Tuesday. Wednesday.
1504.02777
The abundance of satellites depends strongly on the morphology of the host galaxy
Ruiz, Trujillo, Mármol-Queraltó
Using the spectroscopic catalogue of SDSS DR10, explore the abundance of satellites around a sample of 307 massive (M*>1e11 Msun) local (z<0.025) galaxies. Have divided the sample into 4 morphological group (E, S0, Sa, Sb/c). Find that the number of satellites with M*>1e9 Msun and R<300 kpc depends drastically on the morphology of the central galaxy. The average number of satellites per galaxy host (N_sat/N_host) down to a mass ratio of 1:100 is : 5.5±1.0 for E hosts, 2.7±0.4 for S0, 1.4±0.3 for Sa and 1.2±0.3 for Sb/c. The amount of stellar mass enclosed by the satellites around massive E-type galaxies is a factor of 2, 4, and 6 larger than the mass in the satellites of S0, Sa and Sb/c-types, respectively. If these satellites would eventually infall in to the host galaxies, for all the morphological types, the merger channel will be largely dominated by satellites with a mass ratio satellite-host mu<0.1. The fact that massive elliptical galaxies have a significant larger number of satellites than massive spirals could point out that elliptical galaxies inhabit heavier DM haloes than equal massive galaxies with later morphological types. If this hypothesis is correct, the DM haloes of late-type spiral galaxies are a factor ~3 more efficient on producing galaxies with the same stellar mass than those DM haloes of massive ellipticals.
1504.02778
Calibrated ultra fast image simulations for the Dark Energy Survey
Bruderer, Chang, Refregier, Amara, Berge, Gamper
To understand the measurement process of WL and associated systematic effects, image simulations are becoming increasingly important. Present a first implementation of Monte Carlo Control Loops (MCCL), a coherent framework for studying systematic effects in WL. It allows to model and calibrate the shear measurement process using image simulations from the Ultra Fast Image Generator (UFig). Apply this framework to a subset of the data taken during the SV of DES. Calibrate the UFig sims to be statistically consistent with DES images. Then perform tolerance analyses by perturbing the simulation parameters and study their impact on the shear measurement at the 1pt level. This allows determination of the relative importance of different input params to the simulations. For spatially constant systematic errors and 6 sim params, the calibration of the sims reaches the WL precision needed for the DES SV survey area. Furthermore, find a sensitivity of the shear measurement to the intrinsic ellipticity distribution, and an interplay between the magnitude-size and the pixel value diagnostics in constraining the noise model. This work is the first application of the MCCL framework to data and shows how it can be used to methodically study the impact of systematics on the cosmic shear measurement.
1504.02889
Stellar kinematics and metallicities in the ultra-faint dwarf galaxy reticulum II
Simon, et al (+70 others)
Present Magellan, VLT, Gemini South spectroscopy of the newly discovered MW satellite Reticulum II. Based on the spectra of 25 Reg II member stars selected from DES imaging, measure a mean heliocentric velocity of 62.8±0.5 km/s and a velocity dispersion of 3.3±0.7 km/s. The M/L ratio of Ret II within its halon-light radius is 470±210 Msun/Lsun, demonstrating that it is a strongly DM-dominated system. Despite its spatial proximity to the Magellanic clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 km/s, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28±0.09 dex, and identify several extremely metal-poor stars with [Fe/H]<-3. In combination with its luminosity, size and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of [Fe/H]=-2.65±0.07, Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the 3rd closest dwarf galaxy to the MW, the LoS integral of the DM density squared is log J=18.8±0.6 GeV^2/cm^5 within 0.2 degrees, indicating that the predicted gamma-ray flux from DM annihilation in Ret II is lower than that of several other dwarf galaxies.
1504.02900
The dark energy camera
Flaughter et al (+117 others)
The DECam is a new imager with 2.2 deg diameter FoV mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by DES collaboration, and meets or exceeds the stringent requirements designed for the wide-field and SN surveys for which the collaboration uses it. The camera consists of a five element optical corrector, 7 filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250 micron thick fully-depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises a 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs of guiding and focus. The CCDs have 15 microns x 15 microns pixels with a plate scale of 0.263" per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation and current status.
1504.02932
Binary astrometric microlensing with Gaia
Sajadian
The Gaia efficiency for detecting the binary signatures in binary astrometric microlensing events is ~10-20 %. Microlensing binary events being observed wit Gaia with detectable binary signatures for the binary fraction about 0.1, is estimated as 6,11, 77, and 1306, respectively for (1) stellar mass BHs, (b) NSs, (c) WDs, and (d) MS stars as micro lenses. The efficiencies of measuring the mass of populations are 9.8, 2.9, 1.2 and 0.8 % respectively. The number of their astrometric microlensing events being observed in the Gaia era in which the lens mass can be inferred with the relative error less than 0.5 toward the Galactic bulge is estimated as 45, 34, 76 and 786 respectively.
1504.02936
Automated transient identification in the Dark Energy Survey
Goldstein, et al (+65 others)
Describe an algorithm for identifying point-source transients and moving objects on reference -subtracted optic mages containing artifacts of processing and instrumentation. The algorithm makes use of the supervised machine learning technique known as Random Forest. Present results from its use in the DES-SN program, where it was trained using a sample of 898k signal and background events generated by the transient detection pipeline. After reprocessing the data collected during the first DES-SN observing season (9/13 through 2/14) using the algorithm, the number of transient candidates eligible for human scanning decreased by a factor of 13.4, while only 1% of the artificial SNeIa injected into search images to monitor survey efficiency were lost, most of which were very faint events. Characterize the algorithm's performance in detail, and discuss how it can inform pipeline design decisions for future time-domain imaging surveys, such as the LSST and the Zwicky Transient Facility.
1504.02983
Galaxies in X-ray selected clusters and groups in dark energy survey data: stellar mass growth of bright central galaxies since z~1.2
Zhang, et al (+82 others)
Using the DES-SV data for a sample of 106 X-ray selected clusters and groups, study the stellar mass growth of BCGs since z=1.2. Compared with the expectation in a SAM applied to the MS, the observed BCGs become under-massive/under-luminous with decreasing redshift. Incorporate the uncertainties associated with cluster mass, z, and BCG stellar mass measurements into analysis of a z-dependent BCG-cluster mass relation, m*\propto (M200/1.5e14 Msun)^0.34±0.08(1+z)^-0.19±0.34, and compare the observed relation to the simulation prediction. Estimate the average growth rate since z=1.0 for BCGs hosted by clusters of M200,z=1e13.8Msun, at z=1.0: M*,BCG appears to have grown by 0.13±0.11 dex, in tension at ~2.5sigma significance level with the 0.4 dex growth rate expected in the simulation. Show that the buildup of extended ICL after z=1.0 may alleviate this tension in BCG growth rates.
1504. 1504.02996
DESAltert: enabling real-time transient follow-up with dark energy survey data
Poci, et al
DES is currently undertaking an observational program imaging 1/4 of the southern hemisphere sky with unprecedented photometric accuracy. In the process of observing millions of faint stars and galaxies to constrain the parameters of the DE EoS, the DES will obtain pre-discovery images of the regions surrounding an estimated 100 GRBs over 5 years. Once GRBs are detected by, e.g., the Swift satellite, the DES data will be extremely useful for follow-up observations by the transient astronomy community. Describe a recently-commissioned suite of SW that listens continuously for automated notices of GRB activity, collates useful information from archival DES data, and promulgates relevant data products back to the community in near-real-time. Of particular importance are the opportunities that DES data provide for relative photometry of GRBs or their afterglows, as well as for identifying key characteristics (e.g., photo-z) of potential GRB host galaxies. Provide the functional details of the DESAlert SW as it presently operates, as well as the data products that it produces, and show sample results from the application of DESAlert to several previously-detected GRBs.
1504.03002
Wide-field lensing mass maps from DES science verification data
Vikram, Chang, Jain, Bacon, ... et al
WL "mass maps" provide a powerful tool for studying cosmo as they probe both luminous and DM. In this paper, present a WL mass map constructed from shear measurements in a 139 deg.sq. area from DES SV data overlapping with the SPT survey. Compare the distribution of mass with that of the FG distribution of galaxies and clusters. The over densities in the reconstructed map correlated well with the distribution of optically detected clusters. Cross-correlating the mass map with the FG galaxies from the same DES SV data gives results consistent with mock catalogs that include the primary sources of statistical uncertainties in the galaxy, lensing, and photo-z catalogs. The statistical significance of the cross-correlation is at the 6.8 sigma level with 20' smoothing. A major goal of this study is to investigate systematic effects arising from a variety of sources, including PSF and photo-z uncertainties. Make maps derived from 20 variables that may characterize systematics and find the principle component. Find that the contribution of systematics to the lensing mass maps is generally within measurement uncertainties. Test and validate results with mock catalogs from N-body sims. In this work, analyze less than 3% of the final area that will be mapped by the DES; the tools and analysis techniques developed in this paper can be applied to forthcoming larger datasets from the survey.
1504.03039
OzDES multi-fibre spectroscopy for the dark energy survey: first-year operations and results
Yuan et al
OzDES is a five-year, 100-night, spectroscopic survey on AAT, whose primary aim is to measure redshifts of approximately 2500 SNeIa host galaxies over the redshift range 0.1<z<1.2, and derive reverberation-mapped BH masses for approximately 500 AGN and quasars over 0.3<z<4.5. This treasure trove of data forms a major part of the spectroscopic follow-up for the DES for which also galaxy clusters, radio galaxies, strong lensing and unidentified transients are targeted, as well as measuring luminous red galaxies and emission line galaxies to help calibrate photo-z. Present an overview of the OzDES program and the first-year results. Between 12/12 and 12/13, observed over 10k objects and measured more than 6k redshifts. The strategy of retargeting faint objects across many observing runs has allowed to measure redshifts for galaxies as faint as m_r=25 mag. Outline the target selection and observing strategy quantify the redshift success rate for different types of targets, and discuss the implications for the main science goals. Finally, highlight a few interesting objects as examples of the fortuitous yet not totally unexpected discoveries that can come from such a large spectroscopic survey.
1504.03044
Suzaku observations of subclass in the Coma cluster
Sasaki, Matsushita, Sato, Okabe
Observed 3 massive subclass in Coma with Suzaku (ID 1, 2, 32). Subhalos were detected with a WL survey from Suprime-cam, and are located 1.4, 1.2, and 1.6 r500 from the cluster center, respectively. ... Assuming an infall velocity of about 2000 km/s, at the boarder of the excess X-ray emission, the ram pressures for ID 1 and 32 are comparable to the gravitational restoring force per area. No significant excess X-ray emission in the ID 2 sub halo. Although X-ray clumps associated with the WL subhalos were found, their X-ray luminosities are much lower than the total ICM luminosity in the cluster outskirts.
1504.03264
DES J0454$-$4448: discovery of the first luminous z$\ge$ 6 quasar from the dark energy survey
Reed, et al
Present the first results of a survey for z>6 quasars using icy multicolor photometric observations from DES. Report the discovery and spectroscopic confirmation of the (z_AB, Y_AB) = (20.2, 20.2) (M1450=-26.5) quasar DES J0454-5558 with an emission line redshift of z=6.10±0.03 and a HI near zone size of 4.6±1.7 Mpc. The quasar was selected as an i-band dropout with i-z=2.46 and z_AB<21.5 from an area of ~300 sq deg. It is the brightest of the 43 candidates and was identified for follow-up spectroscopically solely based on the DES i-z and z-Y colors. The quasar is detected by WISE and has W1_AB=19.68. The discovery of one spectroscopically confirmed quasar with 5.7<z<6.5 and z_AB<20.2 is consistent with recent determinations of the LF at z~6. DES when completed will have imaged ~5000 deg sq to Y_AB=23.0 (5sigma point source) and expect to discover >50-100 new quasars with z>6 including 3-10 with z>7, dramatically increasing the numbers of quasars currently known that are suitable for detailed studies including determination of the neutral HI fraction of the IGM during the epoch of Hydrogen reionization.
1504.03290
Voids in Ly{\alpha} forest tomographic maps
Stark, Font-Ribera, White, Lee
Present a new method of finding cosmic voids using tomographic maps of Lya first flux. Identify cosmo voids with radii of 2-12 Mpc/h in large N-body sim at z=2.5, and characterize the signal of the high-z voids in density and Lya forest flux. The void properties are similar to what has been found at lower redshifts, but they are smaller and have steeper radial density profiles. Similarly to what has been found for low-z voids, the radial velocity profiles have little scatter and agree very well with the linear theory prediction. Run the same void finder on an ideal Lya flux field and tomographic reconstructions at various spatial samplings. Compare the tomographic map void catalogs to the density void catalog and find good agreement even with modest-sized voids (r>6 Mpc/h). Using the simple void-finding method, the configuration of the ongoing CLAMATO survey covering 1 sq deg would provide a sample of about 100 high-z voids. Also provide void-finding forecasts for larger area surveys, and discuss how these void samples can be used to test modified gravity models, study high-z void galaxies, and to make an Alcock-Paczynski measurement. To aid future work in the area, provide publid access to the simulation products, catalogs, and sample tomographic flux maps.
1504.03317
The dark matter profile of the Milky Way: a non-parametric reconstruction
Pato, Iocco
Present the results of a new, non-parametric method to reconstruct the Galactic dark matter profile directly from observations. Using the latest kinematic data to track the total gravitational potential and the observed distribution of stars and gas to set the baryonic component, infer the DM contribution to the circular velocity across the Galaxy. The radial derivative of this dynamical contribution is then estimated to extract the DM profile. The innovative feature of the approach is that it makes no assumption on the functional form nor shape of the profile, thus allowing for a clean determination with no theoretical bias. Illustrate the power of the method by constraining the spherical DM profile between 2.5 and 25 kpc away from the Galactic centre. The results show that the proposed method, free of widely used assumptions, can already be applied to pinpoint the DM distribution in the MW with competitive accuracy, and paves the way for future developments.
1504.03320
Spectroscopic confirmation of the existence of large, diffuse galaxies in the Coma cluster
van Dokkum, et al
Identified a population of low surface brightness objects in the field of the z=0.023 Coma cluster, using the Dragonfly Telephoto Array. Present Keck spectroscopy of one of the largest of these "ultra-diffuse galaxies" (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption features, including the CA II H+K lines and the G-band, and no detected emission lines. Its radial velocity of cz=6280±120 km/s is within the 1 sigma velocity dispersion of the Coma cluster. The galaxy has an effective radius of 4.3±0.2 kpc and a Sersic index of 0.89±0.06, as measured from Keck imaging. Find no indications of tidal tails or other distortions, at least out to a radius of ~2 r_e. Show that UDGs are located in a previously sparsely populated region of the size-magnitude plane of quiescent stellar systems, as they are ~6 mags fainter than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are needed to determine whether the dark matter haloes of UDGs are similar to those of galaxies with the same luminosity or to those of galaxies with the same size.
1504.03322
Position-dependent correlation function from the SDSS-III Baryon Oscillation Spectroscopic Survey Data Relase 10 CMASS sample
Chiang, Wagner, Sánchez, Schmidt, Komatsu
The new observable measures the correlation between 2pt functions of galaxy pairs within different sub volumes, xi(r,r_L), where r_L is the location of a sub volume, and the corresponding mean over densities, bar_delta(r_L). This correlation, dubbed the "integrated 3pt function", i zeta(r) = <xi(r, r_L) bar_delta(r_L)>, measures a 3pt function of 2 short- and one long-wavelength modes, and is generated by NL gravitational evolution and possibly also by the physics of inflation. The i zeta(r) measured from BOSS lies within the scatter of those from the mock galaxy catalogs in z-space, yielding a 10%-level determination of the amplitude of i zeta(r). The tree-level perturbation theory in z-space predicts how this amplitude depends on the linear and quadratic NL galaxy bias parameters (b1 and b2), as well as on the amplitude and linear growth rate of matter fluctuations (sigma_8 and f). Combining i zeta(r) with the constraints on b1 sigma8 and f sigma8 from the global 2pt correlation function and that on sigma8 from the WL signal of BOSS galaxies, measure b2=1.30±0.54 (68% CL).
1504.03388
The behavior of dark matter associated with 4 bright cluster galaxies in the 10kpc core of Abell 3827
Massey et al
Galaxy cluster A3827 hosts the stellar remnants of four almost equally bright elliptical galaxies within a core of radius 10 kpc. Such corrugation of the stellar distribution is very rare, and suggests recent f formation by several simultaneous mergers. Map the distribution of associated DM, using new HST imaging and VLT/MUSE IFS for a gravitationally lensed system threaded through the cluster core. Find that each of the central galaxies retains a DM halo, but that (at least) one of these is spatially offset from its stars. The best-constrained offset if 1.62±0.48 kpc, where the 68% CL includes both statistical error and systematic biases in mass modeling. Such offsets are not seen in field galaxies, but are predicted during the long infall to a cluster, if dark matter self-interactions generate an extra drag force. With such a small physical separation, it is difficult to definitively rule out astrophysical effects operating exclusively in dense cluster core environments - but if interpreted solely as evidence for self-interacting DM, this offset implies a cross-section sigma/m=(1.7±0.7)e-4 cm^2/g x (t/1e9 yrs)^-2, where t is the infall duration.
1410.0961
Type Ia supernovae yielding distances with 3-4% precision
Kelly, Filippenko, et al
The luminosities of SNIa, the thermonuclear explosions of WD stars, vary systematically with their intrinsic color and light-curve decline rate. These relationships have been used to calibrate their luminosities to within ~0.14-0.20 mag from broadband optical light curves, yielding individual distances accurate to ~7-10%. Identify a subset of SNIa that erupt in environments having high UV surface brightness and SF surface density. When a steep model extinction law is applied, these SN can be calibrated to within ~0.065-0.075 mag, corresponding to ~3-4% in distance -- the best yet in SN Ia by a substantial margin. The small scatter suggests that variations in only one or two progenitor properties account for their light-curve-width/color/luminosity relation.
1503.02632
Search for gamma-ray emission from DES dwarf spheroidal galaxy candidates with Fermi-LAT data
The Fermi-LAT Collaboration + the DES collaboration, Drlica-Wagner
Due to their proximity, high DM content, and apparent absence of non-thermal processes, MW dwarf spheroidal satellite galaxies are excellent targets for the indirect detection of dark matter. Recently, eight new dSph candidates were discovered using the first year of DES data. Searched for gamma-ray emission coincident with the positions of these new objects in 6 years of Fermi LAT data. Found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, compete individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with masses <20 GeV annihilating via the b-bbar or tau+tau- channels.
1504.02165
Identifying the source of preteens at the Parkes radio telescope
Petroff et al
"Perytons" are millisecond-duration transients of terrestrial origin, whose frequency-swept emission mimics the dispersion of an astrophysical pulse that has propagated through tenuous cold plasma. In fact, their similarly to FRB 010724 had previously cast a shadow over the interpretation of "fast radio bursts," which otherwise appear to be of extragalactic origin. Until now, the physical origin of the dispersion-mimicking perytons had remained a mystery. Identified a strong out-of-band emission at 2.3-2.5 GHz associated with several periton events. Subsequent tests revealed that a periton can be generated at 1.4 GHz when a microwave oven door is opened prematurely and the telescope is at an appropriate relative angle. Radio emission escaping from microwave ovens during the magnetron shut-down phase neatly explain all of the observed properties of the peritonea signals. Now that the periton source has been identified, furthermore demonstrate that the microwaves on site could not have caused FRB 010724. This and there distinct observational differences show that FRBs are excellent candidates for genuine extragalactic transients.
1504.01734
Evidence for PopIII-like stellar populations in the most luminous Lyman-$\alpha$ emitters at the epoch of re-ionisation: spectroscopic confirmation
Sobral, et al
Faint Lya emitters become increasingly rarer towards the re-ionization epoch (z~6-7). However, observations from a very large (~5 sq deg) Lya survey at z=6.6 show that this is not the case for the most luminous emitters. Present follow-up observations of the 2 most luminous z~6.6 Lya candidates in the COSMOS field: 'MASOSA' and 'CR7'. Used X-SHOTTER, SINFONI and FORS2 (VLT), and DEIMOS (Keck), to confirm both candidates beyond any doubt. Find redshifts of z=6.541 and z=6.604 for MASOSA and CD7, respectively. MASOSA has a strong detection in Lya with a line width of 386±30 km/s (FWHM) and with high EW0 (>200 AA), but it is undetected in the continuum. CR7, with an observed Lya luminosity of 1e43.93±0.05 erg/s is the most luminous Lya emitter ever found at z>6. CR7 reveals a narrow Lya line with 266±15 km/s FWHM, being detected in the NIR (rest-frame UV, with beta=-2.3±0.1) with an excess in J, and also strongly detected IRAC/Spitzer. Detect a narrow HeII1640AA emission line (6sigma) which explains the excess seen in the J band photometry (EW0~80AA). Find no other emission lines from the UV to the NIR in the X-SHOOTER spectra, nor any signatures of SR stars. Find that CR7 is best explained by a combination of a PopIII-like population which dominates the rest-frame UV and the nebular emission, and a more normal stellar population which dominates the mass. HST/WFC3 observations show that the light is indeed spatially separated between a very blue component, coincident with Lya and HeII emission, and two red components (~5 kpc away), which dominate the mass. Findings are consistent with theoretical predictions of a PopIII wave, with PopIII SF migrating away from the original sites of SF.
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