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1. 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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2. Exploring the Mpc Environment of the Quasar ULAS J1342+0928 at z = 7.54

   https://doi.org/10.3847/1538-4357/ad3bab  

   Rojas-Ruiz, Sofía; Mazzucchelli, Chiara; Finkelstein, Steven L; Bañados, Eduardo; Farina, Emanuele Paolo; Venemans, Bram P; Decarli, Roberto; Willott, Chris J; Wang, Feige; Walter, Fabian; et al (May 2024, The Astrophysical Journal)

   Abstract Theoretical models predict thatz≳ 6 quasars are hosted in the most massive halos of the underlying dark matter distribution and thus would be immersed in protoclusters of galaxies. However, observations report inconclusive results. We investigate the 1.1 proper-Mpc²environment of thez= 7.54 luminous quasar ULAS J1342+0928. We search for Lyman-break galaxy (LBG) candidates using deep imaging from the Hubble Space Telescope (HST) in the Advanced Camera for Surveys (ACS)/F814W, Wide Field Camera 3 (WFC3)/F105W/F125W bands, and Spitzer/Infrared Array Camera at 3.6 and 4.5μm. We report a $z_{\mathrm{phot}}={7.69}_{-0.23}^{+0.33}$LBG with mag_F125W= 26.41 at 223 projected proper kpc (pkpc) from the quasar. We find no HST counterpart to one [Cii] emitter previously found with the Atacama Large millimeter/submillimeter Array (ALMA) at 27 projected pkpc andz_{[C II]}=7.5341 ± 0.0009 (Venemans et al. 2020). We estimate the completeness of our LBG candidates using results from Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey/GOODS deep blank field searches sharing a similar filter setup. We find that >50% of thez∼ 7.5 Lyman-break galaxies (LBGs) with mag_F125W> 25.5 are missed due to the absence of a filter redward of the Lyman break in F105W, hindering the UV color accuracy of the candidates. We conduct a QSO-LBG clustering analysis revealing a low LBG excess of ${0.46}_{-0.08}^{+1.52}$in this quasar field, consistent with an average or low-density field. Consequently, this result does not present strong evidence of an LBG overdensity around ULAS J1342+0928. Furthermore, we identify two LBG candidates with az_photmatching a confirmedz= 6.84 absorber along the line of sight to the quasar. All these galaxy candidates are excellent targets for follow-up observations with JWST and/or ALMA to confirm their redshift and physical properties. 

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3. Mapping Obscuration to Reionization with ALMA (MORA): 2 mm Efficiently Selects the Highest-redshift Obscured Galaxies

   https://doi.org/10.3847/1538-4357/ac2eb4  

   Casey, Caitlin M.; Zavala, Jorge A.; Manning, Sinclaire M.; Aravena, Manuel; Béthermin, Matthieu; Caputi, Karina I.; Champagne, Jaclyn B.; Clements, David L.; Drew, Patrick; Finkelstein, Steven L.; et al (December 2021, The Astrophysical Journal)

   Abstract We present the characteristics of 2 mm selected sources from the largest Atacama Large Millimeter/submillimeter Array (ALMA) blank-field contiguous survey conducted to date, the Mapping Obscuration to Reionization with ALMA (MORA) survey covering 184 arcmin²at 2 mm. Twelve of 13 detections above 5σare attributed to emission from galaxies, 11 of which are dominated by cold dust emission. These sources have a median redshift of $〈z_{2\mathrm{mm}}〉={3.6}_{-0.3}^{+0.4}$primarily based on optical/near-infrared photometric redshifts with some spectroscopic redshifts, with 77% ± 11% of sources atz> 3 and 38% ± 12% of sources atz> 4. This implies that 2 mm selection is an efficient method for identifying the highest-redshift dusty star-forming galaxies (DSFGs). Lower-redshift DSFGs (z< 3) are far more numerous than those atz> 3 yet are likely to drop out at 2 mm. MORA shows that DSFGs with star formation rates in excess of 300M_⊙yr⁻¹and a relative rarity of ∼10⁻⁵Mpc⁻³contribute ∼30% to the integrated star formation rate density at 3 <z< 6. The volume density of 2 mm selected DSFGs is consistent with predictions from some cosmological simulations and is similar to the volume density of their hypothesized descendants: massive, quiescent galaxies atz> 2. Analysis of MORA sources’ spectral energy distributions hint at steeper empirically measured dust emissivity indices than reported in typical literature studies, with $〈\beta 〉={2.2}_{-0.4}^{+0.5}$. The MORA survey represents an important step in taking census of obscured star formation in the universe’s first few billion years, but larger area 2 mm surveys are needed to more fully characterize this rare population and push to the detection of the universe’s first dusty galaxies. 

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4. Strong-lensing Analysis of SPT-CL J2325−4111 and SPT-CL J0049−2440, Two Powerful Cosmic Telescopes ( R _E > 40″) from the SPT Clusters Sample

   https://doi.org/10.3847/1538-4357/ad9aa5  

   Mahler, Guillaume; Sharon, Keren; Bayliss, Matthew; Bleem, Lindsey E; Brodwin, Mark; Floyd, Benjamin; Gassis, Raven; Gladders, Michael D; Khullar, Gourav; Remolina_González, Juan D; et al (February 2025, The Astrophysical Journal)

   Abstract We report the results from a study of two massive (M_500c> 6.0 × 10¹⁴M_⊙) strong-lensing clusters selected from the South Pole Telescope cluster survey for their large Einstein radius (R_E> 40″), SPT-CL J2325−4111 and SPT-CL J0049−2440. Ground-based and shallow Hubble Space Telescope (HST) imaging indicated extensive strong-lensing evidence in these fields, with giant arcs spanning 18″ and 31″, respectively, motivating further space-based imaging follow-up. Here, we present multiband HST imaging and ground-based Magellan spectroscopy of the fields, from which we compile detailed strong-lensing models. The lens models of SPT-CL J2325−4111 and SPT-CL J0049−2440 were optimized using nine and eight secure multiply imaged systems with a final image-plane rms of 0 $\stackrel{″}{.}$63 and 0 $\stackrel{″}{.}$73, respectively. From the lensing analysis, we measure a projected mass density within 500 kpc ofM(<500 kpc) = (7.30 ± 0.07) × 10¹⁴M_⊙and $M(<500\mathrm{kpc})=7.12_{-0.19}^{+0.16}\times 10^{14}$M_⊙for these two clusters, and subhalo mass ratios of 0.12 ± 0.01 and $0.21_{-0.05}^{+0.07}$, respectively. Both clusters produce a large area with high magnification (μ≥ 3) for a source atz= 9, ${\mathcal{A}}_{\left|\mu \right|\ge 3}^{\mathrm{lens}}=4.93_{-0.04}^{+0.03}$arcmin²and ${\mathcal{A}}_{\left|\mu \right|\ge 3}^{\mathrm{lens}}=3.64_{-0.10}^{+0.14}$arcmin², respectively, placing them in the top tier of strong-lensing clusters. We conclude that these clusters are spectacular sightlines for further observations that will reduce the systematic uncertainties due to cosmic variance. This paper provides the community with two additional well-calibrated cosmic telescopes, as strong as the Frontier Fields and suitable for studies of the highly magnified background Universe. 

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5. Constraining the Properties of Black Hole Seeds from the Farthest Quasars

   https://doi.org/10.3847/2041-8213/ad09e5  

   Fragione, Giacomo; Pacucci, Fabio (November 2023, The Astrophysical Journal Letters)

   Abstract Over 60 yr after the discovery of the first quasar, more than 275 such sources are identified in the epoch of reionization atz> 6. JWST is now exploring higher redshifts (z≳ 8) and lower-mass (≲10⁷M_⊙) ranges. The discovery of progressively farther quasars is instrumental to constraining the properties of the first population of black holes (BHs), or BH seeds, formed atz∼ 20–30. For the first time, we use Bayesian analysis of the most comprehensive catalog of quasars atz> 6 to constrain the distribution of BH seeds. We show that the mass distribution of BH seeds can be effectively described by combining a power law and a lognormal function tailored to the mass ranges associated with light and heavy seeds, assuming Eddington-limited growth and early seeding time. Our analysis reveals a power-law slope of $-{0.70}_{-0.46}^{+0.46}$and a lognormal mean of ${4.44}_{-0.30}^{+0.30}$. The inferred values of the Eddington ratio, the duty cycle, and the mean radiative efficiency are ${0.82}_{-0.10}^{+0.10}$, ${0.66}_{-0.23}^{+0.23}$, and ${0.06}_{-0.02}^{+0.02}$, respectively. Models that solely incorporate a power law or a lognormal distribution within the specific mass range corresponding to light and heavy seeds are statistically strongly disfavored, unlike models not restricted to this specific range. Our results suggest that including both components is necessary to comprehensively account for the masses of high-redshift quasars, and that both light and heavy seeds formed in the early Universe and grew to form the population of quasars we observe. 

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