# Browsing by Author "Scolnic, Daniel"

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Item Open Access It's Dust: Solving the Mysteries of the Intrinsic Scatter and Host-Galaxy Dependence of Standardized Type Ia Supernova BrightnessesBrout, Dillon; Scolnic, DanielThe use of Type Ia Supernovae (SNe Ia) as cosmological tools has motivated significant effort to: understand what drives the intrinsic scatter of SN Ia distance modulus residuals after standardization, characterize the distribution of SN Ia colors, and explain why properties of the host galaxies of the SNe correlate with SN Ia distance modulus residuals. We use a compiled sample of $\sim1450$ spectroscopically confirmed, photometric light-curves of SN Ia and propose a solution to these three problems simultaneously that also explains an empirical 11$\sigma$ detection of the dependence of Hubble residual scatter on SN Ia color. We introduce a physical model of color where intrinsic SN Ia colors with a relatively weak correlation with luminosity are combined with extrinsic dust-like colors ($E(B-V)$) with a wide range of extinction parameter values ($R_V$). This model captures the observed trends of Hubble residual scatter and indicates that the dominant component of SN Ia intrinsic scatter is from variation in $R_V$. We also find that the recovered $E(B-V)$ and $R_V$ distributions differ based on global host-galaxy stellar mass and this explains the observed correlation ($\gamma$) between mass and Hubble residuals seen in past analyses as well as an observed 4.5$\sigma$ dependence of $\gamma$ on SN Ia color. This finding removes any need to prescribe different intrinsic luminosities to different progenitor systems. Finally we measure biases in the equation-of-state of dark energy ($w$) up to $|\Delta w|=0.04$ by replacing previous models of SN color with our dust-based model; this bias is larger than any systematic uncertainty in previous SN Ia cosmological analyses.Item Open Access SOAR/Goodman Spectroscopic Assessment of Candidate Counterparts of the LIGO--Virgo Event GW190814Tucker, Douglas; Wiesner, Matthew; Allam, Sahar; Soares-Santos, Marcelle; Bom, Clecio de; Butner, Melissa; Garcia, Alyssa; Morgan, Robert; Olivares, Felipe; Palmese, Antonella; Santana-Silva, Luidhy; Shrivastava, Anushka; Annis, James; Garcia-Bellido, Juan; Gill, Mandeep; Herner, Kenneth; Kilpatrick, Charles; Makler, Martin; Sherman, Nora; Amara, Adam; Lin, Huan; Smith, Mathew; Swann, Elizabeth; Arcavi, Iair; Bachmann, Tristan; Bechtol, Keith; Berlfein, Federico; Briceno, Cesar; Brout, Dillon; Butler, Bobby; Cartier, Regis; Casares, Jorge; Chen, Hsin-Yu; Conselice, Christopher; Contreras, Carlos; Cook, E; Cooke, Jeff; Dage, Kristen; D'Andrea, Chris; Davis, Tamara; Carvalho, Reinaldo de; Diehl, Tom; Dietrich, Joerg; Doctor, Zoheyr; Drlica-Wagner, Alex; Drout, Maria; Farr, Ben; Finley, David; Fishbach, Maya; Foley, Ryan; Foerster-Buron, Francisco; Fosalba, Pablo; Friedel, Douglas; Frieman, Josh; Frohmaier, Christopher; Gruendl, Robert; Hartley, Will; Hiramatsu, Daichi; Holz, Daniel; Howell, Andy; Kawash, Adam; Kessler, Richard; Kuropatkin, Nikolay; Lahav, Ofer; Lundgren, Andrew; Lundquist, Michael; Malik, Umang; Mann, Andrew; Marriner, John; Marshall, Jennifer; Martinez-Vazquez, Clara; McCully, Curtis; Menanteau, Felipe; Meza, Nico; Narayan, Gautham; Neilsen, Eric; Nicolaou, Constantina; Nichol, Bob; Paz-Chinchon, Francisco; Pereira, Maria; Pineda, Jonathan; Points, Sean; Quirola, Jonathan; Rembold, Sandro; Rest, Armin; Rodriguez, Osmar; Romer, Kathy; Sako, Masao; Salim, Samir; Scolnic, Daniel; Smith, Allyn; Strader, Jay; Sullivan, Mark; Swanson, Molly; Thomas, Daniel; Valenti, Stefano; Varga, Tamas Norbert; Walker, Alistair; Weller, Jochen; Wood, Mackenna; Yanny, Brian; Zenteno, Alfredo; Aguena, Michel; Andrade-Oliveira, Felipe; Bertin, Emmanuel; Brooks, David; Burke, David; Rosell, Aurelio Carnero; Kind, Matias Carrasco; Carretero, Jorge; Costanzi, Matteo; Costa, Luiz da; Vicente, Juan De; Desai, Shantanu; Everett, Spencer; Ferrero, Ismael; Flaugher, Brenna; Gaztanaga, Enrique; Gerdes, David; Gruen, Daniel; Gschwend, Julia; Gutierrez, Gaston; Hinton, Samuel; Hollowood, Devon L; Honscheid, Klaus; James, David; Kuehn, Kyler; Lima, Marcos; Maia, Marcio; Miquel, Ramon; Ogando, Ricardo; Pieres, Adriano; Malagon, Andres Plazas; Monroy, Martin Rodriguez; Sanchez, Eusebio; Scarpine, Vic; Schubnell, Michael; Serrano, Santiago; Sevilla, Ignacio; Smith, Mathew; Suchyta, Eric; Tarle, Gregory; To, Chun-Hao; Zhang, YuanyuanOn 2019 August 14 at 21:10:39 UTC, the LIGO/Virgo Collaboration (LVC) detected a possible neutron star-black hole merger (NSBH), the first ever identified. An extensive search for an optical counterpart of this event, designated GW190814, was undertaken using DECam on the CTIO Blanco 4-m telescope. Target of opportunity interrupts were issued on 8 separate nights to observe 11 candidates using the SOAR Goodman Spectrograph in order to assess whether any of these transients was likely to be an optical counterpart of the possible NSBH merger. Here, we describe the process of observing with the SOAR Goodman spectrograph, the analysis of our spectra, our spectroscopic typing methodology, and our resultant conclusion that none of the candidates corresponded to the black hole-neutron star merger but were all instead other transient events. Finally, we describe the lessons learned from this effort. Application of these lessons will be critical for a successful community spectroscopic follow-up program for LVC season 4 (O4) and beyond.Item Open Access The Pantheon+ Analysis: Dependence of Cosmological Constraints on Photometric-Zeropoint Uncertainties of Supernova SurveysBrownsberger, Sasha; Brout, Dillon; Scolnic, Daniel; Stubbs, Christopher W; Riess, Adam GType Ia supernovae (SNe Ia) measurements of the Hubble constant, H$_0$, the cosmological mass density, $\Omega_M$, and the dark energy equation-of-state parameter, $w$, rely on numerous SNe surveys using distinct photometric systems across three decades of observation. Here, we determine the sensitivities of the upcoming SH0ES+Pantheon+ constraints on H$_0$, $\Omega_M$, and $w$ to unknown systematics in the relative photometric zeropoint calibration between the 17 surveys that comprise the Pantheon+ supernovae data set. Varying the zeropoints of these surveys simultaneously with the cosmological parameters, we determine that the SH0ES+Pantheon+ measurement of H$_0$ is robust against inter-survey photometric miscalibration, but that the measurements of $\Omega_M$ and $w$ are not. Specifically, we find that miscalibrated inter-survey systematics could represent a source of uncertainty in the measured value of H$_0$ that is no larger than $0.2$ km s$^{-1}$ Mpc$^{-1}$. This modest increase in H$_0$ uncertainty could not account for the $7$ km s$^{-1}$ Mpc$^{-1}$ "Hubble Tension" between the SH0ES measurement of H$_0$ and the Planck $\Lambda$CDM-based inference of H$_0$. However, we find that the SH0ES+Pantheon+ best-fit values of $\Omega_M$ and $w$ respectively slip, to first order, by $0.04$ and $-0.17$ per $25$ mmag of inter-survey calibration uncertainty, underscoring the vital role that cross-calibration plays in accurately measuring these parameters. Because the Pantheon+ compendium contains many surveys that share low-$z$ Hubble Flow and Cepheid-paired SNe, the SH0ES+Pantheon+ joint constraint of H$_0$ is robust against inter-survey photometric calibration errors, and such errors do not represent an impediment to jointly using SH0ES+Pantheon+ to measure H$_0$ to 1% accuracy.Item Open Access The Pantheon+ Analysis: Evaluating Peculiar Velocity Corrections in Cosmological Analyses with Nearby Type Ia SupernovaePeterson, Erik R; Kenworthy, W D'Arcy; Scolnic, Daniel; Riess, Adam G; Brout, Dillon; Carr, Anthony; Courtois, Helene; Davis, Tamara; Dwomoh, Arianna; Jones, David O; Popovic, Brodie; Rose, Benjamin M; Said, KhaledSeparating the components of redshift due to expansion and motion in the nearby universe ($z<0.1$) is critical for using Type Ia Supernovae (SNe Ia) to measure the Hubble constant ($H_0$) and the equation-of-state parameter of dark energy ($w$). Here, we study the two dominant 'motions' contributing to nearby peculiar redshifts: large-scale, coherent-flow (CF) motions and small-scale motions due to gravitationally-associated galaxies deemed to be in a galaxy group. We use a set of 585 low-$z$ SNe from the Pantheon+ sample, and evaluate the efficacy of corrections to these motions by measuring the improvement of SN distance residuals. We study multiple methods for modeling the large and small-scale motions and show that while group assignments and CF corrections individually contribute to small improvements in Hubble residual scatter, the greatest improvement comes from the combination of the two (relative standard deviation of the Hubble residuals RSD improves from 0.167 mag to 0.157 mag). We find the optimal flow corrections derived from various local density maps significantly reduce Hubble residuals while raising $H_0$ by $\sim0.4$ km s$^{-1}$ Mpc$^{-1}$ as compared to using CMB redshifts, disfavoring the hypothesis that unrecognized local structure could resolve the Hubble tension. We estimate that the systematic uncertainties in cosmological parameters after optimally correcting redshifts are 0.08-0.17 km s$^{-1}$ Mpc$^{-1}$ in $H_0$ and 0.02-0.03 in $w$ which are smaller than the statistical uncertainties for these measurements: 1.5 km s$^{-1}$ Mpc$^{-1}$ for $H_0$ and 0.04 for $w$.Item Open Access The Pantheon+ Analysis: Forward-Modeling the Dust and Intrinsic Colour Distributions of Type Ia Supernovae, and Quantifying their Impact on Cosmological InferencesPopovic, Brodie; Brout, Dillon; Kessler, Richard; Scolnic, DanielRecent studies have shown that the observed colour distributions of Type Ia SNe (SNIa) are well-described by a combination of distributions from dust and intrinsic colour. Here we present a new forward-modeling fitting method (Dust2Dust) to measure the parent dust and colour distributions, including their dependence on host-galaxy mass. At each fit step, the SNIa selection efficiency is determined from a large simulated sample that is re-weighted to reflect the proposed distributions. We use five separate metrics to constrain the Dust2Dust parameters: distribution of fitted light-curve colour $c$, cosmological residual trends with $c$, cosmological residual scatter with $c$, fitted colour-luminosity relationship $\beta_{\rm SALT2}$, and intrinsic scatter $\sigma_{\rm int}$. Using the Pantheon+ data sample, we present results for a Dust2Dust fit that includes 4 parameters describing intrinsic colour variations and 8 parameters describing dust. Furthermore, we propagate the Dust2Dust parameter uncertainties and covariance to the dark energy equation-of-state $w$ and Hubble constant H$_0$: we find $\sigma_w = 0.005$ and $\sigma_{\textrm{H}_0} = 0.145~$km/s/Mpc. The Dust2Dust code is publically available.Item Open Access The Pantheon+ Analysis: Improving the Redshifts and Peculiar Velocities of Type Ia Supernovae Used in Cosmological AnalysesCarr, Anthony; Davis, Tamara M; Scolnic, Daniel; Said, Khaled; Brout, Dillon; Peterson, Erik R; Kessler, RichardWe examine the redshifts of a comprehensive set of published Type Ia supernovae, and provide a combined, improved catalog with updated redshifts. We improve on the original catalogs by using the most up-to-date heliocentric redshift data available; ensuring all redshifts have uncertainty estimates; using the exact formulae to convert heliocentric redshifts into the Cosmic Microwave Background (CMB) frame; and utilizing an improved peculiar velocity model that calculates local motions in redshift-space and more realistically accounts for the external bulk flow at high-redshifts. In total we reviewed 2821 supernova redshifts; 534 are comprised of repeat-observations of the same supernovae and 1764 pass the cosmology sample quality cuts. We found 5 cases of missing or incorrect heliocentric corrections, 44 incorrect or missing supernova coordinates, 230 missing heliocentric or CMB frame redshifts, and 1200 missing redshift uncertainties. Of the 2287 unique Type Ia supernovae in our sample (1594 of which satisfy cosmology-sample cuts) we updated 990 heliocentric redshifts. The absolute corrections range between $10^{-8} \leq \Delta z \leq 0.038$, and RMS$(\Delta z) \sim 3\times 10^{-3}$. The sign of the correction was essentially random, so the mean and median corrections are small: $4\times 10^{-4}$ and $4\times 10^{-6}$ respectively. We examine the impact of these improvements for $H_0$ and the dark energy equation of state $w$ and find that the cosmological results change by $\Delta H_0 = -0.11$ km s$^{-1}$ Mpc$^{-1}$ and $\Delta w = -0.001$, both significantly smaller than previously reported uncertainties for $H_0$ of 1.4 km s$^{-1}$ Mpc$^{-1}$ and $w$ of 0.04 respectively.