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We calibrate and validate different methods of rest-frame color-color selection to identify galaxies in active star-forming and quiescent stages of their evolution. Our method is similar to the widely-used UVJ color-color diagram, which is an effective way to distinguish between quiescent and star-forming galaxies using their rest-frame U-V and V-J colors. UVJ colors suffer known systematics, and at z > 4 the method must be extrapolated because the rest-frame J-band moves beyond the coverage of the deepest bandpasses (typically IRAC 4.5 µm). This leads to biases: for example, spectroscopic campaigns have shown that UVJ-quiescent samples include ~10-30% contamination from galaxies with significant amounts of star formation. Alternative selection methods will be important not just to mitigate these biases, but also in the JWST era where NIRCam coverage is also limited to ~5 µm . In this poster, we present calibrations of alternative rest-frame filter combinations that are applicable for galaxies at redshifts z = 4 - 6. We apply our method to a stellar mass-limited sample of galaxies at 4 < z < 6 from the FLAMINGOS-2 Extragalactic Near-Infrared K-Split (FENIKS) survey. FENIKS is a deep (23.1 - 24.5 AB mag) survey employing two novel filters which split the Ks band ( λc = 2.2 µm) K-blue and K-red filters ( λc = 1.9 and 2.3 µm, respectively), allowing for finer sampling of the Balmer/4000 Å break of galaxies with evolved populations. We quantify the improvement in the selection of quiescent and star-forming galaxies using the alternative color-color selection methods. Furthermore, we investigate correlations between galaxy properties and their rest-frame colors, in particular examining purity and completeness of these selection methods. Finally, we explore the above for a wide range of synthetic filter combinations to inform accurate selections of various galaxy populations and rule out unphysical areas of parameter space for these populations.
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The FENIKS Survey: Spectroscopic Confirmation of Massive Quiescent Galaxies at z~3-5
The measured ages of massive, quiescent galaxies at z∼3-4 imply that massive galaxies quench as early as z~6. While the number of spectroscopic confirmations of quiescent galaxies at z<3 has increased over the years, there are only a handful at z> 3.5. We report spectroscopic redshifts of one secure (z=3.757) and two tentative (z=3.336 and z=4.673) massive quiescent galaxies with 11 hr of Keck/MOSFIRE K-band observations. Our candidates were selected from the FLAMINGOS-2 Extragalactic Near-Infrared K-band Split (FENIKS) survey, which uses deep Gemini/Flamingos-2 Kb/Kr imaging optimized for increased sensitivity to the characteristic red colors of galaxies at z>3 with a strong Balmer/4000 Å break. The rest-frame UVJ and ugi colors of three out of four quiescent candidates are consistent with 1-2 Gyr old stellar populations. This places these galaxies as the oldest objects at these redshifts, and challenges the notion that quiescent galaxies at z>3 are all recently quenched, post-starburst galaxies. Our spectroscopy shows that the other quiescent-galaxy candidate is a broad-line active galactic nucleus (z=3.594) with strong, redshifted Hbeta+[OIII] emission with a velocity offset >1000 km/s, indicative of a powerful outflow. The star formation history of our highest redshift candidate suggests that its progenitor was already in place by z~7-11, reaching ∼10^11 M⊙ by z~8. These observations reveal the limit of what is possible with deep near-infrared photometry and targeted spectroscopy from the ground and demonstrate that secure spectroscopic confirmation of quiescent galaxies at z>4 is feasible only with JWST.
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- PAR ID:
- 10562794
- Publisher / Repository:
- The Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 978
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 90
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/ad8b30
