Eric Huff

The DES Science Verification weak lensing shear catalogues

We present weak lensing shear catalogues for 139 square degrees of data taken during the Science Verification (SV) time for the new Dark Energy Camera (DECam) being used for the Dark Energy Survey (DES). We describe our object selection, point spread function estimation and shear measurement procedures using two independent shear pipelines, IM3SHAPE and NGMIX, which produce catalogues of 2.12 million and 3.44 million galaxies respectively. We detail a set of null tests for the shear measurements and find that they pass the requirements for systematic errors at the level necessary for weak lensing science applications using the SV data. We also discuss some of the planned algorithmic improvements that will be necessary to produce sufficiently accurate shear catalogues for the full 5-year DES, which is expected to cover 5000 square degrees.

Star Formation in Space and Time: The Orion Nebula Cluster

We examine the pattern of star birth in the Orion Nebula cluster (ONC), with the goal of discerning the clusters formation mechanism. Outside the Trapezium, the distribution of stellar masses is remarkably uniform and is not accurately described by the field-star initial mass function. The deconvolved, three-dimensional density of cluster members peaks at the Trapezium stars, which are truly anomalous in mass. Using theoretical pre-main-sequence tracks, we confirm the earlier finding that star formation has accelerated over the past 107 yr. We further show that the rate of acceleration has been the same for all masses. Thus, there is no correlation between stellar age and mass, contrary to previous claims. Finally, the acceleration has been spatially uniform throughout the cluster. Our reconstruction of the parent molecular cloud spawning the cluster shows that it had a mass of 6700 M☉ prior to its destruction by the Trapezium. If the cloud was supported against self-gravity by mildly dissipative turbulence, then it contracted in a quasi-static but accelerating manner. We demonstrate this contraction theoretically through a simple energy argument. The mean turbulent speed increased to its recent value, which is reflected in the present-day stellar velocity dispersion. The current ONC will be gravitationally unbound once cloud destruction is complete, and is destined to become a dispersing OB association. We hypothesize that similarly crowded groups seen at the centers of distant OB associations are also unbound and do not give rise to the Galactic population of open clusters. Finally, accelerating star formation implies that most clumps within giant molecular complexes should have relatively low formation activity. Sensitive infrared surveys could confirm this hypothesis.

Mass and galaxy distributions of four massive galaxy clusters from Dark Energy Survey Science Verification data

We measure the weak-lensing masses and galaxy distributions of four massive galaxy clusters observed during the Science Verification phase of the Dark Energy Survey. This pathfinder study is meant to 1) validate the DECam imager for the task of measuring weak-lensing shapes, and 2) utilize DECams large field of view to map out the clusters and their environments over 90 arcmin. We conduct a series of rigorous tests on astrometry, photometry, image quality, PSF modeling, and shear measurement accuracy to single out flaws in the data and also to identify the optimal data processing steps and parameters. We find Science Verification data from DECam to be suitable for the lensing analysis described in this paper. The PSF is generally well-behaved, but the modeling is rendered difficult by a flux-dependent PSF width and ellipticity. We employ photometric redshifts to distinguish between foreground and background galaxies, and a red-sequence cluster finder to provide cluster richness estimates and cluster-galaxy distributions. By fitting NFW profiles to the clusters in this study, we determine weak-lensing masses that are in agreement with previous work. For Abell 3261, we provide the first estimates of redshift, weak-lensing mass, and richness. In addition, the cluster-galaxy distributions indicate the presence of filamentary structures attached to 1E 0657-56 and RXC J2248.7-4431, stretching out as far as 1 degree (approximately 20 Mpc), showcasing the potential of DECam and DES for detailed studies of degree-scale features on the sky.

Cosmology constraints from shear peak statistics in Dark Energy Survey Science Verification data

Shear peak statistics has gained a lot of attention recently as a practical alternative to the two-point statistics for constraining cosmological parameters. We perform a shear peak statistics analysis of the Dark Energy Survey (DES) Science Verification (SV) data, using weak gravitational lensing measurements from a 139 deg² field. We measure the abundance of peaks identified in aperture mass maps, as a function of their signal-to-noise ratio, in the signal-to-noise range 0 4 would require significant corrections, which is why we do not include them in our analysis. We compare our results to the cosmological constraints from the two-point analysis on the SV field and find them to be in good agreement in both the central value and its uncertainty. We discuss prospects for future peak statistics analysis with upcoming DES data.

MAGNIFICENT MAGNIFICATION: EXPLOITING THE OTHER HALF OF THE LENSING SIGNAL

We describe a new method for measuring galaxy magnification due to weak gravitational lensing. Our method makes use of a tight scaling relation between galaxy properties that are modified by gravitational lensing, such as apparent size, and other properties that are not, such as surface brightness. In particular, we use a version of the well-known fundamental plane relation for early-type galaxies. This modified photometric fundamental plane uses only photometric galaxy properties, eliminating the need for spectroscopic data. We present the first detection of magnification using this method by applying it to photometric catalogs from the Sloan Digital Sky Survey. This analysis shows that the derived magnification signal is within a factor of three of that available from conventional methods using gravitational shear. We suppress the dominant sources of systematic error and discuss modest improvements that may further enhance the lensing signal-to-noise available with this method. Moreover, some of the dominant sources of systematic error are substantially different from those of shear-based techniques. With this new technique, magnification becomes a useful measurement tool for the coming era of large ground-based surveys intending to measure gravitational lensing.

Mapping and simulating systematics due to spatially varying observing conditions in DES Science Verification data

Spatially varying depth and the characteristics of observing conditions, such as seeing, airmass, or sky background, are major sources of systematic uncertainties in modern galaxy survey analyses, particularly in deep multi-epoch surveys. We present a framework to extract and project these sources of systematics onto the sky, and apply it to the Dark Energy Survey (DES) to map the observing conditions of the Science Verification (SV) data. The resulting distributions and maps of sources of systematics are used in several analyses of DES–SV to perform detailed null tests with the data, and also to incorporate systematics in survey simulations. We illustrate the complementary nature of these two approaches by comparing the SV data with BCC-UFig, a synthetic sky catalog generated by forward-modeling of the DES–SV images. We analyze the BCC-UFig simulation to construct galaxy samples mimicking those used in SV galaxy clustering studies. We show that the spatially varying survey depth imprinted in the observed galaxy densities and the redshift distributions of the SV data are successfully reproduced by the simulation and are well-captured by the maps of observing conditions. The combined use of the maps, the SV data, and the BCC-UFig simulation allows us to quantify the impact of spatial systematics on N(z), the redshift distributions inferred using photometric redshifts. We conclude that spatial systematics in the SV data are mainly due to seeing fluctuations and are under control in current clustering and weak-lensing analyses. However, they will need to be carefully characterized in upcoming phases of DES in order to avoid biasing the inferred cosmological results. The framework presented here is relevant to all multi-epoch surveys and will be essential for exploiting future surveys such as the Large Synoptic Survey Telescope, which will require detailed null tests and realistic end-to-end image simulations to correctly interpret the deep, high-cadence observations of the sky.

Simulations of the OzDES AGN reverberation mapping project

As part of the Australian spectroscopic dark energy survey (OzDES) we are carrying out a large-scale reverberation mapping study of >= 500 quasars over five years in the 30 deg(2) area of the Dark Energy Survey (DES) supernova fields. These quasars have redshifts ranging up to 4 and have apparent AB magnitudes between 16.8 mag < r < 22.5 mag. The aim of the survey is to measure time lags between fluctuations in the quasar continuum and broad emission-line fluxes of individual objects in order to measure black hole masses for a broad range of active galactic nuclei (AGN) and constrain the radius-luminosity (R-L) relationship. Here we investigate the expected efficiency of the OzDES reverberation mapping campaign and its possible extensions. We expect to recover lags for similar to 35-45 per cent of the quasars. AGN with shorter lags and greater variability are more likely to yield a lag measurement, and objects with lags less than or similar to 6 months or similar to 1 yr are expected to be recovered the most accurately. The baseline OzDES reverberation mapping campaign is predicted to produce an unbiased measurement of the R-L relationship parameters for H beta, MgII lambda 2798, and C IV lambda 1549. Extending the baseline survey by either increasing the spectroscopic cadence, extending the survey season, or improving the emission-line flux measurement accuracy will significantly improve the R-L parameter constraints for all broad emission lines.

Sloan Digital Sky Survey III photometric quasar clustering: Probing the initial conditions of the Universe

The Sloan Digital Sky Survey has surveyed 14,555 square degrees of the sky, and delivered over a trillion pixels of imaging data. We present the large-scale clustering of 1.6 million quasars between z = 0.5 and z = 2.5 that have been classified from this imaging, representing the highest density of quasars ever studied for clustering measurements. This data set spans ~11,000 square degrees and probes a volume of 80(Gpc/h)^3. In principle, such a large volume and medium density of tracers should facilitate high-precision cosmological constraints. We measure the angular clustering of photometrically classified quasars using an optimal quadratic estimator in four redshift slices with an accuracy of ~25% over a bin width of l ~10 - 15 on scales corresponding to matter-radiation equality and larger (l ~ 2 - 30). Observational systematics can strongly bias clustering measurements on large scales, which can mimic cosmologically relevant signals such as deviations from Gaussianity in the spectrum of primordial perturbations. We account for systematics by employing a new method recently proposed by Agarwal et al. (2014) to the clustering of photometrically classified quasars. We carefully apply our methodology to mitigate known observational systematics and further remove angular bins that are contaminated by unknown systematics. Combining quasar data with the photometric luminous red galaxy (LRG) sample of Ross et al. (2011) and Ho et al. (2012), and marginalizing over all bias and shot noise-like parameters, we obtain a constraint on local primordial non-Gaussianity of fNL = -113+/-154 (1\sigma error). [Abridged]

Cluster Formation in Contracting Molecular Clouds

We explore, through a simplified, semianalytic model, the formation of dense clusters containing massive stars. The parent cloud spawning the cluster is represented as an isothermal sphere. This sphere is in near-force balance between self-gravity and turbulent pressure. Self-gravity, mediated by turbulent dissipation, drives slow contraction of the cloud, eventually leading to a sharp central spike in density and the onset of dynamical instability. We suggest that, in a real cloud, this transition marks the late and rapid production of massive stars. We also offer an empirical prescription, akin to the Schmidt law, for low-mass star formation in our contracting cloud. Applying this prescription to the Orion Nebula Cluster, we are able to reproduce the accelerating star formation previously inferred from the distribution of member stars in the HR diagram. The cloud turns about 10% of its mass into low-mass stars before becoming dynamically unstable. Over a cloud free-fall time, this figure drops to 1%, consistent with the overall star formation efficiency of molecular clouds in the Galaxy.

The Spectral Energy Distributions of Red Two Micron All Sky Survey Active Galactic Nuclei

We present infrared (IR) to X-ray spectral energy distributions (SEDs) for 44 red active galactic nuclei (AGNs) selected from the Two Micron All Sky Survey (2MASS) survey on the basis of their red J – K_S color (>2 mag) and later observed by Chandra. In comparison with optically-, radio-, and X-ray-selected AGNs, their median SEDs are red in the optical and near-IR (NIR) with little/no blue bump. Comparison of the various broadband luminosity ratios shows that the main differences lie at the blue end of the optical and in the NIR to far-IR ratios (when available), with the red 2MASS AGNs being redder than the other samples. It thus seems that NIR color selection isolates the reddest subset of AGNs that can be classified optically. The shape of the SEDs is generally consistent with modest absorption by gas (in the X-ray) and dust (in the optical-IR), as demonstrated by comparing the optical and NIR colors with a reddened median SED and observed optical+NIR to intrinsic X-ray ratios. The levels of obscuration, estimated from X-rays, far-IR, and our detailed optical+NIR color modeling, are all consistent implying N_H ≤ few × 10^(22) cm^(–2). We present SED models that show how the AGN optical/NIR colors change due to differing amounts of reddening, AGN to host galaxy ratio, redshift, and scattered light emission, and apply them to the sources in the sample. We find that the 2MASS AGN optical color, B – R, and to a lesser extent the NIR color, J – K_S , are strongly affected by reddening, host galaxy emission, redshift, and in few, highly polarized objects also by scattered AGN light (<2% of intrinsic AGN light in the R band is scattered; this contribution becomes significant as the direct AGN light is absorbed). The lack of low equivalent widths in the distribution of the [O III] λ5007 emission line implies a predominance of inclined objects in the red 2MASS sample. The obscuration/inclination of the AGN allows us to see weaker emission components which are generally swamped by the AGN.We present infrared (IR) to X–ray spectral energy distributions (SEDs) for 44 red AGN selected from the 2MASS survey on the basis of their red J−KS color (> 2 mag.) and later observed by Chandra. In comparison with optically-, radio-, and X-ray selected AGN, their median SEDs are red in the optical and near-IR with little/no blue bump. Comparison of the various broad-band luminosity ratios show that the main differences lie at the blue end of the optical and in the near-IR to far-IR ratios (when available), with the red 2MASS AGN being redder than the other samples. It thus seems that near-IR color selection isolates the reddest subset of AGN that can be classified optically. The shape of the SEDs is generally consistent with modest absorption by gas (in the X-ray) and dust (in the optical-IR), as demonstrated by comparing the optical and near-IR colors with a reddened median SED and observed optical+near–IR to intrinsic X-ray ratios. The levels of obscuration, estimated from X-rays, far-IR and our detailed optical/near-IR color modeling are all consistent implying NH ≤few×10 cm. We present SED models that show how the AGN optical/near-IR colors change due to differing amounts of reddening, AGN to host galaxy ratio, redshift and scattered light emission and apply them to the sources in the sample. We find that the 2MASS AGN optical color, B−R, and to a lesser extent the near-IR color, J−KS, are strongly affected by reddening, host galaxy emission, redshift, and in few, highly polarized objects, also by scattered AGN light (<2% of intrinsic AGN light in R band is scattered; this contribution becomes significant as the direct AGN light is absorbed). The lack of low equivalent widths in the distribution of the [O III]λ5007 emission line implies a predominance of inclined objects in the red 2MASS sample. The obscuration/inclination of the AGN allows us to see weaker emission components which are generally swamped by the AGN. Subject headings: galaxies: active — quasars: general