Spatially Resolved Stellar Spectroscopy of the Ultra-diffuse Galaxy Dragonfly 44. III. Evidence for an Unexpected Star Formation History under Conventional Galaxy Evolution Processes

We use the Keck Cosmic Web Imager integral field unit spectrograph to (1) measure the global stellar population parameters for the ultra-diffuse galaxy (UDG) Dragonfly 44 (DF44) to much higher precision than previously possible for any UDG and (2) for the first time measure spatially resolved stellar population parameters of a UDG. We find that DF44 falls below the mass–metallicity relation established by canonical dwarf galaxies both in and beyond the Local Group. We measure a flat radial age gradient ( m logage = + 0.01 − 0.08 + 0.08 log Gyr kpc−1) and a flat to positive metallicity gradient ( m [ Fe / H ] = + 0.09 − 0.12 + 0.11 dex kpc−1), which are inconsistent with the gradients measured in similarly pressure-supported dwarf galaxies. We also measure a negative [Mg/Fe] gradient ( m [ Mg / Fe ] = − 0.20 − 0.18 + 0.18 ) dex kpc−1 such that the central 1.5 kpc of DF44 has stellar population parameters comparable to metal-poor globular clusters. Overall, DF44 does not have internal properties similar to other dwarf galaxies and is inconsistent with it having been puffed up through a prolonged, bursty star formation history, as suggested by some simulations. Rather, the evidence indicates that DF44 experienced an intense epoch of “inside-out” star formation and then quenched early and catastrophically, such that star formation was cut off more quickly than in canonical dwarf galaxies.

On the Variation in Stellar α-enhancements of Star-forming Galaxies in the EAGLE Simulation

The ratio of α-elements to iron in galaxies holds valuable information about the star formation history (SFH) since their enrichment occurs on different timescales. The fossil record of stars in galaxies has mostly been excavated for passive galaxies, since the light of star-forming galaxies is dominated by young stars, which have much weaker atmospheric absorption features. Here we use the largest reference cosmological simulation of the EAGLE project to investigate the origin of variations in stellar α-enhancement among star-forming galaxies at z = 0, and their impact on integrated spectra. The definition of α-enhancement in a composite stellar population is ambiguous. We elucidate two definitions—termed “mean” and “galactic” α-enhancement—in more detail. While a star-forming galaxy has a high “mean” α-enhancement when its stars formed rapidly, a galaxy with a large “galactic” α-enhancement generally had a delayed SFH. We find that absorption-line strengths of Mg and Fe correlate with variations in α-enhancement. These correlations are strongest for the “galactic” α-enhancement. However, we show that these are mostly caused by other effects that are cross-correlated with α-enhancement, such as variations in the light-weighted age. This severely complicates the retrieval of α-enhancements in star-forming galaxies. The ambiguity is not severe for passive galaxies, and we confirm that spectral variations in these galaxies are caused by measurable variations in α-enhancements. We suggest that this more complex coupling between α-enhancement and SFHs can guide the interpretation of new observations of star-forming galaxies.

The CHIME Fast Radio Burst Population Does Not Track the Star Formation History of the Universe

The redshift distribution of fast radio bursts (FRBs) is not well constrained. The association of the Galactic FRB 200428 with the young magnetar SGR 1935+2154 raises the working hypothesis that FRB sources track the star formation history of the universe. The discovery of FRB 20200120E in association with a globular cluster in the nearby galaxy M81, however, casts doubts on such an assumption. We apply the Monte Carlo method developed in a previous work to test different FRB redshift distribution models against the recently released first CHIME FRB catalog in terms of their distributions in specific fluence, external dispersion measure (DME), and inferred isotropic energy. Our results clearly rule out the hypothesis that all FRBs track the star formation history of the universe. The hypothesis that all FRBs track the accumulated stars throughout history describes the data better but still cannot meet both the DME and the energy criteria. The data seem to be better modeled with either a redshift distribution model invoking a significant delay with respect to star formation or a hybrid model invoking both a dominant delayed population and a subdominant star formation population. We discuss the implications of this finding for FRB source models.

Development and Formation History of Profit Taxation

Research relevance determined by the importance of tax regulation, which allows the state to concentrate its financial resources, with the ability to significantly influence the economic development of the country at every stage of its development. The article examines the processes and stages of the emergence and evolution of theses on the essence of taxation. Research objectives: analysis of the main and fundamental tax theories, as well as tax systems of ancient states. Research materials and methods: analysis of the history of formation, development, evolution of one of the initial forms of taxation — payment (tax) from the people. Also considered the legal content and the economic content of the tax. Research results: the basic principles of taxation are considered on the basis of the definitions of Adam Smith, who established the basic principles of taxation, which exist and operate to this day. An assessment and comparison of taxation in Kyrgyzstan with other countries is given. Conclusions: a decrease in the tax rate will entail an increase in production, which in the future will compensate for a temporary decrease in tax revenues.

The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. II. The Star-formation History of Andromeda I Derived from Long-period Variables

An optical monitoring survey in the nearby dwarf galaxies was carried out with the 2.5 m Isaac Newton Telescope. 55 dwarf galaxies and four isolated globular clusters in the Local Group were observed with the Wide Field Camera. The main aims of this survey are to identify the most evolved asymptotic giant branch stars and red supergiants at the endpoint of their evolution based on their pulsational instability, use their distribution over luminosity to reconstruct the star-formation history (SFH), quantify the dust production and mass loss from modeling the multiwavelength spectral energy distributions, and relate this to luminosity and radius variations. In this second of a series of papers, we present the methodology used to estimate SFH based on long-period variable (LPV) stars and then derive it for Andromeda I (And I) dwarf galaxy as an example of the survey. Using our identified 59 LPV candidates within two half-light radii of And I and Padova stellar evolution models, we estimated the SFH of this galaxy. A major epoch of star formation occurred in And I peaking around 6.6 Gyr ago, reaching 0.0035 ± 0.0016 M ⊙ yr−1 and only slowly declining until 1–2 Gyr ago. The presence of some dusty LPVs in this galaxy corresponds to a slight increase in recent star formation peaking around 800 Myr ago. We evaluate a quenching time around 4 Gyr ago (z < 0.5), which makes And I a late-quenching dSph. A total stellar mass (16 ± 7) × 106 M ⊙ is calculated within two half-light radii of And I for a constant metallicity Z = 0.0007.

Milky Way–like Gas Excitation in an Ultrabright Submillimeter Galaxy at z = 1.6

Based on observations with the IRAM 30 m and Yebes 40 m telescopes, we report evidence of the detection of Milky Way–like, low-excitation molecular gas, up to the transition CO(J = 5–4), in a distant, dusty star-forming galaxy at z CO = 1.60454. WISE J122651.0+214958.8 (alias SDSS J1226, the Cosmic Seahorse), is strongly lensed by a foreground galaxy cluster at z = 0.44 with a source magnification of μ = 9.5 ± 0.7. This galaxy was selected by cross-correlating near-to-mid-infrared colors within the full-sky AllWISE survey, originally aiming to discover rare analogs of the archetypical strongly lensed submillimeter galaxy SMM J2135–0102, the Cosmic Eyelash. We derive an apparent (i.e., not corrected for lensing magnification) rest-frame 8–1000 μm infrared luminosity of μ L IR = 1.66 − 0.04 + 0.04 × 10 13 L ⊙ and apparent star formation rate μSFRIR = 2960 ± 70 M ⊙ yr−1. SDSS J1226 is ultrabright at S 350μm ≃ 170 mJy and shows similarly bright low-J CO line intensities as SMM J2135–0102, however, with exceptionally small CO(J = 5–4) intensity. We consider different scenarios to reconcile our observations with typical findings of high-z starbursts, and speculate about the presence of a previously unseen star formation mechanism in cosmic noon submillimeter galaxies. In conclusion, the remarkable low line luminosity ratio r 5,2 = 0.11 ± 0.02 is best explained by an extended, main-sequence star formation mode—representing a missing link between starbursts to low-luminosity systems during the epoch of peak star formation history.

Spectroscopic Confirmation of the Sixth Globular Cluster in the Fornax Dwarf Spheroidal Galaxy*

The Fornax dwarf spheroidal galaxy has an anomalous number of globular clusters, five, for its stellar mass. There is a longstanding debate about a potential sixth globular cluster (Fornax 6) that has recently been “rediscovered” in DECam imaging. We present new Magellan/M2FS spectroscopy of the Fornax 6 cluster and Fornax dSph. Combined with literature data we identify ∼15–17 members of the Fornax 6 cluster, showing that this overdensity is indeed a star cluster and associated with the Fornax dSph. The cluster is significantly more metal-rich (mean metallicity of [ Fe / H ] ¯ = −0.71 ± 0.05) than the other five Fornax globular clusters (−2.5 < [Fe/H] < −1.4) and more metal-rich than the bulk of Fornax. We measure a velocity dispersion of 5.6 − 1.6 + 2.0 km s − 1 corresponding to an anomalously high mass-to-light of 15 < M/L < 258 at 90% confidence when calculated assuming equilibrium. Two stars inflate this dispersion and may be either Fornax field stars or as yet unresolved binary stars. Alternatively, the Fornax 6 cluster may be undergoing tidal disruption. Based on its metal-rich nature, the Fornax 6 cluster is likely younger than the other Fornax clusters, with an estimated age of ∼2 Gyr when compared to stellar isochrones. The chemodynamics and star formation history of Fornax shows imprints of major events such as infall into the Milky Way, multiple pericenter passages, star formation bursts, and/or potential mergers or interactions. Any of these events may have triggered the formation of the Fornax 6 cluster.

Noble Gas Hints at Mars’s Rapid Formation

A new study finds that Mars’s mantle is neon-rich, putting constraints on the planet’s formation history.