HOSTFLOWS

Cornering the Hubble tension by studying systematics
and reconstructing the local Universe with supernovae

Funded by the Spanish Ministry of Science, Innovation and Universities (MICIU) project PID2020-115253GA-I00

The expansion rate of the universe parameterized by the Hubble-Lemaître parameter H(z), has been a major endeavour in cosmology since the discovery of the expanding Universe. H(z) is not constant, but rather varies over cosmic time following the deceleration and acceleration of the Universe. In the last years, significant effort has been put forth to measure with high precision the local value of the Hubble-Lemaître parameter known as the Hubble constant H0, and today H0 is estimated from the distance ladder with an uncertainty of <3%. Perplexingly, these findings have revealed a dramatic discrepancy dubbed the Hubble tension: the estimation of H0 from the local distance ladder is in strong disagreement (at 4.4σ or 99.99% level) with the value inferred at high-redshift from the angular scale of fluctuations in the cosmic microwave background (CMB), possibly hinting towards new physics beyond the standard model. This discrepancy represents the most urgent puzzle of modern cosmology, and it is nowadays one of its hottest topics.

HOSTFLOWS aims to advance towards solving of this tension from two different perspectives:

- performing an unprecedented study of the local environments of nearby standard candles. With an exquisite sample of hundreds of nearby galaxies, home to distance beacons and observed with multi-wavelength photometry, integral-field spectroscopy (IFS) and polarimetry, together with novel astrostatistical techniques, we will map their local properties like metallicity, stellar age and mass, and dust extinction to constrain the effects in distance estimation and in the determination of the current expansion of the universe H0.

- extending upon the seminal efforts of peculiar velocities, we aim to reconstruct the panorama of our supercluster Laniakea by studying cosmic flows using type Ia supernovae (SNe Ia) in the near- infrared (NIR). We intend to advance peculiar velocity studies with the addition of systematic-limited SNe Ia distances. In doing so, we will provide a sorely needed roadmap and means to expand the cosmography of the local universe and ultimately make accurate local measurements of H0 and the growth rate of cosmic structure parametrized by fσ8. Our findings will serve as a crucial cross-check to future ground/space-based galaxy and weak lensing surveys of the matter power spectrum at an insignificant fraction of the cost.

Integral Field Spectroscopy of supernova host galaxies

Synthetic r-band image obtained by convoluting the filter transmission with the IFS spectra. Red circles correspond to apertures of 1 to 5 squared kpc centered at SN locations; the blue circle is the galaxy core; yellow dots are objects catalogued in the SDSS catalogue. More info...

Near-infrared imaging of type Ia supernovae

J-band image of the filed where type Ia SN 2021pfs occurred obtained with the OMEGA2000 camera mounted to the 3.5m telescope at the Calar Alto observatory. More info...

Funded by the Spanish Ministry of Science, Innovation and Universities (MICIU) project PID2020-115253GA-I00

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