Browsing by Subject "astro-ph.IM"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Open Access Binning is Sinning (Supernova Version): The Impact of Self-Calibration in Cosmological Analyses with Type Ia SupernovaeBrout, D; Hinton, SR; Scolnic, DRecent cosmological analyses (e.g., JLA, Pantheon) of Type Ia Supernova (SNIa) have propagated systematic uncertainties into a covariance matrix and either binned or smoothed the systematic vectors in redshift space. We demonstrate that systematic error budgets of these analyses can be improved by a factor of $\sim1.5\times$ with the use of unbinned and unsmoothed covariance matrices. To understand this, we employ a separate approach that simultaneously fits for cosmological parameters and additional self-calibrating scale parameters that constrain the size of each systematic. We show that the covariance-matrix approach and scale-parameter approach yield equivalent results, implying that in both cases the data can self-calibrate certain systematic uncertainties, but that this ability is hindered when information is binned or smoothed in redshift space. We review the top systematic uncertainties in current analyses and find that the reduction of systematic uncertainties in the unbinned case depends on whether a systematic is consistent with varying the cosmological model and whether or not the systematic can be described by additional correlations between SN properties and luminosity. Furthermore, we show that the power of self-calibration increases with the size of the dataset, which presents a tremendous opportunity for upcoming analyses of photometrically classified samples, like those of Legacy Survey of Space and Time (LSST) and the Nancy Grace Roman Telescope (NGRST). However, to take advantage of self-calibration in large, photometrically-classified samples, we must first address the issue that binning is required in currently-used photometric methodologies.Item Open Access Optical follow-up of gravitational wave triggers with DECam during the first two LIGO/VIRGO observing runsHerner, K; Annis, J; Brout, D; Soares-Santos, M; Kessler, R; Sako, M; Butler, R; Doctor, Z; Palmese, A; Allam, S; Tucker, DL; Sobreira, F; Yanny, B; Diehl, HT; Frieman, J; Glaeser, N; Garcia, A; Sherman, NF; Bechtol, K; Berger, E; Chen, HY; Conselice, CJ; Cook, E; Cowperthwaite, PS; Davis, TM; Drlica-Wagner, A; Farr, B; Finley, D; Foley, RJ; Garcia-Bellido, J; Gill, MSS; Gruendl, RA; Holz, DE; Kuropatkin, N; Lin, H; Marriner, J; Marshall, JL; Matheson, T; Neilsen, E; Paz-Chinchón, F; Sauseda, M; Scolnic, D; Williams, PKG; Avila, S; Bertin, E; Buckley-Geer, E; Burke, DL; Rosell, AC; Carrasco-Kind, M; Carretero, J; da Costa, LN; De Vicente, J; Desai, S; Doel, P; Eifler, TF; Everett, S; Fosalba, P; Gaztanaga, E; Gerdes, DW; Gschwend, J; Gutierrez, G; Hartley, WG; Hollowood, DL; Honscheid, K; James, DJ; Krause, E; Kuehn, K; Lahav, O; Li, TS; Lima, M; Maia, MAG; March, M; Menanteau, F; Miquel, R; Plazas, AA; Sanchez, E; Scarpine, V; Schubnell, M; Serrano, S; Sevilla-Noarbe, I; Smith, M; Suchyta, E; Tarle, G; Wester, W; Zhang, YGravitational wave (GW) events detectable by LIGO and Virgo have several possible progenitors, including black hole mergers, neutron star mergers, black hole--neutron star mergers, supernovae, and cosmic string cusps. A subset of GW events are expected to produce electromagnetic (EM) emission that, once detected, will provide complementary information about their astrophysical context. To that end, the LIGO--Virgo Collaboration (LVC) sends GW candidate alerts to the astronomical community so that searches for their EM counterparts can be pursued. The DESGW group, consisting of members of the Dark Energy Survey (DES), the LVC, and other members of the astronomical community, uses the Dark Energy Camera (DECam) to perform a search and discovery program for optical signatures of LVC GW events. DESGW aims to use a sample of GW events as standard sirens for cosmology. Due to the short decay timescale of the expected EM counterparts and the need to quickly eliminate survey areas with no counterpart candidates, it is critical to complete the initial analysis of each night's images as quickly as possible. We discuss our search area determination, imaging pipeline, and candidate selection processes. We review results from the DESGW program during the first two LIGO--Virgo observing campaigns and introduce other science applications that our pipeline enables.Item Open Access Optimization of the Observing Cadence for the Rubin Observatory Legacy Survey of Space and Time: a pioneering process of community-focused experimental designBianco, Federica B; Ivezić, Željko; Jones, R Lynne; Graham, Melissa L; Marshall, Phil; Saha, Abhijit; Strauss, Michael A; Yoachim, Peter; Ribeiro, Tiago; Anguita, Timo; Bauer, Franz E; Bellm, Eric C; Blum, Robert D; Brandt, William N; Brough, Sarah; Catelan, Màrcio; Clarkson, William I; Connolly, Andrew J; Gawiser, Eric; Gizis, John; Hlozek, Renee; Kaviraj, Sugata; Liu, Charles T; Lochner, Michelle; Mahabal, Ashish A; Mandelbaum, Rachel; McGehee, Peregrine; Jr, Eric H Neilsen; Olsen, Knut AG; Peiris, Hiranya; Rhodes, Jason; Richards, Gordon T; Ridgway, Stephen; Schwamb, Megan E; Scolnic, Dan; Shemmer, Ohad; Slater, Colin T; Slosar, Anže; Smartt, Stephen J; Strader, Jay; Street, Rachel; Trilling, David E; Verma, Aprajita; Vivas, AK; Wechsler, Risa H; Willman, BethVera C. Rubin Observatory is a ground-based astronomical facility under construction, a joint project of the National Science Foundation and the U.S. Department of Energy, designed to conduct a multi-purpose 10-year optical survey of the southern hemisphere sky: the Legacy Survey of Space and Time. Significant flexibility in survey strategy remains within the constraints imposed by the core science goals of probing dark energy and dark matter, cataloging the Solar System, exploring the transient optical sky, and mapping the Milky Way. The survey's massive data throughput will be transformational for many other astrophysics domains and Rubin's data access policy sets the stage for a huge potential users' community. To ensure that the survey science potential is maximized while serving as broad a community as possible, Rubin Observatory has involved the scientific community at large in the process of setting and refining the details of the observing strategy. The motivation, history, and decision-making process of this strategy optimization are detailed in this paper, giving context to the science-driven proposals and recommendations for the survey strategy included in this Focus Issue.Item Open Access SALT3: An Improved Type Ia Supernova Model for Measuring Cosmic DistancesKenworthy, WD; Jones, DO; Dai, M; Kessler, R; Scolnic, D; Brout, D; Siebert, MR; Pierel, JDR; Dettman, KG; Dimitriadis, G; Foley, RJ; Jha, SW; Pan, Y-C; Riess, A; Rodney, S; Rojas-Bravo, CA spectral-energy distribution (SED) model for Type Ia supernovae (SNe Ia) is a critical tool for measuring precise and accurate distances across a large redshift range and constraining cosmological parameters. We present an improved model framework, SALT3, which has several advantages over current models including the leading SALT2 model (SALT2.4). While SALT3 has a similar philosophy, it differs from SALT2 by having improved estimation of uncertainties, better separation of color and light-curve stretch, and a publicly available training code. We present the application of our training method on a cross-calibrated compilation of 1083 SNe with 1207 spectra. Our compilation is $2.5\times$ larger than the SALT2 training sample and has greatly reduced calibration uncertainties. The resulting trained SALT3.K21 model has an extended wavelength range $2000$-$11000$ angstroms (1800 angstroms redder) and reduced uncertainties compared to SALT2, enabling accurate use of low-$z$ $I$ and $iz$ photometric bands. Including these previously discarded bands, SALT3.K21 reduces the Hubble scatter of the low-z Foundation and CfA3 samples by 15% and 10%, respectively. To check for potential systematic uncertainties we compare distances of low ($0.01Item Open Access SNIa-Cosmology Analysis Results from Simulated LSST Images: from Difference Imaging to Constraints on Dark EnergySánchez, B; Kessler, R; Scolnic, D; Armstrong, B; Biswas, R; Bogart, J; Chiang, J; Cohen-Tanugi, J; Fouchez, D; Gris, Ph; Heitmann, K; Hložek, R; Jha, S; Kelly, H; Liu, S; Narayan, G; Racine, B; Rykoff, E; Sullivan, M; Walter, C; Wood-Vasey, M; Collaboration, The LSST Dark Energy ScienceThe Vera Rubin Observatory Legacy Survey of Space and Time (LSST) is expected to process ${\sim}10^6$ transient detections per night. For precision measurements of cosmological parameters and rates, it is critical to understand the detection efficiency, magnitude limits, artifact contamination levels, and biases in the selection and photometry. Here we rigorously test the LSST Difference Image Analysis (DIA) pipeline using simulated images from the Rubin Observatory LSST Dark Energy Science Collaboration (DESC) Data Challenge (DC2) simulation for the Wide-Fast-Deep (WFD) survey area. DC2 is the first large-scale (300 deg$^2$) image simulation of a transient survey that includes realistic cadence, variable observing conditions, and CCD image artifacts. We analyze ${\sim}$15 deg$^2$ of DC2 over a 5-year time-span in which artificial point-sources from Type Ia Supernovae (SNIa) light curves have been overlaid onto the images. We measure the detection efficiency as a function of Signal-to-Noise Ratio (SNR) and find a $50\%$ efficiency at $\rm{SNR}=5.8$. The magnitude limits for each filter are: $u=23.66$, $g=24.69$, $r=24.06$, $i=23.45$, $z=22.54$, $y=21.62$ $\rm{mag}$. The artifact contamination is $\sim90\%$ of detections, corresponding to $\sim1000$ artifacts/deg$^2$ in $g$ band, and falling to 300 per deg$^2$ in $y$ band. The photometry has biases $<1\%$ for magnitudes $19.5 < m <23$. Our DIA performance on simulated images is similar to that of the Dark Energy Survey pipeline applied to real images. We also characterize DC2 image properties to produce catalog-level simulations needed for distance bias corrections. We find good agreement between DC2 data and simulations for distributions of SNR, redshift, and fitted light-curve properties. Applying a realistic SNIa-cosmology analysis for redshifts $z<1$, we recover the input cosmology parameters to within statistical uncertainties.Item Open Access The Pantheon+ Analysis: SuperCal-Fragilistic Cross Calibration, Retrained SALT2 Light Curve Model, and Calibration Systematic UncertaintyBrout, Dillon; Taylor, Georgie; Scolnic, Dan; Wood, Charlotte M; Rose, Benjamin M; Vincenzi, Maria; Dwomoh, Arianna; Lidman, Christopher; Riess, Adam; Ali, Noor; Qu, Helen; Dai, Mi; Stubbs, ChristopherWe present here a re-calibration of the photometric systems used in the Pantheon+ sample of Type Ia supernovae (SNe Ia) including those used for the SH0ES distance-ladder measurement of H$_0$. We utilize the large and uniform sky coverage of the public Pan-STARRS stellar photometry catalog to cross-calibrate against tertiary standards released by individual SN Ia surveys. The most significant updates over the `SuperCal' cross-calibration used for the previous Pantheon and SH0ES analyses are: 1) expansion of the number of photometric systems (now 25) and filters (now 105), 2) solving for all filter offsets in all systems simultaneously in order to produce a calibration uncertainty covariance matrix that can be used in cosmological-model constraints, and 3) accounting for the change in the fundamental flux calibration of the HST CALSPEC standards from previous versions on the order of $1.5\%$ over a $\Delta \lambda$ of 4000~\AA. The re-calibration of samples used for light-curve fitting has historically been decoupled from the retraining of the light-curve model. Here, we are able to retrain the SALT2 model using this new calibration and find the change in the model coupled with the change to the calibration of the light-curves themselves causes a net distance modulus change ($d\mu/dz$) of 0.04 mag over the redshift range $0