An independent determination of the local Hubble constant

TL;DR

This study delivers an independent local estimate of the Hubble constant $H_{0}$ by calibrating the $L$-$\sigma$ relation for H II galaxies and giant H II regions. It combines a new anchor sample of 36 GHIIRs in 13 galaxies with Cepheid-based distances (including NGC 4258) with a larger HIIG dataset to determine the slope and zero-point of the relation, while carefully correcting for extinction, underlying absorption, and stellar population evolution. The analysis systematically propagates observational and model uncertainties, exploring 16 model variants and employing bootstrap tests to verify the robustness of the slope, ultimately yielding a evolution-corrected $H_{0}=71.0\pm2.8\mathrm{(random)}\pm2.1\mathrm{(systematic)}\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$, with a broader uncorrected value around $74.6\ \mathrm{km\,s^{-1}\,Mpc^{-1}}$. The result provides an important, independent cross-check of the Planck and Riess et al. measurements and highlights ongoing avenues to improve precision by expanding the anchor sample, refining the evolution correction, and reducing extinction-related systematics.

Abstract

The relationship between the integrated H$β$ line luminosity and the velocity dispersion of the ionized gas of HII galaxies and giant HII regions represents an exciting standard candle that presently can be used up to redshifts z ~ 4. Locally it is used to obtain precise measurements of the Hubble constant by combining the slope of the relation obtained from nearby ($z \leq $ 0.2) HII galaxies with the zero point determined from giant HII regions belonging to an `anchor sample' of galaxies for which accurate redshift-independent distance moduli are available. We present new data for 36 giant HII regions in 13 galaxies of the anchor sample that includes the megamaser galaxy NGC 4258. Our data is the result of the first four years of observation of our primary sample of 130 giant HII regions in 73 galaxies with Cepheid determined distances. Our best estimate of the Hubble parameter is $71.0\pm2.8(random)\pm2.1(systematic)$ km /s Mpc This result is the product of an independent approach and, although at present less precise than the latest SNIa results, it is amenable to substantial improvement.

Figures (13)

• Figure 1: Comparison of the distance modulii for our anchor sample obtained using the TRGB or the Cepheids PL relation. The solid line is the 1-to-1 relation and the red dashed line is the fit to the points, r is the correlation coefficient. The inset shows the coefficients of the fit. The residuals are shown in the bottom panel against the adopted distance modulii from Table \ref{['dist']}.
• Figure 2: IC10 C01 low-resolution spectrum obtained at OAN-SPM.
• Figure 3: Comparison between our photometry and Kennicutt1984 (top left) , melnick1987 (top right) and bosch2002 (bottom left). . All together are shown at the bottom right panel.
• Figure 4: Spectrum of NGC 595 using OAGH CanHis (left) and OAN-SPM MEZCAL (right) in H$\alpha$. The dashed (red) line is the fit to the instrumental profile obtained for the calibration lamps at 6585.3Å and 6583.9Å at OAGH and OAN-SPM respectively.
• Figure 5: Velocity dispersion for the 10 objects observed with both OAGH CanHis and OAN-SPM MEZCAL.