Type Ia Supernova Distances at z > 1.5 from the Hubble Space Telescope Multi-Cycle Treasury Programs: The Early Expansion Rate (1710.00844v1)

Abstract: We present an analysis of 15 Type Ia supernovae (SNe Ia) at redshift z > 1 (9 at 1.5 < z < 2.3) recently discovered in the CANDELS and CLASH Multi-Cycle Treasury programs using WFC3 on the Hubble Space Telescope. We combine these SNe Ia with a new compilation of 1050 SNe Ia, jointly calibrated and corrected for simulated survey biases to produce accurate distance measurements. We present unbiased constraints on the expansion rate at six redshifts in the range 0.07 < z < 1.5 based only on this combined SN Ia sample. The added leverage of our new sample at z > 1.5 leads to a factor of ~3 improvement in the determination of the expansion rate at z = 1.5, reducing its uncertainty to ~20%, a measurement of H(z=1.5)/H0=2.67 (+0.83,-0.52). We then demonstrate that these six measurements alone provide a nearly identical characterization of dark energy as the full SN sample, making them an efficient compression of the SN Ia data. The new sample of SNe Ia at z > 1 usefully distinguishes between alternative cosmological models and unmodeled evolution of the SN Ia distance indicators, placing empirical limits on the latter. Finally, employing a realistic simulation of a potential WFIRST SN survey observing strategy, we forecast optimistic future constraints on the expansion rate from SNe Ia.

• The paper achieves a threefold enhancement in measuring the expansion rate at z = 1.5 using 15 newly discovered SNe Ia.
• It employs unbiased SNe Ia distance measurements from Hubble’s CANDELS and CLASH programs, reducing uncertainty to about 20%.
• The analysis strengthens cosmological model constraints and offers prospects for further improvements with missions like WFIRST.

Analysis of Type Ia Supernovae at Redshift > 1.5 to Constrain the Early Expansion Rate

The paper under consideration presents a technique to measure the distances of Type Ia supernovae (SNe Ia) located at redshifts exceeding 1.5, utilizing data acquired via the Hubble Space Telescope's CANDELS and CLASH Multi-Cycle Treasury programs. The main objective of this research is to provide precise constraints on the universe's expansion rate at early epochs, particularly around $z = 1.5$, utilizing 15 newly discovered SNe Ia, nine of which are constrained between $1.5 < z < 2.3$.

The analysis contributes to an expanded sample of over 1050 SNe Ia, allowing the authors to elucidate distance measurements that are unbiased by survey selection effects. Notably, the inclusion of high-redshift SNe Ia permits a threefold enhancement in determining the expansion rate at $z = 1.5$. Specifically, the paper reports a $H(z = 1.5)/H_0$ measurement of $2.67^{+0.83}_{-0.52}$, achieving an uncertainty reduction to approximately 20%.

Implications for Cosmology

The precision measurement of the expansion rate from high-redshift SNe Ia provides empirical constraints to differentiate between alternative cosmological models. It allows further validation of the dark energy component in terms of its equation of state parameter $w$, vis-à-vis its current understanding. The research dismisses significant deviations that could arise from hypothetical evolutionary effects in SNe Ia, thereby reinforcing their applicability as standardizable cosmic distance indicators.

By leveraging SNe Ia data from the earliest available redpackets, the authors demonstrate the capability to independently constrain cosmological models to account for the dynamics observed in the universe's expansion history optimized solely on the SN data without ancillary cosmological information, such as Cosmic Microwave Background (CMB) data. The boxed alternative cosmologies considered in the analysis provide evidence suggesting linear algebraic computational techniques can effectively reveal departures from $\Lambda$CDM parameters.

Prospective Developments

This research underscores the utility of precise SNe Ia measurements at higher redshifts in constraining cosmological parameters. Projected future missions, such as WFIRST, promise substantial advances, furnishing both increased SNe Ia detection at $z > 1.5$ and improving confidence in the cosmological significance of empirical calibrations. By employing simulated WFIRST observational strategies, this paper forecasts constraints on $E(z)$ to improve by factors of up to an order of magnitude beyond current limits, with potential to rigorously test evolving cosmological models.

Conclusion

In conclusion, the paper powerfully exemplifies how precise high-redshift SNe Ia distance measurements enhance our comprehension of the expansion history and facilitate rigorous tests of cosmological models. The results demonstrate the potential of upcoming observational platforms, like WFIRST, to revolutionize our empirical grasp on the universe's accelerating expansion and the mysterious nature of dark energy. The robust analysis provided by the CANDELS and CLASH data sets a precedent for future empirical cosmology focused on early epoch universe constraints.