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1. A search for high-redshift direct-collapse black hole candidates in the PEARLS north ecliptic pole field

   https://doi.org/10.1051/0004-6361/202347724  

   Nabizadeh, Armin; Zackrisson, Erik; Pacucci, Fabio; Peter_Maksym, Walter; Li, Weihui; Civano, Francesca; Cohen, Seth H; D’Silva, Jordan_C J; Koekemoer, Anton M; Summers, Jake; et al (March 2024, Astronomy & Astrophysics)

   Direct-collapse black holes (DCBHs) of mass ∼10⁴ − 10⁵ M_⊙that form in HI-cooling halos in the early Universe are promising progenitors of the ≳10⁹ M_⊙supermassive black holes that fuel observedz ≳ 7 quasars. Efficient accretion of the surrounding gas onto such DCBH seeds may render them sufficiently bright for detection with the JWST up toz ≈ 20. Additionally, the very steep and red spectral slope predicted across the ≈1 − 5 μm wavelength range of the JWST/NIRSpec instrument during their initial growth phase should make them photometrically identifiable up to very high redshifts. In this work, we present a search for such DCBH candidates across the 34 arcmin²in the first two spokes of the JWST cycle-1 PEARLS survey of the north ecliptic pole time-domain field covering eight NIRCam filters down to a maximum depth of ∼29 AB mag. We identify two objects with spectral energy distributions consistent with theoretical DCBH models. However, we also note that even with data in eight NIRCam filters, objects of this type remain degenerate with dusty galaxies and obscured active galactic nuclei over a wide range of redshifts. Follow-up spectroscopy would be required to pin down the nature of these objects. Based on our sample of DCBH candidates and assumptions on the typical duration of the DCBH steep-slope state, we set a conservative upper limit of ≲5 × 10⁻⁴comoving Mpc⁻³(cMpc⁻³) on the comoving density of host halos capable of hosting DCBHs with spectral energy distributions similar to the theoretical models atz ≈ 6 − 14. 

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2. JWST View of Four Infant Galaxies at z = 8.31–8.49 in the MACS J0416.1−2403 Field and Implications for Reionization

   https://doi.org/10.3847/1538-4357/ad7b32  

   Ma, Zhiyuan; Sun, Bangzheng; Cheng, Cheng; Yan, Haojing; Ling, Chenxiaoji; Sun, Fengwu; Foo, Nicholas; Egami, Eiichi; Diego, José M; Cohen, Seth H; et al (October 2024, The Astrophysical Journal)

   Abstract New JWST/NIRCam wide-field slitless spectroscopy provides redshifts for fourz> 8 galaxies located behind the lensing cluster MACS J0416.1−2403. Two of them, “Y1” and “JD,” have previously reported spectroscopic redshifts based on Atacama Large Millimeter/submillimeter Array measurements of [Oiii] 88μm and/or [Cii] 157.7μm lines. Y1 is a merging system of three components, and the existing redshiftz= 8.31 is confirmed. However, JD is atz= 8.34 instead of the previously claimedz= 9.28. JD’s close companion, “JD-N,” which was a previously discoveredz> 8 candidate, is now identified at the same redshift as JD. JD and JD-N form an interacting pair. A new candidate atz> 8, “f090d_018,” is also confirmed and is atz= 8.49. These four objects are likely part of an overdensity that signposts a large structure extending ∼165 kpc in projected distance and ∼48.7 Mpc in radial distance. They are magnified by less than 1 mag and have an intrinsicM_UVranging from −19.57 to −20.83 mag. Their spectral energy distributions show that the galaxies are all very young with ages ∼ 4–18 Myr and stellar masses of about 10^7–8M_⊙. These infant galaxies have very different star formation rates ranging from a few to over a hundred solar masses per year, but only two of them (JD and f090d_018) have blue rest-frame UV slopesβ< −2.0 indicative of a high Lyman-continuum photon escape fraction that could contribute significantly to the cosmic hydrogen-reionizing background. Interestingly, these two galaxies are the least massive and least active ones among the four. The other two systems have much flatter UV slopes largely because of their high dust extinction (A_V= 0.9–1.0 mag). Their much lower indicated escape fractions show that even very young, actively star-forming galaxies can have a negligible contribution to reionization when they quickly form dust throughout their bodies. 

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3. Tip of the Red Giant Branch Distances with JWST. II. I-band Measurements in a Sample of Hosts of 10 Type Ia Supernova Match HST Cepheids

   https://doi.org/10.3847/1538-4357/ad84f3  

   Li, Siyang; Anand, Gagandeep S; Riess, Adam G; Casertano, Stefano; Yuan, Wenlong; Breuval, Louise; Macri, Lucas M; Scolnic, Daniel; Beaton, Rachael; Anderson, Richard I (November 2024, The Astrophysical Journal)

   Abstract The Hubble Tension, a >5σdiscrepancy between direct and indirect measurements of the Hubble constant (H₀), has persisted for a decade and motivated intense scrutiny of the paths used to inferH₀. Comparing independently derived distances for a set of galaxies with different standard candles, such as the tip of the red giant branch (TRGB) and Cepheid variables, can test for systematics in the middle rung of the distance ladder. TheIband is the preferred filter for measuring the TRGB due to constancy with color, a result of low sensitivity to population differences in age and metallicity supported by stellar models. We use James Webb Space Telescope (JWST) observations with the maser host NGC 4258 as our geometric anchor to measureI-band (F090W versus F090W − F150W) TRGB distances to eight hosts of 10 Type Ia supernovae (SNe Ia) within 28 Mpc: NGC 1448, NGC 1559, NGC 2525, NGC 3370, NGC 3447, NGC 5584, NGC 5643, and NGC 5861. We compare these with Hubble Space Telescope (HST) Cepheid-based relative distance moduli for the same galaxies and anchor. We find no evidence of a difference between their weighted means, 0.01 ± 0.04 (stat) ± 0.04 (sys) mag. We produce 14 variants of the TRGB analysis, altering the smoothing level and color range used to measure the tips to explore their impact. For some hosts, this changes the identification of the strongest peak, but this causes little change to the sample mean difference, producing a full range of 0.00–0.02 mag, all consistent at 1σwith no difference. The result matches past comparisons ofI-band TRGB and Cepheids when both use HST. SNe and anchor samples observed with JWST are too small to yield a measure ofH₀that is competitive with the HST sample of 42 SNe Ia and 4 anchors; however, they already provide a vital systematic cross-check to HST measurements of the distance ladder. 

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4. JWST Photometry of Globular Cluster Populations in MACS0417.5−1154

   https://doi.org/10.3847/1538-4357/ae073f  

   Harris, William E; Reina-Campos, Marta; Keatley, Kaitlyn E; Bradač, Maruša; Martis, Nicholas S; Muzzin, Adam; Noirot, Gaël; Sarrouh, Ghassan_T E; Sawicki, Marcin; Willott, Chris J; et al (November 2025, The Astrophysical Journal)

   Deep JWST imaging of the massive galaxy cluster MACS0417.5−1154, at redshiftz= 0.443, reveals a huge population of globular clusters (GCs) and ultracompact dwarfs (UCDs) primarily distributed around its single central giant brightest cluster galaxy (BCG). We present Near-Infrared Camera (NIRCam)/short-wavelength channel photometry of the GC system in four bands (F090W, F115W, F150W, and F200W). The spatial distribution of the system matches well in radial and ellipticity profile with the high elongation (b/a ≃ 0.5) of the BCG halo light. The total GC population within MACS0417 is estimated to be near 1.5 × 10⁵, similar to the systems in Abell 2744, Coma, and other galaxy clusters with comparable masses. With similar results for GC photometry in hand from other lensing clusters at a range of redshifts, it is now possible to trace, on purely observational grounds, the luminosity evolution of GC systems over many gigayears of lookback time, as seen through their color–magnitude diagrams. We show this sequence for five systems reaching lookback times of more than 7 Gyr. A systematic change in the GC/UCD sequence with lookback time is clearly visible, near what is expected for age-fading of a simple stellar population with time. Lastly, we evaluate the effectiveness of the various JWST NIRCam filters for broadband photometry of GC systems as a function of redshift as an aid to planning further studies. 

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5. 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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