BEACON: JWST NIRCam Pure-parallel Imaging Survey. II. Physical Properties of $z=7-14$ Galaxies

TL;DR

BEACON DR2 provides a wide, low-cosmic-variance sample of $z\ge7$ galaxy candidates from JWST/NIRCam pure-parallel imaging and uses a combination of EAZY photometric redshifts and Prospector SED fitting to derive $M_{ m UV}$, $β_{\rm UV}$, $M_*$, and SFR. The analysis reveals UV properties and a well-defined $M_*-{ m SFR}$ main sequence consistent with prior JWST field studies, and it characterizes galaxy sizes and the emergence of compact, dense systems, including a remarkably bright $z\sim13.7$ source with extreme $β_{\rm UV}$ and high $Σ_{\rm SFR}$. Three overdense $z\sim7$ regions are identified, yet no strong environmental dependence on galaxy properties is detected within the current sample, underscoring the need for an order-of-magnitude larger pure-parallel dataset to robustly test environmental effects at cosmic dawn.

Abstract

We present photometric properties of 161 galaxy candidates at $z=7-14$ selected from the second data release (DR2) of BEACON, a JWST Cycle 2 pure-parallel NIRCam imaging program. Carefully selected from 36 independent pointings (corresponding to $\sim350$\,arcmin$^2$ sky coverage), and hence with reduced cosmic variance, our galaxy candidates provide an unbiased sample for investigating galaxy properties over a wide range of environments. We measure the physical properties, including UV continuum slope ($β_{\rm UV}$), stellar mass ($M_*$), star formation rate (SFR), and sizes. Our highest redshift galaxy candidate at $z=13.71\pm0.15$ has a remarkably bright UV luminosity of $M_{\rm UV}=-21.19\pm0.08$, making it the brightest galaxy at $z>12$ if spectroscopically confirmed. With an extremely blue UV slope, compact morphology, and high star formation rate surface density ($Σ_{\rm SFR}$), this candidate may have extremely low metallicity, high ionizing photon escape fraction, or contributions from an AGN. Among our multiple independent sightlines, we identify three fields of galaxy number overdensity with $>3σ$ significance. The properties of galaxies in various environments do not exhibit significant differences, implying either that accelerated galaxy evolution in overdense regions is not yet widespread at $z>7$, or that the current constraints are limited by sample size. Our simulations indicate that increasing the sample by an order of magnitude would allow such environmental trends to be robustly confirmed or ruled out, underscoring the importance of future pure-parallel observations.

Figures (13)

• Figure 1: Top: Comparison between EAZY photometric redshift and spectroscopic redshift in our sample. The black solid line indicates one-to-one relation, while the grey shaded region shows the $|z_{\rm phot}-z_{\rm spec}|/(1+z_{\rm spec})<0.15$. Bottom: similar to the top panel, but for Prospector photometric redshift.
• Figure 2: Examples of our SED fitting results. In the top of each panel, we show the best-fit SEDs from EAZY and Prospector with grey and red curves, respectively. The red solid circles and black open squares indicate the photometry predicted from the best-fit SEDs and the observed photometry, respectively. The normalized residuals are presented in bottom of each panel, with the horizontal shaded region showing the $\pm2\sigma$ interval.
• Figure 3: Rest-frame UV and optical colors of our galaxy candidates at $z>7$ selected in Section \ref{['sec:sample']}. Red data points denote the five objects that are excluded due to their red optical color. The black dashed lines indicates the "little red dot" (LRD) selection criteria from greene24lrd and hainline25lrd.
• Figure 4: Left: histogram of $z_{\rm phot}$ distribution (top) and $M_{\rm UV}$ versus $z_{\rm phot}$ (bottom) for our sample. Objects with spectroscopic confirmation are marked with open red symbols and the red histogram. We also plot other spectroscopically confirmed galaxies at $z>10$ in the literature with green data points. Right: histograms of $M_{\rm UV}$ distributions for the F090 (top), F115 (middle), and F150W (bottom) -dropout galaxies.
• Figure 5: Left: $\beta_{\rm UV}$ versus $M_{\rm UV}$ for our sample of 161 $z\geq7$ galaxies, where the data points are color-coded by redshift. The median $\beta_{\rm UV}$ and its inner 68 percentile distribution in different $M_*$ bins are denoted with green open squares and error bars. The green solid line indicates our best-fit $M_{\rm UV}-\beta_{\rm UV}$ linear relation. The black dashed line shows the $M_{\rm UV}-\beta_{\rm UV}$ relation from topping24. Right: same as the left panel, but for $\beta_{\rm UV}$ versus $M_*$. The black dotted line shows the $M_*-\beta_{\rm UV}$ relation from finkelstein12.