arXiv subjects

Lucas Macri

Publications and source records attributed to Lucas Macri.

At least 19 recordsLinked to original sources

arXiv2025

The Local Distance Network: a community consensus report on the measurement of the Hubble constant at 1% precision

The direct, empirical determination of the local value of the Hubble constant (H0) has markedly advanced thanks to improved instrumentation, measurement techniques, and distance estimators. However, combining determinations from different estimators is non-trivial, due to correlated calibrations and different analysis methodologies. Using covariance weighting and leveraging the broad and comprehensive community of experts, we constructed a rigorous and transparent Distance Network (DN) to find a consensus value and uncertainty for the local H0. All critically reviewed the available data sets, spanning parallaxes, detached eclipsing binaries, masers, Cepheids, the TRGB, Miras, JAGB stars, SN Ia, Surface Brightness Fluctuations, SN II, the Fundamental Plane, and Tully-Fisher relations and voted for indicators to define a `baseline' DN and others to assess robustness and sensitivity of the results. We provide open-source software and data products to support full transparency and future extensions of this effort. Our conclusions: 1) Local H0 is robustly determined, with first-rank indicators internally consistent within their uncertainties; 2) A covariance-weighted combination yields an uncertainty of 1.1% (baseline) or 0.9% (all estimators); 3) The contribution from SNe Ia is consistent across four current compilations of optical magnitudes or using NIR-only magnitudes; 4) Removing either Cepheids or TRGB has minimal effect; 5) Replacing SNe Ia with galaxy-based indicators changes H0 by less than 0.1 km/s/Mpc, while doubling its uncertainty; 6) The baseline result is H0=73.50+/-0.81 km/s/Mpc. Compared to early Universe results, our result differs by 7.1sigma from flat {\Lambda}CDM with Planck+SPT+ACT and 5.0 sigma with BBN+BAO (DESI2). A networked approach is invaluable for enabling further progress in accuracy and precision without overreliance on any single method, sample or group.

astro-ph.CO↗

arXiv2024

The M33 Synoptic Stellar Survey. III. Miras and LPVs in griJHKs

We present the results of a search for Miras and long-period variables (LPVs) in M33 using griJHKs archival observations from the Canada-France-Hawai'i Telescope. We use multiband information and machine learning techniques to identify and characterize these variables. We recover ~1,300 previously-discovered Mira candidates and identify ~13,000 new Miras and LPVs. We detect for the first time a clear first-overtone pulsation sequence among Mira candidates in this galaxy. We use O-rich, fundamental-mode Miras in the LMC and M33 to derive a distance modulus for the latter of 24.629 +/- 0.046 mag.

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arXiv2023

RomAndromeda: The Roman Survey of the Andromeda Halo

As our nearest large neighbor, the Andromeda Galaxy provides a unique laboratory for investigating galaxy formation and the distribution and substructure properties of dark matter in a Milky Way-like galaxy. Here, we propose an initial 2-epoch ($\Delta t\approx 5$yr), 2-band Roman survey of the entire halo of Andromeda, covering 500 square degrees, which will detect nearly every red giant star in the halo (10$\sigma$ detection in F146, F062 of 26.5, 26.1AB mag respectively) and yield proper motions to $\sim$25 microarcsec/year (i.e., $\sim$90 km/s) for all stars brighter than F146 $\approx 23.6$ AB mag (i.e., reaching the red clump stars in the Andromeda halo). This survey will yield (through averaging) high-fidelity proper motions for all satellites and compact substructures in the Andromeda halo and will enable statistical searches for clusters in chemo-dynamical space. Adding a third epoch during the extended mission will improve these proper motions by $\sim t^{-1.5}$, to $\approx 11$ km/s, but this requires obtaining the first epoch in Year 1 of Roman operations. In combination with ongoing and imminent spectroscopic campaigns with ground-based telescopes, this Roman survey has the potential to yield full 3-d space motions of $>$100,000 stars in the Andromeda halo, including (by combining individual measurements) robust space motions of its entire globular cluster and most of its dwarf galaxy satellite populations. It will also identify high-velocity stars in Andromeda, providing unique information on the processes that create this population. These data offer a unique opportunity to study the immigration history, halo formation, and underlying dark matter scaffolding of a galaxy other than our own.

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arXiv2023

Reassessing the Constraints from SH0ES Extragalactic Cepheid Amplitudes on Systematic Blending Bias

The SH0ES collaboration Hubble constant determination is in a ${\sim}5\sigma$ difference with the $Planck$ value, known as the Hubble tension. The accuracy of the Hubble constant measured with extragalactic Cepheids depends on robust stellar-crowding background estimation. Riess et al. (R20) compared the light curves amplitudes of extragalactic and MW Cepheids to constrain an unaccounted systematic blending bias, $\gamma=-0.029\pm0.037\,\rm{mag}$, which cannot explain the required, $\gamma=0.24\pm0.05\,\rm{mag}$, to resolve the Hubble tension. Further checks by Riess et al. demonstrate that a possible blending is not likely related to the size of the crowding correction. We repeat the R20 analysis, with the following main differences: (1) we limit the extragalactic and MW Cepheids comparison to periods $P\lesssim50\,\rm{d}$, since the number of MW Cepheids with longer periods is minimal; (2) we use publicly available data to recalibrate amplitude ratios of MW Cepheids in standard passbands; (3) we remeasure the amplitudes of Cepheids in NGC 5584 and NGC 4258 in two HST filters ($F555W$ and $F350LP$) to improve the empirical constraint on their amplitude ratio $A^{555}/A^{350}$. We show that the filter transformations introduce an ${\approx}0.04\,\rm{mag}$ uncertainty in determining $\gamma$, not included by R20. While our final estimate, $\gamma=0.013\pm0.057\,\rm{mag}$, is consistent with the value derived by R20 and is consistent with no bias, the error is somewhat larger, and the best fitting value is shifted by ${\approx}0.04\,\rm{mag}$ and closer to zero. Future observations, especially with JWST, would allow better calibration of $\gamma$.

astro-ph.CO↗

arXiv2022

Measurements of the Hubble Constant with a Two Rung Distance Ladder: Two Out of Three Ain't Bad

The three rung distance ladder, which calibrates Type Ia supernovae through stellar distances linked to geometric measurements, provides the highest precision direct measurement of the Hubble constant. In light of the Hubble tension, it is important to test the individual components of the distance ladder. For this purpose, we report a measurement of the Hubble constant from 35 extragalactic Cepheid hosts measured by the SH0ES team, using their distances and redshifts at cz < 3300 km /s , instead of any, more distant Type Ia supernovae, to measure the Hubble flow. The Cepheid distances are calibrated geometrically in the Milky Way, NGC 4258, and the Large Magellanic Cloud. Peculiar velocities are a significant source of systematic uncertainty at z $\sim$ 0.01, and we present a formalism for both mitigating and quantifying their effects, making use of external reconstructions of the density and velocity fields in the nearby universe. We identify a significant source of uncertainty originating from different assumptions about the selection criteria of this sample, whether distance or redshift limited, as it was assembled over three decades. Modeling these assumptions yields central values ranging from H0 = 71.8 to 77.0 km/s/Mpc. Combining the four best fitting selection models yields H0 = 73.1 (+2.6/-2.3) km/s/Mpc as a fiducial result, at $2.6σ$ tension with Planck. While Type Ia supernovae are essential for a precise measurement of H0, unknown systematics in these supernovae are unlikely to be the source of the Hubble tension

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arXiv2021

The iron and oxygen content of LMC Classical Cepheids and its implications for the Extragalactic Distance Scale and Hubble constant

Classical Cepheids are primary distance indicators and a crucial stepping stone to determining the present-day Hubble constant Ho to the precision and accuracy required to constrain apparent deviations from the LCDM Concordance Cosmological Model. We have measured the iron and oxygen abundances of of 89 Cepheids in the LMC, one of the anchors of the local Distance Scale, quadrupling the prior sample and including 68 of the 70 Cepheids used to constrain Ho by the SH0ES program. The goal is to constrain the extent to which the Cepheid luminosity is influenced by their chemical composition, an important contributor to the uncertainty on the determination of the Ho itself and a critical factor in the internal consistency of the distance ladder. We have derived stellar parameters and abundances from a self-consistent spectroscopic analysis based on Equivalent Width of absorption lines. The [Fe/H] distribution of LMC Cepheids is a single Gaussian with a mean of -0.4079+-0.003 dex (0.1 dex systematic uncertainty) and sigma 0.076+-0.003 dex. The latter is fully compatible with the measurement error and supports the low dispersion of 0.069 mag seen in the NIR HST LMC period-luminosity relation. The uniformity of the abundance has the important consequence that the LMC Cepheids alone cannot provide any meaningful constraint on the dependence of the Cepheid Period-Luminosity relation on chemical composition at any wavelength. This revises a prior claim based on a small sample of 22 LMC Cepheids that there was little dependence (or uncertainty) between composition and NIR luminosity, a conclusion which would produce a conflict between anchors of the distance ladder with different mean abundance. The chemical homogeneity of the LMC Cepheid population makes it an ideal environment to calibrate the metallicity dependence between the more metal poor SMC and metal rich Milky Way and NGC4258.

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arXiv2021

Cosmic Distances Calibrated to 1% Precision with Gaia EDR3 Parallaxes and Hubble Space Telescope Photometry of 75 Milky Way Cepheids Confirm Tension with LambdaCDM

We present an expanded sample of 75 Milky Way Cepheids with Hubble Space Telescope (HST) photometry and Gaia EDR3 parallaxes which we use to recalibrate the extragalactic distance ladder and refine the determination of the Hubble constant. All HST observations were obtained with the same instrument (WFC3) and filters (F555W, F814W, F160W) used for imaging of extragalactic Cepheids in Type Ia supernova (SN Ia) hosts. The HST observations used the WFC3 spatial scanning mode to mitigate saturation and reduce pixel-to-pixel calibration errors, reaching a mean photometric error of 5 millimags per observation. We use new Gaia EDR3 parallaxes, vastly improved since DR2, and the Period-Luminosity (PL) relation of these Cepheids to simultaneously calibrate the extragalactic distance ladder and to refine the determination of the Gaia EDR3 parallax offset. The resulting geometric calibration of Cepheid luminosities has 1.0% precision, better than any alternative geometric anchor. Applied to the calibration of SNe~Ia, it results in a measurement of the Hubble constant of 73.0 +/- 1.4 km/sec/Mpc, in good agreement with conclusions based on earlier Gaia data releases. We also find the slope of the Cepheid PL relation in the Milky Way, and the metallicity dependence of its zeropoint, to be in good agreement with the mean values derived from other galaxies. In combination with the best complementary sources of Cepheid calibration, we reach 1.8% precision and find H_0=73.2 +/- 1.3 km/sec/Mpc, a 4.2 sigma difference with the prediction from Planck CMB observations under LambdaCDM. We expect to reach ~1.3% precision in the near term from an expanded sample of ~40 SNe Ia in Cepheid hosts.

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arXiv2019

The 2MASS Redshift Survey in the Zone of Avoidance

The 2MASS Redshift Survey was started two decades ago with the goal of mapping the three-dimensional distribution of an all-sky flux-limited (Ks<11.75 mag) sample of ~45,000 galaxies. Our first data release (Huchra et al. 2012) presented an unprecedented uniform coverage for most of the celestial sphere, with redshifts for ~98% of our sample. However, we were missing redshifts for ~18% of the catalog entries that were located within the "Zone of Avoidance" (|b|<10 deg) -- an important region of the sky for studies of large-scale structure and cosmic flows. In this second and final data release, we present redshifts for all 1041 2MRS galaxies that previously lacked this information, as well as updated measurements for 27 others.

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arXiv2018

Seven Problems with the Claims Related to the Hubble Tension in arXiv:1810.02595

Shanks et al. (2018) arXiv:1810.02595 make two claims that they argue bring the local measurement and early Universe prediction of H0 into agreement: A) they claim that Gaia DR2 parallax measurements show the geometric calibration of the Cepheid distance scale used to measure H0 to be grossly in error and B) that we live near the middle of an enormous void, further biasing the local measurement of the Hubble constant. We show that the first claim is caused by five erroneous uses of the data: in decreasing order of importance: 1) the use of a distance indicator, main sequence fitting of cluster stars, which is unrelated to the calibration of Cepheids and therefore has no bearing on current measurements of H0; 2) the use of Gaia data for Cepheids that fully saturate the detector, producing unreliable parallaxes; 3) the use of a fixed parallax offset which is known to depend on source magnitude and color but which is derived for sources with extremely different colors and magnitudes; 4) ignoring the uncertainty in this offset; and 5) ignoring the other geometric sources of Cepheid calibration, the distance of the LMC from detached eclipsing binaries and the masers in NGC 4258, which are independent of Milky Way parallaxes. Just resolving the first two of these issues by not using unrelated or saturated data leads to no inconsistency between Gaia parallaxes and the current Cepheid distance scale. The second claim can be refuted 6) because of the increase in chi-squared that the alleged void would entail in SN measurements in the Hubble flow, and 7) because it would represent a 6 sigma fluctuation of cosmic variance between the local and globally measured expansion, requiring us to live in an exceedingly special location.

astro-ph.CO↗

arXiv2018

Milky Way Cepheid Standards for Measuring Cosmic Distances and Application to Gaia DR2: Implications for the Hubble Constant

We present HST photometry of a selected sample of 50 long-period, low-extinction Milky Way Cepheids measured on the same WFC3 F555W, F814W, and F160W-band photometric system as extragalactic Cepheids in SN Ia hosts. These bright Cepheids were observed with the WFC3 spatial scanning mode in the optical and near-infrared to mitigate saturation and reduce pixel-to-pixel calibration errors to reach a mean photometric error of 5 millimags per observation. We use the new Gaia DR2 parallaxes and HST photometry to simultaneously constrain the cosmic distance scale and to measure the DR2 parallax zeropoint offset appropriate for Cepheids. We find a value for the zeropoint offset of -46 +/- 13 muas or +/- 6 muas for a fixed distance scale, higher than found from quasars, as expected, for these brighter and redder sources. The precision of the distance scale from DR2 has been reduced by a factor of 2.5 due to the need to independently determine the parallax offset. The best fit distance scale is 1.006 +/- 0.033, relative to the scale from Riess et al 2016 with H0=73.24 km/s/Mpc used to predict the parallaxes photometrically, and is inconsistent with the scale needed to match the Planck 2016 CMB data combined with LCDM at the 2.9 sigma confidence level (99.6%). At 96.5% confidence we find that the formal DR2 errors may be underestimated as indicated. We identify additional error associated with the use of augmented Cepheid samples utilizing ground-based photometry and discuss their likely origins. Including the DR2 parallaxes with all prior distance ladder data raises the current tension between the late and early Universe route to the Hubble constant to 3.8 sigma (99.99 %). With the final expected precision from Gaia, the sample of 50 Cepheids with HST photometry will limit to 0.5% the contribution of the first rung of the distance ladder to the uncertainty in the Hubble constant.

astro-ph.CO↗

arXiv2018

New Parallaxes of Galactic Cepheids from Spatially Scanning the Hubble Space Telescope: Implications for the Hubble Constant

We present new parallax measurements of 7 long-period (> 10 days) Milky Way Cepheids (SS CMa, XY Car, VY Car, VX Per, WZ Sgr, X Pup and S Vul) using astrometry from spatial scanning of WFC3 on HST. Observations were obtained at 6 month intervals over 4 years. The distances are 1.7--3.6 kpc with a mean precision of 45 microarcseconds and a best of 29 microarcseconds (SNR = 14). The accuracy of the parallaxes is demonstrated through independent analyses of >100 reference stars. This raises to 10 the number of long-period Cepheids with significant parallax measurements, 8 obtained from this program. We also present high-precision F555W, F814W, and F160W magnitudes of these Cepheids, allowing a direct, zeropoint-independent comparison to >1800 extragalactic Cepheids in the hosts of 19 SNeIa. This sample addresses two outstanding systematic uncertainties affecting prior comparisons of Milky Way and extragalactic Cepheids used to calibrate H_0: their dissimilarity of periods and photometric systems. Comparing the new parallaxes to their predicted values derived from reversing the distance ladder gives a ratio (or independent scale for H_0) of 1.037+/-0.036, consistent with no change and inconsistent at the 3.5 sigma level with a ratio of 0.91 needed to match the value predicted by Planck+LCDM. Using these data instead to augment the Riess et al. (2016) measurement of H_0 improves the precision to 2.3%, yielding 73.48+/-1.66 km/s/Mpc, and tension with Planck+LCDM increases to 3.7 sigma. The future combination of Gaia parallaxes and HST spatial scanning photometry of 50 Milky Way Cepheids can support a < 1% calibration of H_0.

astro-ph.SR↗

arXiv2014

2MTF III. HI 21cm observations of 1194 spiral galaxies with the Green Bank Telescope

We present HI 21cm observations of 1194 galaxies out to a redshift of 10,000 km/s selected as inclined spirals (i>60deg) from the 2MASS Redshift Survey. These observations were carried out at the National Radio Astronomy Observatory Robert C. Byrd Green Bank Telescope (GBT). This observing program is part of the 2MASS Tully-Fisher (2MTF) survey. This project will combine HI widths from these GBT observations with those from further dedicated observing at the Parkes Telescope, from the ALFALFA survey at Arecibo, and S/N>10 and spectral resolution, v_res < 10km/s published widths from a variety of telescopes. We will use these HI widths along with 2MASS photometry to estimate Tully-Fisher distances to nearby spirals and investigate the peculiar velocity field of the local Universe. In this paper we report on detections of neutral hydrogen in emission in 727 galaxies, and measure good signal-to-noise and symmetric HI global profiles suitable for use in the Tully-Fisher relation in 484.

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arXiv2013

A Direct Stellar Metallicity Determination in the Disk of the Maser Galaxy NGC4258

We present the first direct determination of a stellar metallicity in the spiral galaxy NGC4258 (D=7.6 Mpc) based on the quantitative analysis of a low-resolution (~5 AE) Keck LRIS spectrum of a blue supergiant star located in its disk. A determination of stellar metallicity in this galaxy is important for the absolute calibration of the Cepheid Period-Luminosity relation as an anchor for the extragalactic distance scale and for a better characterization of its dependence as a function of abundance. We find a value 0.2 dex lower than solar metallicity at a galactocentric distance of 8.7 kpc, in agreement with recent HII region studies using the weak forbidden auroral oxygen line at 4363 AE. We determine the effective stellar temperature, gravity, luminosity and line-of-sight extinction of the blue supergiant being studied. We show that it fits well on the flux-weighted gravity--luminosity relation (FGLR), strengthening the potential of this method as a new extragalactic distance indicator.

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arXiv2012

Addressing Decadal Survey Science through Community Access to Highly Multiplexed Spectroscopy with BigBOSS on the KPNO Mayall Telescope

This document summarizes the results of a community-based discussion of the potential science impact of the Mayall+BigBOSS highly multiplexed multi-object spectroscopic capability. The KPNO Mayall 4m telescope equipped with the DOE- and internationally-funded BigBOSS spectrograph offers one of the most cost-efficient ways of accomplishing many of the pressing scientific goals identified for this decade by the "New Worlds, New Horizons" report. The BigBOSS Key Project will place unprecedented constraints on cosmological parameters related to the expansion history of the universe. With the addition of an open (publicly funded) community access component, the scientific impact of BigBOSS can be extended to many important astrophysical questions related to the origin and evolution of galaxies, stars, and the IGM. Massive spectroscopy is the critical missing ingredient in numerous ongoing and planned ground- and space-based surveys, and BigBOSS is unique in its ability to provide this to the US community. BigBOSS data from community-led projects will play a vital role in the education and training of students and in maintaining US leadership in these fields of astrophysics. We urge the NSF-AST division to support community science with the BigBOSS multi-object spectrograph through the period of the BigBOSS survey in order to ensure public access to the extraordinary spectroscopic capability.

astro-ph.CO↗

arXiv2011

A 3% Solution: Determination of the Hubble Constant with the Hubble Space Telescope and Wide Field Camera 3

We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope to determine the Hubble constant (H0) from optical and infrared observations of over 600 Cepheid variables in the host galaxies of 8 recent Type Ia supernovae (SNe Ia), providing the calibration for a mag-z relation of 253 SNe Ia. Increased precision over past measurements comes from: (1) more than doubling the number of infrared observations of Cepheids in nearby SN hosts; (2) increasing the sample of ideal SN Ia calibrators from six to eight; (3) increasing by 20% the number of Cepheids with infrared observations in the megamaser host NGC 4258; (4) reducing the difference in the mean metallicity of the Cepheid comparison samples from Δlog [O/H] = 0.08 to 0.05; and (5) calibrating all optical Cepheid colors with one camera, WFC3, to remove cross-instrument zero-point errors. Uncertainty in H0 from beyond the 1st rung of the distance ladder is reduced from 3.5% to 2.3%. The measurement of H0 via the geometric distance to NGC 4258 is 74.8 \pm 3.1 km s- 1 Mpc-1, a 4.1% measurement including systematics. Better precision independent of NGC 4258 comes from two alternative Cepheid absolute calibrations: (1) 13 Milky Way Cepheids with parallaxes and (2) 92 Cepheids in the Large Magellanic Cloud with multiple eclipsing binary distances, yielding 74.4 \pm 2.5 km s- 1 Mpc-1, a 3.4% uncertainty with systematics. Our best estimate uses all three calibrations but a larger uncertainty afforded from any two: H0 = 73.8 \pm 2.4 km s- 1 Mpc-1 including systematics, a 3.3% uncertainty. The improvement in H0, combined with WMAP7yr data, results in a constraint on the EOS parameter of dark energy of w = -1.08 \pm 0.10 and Neff = 4.2 \pm 0.7 for the number of relativistic species in the early universe. It also rules out the best-fitting gigaparsec-scale void models, posited as an alternative to dark energy. (abridged)

astro-ph.CO↗

arXiv2009

A Redetermination of the Hubble Constant with the Hubble Space Telescope from a Differential Distance Ladder

We report observations of 240 Cepheid variables obtained with the Near Infrared Camera (NICMOS) through the F160W filter on the Hubble Space Telescope (HST). The Cepheids are distributed across six recent hosts of Type Ia supernovae (SNe Ia) and the "maser galaxy" NGC 4258, allowing us to directly calibrate the peak luminosities of the SNe Ia from the precise, geometric distance measurements provided by the masers. New features of our measurement include the use of the same instrument for all Cepheid measurements across the distance ladder and homogeneity of the Cepheid periods and metallicities thus necessitating only a differential measurement of Cepheid fluxes and reducing the largest systematic uncertainties in the determination of the fiducial SN Ia luminosity. The NICMOS measurements reduce differential extinction in the host galaxies by a factor of 5 over past optical data. Combined with an expanded of 240 SNe Ia at z<0.1 which define their magnitude-redshift relation, we find H_0=74.2 +/-3.6, a 4.8% uncertainty including both statistical and systematic errors. We show that the factor of 2.2 improvement in the precision of H_0 is a significant aid to the determination of the equation-of-state of dark energy, w = P/(rho c^2). Combined with the WMAP 5-year measurement of Omega_M h^2, we find w= -1.12 +/- 0.12 independent of high-redshift SNe Ia or baryon acoustic oscillations (BAO). This result is also consistent with analyses based on the combination of high-z SNe Ia and BAO. The constraints on w(z) now with high-z SNe Ia and BAO are consistent with a cosmological constant and improved by a factor of 3 from the refinement in H_0 alone. We show future improvements in H_0 are likely and will further contribute to multi-technique studies of dark energy.

astro-ph.CO↗

arXiv2009

Cepheid Calibrations of Modern Type Ia Supernovae:Implications for the Hubble Constant

This is the first of two papers reporting measurements from a program to determine the Hubble constant to 5% precision from a refurbished distance ladder. We present new observations of 110 Cepheid variables in the host galaxies of two recent Type Ia supernovae (SNe Ia), NGC 1309 and NGC 3021, using the Advanced Camera for Surveys on the Hubble Space Telescope (HST). We also present new observations of the hosts previously observed with HST whose SNe Ia provide the most precise luminosity calibrations: SN 1994ae in NGC 3370, SN 1998aq in NGC 3982, SN 1990N in NGC 4639, and SN 1981B in NGC 4536, as well as the maser host, NGC 4258. Increasing the interval between observations enabled the discovery of new, longer-period Cepheids, including 57 with P>60 days, which extend these period-luminosity (PL) relations. We present 93 measurements of the metallicity parameter, 12 + log[O/H], measured from HII regions in the vicinity of the Cepheids and show these are consistent with solar metallicity. We find the slope of the seven dereddened PL relations to be consistent with that of the Large Magellanic Cloud Cepheids and with parallax measurements of Galactic Cepheids, and we address the implications for the Hubble constant. We also present multi-band light curves of SN 2002fk (in NGC 1309) and SN 1995al (in NGC 3021) which may be used to calibrate their luminosities. In the second paper we present observations of the Cepheids in the H-band obtained with the Near Infrared Camera and Multi-Object Spectrometer on HST, further mitigating systematic errors along the distance ladder resulting from dust and chemical variations. The quality and homogeneity of these SN and Cepheid data provide the basis for a more precise determination of the Hubble constant.

astro-ph.CO↗

arXiv2009

Estimation of the Hubble Constant and Constraint on Descriptions of Dark Energy

Joint analysis of Cosmic Microwave Background, Baryon Acoustic Oscillation, and supernova data has enabled precision estimation of cosmological parameters. New programs will push to 1% uncertainty in the dark energy equation of state and tightened constraint on curvature, requiring close attention to systematics. Direct 1% measurement of the Hubble constant (H0) would provide a new constraint. It can be obtained without overlapping systematics directly from recessional velocities and geometric distance estimates for galaxies via the mapping of water maser emission that traces the accretion disks of nuclear black holes. We identify redshifts 0.02 0.02, out of ~100 known masers. A single-dish discovery survey of >10,000 nuclei (>2500 hours on the GBT) would build a sample of tens of potential distance anchors. Beyond 2020, a high-frequency SKA could provide larger maser samples, enabling estimation of H0 from individually less accurate distances, and possibly without the need for peculiar motion corrections.

astro-ph.CO↗