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We present near-infrared JHK photometry for the resolved stellar populations in 13 nearby galaxies: NGC 6822, IC 1613, NGC 3109, Sextans B, Sextans A, NGC 300, NGC 55, NGC 7793, NGC 247, NGC 5253, Cen A, NGC 1313, and M83, acquired from the 6.5 m Baade–Magellan telescope. We measure distances to each galaxy using the J-region asymptotic giant branch (JAGB) method, a new standard candle that leverages the constant luminosities of color-selected, carbon-rich AGB stars. While only single-epoch, random-phase photometry is necessary to derive JAGB distances, our photometry is time-averaged over multiple epochs, thereby decreasing the contribution of the JAGB stars' intrinsic variability to the measured dispersions in their observed luminosity functions. To cross-validate these distances, we also measure near-infrared tip of the red giant branch (TRGB) distances to these galaxies. The residuals obtained from subtracting the distance moduli from the two methods yield an rms scatter of σ JAGB−TRGB = ±0.07 mag. Therefore, all systematics in the JAGB method and TRGB method (e.g., crowding, differential reddening, star formation histories) must be contained within these ±0.07 mag bounds for this sample of galaxies because the JAGB and TRGB distance indicators are drawn from entirely distinct stellar populations and are thus affected by these systematics independently. Finally, the composite JAGB star luminosity function formed from this diverse sample of galaxies is well described by a Gaussian function with a modal value of M J = –6.20 ± 0.003 mag (stat), indicating that the underlying JAGB star luminosity function of a well-sampled full star formation history is highly symmetric and Gaussian based on over 6700 JAGB stars in the composite sample. [ABSTRACT FROM AUTHOR]

We determine the distance to the Sculptor Dwarf Spheroidal via three Population II stellar distance indicators: (a) the Tip of the Red Giant Branch (TRGB), (b) RR Lyrae variables (RRLs), and (c) the ridgeline of the blue horizontal branch (HB). High signal-to-noise, wide-field VI imaging that covers an area 48 ′ Ă— 48 ′ and reaches a photometric depth approximately 2 mag fainter than the HB was acquired with the Magellan-Baade 6.5 m telescope. The true modulus derived from Sculptor’s TRGB is found to be ÎĽ o TRGB = 19.59 ± 0.07 stat ± 0.05 sys mag. Along with periods adopted from the literature, newly acquired RRL phase points are fit with template light curves to determine ÎĽ W I , V âˆ' I RRL = 19.60 ± 0.01 stat ± 0.05 sys mag. Finally, the HB distance is found to be ÎĽ o HB = 19.54 ± 0.03 stat ± 0.09 sys mag. Absolute calibrations of each method are anchored by independent geometric zero-points, utilize a different class of stars, and are determined from the same photometric calibration. [ABSTRACT FROM AUTHOR]

The J-region asymptotic giant branch (JAGB) method is a new standard candle that is based on the stable intrinsic J -band magnitude of color-selected carbon stars, and has a precision comparable to other primary distance indicators such as Cepheids and the TRGB. We further test the accuracy of the JAGB method in the Local Group galaxy M33. M33's moderate inclination, low metallicity, and nearby proximity make it an ideal laboratory for tests of systematics in local distance indicators. Using high-precision optical BVI and near-infrared JHK photometry, we explore the application of three independent distance indicators: the JAGB method, the Cepheid Leavitt law, and the TRGB. We find: ÎĽ 0(TRGB I ) = 24.72 ± 0.02 (stat) ± 0.07 (sys) mag, ÎĽ 0(TRGBNIR) = 24.72 ± 0.04 (stat) ± 0.10 (sys) mag, ÎĽ 0(JAGB) = 24.67 ± 0.03 (stat) ± 0.04 (sys) mag, and ÎĽ 0(Cepheid) = 24.71 ± 0.04 (stat) ± 0.01 (sys) mag. For the first time, we also directly compare a JAGB distance using ground-based and space-based photometry. We measure ÎĽ 0(JAGBF110W) = 24.71 ± 0.06 (stat) ± 0.05 (sys) mag using the (F814Wâˆ'F110W) color combination to effectively isolate the JAGB stars. In this paper, we measure a distance to M33 accurate to 2% and provide further evidence that the JAGB method is a powerful extragalactic distance indicator that can effectively probe a local measurement of the Hubble constant using spaced-based observations. We expect to measure the Hubble constant via the JAGB method in the near future, using observations from the James Webb Space Telescope. [ABSTRACT FROM AUTHOR]

We determine three independent Population II distance moduli to the Fornax dwarf spheroidal (dSph) galaxy, using wide-field, ground-based VI imaging acquired with the Magellan-Baade telescope at Las Campanas Observatory. After subtracting foreground stars using Gaia EDR3 proper motions, we measure an I -band tip of the red giant branch (TRGB) magnitude of I 0 TRGB = 16.753 ± 0.03 stat ± 0.037 sys mag, with a calibration based in the LMC giving a distance modulus of ÎĽ 0 TRGB = 20.80 ± 0.037 stat ± 0.057 sys mag. We determine an RR Lyrae (RRL) distance from template mean magnitudes, with periods adopted from the literature. Adopting a Gaia DR2 calibration of first overtone RRL periodâ€"luminosity and periodâ€"Wesenheit relations, we find ÎĽ 0 PLZ = 20.74 ± 0.01 stat ± 0.12 sys mag and ÎĽ 0 PWZ = 20.68 ± 0.02 stat ± 0.07 sys mag. Finally, we determine a distance from Fornax’s horizontal branch (HB) and two galactic globular cluster calibrators, giving ÎĽ 0 HB = 20.83 ± 0.03 stat ± 0.09 sys mag. These distances are each derived from homogeneous IMACS photometry, are anchored to independent geometric zero-points, and utilize different classes of stars. We therefore average over independent uncertainties and report the combined distance modulus 〈 ÎĽ 0〉 =20.770 ± 0.042stat ± 0.024sys mag (corresponding to a distance of 143 ± 3 kpc). [ABSTRACT FROM AUTHOR]

Using parallaxes from Gaia Early Data Release 3 (EDR3), we determine multi-wavelength BVI c , JHK s , and [3.6] and [4.5] micron absolute magnitudes for 37 nearby Milky Way Cepheids, covering the period range between 5 and 60 days. We apply these periodâ€"luminosity relations to Cepheids in the Large and Small Magellanic Clouds and find that the derived distances are significantly discrepant with the geometric distances according to detached eclipsing binaries (DEBs). We explore several potential causes of these issues, including reddening, metallicity, and the existence of an additional zero-point offset, but none provide a sufficient reconciliation with both DEB distances. We conclude that the combination of the systematic uncertainties on the EDR3 parallaxes with the uncertainties on the effect of metallicity on the Cepheid distance scale leads to a systematic error floor of approximately 3%. We therefore find that the EDR3 data are not sufficiently accurate in the regime of these bright Cepheids to determine extragalactic distances precise to the 1% level at this time, in agreement with a number of contemporary studies. [ABSTRACT FROM AUTHOR]

We present an absolute calibration of the J-region Asymptotic Giant Branch (JAGB) method using published photometry of resolved stars in 20 nearby galaxies observed with the Hubble Space Telescope using the WFC3-IR camera and the F110W (broad J-band) filter. True distance moduli for each of the galaxies are based on the Tip of the Red Giant Branch (TRGB) method as uniformly determined by Dalcanton et al. From a composite color–magnitude diagram composed of over 6 million stars, leading to a sample of 453 JAGB stars in these galaxies, we find mag (statistical error on the mean). The external scatter seen in a comparison of the individual TRGB and the JAGB moduli is ±0.081 mag (or 4% in distance). Some of this scatter can be attributed to small number statistics arising from the sparse JAGB populations found in the generally low-luminosity galaxies that comprise the particular sample studied here. However, if this intermethod scatter is shared equitably between the JAGB and TRGB methods, that implies that each is good to ±0.06 mag, or better than 3% in distance. [ABSTRACT FROM AUTHOR]

Measurement of the distances to nearby galaxies has improved rapidly in recent decades. The ever-present challenge is to reduce systematic effects, especially as greater distances are probed and the uncertainties become larger. In this paper, we combine several recent calibrations of the tip of the red giant branch (TRGB) method. These calibrations are internally self-consistent at the 1% level. New Gaia Early Data Release 3 data provide an additional consistency check at a (lower) 5% level of accuracy, a result of the well-documented Gaia angular covariance bias. The updated TRGB calibration applied to a sample of Type Ia supernovae from the Carnegie Supernova Project results in a value of the Hubble constant of H0 = 69.8 ± 0.6 (stat) ± 1.6 (sys) km s−1 Mpc−1. No statistically significant difference is found between the value of H0 based on the TRGB and that determined from the cosmic microwave background. The TRGB results are also consistent to within 2σ with the SHoES and Spitzer plus Hubble Space Telescope (HST) Key Project Cepheid calibrations. The TRGB results alone do not demand additional new physics beyond the standard (ΛCDM) cosmological model. They have the advantage of simplicity of the underlying physics (the core He flash) and small systematic uncertainties (from extinction, metallicity, and crowding). Finally, the strengths and weaknesses of both the TRGB and Cepheids are reviewed, and prospects for addressing the current discrepancy with future Gaia, HST, and James Webb Space Telescope observations are discussed. Resolving this discrepancy is essential for ascertaining if the claimed tension in H0 between the locally measured and CMB-inferred values is physically motivated. [ABSTRACT FROM AUTHOR]

The primary goal of the Carnegie Chicago Hubble Program (CCHP) is to calibrate the zero-point of the Type Ia supernova (SN Ia) Hubble Diagram through the use of Population II standard candles. So far, the CCHP has measured direct distances to 11 SNe Ia, and here we increase that number to 15 with two new Tip of the Red Giant Branch (TRGB) distances measured to NGC 5643 and NGC 1404. We present resolved, point-source photometry from new Hubble Space Telescope imaging of these two galaxies in the F814W and F606W bandpasses. From each galaxy's stellar halo, we construct an F814W-band luminosity function in which we detect an unambiguous edge feature identified as the TRGB. For NGC 5643, we find μ0 = 30.48 ± 0.03(stat) ± 0.07(sys) mag, and for NGC 1404 we find μ0 = 31.36 ± 0.04(stat) ± 0.05(sys) mag. From a preliminary consideration of the SNe Ia in these galaxies, we find increased confidence in the results presented in Paper VIII. The high precision of our TRGB distances enables a significant measurement of the 3D displacement between the Fornax cluster galaxies NGC 1404 and NGC 1316 (Fornax A) equal to Mpc, which we show is in agreement with independent constraints found in the literature. [ABSTRACT FROM AUTHOR]

The local determination of the Hubble constant sits at a crossroad. Current estimates of the local expansion rate of the universe differ by about 1.7σ, derived from the Cepheid- and TRGB-based calibrations, applied to Type Ia supernovae. To help elucidate possible sources of systematic error causing the tension, we show in this study the recently developed distance indicator, the J-region Asymptotic Giant Branch (JAGB) method, can serve as an independent cross-check and comparison with other local distance indicators. Furthermore, we make the case that the JAGB method has substantial potential as an independent, precise, and accurate calibrator of Type Ia supernovae for the determination of H0. Using the Local Group galaxy Wolf–Lundmark–Melotte (WLM), we present distance comparisons between the JAGB method, a TRGB measurement at near-infrared (JHK) wavelengths, a TRGB measurement in the optical I band, and a multiwavelength Cepheid period–luminosity relation determination. We find μ 0 (JAGB) = 24.97 ± 0.02 (stat) ± 0.04 (sys) mag μ 0 (TRGB NIR) = 24.98 ± 0.04 (stat) ± 0.07 (sys) mag μ 0 (TRGB F 814 W) = 24.93 ± 0.02 (stat) ± 0.06 (sys) mag μ 0 (Cepheids) = 24.98 ± 0.03 (stat) ± 0.04 (sys) mag. All four methods are in good agreement, confirming the local self-consistency of the four distance scales at the 3% level and adding confidence that the JAGB method is as accurate and as precise a distance indicator as either of the other three astrophysically based methods. [ABSTRACT FROM AUTHOR]

In the nearby galaxy NGC 4258, the well-modeled orbital motion of H2O masers about its supermassive black hole provides the means to measure a precise geometric distance. As a result, NGC 4258 is one of a few "geometric anchors" available to calibrate the true luminosities of stellar distance indicators such as the Tip of the Red Giant Branch (TRGB) or the Cepheid Leavitt law. In this paper, we present a detailed study of the apparent magnitude of the TRGB within NGC 4258, using publicly available HST observations optimally situated in the unreddened stellar halo along the minor axis, spanning distances ranging from 8 to 22 kpc in projected galactocentric radius, or (13 kpc) to (66 kpc) in distance along the semimajor axis. We undertake a systematic evaluation of the uncertainties associated with measuring the TRGB in this galaxy, based on an analysis of 54 arcmin2 of HST/ACS imaging. After quantifying these uncertainties, we measure the TRGB in NGC 4258 to be F814W0 = 25.347 ± 0.014 (stat) ± 0.042 (sys) mag. Combined with a recent 1.5% megamaser distance to NGC 4258, we determine the absolute luminosity of the TRGB to be (stat) ± 0.048 (sys) mag. This new calibration agrees to better than 1% with an independent calibration presented in Freedman et al. that was based on detached eclipsing binaries (DEBs) located in the LMC. [ABSTRACT FROM AUTHOR]

We use the spectroscopy and homogeneous photometry of 97 Type Ia supernovae (SNe Ia) obtained by the Carnegie Supernova Project as well as a subset of 36 SNe Ia presented by Zheng et al. to examine maximum-light correlations in a four-dimensional (4D) parameter space: B-band absolute magnitude, MB, Si ii λ6355 velocity, , and Si ii pseudo-equivalent widths pEW(Si ii λ6355) and pEW(Si ii λ5972). It is shown using Gaussian mixture models (GMMs) that the original four groups in the Branch diagram are well-defined and robust in this parameterization. We find three continuous groups that describe the behavior of our sample in [MB, ] space. Extending the GMM into the full 4D space yields a grouping system that only slightly alters group definitions in the [MB, ] projection, showing that most of the clustering information in [MB, ] is already contained in the 2D GMM groupings. However, the full 4D space does divide group membership for faster objects between core-normal and broad-line objects in the Branch diagram. A significant correlation between MB and pseudo-equivalent width (Si ii λ5972) is found, which implies that Branch group membership can be well-constrained by spectroscopic quantities alone. In general, we find that higher-dimensional GMMs reduce the uncertainty of group membership for objects between the originally defined Branch groups. We also find that the broad-line Branch group becomes nearly distinct with the inclusion of , indicating that this subclass of SNe Ia may be somehow different from the other groups. [ABSTRACT FROM AUTHOR]

We present optical and near-infrared (NIR) (ugriYJH) photometry of host galaxies of Type Ia supernovae (SN Ia) observed by the Carnegie Supernova Project-I. We determine host galaxy stellar masses and, for the first time, study their correlation with SN Ia standardized luminosity across optical and NIR (uBgVriYJH) bands. In the individual bands, we find that SNe Ia are more luminous in more massive hosts with luminosity offsets ranging between −0.07 ± 0.03 and −0.15 ± 0.04 mag after light-curve standardization. The slope of the SN Ia Hubble residual-host mass relation is negative across all uBgVriYJH bands with values ranging between −0.029 ± 0.029 and −0.093 ± 0.031 mag dex−1—implying that SNe Ia in more massive galaxies are brighter than expected. The near-constant observed correlations across optical and NIR bands indicate that dust may not play a significant role in the observed luminosity offset–host mass correlation. We measure projected separations between SNe Ia and their host centers, and find that SNe Ia that explode beyond a projected 10 kpc have a 50%– 60% reduction of the dispersion in Hubble residuals across all bands—making them a more uniform subset of SNe Ia. Dust in host galaxies, peculiar velocities of nearby SN Ia, or a combination of both may drive this result as the color excesses of SNe Ia beyond 10 kpc are found to be generally lower than those interior, but there is also a diminishing trend of the dispersion as we exclude nearby events. We do not find that SN Ia average luminosity varies significantly when they are grouped in various host morphological types. Host galaxy data from this work will be useful, in conjunction with future high-redshift samples, in constraining cosmological parameters. [ABSTRACT FROM AUTHOR]

The Type Ia supernova (SN Ia) LSQ14fmg exhibits exaggerated properties that may help to reveal the origin of the "super-Chandrasekhar" (or 03fg-like) group. The optical spectrum is typical of a 03fg-like SN Ia, but the light curves are unlike those of any SNe Ia observed. The light curves of LSQ14fmg rise extremely slowly. At −23 rest-frame days relative to B-band maximum, LSQ14fmg is already brighter than mag before host extinction correction. The observed color curves show a flat evolution from the earliest observation to approximately 1 week after maximum. The near-infrared light curves peak brighter than −20.5 mag in the J and H bands, far more luminous than any 03fg-like SNe Ia with near-infrared observations. At 1 month past maximum, the optical light curves decline rapidly. The early, slow rise and flat color evolution are interpreted to result from an additional excess flux from a power source other than the radioactive decay of the synthesized 56Ni. The excess flux matches the interaction with a typical superwind of an asymptotic giant branch (AGB) star in density structure, mass-loss rate, and duration. The rapid decline starting at around 1 month past B-band maximum may be an indication of rapid cooling by active carbon monoxide (CO) formation, which requires a low-temperature and high-density environment. These peculiarities point to an AGB progenitor near the end of its evolution and the core degenerate scenario as the likely explosion mechanism for LSQ14fmg. [ABSTRACT FROM AUTHOR]

We apply the near-infrared J-region asymptotic giant branch (JAGB) method, recently introduced by Madore & Freedman, to measure the distances to 14 nearby galaxies out to 4 Mpc. We use the geometric detached eclipsing binary (DEB) distances to the LMC and SMC as independent zero-point calibrators. We find excellent agreement with previously published distances based on the tip of the red giant branch (TRGB): the JAGB distance determinations (including the LMC and SMC) agree in the mean to within mag, just over 1%, where the TRGB I-band zero-point is MI = −4.05 mag. With further development and testing, the JAGB method has the potential to provide an independent calibration of Type Ia supernovae, especially with the James Webb Space Telescope. The JAGB stars (with MJ = −6.20 mag) can be detected farther than the fainter TRGB stars, allowing greater numbers of calibrating galaxies for the determination of H0. Along with the TRGB and Cepheids, JAGB stars are amenable to theoretical understanding and further refined empirical calibration. A preliminary test shows little dependence, if any, of the JAGB magnitude on metallicity of the parent galaxy. These early results suggest that the JAGB method has considerable promise for providing high-precision distances to galaxies in the local universe that are independent of distances derived from the Leavitt Law and/or the TRGB method, and it has numerous and demonstrable advantages over the possible use of Mira variables. [ABSTRACT FROM AUTHOR]

A near-infrared, color-selected subset of carbon-rich asymptotic giant branch (C-AGB) stars is found to have tightly constrained luminosities in the near-infrared J band. Based on JK photometry of some 3300 C-AGB stars in the bar of the Large Magellanic Cloud (LMC) we find that these stars have a constant absolute magnitude of mag, adopting the detached eclipsing binary (DEB) distance to the LMC of 18.477 ± 0.004 (stat) ± 0.026 (sys). Undertaking a second, independent calibration in the Small Magellanic Cloud, which also has a DEB geometric distance, we find 0.01 (stat) ± 0.05 (sys) mag. For the LMC the scatter is ± 0.27 mag for single-epoch observations, (falling to ± 0.15 mag for multiple observations averaged over a window of more than one year). We provisionally adopt mag ± 0.01 (stat) ± 0.04 (sys) mag for the mean absolute magnitude of these stars. Applying this calibration to stars recently observed in the galaxy NGC 253, we determine a distance modulus of 27.66 ± 0.01(stat) ± 0.04 mag (syst), corresponding to a distance of 3.40 ± 0.06 Mpc (stat). This is in excellent agreement with the average tip of the red giant branch (TRGB) distance modulus of 27.68 ± 0.05 mag, assuming MI = −4.05 mag for the TRGB zero-point. [ABSTRACT FROM AUTHOR]

We present photometric and spectroscopic observations of SN 2013aa and SN 2017cbv, two nearly identical type Ia supernovae (SNe Ia) in the host galaxy NGC 5643. The optical photometry has been obtained using the same telescope and instruments used by the Carnegie Supernova Project. This eliminates most instrumental systematics and provides light curves in a stable and well-understood photometric system. Having the same host galaxy also eliminates systematics due to distance and peculiar velocity, providing an opportunity to directly test the relative precision of SNe Ia as standard candles. The two SNe have nearly identical decline rates, negligible reddenings, and remarkably similar spectra, and, at a distance of ∼20 Mpc, they are ideal potential calibrators for the absolute distance using primary indicators such as Cepheid variables. We discuss to what extent these two SNe can be considered twins and compare them with other supernova "siblings" in the literature and their likely progenitor scenarios. Using 12 galaxies that hosted two or more SNe Ia, we find that when using SNe Ia, and after accounting for all sources of observational error, one gets consistency in distance to 3%. [ABSTRACT FROM AUTHOR]

We present an analysis of the diversity of V-band light-curves of hydrogen-rich type II supernovae. Analyzing a sample of 116 supernovae, several magnitude measurements are defined, together with decline rates at different epochs, and time durations of different phases. It is found that magnitudes measured at maximum light correlate more strongly with decline rates than those measured at other epochs: brighter supernovae at maximum generally have faster declining light-curves at all epochs. We find a relation between the decline rate during the “plateau” phase and peak magnitudes, which has a dispersion of 0.56 mag, offering the prospect of using type II supernovae as purely photometric distance indicators. Our analysis suggests that the type II population spans a continuum from low-luminosity events which have flat light-curves during the “plateau” stage, through to the brightest events which decline much faster. A large range in optically thick phase durations is observed, implying a range in progenitor envelope masses at the epoch of explosion. During the radioactive tails, we find many supernovae with faster declining light-curves than expected from full trapping of radioactive emission, implying low mass ejecta. It is suggested that the main driver of light-curve diversity is the extent of hydrogen envelopes retained before explosion. Finally, a new classification scheme is introduced where hydrogen-rich events are typed as simply “SN II” with an “s2” value giving the decline rate during the “plateau” phase, indicating its morphological type. [ABSTRACT FROM AUTHOR]

High-dispersion observations of the Na I D λλ5890, 5896 and K I λλ7665, 7699 interstellar lines, and the diffuse interstellar band at 5780 Å in the spectra of 32 Type Ia supernovae are used as an independent means of probing dust extinction. We show that the dust extinction of the objects where the diffuse interstellar band at 5780 Å is detected is consistent with the visual extinction derived from the supernova colors. This strongly suggests that the dust producing the extinction is predominantly located in the interstellar medium of the host galaxies and not in circumstellar material associated with the progenitor system. One quarter of the supernovae display anomalously large Na I column densities in comparison to the amount of dust extinction derived from their colors. Remarkably, all of the cases of unusually strong Na I D absorption correspond to “Blueshifted” profiles in the classification scheme of Sternberg et al. This coincidence suggests that outflowing circumstellar gas is responsible for at least some of the cases of anomalously large Na I column densities. Two supernovae with unusually strong Na I D absorption showed essentially normal K I column densities for the dust extinction implied by their colors, but this does not appear to be a universal characteristic. Overall, we find the most accurate predictor of individual supernova extinction to be the equivalent width of the diffuse interstellar band at 5780 Å, and provide an empirical relation for its use. Finally, we identify ways of producing significant enhancements of the Na abundance of circumstellar material in both the single-degenerate and double-degenerate scenarios for the progenitor system. [ABSTRACT FROM AUTHOR]

The impact of metallicity on the Cepheid period-luminosity (P – L) relation is investigated using Hubble Space Telescope Advanced Camera for Surveys V and I images of M101. Variations in the reddening-free Wesenheit parameter (W), which is employed as a proxy for luminosity, are examined as a function of the radial distance from the center of M101 (and thus metallicity). We determine that there is no dependence of the slope on metallicity. However, the intercept is found to depend on metallicity by γVI = –0.33 ± 0.12 mag dex–1 and γVI = –0.71 ± 0.17 mag dex–1 using 2σ and 3σ rejection criteria, respectively. Sigma-clipping impacts the derived metallicity dependence, and the 2σ criterion applied likely mitigates blending, particularly in the crowded inner regions of M101. A metallicity-corrected distance for M101 is obtained from 619 Cepheids (μ = 28.96 ± 0.11), a result that agrees with the recently determined SN Ia distance. The metallicity effects described can be bypassed by working at near and mid-infrared wavelengths (e.g., the Carnegie Hubble Program). [ABSTRACT FROM AUTHOR]

Using time-resolved, mid-infrared data from the Wide-field Infrared Survey Explorer (WISE) and geometric parallaxes from the Hubble Space Telescope for four Galactic RR Lyrae variables, we derive the following Population II period-luminosity (PL) relations for the WISE [W1], [W2], and [W3] bands at 3.4, 4.6, and 12 μm, respectively: The slopes and the scatter around the fits are consistent with a smooth extrapolation of those same quantities from previously published K-band observations at 2.2 μm, where the asymptotic (long-wavelength) behavior is consistent with a period-radius relation with a slope of 0.5. No obvious correlation with metallicity (spanning 0.4 dex in [Fe/H]) is found in the residuals of the four calibrating RR Lyrae stars about the mean PL regression line. [ABSTRACT FROM AUTHOR]

We have observed the dwarf galaxy IC 1613, at multiple epochs in the mid-infrared using Spitzer and contemporaneously in the near-infrared using the new FourStar near-infrared camera on Magellan. We have constructed Cepheid period–luminosity relations in the J, H, Ks, [3.6] and [4.5] bands and have used the run of their apparent distance moduli as a function of wavelength to derive the line-of-sight reddening and distance to IC 1613. Using a nine-band fit, we find E(B − V ) = 0.05 ± 0.01 mag and an extinction-corrected distance modulus of μ0 = 24.29 ± 0.03statistical ± 0.03systematic mag. By comparing our multi-band and [3.6] distance moduli to results from the tip of the red giant branch and red clump distance indicators, we find that metallicity has no measurable effect on Cepheid distances at 3.6μm in the metallicity range −1.0 ⩽ [Fe/H] ⩽ 0.2, hence derivations of the Hubble constant at this wavelength require no correction for metallicity. [ABSTRACT FROM AUTHOR]

This is the first release of optical spectroscopic data of low-redshift Type Ia supernovae (SNe Ia) by the Carnegie Supernova Project including 604 previously unpublished spectra of 93 SNe Ia. The observations cover a range of phases from 12 days before to over 150 days after the time of B-band maximum light. With the addition of 228 near-maximum spectra from the literature, we study the diversity among SNe Ia in a quantitative manner. For that purpose, spectroscopic parameters are employed such as expansion velocities from spectral line blueshifts and pseudo-equivalent widths (pW). The values of those parameters at maximum light are obtained for 78 objects, thus providing a characterization of SNe Ia that may help to improve our understanding of the properties of the exploding systems and the thermonuclear flame propagation. Two objects, namely, SNe 2005M and 2006is, stand out from the sample by showing peculiar Si ii and S ii velocities but otherwise standard velocities for the rest of the ions. We further study the correlations between spectroscopic and photometric parameters such as light-curve decline rate and color. In agreement with previous studies, we find that the pW of Si ii absorption features are very good indicators of light-curve decline rate. Furthermore, we demonstrate that parameters such as pW2 (Si ii 4130) and pW6 (Si ii 5972) provide precise calibrations of the peak B-band luminosity with dispersions of ≈0.15 mag. In the search for a secondary parameter in the calibration of peak luminosity for SNe Ia, we find a ≈2σ-3σ correlation between B-band Hubble residuals and the velocity at maximum light of S ii and Si ii lines. [ABSTRACT FROM AUTHOR]

Distance measures on a coherent scale around the sky are required to address the outstanding cosmological problems of the Hubble constant and of departures from the mean cosmic flow. The correlation between galaxy luminosities and rotation rates can be used to determine the distances to many thousands of galaxies in a wide range of environments potentially out to 200 Mpc. Mid-infrared (3.6μm) photometry with the Spitzer Space Telescope is particularly valuable as a source of luminosities because it provides products of uniform quality across the sky. From a perch above the atmosphere, essentially the total magnitude of targets can be registered in exposures of a few minutes. Extinction is minimal and the flux is dominated by the light from old stars, which is expected to correlate with the mass of the targets. In spite of the superior photometry, the correlation between mid-infrared luminosities and rotation rates extracted from neutral hydrogen profiles is slightly degraded from the correlation found with I-band luminosities. A color correction recovers a correlation that provides comparable accuracy to that available at the I band (∼20% 1σ in an individual distance) while retaining the advantages identified above. Without color correction, the relation between linewidth and [3.6] magnitudes is Mb,i,k,a [3.6] = -20.34 - 9.74(logWi mx - 2.5). This description is found with a sample of 213 galaxies in 13 clusters that define the slope and 26 galaxies with Cepheid or tip of the red giant branch distances that define the zero point. A color-corrected parameter MC[3.6] is constructed that has reduced scatter: MC[3.6] = -20.34 - 9.13(logWi mx - 2.5). Consideration of the seven calibration clusters beyond 50 Mpc, outside the domain of obvious peculiar velocities, provides a preliminary Hubble constant estimate of H0 = 74 ± 4 km s-1 Mpc-1. [ABSTRACT FROM AUTHOR]

We present a physically motivated explanation for the observed, monotonic increase in slope, and the simultaneous (and also monotonic) decrease in the width/scatter of the Leavitt law (the Cepheid period-luminosity (PL) relation) as one systematically moves from the blue and visual into the near- and mid-infrared. We calibrate the wavelength-dependent, surface-brightness sensitivities to temperature using the observed slopes of PL relations from the optical through the mid-infrared and test the calibration by comparing the theoretical predictions with direct observations of the wavelength dependence of the scatter in the Large Magellanic Cloud Cepheid PL relation. In doing so we find the slope of the period-radius (PR) relation is c = 0.724 ± 0.006. Investigating the effect of differential reddening suggests that this value may be overestimated by as much as 10%; however, the same slope of the PR relation fits the (very much unreddened) Cepheids in IC 1613, albeit with lower precision. The discussion given is general and also applies to RR Lyrae stars, which also show similarly increasing PL slopes and decreasing scatter with increasing wavelength. [ABSTRACT FROM AUTHOR]

The Carnegie Hubble Program is designed to improve the extragalactic distance scale using data from the postcryogenic era of Spitzer. The ultimate goal is a determination of the Hubble constant to an accuracy of 2%. This paper is the first in a series on the Cepheid population of the Large Magellanic Cloud, and focusses on the period-luminosity (PL) relations (Leavitt laws) that will be used, in conjunction with observations of Milky Way Cepheids, to set the slope and zero point of the Cepheid distance scale in the mid-infrared. To this end, we have obtained uniformly sampled light curves for 85 LMC Cepheids, having periods between 6 and 140 days. PL and period-color relations are presented in the 3.6 µm and 4.5 µm bands. We demonstrate that the 3.6/zm band is a superb distance indicator. The cyclical variation of the [3.6]-[4.5] color has been measured for the first time. We attribute the anaplitude and phase of the color curves to the dissociation and recombination of CO molecules in the Cepheid's atmosphere. The CO affects only the 4.5 µm flux making it a potential metallicity indicator. [ABSTRACT FROM AUTHOR]