arXiv subjects

R. Mandelbaum

Publications and source records attributed to R. Mandelbaum.

25 records · Page 2Linked to original sources

arXiv2011

Constraints on intrinsic alignment contamination of weak lensing surveys using the MegaZ-LRG sample

Correlations between the intrinsic shapes of galaxies and the large-scale galaxy density field provide an important tool to investigate galaxy intrinsic alignments, which constitute a major astrophysical systematic in cosmological weak lensing (cosmic shear) surveys, but also yield insight into the formation and evolution of galaxies. We measure galaxy position-shape correlations in the MegaZ-LRG sample for more than 800,000 luminous red galaxies, making the first such measurement with a photometric redshift sample. In combination with a re-analysis of several spectroscopic SDSS samples, we constrain an intrinsic alignment model for early-type galaxies over long baselines in redshift (z ~ 0.7) and luminosity (4mag). We develop and test the formalism to incorporate photometric redshift scatter in the modelling. For r_p > 6 Mpc/h, the fits to galaxy position-shape correlation functions are consistent with the scaling with r_p and redshift of a revised, nonlinear version of the linear alignment model for all samples. An extra redshift dependence proportional to (1+z)^n is constrained to n=-0.3+/-0.8 (1sigma). To obtain consistent amplitudes for all data, an additional dependence on galaxy luminosity proportional to L^b with b=1.1+0.3-0.2 is required. The normalisation of the intrinsic alignment power spectrum is found to be (0.077 +/- 0.008)/rho_{cr} for galaxies at redshift 0.3 and r band magnitude of -22 (k- and evolution-corrected to z=0). Assuming zero intrinsic alignments for blue galaxies, we assess the bias on cosmological parameters for a tomographic CFHTLS-like lensing survey. Both the resulting mean bias and its uncertainty are smaller than the 1sigma statistical errors when using the constraints from all samples combined. The addition of MegaZ-LRG data reduces the uncertainty in intrinsic alignment bias on cosmological parameters by factors of three to seven. (abridged)

astro-ph.CO↗

arXiv2011

Calibrated Tully-Fisher relations for improved estimates of disk rotation velocities

In this paper, we derive scaling relations between photometric observable quantities and disk galaxy rotation velocity V_rot, or Tully-Fisher relations (TFRs). Our methodology is dictated by our purpose of obtaining purely photometric, minimal-scatter estimators of V_rot applicable to large galaxy samples from imaging surveys. To achieve this goal, we have constructed a sample of 189 disk galaxies at redshifts z<0.1 with long-slit H-alpha spectroscopy from Pizagno et al. (2007) and new observations. By construction, this sample is a fair subsample of a large, well-defined parent disk sample of ~170 000 galaxies selected from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7). The optimal photometric estimator of V_rot we find is stellar mass M_* from Bell et al. (2003), based on the linear combination of a luminosity and a colour. Assuming a Kroupa IMF, we find: log [V_{80}/(km s^-1)] = (2.142 +/- 0.004)+(0.278 +/- 0.010)[log (M_*/M_sun)-10.10], where V_{80} is the rotation velocity measured at the radius R_{80} containing 80 per cent of the i-band galaxy light. This relation has an intrinsic Gaussian scatter of 0.036 +/- 0.005 dex and a measured scatter of 0.056 dex in log V_{80}. For a fixed IMF, we find that the dynamical-to-stellar mass ratios within R_{80}, (M_dyn/M_*)(R_{80}), decrease from approximately 10 to 3, as stellar mass increases from M_* ~ 10^9 to 10^{11} M_sun. At a fixed stellar mass, (M_dyn/M_*)(R_{80}) increases with disk size, so that it correlates more tightly with stellar surface density than with stellar mass or disk size alone. In future work, we will use these results to study disk galaxy formation and evolution, and perform a fair, statistical analysis of the dynamics and masses of a photometrically-selected sample of disk galaxies. [Abridged]

astro-ph.CO↗

arXiv2009

Challenges facing young astrophysicists

In order to attract and retain excellent researchers and diverse individuals in astrophysics, we recommend action be taken in several key areas impacting young scientists: (1) Maintain balance between large collaborations and individual projects through distribution of funding; encourage public releases of observational and simulation data for use by a broader community. (2) Improve the involvement of women, particularly at leading institutions. (3) Address the critical shortage of child care options and design reasonable profession-wide parental leave policies. (4) Streamline the job application and hiring process. We summarize our reasons for bringing these areas to the attention of the committee, and we suggest several practical steps that can be taken to address them.

astro-ph.IM↗

arXiv2009

Dark Matter Structures in the Universe: Prospects for Optical Astronomy in the Next Decade

The Cold Dark Matter theory of gravitationally-driven hierarchical structure formation has earned its status as a paradigm by explaining the distribution of matter over large spans of cosmic distance and time. However, its central tenet, that most of the matter in the universe is dark and exotic, is still unproven; the dark matter hypothesis is sufficiently audacious as to continue to warrant a diverse battery of tests. While local searches for dark matter particles or their annihilation signals could prove the existence of the substance itself, studies of cosmological dark matter in situ are vital to fully understand its role in structure formation and evolution. We argue that gravitational lensing provides the cleanest and farthest-reaching probe of dark matter in the universe, which can be combined with other observational techniques to answer the most challenging and exciting questions that will drive the subject in the next decade: What is the distribution of mass on sub-galactic scales? How do galaxy disks form and bulges grow in dark matter halos? How accurate are CDM predictions of halo structure? Can we distinguish between a need for a new substance (dark matter) and a need for new physics (departures from General Relativity)? What is the dark matter made of anyway? We propose that the central tool in this program should be a wide-field optical imaging survey, whose true value is realized with support in the form of high-resolution, cadenced optical/infra-red imaging, and massive-throughput optical spectroscopy.

astro-ph.CO↗

arXiv2007

Precision photometric redshift calibration for galaxy-galaxy weak lensing

Accurate photometric redshifts are among the key requirements for precision weak lensing measurements. Both the large size of the Sloan Digital Sky Survey (SDSS) and the existence of large spectroscopic redshift samples that are flux-limited beyond its depth have made it the optimal data source for developing methods to properly calibrate photometric redshifts for lensing. Here, we focus on galaxy-galaxy lensing in a survey with spectroscopic lens redshifts, as in the SDSS. We develop statistics that quantify the effect of source redshift errors on the lensing calibration and on the weighting scheme, and show how they can be used in the presence of redshift failure and sampling variance. We then demonstrate their use with 2838 source galaxies with spectroscopy from DEEP2 and zCOSMOS, evaluating several public photometric redshift algorithms, in two cases including a full p(z) for each object, and find lensing calibration biases as low as 1% (due to fortuitous cancellation of two types of bias) or as high as 20% for methods in active use (despite the small mean photoz bias of these algorithms). Our work demonstrates that lensing-specific statistics must be used to reliably calibrate the lensing signal, due to asymmetric effects of (frequently non-Gaussian) photoz errors. We also demonstrate that large-scale structure (LSS) can strongly impact the photoz calibration and its error estimation, due to a correlation between the LSS and the photoz errors, and argue that at least two independent degree-scale spectroscopic samples are needed to suppress its effects. Given the size of our spectroscopic sample, we can reduce the galaxy-galaxy lensing calibration error well below current SDSS statistical errors.

astro-ph↗

arXiv2005

SDSS galaxy bias from halo mass-bias relation and its cosmological implications

We combine the measurements of luminosity dependence of bias with the luminosity dependent weak lensing analysis of dark matter around galaxies to derive the galaxy bias and constrain nonlinear mass and cosmological parameters. We take advantage of theoretical and simulation predictions that predict that while halo bias is rapidly increasing with mass for high masses, it is nearly constant in low mass halos. We use a new weak lensing analysis around the same SDSS galaxies to determine their halo mass probability distribution. These halo mass probability distributions are used to predict the bias for each luminosity subsample and we find an excellent agreement with observed values. The required nonlinear mass suggests slightly lower matter density than usually assumed, Omegam=0.25+/- 0.03 for the simplest models. We combine the bias constraints with those from the WMAP and the SDSS power spectrum analysis to derive new constraints on bias and sigma_8. For the most general parameter space we find sigma_8=0.88+/- 0.06 and b_*=0.99+/- 0.07. In the context of spatially flat models we improve the limit on the neutrino mass for the case of 3 degenerate families from m_nu<0.6eV without bias to m_nu<0.18eV with bias (95% c.l.), which is weakened to m_nu<0.24eV if running is allowed. The corresponding limit for 3 massless + 1 massive neutrino is 1.37eV.

astro-ph↗

arXiv2003

Precision Cosmology from the Lyman-alpha Forest: Power Spectrum and Bispectrum

We investigate the promise of the Ly-alpha forest for high precision cosmology in the era of the Sloan Digital Sky Survey using low order N-point statistics. We show that with the existing data one can determine the amplitude, slope and curvature of the slope of the matter power spectrum with a few percent precision. Higher order statistics such as the bispectrum provide independent information that can confirm and improve upon the statistical precision from the power spectrum alone. The achievable precision is comparable to that from the cosmic microwave background with upcoming satellites, and complements it by measuring the power spectrum amplitude and shape at smaller scales. Since the data cover the redshift range 2 2.

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