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1. A Search for Faint Resolved Galaxies Beyond the Milky Way in DES Year 6: A New Faint, Diffuse Dwarf Satellite of NGC 55

   https://doi.org/10.3847/1538-4357/ad07d0  

   McNanna, M; Bechtol, K; Mau, S; Nadler, E O; Medoff, J; Drlica-Wagner, A; Cerny, W; Crnojević, D; Mutlu-Pakdıl, B; Vivas, A K; et al (January 2024, The Astrophysical Journal)

   Abstract We report results from a systematic wide-area search for faint dwarf galaxies at heliocentric distances from 0.3 to 2 Mpc using the full 6 yr of data from the Dark Energy Survey (DES). Unlike previous searches over the DES data, this search specifically targeted a field population of faint galaxies located beyond the Milky Way virial radius. We derive our detection efficiency for faint, resolved dwarf galaxies in the Local Volume with a set of synthetic galaxies and expect our search to be complete toM_V∼ (−7, −10) mag for galaxies atD= (0.3, 2.0) Mpc. We find no new field dwarfs in the DES footprint, but we report the discovery of one high-significance candidate dwarf galaxy at a distance of ${2.2}_{-0.12}^{+0.05}\mathrm{Mpc}$, a potential satellite of the Local Volume galaxy NGC 55, separated by 47′ (physical separation as small as 30 kpc). We estimate this dwarf galaxy to have an absoluteV-band magnitude of $-{8.0}_{-0.3}^{+0.5}\mathrm{mag}$and an azimuthally averaged physical half-light radius of ${2.2}_{-0.4}^{+0.5}\mathrm{kpc}$, making this one of the lowest surface brightness galaxies ever found with $\mu =32.3\mathrm{mag}{\mathrm{arcsec}}^{-2}$. This is the largest, most diffuse galaxy known at this luminosity, suggesting possible tidal interactions with its host. 

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2. TOI-5344 b: A Saturn-like Planet Orbiting a Super-solar Metallicity M0 Dwarf

   https://doi.org/10.3847/1538-3881/ad09c2  

   Han, Te; Robertson, Paul; Kanodia, Shubham; Cañas, Caleb; Lin, Andrea S.; Stefánsson, Gumundur; Libby-Roberts, Jessica E.; Larsen, Alexander; Kobulnicky, Henry A.; Mahadevan, Suvrath; et al (December 2023, The Astronomical Journal)

   Abstract We confirm the planetary nature of TOI-5344 b as a transiting giant exoplanet around an M0-dwarf star. TOI-5344 b was discovered with the Transiting Exoplanet Survey Satellite photometry and confirmed with ground-based photometry (the Red Buttes Observatory 0.6 m telescope), radial velocity (the Habitable-zone Planet Finder), and speckle imaging (the NN-Explore Exoplanet Stellar Speckle Imager). TOI-5344 b is a Saturn-like giant planet (ρ= 0.80 ${}_{-0.15}^{+0.17}$g cm⁻³) with a planetary radius of 9.7 ± 0.5R_⊕(0.87 ± 0.04R_Jup) and a planetary mass of ${135}_{-18}^{+17}{M}_{\oplus }$(0.42 ${}_{-0.06}^{+0.05}{M}_{\mathrm{Jup}}$). It has an orbital period of ${3.792622}_{-0.000010}^{+0.000010}$days and an orbital eccentricity of ${0.06}_{-0.04}^{+0.07}$. We measure a high metallicity for TOI-5344 of [Fe/H] = 0.48 ± 0.12, where the high metallicity is consistent with expectations from formation through core accretion. We compare the metallicity of the M-dwarf hosts of giant exoplanets to that of M-dwarf hosts of nongiants (≲8R_⊕). While the two populations appear to show different metallicity distributions, quantitative tests are prohibited by various sample caveats. 

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3. KMT-2023-BLG-1431Lb: A New q < 10 ⁻⁴ Microlensing Planet from a Subtle Signature

   https://doi.org/10.1088/1538-3873/ad48b8  

   Bell, Aislyn; Zhang, Jiyuan; Zang, Weicheng; Jung, Youn Kil; Yee, Jennifer C; Yang, Hongjing; Sumi, Takahiro; Udalski, Andrzej; Albrow, Michael D; Chung, Sun-Ju; et al (May 2024, Publications of the Astronomical Society of the Pacific)

   Abstract The current studies of microlensing planets are limited by small number statistics. Follow-up observations of high-magnification microlensing events can efficiently form a statistical planetary sample. Since 2020, the Korea Microlensing Telescope Network (KMTNet) and the Las Cumbres Observatory (LCO) global network have been conducting a follow-up program for high-magnification KMTNet events. Here, we report the detection and analysis of a microlensing planetary event, KMT-2023-BLG-1431, for which the subtle (0.05 mag) and short-lived (5 hr) planetary signature was characterized by the follow-up from KMTNet and LCO. A binary-lens single-source (2L1S) analysis reveals a planet/host mass ratio ofq= (0.72 ± 0.07) × 10⁻⁴, and the single-lens binary-source (1L2S) model is excluded by Δχ²= 80. A Bayesian analysis using a Galactic model yields estimates of the host star mass of $M_{\mathrm{host}}={0.57}_{-0.29}^{+0.33}{M}_{\odot }$, the planetary mass of $M_{\mathrm{planet}}={13.5}_{-6.8}^{+8.1}{M}_{\oplus }$, and the lens distance of $D_{\mathrm{L}}={6.9}_{-1.7}^{+0.8}$kpc. The projected planet-host separation of $a_{\perp }={2.3}_{-0.5}^{+0.5}$au or $a_{\perp }={3.2}_{-0.8}^{+0.7}$au, subject to the close/wide degeneracy. We also find that without the follow-up data, the survey-only data cannot break the degeneracy of central/resonant caustics and the degeneracy of 2L1S/1L2S models, showing the importance of follow-up observations for current microlensing surveys. 

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4. OGLE-2019-BLG-1180Lb: Discovery of a Wide-orbit Jupiter-mass Planet around a Late-type Star

   https://doi.org/10.3847/1538-3881/ad0723  

   Chung, Sun-Ju; Udalski, Andrzej; Yee, Jennifer C; Gould, Andrew; Albrow, Michael D; Jung, Youn Kil; Hwang, Kyu-Ha; Han, Cheongho; Ryu, Yoon-Hyun; Shin, In-Gu; et al (November 2023, The Astronomical Journal)

   Abstract We report on the discovery and analysis of the planetary microlensing event OGLE-2019-BLG-1180 with a planet-to-star mass ratioq∼ 0.003. The event OGLE-2019-BLG-1180 has unambiguous cusp-passing and caustic-crossing anomalies, which were caused by a wide planetary caustic withs≃ 2, wheresis the star–planet separation in units of the angular Einstein radiusθ_E. Thanks to well-covered anomalies by the Korea Micorolensing Telescope Network (KMTNet), we measure both the angular Einstein radius and the microlens parallax in spite of a relatively short event timescale oft_E= 28 days. However, because of a weak constraint on the parallax, we conduct a Bayesian analysis to estimate the physical lens parameters. We find that the lens system is a super-Jupiter-mass planet of $M_{\mathrm{p}}={1.75}_{-0.51}^{+0.53}{M}_{\mathrm{J}}$orbiting a late-type star of $M_{\mathrm{h}}={0.55}_{-0.26}^{+0.27}{M}_{\odot }$at a distance $D_{\mathrm{L}}={6.1}_{-1.3}^{+0.9}\mathrm{kpc}$. The projected star–planet separation is $a_{\perp }={5.19}_{-1.23}^{+0.90}\mathrm{au}$, which means that the planet orbits at about four times the snow line of the host star. Considering the relative lens–source proper motion ofμ_rel= 6 mas yr⁻¹, the lens will be separated from the source by 60 mas in 2029. At that time one can measure the lens flux from adaptive optics imaging of Keck or a next-generation 30 m class telescope. OGLE-2019-BLG-1180Lb represents a growing population of wide-orbit planets detected by KMTNet, so we also present a general investigation into prospects for further expanding the sample of such planets. 

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5. The Pan-STARRS1 z > 5.6 Quasar Survey. III. The z ≈ 6 Quasar Luminosity Function

   https://doi.org/10.3847/1538-4357/aca7ca  

   Schindler, Jan-Torge; Bañados, Eduardo; Connor, Thomas; Decarli, Roberto; Fan, Xiaohui; Farina, Emanuele Paolo; Mazzucchelli, Chiara; Nanni, Riccardo; Rix, Hans-Walter; Stern, Daniel; et al (January 2023, The Astrophysical Journal)

   Abstract We present thez≈ 6 type-1 quasar luminosity function (QLF), based on the Pan-STARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars atz≈ 5.7–6.2, with −28 ≲M₁₄₅₀≲ −25. With the addition of 48 fainter quasars from the SHELLQs survey, we evaluate thez≈ 6 QLF over −28 ≲M₁₄₅₀≲ −22. Adopting a double power law with an exponential evolution of the quasar density (Φ(z) ∝ 10^k(z−6);k= −0.7), we use a maximum likelihood method to model our data. We find a break magnitude of $M^{*}=-{26.38}_{-0.60}^{+0.79}\mathrm{mag}$, a faint-end slope of $\alpha =-{1.70}_{-0.19}^{+0.29}$, and a steep bright-end slope of $\beta =-{3.84}_{-1.21}^{+0.63}$. Based on our new QLF model, we determine the quasar comoving spatial density atz≈ 6 to be $n(M_{1450}<-26)={1.16}_{-0.12}^{+0.13}{\mathrm{cGpc}}^{-3}$. In comparison with the literature, we find the quasar density to evolve with a constant value ofk≈ −0.7, fromz≈ 7 toz≈ 4. Additionally, we derive an ionizing emissivity of ${ϵ}_{912}(z=6)={7.23}_{-1.02}^{+1.65}\times {10}^{22}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{Hz}}^{-1}{\mathrm{cMpc}}^{-3}$, based on the QLF measurement. Given standard assumptions, and the recent measurement of the mean free path by Becker et al. atz≈ 6, we calculate an Hiphotoionizing rate of Γ_{H I}(z= 6) ≈ 6 × 10⁻¹⁶s⁻¹, strongly disfavoring a dominant role of quasars in hydrogen reionization. 

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