The Astropy Problem

The Astropy Project (http://astropy.org) is, in its own words, "a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages." For five years this project has been managed, written, and operated as a grassroots, self-organized, almost entirely volunteer effort while the software is used by the majority of the astronomical community. Despite this, the project has always been and remains to this day effectively unfunded. Further, contributors receive little or no formal recognition for creating and supporting what is now critical software. This paper explores the problem in detail, outlines possible solutions to correct this, and presents a few suggestions on how to address the sustainability of general purpose astronomical software

Phylogenetic Relationships of the Marine Haplosclerida (Phylum Porifera) Employing Ribosomal (28S rRNA) and Mitochondrial (cox1, nad1) Gene Sequence Data

The systematics of the poriferan Order Haplosclerida (Class Demospongiae) has been under scrutiny for a number of years without resolution. Molecular data suggests that the order needs revision at all taxonomic levels. Here, we provide a comprehensive view of the phylogenetic relationships of the marine Haplosclerida using many species from across the order, and three gene regions. Gene trees generated using 28S rRNA, nad1 and cox1 gene data, under maximum likelihood and Bayesian approaches, are highly congruent and suggest the presence of four clades. Clade A is comprised primarily of species of Haliclona and Callyspongia, and clade B is comprised of H. simulans and H. vansoesti (Family Chalinidae), Amphimedon queenslandica (Family Niphatidae) and Tabulocalyx (Family Phloeodictyidae), Clade C is comprised primarily of members of the Families Petrosiidae and Niphatidae, while Clade D is comprised of Aka species. The polyphletic nature of the suborders, families and genera described in other studies is also found here

X-Shooting ULLYSES: Massive stars at low metallicity: I. Project description

Observations of individual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational wave events involving spectacular black hole mergers indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding of the physics and evolution of massive stars at low metallicity (Z). The Hubble Space Telescope has devoted 500 orbits to observing ∼250 massive stars at low Z in the ultraviolet (UV) with the COS and STIS spectrographs under the ULLYSES programme. The complementary X-Shooting ULLYSES (XShootU) project provides an enhanced legacy value with high-quality optical and near-infrared spectra obtained with the wide-wavelength coverage X-shooter spectrograph at ESOa's Very Large Telescope. We present an overview of the XShootU project, showing that combining ULLYSES UV and XShootU optical spectra is critical for the uniform determination of stellar parameters such as effective temperature, surface gravity, luminosity, and abundances, as well as wind properties such as mass-loss rates as a function of Z. As uncertainties in stellar and wind parameters percolate into many adjacent areas of astrophysics, the data and modelling of the XShootU project is expected to be a game changer for our physical understanding of massive stars at low Z. To be able to confidently interpret James Webb Space Telescope spectra of the first stellar generations, the individual spectra of low-Z stars need to be understood, which is exactly where XShootU can deliver

The Ionizing Spectra of Extremely Metal-poor O Stars: Constraints from the Only H ii Region in Leo P

Metal-poor, star-forming dwarf galaxies produce extreme nebular emission and likely played a major role in cosmic reionization. Yet, determining their contribution to the high-redshift ionizing photon budget is hampered by the lack of observations constraining the ionizing spectra of individual massive stars more metal-poor than the Magellanic Clouds (20%–50% Z _⊙ ). We present new Keck Cosmic Web Imager (KCWI) optical integral field unit spectroscopy of the only H ii region in Leo P (3% Z _⊙ ), which is powered by a single O star. We calculate the required production rate of photons capable of ionizing hydrogen and helium from the observed H β and He i λ 4471 emission-line fluxes. Remarkably, we find that the ionizing photon production rate and spectral hardness predicted by a tlusty model fit to the stellar spectral energy distribution agrees with our observational measurements within the uncertainties. We then fit C loudy photoionization models to the full suite of optical emission lines in the KCWI data and show that the shape of the same tlusty ionizing continuum simultaneously matches lines across a wide range of ionization energies. Finally, we detect O iii ] and N iii ] nebular emission in the Hubble Space Telescope far-ultraviolet spectrum of the Leo P H ii region, and highlight that the rarely observed N iii ] emission cannot be explained by our C loudy models. These results provide the first observational evidence that widely used, yet purely theoretical, model spectra accurately predict the ionizing photon production rate from late-O stars at very low metallicity, validating their use to model metal-poor galaxies both locally and at high redshift

Mass-to-light Ratios of Spatially Resolved Stellar Populations in M31

A galaxy's stellar mass-to-light ratio (M-star/L) is a useful tool for converting luminosity to stellar mass (M.). However, the practical utility of M-star/L inferred from stellar population synthesis (SPS) models is limited by mismatches between the real and assumed models for star-formation history (SFH) and dust geometry, both of which vary within galaxies. Here, we measure spatial variations in M-star/L and their dependence on color, SFH, and dust across the disk of M31, using a map of M-star(CMD) derived from color-magnitude diagrams of resolved stars in the Panchromatic Hubble Andromeda Treasury survey. First, we find comparable scatter in M-star/L for the optical and mid-IR, contrary to the common idea that M-star/L is less variable in the IR. Second, we confirm that M-star/L is correlated with color for both the optical and mid-IR and report color versus M-star/L relations (CMLRs) in M31 for filters used in the Sloan Digital Sky Survey and Widefield Infrared Survey Explorer. Third, we show that the CMLR residuals correlate with recent SFH, such that quiescent regions are offset to higher M-star/L than star-forming regions at a fixed color. The mid-IR CMLR, however, is not linear due to the high scatter of M-star/L in star-forming regions. Finally, we find a flatter optical CMLR than any SPS-based CMLRs in the literature. We show that this is an effect of dust geometry, which is typically neglected but should be accounted for when using optical data to map M-star.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The Scatter Matters: Circumgalactic Metal Content in the Context of the M−σM-\sigma Relation

The interaction between supermassive black hole (SMBH) feedback and the circumgalactic medium (CGM) continues to be an open question in galaxy evolution. In our study, we use SPH simulations to explore the impact of SMBH feedback on galactic metal retention and the motion of metals and gas into and through the CGM of L$_{*}$ galaxies. We examine 140 galaxies from the 25 Mpc cosmological volume, Romulus25, with stellar masses between 3 $\times$ 10$^{9}$ - 3 $\times$ 10$^{11}$ M$_{\odot}$. We measure the fraction of metals remaining in the ISM and CGM of each galaxy, and calculate the expected mass of its SMBH based on the $M-\sigma$ relation. The deviation of each SMBH from its expected mass, $\Delta M_{BH}$ is compared to the potential of its host via $\sigma$. We find that SMBHs with accreted mass above the empirical $M-\sigma$ relation are about 15\% more effective at removing metals from the ISM than under-massive SMBHs in star forming galaxies. Over-massive SMBHs suppress the overall star formation of their host galaxies and more effectively move metals from the ISM into the CGM. However, we see little evidence for the evacuation of gas from their halos, in contrast with other simulations. Finally, we predict that C IV column densities in the CGM of L$_{*}$ galaxies may depend on host galaxy SMBH mass. Our results show that the scatter in the low mass end of $M-\sigma$ relation may indicate how effective a SMBH is at the local redistribution of mass in its host galaxy.Comment: 16 pages, 14 figures, Submitted to Ap

A Comprehensive Investigation of Metals in the Circumgalactic Medium of Nearby Dwarf Galaxies

Dwarf galaxies are found to have lost most of their metals via feedback processes; however, there still lacks consistent assessment on the retention rate of metals in their circumgalactic medium (CGM). Here we investigate the metal content in the CGM of 45 isolated dwarf galaxies with M _* = 10 ^6.5–9.5 M _⊙ ( M _200m = 10 ^10.0–11.5 M _⊙ ) using the Hubble Space Telescope/Cosmic Origins Spectrograph. While H i (Ly α ) is ubiquitously detected (89%) within the CGM, we find low detection rates (≈5%–22%) in C ii , C iv , Si ii , Si iii , and Si iv , largely consistent with literature values. Assuming these ions form in the cool ( T ≈ 10 ^4 K) CGM with photoionization equilibrium, the observed H i and metal column density profiles can be best explained by an empirical model with low gas density and high volume filling factor. For a typical galaxy with M _200m = 10 ^10.9 M _⊙ (median of the sample), our model predicts a cool gas mass of M _CGM,cool ∼ 10 ^8.4 M _⊙ , corresponding to ∼2% of the galaxy’s baryonic budget. Assuming a metallicity of 0.3  Z _⊙ , we estimate that the dwarf galaxy’s cool CGM likely harbors ∼10% of the metals ever produced, with the rest either in more ionized states in the CGM or transported to the intergalactic medium. We further examine the EAGLE simulation and show that H i and low ions may arise from a dense cool medium, while C iv arises from a diffuse warmer medium. Our work provides the community with a uniform data set on dwarf galaxies’ CGM that combines our recent observations, additional archival data and literature compilation, which can be used to test various theoretical models of dwarf galaxies