Hawaii Two-0 Science

Proposed Research

Dark matter density map at 4.3 < z < 5.3 over 20 deg2 , from the Millennium Simulation (Springel et al. 2005), while small rectangle and circle are comparable to CANDELS and COSMOS respectively. Only H20 has the statistical power to study the rare overdensity peaks (dark orange) and cosmic voids (dark purple) as well as characterizing the overall density field needed for cosmology.
Galaxy stellar mass functions with 1σ statistical errors from existing (hatched) and proposed (solid) data. H20 will improve the constraints by a factor of > 10, thus allowing us to make a more definitive measurement of the overall mass function, link it to the dark matter via clustering, and characterize differences as a function of local environment.
Three proposed models of the galaxy SMF at z~6 are shown, along with current data (shaded area, Grazian et al. 2015) and proposed constraints (red circles, with error bars including expected uncertainties from Poisson noise, cosmic variance, and SED fitting). The three models (solid, dashed, dotted lines) have radically different implications for galaxy evolution in the early universe (e.g. Davidzon et al. 2017). H20 will clearly differentiate between these models. When combined with the proposed clustering measurements it will also directly measure the duty cycle of star formation (e.g. determining typical star formation histories).
Sensitivity limits in the HSC filters of this proposal (blue), along with the IRAC ch. 1 and 2 from our ongoing SLS program (red) and the designed NIR filters of Euclid (green). Light and dark grey lines show spectral energy distributions (SEDs) of two galaxies at z ~ 2.5 and 7 respectively, which the deep H20 imaging will be able to disentangle. To confirm and characterize this differentiation the proposed Keck follow-up is essential.
Stellar-to-halo mass ratio (SHMR) at z~5 from state-of-the-art analyses. The 2 deg2 of the COSMSOS field (blue line, Coupon et al. in prep.) still suffer large statistical uncertainties at z ~ 5 (shaded area). HSC-SSP Wide estimates (Harikane et al. 2016) are apparently more precise, but they rely on MUV converted into stellar mass through average ad-hoc assumptions. Both samples cannot constrain the most massive regime while in the cosmic volume probed by H20 we expect to find at least ~ 40 halos > 7 × 1012 M⊙. Moreover our data will consolidate the SHMR at Mhalo ~ 1012 M⊙, to pin down the peak of efficiency and determine weather it evolves from z ~ 0 (dashed line) to z = 4-6.
SED fitting to our photometric baseline (g, r, i, z, y, [3.6], [4.5]) recovers the redshift of simulated galaxies with an error (normalized median absolute deviation) of σz /(1 + z) . 0.03 at z < 1.5 and z > 3, with the 1.5 < z < 3 range reaching similar performance once Eculid data are avaialable. The fraction of outliers (Δz > 0.15 σz ) is expected to be < 10%; the actual value will be quantified using our spectroscopic sample.
Difference between the intrinsic stellar mass of 3 < z < 6 galaxies and those recovered with SED fitting. When IRAC data are not available estimates have over 1.5 dex of scatter, making impossible to constrain stellar mass assembly as a function of cosmic time. The HSC-SSP survey lacks sufficiently deep IRAC data (> 0.5 dex scatter bellow M☆) except in the two 1.8 deg ultra-deep fields which are too small for the proposed science and suffer from large cosmic variance.

Ongoing Research

High-Redshift Dropout Galaxies

Lead: McPartland

To provide estimates for the ultimate outcomes of the H20 survey, we have identified a sample of high-redshift galaxies using available ultra-deep (limiting mag. ≥27) HSC data in the COSMOS Deep Field. “Dropout” galaxies were selected using standard Lyman break galaxy color selection criteria based on the analysis of Ono et al. (2018). At the conclusion of the H20 observing program, we expect to have a final sample of:


Dropout selection:

Band Redshift Detected Sources
COSMOS 2 sq. deg
Expected Sources
H20 20 sq. deg
g 4 72,098 ~720,000
r 5 3,814 ~40,000
i 6 262 ~3000
z 7 46 ~500


Photo-z selection

2,00,000+  galaxies @ z~3

3,00,000+  galaxies @ z~2

Testing New Statistics for Cosmological Measurements

Lead: Repp

One of the difficulties of extracting cosmological information from galaxy surveys (including the upcoming Euclid and WFIRST missions) is the fact that galaxies are biased tracers of dark matter. Unfortunately, current bias models focus primarily on high-density regions, whereas low-density regions carry significant amounts of information relevant to the constraint of dark energy and alternative gravity theories. For this reason, proper treatment of both high and low densities is important for future surveys. We have developed an interactionless Ising model for this bias (Repp & Szapudi, in prep.) which exhibits a remarkably good fit to both Millennium Simulation and Sloan Digital Sky Survey data, at both density extremes. We intend to test this model against a variety of other galaxy catalogs, one of which will be that produced by Hawaii 2-0. Obtaining spectroscopic redshifts for dropouts will in particular allow us to test our prescription against the data at multiple high redshifts, thus investigating, first, whether the model is accurate at these redshifts and, second, how the bias has evolved with cosmic time.

Galaxy Two-Point Correlation Function and Galaxy-Dark Matter Bias

Lead: Beck

Using high-redshift dropout sources in the COSMOS (comparable to the ultimate depth of the H20 survey), we have made preliminary measurements of the galaxyspherical angular two-point point correlation function. Comparison of these measurements with predictions from cosmological provides the ability to constrain the Galaxy-Dark Matter bias — a key cosmological observable — which quantifies the offset between the two-point correlation function of galaxies and dark matter (see Figure at right).


Measuring the linear galaxy bias at high redshift
Beck, McPartland, Repp, Sanders & Szapudi, in prep. 

Synergy with Other Surveys


Spitzer Legacy Survey


Deep Calibration Fields


Likely to be target of WFIRST deep surveys.

Institute for Astronomy

Manoa  808 956-8312
Hilo       808 932-2300
Maui     808 573-9500