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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Operation and performance of the ATLAS Tile Calorimeter in Run 1

The Tile Calorimeter is the hadron calorimeter covering the central region of the ATLAS experiment at the Large Hadron Collider. Approximately 10,000 photomultipliers collect light from scintillating tiles acting as the active material sandwiched between slabs of steel absorber. This paper gives an overview of the calorimeter’s performance during the years 2008–2012 using cosmic-ray muon events and proton–proton collision data at centre-of-mass energies of 7 and 8 TeV with a total integrated luminosity of nearly 30 fb –1 . The signal reconstruction methods, calibration systems as well as the detector operation status are presented. The energy and time calibration methods performed excellently, resulting in good stability of the calorimeter response under varying conditions during the LHC Run 1. Lastly, the Tile Calorimeter response to isolated muons and hadrons as well as to jets from proton–proton collisions is presented. The results demonstrate excellent performance in accord with specifications mentioned in the Technical Design Report.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Theoretical & Experimental Research in Weak, Electromagnetic & Strong Interactions

The conducted research spans a wide range of topics in the theoretical, experimental and phenomenological aspects of elementary particle interactions. Theory projects involve topics in both the energy frontier and the intensity frontier. The experimental research involves energy frontier with the ATLAS Collaboration at the Large Hadron Collider (LHC). In theoretical research, novel ideas going beyond the Standard Model with strong theoretical motivations were proposed, and their experimental tests at the LHC and forthcoming neutrino facilities were outlined. These efforts fall into the following broad categories: (i) TeV scale new physics models for LHC Run 2, including left-right symmetry and trinification symmetry, (ii) unification of elementary particles and forces, including the unification of gauge and Yukawa interactions, (iii) supersummetry and mechanisms of supersymmetry breaking, (iv) superworld without supersymmetry, (v) general models of extra dimensions, (vi) comparing signals of extra dimensions with those of supersymmetry, (vii) models with mirror quarks and mirror leptons at the TeV scale, (viii) models with singlet quarks and singlet Higgs and their implications for Higgs physics at the LHC, (ix) new models for the dark matter of the universe, (x) lepton flavor violation in Higgs decays, (xi) leptogenesis in radiative models of neutrino masses, (xii) light mediator models of non-standard neutrino interactions, (xiii) anomalous muon decay and short baseline neutrino anomalies, (xiv) baryogenesis linked to nucleon decay, and (xv) a new model for recently observed diboson resonance at the LHC and its other phenomenological implications. The experimental High Energy Physics group has been, and continues to be, a successful and productive contributor to the ATLAS experiment at the LHC. Members of the group performed search for gluinos decaying to stop and top quarks, new heavy gauge bosons decaying to top and bottom quarks, and vector-like quarks produced in pairs and decaying to light quarks. Members of the OSU group played a leading role in the detailed optimization studies for the future ATLAS Inner Tracker (ITk), which will be installed during the Phase-II upgrade, replacing the current tracking system. The proposed studies aim to enhance the ATLAS discovery potential in the high-luminosity LHC era. The group members have contributed to the calibration of algorithms for identifying boosted vector bosons and b-jets, which will help expand the ATLAS reach in many searches for new physics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

CALIBRATING THE STAR FORMATION RATE AT z {approx} 1 FROM OPTICAL DATA

We present a star formation rate (SFR) calibration based on optical data that is consistent with average observed rates in both the red and blue galaxy populations at z {approx} 1. The motivation for this study is to calculate SFRs for DEEP2 Redshift Survey galaxies in the 0.7 < z < 1.4 redshift range, but our results are generally applicable to similar optically selected galaxy samples without requiring UV or IR data. Using SFR fits from UV/optical spectral energy distributions (SEDs) in the All-Wavelength Extended Groth Strip International Survey, we explore the behavior of rest-frame B-band magnitude, observed [O II] luminosity, and rest-frame color with SED-fit SFR for both red sequence and blue cloud galaxies. The resulting SFR calibration is based on three optical-band observables: M{sub B} , (U - B), and (B - V). The best-fit linear relation produces residual errors of 0.3 dex rms scatter for the full color-independent sample with minimal correlated residual error in L[O II] or stellar mass. We then compare the calibrated z {approx} 1 SFRs to two diagnostics that use L[O II] as a tracer in local galaxies and correct for dust extinction at intermediate redshifts through either galaxy B-band luminosity or stellar mass. We find that an L[O II]-M{sub B} SFR calibration commonly used in the literature agrees well with our calculated SFRs after correcting for the average B-band luminosity evolution in L{sub *} galaxies. However, we find better agreement with a local L[O II]-based SFR calibration that includes stellar mass to correct for reddening effects, indicating that stellar mass is a better tracer of dust extinction for all galaxy types and less affected by systematic evolution than galaxy luminosity from z = 1 to the current epoch.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

BREAKING THE LAW: THE M{sub bh}-M{sub spheroid} RELATIONS FOR CORE-SERSIC AND SERSIC GALAXIES

The popular log-linear relation between supermassive black hole mass, M{sub bh}, and the dynamical mass of the host spheroid, M{sub sph}, is shown to require a significant correction. Core galaxies, typically with M{sub bh} {approx}> 2 Multiplication-Sign 10{sup 8} M{sub Sun} and thought to be formed in dry merger events, are shown to be well described by a linear relation for which the median black hole mass is 0.36%-roughly double the old value of constancy. Of greater significance is that M{sub bh}{proportional_to}M{sup 2}{sub sph} among the (non-pseudobulge) lower-mass systems: specifically, log [M{sub bh}/M{sub Sun }] = (1.92 {+-} 0.38)log [M{sub sph}/7 Multiplication-Sign 10{sup 10} M{sub Sun }] + (8.38 {+-} 0.17). 'Classical' spheroids hosting a 10{sup 6} M{sub Sun} black hole will have M{sub bh}/M{sub sph} {approx} 0.025%. These new relations presented herein (1) bring consistency to the relation M{sub bh}{proportional_to}{sigma}{sup 5} and the fact that L{proportional_to}{sigma}{sup x} with exponents of 5 and 2 for bright (M{sub B} {approx}< -20.5 mag) and faint spheroids, respectively, (2) mimic the non-(log-linear) behavior known to exist in the M{sub bh}-(Sersic n) diagram, (3) necessitate the existence of a previously overlooked M{sub bh}{proportional_to}L{sup 2.5} relation for Sersic (i.e., not core-Sersic) galaxies, and (4) resolve past conflicts (in mass prediction) with the M{sub bh}-{sigma} relation at the low-mass end. Furthermore, the bent nature of the M{sub bh}-M{sub sph} relation reported here for 'classical' spheroids will have a host of important implications that, while not addressed in this paper, relate to (1) galaxy/black hole formation theories, (2) searches for the fundamental, rather than secondary, black hole scaling relation, (3) black hole mass predictions in other galaxies, (4) alleged pseudobulge detections, (5) estimates of the black hole mass function and mass density based on luminosity functions, (6) predictions for space-based gravitational wave detections, (7) connections with nuclear star cluster scaling relations, (8) evolutionary studies over different cosmic epochs, (9) comparisons and calibrations matching inactive black hole masses with low-mass active galactic nucleus data, and more.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

SINGLE-STAR H II REGIONS AS A PROBE OF MASSIVE STAR SPECTRAL ENERGY DISTRIBUTIONS

The shape of OB-star ionizing spectral energy distributions (SEDs) is a critical component in many diagnostics of galaxy and interstellar medium properties. To quantitatively examine the shape of the OB-star SED, we compare long slit observations of single-star, Large Magellanic Cloud H II regions to the predictions from CLOUDY photoionization simulations that use CoStar, TLUSTY, and WM-basic stellar atmosphere models as the ionizing source. For each atmosphere model, we run grids of H II region simulations with the effective temperature (T{sub eff}) of the star as a free parameter. The best SEDs from each atmosphere code are found by matching the predicted emission-line spectra with those observed from the nebulae. By assuming a clumpy gas distribution, all atmosphere codes are able to reproduce the observed emission lines, except at the highest energy transitions {approx}> 40 eV. Taking into account both low and high energy transitions, we find that simulations using WM-basic produce the best agreement with the observed line ratios. The rates of ionizing photons from different atmosphere models vary systematically with the relative hardness of the SEDs. However, in general the rates produced by the model SEDs, for standard log(g) = 4.0 models, are consistent with the rates derived from the H{alpha} luminosities. We find that our effective temperatures inferred from the nebular ionization balance are consistent with those predicted by conventional photospheric-based calibrations from the literature. We suggest that future spectral type to T{sub eff} calibrations can be constructed from nebular data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

VLBI ASTROMETRY OF PSR J2222-0137: A PULSAR DISTANCE MEASURED TO 0.4% ACCURACY

The binary pulsar J2222-0137 is an enigmatic system containing a partially recycled millisecond pulsar and a companion of unknown nature. While the low eccentricity of the system favors a white dwarf companion, an unusual double neutron star system is also a possibility, and optical observations will be able to distinguish between these possibilities. In order to allow the absolute luminosity (or upper limit) of the companion object to be properly calibrated, we undertook astrometric observations with the Very Long Baseline Array to constrain the system distance via a measurement of annual geometric parallax. With these observations, we measure the parallax of the PSR J2222-0137 system to be 3.742{sup +0.013}{sub -0.016} mas, yielding a distance of 267.3{sup +1.2}{sub -0.9} pc, and measure the transverse velocity to be 57.1{sup +0.3}{sub -0.2} km s{sup -1}. Fixing these parameters in the pulsar timing model made it possible to obtain a measurement of Shapiro delay and hence the system inclination, which shows that the system is nearly edge-on (sin i = 0.9985 {+-} 0.0005). Furthermore, we were able to detect the orbital motion of PSR J2222-0137 in our very long baseline interferometry (VLBI) observations and measure the longitude of ascending node {Omega}. The VLBI astrometry yields the most accurate distance obtained for a radio pulsar to date, and is furthermore the most accurate parallax for any radio source obtained at ''low'' radio frequencies (below {approx}5 GHz, where the ionosphere dominates the error budget). Using the astrometric results, we show that the companion to PSR J2222-0137 will be easily detectable in deep optical observations if it is a white dwarf. Finally, we discuss the implications of this measurement for future ultra-high-precision astrometry, in particular in support of pulsar timing arrays.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

OPENING ANGLES OF COLLAPSAR JETS

We investigate the jet propagation and breakout from the stellar progenitor for gamma-ray burst (GRB) collapsars by performing two-dimensional relativistic hydrodynamic simulations and analytical modeling. We find that the jet opening angle is given by θ{sub j} ∼ 1/5Γ{sub 0} and infer the initial Lorentz factor of the jet at the central engine, Γ{sub 0}, is a few for existing observations of θ{sub j}. The jet keeps the Lorentz factor low inside the star by converging cylindrically via collimation shocks under the cocoon pressure and accelerates at jet breakout before the free expansion to a hollow-cone structure. In this new picture, the GRB duration is determined by the sound crossing time of the cocoon, after which the opening angle widens, reducing the apparent luminosity. Some bursts violating the maximum opening angle θ{sub j,{sub max}} ∼ 1/5 ∼ 12° imply the existence of a baryon-rich sheath or a long-acting jet. We can explain the slopes in both Amati and Yonetoku spectral relations using an off-centered photosphere model, if we make only one assumption that the total jet luminosity is proportional to the initial Lorentz factor of the jet. We also numerically calibrate the pre-breakout model (Bromberg et al.) for later use.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Tip of the Red Giant Branch Distances to Typa Ia Supernova Host Galaxies. V. NGC 3021, NGC 3370, and NGC 1309 and the Value of the Hubble Constant

We present final results of a program for the determination of the Hubble constant based on the calibration of the Type Ia supernovae (SNe Ia) using the Tip of the Red Giant Branch (TRGB). We report TRGB distances to three SN Ia host galaxies, NGC 3021, NGC 3370, and NGC 1309. We obtain F555W and F814W photometry of resolved stars from the archival Hubble Space Telescope data. Luminosity functions of red giant stars in the outer regions of these galaxies show the TRGB to be at F814W ≈ QT = 28.2 ∼ 28.5 mag. From these TRGB magnitudes and the revised TRGB calibration based on two distance anchors (NGC 4258 and the LMC) in Jang and Lee (2017; Paper IV), we derive the distances: (m−M){sub 0}=32.178±0.033 for NGC 3021, 32.253 ± 0.041 for NGC 3370, and 32.471 ± 0.040 for NGC 1309. We update our previous results on the TRGB distances to five SN Ia host galaxies using the revised TRGB calibration. By combining the TRGB distance estimates to SN Ia host galaxies in this study with the SN Ia calibration provided by Riess et al. (2011), we obtain a value of the Hubble constant: H {sub 0} = 71.66 ± 1.80(random) ± 1.88(systematic) km s{sup −1} Mpc{sup −1} (a 3.6% uncertainty including systematics) from all eight SNe, and H {sub 0} = 73.72 ± 2.03 ± 1.94 km s{sup −1} Mpc{sup −1} (a 3.8% uncertainty) from six low-reddened SNe. We present our best estimate, H {sub 0} = 71.17 ± 1.66 ± 1.87 km s{sup −1} Mpc{sup −1} (a 3.5% uncertainty) from six low-reddened SNe with the recent SN Ia calibration in Riess et al. (2016). This value is between those from the Cepheid calibrated SNe Ia and those from the Cosmic Microwave Background analysis, lowering the Hubble tension.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1996

The Lyman-Continuum Fluxes and Stellar Parameters of O and Early B-Type Stars

Using the results of the most recent stellar atmosphere models applied to a sample of hot stars, we construct calibrations of effective temperature (T(sub eff)), and gravity (log(sub g)) with a spectral type and luminosity class for Galactic 0-type and early B-type stars. From the model results we also derive an empirical relation between the bolometric correction and T(sub eff) and log g. Using a sample of stars with known distances located in OB associations in the Galaxy and the Large Magellanic Cloud, we derive a new calibration of M(sub v) with spectral class. With these new calibrations and the stellar atmosphere models of Kurucz, we calculate the physical parameters and ionizing photon luminosities in the H(0) and He(0) continua for O and early B-type stars. We find substantial differences between our values of the Lyman- continuum luminosity and those reported in the literature. We also discuss the systematic discrepancy between O-type stellar masses derived from spectroscopic models and those derived from evolutionary tracks. Most likely, the cause of this 'mass discrepancy' lies primarily in the atmospheric models, which are plane parallel and hydrostatic and therefore do not account for an extended atmosphere and the velocity fields in a stellar wind. Finally, we present a new computation of the Lyman-continuum luminosity from 429 known O stars located within 2.5 kpc of the Sun. We find the total ionizing luminosity from this population ((Q(sub 0)(sup T(sub ot))) = 7.0 x 10(exp 51) photons/s) to be 47% larger than that determined using the Lyman continuum values tabulated by Panagia.

Vacca, William D.↗
DOE OSTI2013

THE DARK MATTER HALO CONCENTRATION AND STELLAR INITIAL MASS FUNCTION OF A CASSOWARY GROUP

We exploit the group environment of the CAmbridge Sloan Survey Of Wide ARcs in the skY z = 0.3 lens J2158+0257 to measure the group dynamical mass as a complement to the central dynamical and lensing mass constraints. Follow-up spectroscopy of candidate group members is performed using VLT/FORS2. From the resulting N = 21 confirmed members, we measure the group dynamical mass by calibrating an analytic tracer mass estimator with cosmological simulations. The luminosity-weighted line-of-sight velocity dispersion and the Einstein radius of the lens are used as mass probes in the inner regions of the galaxy. Combining these three observational probes allows us to independently constrain the mass and concentration of the dark matter halo, in addition to the total stellar mass of the central galaxy. We find a dark matter halo in remarkably good agreement with simulations (log{sub 10} M{sub 200}/M{sub Sun} = 14.2 {+-} 0.2, c{sub 200}= 4.4{sup +1.6}{sub -1.4}) and a stellar mass-to-light ratio which favors a Salpeter initial mass function ((M/L)* = 5.7 {+-} 1.2). Our measurement of a normal halo concentration suggests that there is no discrepancy between simulations and observations at the group mass scale. This is in contrast to the cluster mass scale for which a number of studies have claimed over-concentrated halos. While the halo mass is robustly determined, and the halo concentration is not significantly affected by systematics, the resulting stellar mass-to-light ratio is sensitive to the choice of stellar parameters, such as density profile and velocity anisotropy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Factory and the Beehive. III. PTFEB132.707+19.810, A Low-mass Eclipsing Binary in Praesepe Observed by PTF and K2

Theoretical models of stars constitute the fundamental bedrock upon which much of astrophysics is built, but large swaths of model parameter space remain uncalibrated by observations. The best calibrators are eclipsing binaries in clusters, allowing measurement of masses, radii, luminosities, and temperatures for stars of known metallicity and age. We present the discovery and detailed characterization of PTFEB132.707+19.810, a P = 6.0 day eclipsing binary in the Praesepe cluster (τ ∼ 600–800 Myr; [Fe/H] = 0.14 ± 0.04). The system contains two late-type stars (SpT{sub P} = M3.5 ± 0.2; SpT{sub S} = M4.3 ± 0.7) with precise masses (M{sub p}=0.3953±0.0020 M {sub ⊙}; M{sub s}=0.2098 ±0.0014 M {sub ⊙}) and radii (R{sub p}=0.363±0.008 R {sub ⊙}; R{sub s}=0.272±0.012 R {sub ⊙}). Neither star meets the predictions of stellar evolutionary models. The primary has the expected radius but is cooler and less luminous, while the secondary has the expected luminosity but is cooler and substantially larger (by 20%). The system is not tidally locked or circularized. Exploiting a fortuitous 4:5 commensurability between P {sub orb} and P{sub rot,prim}, we demonstrate that fitting errors from the unknown spot configuration only change the inferred radii by ≲1%–2%. We also analyze subsets of data to test the robustness of radius measurements; the radius sum is more robust to systematic errors and preferable for model comparisons. We also test plausible changes in limb darkening and find corresponding uncertainties of ∼1%. Finally, we validate our pipeline using extant data for GU Boo, finding that our independent results match previous radii to within the mutual uncertainties (2%–3%). We therefore suggest that the substantial discrepancies are astrophysical; since they are larger than those for old field stars, they may be tied to the intermediate age of PTFEB132.707+19.810.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE X-RAY FLARING PROPERTIES OF Sgr A* DURING SIX YEARS OF MONITORING WITH SWIFT

Starting in 2006, Swift has been targeting a region of {approx_equal} 21' Multiplication-Sign 21' around Sagittarius A* (Sgr A*) with the onboard X-Ray Telescope. The short, quasi-daily observations offer a unique view of the long-term X-ray behavior of the supermassive black hole. We report on the data obtained between 2006 February and 2011 October, which encompasses 715 observations with a total accumulated exposure time of {approx_equal}0.8 Ms. A total of six X-ray flares were detected with Swift, which all had an average 2-10 keV luminosity of L{sub X} {approx_equal} (1 - 3) Multiplication-Sign 10{sup 35} erg s{sup -1} (assuming a distance of 8 kpc). This more than doubles the number of such bright X-ray flares observed from Sgr A*. One of the Swift-detected flares may have been softer than the other five, which would indicate that flares of similar intensity can have different spectral properties. The Swift campaign allows us to constrain the occurrence rate of bright (L{sub X} {approx}> 10{sup 35} erg s{sup -1}) X-ray flares to be {approx_equal}0.1-0.2 day{sup -1}, which is in line with previous estimates. This analysis of the occurrence rate and properties of the X-ray flares seen with Swift offers an important calibration point to assess whether the flaring behavior of Sgr A* changes as a result of its interaction with the gas cloud that is projected to make a close passage in 2013.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Weighing galaxy disks with the baryonic Tully–Fisher relation

We estimate the stellar masses of disk galaxies with two independent methods: a photometrically self-consistent color–mass-to-light ratio relation (CMLR) from population synthesis models, and the baryonic Tully–Fisher relation (BTFR) calibrated by gas-rich galaxies. These two methods give consistent results. The CMLR correctly converts distinct Tully–Fisher relations in different bands into the same BTFR. The BTFR is consistent with M{sub b}∝V{sub f}{sup 4} over nearly six decades in mass, with no hint of a change in slope over that range. The intrinsic scatter in the BTFR is negligible, implying that the IMF of disk galaxies is effectively universal. The gas-rich BTFR suggests an absolute calibration of the stellar mass scale that yields nearly constant mass-to-light ratios in the near-infrared (NIR): 0.57 M/L in K{sub s} and 0.45 M/L at 3.6 μm. There is only modest intrinsic scatter (∼0.12 dex) about these typical values. There is no discernible variation with color or other properties: the NIR luminosity is a good tracer of stellar mass.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Tracing the cosmic velocity field at z∼ 0.1 from galaxy luminosities in the SDSS DR7

Spatial modulations in the distribution of observed luminosities (computed using redshifts) of ∼ 5× 10{sup 5} galaxies from the SDSS Data Release 7, probe the cosmic peculiar velocity field out to z∼ 0.1. Allowing for luminosity evolution, the r-band luminosity function, determined via a spline-based estimator, is well represented by a Schechter form with M{sup *}(z)-5 log{sub 10} h = -20.52 -1.6(z-0.1)± 0.05 and α{sup *} = -1.1± 0.03. Bulk flows and higher velocity moments in two redshift bins, 0.02 < z < 0.07 and 0.07 < z < 0.22, agree with the predictions of the ΛCDM model, as obtained from mock galaxy catalogs designed to match the observations. Assuming a ΛCDM model, we estimate σ{sub 8} ≈ 1.1± 0.4 for the amplitude of the linear matter power spectrum, where the low accuracy is due to the limited number of galaxies. While the low z bin is robust against coherent photometric uncertainties, the bias of results from the second bin is consistent with the ∼1% magnitude tilt reported by the SDSS collaboration. The systematics are expected to have a significantly lower impact in future datasets with larger sky coverage and better photometric calibration.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

TOWARD UNBIASED GALAXY CLUSTER MASSES FROM LINE-OF-SIGHT VELOCITY DISPERSIONS

We study the use of red-sequence-selected galaxy spectroscopy for unbiased estimation of galaxy cluster masses by using a publicly available simulated galaxy catalog. We explore the impact of selection using galaxy color, projected separation from the cluster center, galaxy luminosity, and spectroscopic redshift. We identify and characterize each of the following sources of bias and scatter in velocity dispersion at fixed mass: the intrinsic properties of halos in the form of halo triaxiality, sampling noise, the presence of multiple kinematic populations within the cluster, and the effect of interlopers. We show that even in red-sequence and spectroscopically selected galaxy samples, the interloper fraction is significant, and that the variations in the interloper population from cluster to cluster provide the dominant contribution to the velocity dispersion scatter at fixed mass. We present measurements of the total scatter in dispersion at fixed mass as a function of the number of redshifts. Results indicate that improvements in scatter are modest beyond samples of {approx}30 redshifts per cluster. Our results show that while cluster velocity dispersions extracted from a few dozen red-sequence-selected galaxies do not provide precise masses on a single cluster basis, an ensemble of cluster velocity dispersions can be combined to produce a precise calibration of a cluster survey-mass-observable relation. Currently, disagreements in the literature on simulated subhalo velocity dispersion-mass relations place a systematic floor on velocity dispersion mass calibration at the 5% level in dispersion.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Carnegie-Chicago Hubble Program. II. The Distance to IC 1613: The Tip of the Red Giant Branch and RR Lyrae Period–luminosity Relations

IC 1613 is an isolated dwarf galaxy within the Local Group. Low foreground and internal extinction, low metallicity, and low crowding make it an invaluable testbed for the calibration of the local distance ladder. We present new, high-fidelity distance estimates to IC 1613 via its Tip of the Red Giant Branch (TRGB) and its RR Lyrae (RRL) variables as part of the Carnegie-Chicago Hubble Program, which seeks an alternate local route to H {sub 0} using Population II stars. We have measured a TRGB magnitude I{sub ACS}{sup TRGB}=20.35±0.01{sub stat}±0.01{sub sys} mag using wide-field observations obtained from the IMACS camera on the Magellan-Baade telescope. We have further constructed optical and near-infrared RRL light curves using archival BI- and new H-band observations from the ACS/WFC and WFC3/IR instruments on board the Hubble Space Telescope (HST). In advance of future Gaia data releases, we set provisional values for the TRGB luminosity via the Large Magellanic Cloud and Galactic RRL zero-points via HST parallaxes. We find corresponding true distance moduli μ{sub 0}{sup TRGB}=24.30±0.03{sub stat}±0.05{sub sys} mag and 〈μ{sub 0}{sup RRL}〉=24.28±0.04{sub stat+sys} mag. We compare our results to a body of recent publications on IC 1613 and find no statistically significant difference between the distances derived from Population I and II stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

COSMICFLOWS-2: TYPE Ia SUPERNOVA CALIBRATION AND H{sub 0}

The construction of the Cosmicflows-2 compendium of distances involves the merging of distance measures contributed by the following methods: (Cepheid) period-luminosity, tip of the red giant branch (TRGB), surface brightness fluctuation (SBF), luminosity-linewidth (TF), fundamental plane (FP), and Type Ia supernova (SNIa). The method involving SNIa is at the top of an interconnected ladder, providing accurate distances to well beyond the expected range of distortions to Hubble flow from peculiar motions. In this paper, the SNIa scale is anchored by 36 TF spirals with Cepheid or TRGB distances, 56 SNIa hosts with TF distances, and 61 groups or clusters hosting SNIa with Cepheid, SBF, TF, or FP distances. With the SNIa scale zero-point set, a value of the Hubble constant is evaluated over a range of redshifts 0.03 < z < 0.5, assuming a cosmological model with {Omega}{sub m} = 0.27 and {Omega}{sub {Lambda}} = 0.73. The value determined for the Hubble constant is H{sub 0} = 75.9 {+-} 3.8 km s{sup -1} Mpc{sup -1}.

79 ASTRONOMY AND ASTROPHYSICS↗