More Like this

1. Detailed Chemical Abundances of Stars in the Outskirts of the Tucana II Ultrafaint Dwarf Galaxy*

   https://doi.org/10.3847/1538-3881/aca416  

   Chiti, Anirudh; Frebel, Anna; Ji, Alexander P; Mardini, Mohammad K; Ou, Xiaowei; Simon, Joshua D; Jerjen, Helmut; Kim, Dongwon; Norris, John E (January 2023, The Astronomical Journal)

   Abstract We present chemical abundances and velocities of five stars between 0.3 and 1.1 kpc from the center of the Tucana II ultrafaint dwarf galaxy (UFD) from high-resolution Magellan/MIKE spectroscopy. We find that every star is deficient in metals (−3.6 < [Fe/H] < −1.9) and in neutron-capture elements as is characteristic of UFD stars, unambiguously confirming their association with Tucana II. Other chemical abundances (e.g., C, iron peak) largely follow UFD trends and suggest that faint core-collapse supernovae (SNe) dominated the early evolution of Tucana II. We see a downturn in [α/Fe] at [Fe/H] ≈ −2.8, indicating the onset of Type Ia SN enrichment and somewhat extended chemical evolution. The most metal-rich star has strikingly low [Sc/Fe] = −1.29 ± 0.48 and [Mn/Fe] = −1.33 ± 0.33, implying significant enrichment by a sub-Chandrasekhar mass Type Ia SN. We do not detect a radial velocity gradient in Tucana II ( ${\mathit{dv}}_{\mathrm{helio}}/d{\theta }_1=-{2.6}_{-2.9}^{+3.0}$km s⁻¹kpc⁻¹), reflecting a lack of evidence for tidal disruption, and derive a dynamical mass of $M_{1/2}\left(r_h\right)={1.6}_{-0.7}^{+1.1}\times {10}^6$M_⊙. We revisit formation scenarios of the extended component of Tucana II in light of its stellar chemical abundances. We find no evidence that Tucana II had abnormally energetic SNe, suggesting that if SNe drove in situ stellar halo formation, then other UFDs should show similar such features. Although not a unique explanation, the decline in [α/Fe] is consistent with an early galactic merger triggering later star formation. Future observations may disentangle such formation channels of UFD outskirts. 

   more » « less
2. The Chemodynamics of the Stellar Populations in M31 from APOGEE Integrated-light Spectroscopy

   https://doi.org/10.3847/1538-4357/acd9a9  

   Gibson, Benjamin J.; Zasowski, Gail; Seth, Anil; Ashok, Aishwarya; Goold, Kameron; Wainer, Tobin; Hasselquist, Sten; Holtzman, Jon; Imig, Julie; Bizyaev, Dmitry; et al (July 2023, The Astrophysical Journal)

   Abstract We present an analysis of nearly 1000 near-infrared, integrated-light spectra from APOGEE in the inner ∼7 kpc of M31. We utilize full-spectrum fitting with A-LIST simple stellar population spectral templates that represent a population of stars with the same age, [M/H], and [α/M]. With this, we determine the mean kinematics, metallicities,αabundances, and ages of the stellar populations of M31's bar, bulge, and inner disk (∼4–7 kpc). We find a nonaxisymmetric velocity field in M31 resulting from the presence of a bar. The bulge of M31 is less metal-rich (mean [M/H] = $-{0.149}_{-0.081}^{+0.067}$dex) than the disk, features minima in metallicity on either side of the bar ([M/H] ∼ −0.2), and is enhanced inαabundance (mean [α/M] = ${0.281}_{-0.038}^{+0.035}$). The disk of M31 within ∼7 kpc is enhanced in both metallicity ([M/H] = $-{0.023}_{-0.052}^{+0.050}$) andαabundance ([α/M] = ${0.274}_{-0.025}^{+0.020}$). Both of these structural components are uniformly old at ≃12 Gyr. We find the mean metallicity increases with distance from the center of M31, with the steepest gradient along the disk major axis (0.043 ± 0.021 dex kpc⁻¹). This gradient is the result of changing light contributions from the bulge and disk. The chemodynamics of stellar populations encodes information about a galaxy’s chemical enrichment, star formation history, and merger history, allowing us to discuss new constraints on M31's formation. Our results provide a stepping stone between our understanding of the Milky Way and other external galaxies. 

   more » « less
3. A Pride of Satellites in the Constellation Leo? Discovery of the Leo VI Milky Way Satellite Ultra-faint Dwarf Galaxy with DELVE Early Data Release 3

   https://doi.org/10.3847/1538-4357/ad9b0c  

   Tan, C_Y; Cerny, W.; Drlica-Wagner, A.; Pace, A_B; Geha, M.; Ji, A_P; Li, T_S; Adamów, M.; Anbajagane, D.; Bom, C_R; et al (January 2025, The Astrophysical Journal)

   Abstract We report the discovery and spectroscopic confirmation of an ultra-faint Milky Way satellite in the constellation of Leo. This system was discovered as a spatial overdensity of resolved stars observed with Dark Energy Camera (DECam) data from an early version of the third data release of the DECam Local Volume Exploration (or DELVE) survey. The low luminosity ( $M_V=-3.56_{-0.37}^{+0.47}$; $L_V=2300_{-700}^{+1200}{L}_{\odot }$), large size ( $R_{1/2}=90_{-30}^{+30}$pc), and large heliocentric distance ( $D=111_{-6}^{+9}$kpc) are all consistent with the population of ultra-faint dwarf galaxies (UFDs). Using Keck/DEIMOS observations of the system, we were able to spectroscopically confirm nine member stars, while measuring a tentative mass-to-light ratio of $700_{-500}^{+1400}{M}_{\odot }/L_{\odot }$and a nonzero metallicity dispersion of ${\sigma }_{[\mathrm{Fe}/\mathrm{H}]}=0.19_{-0.11}^{+0.14}$, further confirming Leo VI’s identity as a UFD. While the system has a highly elliptical shape, $ϵ=0.54_{-0.29}^{+0.19}$, we do not find any conclusive evidence that it is tidally disrupting. Moreover, despite the apparent on-sky proximity of Leo VI to members of the proposed Crater-Leo infall group, its smaller heliocentric distance and inconsistent position in energy–angular momentum space make it unlikely that Leo VI is part of the proposed infall group. 

   more » « less
4. The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO). XI. Beam-corrected Gas Disk Sizes from Fitting ¹² CO Moment Zero Maps

   https://doi.org/10.3847/1538-4357/adc7af  

   Trapman, Leon; Vioque, Miguel; Kurtovic, Nicolás T; Zhang, Ke; Rosotti, Giovanni P; Pinilla, Paola; Carpenter, John; Cieza, Lucas A; Pascucci, Ilaria; Anania, Rossella; et al (July 2025, The Astrophysical Journal)

   Abstract The inward drift of millimeter–centimeter sized pebbles in protoplanetary disks has become an important part of our current theories of planet formation and, more recently, planet composition as well. The gas-to-dust size ratio of protoplanetary disks can provide an important constraint on how pebbles have drifted inward, provided that observational effects, especially resolution, can be accounted for. Here we present a method for fitting beam-convolved models to integrated intensity maps of line emission using theastropyPython package and use it to fit¹²CO moment zero maps of 10 Lupus and 10 Upper Scorpius protoplanetary disks from the ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO) Program, a sample of disks around M3-K6 stars that cover the  ∼1–6 Myr of gas disk evolution. From the unconvolved best fit models, we measure the gas disk size ( $R_{\mathrm{CO},90\%}^{\mathrm{model}}$), which we combine with the dust disk size ( $R_{\mathrm{dust},90\%}^{\mathrm{FRANK}}$) from continuum visibility fits from M. Vioque et al. to compute beam-corrected gas-to-dust size ratios. In our sample, we find gas-to-dust size ratios between  ∼1 and  ∼5.5, with a median value of $2.78_{-0.32}^{+0.37}$. Contrary to models of dust evolution that predict an increasing size ratio with time, we find that the younger disks in Lupus have similar (or even larger) median ratios $\left(3.02_{-0.33}^{+0.33}\right)$than the older disks in Upper Sco $\left(2.46_{-0.38}^{+0.53}\right)$. A possible explanation for this discrepancy is that pebble drift is halted in dust traps combined with truncation of the gas disk by external photoevaporation in Upper Sco, although survivorship bias could also play a role. 

   more » « less
5. JWST Spectroscopy of SN H0pe: Classification and Time Delays of a Triply Imaged Type Ia Supernova at z = 1.78

   https://doi.org/10.3847/1538-4357/ad50a5  

   Chen, Wenlei; Kelly, Patrick_L; Frye, Brenda_L; Pierel, Justin; Willner, S_P; Pascale, Massimo; Cohen, Seth_H; Conselice, Christopher_J; Engesser, Michael; Furtak, Lukas_J; et al (July 2024, The Astrophysical Journal)

   Abstract SN H0pe is a triply imaged supernova (SN) at redshiftz= 1.78 discovered using the James Webb Space Telescope. In order to classify the SN spectroscopically and measure the relative time delays of its three images (designated A, B, and C), we acquired NIRSpec follow-up spectroscopy spanning 0.6–5μm. From the high signal-to-noise spectra of the two bright images B and C, we first classify the SN, whose spectra most closely match those of SN 1994D and SN 2013dy, as a Type Ia SN. We identify prominent blueshifted absorption features corresponding to Siiiλ6355 and CaiiHλ3970 and Kλ3935. We next measure the absolute phases of the three images from our spectra, which allow us to constrain their relative time delays. The absolute phases of the three images, determined by fitting the three spectra to Hsiao07 SN templates, are ${6.5}_{-1.8}^{+2.4}$days, ${24.3}_{-3.9}^{+3.9}$days, and ${50.6}_{-15.3}^{+16.1}$days for the brightest to faintest images. These correspond to relative time delays between Image A and Image B and between Image B and Image C of $-{122.3}_{-43.8}^{+43.7}$days and ${49.3}_{-14.7}^{+12.2}$days, respectively. The SALT3-NIR model yields phases and time delays consistent with these values. After unblinding, we additionally explored the effect of using Hsiao07 template spectra for simulations through 80 days instead of 60 days past maximum, and found a small (11.5 and 1.0 days, respectively) yet statistically insignificant (∼0.25σand ∼0.1σ) effect on the inferred image delays. 

   more » « less