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To understand the origin of extended disks of low-surface brightness (LSB) galaxies, we studied in detail four such systems with large disks seen edge on. Two of them are edge-on giant LSB galaxies (gLSBGs) recently identified by our team. The edge-on orientation of these systems boosts their surface brightnesses that provided an opportunity to characterize stellar populations spectroscopically and yielded the first such measurements for edge-on gLSBGs. We collected deep images of one galaxy using the 1.4 m Milanković Telescope, which we combined with the archival Subaru Hyper Suprime-Cam and DESI Legacy Surveys data available for the three other systems, and measured the structural parameters of the disks. We acquired deep long-slit spectra with the Russian 6 m telescope and the 10 m Keck II telescope and estimated stellar population properties in the high-surface brightness and LSB regions as well as the gas-phase metallicity distribution. The gas metallicity gradients are shallow to flat in the range between 0 and −0.03 dex per exponential disk scale length, which is consistent with the extrapolation of the gradient–scale length relation for smaller disk galaxies. Our estimates of stellar velocity dispersion in the LSB disks as well as the relative thickness of the disks indicate the dynamical overheating. Our observations favor mergers as the essential stage in the formation scenario for massive LSB galaxies.

Stellar counterrotation in disk galaxies directly relates to the complex phenomenon of the disk mass assembly believed to be driven by external processes, such as accretion and mergers. The study of such systems makes it possible to reveal the source of external accretion and establish the details of this process. In this paper, we investigate the galaxy PGC 66551 (MaNGA ID 1-179561), which hosts two large-scale counterrotating (CR) stellar disks identified in the Sloan Digital Sky Survey MaNGA data and then confirmed using deep follow-up spectroscopy with the 10 m Southern African Large Telescope. We measured the properties of ionized gas and stellar populations of both CR disks in PGC 66551. We found that the CR disk is compact, contains young stars with subsolar metallicity, and has a stellar mass of 5 × 10 ^9 M _⊙ , which amounts to ≈20% of the galaxy’s total. Surprisingly, the main 8 Gyr old disk has a significantly lower metallicity of −0.8 dex than other CR galaxies. We developed a simple analytic model of the history of the metal enrichment, which we applied to PGC 66551 and constrained the parameters of the galactic outflow wind, and estimated the metallicity of the infalling gas that formed the CR disk to be −0.9... −0.5 dex. Our interpretation prefers a merger with a gas-rich satellite over cold accretion from a cosmic filament as a source of gas, which then formed the CR disk in PGC 66551.

The outermost edges of some supernova remnants are marked by filaments of pure Balmer line emission produced by nonradiative shock fronts. The H α profiles of these filaments provide the shock speed and electron–proton temperature ratio in the shock. We have used the Hectochelle multiobject spectrograph on the MMT telescope to observe nine positions along the eastern nonradiative filaments of the Cygnus Loop, thereby extending the studies of Medina et al. to lower shock speeds. We complement the spectra with images from 1993 to 2020 to measure proper motions to further constrain the parameters. We also present observations of the photoionization precursor to show that the gas is strongly heated, and that the H α emission from the precursor is dominated by collisional excitation rather than recombination.

We present reprocessed flux-calibrated spectra of 406 stars from the UVES-POP stellar library in the wavelength range 320–1025 nm, which can be used for stellar population synthesis. The spectra are provided in the two versions having spectral resolving power R = 20,000 and R = 80,000. Raw spectra from the ESO data archive were re-reduced using the latest version of the UVES data reduction pipeline with some additional algorithms that we developed. The most significant improvements in comparison with the original UVES-POP release are (i) an updated echelle order merging, which eliminates “ripples” present in the published spectra; (ii) a full telluric correction; (iii) merging of nonoverlapping UVES spectral setups taking into account the global continuum shape; (iv) a spectrophotometric correction and absolute flux calibration; and (v) estimates of the interstellar extinction. For 364 stars from our sample, we computed atmospheric parameters T _eff , surface gravity log g , metallicity [Fe/H], and α -element enhancement [ α /Fe] by using a full-spectrum fitting technique based on a grid of synthetic stellar atmospheres and a novel minimization algorithm. We also provide projected rotational velocity $v\sin i$ and radial velocity v _rad estimates. The overall absolute flux uncertainty in the reprocessed data set is better than 2%, with subpercent accuracy for about half of the stars. A comparison of the recalibrated UVES-POP spectra with other spectral libraries shows a very good agreement in flux; at the same time, Gaia DR3 BP/RP spectra are often discrepant with our data, which we attribute to spectrophotometric calibration issues in Gaia DR3.

The occurrence of planetary nebulae (PNe) in globular clusters (GCs) provides an excellent chance to study low-mass stellar evolution in a special (low-metallicity, high stellar density) environment. We report a systematic spectroscopic survey for the [O iii] 5007 Å emission line of PNe in 1469 Virgo GCs and 121 Virgo ultra-compact dwarfs (UCDs), mainly hosted in the giant elliptical galaxies M87, M49, M86, and M84. We detected zero PNe in our UCD sample and discovered one PN () associated with an M87 GC. We used the [O iii] detection limit for each GC to estimate the luminosity-specific frequency of PNe, α, and measured α in the Virgo cluster GCs to be . The value of α in the Virgo GCs is among the lowest reported in any environment, due in part to the large sample size, and it is 5–6 times lower than that for the Galactic GCs. We suggest that α decreases toward brighter and more massive clusters, sharing a similar trend as the binary fraction, and the discrepancy between the Virgo and Galactic GCs can be explained by the observational bias in extragalactic surveys toward brighter GCs. This low but nonzero efficiency in forming PNe may highlight the important role played by binary interactions in forming PNe in GCs. We argue that a future survey of less massive Virgo GCs will be able to determine whether PN production in the Virgo GCs is governed by an internal process (mass, density, binary fraction) or if it is largely regulated by the external environment. [ABSTRACT FROM AUTHOR]

Ultra-diffuse galaxies (UDGs) are spatially extended, low surface brightness stellar systems with regular elliptical-like morphology found in a wide range of environments. Studies of the internal dynamics and dark matter content of UDGs that would elucidate their formation and evolution have been hampered by their low surface brightnesses. Here, we present spatially resolved velocity profiles, stellar velocity dispersions, ages, and metallicities for nine UDGs in the Coma cluster. We use intermediate-resolution spectra obtained with Binospec, the MMT's new high-throughput optical spectrograph. We derive dark matter fractions between 50% and 90% within the half-light radius using Jeans dynamical models. Three galaxies exhibit major axis rotation, two others have highly anisotropic stellar orbits, and one shows signs of triaxiality. In the Faber–Jackson and mass–metallicity relations, the nine UDGs fill the gap between cluster dwarf elliptical (dE) and fainter dwarf spheroidal galaxies. Overall, the observed properties of all nine UDGs can be explained by a combination of internal processes (supernovae feedback) and environmental effects (ram pressure stripping, interaction with neighbors). These observations suggest that UDGs and dEs are members of the same galaxy population. [ABSTRACT FROM AUTHOR]

Nearly every massive galaxy harbors a supermassive black hole (SMBH) in its nucleus. SMBH masses are millions to billions of solar mass, and they correlate with properties of spheroids of their host galaxies. While the SMBH growth channels, mergers, and gas accretion are well established, their origin remains uncertain: they could have emerged either from massive “seeds” (105–106M⊙) formed by direct collapse of gas clouds in the early universe or from smaller (100 M⊙) BHs, end products of first stars. The latter channel would leave behind numerous intermediate-mass BHs (IMBHs, 102–105M⊙). Although many IMBH candidates have been identified, none are accepted as definitive; thus, their very existence is still debated. Using data mining in wide-field sky surveys and applying dedicated analysis to archival and follow-up optical spectra, we identified a sample of 305 IMBH candidates having masses , which reside in galaxy centers and are accreting gas that creates characteristic signatures of a type I active galactic nucleus (AGN). We confirmed the AGN nature of 10 sources (including five previously known objects that validate our method) by detecting the X-ray emission from their accretion disks, thus defining the first bona fide sample of IMBHs in galactic nuclei. All IMBH host galaxies possess small bulges and sit on the low-mass extension of the scaling relation, suggesting that they must have experienced very few if any major mergers over their lifetime. The very existence of nuclear IMBHs supports the stellar-mass seed scenario of the massive BH formation. [ABSTRACT FROM AUTHOR]

The star formation (SFH) and chemical enrichment (CEH) histories of Local Group galaxies are traditionally studied by analyzing their resolved stellar populations in a form of color–magnitude diagrams obtained with the Hubble Space Telescope. Star clusters can be studied in integrated light using ground-based telescopes to much larger distances. They represent snapshots of the chemical evolution of their host galaxy at different ages. Here we present a simple theoretical framework for the chemical evolution based on the instantaneous recycling approximation (IRA) model. We infer a CEH from an SFH and vice versa using observational data. We also present a more advanced model for the evolution of individual chemical elements that takes into account the contribution of supernovae type Ia. We demonstrate that ages, iron, and α-element abundances of 15 star clusters derived from the fitting of their integrated optical spectra reliably trace the CEH of the Large Magellanic Cloud obtained from resolved stellar populations in the age range 40 Myr < t < 3.5 Gyr. The CEH predicted by our model from the global SFH of the LMC agrees remarkably well with the observed cluster age–metallicity relation. Moreover, the present-day total gas mass of the LMC estimated by the IRA model () matches within uncertainties the observed H i mass corrected for the presence of molecular gas (). We briefly discuss how our approach can be used to study SFHs of galaxies as distant as 10 Mpc at the level of detail that is currently available only in a handful of nearby Milky Way satellites. [ABSTRACT FROM AUTHOR]

The progenitor systems of the class of “Ca-rich transients” is a key open issue in time domain astrophysics. These intriguing objects exhibit unusually strong calcium line emissions months after explosion, fall within an intermediate luminosity range, are often found at large projected distances from their host galaxies, and may play a vital role in enriching galaxies and the intergalactic medium. Here we present multiwavelength observations of iPTF15eqv in NGC 3430, which exhibits a unique combination of properties that bridge those observed in Ca-rich transients and SNe Ib/c. iPTF15eqv has among the highest [Ca ii]/[O i] emission line ratios observed to date, yet is more luminous and decays more slowly than other Ca-rich transients. Optical and near-infrared photometry and spectroscopy reveal signatures consistent with the supernova explosion of a star that was stripped of its H-rich envelope via binary interaction. Distinct chemical abundances and ejecta kinematics suggest that the core collapse occurred through electron-capture processes. Deep limits on possible radio emission made with the Jansky Very Large Array imply a clean environment (n ≲ 0.1 cm−3) within a radius of cm. Chandra X-ray Observatory observations rule out alternative scenarios involving the tidal disruption of a white dwarf (WD) by a black hole, for masses >100 M⊙. Our results challenge the notion that spectroscopically classified Ca-rich transients only originate from WD progenitor systems, complicate the view that they are all associated with large ejection velocities, and indicate that their chemical abundances may vary widely between events. [ABSTRACT FROM AUTHOR]

Selected from a sample of nine, isolated, dwarf early-type galaxies (ETGs) with the same range of kinematic properties as dwarf ETGs in clusters, we use LEDA 2108986 (CG 611) to address the nature versus nurture debate regarding the formation of dwarf ETGs. The presence of faint disk structures and rotation within some cluster dwarf ETGs has often been heralded as evidence that they were once late-type spiral or dwarf irregular galaxies prior to experiencing a cluster-induced transformation into an ETG. However, CG 611 also contains significant stellar rotation (≈20 km s−1) over its inner half-light radius ( kpc), and its stellar structure and kinematics resemble those of cluster ETGs. In addition to hosting a faint young nuclear spiral within a possible intermediate-scale stellar disk, CG 611 has accreted an intermediate-scale, counter-rotating gas disk. It is therefore apparent that dwarf ETGs can be built by accretion events, as opposed to disk-stripping scenarios. We go on to discuss how both dwarf and ordinary ETGs with intermediate-scale disks, whether under (de)construction or not, are not fully represented by the kinematic scaling , and we also introduce a modified spin–ellipticity diagram – with the potential to track galaxies with such disks. [ABSTRACT FROM AUTHOR]

Neutron stars are thought to be born rapidly rotating and then exhibit a phase of rotation-powered pulsations as they slow down to 1–10 s periods. The significant population of millisecond pulsars observed in our Galaxy is explained by the recycling concept: during an epoch of accretion from a donor star in a binary system, the neutron star is spun up to millisecond periods. However, only a few pulsars are observed during this recycling process, with relatively high rotational frequencies. Here we report the detection of an X-ray pulsar with in the globular cluster B091D in the Andromeda galaxy, the slowest pulsar ever found in a globular cluster. This bright (up to 30% of the Eddington luminosity) spinning-up pulsar, persistent over the 12 years of observations, must have started accreting less than 1 Myr ago and has not yet had time to accelerate to hundreds of Hertz. The neutron star in this unique wide binary with an orbital period in a 12 Gyr old, metal-rich star cluster accretes from a low-mass, slightly evolved post-main-sequence companion. We argue that we are witnessing a binary formed at a relatively recent epoch by getting a ∼0.8 star in a dynamical interaction—a viable scenario in a massive, dense globular cluster like B091D with high global and specific stellar encounter rates. This intensively accreting non-recycled X-ray pulsar therefore provides a long-sought missing piece in the standard pulsar recycling picture. [ABSTRACT FROM AUTHOR]

We search the Sloan Digital Sky Survey and the Baryon Oscillation Sky Survey to identify ∼5500 massive compact quiescent galaxy candidates at 0.2 < z < 0.8. We robustly classify a subsample of 438 E+A galaxies based on their spectral properties and make this catalog publicly available. We examine sizes, stellar population ages, and kinematics of galaxies in the sample and show that the physical properties of compact E+A galaxies suggest that they are a progenitor of massive compact quiescent galaxies. Thus, two classes of objects—compact E+A and compact quiescent galaxies—may be linked by a common formation scenario. The typical stellar population age of compact E+A galaxies is <1 Gyr. The existence of compact E+A galaxies with young stellar populations at 0.2 < z < 0.8 means that some compact quiescent galaxies first appear at intermediate redshifts. We derive a lower limit for the number density of compact E+A galaxies. Assuming passive evolution, we convert this number density into an appearance rate of new compact quiescent galaxies at 0.2 < z < 0.8. The lower limit number density of compact quiescent galaxies that may appear at z < 0.8 is comparable to the lower limit of the total number density of compact quiescent galaxies at these intermediate redshifts. Thus, a substantial fraction of the z < 0.8 massive compact quiescent galaxy population may descend from compact E+A galaxies at intermediate redshifts. [ABSTRACT FROM AUTHOR]