Tuesday.
Nature
Positron annihilation signatures associated with the outburst of the micro quasar V404 Cygni
Siegert et al.
Micro quasars are stellar-mass BHs accreting matter from a companion star and ejecting plasma jets at almost the speed of light. They are analogues of quasars that contain SMBHs of 1e6 to 1e10 Msun. Accretion in micro quasars varies on much shorter timescales than in quasars and occasionally produces exceptionally bright X-ray flares. How the flares are produced is unclear, as is the mechanism for launching the relativistic jets and their composition. An emission line near 511 keV has ling been sought in the emission spectrum of micro quasars as evidence for the expected electron-positron plasma. Transient high-energy spectral features have been reported in two objects, but their positron interpretation remains contentious. Report observations of gamma-ray emission from the micro quasar V404 Cygni during a recent period of strong flairing activity. The emission spectra around 511 keV shows clear signatures of variable positron annihilation, which implies a high rate of positron production. This supports the earlier conjecture that micro quasars may be the main sources of the electron-positron plasma responsible for the bright diffuse emission of annihilation gamma-rays in the bulge region of our Galaxy. Additionally, micro quasars could be the origin of the observed MeV continuum excess in the inner Galaxy.
1602.08503
Improving lognormal models for cosmological fields
Xavier, Abdallah, Joachimi
It is common practice in cosmology to model LSS observables as lognormal random fields, and this approach has been successfully applied in the past to the matter density and WL convergence fields separately. Argue that this approach has fundamental limitations which prevent its use for jointly modeling these two fields since the lognormal distribution's shape can prevent certain correlations to be attainable. Given the need of ongoing and future LSS surveys for fast joint simulations of clustering and WL, propose two ways of overcoming these limitations. The first approach slightly distorts the PS of the fields using one of two algorithms that minimizes either the absolute or the fractional distortions. The second one is by obtaining more accurate convergence marginal distributions, for which a fitting function is provided, by integrating the lognormal density along the line of sight. The latter approach also provides a way to determine directly from theory the skewness of the convergence distribution and, therefore, the parameters for a lognormal fit. Present the public code Full-sky Lognormal Astro-fields Simulation Kit (FLASK) which can make tomographic realizations on the sphere of an arbitrary number of correlated lognormal or Gaussian random fields by applying either of the two proposed solutions, and show that it can create joint simulations of clustering and lensing with sub-per-cent accuracy over relevant angular scales and redshift ranges.
1602.09010
A 14 $h^{-3}$ Gpc$^3$ study of cosmic homogeneity using BOSS DR12 quasar sample
Laurent et al
47,858 quasars over 5983 deg2 and 2.2<z<2.8. Measure the count-in-sphere N(<r), i.e., the average number of objects around a given object, and its logarithmic derivative, the fractal correlation dimension D_2(r). For a homogeneous distribution N(<r) ~ r^3 and D_2(r)=3. With the simplest DD/RR estimator, these behaviors can be checked without determining an average density, which requires homogeneity to be defined. Observe the predicted behavior over one decade in the radius r. In particular, the fractal correlation dimension D_2 is found to be compatible with 3 on large scales at a high accuracy: 3-<D_2> < 6e-4 (2 sigma) over the range 250 <r< 1200 Mpc/h. This result establishes homogeneity on large scales, therefore allowing to define a reliable average density. Then introduce a more accurate estimator which requires a crude estimate of the average density, and find that the transition to homogeneity, described by N(<r) and D_2(r), quantitatively agrees with the LCDM prediction and that D_2 is still compatible with 3 at an even higher accuracy: 3-<D_2><1.5e-4 (2 sigma) over the range 250 <r< 1200 Mpc/h.
Monday, February 29, 2016
Sunday, February 28, 2016
Day 1057
Monday.
1602.08098
Hubble space telescope observations of the host galaxies and environments of calcium-rich supernovae
Lyman, et al
Ca-rich SNe explosions sites have galactocentric offset distribution strongly skewed to very large offsets (~1/3 >20 kpc), meaning they do not trace the stellar light of their hosts. No detection of host system of 5 nearby Ca-rich SNe. In this case the offset distribution is most readily explained as a signature of high-velocity progenitor systems that have travelled significant distances before exploding.
1602.08108
Neutrino mass without cosmic variance
LoVerde
Measuring the absolute scale of the neutrino masses is one of the most exciting opportunities available with near-term cosmological datasets. Two quantities that are sensitive to neutrino mass, scale-dependent halo bias b(k) and the linear growth parameter f(k) inferred from redshift-space distortions, can be measured without cosmic variance. Unlike the amplitude of the matter power spectrum, which always has a finite error, the error on b(k) and f(k) continues to decrease as the number density of tracers increases. This paper presents forecasts for statistics of galaxy and lensing fields that are sensitive to neutrino mass via b(k) and f(k). The constraints on neutrino mass from the auto- and cross-power spectra of spectroscopic and photometric galaxy samples are weakened by scale-dependent bias unless a very high density of tracers is available. In the high density limit, using multiple tracers allows cosmic variance to be beaten and the forecasted errors on neutrino mass shrink dramatically. In practice, beating the cosmic variance errors on neutrino mass with b(k) will be a challenge, but this signal is nevertheless a new probe of neutrino effects on structure formation that is interesting in its own right.
1602.08430
Neutrino footprint in large scale structure
Jimenez, Pena-Garay, Verde
Recent constrains on the sum of neutrino masses inferred by analyzing cosmological data, show that detecting a non-zero neutrino mass is within reach of forthcoming cosmological surveys, implying a direct determination of the absolute neutrino mass scale. The measurement relies on constraining the shape of the matter power spectrum below the neutrino free streaming scale: massive neutrinos erase power at thesis scales. Detection of a lack of small-scale power, however, could also be due to a host of other effects. It is therefore of paramount importance to validate neutrinos as the source of power suppression at small scales. Show that, independent on hierarchy, neutrinos always show a footprint on large, linear scales; the exact location and properties can be related to the measured power suppression (an astrophysical measurement) and atmospheric neutrinos mass spitting (a neutrino oscillation experiment measurement). This feature can not be easily mimicked by systematic uncertainties or modifications in the cosmological model. The measurement of such a feature, up to 1% relative change in the power spectrum, is a smoking gun for confirming the determination of the absolute neutrino mass scale from cosmological observations. It also demonstrates the synergy of astrophysics and particle physics experiments.
1602.08098
Hubble space telescope observations of the host galaxies and environments of calcium-rich supernovae
Lyman, et al
Ca-rich SNe explosions sites have galactocentric offset distribution strongly skewed to very large offsets (~1/3 >20 kpc), meaning they do not trace the stellar light of their hosts. No detection of host system of 5 nearby Ca-rich SNe. In this case the offset distribution is most readily explained as a signature of high-velocity progenitor systems that have travelled significant distances before exploding.
1602.08108
Neutrino mass without cosmic variance
LoVerde
Measuring the absolute scale of the neutrino masses is one of the most exciting opportunities available with near-term cosmological datasets. Two quantities that are sensitive to neutrino mass, scale-dependent halo bias b(k) and the linear growth parameter f(k) inferred from redshift-space distortions, can be measured without cosmic variance. Unlike the amplitude of the matter power spectrum, which always has a finite error, the error on b(k) and f(k) continues to decrease as the number density of tracers increases. This paper presents forecasts for statistics of galaxy and lensing fields that are sensitive to neutrino mass via b(k) and f(k). The constraints on neutrino mass from the auto- and cross-power spectra of spectroscopic and photometric galaxy samples are weakened by scale-dependent bias unless a very high density of tracers is available. In the high density limit, using multiple tracers allows cosmic variance to be beaten and the forecasted errors on neutrino mass shrink dramatically. In practice, beating the cosmic variance errors on neutrino mass with b(k) will be a challenge, but this signal is nevertheless a new probe of neutrino effects on structure formation that is interesting in its own right.
1602.08430
Neutrino footprint in large scale structure
Jimenez, Pena-Garay, Verde
Recent constrains on the sum of neutrino masses inferred by analyzing cosmological data, show that detecting a non-zero neutrino mass is within reach of forthcoming cosmological surveys, implying a direct determination of the absolute neutrino mass scale. The measurement relies on constraining the shape of the matter power spectrum below the neutrino free streaming scale: massive neutrinos erase power at thesis scales. Detection of a lack of small-scale power, however, could also be due to a host of other effects. It is therefore of paramount importance to validate neutrinos as the source of power suppression at small scales. Show that, independent on hierarchy, neutrinos always show a footprint on large, linear scales; the exact location and properties can be related to the measured power suppression (an astrophysical measurement) and atmospheric neutrinos mass spitting (a neutrino oscillation experiment measurement). This feature can not be easily mimicked by systematic uncertainties or modifications in the cosmological model. The measurement of such a feature, up to 1% relative change in the power spectrum, is a smoking gun for confirming the determination of the absolute neutrino mass scale from cosmological observations. It also demonstrates the synergy of astrophysics and particle physics experiments.
Thursday, February 25, 2016
Day 1056
Friday.
1602.08054
Luminosity function of luminous compact star-forming galaxies
Parnovsky, Izotova
Study H-alpha, far- and near-UV LFs of the sample of 795 luminous compact SF galaxies with z<0.65. The parameters of optimal functions for LFs are obtained using the maximum likelihood method and the accuracy of fitting is estimated with the chi-squared method. Find that these LFs cannot be reproduced by the Schechter function because of an excess of very luminous galaxies. On the other hand, the Saunders function, the log-normal distribution and some new related functions are good approximations of LFs. The fact that LFs are not reproduced by the Schechter function can be explained by the propagating SF. This may result in an excess of luminous starbursts with the mass of a young stellar population above 2e8 Msun as compared to the LF of the quiescent galaxies. The most luminous compact galaxies are characterized by H-alpha luminosities of >5e42 erg/s and SFRs of >40 Msun/yr.
1602.08054
Luminosity function of luminous compact star-forming galaxies
Parnovsky, Izotova
Study H-alpha, far- and near-UV LFs of the sample of 795 luminous compact SF galaxies with z<0.65. The parameters of optimal functions for LFs are obtained using the maximum likelihood method and the accuracy of fitting is estimated with the chi-squared method. Find that these LFs cannot be reproduced by the Schechter function because of an excess of very luminous galaxies. On the other hand, the Saunders function, the log-normal distribution and some new related functions are good approximations of LFs. The fact that LFs are not reproduced by the Schechter function can be explained by the propagating SF. This may result in an excess of luminous starbursts with the mass of a young stellar population above 2e8 Msun as compared to the LF of the quiescent galaxies. The most luminous compact galaxies are characterized by H-alpha luminosities of >5e42 erg/s and SFRs of >40 Msun/yr.
Wednesday, February 24, 2016
Day 1055
Thursday.
1602.07482
Weak lensing with radio continuum surveys
Patel
Show how the larger radio facilities such as SKA can produce game changing cosmological measurements compared to future optical telescopes; also discuss how radio surveys can also provide unique ways in which some of the most problematic systematic errors can be mitigated through the extra information that can be provided in the form of polarization and rotational velocity measurements. Also demonstrate the advantages to having overlapping optical and radio WL surveys and how their cross-correlation leads to a cleaner extraction of the cosmo information. Key to the realization of the great promise of radio WL is the suitable measurements of galaxy shapes in the radio data, either from images or from the visibility data. End with a description of the key issues related to this matter and the radioGREAT challenge which has been proposed to address them.
1602.07482
Weak lensing with radio continuum surveys
Patel
Show how the larger radio facilities such as SKA can produce game changing cosmological measurements compared to future optical telescopes; also discuss how radio surveys can also provide unique ways in which some of the most problematic systematic errors can be mitigated through the extra information that can be provided in the form of polarization and rotational velocity measurements. Also demonstrate the advantages to having overlapping optical and radio WL surveys and how their cross-correlation leads to a cleaner extraction of the cosmo information. Key to the realization of the great promise of radio WL is the suitable measurements of galaxy shapes in the radio data, either from images or from the visibility data. End with a description of the key issues related to this matter and the radioGREAT challenge which has been proposed to address them.
Day 1054
Wednesday.
Proceedings of the National Academy of Sciences
Seas are rising at fastest rate in last 28 centuries
Kopp et al
The first estimate of global sea-level (GSL) change of the last ~3000 years that is based upon statistical synthesis of global database of regional sea-level reconstructions. The 20th century rise was extremely likely faster than during any of the 27 previous centuries. Semi empirical modeling indicates that, without global warming, GSL in the 20th centre very likely would have risen by between -3cm and +7cm, rather than the -14 cm observed. Semi empirical 21st centre projections largely reconcile differences between intergovernmental panel on climate change projects and semi empirical models.
2/3 of US coastal flood days are estimated (based on above GSL analysis) to be climate change-driven.
1602.06947
Accelerated fitting of stellar spectra
Ting, Conroy, Rix
The number of synthetic spectra needed for a rectilinear grid grows exponentially with the label space dimensions, precluding the simultaneous and self-consistent fitting of more than a few elemental abundances. Shortcuts such as fitting subsets of parameters separately an introduce unknown systematics and do not produce correct error covariance in the derived labels. Present a new approach -- CHAT (Convex Hull Adaptive Tessellation) -- which includes several new ideas for inexpensively generating a sufficient stellar synthetic library, using linear algebra and the concept of an adaptive, data-driven grid. A convex hull approximates the region where the data lie in the label space. A variety of tests with mock datasets demonstrate that CHAT can reduce the number of required synthetic model calculations by 3 orders of magnitude in an 8D label space. The reduction will be even larger for higher-dimensional label spaces. In CHAT the computational effort increases only linearly with the number of labels that are fit simultaneously. Around each of these grid points in label space and approximate synthetic spectrum can be generated through linear expansion using a set of "gradient spectra" that represent flux derivatives at every wavelength point with respect to all labels. On this basis, these techniques provide new opportunities to fit the full stellar spectra from large surveys with 15-30 parameters simultaneously, as it reduces the spectral fitting problem to a series of simple linear regressions.
Proceedings of the National Academy of Sciences
Seas are rising at fastest rate in last 28 centuries
Kopp et al
The first estimate of global sea-level (GSL) change of the last ~3000 years that is based upon statistical synthesis of global database of regional sea-level reconstructions. The 20th century rise was extremely likely faster than during any of the 27 previous centuries. Semi empirical modeling indicates that, without global warming, GSL in the 20th centre very likely would have risen by between -3cm and +7cm, rather than the -14 cm observed. Semi empirical 21st centre projections largely reconcile differences between intergovernmental panel on climate change projects and semi empirical models.
2/3 of US coastal flood days are estimated (based on above GSL analysis) to be climate change-driven.
1602.06947
Accelerated fitting of stellar spectra
Ting, Conroy, Rix
The number of synthetic spectra needed for a rectilinear grid grows exponentially with the label space dimensions, precluding the simultaneous and self-consistent fitting of more than a few elemental abundances. Shortcuts such as fitting subsets of parameters separately an introduce unknown systematics and do not produce correct error covariance in the derived labels. Present a new approach -- CHAT (Convex Hull Adaptive Tessellation) -- which includes several new ideas for inexpensively generating a sufficient stellar synthetic library, using linear algebra and the concept of an adaptive, data-driven grid. A convex hull approximates the region where the data lie in the label space. A variety of tests with mock datasets demonstrate that CHAT can reduce the number of required synthetic model calculations by 3 orders of magnitude in an 8D label space. The reduction will be even larger for higher-dimensional label spaces. In CHAT the computational effort increases only linearly with the number of labels that are fit simultaneously. Around each of these grid points in label space and approximate synthetic spectrum can be generated through linear expansion using a set of "gradient spectra" that represent flux derivatives at every wavelength point with respect to all labels. On this basis, these techniques provide new opportunities to fit the full stellar spectra from large surveys with 15-30 parameters simultaneously, as it reduces the spectral fitting problem to a series of simple linear regressions.
Tuesday, February 23, 2016
Day 1053
Tuesday.
1502.06294
Stacking for machine learning redshifts applied to SDSS galaxies
Zitlau, et al
Show how all tested machine learning technique base algorithms benefit from at least one additional 'stacking' (a layering of an output which is input in a subsequent learning round). Apply the method to both unsupervised machine learning techniques based on self-organizing maps, and supervised machine learning methods based on decision trees. Explore a range of stacking architectures, such as the number of layers and the number of base learners per layer. Explore the effectiveness of stacking even when using a successful algorithm such as AdaBoost. Observe a signifiant improvement of between 1.9% and 21% on all computed metrics when stacking is applied to weak learners (such as SOM and decision trees). When applied to strong learning algorithms (such as AdaBoost) the ratio of improvement shrinks, but still remains positive and is between 0.4% and 2.5% for the explored metrics and comes at almost no additional computational cost.
1602.06305
The need for laboratory work to aid in the understanding of exoplanetary atmospheres
Forty, et al
While exoplanet science currently has a wide range of sophisticated models that can be applied to the tide of forthcoming observations, the trajectory for preparing these models for the upcoming observational challenges is unclear. Thus, the ability to maximize the insights gained from the next generation of observatories is not certain. In many cases, uncertainties in a path towards model advancement stems from insufficiencies in the laboratory data that serve as critical inputs to atmospheric physical and chemical tools. Outline a number of areas where laboratory or ab initio investigations could fill critical gaps in the ability to model exoplanet atmospheric opacities, clouds, and chemistry. Specifically highlighted are needs for : (1) molecular opacity libelists with parameters for a diversity of broadening gases, (2) extended databases for collision-induced absorption and dimer opacities, (2) high spectral resolution opacity data for relevant molecular species, (4) laboratory studies of haze and condensate formation and optical properties, (5) significantly expanded database of chemical reaction rates, and (6) measurements of gals photo-adsorption cross sections at high temperatures. Hope that by meeting these needs, the next two decades of exoplanet science can be made as productive and insightful as the previous tow decades.
1602.06306
Cosmic voids in the SDSS DR12 BOSS galaxy sample: the Alcock-Paczynski test
Mao, et al
AP test on SDSS DR12: also use 1000 mock galaxy catalogs that match the geometry, density and clustering properties of the BOSS sample to characterize the statistical uncertainties of the measurements and take into account systematic errors such as RSD. For both BOSS data and mock catalogs, use ZOBOV algorithm to identify voids, stack together all voids with effective radii of 30-100 Mpc/h in the redshift range 0.43-0.7. Accurately measure the shape of the stacked voids. Tests with the mock catalogs show that the stacked void ellipticity is measured with a precision of 2.6%. Find that the stacked voids in redshift space are slightly squashed long the LoS, which is consistent with previous studies. Repeat this measurement of stacked void shape the BOSS data assuming several values of Omega_m within the flat LCDM model, and we compare to the mock catalogs in redshift space in order to perform the AP test. Obtain a constraint of Omega_m=0.38+0.18-0.15 at the 68% CL from the AP test. Discuss the various sources of statistical and systematic noise that affect the constraining power of this method. In particular, find that the measured ellipticity of stacked voids scales more weakly with cosmology than the standard AP prediction, leading to significantly weaker constraints. Discuss how AP constraints will improve in future surveys with larger volumes and densities.
1602.06711
3D weak lensing: modified theories of gravity
Pratten, et al
WL promises to be a particularly sensitive probe of both the growth of LSS as well as the fundamental relation between matter density perturbations and metric perturbations, thus providing a powerful tool with which we may constrain modified theories of gravity (MG) on cosmological scales. Future deep, wide-field WL surveys will provide an unprecedented opportunity to constrain deviations from GR. Employing a 3D analysis based on the spherical Fourier-Bessel (sFB) expansion, investigate the extent to which MG theories will be constrained by a typical 3D WL survey configurations including noise from the intrinsic ellipticity distribution sigma_epsilon of source galaxies. Focus on two classes of screened theories of gravity: i) f(R) chameleon models and ii) environmentally dependent dilation models. Use one-loop perturbation theory combined with halo models in order to accurately model the evolution of matter power-spectrum with redshift in these theories. Using a Fisher information matrix based approach, show that for an all-sky spectroscopic survey, the parameter f_R0 can be constrained in the range f_R0<5e-6(9e-6) for n=1(2) with a 3 sigma CL. This can be achieved by using relatively low order angular harmonics ell<100. Including higher order harmonics ell>100 an further tighten the constraints, making them comparable to current solar-system constraints. Also employ PCA in order to study the parameter degeneracies in the MG parameters. Results can trivially be extended to other MG theories, such as the K-mouflage models. The confusion from IA correlation and modification of the matter power-spectrum at small scale due to feedback mechanisms is briefly discussed.
1602.06854
Computer-generated visual morphology catalog of ~3,000,000 SDSS galaxies
Kuminski, Shamir
Agreement rate of ~98% with Galaxy Zoo debased 'super clean' dataset. Find ~900,000 spiral galaxies, and ~600,000 elliptical galaxies.
1502.06294
Stacking for machine learning redshifts applied to SDSS galaxies
Zitlau, et al
Show how all tested machine learning technique base algorithms benefit from at least one additional 'stacking' (a layering of an output which is input in a subsequent learning round). Apply the method to both unsupervised machine learning techniques based on self-organizing maps, and supervised machine learning methods based on decision trees. Explore a range of stacking architectures, such as the number of layers and the number of base learners per layer. Explore the effectiveness of stacking even when using a successful algorithm such as AdaBoost. Observe a signifiant improvement of between 1.9% and 21% on all computed metrics when stacking is applied to weak learners (such as SOM and decision trees). When applied to strong learning algorithms (such as AdaBoost) the ratio of improvement shrinks, but still remains positive and is between 0.4% and 2.5% for the explored metrics and comes at almost no additional computational cost.
1602.06305
The need for laboratory work to aid in the understanding of exoplanetary atmospheres
Forty, et al
While exoplanet science currently has a wide range of sophisticated models that can be applied to the tide of forthcoming observations, the trajectory for preparing these models for the upcoming observational challenges is unclear. Thus, the ability to maximize the insights gained from the next generation of observatories is not certain. In many cases, uncertainties in a path towards model advancement stems from insufficiencies in the laboratory data that serve as critical inputs to atmospheric physical and chemical tools. Outline a number of areas where laboratory or ab initio investigations could fill critical gaps in the ability to model exoplanet atmospheric opacities, clouds, and chemistry. Specifically highlighted are needs for : (1) molecular opacity libelists with parameters for a diversity of broadening gases, (2) extended databases for collision-induced absorption and dimer opacities, (2) high spectral resolution opacity data for relevant molecular species, (4) laboratory studies of haze and condensate formation and optical properties, (5) significantly expanded database of chemical reaction rates, and (6) measurements of gals photo-adsorption cross sections at high temperatures. Hope that by meeting these needs, the next two decades of exoplanet science can be made as productive and insightful as the previous tow decades.
1602.06306
Cosmic voids in the SDSS DR12 BOSS galaxy sample: the Alcock-Paczynski test
Mao, et al
AP test on SDSS DR12: also use 1000 mock galaxy catalogs that match the geometry, density and clustering properties of the BOSS sample to characterize the statistical uncertainties of the measurements and take into account systematic errors such as RSD. For both BOSS data and mock catalogs, use ZOBOV algorithm to identify voids, stack together all voids with effective radii of 30-100 Mpc/h in the redshift range 0.43-0.7. Accurately measure the shape of the stacked voids. Tests with the mock catalogs show that the stacked void ellipticity is measured with a precision of 2.6%. Find that the stacked voids in redshift space are slightly squashed long the LoS, which is consistent with previous studies. Repeat this measurement of stacked void shape the BOSS data assuming several values of Omega_m within the flat LCDM model, and we compare to the mock catalogs in redshift space in order to perform the AP test. Obtain a constraint of Omega_m=0.38+0.18-0.15 at the 68% CL from the AP test. Discuss the various sources of statistical and systematic noise that affect the constraining power of this method. In particular, find that the measured ellipticity of stacked voids scales more weakly with cosmology than the standard AP prediction, leading to significantly weaker constraints. Discuss how AP constraints will improve in future surveys with larger volumes and densities.
1602.06711
3D weak lensing: modified theories of gravity
Pratten, et al
WL promises to be a particularly sensitive probe of both the growth of LSS as well as the fundamental relation between matter density perturbations and metric perturbations, thus providing a powerful tool with which we may constrain modified theories of gravity (MG) on cosmological scales. Future deep, wide-field WL surveys will provide an unprecedented opportunity to constrain deviations from GR. Employing a 3D analysis based on the spherical Fourier-Bessel (sFB) expansion, investigate the extent to which MG theories will be constrained by a typical 3D WL survey configurations including noise from the intrinsic ellipticity distribution sigma_epsilon of source galaxies. Focus on two classes of screened theories of gravity: i) f(R) chameleon models and ii) environmentally dependent dilation models. Use one-loop perturbation theory combined with halo models in order to accurately model the evolution of matter power-spectrum with redshift in these theories. Using a Fisher information matrix based approach, show that for an all-sky spectroscopic survey, the parameter f_R0 can be constrained in the range f_R0<5e-6(9e-6) for n=1(2) with a 3 sigma CL. This can be achieved by using relatively low order angular harmonics ell<100. Including higher order harmonics ell>100 an further tighten the constraints, making them comparable to current solar-system constraints. Also employ PCA in order to study the parameter degeneracies in the MG parameters. Results can trivially be extended to other MG theories, such as the K-mouflage models. The confusion from IA correlation and modification of the matter power-spectrum at small scale due to feedback mechanisms is briefly discussed.
1602.06854
Computer-generated visual morphology catalog of ~3,000,000 SDSS galaxies
Kuminski, Shamir
Agreement rate of ~98% with Galaxy Zoo debased 'super clean' dataset. Find ~900,000 spiral galaxies, and ~600,000 elliptical galaxies.
Monday, February 22, 2016
Day 1052
Monday.
1602.05957
Reconciling dwarf galaxies with LCDM cosmology: simulating a realistic population of satellites around a Milky Way-mass galaxy
Wentzel, Hopkins, Kim, Faucher-Giguere, Keres, Quahaert
Low-mass "dwarf" galaxies represent the most significant challenges to the CDM model of cosmo structure formation. Because these faint galaxies are (best) observed within the LG of the MW and M31, understanding their formation in such an environment is critical. Present the first results from the Latte Project: the MW on FIRE (Feedback in Realistic Environments). This simulation models the formation of a MW-mass galaxy to z=0 within LCDM cosmology, including DM, gas, and stars at unprecedented resolution: baryon mass of 7070 Msun at spatial resolution down to 1pc. Latte was simulated using the GIZMO code with a mesh-free method for accurate hydrodynamics and the FIRE model for SF and explicit feedback within a multi-phase ISM. For the first time, Latte self-consistently resolve the internal structure of dwarf galaxies that form around a MW-mass shot down to M*>1e5 Msun. Latte's population of dwarf galaxies agrees well with hose observed in the LG across a broad range of properties: (1) distributions of stellar masses and stellar velocity dispersions (dynamical masses), including their joint relation, (2) the mass-metallicity relation, and (3) a diverse range of SFHs, including their mass dependence. Thus, Latte produces a realistic population of dwarf galaxies at M*>1e5 Msun that does not suffer from the "missing satellites" or "too big to fail" problems of small-scale structure formation. Conclude that baryonic physics can reconcile observed dwarf galaxies with standard LCDM cosmology.
1502.05960
Hierarchical Bayesian inference of galaxy redshift distributions from photometric surveys
Listed, Mortlock, Peiris
Accurately characterizing the redshift distributions of galaxies is essential for analyzing deep photometric surveys and testing cosmo models. Present a technique to simultaneously infer redshift distributions and individual redshifts from photometric galaxy catalogues. The model constructs a piecewise constant representation (effectively a histogram) of the distribution of galaxy types and redshifts, the parameters of which are efficiently inferred from noisy photometric flux measurements. This approach can be seen as a generalization of template-fitting photometric redshift methods and relies on a library of spectral templates to relate the photometric fluxes of individual galaxies to their redshifts. Illustrate this technique on simulated galaxy survey data, and demonstrate that it delivers correct poster distributions on the underlying type and redshift distributions, as well as on the individual types and redshifts of galaxies. Show that even with uninformative priors, large photometric errors and parameter degeneracies, the redshift and type distributions can be recovered robustly thanks to the hierarchical nature of the model, which is not possible with common photometric redshift estimation techniques. As a result, redshift uncertainties can be fully propagated in cosmological analyses for the first time, fulfilling a essential requirement for the current and future generation of surveys.
1602.05957
Reconciling dwarf galaxies with LCDM cosmology: simulating a realistic population of satellites around a Milky Way-mass galaxy
Wentzel, Hopkins, Kim, Faucher-Giguere, Keres, Quahaert
Low-mass "dwarf" galaxies represent the most significant challenges to the CDM model of cosmo structure formation. Because these faint galaxies are (best) observed within the LG of the MW and M31, understanding their formation in such an environment is critical. Present the first results from the Latte Project: the MW on FIRE (Feedback in Realistic Environments). This simulation models the formation of a MW-mass galaxy to z=0 within LCDM cosmology, including DM, gas, and stars at unprecedented resolution: baryon mass of 7070 Msun at spatial resolution down to 1pc. Latte was simulated using the GIZMO code with a mesh-free method for accurate hydrodynamics and the FIRE model for SF and explicit feedback within a multi-phase ISM. For the first time, Latte self-consistently resolve the internal structure of dwarf galaxies that form around a MW-mass shot down to M*>1e5 Msun. Latte's population of dwarf galaxies agrees well with hose observed in the LG across a broad range of properties: (1) distributions of stellar masses and stellar velocity dispersions (dynamical masses), including their joint relation, (2) the mass-metallicity relation, and (3) a diverse range of SFHs, including their mass dependence. Thus, Latte produces a realistic population of dwarf galaxies at M*>1e5 Msun that does not suffer from the "missing satellites" or "too big to fail" problems of small-scale structure formation. Conclude that baryonic physics can reconcile observed dwarf galaxies with standard LCDM cosmology.
1502.05960
Hierarchical Bayesian inference of galaxy redshift distributions from photometric surveys
Listed, Mortlock, Peiris
Accurately characterizing the redshift distributions of galaxies is essential for analyzing deep photometric surveys and testing cosmo models. Present a technique to simultaneously infer redshift distributions and individual redshifts from photometric galaxy catalogues. The model constructs a piecewise constant representation (effectively a histogram) of the distribution of galaxy types and redshifts, the parameters of which are efficiently inferred from noisy photometric flux measurements. This approach can be seen as a generalization of template-fitting photometric redshift methods and relies on a library of spectral templates to relate the photometric fluxes of individual galaxies to their redshifts. Illustrate this technique on simulated galaxy survey data, and demonstrate that it delivers correct poster distributions on the underlying type and redshift distributions, as well as on the individual types and redshifts of galaxies. Show that even with uninformative priors, large photometric errors and parameter degeneracies, the redshift and type distributions can be recovered robustly thanks to the hierarchical nature of the model, which is not possible with common photometric redshift estimation techniques. As a result, redshift uncertainties can be fully propagated in cosmological analyses for the first time, fulfilling a essential requirement for the current and future generation of surveys.
Friday, February 19, 2016
Day 1051
Thursday. Friday.
1602.05345
Bayesian hierarchical modeling of weak lensing - the golden goal
Heavens, et al
To accomplish correct Bayesian inference from WL shear data requires a complete statistical description of the data. Starting with a catalogue of shear estimates in tomographic bins, build a model that allows to sample simultaneously from the underlying tomographic shear fields and the relevant power spectra (E-mode, B-mode, and E-B, for auto- and cross-power spectra). The procedure deals easily with masked data and intrinsic alignments. Using Gibbs sampling and messenger fields, show with simulated data that the large (>67000-)dimensional parameter space can be efficiently sampled and the full joint posterior probability density function for the parameters can feasibly be obtained. The method correctly recovers the underlying shear fields and all of the power spectra, including at levels well below the shot noise.
1602.05580
Pixel color magnitude diagrams for semi-resolved stellar populations: the star formation history of regions within the disk and bulge of M31
Conroy, van Dokkum
The analysis of stellar populations has been developed for two limiting cases: spatially-resolved stellar populations in the color-magnitude diagram, and integrated light observations of distant systems. In between these two extremes lies the semi-resoled regime, which encompasses a rich and relatively unexplored realm of observational phenomena. Develop the concept of pixel color magnitude diagrams (pCMDs) as a powerful technique for analyzing stellar populations in the semi-resolved regime. pCMDs show the distribution of imaging data in the plane of pixel luminosity vs. pixel color. A key feature of pCMDs is that they are sensitive to all stars, including both the evolved giants and the unevolved main sequence stars. An important variable in this regime is the mean number of stars per pixel, N_pix. Simulated pCMDs demonstrate a strong sensitivity to the star formation history (SFH) and allow one to break degeneracies between age, metallicity and dust based on two filter data for values of N_pix up to at least 1e4. Extract pCMDs from HST optical imaging of M31 and derive non-parametric SFHs from 1e6 yr to 1e10 yr for both the crowded disk and bulge regions (where N_pix~30-1e3). From analyzing a small region of the disk, find a non-parametric SFH that is smooth and consistent with an exponential decay timescale of 4Gyr. The bulge SFH is also smooth and consistent with a 2 Gyr decay timescale. pCMDs will likely play an important role in maximizing the science returns from next generation ground and space-base facilities.
1602.05836
RadioLensfit: Bayesian weak lensing measurement in the visibility domain
Rivi, Miller, Makhathini, Abdalla
New gen radio telescopes such as SKA will provide a density of detected galaxies that is comparable to that found at optical wavelengths, and with signifiant source shape measurements to make large area radio surveys competitive for WL studies. This will lead WL to become one of the primary science drivers in radio surveys, too, with the advantage that they will access the largest scales in the Universe going beyond optical surveys, like LSST and Euclid, in terms of redshifts that are probed. RadioLensfit is an adaptation to radio data of "lensfit", a model-fitting approach for galaxy shear measurement, originally developed for optical WL surveys. Its key advantage is working directly in the visibility domain, which is the natural approach to adopt with radio data, avoiding systematics due to the imaging process. Present results on galaxy shear measurements, including investigation of sensitivity to instrumental parameters such as the visibilities gridding size, based on simulations of individual galaxy visibilities performed by using SKA1-MID baseline configuration. Get an amplitude of the shear bias in the method comparable with SKA1 requirements for a population of galaxies with realistic flux and scale length distributions estimated from the VLA SWIRE catalog.
1602.05345
Bayesian hierarchical modeling of weak lensing - the golden goal
Heavens, et al
To accomplish correct Bayesian inference from WL shear data requires a complete statistical description of the data. Starting with a catalogue of shear estimates in tomographic bins, build a model that allows to sample simultaneously from the underlying tomographic shear fields and the relevant power spectra (E-mode, B-mode, and E-B, for auto- and cross-power spectra). The procedure deals easily with masked data and intrinsic alignments. Using Gibbs sampling and messenger fields, show with simulated data that the large (>67000-)dimensional parameter space can be efficiently sampled and the full joint posterior probability density function for the parameters can feasibly be obtained. The method correctly recovers the underlying shear fields and all of the power spectra, including at levels well below the shot noise.
1602.05580
Pixel color magnitude diagrams for semi-resolved stellar populations: the star formation history of regions within the disk and bulge of M31
Conroy, van Dokkum
The analysis of stellar populations has been developed for two limiting cases: spatially-resolved stellar populations in the color-magnitude diagram, and integrated light observations of distant systems. In between these two extremes lies the semi-resoled regime, which encompasses a rich and relatively unexplored realm of observational phenomena. Develop the concept of pixel color magnitude diagrams (pCMDs) as a powerful technique for analyzing stellar populations in the semi-resolved regime. pCMDs show the distribution of imaging data in the plane of pixel luminosity vs. pixel color. A key feature of pCMDs is that they are sensitive to all stars, including both the evolved giants and the unevolved main sequence stars. An important variable in this regime is the mean number of stars per pixel, N_pix. Simulated pCMDs demonstrate a strong sensitivity to the star formation history (SFH) and allow one to break degeneracies between age, metallicity and dust based on two filter data for values of N_pix up to at least 1e4. Extract pCMDs from HST optical imaging of M31 and derive non-parametric SFHs from 1e6 yr to 1e10 yr for both the crowded disk and bulge regions (where N_pix~30-1e3). From analyzing a small region of the disk, find a non-parametric SFH that is smooth and consistent with an exponential decay timescale of 4Gyr. The bulge SFH is also smooth and consistent with a 2 Gyr decay timescale. pCMDs will likely play an important role in maximizing the science returns from next generation ground and space-base facilities.
1602.05836
RadioLensfit: Bayesian weak lensing measurement in the visibility domain
Rivi, Miller, Makhathini, Abdalla
New gen radio telescopes such as SKA will provide a density of detected galaxies that is comparable to that found at optical wavelengths, and with signifiant source shape measurements to make large area radio surveys competitive for WL studies. This will lead WL to become one of the primary science drivers in radio surveys, too, with the advantage that they will access the largest scales in the Universe going beyond optical surveys, like LSST and Euclid, in terms of redshifts that are probed. RadioLensfit is an adaptation to radio data of "lensfit", a model-fitting approach for galaxy shear measurement, originally developed for optical WL surveys. Its key advantage is working directly in the visibility domain, which is the natural approach to adopt with radio data, avoiding systematics due to the imaging process. Present results on galaxy shear measurements, including investigation of sensitivity to instrumental parameters such as the visibilities gridding size, based on simulations of individual galaxy visibilities performed by using SKA1-MID baseline configuration. Get an amplitude of the shear bias in the method comparable with SKA1 requirements for a population of galaxies with realistic flux and scale length distributions estimated from the VLA SWIRE catalog.
Wednesday, February 17, 2016
Day 1050
Monday. (Tuesday?) Wednesday.
1602.03909
Evolution of intrinsic water in the SFR-stellar mass correlation at 0.5<z<3
Kurczynski et al
Present estimates of intrinsic scatter in the SFR-M* correlation in the 0.5<z<3.0 and in the mass range 1e7<M*<1e11 Msun. Utilize photometry in HUDF12, UVUDF campaigns and CANDELS/GOODS-S. Estimate SFR, M* from broadband SEDs and the best available redshifts. The maximum depth of the UDF photometry (F160W 29.9 AB, 5 sigma depth) probes the SFR-M* correlation down to M*~1e7 Msun, a factor of 10-100x lower in M* than previous studies, and comparable to dwarf galaxies in the local universe. Find the slope of the SFR-M* relationship to be near unity at all redshifts and the normalization to decrease with cosmic time. Find a moderate increase in intrinsic scatter wth cosmic time from 0.2 to 0.4 dex across the epoch of peak cosmic SF. None of the redshift bins show a statistically significant increase in intrinsic scatter at low mass. However, it remains possible that intrinsic scatter increases at low mass on timescales shorter than ~100 Myr. Results are consistent with a picture of gradual and self-similar assembly of galaxies across more than 3 orders of magnitude in stellar mass from as low as 1e7 Msun.
1602.04002
An over massive dark halo around an ultra-diffuse galaxy in the Virgo cluster
Beasley, et al
UDG's have the sizes of giant galaxies but the luminosities of dwarfs. A key to understanding their origins comes from their total masses, but their low surface brightnesses generally prohibit dynamical studies. Report the first such measurements for a UDG based on its globular cluster system dynamics and size. From 7 GCs, measure a mean systemic velocity 1071±15 km/s, thereby confirming a Virgo-cluster association. Measure a velocity dispersion of 33+16-10 km/s within 8.1 kpc, corresponding to an enclosed mass of (4.5±2.8)e9 Msun and a g-band M/L=106+126-54. From the cumulative mass curve, along with the GC numbers, estimate a viral mass of 8e10 Msun, yielding a dark-to-stellar mass fraction of ~3000. Show that this UDG is an outlier in M*-Mhalo relations, suggesting extreme stochasticity in relatively massive SF'ing halos in clusters. Discuss how counting GCs offers an efficient route to determining viral masses for UDGs.
1602.04156
Pan-STARRS and PESSTO search for the optical counterpart to the LIGO gravitational wave source GW150914
Smart et al
No promising optical counterpart to the GW event.
1602.04180
INTEGRAL upper limits on gamma-ray emission associated with the gravitational wave event GW150914
Savchenko, et al
Upper limits on gamma and hard X-ray. Hard X-ray = EM component from 2e-8 erg/cm2 to 1e-6 erg/cm2 in the 75 keV to 2 MeV range. Constraint: E_gamma / E_GW < 1e-6.
1602.04199
A dark energy camera search for missing supergiants in the LMC after the advanced LIGO gravitational event GW150914
Annis, et al
Pointed DECam shortly after the GW event, covering the LMC area looking for direct stellar collapse to a BH. None of the 152 LMC luminous red supergiants have disappeared. Recovered all from existing catalogs of red supergiants, yellow supergiants, WR stars, and luminous blue variable stars, that were inside the imaging area. Conclude that it was unlikely that GW150914 was caused by the core collapse of a supergiant in the LMC.
1602.03909
Evolution of intrinsic water in the SFR-stellar mass correlation at 0.5<z<3
Kurczynski et al
Present estimates of intrinsic scatter in the SFR-M* correlation in the 0.5<z<3.0 and in the mass range 1e7<M*<1e11 Msun. Utilize photometry in HUDF12, UVUDF campaigns and CANDELS/GOODS-S. Estimate SFR, M* from broadband SEDs and the best available redshifts. The maximum depth of the UDF photometry (F160W 29.9 AB, 5 sigma depth) probes the SFR-M* correlation down to M*~1e7 Msun, a factor of 10-100x lower in M* than previous studies, and comparable to dwarf galaxies in the local universe. Find the slope of the SFR-M* relationship to be near unity at all redshifts and the normalization to decrease with cosmic time. Find a moderate increase in intrinsic scatter wth cosmic time from 0.2 to 0.4 dex across the epoch of peak cosmic SF. None of the redshift bins show a statistically significant increase in intrinsic scatter at low mass. However, it remains possible that intrinsic scatter increases at low mass on timescales shorter than ~100 Myr. Results are consistent with a picture of gradual and self-similar assembly of galaxies across more than 3 orders of magnitude in stellar mass from as low as 1e7 Msun.
1602.04002
An over massive dark halo around an ultra-diffuse galaxy in the Virgo cluster
Beasley, et al
UDG's have the sizes of giant galaxies but the luminosities of dwarfs. A key to understanding their origins comes from their total masses, but their low surface brightnesses generally prohibit dynamical studies. Report the first such measurements for a UDG based on its globular cluster system dynamics and size. From 7 GCs, measure a mean systemic velocity 1071±15 km/s, thereby confirming a Virgo-cluster association. Measure a velocity dispersion of 33+16-10 km/s within 8.1 kpc, corresponding to an enclosed mass of (4.5±2.8)e9 Msun and a g-band M/L=106+126-54. From the cumulative mass curve, along with the GC numbers, estimate a viral mass of 8e10 Msun, yielding a dark-to-stellar mass fraction of ~3000. Show that this UDG is an outlier in M*-Mhalo relations, suggesting extreme stochasticity in relatively massive SF'ing halos in clusters. Discuss how counting GCs offers an efficient route to determining viral masses for UDGs.
1602.04156
Pan-STARRS and PESSTO search for the optical counterpart to the LIGO gravitational wave source GW150914
Smart et al
No promising optical counterpart to the GW event.
1602.04180
INTEGRAL upper limits on gamma-ray emission associated with the gravitational wave event GW150914
Savchenko, et al
Upper limits on gamma and hard X-ray. Hard X-ray = EM component from 2e-8 erg/cm2 to 1e-6 erg/cm2 in the 75 keV to 2 MeV range. Constraint: E_gamma / E_GW < 1e-6.
1602.04199
A dark energy camera search for missing supergiants in the LMC after the advanced LIGO gravitational event GW150914
Annis, et al
Pointed DECam shortly after the GW event, covering the LMC area looking for direct stellar collapse to a BH. None of the 152 LMC luminous red supergiants have disappeared. Recovered all from existing catalogs of red supergiants, yellow supergiants, WR stars, and luminous blue variable stars, that were inside the imaging area. Conclude that it was unlikely that GW150914 was caused by the core collapse of a supergiant in the LMC.
Saturday, February 13, 2016
Day 1049
Thursday. Friday.
dcc.ligo.org/LIGO-P150914/public
Observation of Gravitational waves from a binary black hole merger
On Sept. 14, 2015 at 9:50:45 UTC the two detectors of the LIGO simultaneously observed a transient gravitational wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1e-21. It matches the waveform predicted by GR for the inspired and merger of pair of BHs and the bringdown of the resulting single BH. The signal was observed with a matched-filter S/N ratio of 24 and a false alarm rate estimated two be less than1 event per 203000 years, equivalent to a significance greater than 5.1 sigma. The source lies at a luminosity distance of 410+160-180 Mpc corresponding to a redshift z=0.09+0.03-0.04. In the source frame, the initial BH masses are 36+5-4 Msun and 29±4 Msun, and the final BH mass is 62±4 Msun, with 3.0±0.5 Msun c^2 radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass BH systems. This is the first direct detection of GWs and the first observation of a binary BH merger.
1602.03512
Extragalactic background light: measurements and applications
Cooray
A review: measurements of extragalactic background light (EBL) intensity from gamma-rays to radio in the EM spectrum over 20 decades in wavelength. CMB: best measured spectrum. COB (optical), centered at 1 microns: impacted by the large zodiacal light associated with interplanetary dust in the inner solar system. Best measurements of COB come from an indirect technique involves gamma-ray spectra of bright blasars with an absorption feature resulting from pair-production off of COB photons. The CIB (infrared): peaking at ~100 microns, established an energetically important background with an intensity comparable to the optical background. This discovery paved the path for large aperture far-IR and sub-millimeter observations resulting in the discovery of dusty, star bursting galaxies. Their role in galaxy formation and evolution remains an active area of research. The extreme UV background remains mostly unexplored and will be a challenge to measure due to the high Galactic background and absorption of extragalactic photons by the IGM at these EUV/soft X-ray energies. Also summarize the understanding of the spatial anisotropies and angular power spectra of intensity fluctuations. Motivate a precise direct measurement of the COB between 0.1 and 5 microns using a small aperture telescope observing either from the outer SS, at distances 5 AU or more, or out of the ecliptic plane. Other future applications include improving the understanding of the background at TeV energies and spectral distortions of CMB and CIB.
1602.03842
The rate of binary black hole mergers inferred from advanced LIGO observations surrounding GW150914
Abbott et al
Report on the constraints the LIGO observations place on the rate of BBH coalescences. Considering only GW150914, assuming that allBBHs in the universe have the same masses and spins as this event, imposing false alarm threshold for 1 per 100 years, and assuming that the BBH merger rage is constant in the comoving frame, infer a 90% credible range of 2-53 /Gpc^3/yr (comoving frame). Incorporating all triggers that pass the search threshold while accounting for the uncertainty in the astrophysical origin of each trigger, estimate a higher range, ranging from 6-400 /Gpc^3/yr depending on assumptions about the BBH mass distribution. All together, the various rate estimates fall in the conservative range 2-400 /Gpc^3/yr.
1602.03846
Astrophysical implications of the binary black-hole merger GW150914
The LIGO scientific collaboration, the Virgo Collaboration
The discovery of GW150914 with advanced LIGO provides the first observational evidence for the existence of binary BH systems that inspiral and merge within the age of the Universe. Such BH mergers have been predicted in 2 main type of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively "heavy" BHs (<~25 Msun) can form in nature. This discovery implies relatively weak massive-star winds and the the formation of GW150914 in an environment with metallicity lower than ~1/2 of the solar value. The rate of binary BH mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions (>1/Gpc^3/yr) from both types of formation models. The low measured redshift (z~0.1) of GW150914 and the low inferred metallicity of the stellar progenitor imply either binary BH formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-BH formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and GW detectors in space.
1602.03868
Swift follow-up of the Gravitational wave source GW150914
Evans, et al
No new X-ray, optical, UV or hard X-ray sources were detected in the observations, which were focussed on nearby galaxies in the GW error region; discuss the implications of this.
1601.03718
A new route towards merging massive black holes
Merchant, Langer, Podsiadlowski, Tauris, Moria
Recent advances in GW astronomy make the direct detection of GW from the merger of two stellar-mass compact objects a realistic prospect. Evolutionary scenarios towards mergers of double compact objects generally invoke common-envelope evolution which is poorly understood, leading to large uncertainties in merger rates. Explore he alternative scenario of massive over contact binary (MOB) evolution, which involves two very massive stars in a very tight binary which remain fully mixed due to their tidally induced high spin. Use the public stellar-evolution code MESA to systematically study this channel by means of detailed simulations. Find that, at low metallicity, MOBs produce double-BH (BH+BH) systems that will merge within a Hubble time with mass ratios close to one, in two mass ranges, ~25-60 Msun and >~130 Msun, with pair instability supernovae (PISNe) being produced in-between. The models are also able to reproduce counterparts of various stages in the MOB scenario in the local Universe, providing direct support for it. Map the initial parameter space that produces BH+BH mergers, determine the expected chirp mass distribution, merger times, Kerr parameters and predict event rates. Typically find that for Z~Zsun/10, there is one BH+BH merger for ~1000 core-collapse SNe. The advanced LIGO (aLIGO) detection rate is more uncertain and depends on the metallicity evolution. Deriving upper and lower limits from a local and a global approximation for the metallicity distribution of massive stars, estimate aLIGO detection rates (at design limit) of ~19-550/yr for BH+BH mergers below the PISN gap and of ~2.1-370/yr above the PISN gap. Even with conservative assumptions, find that aLIGO should soon detect BH+BH mergers from the MOB scenario and that these could be the dominant source for aLIGO detections.
dcc.ligo.org/LIGO-P150914/public
Observation of Gravitational waves from a binary black hole merger
On Sept. 14, 2015 at 9:50:45 UTC the two detectors of the LIGO simultaneously observed a transient gravitational wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1e-21. It matches the waveform predicted by GR for the inspired and merger of pair of BHs and the bringdown of the resulting single BH. The signal was observed with a matched-filter S/N ratio of 24 and a false alarm rate estimated two be less than1 event per 203000 years, equivalent to a significance greater than 5.1 sigma. The source lies at a luminosity distance of 410+160-180 Mpc corresponding to a redshift z=0.09+0.03-0.04. In the source frame, the initial BH masses are 36+5-4 Msun and 29±4 Msun, and the final BH mass is 62±4 Msun, with 3.0±0.5 Msun c^2 radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass BH systems. This is the first direct detection of GWs and the first observation of a binary BH merger.
1602.03512
Extragalactic background light: measurements and applications
Cooray
A review: measurements of extragalactic background light (EBL) intensity from gamma-rays to radio in the EM spectrum over 20 decades in wavelength. CMB: best measured spectrum. COB (optical), centered at 1 microns: impacted by the large zodiacal light associated with interplanetary dust in the inner solar system. Best measurements of COB come from an indirect technique involves gamma-ray spectra of bright blasars with an absorption feature resulting from pair-production off of COB photons. The CIB (infrared): peaking at ~100 microns, established an energetically important background with an intensity comparable to the optical background. This discovery paved the path for large aperture far-IR and sub-millimeter observations resulting in the discovery of dusty, star bursting galaxies. Their role in galaxy formation and evolution remains an active area of research. The extreme UV background remains mostly unexplored and will be a challenge to measure due to the high Galactic background and absorption of extragalactic photons by the IGM at these EUV/soft X-ray energies. Also summarize the understanding of the spatial anisotropies and angular power spectra of intensity fluctuations. Motivate a precise direct measurement of the COB between 0.1 and 5 microns using a small aperture telescope observing either from the outer SS, at distances 5 AU or more, or out of the ecliptic plane. Other future applications include improving the understanding of the background at TeV energies and spectral distortions of CMB and CIB.
1602.03842
The rate of binary black hole mergers inferred from advanced LIGO observations surrounding GW150914
Abbott et al
Report on the constraints the LIGO observations place on the rate of BBH coalescences. Considering only GW150914, assuming that allBBHs in the universe have the same masses and spins as this event, imposing false alarm threshold for 1 per 100 years, and assuming that the BBH merger rage is constant in the comoving frame, infer a 90% credible range of 2-53 /Gpc^3/yr (comoving frame). Incorporating all triggers that pass the search threshold while accounting for the uncertainty in the astrophysical origin of each trigger, estimate a higher range, ranging from 6-400 /Gpc^3/yr depending on assumptions about the BBH mass distribution. All together, the various rate estimates fall in the conservative range 2-400 /Gpc^3/yr.
1602.03846
Astrophysical implications of the binary black-hole merger GW150914
The LIGO scientific collaboration, the Virgo Collaboration
The discovery of GW150914 with advanced LIGO provides the first observational evidence for the existence of binary BH systems that inspiral and merge within the age of the Universe. Such BH mergers have been predicted in 2 main type of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively "heavy" BHs (<~25 Msun) can form in nature. This discovery implies relatively weak massive-star winds and the the formation of GW150914 in an environment with metallicity lower than ~1/2 of the solar value. The rate of binary BH mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions (>1/Gpc^3/yr) from both types of formation models. The low measured redshift (z~0.1) of GW150914 and the low inferred metallicity of the stellar progenitor imply either binary BH formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-BH formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and GW detectors in space.
1602.03868
Swift follow-up of the Gravitational wave source GW150914
Evans, et al
No new X-ray, optical, UV or hard X-ray sources were detected in the observations, which were focussed on nearby galaxies in the GW error region; discuss the implications of this.
1601.03718
A new route towards merging massive black holes
Merchant, Langer, Podsiadlowski, Tauris, Moria
Recent advances in GW astronomy make the direct detection of GW from the merger of two stellar-mass compact objects a realistic prospect. Evolutionary scenarios towards mergers of double compact objects generally invoke common-envelope evolution which is poorly understood, leading to large uncertainties in merger rates. Explore he alternative scenario of massive over contact binary (MOB) evolution, which involves two very massive stars in a very tight binary which remain fully mixed due to their tidally induced high spin. Use the public stellar-evolution code MESA to systematically study this channel by means of detailed simulations. Find that, at low metallicity, MOBs produce double-BH (BH+BH) systems that will merge within a Hubble time with mass ratios close to one, in two mass ranges, ~25-60 Msun and >~130 Msun, with pair instability supernovae (PISNe) being produced in-between. The models are also able to reproduce counterparts of various stages in the MOB scenario in the local Universe, providing direct support for it. Map the initial parameter space that produces BH+BH mergers, determine the expected chirp mass distribution, merger times, Kerr parameters and predict event rates. Typically find that for Z~Zsun/10, there is one BH+BH merger for ~1000 core-collapse SNe. The advanced LIGO (aLIGO) detection rate is more uncertain and depends on the metallicity evolution. Deriving upper and lower limits from a local and a global approximation for the metallicity distribution of massive stars, estimate aLIGO detection rates (at design limit) of ~19-550/yr for BH+BH mergers below the PISN gap and of ~2.1-370/yr above the PISN gap. Even with conservative assumptions, find that aLIGO should soon detect BH+BH mergers from the MOB scenario and that these could be the dominant source for aLIGO detections.
Wednesday, February 10, 2016
Day 1048
Tuesday. Wednesday.
1602.02167
Firedec: a two-channel finite-resolution image deconvolution algorithm
Cantale, Courbin, Tewes, Jablonka, Meylan
Present a two-channel deconvolution method that decomposes images into a parametric point-source channel and a pixelized extended-source channel. Based on the central idea of the deconvolution algorithm proposed by Magain, Courbin & Sohy (1998), the method aims at improving the resolution of the data rather than at completely removing the PSF. Improvements over the original method include a better regularization of the pixel channel of the image, based on wavelet filtering and multiple analysis, and a better controlled separation of the point source vs. the extended source. In addition, the method is able to simultaneously deconvolve many individual frames of the same object taken with different instruments under different PSF conditions. For this purpose, introduce a general geometric transformation between individual images. This transformation allows the combination of the images without having to interpolate them. Illustrate the capability of the algorithm using real and simulated images with complex diffraction-limited PSF.
1602.02960
Discrepancies between CFHTLenS cosmic shear & Planck: new physics or systematic effects?
Kitching, Verde, Heavens, Jimenez
There is currently a discrepancy in the measured value of the amplitude of matter clustering, parameterized using sigma8, inferred from WL and CMB data. Investigate what could mitigate this discrepancy. Consider systematic effects in the WL data and include IA, and biases in photometric z estimates. Also apply a non-parametric approach to model the baryonic feedback on the DM clustering, which is flexible enough to reproduce the OWLS and Illustris sims. Finally, extend the cosmo analysis of the WL data to include the effect of massive neutrinos. The statistic used, 3D cosmic shear, is a method that extracts cosmo info from WL data using a spherical-Bessel function PS approach. There are several advantages that this affords, in particular that the method does not rely on binning in z, or covariance estimation from sims. It also allows for a robust scale-dependent analysis of data. Analyse the CFHTLenS WL data and, assuming best fit cosmo parameters from the Planck CMB experiment, find that there is no evidence for baryonic feedback on the DM PS; if the IA amplitude is close to zero, then there is evidence for a bias in the photo-z in CFHTLenS data. Also find an upper limit to the sum of neutrino masses, directly from the shape of the matter PS, <0.28 eV (1 sigma), similar to the one obtained from other indirect probes of the matter distribution.
1602.02167
Firedec: a two-channel finite-resolution image deconvolution algorithm
Cantale, Courbin, Tewes, Jablonka, Meylan
Present a two-channel deconvolution method that decomposes images into a parametric point-source channel and a pixelized extended-source channel. Based on the central idea of the deconvolution algorithm proposed by Magain, Courbin & Sohy (1998), the method aims at improving the resolution of the data rather than at completely removing the PSF. Improvements over the original method include a better regularization of the pixel channel of the image, based on wavelet filtering and multiple analysis, and a better controlled separation of the point source vs. the extended source. In addition, the method is able to simultaneously deconvolve many individual frames of the same object taken with different instruments under different PSF conditions. For this purpose, introduce a general geometric transformation between individual images. This transformation allows the combination of the images without having to interpolate them. Illustrate the capability of the algorithm using real and simulated images with complex diffraction-limited PSF.
1602.02960
Discrepancies between CFHTLenS cosmic shear & Planck: new physics or systematic effects?
Kitching, Verde, Heavens, Jimenez
There is currently a discrepancy in the measured value of the amplitude of matter clustering, parameterized using sigma8, inferred from WL and CMB data. Investigate what could mitigate this discrepancy. Consider systematic effects in the WL data and include IA, and biases in photometric z estimates. Also apply a non-parametric approach to model the baryonic feedback on the DM clustering, which is flexible enough to reproduce the OWLS and Illustris sims. Finally, extend the cosmo analysis of the WL data to include the effect of massive neutrinos. The statistic used, 3D cosmic shear, is a method that extracts cosmo info from WL data using a spherical-Bessel function PS approach. There are several advantages that this affords, in particular that the method does not rely on binning in z, or covariance estimation from sims. It also allows for a robust scale-dependent analysis of data. Analyse the CFHTLenS WL data and, assuming best fit cosmo parameters from the Planck CMB experiment, find that there is no evidence for baryonic feedback on the DM PS; if the IA amplitude is close to zero, then there is evidence for a bias in the photo-z in CFHTLenS data. Also find an upper limit to the sum of neutrino masses, directly from the shape of the matter PS, <0.28 eV (1 sigma), similar to the one obtained from other indirect probes of the matter distribution.
Day 1047
Wednesday. Thursday. Friday. Monday.
1602.01099
Hierarchical galaxy growth and scatter in the stellar mass - halo mass relation
Gu, Conroy, Behroozi
The relation between galaxies and DM halos reflects the combined effects of many distinct physical processes. Observations indicate that the z=0 SM-HM relation has remarkably small scatter in stellar mass at fixed halo mass (<0.2 dex) with little dependence on halo mass. Investigate the origins of this scatter by combining N-body sims with observational constraints on the SMHM relation. Find that at the group and cluster scale (Mvir > 1e14 Msun) the scatter due purely to hierarchical assembly is ~0.16 dex, which is comparable to recent direct observational estimates. At lower masses, mass buildup since z~2 is driven largely by in-situ growth. Include a model for the in-situ buildup of stellar mass and find that an intrinsic scatter in this growth channel of 0.2 dex produces a relation between scatter and halo mass that is consistent with observations from 1e12 Msun < Mvir < 1e14.75 Msun. The approximately constant scatter across a wide range of halo masses at z=0 thus appears to be a coincidence as it is determined largely by in-situ growth at low masses and by hierarchical assembly at high masses. These results indicate that the scatter in the SMHM relation can provide unique insight into the regularity of the galaxy formation process.
1602.02154
Accurate halo-model matter power spectra with dark energy, massive neutrinos and modified gravitational forces
Mead, Heymans, Lombriser, Peacock, Steele, Winther
Show that the tuned halo model method can predict the non-linear matter PS to measurements from sims of parameterized w(a) DE models at the few per cent level for k<10 h/Mpc, and present theoretically motivated extensions to cover non-minimally coupled scaler fields, massive neutrinos and Vainshtein screened modified gravity models that result in few per cent accurate power spectra for k<10 h/Mpc. For Chameleon screened models, achieve only 10% accurate PS for the same range of scales.
1602.01099
Hierarchical galaxy growth and scatter in the stellar mass - halo mass relation
Gu, Conroy, Behroozi
The relation between galaxies and DM halos reflects the combined effects of many distinct physical processes. Observations indicate that the z=0 SM-HM relation has remarkably small scatter in stellar mass at fixed halo mass (<0.2 dex) with little dependence on halo mass. Investigate the origins of this scatter by combining N-body sims with observational constraints on the SMHM relation. Find that at the group and cluster scale (Mvir > 1e14 Msun) the scatter due purely to hierarchical assembly is ~0.16 dex, which is comparable to recent direct observational estimates. At lower masses, mass buildup since z~2 is driven largely by in-situ growth. Include a model for the in-situ buildup of stellar mass and find that an intrinsic scatter in this growth channel of 0.2 dex produces a relation between scatter and halo mass that is consistent with observations from 1e12 Msun < Mvir < 1e14.75 Msun. The approximately constant scatter across a wide range of halo masses at z=0 thus appears to be a coincidence as it is determined largely by in-situ growth at low masses and by hierarchical assembly at high masses. These results indicate that the scatter in the SMHM relation can provide unique insight into the regularity of the galaxy formation process.
1602.02154
Accurate halo-model matter power spectra with dark energy, massive neutrinos and modified gravitational forces
Mead, Heymans, Lombriser, Peacock, Steele, Winther
Show that the tuned halo model method can predict the non-linear matter PS to measurements from sims of parameterized w(a) DE models at the few per cent level for k<10 h/Mpc, and present theoretically motivated extensions to cover non-minimally coupled scaler fields, massive neutrinos and Vainshtein screened modified gravity models that result in few per cent accurate power spectra for k<10 h/Mpc. For Chameleon screened models, achieve only 10% accurate PS for the same range of scales.
Monday, February 1, 2016
Day 1046
Tuesday.
1602.00002
The abundance and spatial distribution of ultra-diffuse galaxies in nearby galaxy clusters
van de Burg, Muezzin, Hoekstra
Recent observations have highlighted a significant population of faint but large (r_eff>1.5 kpc) galaxies in the Coma cluster. The origin of these UDGs remains puzzling,as the interpretation of these observational results has been hindered by the subjective selection of UDGs, and the limited study of only the Coma (and some examples in the Virgo) Cluster. In this paper, extend the study of UDGs using 8 clusters in 0.044<z<0.063 with deep g- and r-band imaging data taken with MegaCam at the CFHT. Describe an automatic selection pipeline for a quantitative identification, tested for completeness using image simulations of these galaxies. Find that the abundance of the UDGs increases with cluster mass, reaching ~200 in typical haloes of M200~1e15 Msun. The cluster UDGs have colors consistent with the cluster red sequence, and have a steep size distribution that declines as n~r_eff^-3.4. Their radial distribution is significantly steeper than NFW in the outskirts, and significantly shallower in the inner parts. They follow the same radial distribution as the more massive quiescent galaxies in the clusters, except within the core region of r<0.15 x R200 (or <300 kpc). Within this region the number density of UDGs drops and is consistent with zero. These diffuse galaxies can only resist tidal forces down to this cluster-centric distance if they are completely DM dominated. Moreover, this picture is consistent with the observation that the radial distribution of more compact dwarf galaxies (r_eff<1.0 kpc) with similar luminosities follows the same distribution as the UDGs, but they exist down to a smaller distance of 100 kpc from the cluster centre. Although a number of scenarios can give rise to the UDG population, the results point to difference in the formation history as the most plausible explanation.
1602.00611
Cosmology with velocity diversion counts: an alternative to measuring cluster halo masses
Caldwell, McCarthy, Baldry, Collins, Schaye, Bird
[...] Propose an alternative strategy: directly compare predicted and observed cluster counts as a function of the 1-d velocity dispersion of the cluster galaxies. Argue that the velocity dispersion of groups/clusters can be theoretically predicted as robustly as mass but, unlike mass, it can also be directly observed, thus circumventing the main systematic bias in traditional cluster counts studies. With the aid of the BAHAMAS suite of cosmo hydro sims, demonstrate the potential of the velocity diversion counts for discriminating been similar lambda CDM models. These predictions can be compared with the results from z surveys such as the highly complete GAMA survey.
1602.00002
The abundance and spatial distribution of ultra-diffuse galaxies in nearby galaxy clusters
van de Burg, Muezzin, Hoekstra
Recent observations have highlighted a significant population of faint but large (r_eff>1.5 kpc) galaxies in the Coma cluster. The origin of these UDGs remains puzzling,as the interpretation of these observational results has been hindered by the subjective selection of UDGs, and the limited study of only the Coma (and some examples in the Virgo) Cluster. In this paper, extend the study of UDGs using 8 clusters in 0.044<z<0.063 with deep g- and r-band imaging data taken with MegaCam at the CFHT. Describe an automatic selection pipeline for a quantitative identification, tested for completeness using image simulations of these galaxies. Find that the abundance of the UDGs increases with cluster mass, reaching ~200 in typical haloes of M200~1e15 Msun. The cluster UDGs have colors consistent with the cluster red sequence, and have a steep size distribution that declines as n~r_eff^-3.4. Their radial distribution is significantly steeper than NFW in the outskirts, and significantly shallower in the inner parts. They follow the same radial distribution as the more massive quiescent galaxies in the clusters, except within the core region of r<0.15 x R200 (or <300 kpc). Within this region the number density of UDGs drops and is consistent with zero. These diffuse galaxies can only resist tidal forces down to this cluster-centric distance if they are completely DM dominated. Moreover, this picture is consistent with the observation that the radial distribution of more compact dwarf galaxies (r_eff<1.0 kpc) with similar luminosities follows the same distribution as the UDGs, but they exist down to a smaller distance of 100 kpc from the cluster centre. Although a number of scenarios can give rise to the UDG population, the results point to difference in the formation history as the most plausible explanation.
1602.00611
Cosmology with velocity diversion counts: an alternative to measuring cluster halo masses
Caldwell, McCarthy, Baldry, Collins, Schaye, Bird
[...] Propose an alternative strategy: directly compare predicted and observed cluster counts as a function of the 1-d velocity dispersion of the cluster galaxies. Argue that the velocity dispersion of groups/clusters can be theoretically predicted as robustly as mass but, unlike mass, it can also be directly observed, thus circumventing the main systematic bias in traditional cluster counts studies. With the aid of the BAHAMAS suite of cosmo hydro sims, demonstrate the potential of the velocity diversion counts for discriminating been similar lambda CDM models. These predictions can be compared with the results from z surveys such as the highly complete GAMA survey.
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