More Like this

1. The Heavy Metal Survey: The Evolution of Stellar Metallicities, Abundance Ratios, and Ages of Massive Quiescent Galaxies since z ∼ 2

   https://doi.org/10.3847/1538-4357/ad372d  

   Beverage, Aliza G.; Kriek, Mariska; Suess, Katherine A.; Conroy, Charlie; Price, Sedona H.; Barro, Guillermo; Bezanson, Rachel; Franx, Marijn; Lorenz, Brian; Ma, Yilun; et al (May 2024, The Astrophysical Journal)

   Abstract We present the elemental abundances and ages of 19 massive quiescent galaxies atz∼ 1.4 andz∼ 2.1 from the Keck Heavy Metal Survey. The ultradeep LRIS and MOSFIRE spectra were modeled using a full-spectrum stellar population fitting code with variable abundance patterns. The galaxies have iron abundances between [Fe/H] = −0.5 and −0.1 dex, with typical values of −0.2 [−0.3] atz∼ 1.4 [z∼ 2.1]. We also find a tentative $\log {\sigma }_v$–[Fe/H] relation atz∼ 1.4. The magnesium-to-iron ratios span [Mg/Fe] = 0.1–0.6 dex, with typical values of 0.3 [0.5] dex atz∼ 1.4 [z∼ 2.1]. The ages imply formation redshifts ofz_form= 2–8. Compared to quiescent galaxies at lower redshifts, we find that [Fe/H] was ∼0.2 dex lower atz= 1.4–2.1. We find no evolution in [Mg/Fe] out toz∼ 1.4, though thez∼ 2.1 galaxies are 0.2 dex enhanced compared toz= 0–0.7. A comparison of these results to a chemical evolution model indicates that galaxies at higher redshift form at progressively earlier epochs and over shorter star formation timescales, with thez∼ 2.1 galaxies forming the bulk of their stars over 150 Myr atz_form∼ 4. This evolution cannot be solely attributed to an increased number of quiescent galaxies at later times; several Heavy Metal galaxies have extreme chemical properties not found in massive galaxies atz∼ 0.0–0.7. Thus, the chemical properties of individual galaxies must evolve over time. Minor mergers also cannot fully account for this evolution as they cannot increase [Fe/H], particularly in galaxy centers. Consequently, the buildup of massive quiescent galaxies sincez∼ 2.1 may require further mechanisms, such as major mergers and/or central star formation. 

   more » « less
2. Chemo-dynamical Evolution of Simulated Satellites for a Milky Way–like Galaxy

   https://doi.org/10.3847/1538-4357/ad500c  

   Hirai, Yutaka; Kirby, Evan_N; Chiba, Masashi; Hayashi, Kohei; Anguiano, Borja; Saitoh, Takayuki_R; Ishigaki, Miho_N; Beers, Timothy_C (July 2024, The Astrophysical Journal)

   Abstract The chemical abundances of Milky Way’s (MW's) satellites reflect their star formation histories (SFHs), yet, due to the difficulty of determining the ages of old stars, the SFHs of most satellites are poorly measured. Ongoing and upcoming surveys will obtain around 10 times more medium-resolution spectra for stars in satellites than are currently available. To correctly extract SFHs from large samples of chemical abundances, the relationship between chemical abundances and SFHs needs to be clarified. Here, we perform a high-resolution cosmological zoom-in simulation of a MW-like galaxy with detailed models of star formation, supernova (SN) feedback, and metal diffusion. We quantify SFHs, metallicity distribution functions, and theα-element (Mg, Ca, and Si) abundances in satellites of the host galaxy. We find that star formation in most simulated satellites is quenched before infalling to their host. Star formation episodes in simulated satellites are separated by a few hundred Myr owing to SN feedback; each star formation event produces groups of stars with similar [α/Fe] and [Fe/H]. We then perform a mock observation of the upcoming Subaru Prime Focus Spectrograph (PFS) observations. We find that Subaru PFS will be able to detect distinct groups of stars in [α/Fe] versus [Fe/H] space, produced by episodic star formation. This result means that episodic SFHs can be estimated from the chemical abundances of ≳1000 stars determined with medium-resolution spectroscopy. 

   more » « less
3. 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
4. Chemical Abundances in the Leiptr Stellar Stream: A Disrupted Ultra-faint Dwarf Galaxy?

   https://doi.org/10.33232/001c.139013  

   Atzberger, Kaia R; Usman, Sam A; Ji, Alexander P; Cullinane, Lara R; Erkal, Denis; Hansen, Terese T; Lewis, Geraint F; Li, Ting S; Limberg, Guilherme; Luna, Alice; et al (January 2025, The Open Journal of Astrophysics)

   Chemical abundances of stellar streams can be used to determine the nature of a stream’s progenitor. Here we study the progenitor of the recently discovered Leiptr stellar stream, which was previously suggested to be a tidally disrupted halo globular cluster. We obtain high-resolution spectra of five red giant branch stars selected from the Gaia DR2 $\text{𝚂𝚃𝚁𝙴𝙰𝙼𝙵𝙸𝙽𝙳𝙴𝚁}$catalog with Magellan/MIKE. One star is a clear non-member. The remaining four stars display chemical abundances consistent with those of a low-mass dwarf galaxy: they have a low mean metallicity, ; they do not all have identical metallicities; and they display low [ $\alpha$/Fe] $\sim 0$and [Sr/Fe] and [Ba/Fe] $\sim -1$. This pattern of low $\alpha$and neutron-capture element abundances is only found in intact dwarf galaxies with stellar mass $\lesssim {10}^5{M}_{\odot }$. Although more data are needed to be certain, Leiptr’s chemistry is consistent with being the lowest-mass dwarf galaxy stream without a known intact progenitor, possibly in the mass range of ultra-faint dwarf galaxies. Leiptr thus preserves a record of one of the lowest-mass early accretion events into the Milky Way. 

   more » « less
5. Merger Signatures are Common, but not Universal, in Massive, Recently Quenched Galaxies at z ∼ 0.7

   https://doi.org/10.3847/1538-4357/acc38b  

   Verrico, Margaret E.; Setton, David J.; Bezanson, Rachel; Greene, Jenny E.; Suess, Katherine A.; Goulding, Andy D.; Spilker, Justin S.; Kriek, Mariska; Feldmann, Robert; Narayanan, Desika; et al (May 2023, The Astrophysical Journal)

   Abstract We present visual classifications of merger-induced tidal disturbances in 143M_*∼ 10¹¹M_⊙post-starburst galaxies atz∼ 0.7 identified in the $\mathrm{SQuIGG}\vec{L}\mathrm{E}$Sample. This sample spectroscopically selects galaxies from the Sloan Digital Sky Survey that have stopped their primary epoch of star formation within the past ∼500 Myr. Visual classifications are performed on Hyper Suprime-Cam imaging. We compare to a control sample of mass- and redshift-matched star-forming and quiescent galaxies from the Large Early Galaxy Census and find that post-starburst galaxies are more likely to be classified as disturbed than either category. This corresponds to a factor of ${3.6}_{-1.3}^{+2.9}$times the disturbance rate of older quiescent galaxies and ${2.1}_{-.73}^{+1.9}$times the disturbance rate of star-forming galaxies. Assuming tidal features persist for ≲500 Myr, this suggests merging is coincident with quenching in a significant fraction of these post-starbursts. Galaxies with tidal disturbances are younger on average than undisturbed post-starburst galaxies in our sample, suggesting tidal features from a major merger may have faded over time. This may be exacerbated by the fact that, on average, the undisturbed subset is fainter, rendering low-surface-brightness tidal features harder to identify. However, the presence of 10 young (≲150 Myr since quenching) undisturbed galaxies suggests that major mergers are not the only fast physical mechanism that shut down the primary epoch of star formation in massive galaxies at intermediate redshift. 

   more » « less