The PHANGS-HST Survey: Physics at High Angular Resolution in Nearby Galaxies with the Hubble Space Telescope

The PHANGS program is building the first data set to enable the multiphase, multiscale study of star formation across the nearby spiral galaxy population. This effort is enabled by large survey programs with the Atacama Large Millimeter/submillimeter Array (ALMA), MUSE on the Very Large Telescope, and the Hubble Space Telescope (HST), with which we have obtained CO(2–1) imaging, optical spectroscopic mapping, and high-resolution UV–optical imaging, respectively. Here, we present PHANGS-HST, which has obtained NUV–U–B–V–I imaging of the disks of 38 spiral galaxies at distances of 4–23 Mpc, and parallel V- and I-band imaging of their halos, to provide a census of tens of thousands of compact star clusters and multiscale stellar associations. The combination of HST, ALMA, and VLT/MUSE observations will yield an unprecedented joint catalog of the observed and physical properties of ∼100,000 star clusters, associations, H ii regions, and molecular clouds. With these basic units of star formation, PHANGS will systematically chart the evolutionary cycling between gas and stars across a diversity of galactic environments found in nearby galaxies. We discuss the design of the PHANGS-HST survey and provide an overview of the HST data processing pipeline and first results. We highlight new methods for selecting star cluster candidates, morphological classification of candidates with convolutional neural networks, and identification of stellar associations over a range of physical scales with a watershed algorithm. We describe the cross-observatory imaging, catalogs, and software products to be released. The PHANGS high-level science products will seed a broad range of investigations, in particular, the study of embedded stellar populations and dust with the James Webb Space Telescope, for which a PHANGS Cycle 1 Treasury program to obtain eight-band 2–21 μm imaging has been approved.

Confining density functional approach for color superconducting quark matter and mesonic correlations

We present a novel relativistic density-functional approach to modeling quark matter with a mechanism to mimic confinement. The quasiparticle treatment of quarks provides their suppression due to large quark selfenergy already at the mean-field level. We demonstrate that our approach is equivalent to a chiral quark model with medium-dependent couplings. The dynamical restoration of the chiral symmetry is ensured by construction of the density functional. Beyond the mean field, quark correlations in the pseudoscalar channel are described within the Gaussian approximation. This explicitly introduces pionic states into the model. Their contribution to the thermodynamic potential is analyzed within the Beth–Uhlenbeck framework. The modification of the meson mass spectrum in the vicinity of thee (de)confinement transition is interpreted as the Mott transition. Supplemented with the vector repulsion and diquark pairing the model is applied to construct a hybrid quark-hadron EoS of cold compact-star matter. We study the connection of such a hybrid EoS with the stellar mass-radius relation and tidal deformability. The model results are compared to various observational constraints including the NICER radius measurement of PSR J0740+6620 and the tidal deformability constraint from GW170817. The model is shown to be consistent with the constraints, still allowing for further improvement by adjusting the vector repulsion and diquark pairing couplings.

Finite-resolution Deconvolution of Multiwavelength Imaging of 20,000 Galaxies in the COSMOS Field: The Evolution of Clumpy Galaxies over Cosmic Time

Compact star-forming clumps observed in distant galaxies are often suggested to play a crucial role in galaxy assembly. In this paper, we use a novel approach of applying finite-resolution deconvolution on ground-based images of the COSMOS field to resolve 20,185 star-forming galaxies (SFGs) at 0.5 < z < 2 to an angular resolution of 0.″3 and study their clump fractions. A comparison between the deconvolved images and HST images across four different filters shows good agreement and validates image deconvolution. We model spectral energy distributions using the deconvolved 14-band images to provide resolved surface brightness and stellar-mass density maps for these galaxies. We find that the fraction of clumpy galaxies decreases with increasing stellar masses and with increasing redshift: from ∼30% at z ∼ 0.7 to ∼50% at z ∼ 1.7. Using abundance matching, we also trace the progenitors for galaxies at z ∼ 0.7 and measure the fractional mass contribution of clumps toward their total mass budget. Clumps are observed to have a higher fractional mass contribution toward galaxies at higher redshift: increasing from ∼1% at z ∼ 0.7 to ∼5% at z ∼ 1.7. Finally, the majority of clumpy SFGs have higher specific star formation rates (sSFR) compared to the average SFGs at fixed stellar mass. We discuss the implication of this result for in situ clump formation due to disk instability.

Equation of state for holographic nuclear matter as instanton gas

In a holographic model, which was used to investigate the color superconducting phase of QCD, a dilute gas of instantons is introduced to study the nuclear matter. The free energy of the nuclear matter is computed as a function of the baryon chemical potential in the probe approximation. Then the equation of state is obtained at low temperature. Using the equation of state for the nuclear matter, the Tolman-Oppenheimer-Volkov equations for a cold compact star are solved. We find the mass-radius relation of the star, which is similar to the one for quark star. This similarity implies that the instanton gas given here is a kind of self-bound matter.

Self-gravitating anisotropic star using gravitational decoupling

This paper addresses a new gravitationally decoupled anisotropic solution for the compact star model via the minimal geometric deformation (MGD) approach. We consider a non-singular well-behaved gravitational potential corresponding to the radial component of the seed spacetime and embedding class I condition that determines the temporal metric function to solve the seed system completely. However, two different well-known mimic approaches such as pr = Θ1 1 and ρ = Θ0 0 have been employed to determine the deformation function which gives the solution of the second system corresponding to the extra source. In order to test the physical viability of the solution, we have checked several conditions such as regularity conditions, energy conditions, causality conditions, hydrostatic equilibrium, etc. Moreover, the stability of the solutions has been also discussed by the adiabatic index and its critical value. We find that the solutions set seems viable as far as observational data are concerned.

Generalized compact star models with conformal symmetry

We generate a new generalized regular charged anisotropic exact model that admits conformal symmetry in static spherically symmetric spacetime. Our model was examined for physical acceptability as realistic stellar models. The regularity is not violated, the energy conditions are satisfied, the physical forces balanced at equilibrium, the stability is satisfied via adiabatic index, and the surface red shift and mass–radius ratio are within the required bounds. Our conformal charged anisotropic exact solution contains models generated by Finch–Skea, Vaidya–Tikekar and Schwarzschild. Also, some recent charged or neutral and anisotropic or isotropic conformally symmetric models are found as special cases of our exact model. Our approach using a conformal symmetry provides a generalized geometric framework for studying compact objects.

Could the GW190814 Secondary Component Be a Bosonic Dark Matter Admixed Compact Star?

We investigate whether the recently observed 2.6 M ⊙ compact object in the gravitational wave event GW190814 can be a bosonic dark matter (DM) admixed compact star. By considering the three constraints of mass, radius, and the stability of such an object, we find that if the DM is made of QCD axions, their particle mass m is constrained to a range that has already been ruled out by the independent constraint imposed by the stellar-mass black hole superradiance process. The 2.6 M ⊙ object can still be a neutron star admixed with at least 2.0 M ⊙ of DM made of axion-like particles (or even a pure axion-like particle star) if 2 × 10−11 eV ≤ m ≤ 2.4 × 10−11 eV (2.9 × 10−11 eV ≤ m ≤ 3.2 × 10−11 eV) with a decay constant of f ≥ 8 × 1017 GeV.

Globular Clusters and Streaming Velocities: Testing the New Formation Channel in High-resolution Cosmological Simulations

The formation of globular clusters and their relation to the distribution of dark matter have long puzzled astronomers. One of the most recently proposed globular cluster formation channels ties ancient star clusters to the large-scale streaming velocity of baryons relative to dark matter in the early universe. These streaming velocities affect the global infall of baryons into dark matter halos, the high-redshift halo mass function, and the earliest generations of stars. In some cases, streaming velocities may result in dense regions of dark matter-free gas that becomes Jeans unstable, potentially leading to the formation of compact star clusters. We investigate this hypothesis using cosmological hydrodynamical simulations that include a full chemical network and the formation and destruction of H2, a process crucial for the formation of the first stars. We find that high-density gas in regions with significant streaming velocities is indeed somewhat offset from the centers of dark matter halos, but this offset is typically significantly smaller than the virial radius. Gas outside of dark matter halos never reaches Jeans-unstable densities in our simulations. We postulate that low-level (Z ≈ 10−3 Z ⊙) metal enrichment by Population III supernovae may enable cooling in the extra-virial regions, allowing gas outside of dark matter halos to cool to the cosmic microwave background temperature and become Jeans unstable. Follow-up simulations that include both streaming velocities and metal enrichment by Population III supernovae are needed to understand if streaming velocities provide one path for the formation of globular clusters in the early universe.

Point-wise Self-similar Solution for Spiral Shocks in an Accretion Disk with Mass Outflow in a Binary

We examine the properties of spiral shocks from a steady, adiabatic, non-axisymmetric accretion disk around a compact star in a binary. We first incorporate all possible influences from a binary through adopting the Roche potential and Coriolis forces in the basic conservation equations. In this paper, we assume spiral shocks to be point-wise and self-similar, and that the flow is in vertical hydrostatic equilibrium to simplify the study. We also investigate mass outflow due to shock compression and apply it to an accreting white dwarf in a binary. We find that our model will be beneficial for overcoming the ad hoc assumption of an optically thick wind generally used in studies of the progenitors of supernovae Ia.