New Determinations of the UV Luminosity Functions from z~9 to z~2 show a remarkable consistency with halo growth and a constant star formation efficiency

TL;DR

The paper delivers the most comprehensive rest-frame UV luminosity functions from z~2 to z~9 using blank-field HST data across HDUV, UVUDF/XDF, HUDF parallals, and HFF parallels, totaling over 24,000 sources. It employs SWML and extensive simulations to derive selection volumes, correct for contamination, and fit Schechter parameters, revealing a smooth evolution: α steepens at high redshift, M* remains nearly constant for z>~2.5, and φ* increases with cosmic time in a quadratic fashion. The authors demonstrate that these trends are naturally explained by the evolving halo mass function under a constant star formation efficiency, linking galaxy build-up to dark matter growth. This work provides a robust blank-field benchmark for UV LF evolution and sets the stage for incorporating lensing-field results in future analyses to achieve full consistency across environments.

Abstract

Here we provide the most comprehensive determinations of the rest-frame $UV$ LF available to date with HST at z~2, 3, 4, 5, 6, 7, 8, and 9. Essentially all of the non-cluster extragalactic legacy fields are utilized, including the Hubble Ultra Deep Field (HUDF), the Hubble Frontier Field parallel fields, and all five CANDELS fields, for a total survey area of 1136 arcmin^2. Our determinations include galaxies at z~2-3 leveraging the deep HDUV, UVUDF, and ERS WFC3/UVIS observations available over a ~150 arcmin^2 area in the GOODS North and GOODS South regions. All together, our collective samples include >24,000 sources, >2.3x larger than previous selections with HST. 5766, 6332, 7240, 3449, 1066, 601, 246, and 33 sources are identified at z~2, 3, 4, 5, 6, 7, 8, and 9, respectively. Combining our results with an earlier z~10 LF determination by Oesch+2018a, we quantify the evolution of the $UV$ LF. Our results indicate that there is (1) a smooth flattening of the faint-end slope alpha from alpha~-2.4 at z~10 to -1.5 at z~2, (2) minimal evolution in the characteristic luminosity M* at z>~2.5, and (3) a monotonic increase in the normalization log_10 phi* from z~10 to z~2, which can be well described by a simple second-order polynomial, consistent with an "accelerated" evolution scenario. We find that each of these trends (from z~10 to z~2.5 at least) can be readily explained on the basis of the evolution of the halo mass function and a simple constant star formation efficiency model.

Figures (10)

• Figure 1: The layout of the search fields we utilize with WFC3/UVIS $UV_{275}U_{336}$$\sim$0.25-0.4$\mu$m data to identify $z\sim2$-3 galaxies. These include the $\sim$93 arcmin$^2$ HDUV fields (Oesch et al. 2018b), the $\sim$7 arcmin$^2$ UVUDF field (Teplitz et al. 2013), and the $\sim$50 arcmin$^2$ ERS (Windhorst et al. 2011) data set. The cyan footprint shown over the GOODS-North shows the WFC3/UVIS imaging data available from the CANDELS program in the F275W (Grogin et al. 2011) and has an exposure time equivalent to $\sim$6 orbits (Oesch et al. 2018b). All together we leverage a $\sim$150 arcmin$^2$ search area to identify $>$11,000 $z\sim2$-3 galaxies over GOODS South and GOODS North.
• Figure 2: Surface densities of the candidate $z\sim2$ and $z\sim3$ galaxies for the three search fields considered in this analysis, i.e., ERS (blue points), HDUV (black points), and the UVUDF (red points). Surface densities are presented as a function of the $V_{606}$ and $I_{814}$ band magnitudes that provide the best measure of the rest-frame $UV$ flux of galaxies at 1600$\AA$ for our $z\sim2$ and $z\sim3$ selections, respectively. For the UVUDF $z\sim3$ results, the $i_{775}$ band magnitudes are presented here instead (due to the significantly greater depth of the $i_{775}$-band data). A slight horizontal offset of the points relative to each other has been applied for clarity. The onset of incompleteness in our different samples is clearly seen in the observed decrease in surface density of sources near the magnitude limit. We do not make use of the faintest sources in each search field, i.e., $V_{606}/i_{775}/I_{814}$ magnitudes fainter than 26.5, 28.0, and 29.0 for the ERS, HDUV, and UVUDF fields, respectively, given the large uncertainties in the completeness (and contamination) corrections.
• Figure 3: Shown is the approximate redshift distribution expected for sources in our selections of $z\sim2$, $z\sim3$, $z\sim4$, $z\sim5$, $z\sim6$, $z\sim7$, $z\sim8$, and $z\sim9$ galaxies with the grey, magenta, blue, green, cyan, black, red, and magenta lines, respectively. The expected redshift distributions shown here are based on our HDUV and HUDF/XDF selection volume simulation results at $z\sim2$-3 and $z\sim4$-9, respectively. The dark blue line shows the expected redshift distribution for the $z\sim10$ selection from the companion study of Oesch et al. (2018a). The precise redshift distribution exhibits a modest dependence on the available HST passbands for a data set, as illustrated e.g. in Figure 4 of Bouwens et al. (2015).
• Figure 4: (upper) Histogram of the # of sources vs. redshift for the HST selections considered here. (lower) Redshift vs. apparent magnitudes (blue filled circles) for all sources in the present HST samples (and those of Oesch et al. 2018a). The source at $z\sim11.1$ and with an $H_{160,AB}$ magnitude of 25.9 mag is GN-z11 (Bouwens et al. 2010; Oesch et al. 2014, 2016).
• Figure 5: The stepwise LF constraints (solid circles)) we derive on the $UV$ LFs at $z\sim2$, $z\sim3$, $z\sim4$, $z\sim5$, $z\sim6$, $z\sim7$, $z\sim8$, and $z\sim9$ based on our comprehensive blank-field searches with HST (shown in grey, blue, magenta, green, cyan, black, red, orange, and dark purple, respectively). The recent stepwise LF constraints at $z\sim10$ from Oesch et al. (2018a) are shown with the dark purple circles. The best-fit Schechter LFs are shown with the grey, blue, magenta, green, cyan, black, red, orange, and dark purple lines, respectively.