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1. The Galaxy–Halo Connection of DESI Luminous Red Galaxies with Subhalo Abundance Matching

   https://doi.org/10.3847/1538-4357/ace76e  

   Berti, Angela M; Dawson, Kyle S; Dominguez, Wilber (August 2023, The Astrophysical Journal)

   Abstract We use subhalo abundance and age distribution matching to create magnitude-limited mock galaxy catalogs atz∼ 0.43, 0.52, and 0.63 withz-band and 3.4μmW1-band absolute magnitudes andr−zandr−W1 colors. From these magnitude-limited mocks, we select mock luminous red galaxy (LRG) samples according to the (r−z)-based (optical) and (r−W1)-based (infrared) selection criteria for the LRG sample of the Dark Energy Spectroscopic Instrument (DESI) survey. Our models reproduce the number densities, luminosity functions, color distributions, and projected clustering of the DESI Legacy Surveys that are the basis for DESI LRG target selection. We predict the halo occupation statistics of both optical and IR DESI LRGs at fixed cosmology and assess the differences between the two LRG samples. We find that IR-based SHAM modeling represents the differences between the optical and IR LRG populations better than using thezband and that age distribution matching overpredicts the clustering of LRGs, implying that galaxy color is uncorrelated with halo age in the LRG regime. Both the optical and IR DESI LRG target selections exclude some of the most luminous galaxies that would appear to be LRGs based on their position on the red sequence in optical color–magnitude space. Both selections also yield populations with a nontrivial LRG–halo connection that does not reach unity for the most massive halos. We find that the IR selection achieves greater completeness (≳90%) than the optical selection across all redshift bins studied. 

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2. Beyond UVJ: Color Selection of Galaxies at z > 3

   Antwi-Danso, J. Papovich (January 2021, Bulletin of the American Astronomical Society)

   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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3. A Southern Photometric Quasar Catalog from the Dark Energy Survey Data Release 2

   https://doi.org/10.3847/1538-4365/ac9ea8  

   Yang, Qian; Shen, Yue (December 2022, The Astrophysical Journal Supplement Series)

   Abstract We present a catalog of 1.4 million photometrically selected quasar candidates in the southern hemisphere over the ∼5000 deg²Dark Energy Survey (DES) wide survey area. We combine optical photometry from the DES second data release (DR2) with available near-infrared (NIR) and the all-sky unWISE mid-infrared photometry in the selection. We build models of quasars, galaxies, and stars with multivariate skew-tdistributions in the multidimensional space of relative fluxes as functions of redshift (or color for stars) and magnitude. Our selection algorithm assigns probabilities for quasars, galaxies, and stars and simultaneously calculates photometric redshifts (photo-z) for quasar and galaxy candidates. Benchmarking on spectroscopically confirmed objects, we successfully classify (with photometry) 94.7% of quasars, 99.3% of galaxies, and 96.3% of stars when all IR bands (NIRYJHKand WISE W1W2) are available. The classification and photo-zregression success rates decrease when fewer bands are available. Our quasar (galaxy) photo-zquality, defined as the fraction of objects with the difference between the photo-z z_pand the spectroscopic redshiftz_s, ∣Δz∣ ≡ ∣z_s−z_p∣/(1 +z_s) ≤ 0.1, is 92.2% (98.1%) when all IR bands are available, decreasing to 72.2% (90.0%) using optical DES data only. Our photometric quasar catalog achieves an estimated completeness of 89% and purity of 79% atr< 21.5 (0.68 million quasar candidates), with reduced completeness and purity at 21.5 <r≲ 24. Among the 1.4 million quasar candidates, 87,857 have existing spectra, and 84,978 (96.7%) of them are spectroscopically confirmed quasars. Finally, we provide quasar, galaxy, and star probabilities for all (0.69 billion) photometric sources in the DES DR2 coadded photometric catalog. 

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4. Beyond UVJ: Color Selection of Galaxies in the JWST Era

   https://doi.org/10.3847/1538-4357/aca294  

   Antwi-Danso, Jacqueline; Papovich, Casey; Leja, Joel; Marchesini, Danilo; Marsan, Z C; Martis, Nicholas S.; Labbe, Ivo; Muzzin, Adam; Glazebrook, Karl; Straatman, Caroline M.; et al (February 2023, The Astrophysical journal)

   We present a new rest-frame color–color selection method using synthetic us − gs and gs − is, (ugi)s colors to identify star-forming and quiescent galaxies. Our method is similar to the widely used U − V versus V − J (UVJ) diagram. However, UVJ suffers known systematics. Spectroscopic campaigns have shown that UVJ-selected quiescent samples at z ≳ 3 include ∼10%–30% contamination from galaxies with dust-obscured star formation and strong emission lines. Moreover, at z > 3, UVJ colors are extrapolated because the rest-frame band shifts beyond the coverage of the deepest bandpasses at <5 μm (typically Spitzer/IRAC 4.5 μm or future JWST/NIRCam observations). We demonstrate that (ugi)s offers improvements to UVJ at z > 3, and can be applied to galaxies in the JWST era. We apply (ugi)s selection to galaxies at 0.5 < z < 6 from the (observed) 3D-HST and UltraVISTA catalogs, and to the (simulated) JAGUAR catalogs. We show that extrapolation can affect (V − J)0 color by up to 1 mag, but changes $${({g}_{s}-{i}_{s})}_{0}$$ color by ≤0.2 mag, even at z ≃ 6. While (ugi)s-selected quiescent samples are comparable to UVJ in completeness (both achieve ∼85%–90% at z = 3–3.5), (ugi)s reduces contamination in quiescent samples by nearly a factor of 2, from ≃35% to ≃17% at z = 3, and from ≃60% to ≃33% at z = 6. This leads to improvements in the true-to-false-positive ratio (TP/FP), where we find TP/FP ≳2.2 for (ugi)s at z ≃ 3.5 − 6, compared to TP/FP < 1 for UVJ-selected samples. This indicates that contaminants will outnumber true quiescent galaxies in UVJ at these redshifts, while (ugi)s will provide higher-fidelity samples. 

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5. JWST's PEARLS: Bright 1.5–2.0 μm Dropouts in the Spitzer/IRAC Dark Field

   https://doi.org/10.3847/2041-8213/aca974  

   Yan, Haojing; Cohen, Seth H.; Windhorst, Rogier A.; Jansen, Rolf A.; Ma, Zhiyuan; Beacom, John F.; Ling, Chenxiaoji; Cheng, Cheng; Huang, Jia-Sheng; Grogin, Norman A.; et al (December 2022, The Astrophysical Journal Letters)

   Abstract Using the first epoch of four-band NIRCam observations obtained by the James Webb Space Telescope (JWST) Prime Extragalactic Areas for Reionization and Lensing Science Program in the Spitzer IRAC Dark Field, we search for F150W and F200W dropouts. In 14.2 arcmin², we have found eight F150W dropouts and eight F200W dropouts, all brighter than 27.5 mag (the brightest being ∼24 mag) in the band to the red side of the break. As they are detected in multiple bands, these must be real objects. Their nature, however, is unclear, and characterizing their properties is important for realizing the full potential of JWST. If the observed color decrements are due to the Lyman break, these objects should be atz≳ 11.7 andz≳ 15.4, respectively. The color diagnostics show that at least four F150W dropouts are far away from the usual contaminators encountered in dropout searches (red galaxies at much lower redshifts or brown dwarf stars). While the diagnostics of the F200W dropouts are less certain due to the limited number of passbands, at least one of them is likely not a known type of contaminant, and the rest are consistent with either high-redshift galaxies with evolved stellar populations or old galaxies atz≈ 3–8. If a significant fraction of our dropouts are indeed atz≳ 12, we have to face the severe problem of explaining their high luminosities and number densities. Spectroscopic identifications of such objects are urgently needed. 

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