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1. Resolved Measurements of the CO-to-H ₂ Conversion Factor in 37 Nearby Galaxies

   https://doi.org/10.3847/1538-4357/ad23ed  

   Chiang 江, I-Da 宜達; Sandstrom, Karin M.; Chastenet, Jérémy; Bolatto, Alberto D.; Koch, Eric W.; Leroy, Adam K.; Sun 孙, Jiayi 嘉懿; Teng, Yu-Hsuan; Williams, Thomas G. (March 2024, The Astrophysical Journal)

   Abstract We measure the CO-to-H₂conversion factor (α_CO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofα_COfor CO (2–1) and (1–0), respectively. The mean values forα_{CO (2–1)}andα_{CO (1–0)}are ${9.3}_{-5.4}^{+4.6}$and ${4.2}_{-2.0}^{+1.9}{M}_{\odot }{\mathrm{pc}}^{-2}{\left(\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1}\right)}^{-1}$, respectively. The CO-intensity-weighted mean is 5.69 forα_{CO (2–1)}and 3.33 forα_{CO (1–0)}. We examine howα_COscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ( $\overline{U}$). Among them, $\overline{U}$, Σ_SFR, and the integrated CO intensity (W_CO) have the strongest anticorrelation with spatially resolvedα_CO. We provide linear regression results toα_COfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenα_COandW_CO, metallicity, $\overline{U}$, and Σ_SFR. We also find thatα_COin each galaxy decreases with the stellar mass surface density (Σ_⋆) in high-surface-density regions (Σ_⋆≥ 100M_⊙pc⁻²), following the power-law relations ${\alpha }_{\mathrm{CO}(2–1)}\propto {\mathrm{\Sigma }}_{\star }^{-0.5}$and ${\alpha }_{\mathrm{CO}(1–0)}\propto {\mathrm{\Sigma }}_{\star }^{-0.2}$. The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inα_COwith increasing Σ_⋆as a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inα_CO. The decrease inα_COat high Σ_⋆is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors. 

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2. What Does the Geometry of the Hβ BLR Depend On?

   https://doi.org/10.3847/1538-4357/accc84  

   Villafaña, Lizvette; Williams, Peter R.; Treu, Tommaso; Brewer, Brendon J.; Barth, Aaron J.; U, Vivian; Bennert, Vardha N.; Guo, Hengxiao; Bentz, Misty C.; Canalizo, Gabriela; et al (May 2023, The Astrophysical Journal)

   Abstract We combine our dynamical modeling black-hole mass measurements from the Lick AGN Monitoring Project 2016 sample with measured cross-correlation time lags and line widths to recover individual scale factors,f, used in traditional reverberation-mapping analyses. We extend our sample by including prior results from Code for AGN Reverberation and Modeling of Emission Lines (caramel) studies that have utilized our methods. Aiming to improve the precision of black-hole mass estimates, as well as uncover any regularities in the behavior of the broad-line region (BLR), we search for correlations betweenfand other AGN/BLR parameters. We find (i) evidence for a correlation between the virial coefficient ${\log }_{10}\left(f_{\mathrm{mean},\sigma }\right)$and black-hole mass, (ii) marginal evidence for a similar correlation between ${\log }_{10}\left(f_{\mathrm{rms},\sigma }\right)$and black-hole mass, (iii) marginal evidence for an anticorrelation of BLR disk thickness with ${\log }_{10}\left(f_{\mathrm{mean},\mathrm{FWHM}}\right)$and ${\log }_{10}\left(f_{\mathrm{rms},\mathrm{FWHM}}\right)$, and (iv) marginal evidence for an anticorrelation of inclination angle with ${\log }_{10}\left(f_{\mathrm{mean},\mathrm{FWHM}}\right)$, ${\log }_{10}\left(f_{\mathrm{rms},\sigma }\right)$, and ${\log }_{10}\left(f_{\mathrm{mean},\sigma }\right)$. Last, we find marginal evidence for a correlation between line-profile shape, when using the root-mean-square spectrum, ${\log }_{10}{\left(\mathrm{FWHM}/\sigma \right)}_{\mathrm{rms}}$, and the virial coefficient, ${\log }_{10}\left(f_{\mathrm{rms},\sigma }\right)$, and investigate how BLR properties might be related to line-profile shape usingcaramelmodels. 

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3. The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters

   https://doi.org/10.3847/1538-4357/acff5f  

   Madhavacheril, Mathew S.; Qu, Frank J.; Sherwin, Blake D.; MacCrann, Niall; Li, Yaqiong; Abril-Cabezas, Irene; Ade, Peter A. R.; Aiola, Simone; Alford, Tommy; Amiri, Mandana; et al (February 2024, The Astrophysical Journal)

   Abstract We present cosmological constraints from a gravitational lensing mass map covering 9400 deg²reconstructed from measurements of the cosmic microwave background (CMB) made by the Atacama Cosmology Telescope (ACT) from 2017 to 2021. In combination with measurements of baryon acoustic oscillations and big bang nucleosynthesis, we obtain the clustering amplitudeσ₈= 0.819 ± 0.015 at 1.8% precision, $S_8\equiv {\sigma }_8{\left({\mathrm{\Omega }}_{\mathrm{m}}/0.3\right)}^{0.5}=0.840\pm 0.028$, and the Hubble constantH₀= (68.3 ± 1.1) km s⁻¹Mpc⁻¹at 1.6% precision. A joint constraint with Planck CMB lensing yieldsσ₈= 0.812 ± 0.013, $S_8\equiv {\sigma }_8{\left({\mathrm{\Omega }}_{\mathrm{m}}/0.3\right)}^{0.5}=0.831\pm 0.023$, andH₀= (68.1 ± 1.0) km s⁻¹Mpc⁻¹. These measurements agree with ΛCDM extrapolations from the CMB anisotropies measured by Planck. We revisit constraints from the KiDS, DES, and HSC galaxy surveys with a uniform set of assumptions and find thatS₈from all three are lower than that from ACT+Planck lensing by levels ranging from 1.7σto 2.1σ. This motivates further measurements and comparison, not just between the CMB anisotropies and galaxy lensing but also between CMB lensing probingz∼ 0.5–5 on mostly linear scales and galaxy lensing atz∼ 0.5 on smaller scales. We combine with CMB anisotropies to constrain extensions of ΛCDM, limiting neutrino masses to ∑m_ν< 0.13 eV (95% c.l.), for example. We describe the mass map and related data products that will enable a wide array of cross-correlation science. Our results provide independent confirmation that the universe is spatially flat, conforms with general relativity, and is described remarkably well by the ΛCDM model, while paving a promising path for neutrino physics with lensing from upcoming ground-based CMB surveys. 

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4. Stellar Metallicities and Gradients in the Faint M31 Satellites Andromeda XVI and Andromeda XXVIII

   https://doi.org/10.3847/1538-4357/ad76a2  

   Fu, Sal_Wanying; Weisz, Daniel_R; Starkenburg, Else; Martin, Nicolas; Collins, Michelle_L_M; Savino, Alessandro; Boylan-Kolchin, Michael; Côté, Patrick; Dolphin, Andrew_E; Longeard, Nicolas; et al (October 2024, The Astrophysical Journal)

   Abstract We present ∼300 stellar metallicity measurements in two faint M31 dwarf galaxies, Andromeda XVI (M_V= −7.5) and Andromeda XXVIII (M_V= –8.8), derived using metallicity-sensitive calcium H and K narrowband Hubble Space Telescope imaging. These are the first individual stellar metallicities in And XVI (95 stars). Our And XXVIII sample (191 stars) is a factor of ∼15 increase over literature metallicities. For And XVI, we measure $〈\mathrm{[Fe/H]}〉=-{2.17}_{-0.05}^{+0.05}$, ${\sigma }_{\mathrm{[Fe/H]}}={0.33}_{-0.07}^{+0.07}$, and ∇_[Fe/H]= −0.23 ± 0.15 dex $R_e^{-1}$. We find that And XVI is more metal-rich than Milky Way ultrafaint dwarf galaxies of similar luminosity, which may be a result of its unusually extended star formation history. For And XXVIII, we measure $〈\mathrm{[Fe/H]}〉=-{1.95}_{-0.04}^{+0.04}$, ${\sigma }_{\mathrm{[Fe/H]}}={0.34}_{-0.05}^{+0.05}$, and ∇_[Fe/H]= −0.46 ± 0.10 dex $R_e^{-1}$, placing it on the dwarf galaxy mass–metallicity relation. Neither galaxy has a metallicity distribution function (MDF) with an abrupt metal-rich truncation, suggesting that star formation fell off gradually. The stellar metallicity gradient measurements are among the first for faint (L≲ 10⁶L_⊙) galaxies outside the Milky Way halo. Both galaxies’ gradients are consistent with predictions from the FIRE simulations, where an age–gradient strength relationship is the observational consequence of stellar feedback that produces dark matter cores. We include a catalog for community spectroscopic follow-up, including 19 extremely metal-poor ([Fe/H] < –3.0) star candidates, which make up 7% of And XVI’s MDF and 6% of And XXVIII’s. 

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5. The Dark Energy Survey: Cosmology Results with ∼1500 New High-redshift Type Ia Supernovae Using the Full 5 yr Data Set

   https://doi.org/10.3847/2041-8213/ad6f9f  

   Abbott, DES_Collaboration_T_M_C; Acevedo, M.; Aguena, M.; Alarcon, A.; Allam, S.; Alves, O.; Amon, A.; Andrade-Oliveira, F.; Annis, J.; Armstrong, P.; et al (October 2024, The Astrophysical Journal Letters)

   Abstract We present cosmological constraints from the sample of Type Ia supernovae (SNe Ia) discovered and measured during the full 5 yr of the Dark Energy Survey (DES) SN program. In contrast to most previous cosmological samples, in which SNe are classified based on their spectra, we classify the DES SNe using a machine learning algorithm applied to their light curves in four photometric bands. Spectroscopic redshifts are acquired from a dedicated follow-up survey of the host galaxies. After accounting for the likelihood of each SN being an SN Ia, we find 1635 DES SNe in the redshift range 0.10 <z< 1.13 that pass quality selection criteria sufficient to constrain cosmological parameters. This quintuples the number of high-qualityz> 0.5 SNe compared to the previous leading compilation of Pantheon+ and results in the tightest cosmological constraints achieved by any SN data set to date. To derive cosmological constraints, we combine the DES SN data with a high-quality external low-redshift sample consisting of 194 SNe Ia spanning 0.025 <z< 0.10. Using SN data alone and including systematic uncertainties, we find Ω_M= 0.352 ± 0.017 in flat ΛCDM. SN data alone now require acceleration (q₀< 0 in ΛCDM) with over 5σconfidence. We find $({\mathrm{\Omega }}_{\mathrm{M}},w)=({0.264}_{-0.096}^{+0.074},-{0.80}_{-0.16}^{+0.14})$in flatwCDM. For flatw₀w_aCDM, we find $({\mathrm{\Omega }}_{\mathrm{M}},w_0,w_a)=({0.495}_{-0.043}^{+0.033},-{0.36}_{-0.30}^{+0.36},-{8.8}_{-4.5}^{+3.7})$, consistent with a constant equation of state to within ∼2σ. Including Planck cosmic microwave background, Sloan Digital Sky Survey baryon acoustic oscillation, and DES 3 × 2pt data gives (Ω_M,w) = (0.321 ± 0.007, −0.941 ± 0.026). In all cases, dark energy is consistent with a cosmological constant to within ∼2σ. Systematic errors on cosmological parameters are subdominant compared to statistical errors; these results thus pave the way for future photometrically classified SN analyses. 

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