分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: NGC 4258 is one of the most important anchors for calibrating the Cepheid period--luminosity relations (PLRs) owing to its accurate distance measured from water maser motions. We expand on previous efforts and carry out a new Cepheid search in this system using the Hubble Space Telescope (HST). We discover and measure a sample of 669 Cepheids in four new and two archival NGC 4258 fields, doubling the number of known Cepheids in this galaxy and obtaining an absolute calibration of their optical PLRs. We determine a Wesenheit PLR of $-2.574(\pm0.034) -3.294(\pm0.042) \log P$, consistent with an independent Large Magellanic Cloud (LMC) calibration at the level of $0.032\pm0.044$~mag in its zeropoint, after accounting for a metallicity dependence of $-0.20\pm0.05$~mag\,dex$^{-1}$ (Riess et al. 2006). Our determination of the PLR slope also agrees with the LMC-based value within their uncertainties. We attempt to characterize the metallicity effect of Cepheid PLRs using only the NGC 4258 sample, but a relatively narrow span of abundances limits our sensitivity and yields a Wesenheit zero-point dependence of $-0.07 \pm 0.21$ mag\,dex$^{-1}$. The Cepheid measurements presented in this study have been used as part of the data to derive the Hubble constant in a companion paper by the SH0ES team.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present here a re-calibration of the photometric systems used in the
Pantheon+ sample of Type Ia supernovae (SNe Ia) including those used for the
SH0ES distance-ladder measurement of H$_0$. We utilize the large and uniform
sky coverage of the public Pan-STARRS stellar photometry catalog to
cross-calibrate against tertiary standards released by individual SN Ia
surveys. The most significant updates over the `SuperCal' cross-calibration
used for the previous Pantheon and SH0ES analyses are: 1) expansion of the
number of photometric systems (now 25) and filters (now 105), 2) solving for
all filter offsets in all systems simultaneously in order to produce a
calibration uncertainty covariance matrix that can be used in
cosmological-model constraints, and 3) accounting for the change in the
fundamental flux calibration of the HST CALSPEC standards from previous
versions on the order of $1.5\%$ over a $\Delta \lambda$ of 4000~\AA. The
re-calibration of samples used for light-curve fitting has historically been
decoupled from the retraining of the light-curve model. Here, we are able to
retrain the SALT2 model using this new calibration and find the change in the
model coupled with the change to the calibration of the light-curves themselves
causes a net distance modulus change ($d\mu/dz$) of 0.04 mag over the redshift
range $0
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present constraints on cosmological parameters from the Pantheon+ analysis of 1701 light curves of 1550 distinct Type Ia supernovae (SNe Ia) ranging in redshift from $z=0.001$ to 2.26. This work features an increased sample size, increased redshift span, and improved treatment of systematic uncertainties in comparison to the original Pantheon analysis and results in a factor of two improvement in cosmological constraining power. For a Flat$\Lambda$CDM model, we find $\Omega_M=0.334\pm0.018$ from SNe Ia alone. For a Flat$w_0$CDM model, we measure $w_0=-0.90\pm0.14$ from SNe Ia alone, H$_0=73.5\pm1.1$ km s$^{-1}$ Mpc$^{-1}$ when including the Cepheid host distances and covariance (SH0ES), and $w_0=-0.978^{+0.024}_{-0.031}$ when combining the SN likelihood with constraints from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO); both $w_0$ values are consistent with a cosmological constant. We also present the most precise measurements to date on the evolution of dark energy in a Flat$w_0w_a$CDM universe, and measure $w_a=-0.1^{+0.9}_{-2.0}$ from Pantheon+ alone, H$_0=73.3\pm1.1$ km s$^{-1}$ Mpc$^{-1}$ when including SH0ES, and $w_a=-0.65^{+0.28}_{-0.32}$ when combining Pantheon+ with CMB and BAO data. Finally, we find that systematic uncertainties in the use of SNe Ia along the distance ladder comprise less than one third of the total uncertainty in the measurement of H$_0$ and cannot explain the present "Hubble tension" between local measurements and early-Universe predictions from the cosmological model.