square distribution for $\xi_{\pm}$ among the mock catalogs and find the wider distribution than that naively expected for the distribution with the degrees-of-freedom of data vector used. Finally, we propose a method to include non-zero multiplicative bias in mock shape catalog and show the non-zero multiplicative bias can change the effective shape noise term in cosmic shear analyses. Our results suggest an importance of estimating an accurate form of the likelihood function (and therefore the covariance) for robust cosmological parameter inference from the precise measurements.
1901.09737
Implications of the lens redshift distribution of strong lensing systems: cosmological parameters and the global properties of early-type galaxies
Ma, et al
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