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We analyze TYPHOON long-slit-absorption line spectra of the starburst barred spiral galaxy NGC 1365 obtained with the Progressive Integral Step Method covering an area of 15 kpc2. Applying a population synthesis technique, we determine the spatial distribution of ages and metallicities of the young and old stellar populations together with star formation rates, reddening, extinction, and the ratio R V of extinction to reddening. We detect a clear indication of inside-out growth of the stellar disk beyond 3 kpc characterized by an outward increasing luminosity fraction of the young stellar population, a decreasing average age, and a history of mass growth, which was finished 2 Gyr later in the outermost disk. The metallicity of the young stellar population is clearly super solar but decreases toward larger galactocentric radii with a gradient of −0.02 dex kpc−1. On the other hand, the metal content of the old population does not show a gradient and stays constant at a level roughly 0.4 dex lower than that of the young population. In the center of NGC 1365, we find a confined region where the metallicity of the young population drops dramatically and becomes lower than that of the old population. We attribute this to the infall of metal-poor gas, and additionally, to interrupted chemical evolution where star formation is stopped by active galactic nuclei and supernova feedback and then after several gigayears resumes with gas ejected by stellar winds from earlier generations of stars. We provide a simple model calculation as support for the latter.

We apply population synthesis techniques to analyze TYPHOON long slit spectra of the starburst barred spiral galaxy M83. The analysis covers a central square of 5′ side length. We determine the spatial distribution of dust through the analysis of reddening and extinction, together with star formation rates, ages, and metallicities of young and old stellar populations. For the first time, a spatial one-to-one comparison of metallicities derived from full spectral fitting techniques with those obtained from individual young stellar probes has been carried out. The comparison with blue supergiant stars, young massive star clusters, and super star clusters shows a high degree of concordance when wavelength coverage in the B band is available. The metallicity of the young population is supersolar and does not show a radial metallicity gradient along the investigated part of the disk, in agreement with our chemical evolution model. However, a notable decrease in metallicity is observed in a tightly confined region at the galaxy center, coinciding with circumnuclear orbits. We attribute this to matter infall either from the circumgalactic medium, a dwarf galaxy interloper, or, alternatively, to active-galactic-nucleus-interrupted chemical evolution. We confirm the presence of a dust cavity with a diameter of 260 pc close to the galaxy center. Dust absorption and molecular CO emission are spatially well correlated. We find an anticorrelation between RV, the ratio of dust attenuation to reddening, and the emission strength of molecular species present in photodissociation regions. We confirm our results by using alternative fitting algorithms and stellar libraries.

A Mira image Mira is one of a class of low to slightly more than solar mass stars in the late stages of stellar evolution. These stars have a direct impact on star and planet formation in their host galaxy via the winds that they send out. Martin et al . report the discovery of an ultraviolet-emitting bow shock and turbulent wake extending over 2 degrees on the sky, arising from Mira's large space velocity and the interaction between its wind and the interstellar medium. This wind wake is a tracer of the past 30,000 years of Mira's mass loss history. Mira is one of a class of low-to-intermediate mass stars in the late stages of stellar evolution. This paper reports the discovery of an ultraviolet-emitting bow shock and turbulent wake extending over 2 degrees on the sky, arising from Mira's large space velocity and the interaction between its wind and the interstellar medium. This wind wake is a tracer of the last 30,000 years of Mira's mass-loss history. Mira is one of the first variable stars ever discovered 1 and it is the prototype (and also the nearest example) of a class of low-to-intermediate-mass stars in the late stages of stellar evolution. These stars are relatively common and they return a large fraction of their original mass to the interstellar medium (ISM) (ref. 2 ) through a processed, dusty, molecular wind. Thus stars in Mira’s stage of evolution have a direct impact on subsequent star and planet formation in their host galaxy. Previously, the only direct observation 3 of the interaction between Mira-type stellar winds and the ISM was in the infrared. Here we report the discovery of an ultraviolet-emitting bow shock and turbulent wake extending over 2 degrees on the sky, arising from Mira’s large space velocity and the interaction between its wind and the ISM. The wake is visible only in the far ultraviolet and is consistent with an unusual emission mechanism whereby molecular hydrogen is excited by turbulent mixing of cool molecular gas and shock-heated gas. This wind wake is a tracer of the past 30,000 years of Mira’s mass-loss history and provides an excellent laboratory for studying turbulent stellar wind–ISM interactions.

Galaxies versus black holes Observations in the near-ultraviolet from the the GALEX satellite provide new data on the link between the formation of young stars in massive elliptical galaxies and the supermassive black holes thought to reside at their centres, where they may interact with their hosts by means of 'feedback' in the form of energy and material jets. The data provide constraints in a sophisticated computer model of galaxy evolution, and suggest that there is a critical supermassive black hole mass at which jets and outflows from the black hole become so powerful as to stop all gas accretion and further growth of the host galaxy. Detailed high-resolution observations of the innermost regions of nearby galaxies have revealed the presence of supermassive black holes 1 , 2 , 3 , 4 . These black holes may interact with their host galaxies by means of ‘feedback’ in the form of energy and material jets; this feedback affects the evolution of the host and gives rise to observed relations between the black hole and the host 5 . Here we report observations of the ultraviolet emissions of massive early-type galaxies. We derive an empirical relation for a critical black-hole mass (as a function of velocity dispersion) above which the outflows from these black holes suppress star formation in their hosts by heating and expelling all available cold gas. Supermassive black holes are negligible in mass compared to their hosts but nevertheless seem to play a critical role in the star formation history of galaxies.

Stellar mergers are a brief but common phase in the evolution of binary star systems 1 , 2 . These events have many astrophysical implications; for example, they may lead to the creation of atypical stars (such as magnetic stars 3 , blue stragglers 4 and rapid rotators 5 ), they play an important part in our interpretation of stellar populations 6 and they represent formation channels of compact-object mergers 7 . Although a handful of stellar mergers have been observed directly 8 , 9 , the central remnants of these events were shrouded by an opaque shell of dust and molecules 10 , making it impossible to observe their final state (for example, as a single merged star or a tighter, surviving binary 11 ). Here we report observations of an unusual, ring-shaped ultraviolet (‘blue’) nebula and the star at its centre, TYC 2597-735-1. The nebula has two opposing fronts, suggesting a bipolar outflow of material from TYC 2597-735-1. The spectrum of TYC 2597-735-1 and its proximity to the Galactic plane suggest that it is an old star, yet it has abnormally low surface gravity and a detectable long-term luminosity decay, which is uncharacteristic for its evolutionary stage. TYC 2597-735-1 also exhibits Hα emission, radial-velocity variations, enhanced ultraviolet radiation and excess infrared emission—signatures of dusty circumstellar disks 12 , stellar activity 13 and accretion 14 . Combined with stellar evolution models, the observations suggest that TYC 2597-735-1 merged with a lower-mass companion several thousand years ago. TYC 2597-735-1 provides a look at an unobstructed stellar merger at an evolutionary stage between its dynamic onset and the theorized final equilibrium state, enabling the direct study of the merging process. Observations and stellar evolution models of a blue ring nebula and its central star (TYC 2597-735-1) suggest that the remnant star merged with a lower-mass companion several thousand years ago.

The Spitzer Survey of Stellar Structure in Galaxies ([inline image]) is an Exploration Science Legacy Program approved for the Spitzer post-cryogenic mission. It is a volume-, magnitude-, and size-limited (d < 40 Mpc,

We determine three independent Population II distance moduli to the Fornax dwarf spheroidal (dSph) galaxy, using wide-field, ground-based VI imaging acquired with the Magellan-Baade telescope at Las Campanas Observatory. After subtracting foreground stars using Gaia EDR3 proper motions, we measure an I-band tip of the red giant branch (TRGB) magnitude of I0TRGB=16.753±0.03stat±0.037sys mag, with a calibration based in the LMC giving a distance modulus of μ0TRGB=20.80±0.037stat±0.057sys mag. We determine an RR Lyrae (RRL) distance from template mean magnitudes, with periods adopted from the literature. Adopting a Gaia DR2 calibration of first overtone RRL period–luminosity and period–Wesenheit relations, we find μ0PLZ=20.74±0.01stat±0.12sys mag and μ0PWZ=20.68±0.02stat±0.07sys mag. Finally, we determine a distance from Fornax’s horizontal branch (HB) and two galactic globular cluster calibrators, giving μ0HB=20.83±0.03stat±0.09sys mag. These distances are each derived from homogeneous IMACS photometry, are anchored to independent geometric zero-points, and utilize different classes of stars. We therefore average over independent uncertainties and report the combined distance modulus 〈μ 0〉 =20.770 ± 0.042stat ± 0.024sys mag (corresponding to a distance of 143 ± 3 kpc).

TheSpitzerSurvey of Stellar Structure in Galaxies ( S 4 G ) is an Exploration Science Legacy Program approved for theSpitzerpost–cryogenic mission. It is a volume-, magnitude-, and size-limited ( d < 40 Mpc d < 40     Mpc ,|b| > 30° | b | > 30 ° , m Bcorr < 15.5 m B corr < 15.5 , and D 25 > 1′ D 25 > 1 ′ ) survey of 2331 galaxies using the Infrared Array Camera (IRAC) at 3.6 and 4.5 μm. Each galaxy is observed for 240 s and mapped to≥1.5 × D 25 ≥ 1.5 × D 25 . The final mosaicked images have a typical 1σ rms noise level of 0.0072 and0.0093 MJy sr-1 0.0093     MJy   sr - 1 at 3.6 and 4.5 μm, respectively. Our azimuthally averaged surface brightness profile typically traces isophotes atμ3.6μm(AB)(1σ) ∼ 27 mag arcsec-2 μ 3.6 μ m ( AB ) ( 1 σ ) ∼ 27     mag   arcsec - 2 , equivalent to a stellar mass surface density of∼1 M ⊙pc-2 ∼ 1     M ⊙ pc - 2 . S 4 G thus provides an unprecedented data set for the study of the distribution of mass and stellar structures in the local universe. This large, unbiased, and extremely deep sample of all Hubble types from dwarfs to spirals to ellipticals will allow for detailed structural studies, not only as a function of stellar mass, but also as a function of the local environment. The data from this survey will serve as a vital testbed for cosmological simulations predicting the stellar mass properties of present-day galaxies. This article introduces the survey and describes the sample selection, the significance of the 3.6 and 4.5 μm bands for this study, and the data collection and survey strategies. We describe the S 4 G data analysis pipeline and present measurements for a first set of galaxies, observed in both the cryogenic and warm mission phases ofSpitzer. For every galaxy we tabulate the galaxy diameter, position angle, axial ratio, inclination atμ3.6μm(AB) = 25.5 μ 3.6 μ m ( AB ) = 25.5 , and26.5 mag arcsec-2 26.5     mag   arcsec - 2 (equivalent to≈μB(AB) = 27.2 ≈ μ B ( AB ) = 27.2 and28.2 mag arcsec-2 28.2     mag   arcsec - 2 , respectively). These measurements will form the initial S 4 G catalog of galaxy properties. We also measure the total magnitude and the azimuthally averaged radial profiles of ellipticity, position angle, surface brightness, and color. Finally, using the galaxy-fitting code GALFIT, we deconstruct each galaxy into its main constituent stellar components: the bulge/spheroid, disk, bar, and nuclear point source, where necessary. Together, these data products will provide a comprehensive and definitive catalog of stellar structures, mass, and properties of galaxies in the nearby universe and will enable a variety of scientific investigations, some of which are highlighted in this introductory S 4 G survey paper.

The bright and distant past A dwarf nova is a type of cataclysmic variable containing a collapsed white dwarf star that accretes matter from its close companion in a binary system, a red dwarf. An instability periodically dumps material onto the white dwarf, increasing the luminosity by up to a hundredfold. Classical novae are thousands of times brighter than dwarf novae, and are accompanied by the formation of shells around the system. Theory predicts that dwarf novae will eventually gain sufficient mass to undergo classical nova eruptions. This suspected link between dwarf and classical novae now has an observational basis with the discovery of an ancient nova shell around the dwarf nova Z Camelopardalis. The nature of the shell suggests that a few thousand years ago, Z Cam underwent a classical nova eruption and for some days was one of the brightest stars in the sky. Classical novae are thousands of times brighter than dwarf novae, and are accompanied by the formation of shells around the system. This paper reports the discovery of a shell an order of magnitude more extended than those detected around many other classical novae surrounding the prototypical dwarf nova Z Camelopardalis, thereby observationally linking the objects. Cataclysmic variables (classical novae and dwarf novae) are binary star systems in which a red dwarf transfers hydrogen-rich matter, by way of an accretion disk, to its white dwarf companion 1 . In dwarf novae, an instability 2 is believed to episodically dump much of the accretion disk onto the white dwarf. The liberation of gravitational potential energy then brightens these systems by up to 100-fold every few weeks or months 2 . Thermonuclear-powered eruptions thousands of times more luminous 3 , 4 occur in classical novae 5 , accompanied by significant mass ejection 6 and formation of clearly visible shells 7 , 8 from the ejected material. Theory predicts that the white dwarfs in all dwarf novae must eventually accrete enough mass to undergo classical nova eruptions 9 . Here we report a shell, an order of magnitude more extended than those detected around many classical novae, surrounding the prototypical dwarf nova Z Camelopardalis. The derived shell mass matches that of classical novae, and is inconsistent with the mass expected from a dwarf nova wind or a planetary nebula. The shell observationally links the prototypical dwarf nova Z Camelopardalis with an ancient nova eruption and the classical nova process.

Stars of the Leo ring A massive ring of neutral hydrogen (H i ) was detected during radio observations in the 1980s, orbiting the M105 and NGC 3384 galaxies in the constellation Leo. Called the Leo ring, it remains a mysterious structure, thought to be a remnant primordial cloud left over from when the Leo I group galaxies formed. Until now the Leo ring has been detected only in the radio region of the spectrum (H i emission), suggesting an absence of stars. Now observations from the GALEX (Galaxy Evolution Explorer) orbiting space telescope have detected ultraviolet light originating from parts of the ring, indicating recent massive star formation in substructures. If such structures were common in the early Universe, they may have produced a large, as yet undetected population of faint, metal-poor, halo-lacking dwarf galaxies. The Leo ring is a massive, 200-kpc-wide structure orbiting the galaxies M105 and NGC3384 with a 4-Gyr period. This paper reports ultraviolet light originating from gaseous substructures, which is attributed to recent massive star formation. If structures like the Leo ring were common in the early Universe, they may have produced a large, yet undetected population of faint, metal-poor, halo-lacking dwarf galaxies. Few intergalactic, plausibly primordial clouds of neutral atomic hydrogen (H  i ) have been found in the local Universe, suggesting that such structures have either dispersed, become ionized or produced a stellar population on gigayear timescales. The Leo ring 1 , 2 , a massive ( M H  i  ≈ 1.8 × 10 9 , denoting the solar mass), 200-kpc-wide structure orbiting the galaxies M105 and NGC 3384 with a 4-Gyr period, is a candidate primordial cloud. Despite repeated atttempts 3 , 4 , it has previously been seen only from H  i emission, suggesting the absence of a stellar population. Here we report the detection of ultraviolet light from gaseous substructures of the Leo ring, which we attribute to recent massive star formation. The ultraviolet colour of the detected complexes is blue, implying the onset of a burst of star formation or continuous star formation of moderate (∼10 8 -yr) duration. Measured ultraviolet–visible photometry favours models with low metallicity ( Z  ≈  /50– /5, denoting the solar metallicity), that is, a low proportion of elements heavier than helium, although spectroscopic confirmation is needed. We speculate that the complexes are dwarf galaxies observed during their formation, but distinguished by their lack of a dark matter component 5 . In this regard, they resemble tidal dwarf galaxies, although without the enrichment preceding tidal stripping. If structures like the Leo ring were common in the early Universe, they may have produced a large, yet undetected, population of faint, metal-poor, halo-lacking dwarf galaxies.