Friday.
1706.09507
Photometric redshifts with the LSST: evaluating survey observing strategies
Graham et al
Present and charaterize a nearest-neighbors color-matching photometric redshift estimator that features a direct relationship between the precision and accuracy of the input magnitudes and the output photometric redshifts. This aspect makes the estimator an ideal tool for evaluating the impact of changes to LSST survey parameters that affect the measurement errors of the photometry, which is the main motivation of this work (i.e., it is not intended to provide the "best" photometric z for LSST data). Show how the photometric redshifts will improve with time over the 10-yr LSST survey and confirm that the nominal distribution of visits per filter provides the most accurate photo-z results. Also demonstrate how deep LSST imaging of a spectroscopic galaxy sample can significantly improve photo-z quality, especially in the survey's early years. The LSST survey strategy naturally produces observations over a range of airmass, which offers the opportunity of using an SED- and z-dependent atmospheric affect on the observed photometry as a color-independent redshift indicator. Show that measuring this airmass effect and including it as a prior has the potential to improve the photometric z and can ameliorate extreme outliers, but also find that it will only be adequately measured for the brightest galaxies, which limits its overall impact on LSST photo-z. Ultimately intend for this to work to serve as a guide for the expectations and preparations of the LSST science community with regards to the minimum quality of photo-z as the survey progresses.
1706.09586
Dependency of photo-z accuracy on filter definition of photometric surveys
Cao et al
Accurate measurement of photo-z is crucial for photometric galaxy surveys, hence it is very important to study how the photo-z accuracy depends on the design of filter systems, and find the best filter parameters which can optimize photo-z fitting. Investigate this problem for the Chinese Space Station Optical Survey (CSS-OS) as an example, which covers wide wavelength range from near-UV to near-IR bands. Use COSMOS galaxy catalog to create mock flux data, whose galaxy redshift and magnitude distributions are similar to that of the CSS-OS. Compared different public photo-z SED template-fitting codes, and choose to use a modified LePhare code in the filter calibration process. The code exploits information in flux upper-limits, which has been proven to be effective in the photo-z measurement. Then investigate the effect of each filter passband and filter parameters on photo-z fitting. Find that the g, r, and i bands can significantly affect the photo-z accuracy and fraction of catastrophic redshift in the CSS-OS or any survey with similar magnitude limits, and the current CSS-OS filter design can optimize the photo-z fitting process.
1706.09723
Sample variance in the local measurements of the Hubble constant
Wu, Huterer
The current >3 sigma tension between the H0 measured from local distance indicators and from CMB is one of the most highly debated issues in cosmology, as it possibly indicates new physics or unknown systematics. In this work, explore whether this tension can be alleviated by the sample variance in the local measurements, which use a small fraction of the Hubble volume. Use a large-volume cosmo N-body simulation to model the local measurements and to quantify the variance due to local density fluctuations and sample selection. Explicitly take into account the inhomogeneous spatial distribution of SNe Ia. Despite the faithful modeling of the observations, the results confirm previous findings that sample variance in local Hubble constant measurements is small; find sigma(local H0)=0.31 km/s/Mpc, a nearly negligible fraction of the ~6 km/s/Mpc necessary t explain the difference between the local and the global H0 measurements. While the H0 tension could in principle be explained by the local neighborhood being a underdense region of radius ~150 Mpc, the extreme required under density of such a void (delta~=0.8) makes it very unlikely in a LCDM Universe, and it also violates existing observations constraints. Therefore, sample variance in a LCDM Universe cannot appreciably alleviates the tension in H0 measurements even after taking into account the inhomogeneous selection of SNe Ia.
1706.09853
Cosmological constraints from the redshift dependence of the volume effect using the galaxy 2-point correlation function across the line-of-sight
Li et al
Develop a methodology to use the z dependence of the galaxy 2PCF across the LoS, xi(r_p), as a probe of cosmo parameters. The positions of galaxies in comoving Cartesian space varies under different cosmo parameter choices, inducing a z-dependent scaling in the galaxy distribution. This geometrical distortion can be observed as a z-dependent rescaling in the measured xi(r_p). Test this methodology using a sample of 1.75 billion mock galaxies at z=0,0.5,1,1.5,2, drawn from the Horizon Runs 4 N-body sim. The shape of xi(r_p) can exhibit a significant z evolution when the galaxy sample is analyzed under a cosmology different from the true, simulated one. Other contributions, including the gravitational growth of structure, galaxy bias, and the z-space distortions, do not produce large z evolution in the shape. Show that one can make use of this geometrical distortion to constrain the values of cosmo parameters governing the expansion history of the universe. This method could be applicable to future large scale structure surveys, especially photometric surveys such as DES, LSST, ate derive tight cosmo constraints. This work is a continuation of previous works as a strategy to consorting cosmo parameters using z-invariang physical quantities.
Friday, June 30, 2017
Wednesday, June 28, 2017
Day 1280
Thursday.
1706.09195
Generating log-normal mock catalog of galaxies in redshift space
Agrawal, et al
Present a public code to generate a mock galaxy catalog in redshift space assuming a log-normal probability density function of galaxy and matter density fields. Draw galaxies by Poisson-sampling the log-normal field, and calculate the velocity field from the linearized continuity equation of matter fields, assuming zero vorticity. This procedure yields a PDF of the pairwise velocity fields that is quantitatively similar to that of N-body sims. Check fidelity of the catalog, showing that the measured 2pt correlation function and power spectrum in real space agree with the input precisely. Find that a linear bias relation in the power spectrum does not guarantee a linear bias relation in the density contrasts, leading to a cross-correlation coefficient of matter and galaxies devoting from unity on small scales. Also find that linearizing the Jacobian of the real-to-redshift space mapping provides a poor model for the 2pt statistics in z space. That is, non-linear redshift-space distortion is dominated by non-linearity in the Jacobian. The power spectrum in z space shows a damping on small scales that is qualitatively similar to that of the well-known FoG effect due to random velocities, except that the log-normal mock does not include random velocities. This damping is a consequence of NL in the Jacobian, and thus attributing the damping of the PS solely to FoG, as commonly done in the literature is misleading.
1706.09359
Dark energy survey year 1 results: multi-probe methodology and simulated likelihood analyses
Krause, Eifler, Zuntz, et al
Present the methodology for and detail the implementation of the DES 3x2pt DES Y1 analysis, which combines configuration-space 2pt statistics from 3 different cosmological probes: cosmic shear, gg lensing, and galaxy clustering, using data from the first year of DES observations. Developed 2 independent modeling pipelines and describe the code validation process. Derive expressions for analytical real-space multi-probe covariances, and describe their validation with numerical sims. Stress-test the inference pipelines in simulated likelihood analyses that vary 6-7 cosmology parameters plus 20 nuisance parameters and precisely resemble the analysis to be presented in the DES 3x2pt analysis paper, using a variety of simulated input data vectors with varying assumptions. Find that any disagreement between pipelines leads to changes in assigned likelihood Delta chi2 <= 0.045 with respect to the statistical error of the DES Y1 data vector. Also find that angular binning and survey do not impact the analytic covariance at a significant level. Determine lower bounds on scales used for analysis of galaxy clustering (8 Mpc/h) and gg lensing (12 Mpc/h) such that their impact of modeling uncertainties in the non-linear regime is well below statistical errors, and show that the analysis choices are robust against a variety of systematics. These tests demonstrate that the analysis pipeline is robust, which yields unbiased cosmological parameter inferences for the flagship 3x2pt DES Y1 analysis. Emphasize that the level of independent code development and subsequent code comparison as demonstrated in this paper is necessary to produce credible constraints from increasingly complex multi-probe analyses of current data.
1706.09195
Generating log-normal mock catalog of galaxies in redshift space
Agrawal, et al
Present a public code to generate a mock galaxy catalog in redshift space assuming a log-normal probability density function of galaxy and matter density fields. Draw galaxies by Poisson-sampling the log-normal field, and calculate the velocity field from the linearized continuity equation of matter fields, assuming zero vorticity. This procedure yields a PDF of the pairwise velocity fields that is quantitatively similar to that of N-body sims. Check fidelity of the catalog, showing that the measured 2pt correlation function and power spectrum in real space agree with the input precisely. Find that a linear bias relation in the power spectrum does not guarantee a linear bias relation in the density contrasts, leading to a cross-correlation coefficient of matter and galaxies devoting from unity on small scales. Also find that linearizing the Jacobian of the real-to-redshift space mapping provides a poor model for the 2pt statistics in z space. That is, non-linear redshift-space distortion is dominated by non-linearity in the Jacobian. The power spectrum in z space shows a damping on small scales that is qualitatively similar to that of the well-known FoG effect due to random velocities, except that the log-normal mock does not include random velocities. This damping is a consequence of NL in the Jacobian, and thus attributing the damping of the PS solely to FoG, as commonly done in the literature is misleading.
1706.09359
Dark energy survey year 1 results: multi-probe methodology and simulated likelihood analyses
Krause, Eifler, Zuntz, et al
Present the methodology for and detail the implementation of the DES 3x2pt DES Y1 analysis, which combines configuration-space 2pt statistics from 3 different cosmological probes: cosmic shear, gg lensing, and galaxy clustering, using data from the first year of DES observations. Developed 2 independent modeling pipelines and describe the code validation process. Derive expressions for analytical real-space multi-probe covariances, and describe their validation with numerical sims. Stress-test the inference pipelines in simulated likelihood analyses that vary 6-7 cosmology parameters plus 20 nuisance parameters and precisely resemble the analysis to be presented in the DES 3x2pt analysis paper, using a variety of simulated input data vectors with varying assumptions. Find that any disagreement between pipelines leads to changes in assigned likelihood Delta chi2 <= 0.045 with respect to the statistical error of the DES Y1 data vector. Also find that angular binning and survey do not impact the analytic covariance at a significant level. Determine lower bounds on scales used for analysis of galaxy clustering (8 Mpc/h) and gg lensing (12 Mpc/h) such that their impact of modeling uncertainties in the non-linear regime is well below statistical errors, and show that the analysis choices are robust against a variety of systematics. These tests demonstrate that the analysis pipeline is robust, which yields unbiased cosmological parameter inferences for the flagship 3x2pt DES Y1 analysis. Emphasize that the level of independent code development and subsequent code comparison as demonstrated in this paper is necessary to produce credible constraints from increasingly complex multi-probe analyses of current data.
Tuesday, June 27, 2017
Day 1279
Wednesday.
1706.08738
Shot noise and biased tracers: a new look at the halo model
Ginzburg, Desjacques, Chan
Shot noise is an important ingredient to any measurement or theoretical modeling of discrete tracers of the LSS. Recent work has shown that the shot noise in the halo power spectrum becomes increasingly sub-Poissonian at high mass. While the halo model predicts a shot noise PS in qualitative agreement with the data, it leads to an unphysical white noise in the cross halo-matter and matter PS. In this work, show that absorbing all the halo model sources of shot noise into the halo fluctuation field leads to meaningful predictions for the shot noise contributions to halo clustering statistics and remove the unphysical white noise from the cross halo-matter statistics. The prescription straightforwardly maps onto the general bias expansion, so that the renormalized shot noise terms can be expressed as combinations of the halo model shot noises. Furthermore, demonstrate that non-Poissonian contributions are related to volume integrals over correlation functions and their response to long-wavelength density perturbations. This leads to a new class of consistency relations for discrete tracers, which appear to be satisfied by the reformulation of the halo model. Test the theoretical predictions against measurements of halo shot noise bispectra extracted from a large suite of numerical sims. The model reproduces qualitatively the observed sub-Poissonian noise, although it underestimates the magnitude of this effect.
1706.08860
Intrinsic alignments and splash back radius of dark matter halos from cosmic density and velocity fields
Okumura, Nishimichi, Umetsu, Osato
Investigate the effects of IA of DM halo shapes on cosmic density and velocity fields from cluster to cosmic scales beyond 100 Mpc/h. Besides the density correlation function binned by he halo orientation angle which was used in the literature, introduce the corresponding two velocity statistics, the angle-binned parities infall momentum and momentum correlation function. Using large-volume, high-resolution N-body sims, measure the alignment statistics of density and velocity, both in real and redshift space. Find that the alignment signal is not amplified by z-space distortions at linear scales. Behaviours of IA in the velocity statistics are similar to those in the density statistics, except that the halo orientations are aligned with the velocity field up to a scale larger than those with the density field, x>100 Mpc/h. On halo scales, x~R_200m ~ 1 Mpc/h, detect a short steepening in the momentum correlation associated with the physical halo boundary, or the splash back feature, which is found more prominent than in the density correlation. The results indicate that observations of IA with the velocity field can provide additional information on cosmological models form large scales and on physical sizes of halos from small scales.
1706.08738
Shot noise and biased tracers: a new look at the halo model
Ginzburg, Desjacques, Chan
Shot noise is an important ingredient to any measurement or theoretical modeling of discrete tracers of the LSS. Recent work has shown that the shot noise in the halo power spectrum becomes increasingly sub-Poissonian at high mass. While the halo model predicts a shot noise PS in qualitative agreement with the data, it leads to an unphysical white noise in the cross halo-matter and matter PS. In this work, show that absorbing all the halo model sources of shot noise into the halo fluctuation field leads to meaningful predictions for the shot noise contributions to halo clustering statistics and remove the unphysical white noise from the cross halo-matter statistics. The prescription straightforwardly maps onto the general bias expansion, so that the renormalized shot noise terms can be expressed as combinations of the halo model shot noises. Furthermore, demonstrate that non-Poissonian contributions are related to volume integrals over correlation functions and their response to long-wavelength density perturbations. This leads to a new class of consistency relations for discrete tracers, which appear to be satisfied by the reformulation of the halo model. Test the theoretical predictions against measurements of halo shot noise bispectra extracted from a large suite of numerical sims. The model reproduces qualitatively the observed sub-Poissonian noise, although it underestimates the magnitude of this effect.
1706.08860
Intrinsic alignments and splash back radius of dark matter halos from cosmic density and velocity fields
Okumura, Nishimichi, Umetsu, Osato
Investigate the effects of IA of DM halo shapes on cosmic density and velocity fields from cluster to cosmic scales beyond 100 Mpc/h. Besides the density correlation function binned by he halo orientation angle which was used in the literature, introduce the corresponding two velocity statistics, the angle-binned parities infall momentum and momentum correlation function. Using large-volume, high-resolution N-body sims, measure the alignment statistics of density and velocity, both in real and redshift space. Find that the alignment signal is not amplified by z-space distortions at linear scales. Behaviours of IA in the velocity statistics are similar to those in the density statistics, except that the halo orientations are aligned with the velocity field up to a scale larger than those with the density field, x>100 Mpc/h. On halo scales, x~R_200m ~ 1 Mpc/h, detect a short steepening in the momentum correlation associated with the physical halo boundary, or the splash back feature, which is found more prominent than in the density correlation. The results indicate that observations of IA with the velocity field can provide additional information on cosmological models form large scales and on physical sizes of halos from small scales.
Day 1278
Tuesday.
1706.07814
Halo intrinsic alignment: dependence on mass, formation time and environment
Xia et al
In this paper, use high-resolution cosmo sims to study halo IA and its dependence on mass, formation time and LS environment. In agreement with previous studies using N-body simulations, it is found that massive halos have stronger alignment. For a given mass, older halos have stronger alignment than younger ones. By identifying the cosmic environment of halo using a Hessian matrix, find that for a given mass, halos in cluster regions also have a stronger alignment than those in a filament. The existing theory has not addressed these dependencies explicitly. In this work, extend the linear alignment model with inclusion of halo bias and find that the halo alignment with its mass and formation time dependence can be explained by halo bias. However, the model can not account for the environment dependence, as it is found that halo bias is lower in cluster and higher in filament. The results suggest that halo bias and environment are independent factors in determining halo alignment. Also study the halo alignment correlation function and find that haloes are strongly clustered along their major axes and less clustered along the minor axes. The correlated halo alignment can extend to scale as large as 100 Mpc/h where its feature is mainly driven by the baryon acoustic oscillation effect.
1706.07815
MACS J0416.1-2403: impact of line-of-sight structures on strong gravitational lensing modeling of galaxy clusters
Chirivì, Suyu, et al
Exploiting the powerful tool of SL by galaxy clusters to study the highest-redshift Universe and cluster mass distributions relies on precise lens mass modeling. In this work, present the first attempt at modeling line-of-sight mass distribution in addition to that of the cluster, extending previous modeling techniques that assume mass distributions to be on a single lens plane. Focus on the Hubble Frontier Field cluster MACS J0416.1-2403, and the multi-plane model reproduces the observed image positions with a rms offset of ~0.53". Starting from this best-fitting model, simulate a mock cluster that resembles MACS J0416 in order to explore the effects of LoS structures on cluster mass modeling. By systematically analysing the mock cluster under different model assumptions, find that neglecting the lensing environment has a significant impact on the reconstruction of image positions (rms~0.3"); accounting for LoS galaxies as if they were at the cluster redshift can partially reduce this offset. Moreover, FG galaxies are more important to include into the model than the BG ones. While the magnification factors of the lensed multiple images are recovered within ~10% for ~95% of them, those ~5% that lie near critical curves can be significantly affected by the exclusion of the lensing environment in the models (up to a factor of ~200). In addition, LoS galaxies cannot explain the apparent discrepancy in the properties of massive sub halos between MACS J0416.1-2403 and N-body simulated clusters. Since the model of MACS J0416 with LoS galaxies only reduced modestly the rms offset in the image positions, conclude that additional complexities, such as more flexible halo shapes, would be needed in future models of MACS J0416.
1706.07870
Weak lensing of the Lyman-alpha forest
Croft, Romeo, Metcalf
The angular positions of quasars are deflected by the gravitational lensing effect of FG matter. The Lyman-alpha forest seen in the spectrum of these quasars is therefore also lensed. Propose that the signature of WL of the forest could be measured using similar techniques that have been applied to the lensed CMB, and which have also been proposed for application to spectral data from 21cm radio telescopes. As with 21cm data, the forest has the advantage of spectral information, potentially yielding many lensed "slices" at different redshifts. Perform an illustrative idealized test, generating a high resolution angular grid of quasars (of order arc minute separation), and lensing the Lyman-alpha forest spectra at z=2-3 using a FG density field. Find that standard quadratic estimators can be used to reconstruct images of the FG mass distribution at z~1. There currently exists a wealth of Lya forest data from quasar and galaxy spectral surveys, with smaller sightline separations expected in the future. Lya forest lensing is sensitive to the FG mass distribution at z intermediate between CMB lensing and galaxy shear, and avoids the difficulties of shape measurement associated with the latter. With further refinement and application of mass reconstruction techniques, WL of the high-z Lya forest may become a useful new cosmological probe.
1706.07871
The impact of assembly bias on the galaxy content of dark matter halos
Zehavi, et al
Study the dependence of the galaxy content of DM haloes on LS environment and halo formation time using semi-analytic galaxy models applied to the Millennium sim. Analyze subsamples of halos at the extremes of these distributions and measure the occupation functions for the galaxies they host. Find distinct differences in these occupation functions. The main effect with environment is that central galaxies (and in one model also the satellite) in denser regions start populating lower-mass halos. A similar, but significant stronger, trend exists with halo age, where early-forming haloes are more likely to host central galaxies at lower halo mass. Discuss the origin of these trends and the connection to the stellar mass -- halo mass relation. Find that, at fixed halo mass, older halos and to some extent also halos in dense environments tend to host more massive galaxies. Additionally, see a reverse trend for the satellite galaxies occupation where early-forming halos have fewer satellites, likely due to having more time for them to merge with the central galaxy. Describe these occupancy variations also in terms of the changes in the occupation function parameters, which can aid in constructing realistic mock galaxy catalogs. Finally, study the corresponding galaxy auto- and cross-correlation functions of the different samples and elucidate the impact of assembly bias on galaxy clustering. The realists can inform theoretical models of assembly bias and attempts to detect it in the real universe.
1706.07814
Halo intrinsic alignment: dependence on mass, formation time and environment
Xia et al
In this paper, use high-resolution cosmo sims to study halo IA and its dependence on mass, formation time and LS environment. In agreement with previous studies using N-body simulations, it is found that massive halos have stronger alignment. For a given mass, older halos have stronger alignment than younger ones. By identifying the cosmic environment of halo using a Hessian matrix, find that for a given mass, halos in cluster regions also have a stronger alignment than those in a filament. The existing theory has not addressed these dependencies explicitly. In this work, extend the linear alignment model with inclusion of halo bias and find that the halo alignment with its mass and formation time dependence can be explained by halo bias. However, the model can not account for the environment dependence, as it is found that halo bias is lower in cluster and higher in filament. The results suggest that halo bias and environment are independent factors in determining halo alignment. Also study the halo alignment correlation function and find that haloes are strongly clustered along their major axes and less clustered along the minor axes. The correlated halo alignment can extend to scale as large as 100 Mpc/h where its feature is mainly driven by the baryon acoustic oscillation effect.
1706.07815
MACS J0416.1-2403: impact of line-of-sight structures on strong gravitational lensing modeling of galaxy clusters
Chirivì, Suyu, et al
Exploiting the powerful tool of SL by galaxy clusters to study the highest-redshift Universe and cluster mass distributions relies on precise lens mass modeling. In this work, present the first attempt at modeling line-of-sight mass distribution in addition to that of the cluster, extending previous modeling techniques that assume mass distributions to be on a single lens plane. Focus on the Hubble Frontier Field cluster MACS J0416.1-2403, and the multi-plane model reproduces the observed image positions with a rms offset of ~0.53". Starting from this best-fitting model, simulate a mock cluster that resembles MACS J0416 in order to explore the effects of LoS structures on cluster mass modeling. By systematically analysing the mock cluster under different model assumptions, find that neglecting the lensing environment has a significant impact on the reconstruction of image positions (rms~0.3"); accounting for LoS galaxies as if they were at the cluster redshift can partially reduce this offset. Moreover, FG galaxies are more important to include into the model than the BG ones. While the magnification factors of the lensed multiple images are recovered within ~10% for ~95% of them, those ~5% that lie near critical curves can be significantly affected by the exclusion of the lensing environment in the models (up to a factor of ~200). In addition, LoS galaxies cannot explain the apparent discrepancy in the properties of massive sub halos between MACS J0416.1-2403 and N-body simulated clusters. Since the model of MACS J0416 with LoS galaxies only reduced modestly the rms offset in the image positions, conclude that additional complexities, such as more flexible halo shapes, would be needed in future models of MACS J0416.
1706.07870
Weak lensing of the Lyman-alpha forest
Croft, Romeo, Metcalf
The angular positions of quasars are deflected by the gravitational lensing effect of FG matter. The Lyman-alpha forest seen in the spectrum of these quasars is therefore also lensed. Propose that the signature of WL of the forest could be measured using similar techniques that have been applied to the lensed CMB, and which have also been proposed for application to spectral data from 21cm radio telescopes. As with 21cm data, the forest has the advantage of spectral information, potentially yielding many lensed "slices" at different redshifts. Perform an illustrative idealized test, generating a high resolution angular grid of quasars (of order arc minute separation), and lensing the Lyman-alpha forest spectra at z=2-3 using a FG density field. Find that standard quadratic estimators can be used to reconstruct images of the FG mass distribution at z~1. There currently exists a wealth of Lya forest data from quasar and galaxy spectral surveys, with smaller sightline separations expected in the future. Lya forest lensing is sensitive to the FG mass distribution at z intermediate between CMB lensing and galaxy shear, and avoids the difficulties of shape measurement associated with the latter. With further refinement and application of mass reconstruction techniques, WL of the high-z Lya forest may become a useful new cosmological probe.
1706.07871
The impact of assembly bias on the galaxy content of dark matter halos
Zehavi, et al
Study the dependence of the galaxy content of DM haloes on LS environment and halo formation time using semi-analytic galaxy models applied to the Millennium sim. Analyze subsamples of halos at the extremes of these distributions and measure the occupation functions for the galaxies they host. Find distinct differences in these occupation functions. The main effect with environment is that central galaxies (and in one model also the satellite) in denser regions start populating lower-mass halos. A similar, but significant stronger, trend exists with halo age, where early-forming haloes are more likely to host central galaxies at lower halo mass. Discuss the origin of these trends and the connection to the stellar mass -- halo mass relation. Find that, at fixed halo mass, older halos and to some extent also halos in dense environments tend to host more massive galaxies. Additionally, see a reverse trend for the satellite galaxies occupation where early-forming halos have fewer satellites, likely due to having more time for them to merge with the central galaxy. Describe these occupancy variations also in terms of the changes in the occupation function parameters, which can aid in constructing realistic mock galaxy catalogs. Finally, study the corresponding galaxy auto- and cross-correlation functions of the different samples and elucidate the impact of assembly bias on galaxy clustering. The realists can inform theoretical models of assembly bias and attempts to detect it in the real universe.
Sunday, June 25, 2017
Day 1277
Monday.
1706.07733
Reducing biases on $H_0$ measurements using strong lensing and galaxy dynamics: results from the EAGLE simulation
Tagore, et al
Cosmological parameter constraints from observations of time-delay lenses are becoming increasingly precise. However, there may be significant bias and scatter in these measurements due to, among other things, the so-called mass-sheet degeneracy. To estimate these uncertainties, analyze SLR from the largest EAGLE hydro sim. Apply a mass-sheet transformation to the radial density profiles of lenses, and by selecting lenses near isothermality, find that the bias on H0 can be reduced to 5% with an intrinsic scatter of 10%, confirming previous results performed on a different simulation data set. Further investigate whether combining lensing observables with kinematic constraints helps to minimize this bias. Do not detect any significant dependence of the bias on lens model parameters or observations properties of the galaxy, but depending on the source--lens configuration, a bias may still exist. Cross lenses provide an accurate estimate of the Hubble constant, while fold (double) lenses tend to be biased low (high). With kinematic constraints, double lenses show bias and intrinsic scatter of 6% and 10%, respectively, while quad lenses show bias and intrinsic scatter of 0.5% and 10%, respectively. For lenses with a reduced chi2>1, a power-law dependence of the chi2 on the lens environment (number of nearby galaxies) is seen. Lastly, model in greater detail, the cases of 2 double lenses that are significantly biased. Able to remove the bias, suggesting that the remaining biases could also be reduced by carefully taking into account additional sources of systematic uncertainty.
1706.07733
Reducing biases on $H_0$ measurements using strong lensing and galaxy dynamics: results from the EAGLE simulation
Tagore, et al
Cosmological parameter constraints from observations of time-delay lenses are becoming increasingly precise. However, there may be significant bias and scatter in these measurements due to, among other things, the so-called mass-sheet degeneracy. To estimate these uncertainties, analyze SLR from the largest EAGLE hydro sim. Apply a mass-sheet transformation to the radial density profiles of lenses, and by selecting lenses near isothermality, find that the bias on H0 can be reduced to 5% with an intrinsic scatter of 10%, confirming previous results performed on a different simulation data set. Further investigate whether combining lensing observables with kinematic constraints helps to minimize this bias. Do not detect any significant dependence of the bias on lens model parameters or observations properties of the galaxy, but depending on the source--lens configuration, a bias may still exist. Cross lenses provide an accurate estimate of the Hubble constant, while fold (double) lenses tend to be biased low (high). With kinematic constraints, double lenses show bias and intrinsic scatter of 6% and 10%, respectively, while quad lenses show bias and intrinsic scatter of 0.5% and 10%, respectively. For lenses with a reduced chi2>1, a power-law dependence of the chi2 on the lens environment (number of nearby galaxies) is seen. Lastly, model in greater detail, the cases of 2 double lenses that are significantly biased. Able to remove the bias, suggesting that the remaining biases could also be reduced by carefully taking into account additional sources of systematic uncertainty.
Thursday, June 22, 2017
Day 1276
Friday.
1706.02739
1706.07054
Predicting the locations of possible long-lived low-mass first stars: importance of satellite dwarf galaxies
Magg, et al
The search for metal-free stars has so far been unsuccessful, proving that if there are surviving stars from the first generation, they are rare, they have been polluted, or we have been looking in the wrong place. To predict the likely location of Pop III survivors, model semi-analytically early SF in progenitors of MW-like galaxies and their environments. Base the model on merger trees from the high-resolution DM only simulation suite Caterpillar. Radiative and chemical feedback are taken into account self-consistently, based on the spatial distribution of the haloes. The results are consistent with the non-detection of Pop III survivors in the MW today. Find that possible surviving Pop III stars are more common in MW satellites than in the main Galaxy. In particular, low mass MW satellites contain a much larger fraction of Pop III stars than the MW. Such nearby, low mass MW satellite are promising targets for future attempts to find Pop III survivors, especially for high-resolution, high signal-to-noise spectroscopic observations. Provide the probabilities to find a Pop III survivor in the red giant branch phase for all known MW satellites to guide future observations.
1706.07400
Is flat fielding safe for precision CCD astronomy?
Baumer et al
The ambitious goals of precision cosmology with wide-field optical surveys such as DES and LSST demand, at their foundation, precision CCD astronomy. This in turn requires an understanding of previously uncharacterized sources of systematic error in CCD sensors, many of which manifest themselves as static effective variations in pixel area. Such variation renders a critical assumption behind the traditional procedure of flat fielding--that a sensor's pixels comprise a uniform grid--invalid. In this work, present a method to infer a curl-free model of a sensor's underlying pixel grid from flat field images, incorporating the superposition of all electrostatic sensor effects--both known and unknown--present in flat field data. Use these pixel grid models to estimate the overall impact of sensor systematics on photometry, astrometry, and PSF shape measurements in a representative sensor effects for which corrections are currently being developed within DES. For an LSST prototype CCD with pixel-response non-uniformity (PRNU) of 0.4%, find the impact of "improper" flat-fielding on these observables is negligible in nominal .7" seeing conditions. These errors scale linearly with the PRNU, so for future LSST production sensors, which may have larger PRNU, the method provides a way to assess whether pixel-level calibration beyond flat fielding will be required.
1706.02739
Freedman
The accuracy in measurement of the Hubble constant has vastly improved, but a recent tension has arisen that is either signaling new physics or as-yet unrecognized uncertainties.
1706.07054
Predicting the locations of possible long-lived low-mass first stars: importance of satellite dwarf galaxies
Magg, et al
The search for metal-free stars has so far been unsuccessful, proving that if there are surviving stars from the first generation, they are rare, they have been polluted, or we have been looking in the wrong place. To predict the likely location of Pop III survivors, model semi-analytically early SF in progenitors of MW-like galaxies and their environments. Base the model on merger trees from the high-resolution DM only simulation suite Caterpillar. Radiative and chemical feedback are taken into account self-consistently, based on the spatial distribution of the haloes. The results are consistent with the non-detection of Pop III survivors in the MW today. Find that possible surviving Pop III stars are more common in MW satellites than in the main Galaxy. In particular, low mass MW satellites contain a much larger fraction of Pop III stars than the MW. Such nearby, low mass MW satellite are promising targets for future attempts to find Pop III survivors, especially for high-resolution, high signal-to-noise spectroscopic observations. Provide the probabilities to find a Pop III survivor in the red giant branch phase for all known MW satellites to guide future observations.
1706.07400
Is flat fielding safe for precision CCD astronomy?
Baumer et al
The ambitious goals of precision cosmology with wide-field optical surveys such as DES and LSST demand, at their foundation, precision CCD astronomy. This in turn requires an understanding of previously uncharacterized sources of systematic error in CCD sensors, many of which manifest themselves as static effective variations in pixel area. Such variation renders a critical assumption behind the traditional procedure of flat fielding--that a sensor's pixels comprise a uniform grid--invalid. In this work, present a method to infer a curl-free model of a sensor's underlying pixel grid from flat field images, incorporating the superposition of all electrostatic sensor effects--both known and unknown--present in flat field data. Use these pixel grid models to estimate the overall impact of sensor systematics on photometry, astrometry, and PSF shape measurements in a representative sensor effects for which corrections are currently being developed within DES. For an LSST prototype CCD with pixel-response non-uniformity (PRNU) of 0.4%, find the impact of "improper" flat-fielding on these observables is negligible in nominal .7" seeing conditions. These errors scale linearly with the PRNU, so for future LSST production sensors, which may have larger PRNU, the method provides a way to assess whether pixel-level calibration beyond flat fielding will be required.
Wednesday, June 21, 2017
Day 1275
Thursday.
1706.06593
Integrated cosmological probes: concordance quantified
Nicola, Amara, Refregier
Assessing the consistency of parameter constraints derived from different cosmological probes is an important way to test the validity of the underlying cosmo model. An earlier work computed constraints on cosmo parameters for LCDM from an integrated analysis of CMB temperature anisotropies and CMB lensing from Planck, galaxy clustering and WL from SDSS, WL from DES SV as well as Type Ia SNe and Hubble parameter measurements. In this work, extend this analysis and quantify the concordance between the derived constraints and those derived by the Planck Collaboration as well as WMAP9, SPT and ACT. As a measure for consistency, use the Surprise statistic (Seehars+2014), which is based on the relative entropy. In the framework of a flat LCDM cosmo model, find all datasets to be consistent with one another at a level of less than 1 sigma. Highlight that the relative entropy is sensitive to inconsistencies in the models that are used in different parts of the analysis. In particular, inconsistent assumptions for the neutrino mass break its invariance on the parameter choice. When consistent model assumptions are used, the data sets considered in this work all agree with each other and LCDM, without evidence for tensions.
1706.06645
Towards optimal extraction of cosmological information from nonlinear data
Seljak, et al
One of the main unsolved problems of cosmology is how to maximize the extraction of information from nonlinear data. If the data are NL the usual approach is to employ a sequence of statistics (N-point statistics, counting statistics of clusters, density peaks or voids etc.), along with the corresponding covariance matrices. However, this approach is computationally prohibitive and has not been shown to be exhaustive in terms of information content. Instead, develop a Bayesian approach, expanding the likelihood around the maximum posterior of linear modes, which is solved using optimization methods. By integrating out the modes using perturbative expansion of the likelihood, construct an initial power spectrum estimator, which for a fixed forward model contains all the cosmo information if the initial modes are gaussian distributed. Develop a method to construct the window and covariance matrix such that the estimator is explicitly unbiased and nearly optimal. Then generalize the method to include the forward mode parameters, including cosmo and nuisance parameters, and primordial non-gaussianity. Apply the method in the simplified context of NL structure formation, using either simplified 2-LPT dynamics or N-body sims as the nonlinear mapping between linear and nonlinear density, and 2-LPT dynamics in the optimization steps used to reconstruct the initial density modes. Demonstrate that the method gives an unbiased estimator of the initial PS, providing among others a near optimal reconstruction of linear baryonic acoustic oscillations.
1706.06842
A warm or cold early Earth? New insights from a 3-D climate-carbon model
Charnay, et al
Oxygen isotopes in marine cherts have been used to infer hot oceans during the Archean with temperatures between 60 deg C (333K) and 80 deg C (353K). Such climates are challenging for the early Earth warmed by the faint young Sun. The interpretation of the data has therefore been controversial. 1D climate modeling inferred that such hot climates would require very high levels of CO2 (2-6 bars). Previous carbon cycle modeling concluded that such stable hot climates were impossible and that the carbon cycle should lead to cold climates during the Hadean and the Archean. Here, revisit the climate and carbon cycle of the early Earth at 3.8 Ga using a 3D climate-carbon model. Find that CO2 partial pressures of around 1 bar could have produced hot climates given a low land fraction and cloud feedback effects. However, such high CO2 partial pressures should not have been stable because of the weathering of terrestrial and oceanic basalts, producing an efficient stabilizing feedback. Moreover, the weathering of impact ejecta during the Late Heavy Bombardment (LHB) would have strongly reduced the CO2 partial pressure leading to cold climates and potentially snowball Earth events after large impacts. The results therefore favor cold or temperate climates with global mean temperatures between around 8 deg C (281K) and 30 deg C (303 K) and with 0.1-0.36 bar of CO2 for the late Hadean and early Archean. Finally, the model suggests that the carbon cycle was efficient for preserving clement conditions on the early Earth without necessarily requiring any other greenhouse gas or warming process.
1706.06593
Integrated cosmological probes: concordance quantified
Nicola, Amara, Refregier
Assessing the consistency of parameter constraints derived from different cosmological probes is an important way to test the validity of the underlying cosmo model. An earlier work computed constraints on cosmo parameters for LCDM from an integrated analysis of CMB temperature anisotropies and CMB lensing from Planck, galaxy clustering and WL from SDSS, WL from DES SV as well as Type Ia SNe and Hubble parameter measurements. In this work, extend this analysis and quantify the concordance between the derived constraints and those derived by the Planck Collaboration as well as WMAP9, SPT and ACT. As a measure for consistency, use the Surprise statistic (Seehars+2014), which is based on the relative entropy. In the framework of a flat LCDM cosmo model, find all datasets to be consistent with one another at a level of less than 1 sigma. Highlight that the relative entropy is sensitive to inconsistencies in the models that are used in different parts of the analysis. In particular, inconsistent assumptions for the neutrino mass break its invariance on the parameter choice. When consistent model assumptions are used, the data sets considered in this work all agree with each other and LCDM, without evidence for tensions.
1706.06645
Towards optimal extraction of cosmological information from nonlinear data
Seljak, et al
One of the main unsolved problems of cosmology is how to maximize the extraction of information from nonlinear data. If the data are NL the usual approach is to employ a sequence of statistics (N-point statistics, counting statistics of clusters, density peaks or voids etc.), along with the corresponding covariance matrices. However, this approach is computationally prohibitive and has not been shown to be exhaustive in terms of information content. Instead, develop a Bayesian approach, expanding the likelihood around the maximum posterior of linear modes, which is solved using optimization methods. By integrating out the modes using perturbative expansion of the likelihood, construct an initial power spectrum estimator, which for a fixed forward model contains all the cosmo information if the initial modes are gaussian distributed. Develop a method to construct the window and covariance matrix such that the estimator is explicitly unbiased and nearly optimal. Then generalize the method to include the forward mode parameters, including cosmo and nuisance parameters, and primordial non-gaussianity. Apply the method in the simplified context of NL structure formation, using either simplified 2-LPT dynamics or N-body sims as the nonlinear mapping between linear and nonlinear density, and 2-LPT dynamics in the optimization steps used to reconstruct the initial density modes. Demonstrate that the method gives an unbiased estimator of the initial PS, providing among others a near optimal reconstruction of linear baryonic acoustic oscillations.
1706.06842
A warm or cold early Earth? New insights from a 3-D climate-carbon model
Charnay, et al
Oxygen isotopes in marine cherts have been used to infer hot oceans during the Archean with temperatures between 60 deg C (333K) and 80 deg C (353K). Such climates are challenging for the early Earth warmed by the faint young Sun. The interpretation of the data has therefore been controversial. 1D climate modeling inferred that such hot climates would require very high levels of CO2 (2-6 bars). Previous carbon cycle modeling concluded that such stable hot climates were impossible and that the carbon cycle should lead to cold climates during the Hadean and the Archean. Here, revisit the climate and carbon cycle of the early Earth at 3.8 Ga using a 3D climate-carbon model. Find that CO2 partial pressures of around 1 bar could have produced hot climates given a low land fraction and cloud feedback effects. However, such high CO2 partial pressures should not have been stable because of the weathering of terrestrial and oceanic basalts, producing an efficient stabilizing feedback. Moreover, the weathering of impact ejecta during the Late Heavy Bombardment (LHB) would have strongly reduced the CO2 partial pressure leading to cold climates and potentially snowball Earth events after large impacts. The results therefore favor cold or temperate climates with global mean temperatures between around 8 deg C (281K) and 30 deg C (303 K) and with 0.1-0.36 bar of CO2 for the late Hadean and early Archean. Finally, the model suggests that the carbon cycle was efficient for preserving clement conditions on the early Earth without necessarily requiring any other greenhouse gas or warming process.
Tuesday, June 20, 2017
Day 1274
Tuesday. Wednesday.
1706.06125
The galaxy-subhalo connection in low-redshift galaxy clusters from weak gravitational lensing
Sifón, et al
Measure the gravitational lensing signal around satellite galaxies in a sample of galaxy clusters at z<0.15 by combining high-quality imaging data from CFHT with a large sample of spectroscopically-confirmed cluster members. Use extensive image sims to assess the accuracy of shape measurements of faint, background sources in the vicinity of bright satellite galaxies. Find a small but significant bias, as light from the lenses makes the shapes of background galaxies appear radially aligned with the lens. Account for this bias by applying a correction that depends on both lens size and magnitude. Also correct for contamination of the source sample by cluster members. Use a physically-motivated definition of sub halo mass, namely the mass bound to the sub halo, m_bg, similar to definitions used by common sub halo finders in numerical sims. Binning the satellites by stellar mass, provide a direct measurement of the subhalo-to-stellar-mass relation, log m_bg/Msun=(11.66±0.07)+(0.94±0.15) log [m*/(2e10Msun)]. This best-fitting relation implies that, at a stellar mass m*~3e10 Msun, sub halo masses are roughly 50% lower than their central counterparts, and this fraction decreases at higher stellar masses. On the other hand, find no statistically significant evidence for mass segregation when lenses are binned by their projected cluster-centric distance, contrary to recent claims, with an average total-to-stellar mass ratio <m_bg/m*>=21.5+6.3-5.5. Find that, once the projected effects and for differences between DM sub haloes and satellite galaxies are accounted for, the results are consistent with theoretical predictions.
1706.06125
The galaxy-subhalo connection in low-redshift galaxy clusters from weak gravitational lensing
Sifón, et al
Measure the gravitational lensing signal around satellite galaxies in a sample of galaxy clusters at z<0.15 by combining high-quality imaging data from CFHT with a large sample of spectroscopically-confirmed cluster members. Use extensive image sims to assess the accuracy of shape measurements of faint, background sources in the vicinity of bright satellite galaxies. Find a small but significant bias, as light from the lenses makes the shapes of background galaxies appear radially aligned with the lens. Account for this bias by applying a correction that depends on both lens size and magnitude. Also correct for contamination of the source sample by cluster members. Use a physically-motivated definition of sub halo mass, namely the mass bound to the sub halo, m_bg, similar to definitions used by common sub halo finders in numerical sims. Binning the satellites by stellar mass, provide a direct measurement of the subhalo-to-stellar-mass relation, log m_bg/Msun=(11.66±0.07)+(0.94±0.15) log [m*/(2e10Msun)]. This best-fitting relation implies that, at a stellar mass m*~3e10 Msun, sub halo masses are roughly 50% lower than their central counterparts, and this fraction decreases at higher stellar masses. On the other hand, find no statistically significant evidence for mass segregation when lenses are binned by their projected cluster-centric distance, contrary to recent claims, with an average total-to-stellar mass ratio <m_bg/m*>=21.5+6.3-5.5. Find that, once the projected effects and for differences between DM sub haloes and satellite galaxies are accounted for, the results are consistent with theoretical predictions.
Friday, June 16, 2017
Day 1273
Monday.
1706.05004
KiDS+GAMA: Cosmology constraints from a joint analysis of cosmic shear, galaxy-galaxy lensing and angular clustering
van Uitert, Joachimi, et al
Present cosmological parameter constraints from a joint analysis of 3 cosmological probes: the tomographic cosmic shear signal in ~450 deg2 of data from KiDS, the galaxy-mater cross-correlation signal of galaxies from GAMA determined with KiDS WL, and the angular correlation function of the same GAMA galaxies. Use fast power spectrum estimators that are based on simple integrals over the real-space correlation functions, and show that they are unbiased over relevant angular frequency ranges. Test the full pipeline on numerical sims that are tailored to KiDS and retrieve the input cosmology. By fitting different combinations of PS, demonstrate that the 3 probes are internally consistent. For all probes combined, obtain S8=sigma8 x sort(Omega_m/0.3) = 0.801±0.032, consistent with Planck and the fiducial KiDS-450 cosmic shear correlation function results. The combination of probes results in a 21% reduction in uncertainties over using the cosmic shear power spectra alone. The main gain from these additional probes comes through their constraining power on nuisance parameters, such as the galaxy IA or potential shifts in the redshift distributions, which are up to a factor of 2 better constrained compared to using cosmic shear alone, demonstrating the value of LSS probe combination.
1706.05133
Geometry and growth contributions to cosmic shear observables
Zorrilla Matilla, Hainan, Petri, Namikawa
Explore the sensitivity of WL observables to the expansion history of the universe and to the growth of cosmic structures, as well as the relative contribution of both effects to constraining cosmo parameters. Utilize ray-tracing dark-matter-only N-body sims and validate the technique by comparing the results for the convergence PS with analytic results from past studies. Then extend the analysis to non-Gaussian observables which cannot be easily treated analytically. Study the convergence (equilateral) bispectrum and 2 topological observables, lensing peaks and Minkowski functionals, focusing on their sensitivity to the matter density Omega_m and the DE EoS w. Find that a cancelation between the geometry and growth effects is a common feature for all observables, and exists at the map level. It weakens the overall sensitivity by up to a factor of 3 and 1.5 for w and Omega_m, respectively, with the bispectrum worst affected. However, combining geometry and growth information alleviates the degeneracy between Omega_m and w from either effect alone. As a result, the magnitude of marginalized errors remain similar to those obtained from growth-only effects, but with the correlation between the 2 parameters switching sign. These results shed light on the origin of cosmology-sensitivity of non-Gaussian statistics, and should be useful in optimizing combinations of observables.
1706.05004
KiDS+GAMA: Cosmology constraints from a joint analysis of cosmic shear, galaxy-galaxy lensing and angular clustering
van Uitert, Joachimi, et al
Present cosmological parameter constraints from a joint analysis of 3 cosmological probes: the tomographic cosmic shear signal in ~450 deg2 of data from KiDS, the galaxy-mater cross-correlation signal of galaxies from GAMA determined with KiDS WL, and the angular correlation function of the same GAMA galaxies. Use fast power spectrum estimators that are based on simple integrals over the real-space correlation functions, and show that they are unbiased over relevant angular frequency ranges. Test the full pipeline on numerical sims that are tailored to KiDS and retrieve the input cosmology. By fitting different combinations of PS, demonstrate that the 3 probes are internally consistent. For all probes combined, obtain S8=sigma8 x sort(Omega_m/0.3) = 0.801±0.032, consistent with Planck and the fiducial KiDS-450 cosmic shear correlation function results. The combination of probes results in a 21% reduction in uncertainties over using the cosmic shear power spectra alone. The main gain from these additional probes comes through their constraining power on nuisance parameters, such as the galaxy IA or potential shifts in the redshift distributions, which are up to a factor of 2 better constrained compared to using cosmic shear alone, demonstrating the value of LSS probe combination.
1706.05133
Geometry and growth contributions to cosmic shear observables
Zorrilla Matilla, Hainan, Petri, Namikawa
Explore the sensitivity of WL observables to the expansion history of the universe and to the growth of cosmic structures, as well as the relative contribution of both effects to constraining cosmo parameters. Utilize ray-tracing dark-matter-only N-body sims and validate the technique by comparing the results for the convergence PS with analytic results from past studies. Then extend the analysis to non-Gaussian observables which cannot be easily treated analytically. Study the convergence (equilateral) bispectrum and 2 topological observables, lensing peaks and Minkowski functionals, focusing on their sensitivity to the matter density Omega_m and the DE EoS w. Find that a cancelation between the geometry and growth effects is a common feature for all observables, and exists at the map level. It weakens the overall sensitivity by up to a factor of 3 and 1.5 for w and Omega_m, respectively, with the bispectrum worst affected. However, combining geometry and growth information alleviates the degeneracy between Omega_m and w from either effect alone. As a result, the magnitude of marginalized errors remain similar to those obtained from growth-only effects, but with the correlation between the 2 parameters switching sign. These results shed light on the origin of cosmology-sensitivity of non-Gaussian statistics, and should be useful in optimizing combinations of observables.
Day 1272
Friday.
1706.04981
Probing the shape and internal structure of dark matter halos with the halo-shear-shear three-point correlation function
Shirasaki, Yoshida
WL 3pt statistics are powerful probes of the structure of DM haloes. Propose to use the correlation of the positions of galaxies with the shapes of BG galaxy pairs, known as the halo-shear-shear correlation (HSSC), to measure the mean halo ellipticity and the abundance of sub halos in a statistical manner. Run high-resolution cosmo N-body sims and use the outputs to measure the HSSC for galaxy haloes and cluster halos. Non-spherical halos cause a characteristic azimuthal variation of the HSSC, and massive sub halos in the outer region near the viral radius contribute to ~10% of the HSSC amplitude. Develop an analytic model of the 3pt statistics and test its accuracy using the sim results. Then make forecast for constraining the internal structure of dark matter halos with future galaxy surveys. With 1000 galaxy groups with mass greater than 1e13.5 Msun/h, the average halo ellipticity can be measured with an accuracy of 10%. A spherical, smooth mass distribution can be ruled out at a ~5 sigma significance level. The existence of sub halos whose masses are in 1-10 % of the main halo mass can be detected with ~1e4 galaxies/clusters. Conclude that the HSSC provides valuable information on the structure of dark halos and hence on the nature of DM.
1706.04981
Probing the shape and internal structure of dark matter halos with the halo-shear-shear three-point correlation function
Shirasaki, Yoshida
WL 3pt statistics are powerful probes of the structure of DM haloes. Propose to use the correlation of the positions of galaxies with the shapes of BG galaxy pairs, known as the halo-shear-shear correlation (HSSC), to measure the mean halo ellipticity and the abundance of sub halos in a statistical manner. Run high-resolution cosmo N-body sims and use the outputs to measure the HSSC for galaxy haloes and cluster halos. Non-spherical halos cause a characteristic azimuthal variation of the HSSC, and massive sub halos in the outer region near the viral radius contribute to ~10% of the HSSC amplitude. Develop an analytic model of the 3pt statistics and test its accuracy using the sim results. Then make forecast for constraining the internal structure of dark matter halos with future galaxy surveys. With 1000 galaxy groups with mass greater than 1e13.5 Msun/h, the average halo ellipticity can be measured with an accuracy of 10%. A spherical, smooth mass distribution can be ruled out at a ~5 sigma significance level. The existence of sub halos whose masses are in 1-10 % of the main halo mass can be detected with ~1e4 galaxies/clusters. Conclude that the HSSC provides valuable information on the structure of dark halos and hence on the nature of DM.
Thursday, June 15, 2017
Day 1271
Thursday.
1706.04201
Formation of hypervelocity stars in AGN outflows
Wang, Loeb
Study SF within outflows driven by AGN as a new source of hypervelocity stars (HVSs). Recent observations revealed active SF inside a galactic outflow at a rate of ~15 Msun/yr. Show that the shells swept up by an AGN outflow are capable of cooling and fragmentation into cold clumps embedded in a hot tenuous gas via thermal instabilities. As a result, stars are produced along outflow's path, endowed with the outflow speed at their formation site. These HVSs travel through the galactic halo and eventually escape into the IGM. The expected instantaneous rate of SF inside the outflow is ~4-5 orders of magnitude greater than the average rate associated with previously proposed mechanisms for producing HVSs, such as the Hills mechanism and 3-body interaction between a star and a BH binary.
1706.04583
Cosmological constraints from a joint analysis of cosmic microwave background and large-scale structure
Doux, et al
The standard model of cosmology, LCDM, is the simplest model that matches the current observations, but relies on 2 hypothetical components, to wit, dark matter and dark energy. Further galaxy surveys and CMB experiments will independently shed light on these components, but a joint analysis that includes cross-correlations will be necessary to extract as much information as possible from the observations. In this paper, aim at developing the methods needed to perform such an analysis, and test it on publicly available data sets. In particular, use CMB temperature anisotropies and CMB lensing observations from Planck, and the spectroscopic galaxy and quasar samples of SDSS-III/BOSS. Build a likelihood to simultaneously analyze the auto and cross spectra of the CMB lensing and the galaxy overdensity maps before running MCMC to assess the constraining power of the combined analysis. Then add CMB temperature information and run MCMCs to test the LCDM model. Present constraints on cosmo parameter and galaxy biases, and demonstrate that the joint analysis can additionally constrain the mass of neutrinos as well as the DE EoS. Finally, discuss several difficulties regarding the analysis itself and the theoretical precision of the models, which will require additional work to properly analyse the observations of the next generation of cosmo experiments.
1706.04201
Formation of hypervelocity stars in AGN outflows
Wang, Loeb
Study SF within outflows driven by AGN as a new source of hypervelocity stars (HVSs). Recent observations revealed active SF inside a galactic outflow at a rate of ~15 Msun/yr. Show that the shells swept up by an AGN outflow are capable of cooling and fragmentation into cold clumps embedded in a hot tenuous gas via thermal instabilities. As a result, stars are produced along outflow's path, endowed with the outflow speed at their formation site. These HVSs travel through the galactic halo and eventually escape into the IGM. The expected instantaneous rate of SF inside the outflow is ~4-5 orders of magnitude greater than the average rate associated with previously proposed mechanisms for producing HVSs, such as the Hills mechanism and 3-body interaction between a star and a BH binary.
1706.04583
Cosmological constraints from a joint analysis of cosmic microwave background and large-scale structure
Doux, et al
The standard model of cosmology, LCDM, is the simplest model that matches the current observations, but relies on 2 hypothetical components, to wit, dark matter and dark energy. Further galaxy surveys and CMB experiments will independently shed light on these components, but a joint analysis that includes cross-correlations will be necessary to extract as much information as possible from the observations. In this paper, aim at developing the methods needed to perform such an analysis, and test it on publicly available data sets. In particular, use CMB temperature anisotropies and CMB lensing observations from Planck, and the spectroscopic galaxy and quasar samples of SDSS-III/BOSS. Build a likelihood to simultaneously analyze the auto and cross spectra of the CMB lensing and the galaxy overdensity maps before running MCMC to assess the constraining power of the combined analysis. Then add CMB temperature information and run MCMCs to test the LCDM model. Present constraints on cosmo parameter and galaxy biases, and demonstrate that the joint analysis can additionally constrain the mass of neutrinos as well as the DE EoS. Finally, discuss several difficulties regarding the analysis itself and the theoretical precision of the models, which will require additional work to properly analyse the observations of the next generation of cosmo experiments.
Wednesday, June 14, 2017
Day 1270
Wednesday.
1706.03770
Testing for a redshift evolution of Type Ia supernovae using the strongly lensed PS1-10afx at z=1.4
Petrushevska, et al
The light from stint supernovae She can be magnified through gravitational lensing when a foreground galaxy is located along the line of sight. This line-up allows for detailed studies of SNe at high redshift that otherwise would not be possible. Spectroscopic observations of lensed high-z She Ia are of particular interest since they can be used to test for evolution of their intrinsic properties. The use of SNe Ia for probing the cosmic expansion history has proven to be an extremely powerful method for measuring cosmological parameters. However, if systematic z-dependent properties are found, their usefulness for future surveys could be challenged. Investigate whether the spectroscopic properties of the strongly lensed and very distant SN Ia PS1-10afx at z=1.4 deviates from the well-studied populations of normal SNe Ia at nearby or intermediate distance. Create median spectra from nearby and intermediate-z spectroscopically normal She Ia from the literature at -5 and +1 days from light-curve maximum. Then compared these median spectra to those of PS1-10afx. Do not find signs of spectral evolution in PS1-10afx. The observed deviation between PA1-10afx and the median templates are within what is found for She at low- and intermediate-z. There is a noticeable broad feature centered at lambda~3500 A, which is present only to a lesser extent in individual low and intermediate redshift SN Ia spectra. From a comparison with a recently developed explosion model, find this feature to be dominated by Fe peak elements, in particular, singly ionized Co and Cr.
1706.03798
Ten billion years of brightest cluster galaxy alignments
West, De Props, Bremer, Phillipps
A galaxy's orientation is one of its most basic observable properties. Astronomers once assumed that galaxies are randomly oriented in space, however it is now clear that some have preferred orientations with respect to their surroundings. Chief among these are giant elliptical galaxies found in the centers of rich galaxy clusters. Numerous studies have shown that the major axes of these galaxies often share the same orientation as the surrounding matter distribution on large scales. Using HST observations of 65 distant galaxy clusters, show for the first time that similar alignments are seen at earlier epochs when the universe was only one-third its current age. These results suggest that the brightest galaxies in clusters are the product of a special formation history, one influenced by development of the cosmic web over billions of years.
1706.03834
Diffuse neutrino supernova background as a cosmological test
Barranco, Bernal, Delepine
The future detection and measurement of the diffuse neutrino SN background will shed light on the rate of SNe events in the Universe, the SFR and the neutrino spectrum from each SN. Little has been said about what those measurements will tell us about the expansion history of the universe. The purpose of this article is to show that the detection of the diffuse SN neutrino background will be a complementary tool for the study and possible discrimination of cosmological models. In particular, study 3 different cosmological models: the LCDM model, the Logotropic universe and a bulk viscous matter-dominated universe. By fitting the free parameters of each model with the SN Ia probe, find that the predicted number of events computed with the best fit parameters for the LCDM model and with the Logotropic model are the same, while a bulk viscous matter-dominated cosmological model predicts ~3x more events. Show that the current limit set by Super-Kamiokande on the diffuse SN neutrino background flux gives complementary constraints on the free parameters of a bulk viscous matter-dominated universe. Furthermore, this limit implies, within a LCDM model, that the universe should be expanding with H0>21.5 km/s/Mpc independently of the content of dark matter Omega_m.
1706.03903
Pixel noise effect and its correction method by ERA method for precise weak gravitational lensing shear measurement
Okura, Futamase
Highly precise weak lensing shear measurement is required for statistical WL analysis such as cosmic shear to achieve stringent constraint on the cosmological parameters. For this purpose any systematic error in the measurement should be corrected. One of the main systematic error comes from [Poisson pixel noise of flux through the atmosphere]. Investigate how the pixel noise makes systematic error in shear measurement based on ERA method and develop a correction method. This method is tested by simulations with various conditions and it is confirmed that the correction method can correct 80-90% of the systematic error except very low signal to noise galaxies.
1706.03770
Testing for a redshift evolution of Type Ia supernovae using the strongly lensed PS1-10afx at z=1.4
Petrushevska, et al
The light from stint supernovae She can be magnified through gravitational lensing when a foreground galaxy is located along the line of sight. This line-up allows for detailed studies of SNe at high redshift that otherwise would not be possible. Spectroscopic observations of lensed high-z She Ia are of particular interest since they can be used to test for evolution of their intrinsic properties. The use of SNe Ia for probing the cosmic expansion history has proven to be an extremely powerful method for measuring cosmological parameters. However, if systematic z-dependent properties are found, their usefulness for future surveys could be challenged. Investigate whether the spectroscopic properties of the strongly lensed and very distant SN Ia PS1-10afx at z=1.4 deviates from the well-studied populations of normal SNe Ia at nearby or intermediate distance. Create median spectra from nearby and intermediate-z spectroscopically normal She Ia from the literature at -5 and +1 days from light-curve maximum. Then compared these median spectra to those of PS1-10afx. Do not find signs of spectral evolution in PS1-10afx. The observed deviation between PA1-10afx and the median templates are within what is found for She at low- and intermediate-z. There is a noticeable broad feature centered at lambda~3500 A, which is present only to a lesser extent in individual low and intermediate redshift SN Ia spectra. From a comparison with a recently developed explosion model, find this feature to be dominated by Fe peak elements, in particular, singly ionized Co and Cr.
1706.03798
Ten billion years of brightest cluster galaxy alignments
West, De Props, Bremer, Phillipps
A galaxy's orientation is one of its most basic observable properties. Astronomers once assumed that galaxies are randomly oriented in space, however it is now clear that some have preferred orientations with respect to their surroundings. Chief among these are giant elliptical galaxies found in the centers of rich galaxy clusters. Numerous studies have shown that the major axes of these galaxies often share the same orientation as the surrounding matter distribution on large scales. Using HST observations of 65 distant galaxy clusters, show for the first time that similar alignments are seen at earlier epochs when the universe was only one-third its current age. These results suggest that the brightest galaxies in clusters are the product of a special formation history, one influenced by development of the cosmic web over billions of years.
1706.03834
Diffuse neutrino supernova background as a cosmological test
Barranco, Bernal, Delepine
The future detection and measurement of the diffuse neutrino SN background will shed light on the rate of SNe events in the Universe, the SFR and the neutrino spectrum from each SN. Little has been said about what those measurements will tell us about the expansion history of the universe. The purpose of this article is to show that the detection of the diffuse SN neutrino background will be a complementary tool for the study and possible discrimination of cosmological models. In particular, study 3 different cosmological models: the LCDM model, the Logotropic universe and a bulk viscous matter-dominated universe. By fitting the free parameters of each model with the SN Ia probe, find that the predicted number of events computed with the best fit parameters for the LCDM model and with the Logotropic model are the same, while a bulk viscous matter-dominated cosmological model predicts ~3x more events. Show that the current limit set by Super-Kamiokande on the diffuse SN neutrino background flux gives complementary constraints on the free parameters of a bulk viscous matter-dominated universe. Furthermore, this limit implies, within a LCDM model, that the universe should be expanding with H0>21.5 km/s/Mpc independently of the content of dark matter Omega_m.
1706.03903
Pixel noise effect and its correction method by ERA method for precise weak gravitational lensing shear measurement
Okura, Futamase
Highly precise weak lensing shear measurement is required for statistical WL analysis such as cosmic shear to achieve stringent constraint on the cosmological parameters. For this purpose any systematic error in the measurement should be corrected. One of the main systematic error comes from [Poisson pixel noise of flux through the atmosphere]. Investigate how the pixel noise makes systematic error in shear measurement based on ERA method and develop a correction method. This method is tested by simulations with various conditions and it is confirmed that the correction method can correct 80-90% of the systematic error except very low signal to noise galaxies.
Monday, June 12, 2017
Day 1269
Tuesday.
1705.08662
Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6
Declare, Walter, et al
The existence of massive (1e11 Msun) elliptical galaxies by z~4 (when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 Msun/year at z>6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their SFRs are more than an order of magnitude lower. The only known galaxies with very high SFRs at z>6 are, with only one exception, the host galaxies of quasars, but these galaxies also host accreting SMBHs (>1e9 Msun), which probably affect the properties of the galaxies. Report here the observations of an emission line of singly ionized carbon ([CII] at a wavelength of 158 um) in 4 galaxies at z>6 that are companions of quasars, with velocity offsets of less than 600 km/s and linear offset of less than 600 kpc. The discovery of these 4 galaxies was serendipitous; they are close to their companion quasars and appear bright in the IR. On the basis of the [CII] measurements, estimate SFRs in the companions of more than 100 Msun per year. These sources are similar to the host galaxies of the quasars in [CII] brightness, line width and implied dynamical masses, but do not show evidence for accreting SMBHs. Similar systems have previously been found at lower z. Find such close companions in 4 out of 25 z>6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [CII] luminosity function, then they can account for the population of massive elliptical galaxies at z~4 in terms of cosmic space density.
1705.05840
Knowledge discovery through text-based similarity searches for astronomy literature
Kerzendorf
The increase in the number of researchers coupled with the ease of publishing and distribution of scientific papers (due to technological advancements) has resulted in a dramatic increase in astronomy literature. This has likely led to the predicament that the body of the literature is too large for traditional human consumption and that related and crucial knowledge is not discovered by researchers. In addition to the increased production of astronomical literature, recent decades have also brought several advancements in computer linguistics. The machine aided processing of literature dissemination might make it possible to convert this stream of papers into a coherent knowledge set. In this paper, present the application of computer linguistics techniques on astronomy literature. In particular, develop a tool that will find similar articles purely based on text content given an input paper. Find that this technique performs robustly in comparison with other tools recommending articles given a reference paper (known as recommender system). The novel tool shows the great power in combining computer linguistics with astronomy literature and suggests that additional research in this endeavor will likely produce even better tools that will help researchers cope with the vast amounts of knowledge being produced.
1706.03173
Modeling CMB lensing cross correlations with CLEFT
Modi, White, Vlah
A new generation of surveys will soon map large fractions of sky to ever greater depths and their science goals can be enhanced by exploiting cross correlations between them. In this paper, study cross correlations between the lensing of the CMB and biased tracers of large-scale structure at high z. Motivate the need for more sophisticated bias models for modeling increasingly biased tracers at these redshifts and propose the use of perturbation theories, specifically Convolution Lagrangian Effective Field Theory (CLEFT). Since such signals reside at large scales and redshifts, they can be well described by perturbative approaches. Compare the model with the current approach of using scale independent bias coupled with fitting functions for non-linear matter power spectra, showing that the latter will not be sufficient for upcoming surveys. Illustrate the ideas by estimating sigma8 from the auto- and cross-spectra of mock surveys, finding that CLEFT returns accurate and unbiased results at high z. Discuss uncertainties due to the redshift distribution of the tracers, and several avenues for future development.
1706.03753
The two-halo term in stacked thermal Sunyaev-Zel'dovich measurements: implications for self-similarity
Hill, Baxter, Lidz, Greco, Jain
Relation between the mass and integrated electron pressure of galaxy group and cluster haloes can be probed by stacking maps of the tSZ effect. Surprisingly, recent observational results have indicated that the scaling relation between integrated pressure and mass follows the prediction of simple, self-similar models down to halo masses as low as 1e12.5 Msun. Hydrodynamical sims that incorporate energetic feedback processes suggest that gas should be depleted from such low-mass halos, thus decreasing their tSZ signal relative to self-similar predictions. Here, build on the modeling of Vikram, Lidz, & Jain (2017) to evaluate the bias in the interpretation of stacked tSZ measurements due to the signal from correlated haloes (the 2-halo term), which has generally been neglected in the literature. Fit theoretical models to a measurement of the tSZ -- galaxy group X-correlation function, accounting explicitly for the 1- and 2-halo contributions. Find moderate evidence of a deviation from self-similarity in the pressure -- mass relation, even after marginalizing over conservative miscentering effects. Explore pressure -- mass models with a break at 1e14 Msun, as well as other variants. Discuss and test for sources of uncertainty in the analysis, in particular a possible bias in the halo mass estimates and the coarse resolution of the Planck beam. Compare the findings with earlier analyses by exploring the extent to which halo isolation criteria can reduce the 2-halo contribution. Show that ongoing 3rd generation CMB experiments will explicitly resolve the 1-halo term in low-mass groups; the methodology can be applied to these upcoming data sets to obtain a clear answer to the question of self-similarity and an improved understanding of hot has in low-mass halos.
1705.08662
Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6
Declare, Walter, et al
The existence of massive (1e11 Msun) elliptical galaxies by z~4 (when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 Msun/year at z>6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their SFRs are more than an order of magnitude lower. The only known galaxies with very high SFRs at z>6 are, with only one exception, the host galaxies of quasars, but these galaxies also host accreting SMBHs (>1e9 Msun), which probably affect the properties of the galaxies. Report here the observations of an emission line of singly ionized carbon ([CII] at a wavelength of 158 um) in 4 galaxies at z>6 that are companions of quasars, with velocity offsets of less than 600 km/s and linear offset of less than 600 kpc. The discovery of these 4 galaxies was serendipitous; they are close to their companion quasars and appear bright in the IR. On the basis of the [CII] measurements, estimate SFRs in the companions of more than 100 Msun per year. These sources are similar to the host galaxies of the quasars in [CII] brightness, line width and implied dynamical masses, but do not show evidence for accreting SMBHs. Similar systems have previously been found at lower z. Find such close companions in 4 out of 25 z>6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [CII] luminosity function, then they can account for the population of massive elliptical galaxies at z~4 in terms of cosmic space density.
1705.05840
Knowledge discovery through text-based similarity searches for astronomy literature
Kerzendorf
The increase in the number of researchers coupled with the ease of publishing and distribution of scientific papers (due to technological advancements) has resulted in a dramatic increase in astronomy literature. This has likely led to the predicament that the body of the literature is too large for traditional human consumption and that related and crucial knowledge is not discovered by researchers. In addition to the increased production of astronomical literature, recent decades have also brought several advancements in computer linguistics. The machine aided processing of literature dissemination might make it possible to convert this stream of papers into a coherent knowledge set. In this paper, present the application of computer linguistics techniques on astronomy literature. In particular, develop a tool that will find similar articles purely based on text content given an input paper. Find that this technique performs robustly in comparison with other tools recommending articles given a reference paper (known as recommender system). The novel tool shows the great power in combining computer linguistics with astronomy literature and suggests that additional research in this endeavor will likely produce even better tools that will help researchers cope with the vast amounts of knowledge being produced.
1706.03173
Modeling CMB lensing cross correlations with CLEFT
Modi, White, Vlah
A new generation of surveys will soon map large fractions of sky to ever greater depths and their science goals can be enhanced by exploiting cross correlations between them. In this paper, study cross correlations between the lensing of the CMB and biased tracers of large-scale structure at high z. Motivate the need for more sophisticated bias models for modeling increasingly biased tracers at these redshifts and propose the use of perturbation theories, specifically Convolution Lagrangian Effective Field Theory (CLEFT). Since such signals reside at large scales and redshifts, they can be well described by perturbative approaches. Compare the model with the current approach of using scale independent bias coupled with fitting functions for non-linear matter power spectra, showing that the latter will not be sufficient for upcoming surveys. Illustrate the ideas by estimating sigma8 from the auto- and cross-spectra of mock surveys, finding that CLEFT returns accurate and unbiased results at high z. Discuss uncertainties due to the redshift distribution of the tracers, and several avenues for future development.
1706.03753
The two-halo term in stacked thermal Sunyaev-Zel'dovich measurements: implications for self-similarity
Hill, Baxter, Lidz, Greco, Jain
Relation between the mass and integrated electron pressure of galaxy group and cluster haloes can be probed by stacking maps of the tSZ effect. Surprisingly, recent observational results have indicated that the scaling relation between integrated pressure and mass follows the prediction of simple, self-similar models down to halo masses as low as 1e12.5 Msun. Hydrodynamical sims that incorporate energetic feedback processes suggest that gas should be depleted from such low-mass halos, thus decreasing their tSZ signal relative to self-similar predictions. Here, build on the modeling of Vikram, Lidz, & Jain (2017) to evaluate the bias in the interpretation of stacked tSZ measurements due to the signal from correlated haloes (the 2-halo term), which has generally been neglected in the literature. Fit theoretical models to a measurement of the tSZ -- galaxy group X-correlation function, accounting explicitly for the 1- and 2-halo contributions. Find moderate evidence of a deviation from self-similarity in the pressure -- mass relation, even after marginalizing over conservative miscentering effects. Explore pressure -- mass models with a break at 1e14 Msun, as well as other variants. Discuss and test for sources of uncertainty in the analysis, in particular a possible bias in the halo mass estimates and the coarse resolution of the Planck beam. Compare the findings with earlier analyses by exploring the extent to which halo isolation criteria can reduce the 2-halo contribution. Show that ongoing 3rd generation CMB experiments will explicitly resolve the 1-halo term in low-mass groups; the methodology can be applied to these upcoming data sets to obtain a clear answer to the question of self-similarity and an improved understanding of hot has in low-mass halos.
Day 1268
Monday.
1706.02704
The abundance of ultra-diffuse galaxies from groups to clusters: UDGs are relatively more common in more massive haloes
van der Burg, Hoekstra, et al
In recent years, multiple studies have reported substantial populations of large, low-surface-brightness galaxies in local galaxy clusters. Various theories that aim to explain the presence of such UDGs have since been proposed. A key question that will help to differentiate between models is whether UDGs have counterparts in lower-mass host haloes, and what their abundance as a function of halo mass is. In this study, extend the previous study of UDGs in galaxy clusters to galaxy groups. Measure the abundance of UDGs in 325 spectroscopically-selected groups from GAMA. Make use of the overlapping image from KiDS, from which galaxies can be identified with mean surface brightnesses within their effective radii down to ~25.5 mag/arcsec^2 in the r-band. Able to measure a significant overdensity of UDGs (with sizes r_eff>1.5 kpc) in galaxy groups down to M200=1e12 Msun, a regime where approximately only 1 in 10 groups contains a UDG that can be detected. Combine measurements of the abundance of UDGs in haloes that cover 3 orders of magnitude in halo mass, finding that their numbers scale quite steeply with halo mass; N_UDG (R<R200) ~ M200^(1.11±0.07). To better interpret this, also measure the mass-richness relation for brighter galaxies down to M*_r +2.5 in the same GAMA groups, and find a much shallower relation of N_Bright (R<R200) ~ M200^(0.78±0.05). This shows that UDGs are relatively more abundant, compared to bright galaxies, in massive clusters than in groups. Discuss implications, but whether this difference is related to a higher destruction rate of UDGs in groups, or whether massive haloes have a positive effect on their formation, is not yet clear.
1706.02892
KiDS-450: The tomographic weak lensing power spectrum and constraints on cosmological parameters
Köhlinger, Viola, Joachimi, Hoekstra, van Uitert, et al
Present measurements of the WL shear power spectrum based on 450 sq. deg. of imaging data from KiDS. Employ a quadratic estimator in 2 and 3 z bins and extract band powers of z auto-correlation and cross-correlation spectra in the multipole range 76<ell<1310. The cosmo interpretation of the measured shear PS is performed in a Bayesian framework assuming a LCDM model with spatially flat geometry, while accounting for small residual uncertainties in the shear calibration and redshift distributors as well as marginalizing over intrinsic alignments, baryon feedback and an excess-noise power model. Moreover, massive neutrinos are included in the modeling. The cosmo main result is expressed in terms of the parameter combination S8=sigma_8xsqrt(Omega_m/0.3) yielding S8=0.651±0.058 (3 z-bins), confirming the recently reported tension in this parameter with constraints from Planck at 3.2 sigma (3 z-bins). Cross-check the results of the 3 z-bin analysis with the weaker constraints from the 2 z-bin analysis and find them to be consistent. The high-level data products of this analysis, such as the band power measurements, covariance matrices, z distributions, and likelihood evaluation changes are available at http://kids.strw.leidenuniv.nl/.
1706.02704
The abundance of ultra-diffuse galaxies from groups to clusters: UDGs are relatively more common in more massive haloes
van der Burg, Hoekstra, et al
In recent years, multiple studies have reported substantial populations of large, low-surface-brightness galaxies in local galaxy clusters. Various theories that aim to explain the presence of such UDGs have since been proposed. A key question that will help to differentiate between models is whether UDGs have counterparts in lower-mass host haloes, and what their abundance as a function of halo mass is. In this study, extend the previous study of UDGs in galaxy clusters to galaxy groups. Measure the abundance of UDGs in 325 spectroscopically-selected groups from GAMA. Make use of the overlapping image from KiDS, from which galaxies can be identified with mean surface brightnesses within their effective radii down to ~25.5 mag/arcsec^2 in the r-band. Able to measure a significant overdensity of UDGs (with sizes r_eff>1.5 kpc) in galaxy groups down to M200=1e12 Msun, a regime where approximately only 1 in 10 groups contains a UDG that can be detected. Combine measurements of the abundance of UDGs in haloes that cover 3 orders of magnitude in halo mass, finding that their numbers scale quite steeply with halo mass; N_UDG (R<R200) ~ M200^(1.11±0.07). To better interpret this, also measure the mass-richness relation for brighter galaxies down to M*_r +2.5 in the same GAMA groups, and find a much shallower relation of N_Bright (R<R200) ~ M200^(0.78±0.05). This shows that UDGs are relatively more abundant, compared to bright galaxies, in massive clusters than in groups. Discuss implications, but whether this difference is related to a higher destruction rate of UDGs in groups, or whether massive haloes have a positive effect on their formation, is not yet clear.
1706.02892
KiDS-450: The tomographic weak lensing power spectrum and constraints on cosmological parameters
Köhlinger, Viola, Joachimi, Hoekstra, van Uitert, et al
Present measurements of the WL shear power spectrum based on 450 sq. deg. of imaging data from KiDS. Employ a quadratic estimator in 2 and 3 z bins and extract band powers of z auto-correlation and cross-correlation spectra in the multipole range 76<ell<1310. The cosmo interpretation of the measured shear PS is performed in a Bayesian framework assuming a LCDM model with spatially flat geometry, while accounting for small residual uncertainties in the shear calibration and redshift distributors as well as marginalizing over intrinsic alignments, baryon feedback and an excess-noise power model. Moreover, massive neutrinos are included in the modeling. The cosmo main result is expressed in terms of the parameter combination S8=sigma_8xsqrt(Omega_m/0.3) yielding S8=0.651±0.058 (3 z-bins), confirming the recently reported tension in this parameter with constraints from Planck at 3.2 sigma (3 z-bins). Cross-check the results of the 3 z-bin analysis with the weaker constraints from the 2 z-bin analysis and find them to be consistent. The high-level data products of this analysis, such as the band power measurements, covariance matrices, z distributions, and likelihood evaluation changes are available at http://kids.strw.leidenuniv.nl/.
Sunday, June 11, 2017
Day 1267
Friday. Monday. Tuesday. Wednesday. Thursday. Friday.
1706.00427
Source selection for cluster weak lensing measurements in the Hyper Suprime-Cam survey
Medezinski, et al
Present optimal source galaxy selection schemes for measuring unbiased cluster WL mass profiles from HSC-SSP. The ongoing HSC-SSP survey will uncover thousands of galaxy clusters to z<~1.5. In deriving cluster masses via WL, a critical source of systematics is contamination and dilution of the lensing signal by cluster and FG galaxies. Using the first-year CAMIRA catalog of ~900 clusters with richness larger than 20 found in ~140 deg^2 of HSC-SSP data, devise and compare several source selection methods, including selection in color-color space (CC-cut), and selection of robust photometric redshifts by applying constraints on their cumulative probability distribution function (PDF; P-cut). Examine the dependence of the contamination on the chosen limits adopted for each method. Using the proper limits, these methods give dilution-free mass profiles in agreement with one another. Find that not adopting either the CC-cut or P-cut methods results in a underestimation of the total cluster mass (13±4%) and the concentration of the profile (24±11%). The robust methods yield a ~60sigma detection of the stacked CAMIRA surface mass density profile, with a mean mass of M_200c=1.67±0.05 e14 Msun/h.
1706.00434
Planck Sunyaev-Zel'dovich cluster mass calibration using Hyper Suprime-Cam weak lensing
Medezinski, et al
Using ~140 deg&2 HSC survey data, stack the WL signal around 5 Planck clusters found within the footprint. This yields a 15 sigma detection of the mean Planck cluster mass density profile. The 5 Planck clusters span a relatively wide mass range, M_WL,500c=2-25e14 Msun with a mean mass of M_WL,500c=4.1±0.5e14 Msun. The mean ratio of the SZ mass to the WL mass is M_SZ/M_WL=1-b=0.8±0.1. This mass bias is consistent with previous WL mass calibrations of Planck clusters within the errors. Discuss the implications of the findings for the calibration of SZ cluster counts and the much discussed tension between Planck SZ cluster counts and Planck LCDM cosmology.
1706.00566
Deep optical imaging of the COSMOS field with Hyper Suprime-Cam using data from the Subaru Strategic Program and the University of Hawaii
Tanaka, et al
Present the deepest optical images of the COSMOS field based on a joint dataset taken with HSC by the HSC-SSP team and UH. The COSMOS field is one of the key extragalactic fields with a wealth of deep, multi-wavelength data. However, the current optical data are not sufficiently deep to match with, e.g., the UltraVista data in the NIR. The SSP team and UH have jointed forces to produce very deep optical images of the COSMOS field by combining data from both teams. The coadd images reach depths of g=27.8, r-27.7, i-27.6, z-26.8, and y-26.2 mag at 5 sigma for point sources based on flux uncertainties quoted by the pipeline and they cover essentially the entire COSMOS 2 sq deg field. The seeing is between 0.6 and 0.9 arcsec on the coadds. Perform several quality checks and confirm tat the data are of science quality; ~2% photometry and 30 has astrometry. This accuracy is identical to the Public DR1 from HSC-SSP. Make the joint dataset including fully calibrated catalogs of detected objects available to the community at https://hsc-release.mtk.nao.ac.jp/.
1706.01542
Forward globara photometric calibration of the Dark Energy Survey
Burke, Rykoff, ... Bernstein, ... et al
Many scientific goals for the DES require calibration of optical/NIR broadband b=grizY photometry that is stable in time and uniform over the celestial sky to one percent or better. It is also necessary to limit to similar accuracy systematic uncertainty in the calibrated broadband magnitudes due to uncertainty in the spectrum of the source. Here present a "Forward Global Calibration Method (FGCM)" for photometric calibration of the DES, and present results of its application to the first 3 years of the survey (Y3A1). The FGCM combines data taken with auxiliary instrumentation at the observatory with data from the broad-band survey imaging itself and models of the instrument and atmosphere to estimate the spatial- and time-dependence of the passbands of individual DES survey exposures. "Standard" passbands are chosen that are typical of the passbands encountered during the survey. The passband of any individual observation is combined with an estimate of the source spectral space to yield a magnitude M_b^std in the standard system. This "chromatic correction" to the standard system is necessary to achieve sub-percent calibrations. The FGCM achieves reproducible and stable photometric calibration of standard magnitudes M_b^std of stellar sources over the multi-year Y3A1 data sample with residual random calibration errors of sigma=5-6 mmag per exposure. The accuracy of the calibration is uniform across the 5000 deg^2 DES footprint to within sigma=7 mmag. The systematic uncertainties of magnitudes in the standard system due to the spectra of sources are less than 5 mmag for main sequence stars with 0.5<g-i<3.0.
1706.01916
Understanding 'galaxy groups' as a unique structure in the universe
Paul, John, Gupta, Kumar
'Galaxy groups' have hardly been realized as a separate class of objects with specific characteristics in the structural hierarchy The presumption that the self-similarity of DM structures is a valid prescription for the baryonic universe at all scales has rendered smaller structures undetectable by current observational facilities, leading to lesser dedicated studies on them. Some recent reports that indicate a deviation from Lx-T scaling in groups compared to clusters have motivated the study of their physical properties in depth. In this article, report the extensive study on physical properties of groups in comparison to the clusters through cosmological hydrodynamic plus N-body sims using ENZO 2.2 code. As additional physics, radiative cooling, heating due to SNe and star motions, SF and stellar feedback has been implemented. Produce a mock sample of 362 objects with mass ranging from 5e12 Msun to 2.5e15 Msun. Strikingly, found that objects with mass below ~8e13 Msun do not follow any of the cluster self-similar laws in hydrostatistics, not even in thermal and non-thermal energies. Two distinct scaling laws are observed to be followed with breaks at ~8e13 Msun for mass, ~1 keV for temperature and ~1 Mpc for radius. This places groups as a distinct entity in the hierarchical structures, well demarcated from clusters. This study reveals that groups are mostly far away from virtualization, suggesting the need for formulating new models for deciphering their physical parameters. They are also shown to have high turbulence and more non-thermal energy stored, indicating better visibility in the non-thermal regimes.
1706.02018
On the age of the TRAPPIST-1 system
Burgasser, Mamajek
Given the TRAPPIST-1 system importance for testing planet formation and evolution theories, and for assessing the prospects for habitability among Earth-size exoplanets orbiting the most common type of star in the Galaxy, present a comprehensive assessment of the age of this system. Collate empirical age constraints based on the color-absolute magnitude diagram, average density, Li absorption, surface gravity features, metallicity, kinematics, rotation, and magnetic activity; and conclude that TRAPPIST-1 is a transitional thin/thick disk star with an age of 7.6±2.2 Ghr. The star's color-magnitude position is consistent with it being slightly metal-rich ([Fe/H]~ +0.06), in line with its previously reported NIR spectroscopic metallicity; and it has a radius (R=0.121±0.003 Rsun) that is larger by 8-14% compared to solar-metallicity evolutionary models. Discuss some implications of the old age of this system with regard to the stability and habitability of its planets.
1706.02362
Extending the modeling of the anisotropic galaxy power spectrum to k=0.4 h/Mpc
Hand, Seljak, Beutler, Vlah
Present a new model for the z-space power spectrum of galaxies and demonstrate its accuracy in modeling the monopole, quadrupole, and hexadecapole of the galaxy density field down to scales of k=0.4 h/Mpc. The model describes the clustering of galaxies in the context of a halo model and the clustering of the underlying haloes in redshift space using a combination of Eulerian perturbation theory and N-body sims. The modeling of z-space distortions is done using the so-called distribution function approach. The final model has 13 free parameters, and each parameter is physically motivated rather than a nuisance parameter, which allows the use of well-motivated priors. Account for the FoG effect from centrals and both isolated and non-isolated satellites rather than using a single velocity dispersion to describe the combined effect. Test and validate the accuracy of the model on several sets of high-fidelity N-body sims, as well as realistic mock catalogs designed to simulate the BOSS DR12 CMASS data set. The suite of sims covers a range of cosmologies and galaxy bias models, providing a rigorous test of the level of theoretical systematics present in the model. The level of bias in the recovered values of f-sigma_8 is found to be small. When including scales to k=0.4 h/Mpc, find 15-30% gains in the statistical precision of f-sigma_8 relative to k=0.2 h/Mpc and a roughly 10-15% improvement for the perpendicular Alcock-Paczynski parameter alpha_perp. Using the BOSS DR12 CMASS mocks as a benchmark for comparison, estimate an uncertainty on f-sigma_8 that is ~10-20% larger than other similar Fourier-space RSD models in the literature that use k<0.2h/Mpc, suggesting that these models likely have a too-limited paramterization.
1706.00427
Source selection for cluster weak lensing measurements in the Hyper Suprime-Cam survey
Medezinski, et al
Present optimal source galaxy selection schemes for measuring unbiased cluster WL mass profiles from HSC-SSP. The ongoing HSC-SSP survey will uncover thousands of galaxy clusters to z<~1.5. In deriving cluster masses via WL, a critical source of systematics is contamination and dilution of the lensing signal by cluster and FG galaxies. Using the first-year CAMIRA catalog of ~900 clusters with richness larger than 20 found in ~140 deg^2 of HSC-SSP data, devise and compare several source selection methods, including selection in color-color space (CC-cut), and selection of robust photometric redshifts by applying constraints on their cumulative probability distribution function (PDF; P-cut). Examine the dependence of the contamination on the chosen limits adopted for each method. Using the proper limits, these methods give dilution-free mass profiles in agreement with one another. Find that not adopting either the CC-cut or P-cut methods results in a underestimation of the total cluster mass (13±4%) and the concentration of the profile (24±11%). The robust methods yield a ~60sigma detection of the stacked CAMIRA surface mass density profile, with a mean mass of M_200c=1.67±0.05 e14 Msun/h.
1706.00434
Planck Sunyaev-Zel'dovich cluster mass calibration using Hyper Suprime-Cam weak lensing
Medezinski, et al
Using ~140 deg&2 HSC survey data, stack the WL signal around 5 Planck clusters found within the footprint. This yields a 15 sigma detection of the mean Planck cluster mass density profile. The 5 Planck clusters span a relatively wide mass range, M_WL,500c=2-25e14 Msun with a mean mass of M_WL,500c=4.1±0.5e14 Msun. The mean ratio of the SZ mass to the WL mass is M_SZ/M_WL=1-b=0.8±0.1. This mass bias is consistent with previous WL mass calibrations of Planck clusters within the errors. Discuss the implications of the findings for the calibration of SZ cluster counts and the much discussed tension between Planck SZ cluster counts and Planck LCDM cosmology.
1706.00566
Deep optical imaging of the COSMOS field with Hyper Suprime-Cam using data from the Subaru Strategic Program and the University of Hawaii
Tanaka, et al
Present the deepest optical images of the COSMOS field based on a joint dataset taken with HSC by the HSC-SSP team and UH. The COSMOS field is one of the key extragalactic fields with a wealth of deep, multi-wavelength data. However, the current optical data are not sufficiently deep to match with, e.g., the UltraVista data in the NIR. The SSP team and UH have jointed forces to produce very deep optical images of the COSMOS field by combining data from both teams. The coadd images reach depths of g=27.8, r-27.7, i-27.6, z-26.8, and y-26.2 mag at 5 sigma for point sources based on flux uncertainties quoted by the pipeline and they cover essentially the entire COSMOS 2 sq deg field. The seeing is between 0.6 and 0.9 arcsec on the coadds. Perform several quality checks and confirm tat the data are of science quality; ~2% photometry and 30 has astrometry. This accuracy is identical to the Public DR1 from HSC-SSP. Make the joint dataset including fully calibrated catalogs of detected objects available to the community at https://hsc-release.mtk.nao.ac.jp/.
1706.01542
Forward globara photometric calibration of the Dark Energy Survey
Burke, Rykoff, ... Bernstein, ... et al
Many scientific goals for the DES require calibration of optical/NIR broadband b=grizY photometry that is stable in time and uniform over the celestial sky to one percent or better. It is also necessary to limit to similar accuracy systematic uncertainty in the calibrated broadband magnitudes due to uncertainty in the spectrum of the source. Here present a "Forward Global Calibration Method (FGCM)" for photometric calibration of the DES, and present results of its application to the first 3 years of the survey (Y3A1). The FGCM combines data taken with auxiliary instrumentation at the observatory with data from the broad-band survey imaging itself and models of the instrument and atmosphere to estimate the spatial- and time-dependence of the passbands of individual DES survey exposures. "Standard" passbands are chosen that are typical of the passbands encountered during the survey. The passband of any individual observation is combined with an estimate of the source spectral space to yield a magnitude M_b^std in the standard system. This "chromatic correction" to the standard system is necessary to achieve sub-percent calibrations. The FGCM achieves reproducible and stable photometric calibration of standard magnitudes M_b^std of stellar sources over the multi-year Y3A1 data sample with residual random calibration errors of sigma=5-6 mmag per exposure. The accuracy of the calibration is uniform across the 5000 deg^2 DES footprint to within sigma=7 mmag. The systematic uncertainties of magnitudes in the standard system due to the spectra of sources are less than 5 mmag for main sequence stars with 0.5<g-i<3.0.
1706.01916
Understanding 'galaxy groups' as a unique structure in the universe
Paul, John, Gupta, Kumar
'Galaxy groups' have hardly been realized as a separate class of objects with specific characteristics in the structural hierarchy The presumption that the self-similarity of DM structures is a valid prescription for the baryonic universe at all scales has rendered smaller structures undetectable by current observational facilities, leading to lesser dedicated studies on them. Some recent reports that indicate a deviation from Lx-T scaling in groups compared to clusters have motivated the study of their physical properties in depth. In this article, report the extensive study on physical properties of groups in comparison to the clusters through cosmological hydrodynamic plus N-body sims using ENZO 2.2 code. As additional physics, radiative cooling, heating due to SNe and star motions, SF and stellar feedback has been implemented. Produce a mock sample of 362 objects with mass ranging from 5e12 Msun to 2.5e15 Msun. Strikingly, found that objects with mass below ~8e13 Msun do not follow any of the cluster self-similar laws in hydrostatistics, not even in thermal and non-thermal energies. Two distinct scaling laws are observed to be followed with breaks at ~8e13 Msun for mass, ~1 keV for temperature and ~1 Mpc for radius. This places groups as a distinct entity in the hierarchical structures, well demarcated from clusters. This study reveals that groups are mostly far away from virtualization, suggesting the need for formulating new models for deciphering their physical parameters. They are also shown to have high turbulence and more non-thermal energy stored, indicating better visibility in the non-thermal regimes.
1706.02018
On the age of the TRAPPIST-1 system
Burgasser, Mamajek
Given the TRAPPIST-1 system importance for testing planet formation and evolution theories, and for assessing the prospects for habitability among Earth-size exoplanets orbiting the most common type of star in the Galaxy, present a comprehensive assessment of the age of this system. Collate empirical age constraints based on the color-absolute magnitude diagram, average density, Li absorption, surface gravity features, metallicity, kinematics, rotation, and magnetic activity; and conclude that TRAPPIST-1 is a transitional thin/thick disk star with an age of 7.6±2.2 Ghr. The star's color-magnitude position is consistent with it being slightly metal-rich ([Fe/H]~ +0.06), in line with its previously reported NIR spectroscopic metallicity; and it has a radius (R=0.121±0.003 Rsun) that is larger by 8-14% compared to solar-metallicity evolutionary models. Discuss some implications of the old age of this system with regard to the stability and habitability of its planets.
1706.02362
Extending the modeling of the anisotropic galaxy power spectrum to k=0.4 h/Mpc
Hand, Seljak, Beutler, Vlah
Present a new model for the z-space power spectrum of galaxies and demonstrate its accuracy in modeling the monopole, quadrupole, and hexadecapole of the galaxy density field down to scales of k=0.4 h/Mpc. The model describes the clustering of galaxies in the context of a halo model and the clustering of the underlying haloes in redshift space using a combination of Eulerian perturbation theory and N-body sims. The modeling of z-space distortions is done using the so-called distribution function approach. The final model has 13 free parameters, and each parameter is physically motivated rather than a nuisance parameter, which allows the use of well-motivated priors. Account for the FoG effect from centrals and both isolated and non-isolated satellites rather than using a single velocity dispersion to describe the combined effect. Test and validate the accuracy of the model on several sets of high-fidelity N-body sims, as well as realistic mock catalogs designed to simulate the BOSS DR12 CMASS data set. The suite of sims covers a range of cosmologies and galaxy bias models, providing a rigorous test of the level of theoretical systematics present in the model. The level of bias in the recovered values of f-sigma_8 is found to be small. When including scales to k=0.4 h/Mpc, find 15-30% gains in the statistical precision of f-sigma_8 relative to k=0.2 h/Mpc and a roughly 10-15% improvement for the perpendicular Alcock-Paczynski parameter alpha_perp. Using the BOSS DR12 CMASS mocks as a benchmark for comparison, estimate an uncertainty on f-sigma_8 that is ~10-20% larger than other similar Fourier-space RSD models in the literature that use k<0.2h/Mpc, suggesting that these models likely have a too-limited paramterization.
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