S. Desai

Weak-lensing mass calibration of redMaPPer galaxy clusters in Dark Energy Survey Science Verification data

NASA through the Einstein Fellowship Program [PF5-160138]; DOE [DE-SC0015975, DE-AC02-98CH10886]; DAAD (Deutscher Akademischer Austauschdienst); Deutsche Forschungsgemeinschaft (DFG) [SFB-Transregio 33]; DFG cluster of excellence Origin and Structure of the Universe; Sloan Foundation [FG-2016-6443]; U.S. Department of Energy; U.S. National Science Foundation; Ministry of Science and Education of Spain; Science and Technology Facilities Council of the United Kingdom; Higher Education Funding Council for England; National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign; Kavli Institute of Cosmological Physics at the University of Chicago; Center for Cosmology and Astro-Particle Physics at the Ohio State University; Mitchell Institute for Fundamental Physics and Astronomy at Texas AM Ministerio da Ciencia, Tecnologia e Inovacao; Deutsche Forschungsgemeinschaft; Argonne National Laboratory; University of California at Santa Cruz; University of Cambridge, Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas-Madrid; University of Chicago, University College London; DES-Brazil Consortium; University of Edinburgh; Eidgenossische Technische Hochschule (ETH) Zurich, Fermi National Accelerator Laboratory; University of Illinois at Urbana-Champaign; Institut de Ciencies de lEspai (IEEC/CSIC); Institut de Fisica dAltes Energies, Lawrence Berkeley National Laboratory; Ludwig-Maximilians Universit sitat Munchen; University of Michigan; National Optical Astronomy Observatory; University of Nottingham; Ohio State University; University of Pennsylvania; University of Portsmouth, SLAC National Accelerator Laboratory, Stanford University; University of Sussex, Texas AM University; OzDES Membership Consortium; National Science Foundation [AST-1138766]; MINECO [AYA2012-39559, ESP2013-48274, FPA2013-47986]; Centro de Excelencia Severo Ochoa [SEV-2012-0234, SEV-2012-0249]; European Research Council under the European Unions Seventh Framework Programme (FP7); ERC [240672, 291329, 306478]; Excellence Cluster Universe

Farthest neighbor: the distant Milky Way satellite Eridanus II*

We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite Eridanus II (Eri II). We identify 28 member stars in Eri II, from which we measure a systemic radial velocity of nu(hel)= 75.6 +/- 1.3(stat.) +/- 2.0 (sys.) km s(-1) and a velocity dispersion of 6.9(-0.9)(+1.2) km s(-1). Assuming that Eri. II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of 1.2(-0.3)(+0.4) x 10(7) M-circle dot, indicating a mass-tolight ratio of 420(-140)(+210) M-circle dot/L-circle dot and confirming that it is a dark matter-dominated dwarf galaxy. From the equivalent width measurements of the Ca triplet lines of 16 red giant member stars, we derive a mean metallicity of [ Fe/H] = -2.38 +/- 0.13 and a metallicity dispersion of sigma[Fe/H]= 0.47(-0.09)(+0.12). The velocity of Eri. II in the Galactic standard of rest frame is nu(GSR) = -66.6 km s(-1), indicating that either Eri. II is falling into the Milky Way potential for the first time or that it has passed the apocenter of its orbit on a subsequent passage. At a Galactocentric distance of similar to 370 kpc, Eri II is one of the Milky Ways most distant satellites known. Additionally, we show that the bright blue stars previously suggested to be a young stellar population are not associated with Eri. II. The lack of gas and recent star formation in Eri II is surprising given its mass and distance from the Milky Way, and may place constraints on models of quenching in dwarf galaxies and on the distribution of hot gas in the Milky Way halo. Furthermore, the large velocity dispersion of Eri II can be combined with the existence of a central star cluster to constrain massive compact halo object dark matter with mass greater than or similar to 10 M-circle dot.

A Search for Kilonovae in the Dark Energy Survey

The coalescence of a binary neutron star pair is expected to produce gravitational waves (GW) and electromagnetic radiation, both of which may be detectable with currently available instruments. We describe a search for a predicted r-process optical transient from these mergers, dubbed the kilonova (KN), using griz broadband data from the Dark Energy Survey Supernova Program (DES-SN). Some models predict KNe to be redder, shorter-lived, and dimmer than supernovae (SNe), but the event rate of KNe is poorly constrained. We simulate KN and SN light curves with the Monte-Carlo simulation code SNANA to optimize selection requirements, determine search efficiency, and predict SN backgrounds. Our analysis of the first two seasons of DES-SN data results in 0 events, and is consistent with our prediction of 1.1 ± 0.2 background events based on simulations of SNe. From our prediction, there is a 33% chance of finding 0 events in the data. Assuming no underlying galaxy flux, our search sets 90% upper limits on the KN volumetric rate of 1.0 x 10^7 Gpc−3 yr−1 for the dimmest KN model we consider (peak i-band absolute magnitude Mi=-11.4 mag and 2.4 x 10^4 Gpc−3 yr−1 for the brightest (Mi=-16.2 mag). Accounting for anomalous subtraction artifacts on bright galaxies, these limits are ~3 times higher. This analysis is the first untriggered optical KN search and informs selection requirements and strategies for future KN searches. Our upper limits on the KN rate are consistent with those measured by GW and gamma-ray burst searches.

Galaxy populations in the 26 most massive galaxy clusters in the South Pole Telescope SPT-SZ survey

We present a study of the optical properties of the 26 most massive galaxy clusters within the South Pole Telescope Sunyaev-Zeldovich (SPT-SZ) 2500 deg(2) survey spanning the redshift range 0.10 < z < 1.13. We measure the radial profiles, the luminosity functions (LFs), and the halo occupation numbers (HONs) using optical data of typical depth m* + 2. The stacked radial profiles are consistent with a Navarro-Frenk-White profile of concentration 2.84(-0.37)(+0.40) for the red sequence (RS) and 2.36(-0.35)(+0.38) for the total population. Stacking the data in multiple redshift bins shows slight redshift evolution in the concentration when both the total population is used, and when only RS galaxies are used (at 2.1 sigma and 2.8 sigma, respectively). The stacked LF shows a faint end slope alpha = -1.06(-0.03)(+0.04) for the total and a = -0.80(-0.03)(+0.04) for the RS population. The redshift evolution of m* is consistent with a passively evolving composite stellar population (CSP) model. Adopting the CSP model predictions, we explore the redshift evolution of the Schechter parameters alpha and phi*. We find alpha for the total population to be consistent with no evolution (0.3 sigma), and mildly significant evidence of evolution for the red galaxies (1.1-2.1 sigma). The data show that the density phi*/E-2(z) decreases with redshift, in tension with the self-similar expectation at a 2.4 sigma level for the total population. The measured HON-mass relation has a lower normalization than previous low redshift studies. Finally, our data support HON redshift evolution at a 2.1 sigma level, with clusters at higher redshift containing fewer galaxies than their low-z counterparts.

Nearest Neighbor: The Low-mass Milky Way Satellite Tucana III*

We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite Tucana III (Tuc III). We identify 26 member stars in Tuc III from which we measure a mean radial velocity of v hel = −102.3 ± 0.4 (stat.) ± 2.0 (sys.) km s-1, a velocity dispersion of 0.1 -0.1+0.7 km s-1, and a mean metallicity of [Fe/H]=-2.42 -0.08+0.07. The upper limit on the velocity dispersion is σ < 1.5 km s-1 at 95.5% confidence, and the corresponding upper limit on the mass within the half-light radius of Tuc III is 9.0 × 104 M ⊙. We cannot rule out mass-to-light ratios as large as 240 M ⊙/L ⊙ for Tuc III, but much lower mass-to-light ratios that would leave the system baryon-dominated are also allowed. We measure an upper limit on the metallicity spread of the stars in Tuc III of 0.19 dex at 95.5% confidence. Tuc III has a smaller metallicity dispersion and likely a smaller velocity dispersion than any known dwarf galaxy, but a larger size and lower surface brightness than any known globular cluster. Its metallicity is also much lower than those of the clusters with similar luminosity. We therefore tentatively suggest that Tuc III is the tidally stripped remnant of a dark matter-dominated dwarf galaxy, but additional precise velocity and metallicity measurements will be necessary for a definitive classification. If Tuc III is indeed a dwarf galaxy, it is one of the closest external galaxies to the Sun. Because of its proximity, the most luminous stars in Tuc III are quite bright, including one star at V = 15.7 that is the brightest known member star of an ultra-faint satellite.

SPT-GMOS: A Gemini/GMOS-South Spectroscopic Survey of Galaxy Clusters in the SPT-SZ Survey

National Science Foundation [AST-1009012, PHY-1125897]; Kavli Foundation; Gordon and Betty Moore Foundation [GBMF 947]; NSF [AST-1009649, MRI-0723073]; Alfred P. Sloan Foundation; U.S. Department of Energy [DE-AC02-06CH11357]; Fermi Research Alliance, LLC [DE-AC02-07CH11359]; United States Department of Energy; NASA through Space Telescope Science Institute [HST-GO-13412.004-A]; NASA [NAS 5-26555]; [GS-2011A-C-03]; [GS-2011A-C-04]; [GS-2011B-C-06]; [GS-2011B-C-33]; [GS-2012A-Q-04]; [GS-2012A-Q-37]; [GS-2012B-Q-29]; [GS-2012B-Q-59]; [GS-2013A-Q-05]; [GS-2013A-Q-45]; [GS-2013B-Q-25]; [GS-2013B-Q-72]; [GS-2014B-Q-31]; [GS-2014B-Q-64]; [13412]

DES15E2mlf: A Spectroscopically Confirmed Superluminous Supernova that Exploded 3.5 Gyr After the Big Bang

We present the Dark Energy Survey (DES) discovery of DES15E2mlf, the most distant superluminous supernova (SLSN) spectroscopically confirmed to date. The light curves and Gemini spectroscopy of DES15E2mlf indicate that it is a Type I superluminous supernova (SLSN-I) at z = 1.861 (a lookback time of ∼10 Gyr) and peaking at MAB = −22.3 ± 0.1 mag. Given the high redshift, our data probe the rest-frame ultraviolet (1400–3500 A) properties of the SN, finding velocity of the C III feature changes by ∼5600 km s−1 over 14 d around maximum light. We find the host galaxy of DES15E2mlf has a stellar mass of 3.5+3.6 −2.4 × 109 M, which is more massive than the typical SLSN-I host galaxy.

Discovery and Physical Characterization of a Large Scattered Disk Object at 92 au

We report the observation and physical characterization of the possible dwarf planet 2014 UZ224 (DeeDee), a dynamically detached trans-Neptunian object discovered at 92 au. This object is currently the second-most distant known trans-Neptunian object with reported orbital elements, surpassed in distance only by the dwarf planet Eris. The object was discovered with an r-band magnitude of 23.0 in data collected by the Dark Energy Survey between 2014 and 2016. Its 1140 year orbit has (a,e,i)=(109 au,0.65,26.8. It will reach its perihelion distance of 38 au in the year 2142. Integrations of its orbit show it to be dynamically stable on Gyr timescales, with only weak interactions with Neptune. We have performed follow-up observations with ALMA, using 3 hr of on-source integration time to measure the objects thermal emission in the Rayleigh–Jeans tail. The signal is detected at 7σ significance, from which we determine a V-band albedo of 13.1 -2.4+3.3(stat) -1.4+2.0(sys) percent and a diameter of 635 -61+57(stat) -39+32(sys) km, assuming a spherical body with uniform surface properties.

Statistical significance of spectral lag transition in GRB 160625B

Abstract Recently Wei etu202fal.[1] have found evidence for a transition from positive time lags to negative time lags in the spectral lag data of GRB 160625B. They have fit these observed lags to a sum of two components: an assumed functional form for intrinsic time lag due to astrophysical mechanisms and an energy-dependent speed of light due to quadratic and linear Lorentz invariance violation (LIV) models. Here, we examine the statistical significance of the evidence for a transition to negative time lags. Such a transition, even if present in GRB 160625B, cannot be due to an energy dependent speed of light as this would contradict previous limits by some 3-4 orders of magnitude, and must therefore be of intrinsic astrophysical origin. We use three different model comparison techniques: a frequentist test and two information based criteria (AIC and BIC). From the frequentist model comparison test, we find that the evidence for transition in the spectral lag data is favored at 3.05 σ and 3.74 σ for the linear and quadratic models respectively. We find that ΔAIC and ΔBIC have values u202f≳u202f 10 for the spectral lag transition that was motivated as being due to quadratic Lorentz invariance violating model pointing to “decisive evidence”. We note however that none of the three models (including the model of intrinsic astrophysical emission) provide a good fit to the data.

Classifying Exoplanets with Gaussian Mixture Model

Recently, Odrzywolek and Rafelski (arXiv:1612.03556) have found three distinct categories of exoplanets, when they are classified based on density. We first carry out a similar classification of exoplanets according to their density using the Gaussian Mixture Model, followed by information theoretic criterion (AIC and BIC) to determine the optimum number of components. Such a one-dimensional classification favors two components using AIC and three using BIC, but the statistical significance from both the tests is not significant enough to decisively pick the best model between two and three components. We then extend this GMM-based classification to two dimensions by using both the density and the Earth similarity index (arXiv:1702.03678), which is a measure of how similar each planet is compared to the Earth. For this two-dimensional classification, both AIC and BIC provide decisive evidence in favor of three components.