A high incidence of dusty H$\alpha$ emitters at $z>3$ among UltraVISTA dropout galaxies in COSMOS revealed by JWST

Abstract

We have characterized 26 Spitzer/IRAC-selected sources from the SMUVS program that are undetected in the UltraVISTA DR5 H- and/or Ks-band images, covering 94 square arcmin of the COSMOS field which have deep multiwavelength JWST photometry. We analyzed the JWST/NIRCam imaging from the PRIMER survey and ancillary HST data to reveal the properties of these galaxies from spectral energy distribution (SED) fitting. We find that the majority of these galaxies are detected by NIRCam at <2 micron, with only four remaining as near-infrared dropouts in the deeper JWST images. Our results indicate that the UltraVISTA dropouts candidates are primarily located at z>3 and are characterized by high dust extinctions, with a typical color excess E(B-V) = 0.5 pm 0.3 and stellar mass log(M*/Msun) = 9.5 pm 1.0. Remarkably, ~75% of these sources show a flux enhancement between the observed photometry and modeled continuum SED that can be attributed to Halpha emission in the corresponding NIRCam bands. The derived (Halpha+ N[II] + S[II]) rest-frame equivalent widths and Halpha star formation rates (SFRs) span values ~100-2200 A and ~5-375 Msun/yr, respectively. The location of these sources on the SFR-M* plane indicates that 35% of them are starbursts, 40% are main-sequence galaxies and the remaining 25% are located in the star-formation valley. Our sample includes one active galactic nucleus and six submillimeter sources, as revealed from ancillary X-ray and submillimeter photometry. The high dust extinctions combined with the flux boosting from Halpha emission explain why these sources are relatively bright Spitzer galaxies and yet unidentified in the ultradeep UltraVISTA near-infrared images.