Entire Galaxy Research Articles

Fully comprehensive diagnostic of galaxy activity using principal components of visible spectra: implementation on nearby S0s

Abstract We introduce a novel galaxy classification methodology based on the visible spectra of a sample of over 68,000 nearby (z ≤ 0.1) Sloan Digital Sky Survey lenticular (S0) galaxies. Unlike traditional diagnostic diagrams, which rely on a limited set of emission lines and class dividers to identify ionizing sources, our approach provides a comprehensive framework for characterizing galaxies regardless of their activity level. By projecting galaxies into the 2D latent space defined by the first three principal components (PCs) of their entire visible spectra, our method remains robust even when data from individual emission lines are missing. We employ Gaussian kernel density estimates of the classical Baldwin-Phillips-Terlevich (BPT) activity classes in the new classification subspace, adjusted according to their relative abundance in our S0 sample, to generate probability maps for star-forming, Seyfert, composite, and LINER galaxies. These maps closely mirror the canonical distribution of BPT classes shown by the entire galaxy population, demonstrating that our PC-based taxonomy effectively predicts the dominant ionizing mechanisms through a probabilistic approach that provides a realistic reflection of galaxy activity and allows for refined class membership. Our analysis further reveals that flux-limited BPT-like diagrams are inherently biased against composite and star-forming galaxies due to their weaker [O iii] emission. Besides, it suggests that although most low-activity galaxies excluded from these diagnostics exhibit visual spectra with LINER-like characteristics, their remaining activity is likely driven by mechanisms unrelated to either star formation or supermassive black hole accretion. A machine-readable catalogue listing BPT-class probabilities for the galaxies analysed is available online at CDS website.

Antimatter in astronomy and cosmology: the early history

ABSTRACT So-called antimatter in the form of elementary particles such as positive electrons (antielectrons alias positrons) and negative protons (antiprotons) has for long been investigated by physicists. However, atoms or molecules of this exotic kind are conspicuously absent from nature. Since antimatter is believed to be symmetric with ordinary matter, the flagrant asymmetry constitutes a problem that still worries physicists and cosmologists. As first suggested by Paul Dirac in 1933, in distant parts of the universe there might be entire stars and galaxies made of antiparticles alone. Why not? This paper examines how the concepts of antiparticles and antimatter slowly migrated from particle physics to astronomy and cosmology. At around 1970 a few physicists speculated about an anti-universe separate from ours while others looked for the charge asymmetry in quantum processes in the early big-bang explosion of the universe. Others again proposed a ‘plasma cosmology’ that kept our world and the hypothetical world of antimatter apart. Soviet physicists and astronomers were no less interested in the problem than their colleagues in the West. The paper details the development up to the late 1970s, paying attention not only to mainstream scientific works but also to more speculative ideas, some of them very speculative. By that time the antimatter mystery remained mysterious – which is still the situation.

First study of the supernova remnant population in the Large Magellanic Cloud with eROSITA

Aims. The all-sky survey carried out by the extended Roentgen Survey with an Imaging Telescope Array (eROSITA) on board Spektrum-Roentgen-Gamma (Spektr-RG, SRG) has provided spatially and spectrally resolved X-ray data of the entire Large Magellanic Cloud (LMC) and its immediate surroundings in the soft X-ray band down to 0.2 keV, with an average angular resolution of 26″ in the field of view. In this work, we study the supernova remnants (SNRs) and SNR candidates in the LMC using data from the first four all-sky surveys (eRASS:4). From the X-ray data, in combination with results at other wavelengths, we obtain information about the SNRs, their progenitors, and the surrounding interstellar medium (ISM). Studying the entire population of SNRs in a galaxy aids in understanding the underlying stellar populations, the environments in which the SNRs are evolving, and the stellar feedback on the ISM. Methods. The eROSITA telescopes are the best instruments currently available for the study of extended soft sources such as SNRs in an entire galaxy due to their large field of view and high sensitivity in the softer part of the X-ray band. We applied the Gaussian gradient magnitude filter to the eROSITA images of the LMC in order to highlight the edges of the shocked gas and find new SNRs. We visually compared the X-ray images with those of their optical and radio counterparts to investigate the true nature of the extended emission. The X-ray emission was evaluated using the contours with respect to the background, while for the optical, we used line ratio diagnostics and non-thermal emission in the radio images. We used the Magellanic Cloud Emission Line Survey for the optical data. For the radio comparison, we used data from the Australian Square Kilometre Array Pathfinder survey of the LMC. Using the star formation history derived from the near-IR photometry of the VISTA survey of the Magellanic Clouds, we investigated the possible progenitor type of the new SNRs and SNR candidates in our sample. Results. We present the most up-to-date catalogue of SNRs in the LMC. Previously known SNRs and SNR candidates were detected with a 1σ significance down to a surface brightness of Σ [0.2–5.0 keV] = 3.0 × 10−15 erg s−1 cm−2 arcmin−2 and were examined. The eROSITA data allowed us to confirm one of the previous candidates as an SNR. We confirm three newly detected extended sources as new SNRs, while we propose 13 extended sources as new X-ray SNR candidates. We also present the analysis of the follow-up XMM-Newton observation of MCSNR J0456–6533 discovered with eROSITA. Among the new candidates, we propose J0614–7251 (4eRASSU J061438.1–725112) as the first X-ray SNR candidate in the outskirts of the LMC.

JWST/NIRSpec insights into the circumnuclear region of Arp 220: A detailed kinematic study

The study of starburst and active galactic nuclei (AGN) feedback is crucial for understanding the regulation of star formation and the evolution of galaxies across cosmic time. Arp 220, the closest ultraluminous infrared galaxy (ULIRG), is in an advanced phase of a major merger with two distinct nuclei, and it shows evidence of multiphase (molecular, ionized, and neutral) and multiscale (from < 0.1 to > 5 kpc) outflows. Therefore, it represents an ideal system for investigating outflow mechanisms and feedback phenomena in detail. Using new JWST NIRSpec IFU observations, we investigated the spatially resolved gaseous (in both ionized and hot molecular phases) and stellar kinematics in the innermost 1 kpc. We decoupled the different gas kinematic components through multi-Gaussian fitting, identifying two multiphase outflows, each associated with one nucleus, with velocities up to $ We also resolved two counter-rotating discs around each nucleus embedded in a larger-scale rotational disk. We compute the total (including ionized, cold, and hot molecular) outflow mass ($ 10^7$ M$_ the mass rate ($ and the energetics ($ out for each nucleus, and we found that the ionized and hot molecular outflowing gas contribute around 2-30<!PCT!> of the total mass and the energy of the outflows, as inferred from the combination of multiwavelength information. We discuss the possible origin of the outflows, finding no compelling evidence to prefer a starburst- or AGN-driven scenario. Regardless of their nature, outflows in Arp 220 propagate in multiple directions from parsec to kiloparsec scales, potentially impacting a significant portion of the host galaxy. This contrasts with isolated systems where outflows typically follow a more collimated path or are limited to the central region of the galaxy and hence do not affect the interstellar medium throughout the entire galaxy. This study highlights the importance of investigating merging systems with multiwavelength facilities, including JWST/NIRSpec IFU, to obtain a comprehensive understanding of feedback mechanisms in galaxy evolution.

Dark matter limits from the tip of the red giant branch of globular clusters

Capture and annihilation of weakly interacting massive particle (WIMP)-like dark matter in red giant stars can lead to faster-than-expected ignition of the helium core, and thus a lower tip of the red giant branch (TRGB) luminosity. We use data to place constraints on the dark matter-nucleon cross section using 22 globular clusters with measured TRGB luminosities, and place projections on the sensitivity resulting from 161 clusters with full phase space distributions observed by . Although limits remain weaker than those from Earth-based direct detection experiments, they represent a constraint that is fully independent of dark matter properties in the solar neighborhood, probing its properties across the entire Milky Way galaxy. Based on our findings, it is likely that the use of the TRGB as a standard candle in H0 measurements is very robust against the effects of dark matter. Published by the American Physical Society 2024

Gravitational-wave and Gravitational-wave Memory Signatures of Core-collapse Supernovae

In this paper, we calculate the energy, signal-to-noise ratio (SNR), detection range, and angular anisotropy of the matter, matter memory, and neutrino memory gravitational-wave (GW) signatures of 21 three-dimensional initially nonrotating core-collapse supernova (CCSN) models carried to late times. We find that inferred energy, SNR, and detection range are angle-dependent quantities, and that the spread of possible energy, signal to noise, and detection ranges across all viewing angles generally increases with progenitor mass. When examining the low-frequency matter memory and neutrino memory components of the signal, we find that the neutrino memory is the most detectable component of a CCSN GW signal, and that DECIGO is best equipped to detect both matter memory and neutrino memory. Moreover, we find that the polarization angle between the h + and h × strains serves as a unique identifier of matter and neutrino memory. Finally, we develop a Galactic density- and stellar mass-weighted formalism to calculate the rate at which we can expect to detect CCSN GW signals with the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). When considering only the matter component of the signal, the aLIGO detection rate is around 65% of the total Galactic supernova rate, but increases to 90% when incorporating the neutrino memory component. We find that all future detectors (Einstein Telescope, Cosmic Explorer, DECIGO) will be able to detect CCSN GW signals from the entire Galaxy, and for the higher-mass progenitors even into the Local Group of galaxies.

Novae: An Important Source of Lithium in the Galaxy

The source of the Galactic lithium (Li) has long been a puzzle. With the discovery of Li in novae, extensive research has been conducted. However, there still exists a significant disparity between the observed abundance of Li in novae and the existing theoretical predictions. Using the Modules for Experiments in Stellar Astrophysics, we simulate the evolution of novae with element diffusion and appropriately increase the amount of 3He in the mixtures. Element diffusion enhances the transport efficiency between the nuclear reaction zone and the convective region on the surface of the white dwarf (WD) during nova eruptions, which results in more 7Be being transmitted to the WD surface and ultimately ejected. Compared to the previous predictions, the abundance of 7Be in novae simulated in our model significantly increases. The result is able to explain almost all observed novae. Using the method of population synthesis, we calculate Li yield in the Galaxy. We find that the Galactic occurrence rate of novae is about 130 yr−1, and about 110 M ⊙ Li produced by nova eruption is ejected into the interstellar medium (ISM). About 73% of Li in the Galactic ISM originates from novae and approximately 15%–20% of the entire Galaxy. This means that novae are the important source of Li in the Galaxy.

Observational signatures of the dust size evolution in isolated galaxy simulations

We aim to provide observational signatures of the dust size evolution in the interstellar medium (ISM). In particular, we explore indicators of the polycyclic aromatic hydrocarbon (PAH) mass fraction ($q_ PAH $), defined as the mass fraction of PAHs relative to the total dust grains. In addition, we validate our dust evolution model by comparing the observational signatures from our simulations to observations. We used the hydrodynamic simulation code, GADGET4-OSAKA to model the dust properties of Milky Way-like and NGC 628-like galaxies representing star-forming galaxies. This code incorporates the evolution of grain size distributions driven by dust production and interstellar processing. Furthermore, we performed post-processing dust radiative transfer calculations with SKIRT based on the hydrodynamic simulations to predict the observational properties of the simulations. We find that the intensity ratio between 8 um and 24 um ($I_ nu um )/I_ nu um )$) is correlated with $q_ PAH $ and can be used as an indicator of the PAH mass fraction. However, this ratio is influenced by the local radiation field. We suggest the 8 um -to-total infrared intensity ratio ($ I_ nu um )/ I_ TIR $) as another indicator of the PAH mass fraction, since it is tightly correlated with the PAH mass fraction. Furthermore, we explored the spatially resolved evolutionary properties of the PAH mass fraction in the simulated Milky Way-like galaxy using $ I_ nu um )/ I_ TIR $. We find that the spatially resolved PAH mass fraction increases with metallicity at $Z due to the interplay between accretion and shattering, whereas it decreases at $Z because of coagulation. Also, coagulation decreases the PAH mass fraction in regions with a high hydrogen surface density. Finally, we compared the above indicators in the NGC 628-like simulation with those observed in NGC 628 by Herschel Spitzer and JWST . Consequently, we find that our simulation underestimates the PAH mass fraction throughout the entire galaxy by a factor of $ 8$ on average. This could be due to the efficient loss of PAHs by coagulation in our model, suggesting that our treatment of PAHs in dense regions needs to be improved.

Exploring the dependence of chemical traits on metallicity

Context. Given the massive spectroscopic surveys and the Gaia mission, the Milky Way has turned into a unique laboratory to be explored using abundance ratios that show a strong dependence on time. Within this framework, the data provided through asteroseismology serve as a valuable complement. Even so, it has been demonstrated that chemical traits cannot be used as universal relations across the Galaxy. Aims. To complete this picture, it is important to investigate the dependence on metallicity of the chemical ratios employed for inferring stellar ages. We aim to explore different combinations of neutron-capture, odd-Z, and α elements as a function of age, particularly focusing on their metallicity dependence for a sample of 74 giant field stars. Methods. Using UVES observations, we derived atmospheric parameters and high-precision line-by-line chemical abundances (< 0.04 dex) for the entire set of spectra, which covers a wide spread in ages (up to 14 Gyr) and metallicities (−0.7 < [Fe/H] < +0.1). Stellar ages are inferred from astereoseismic information. Results. By fitting chemical-age trends for three different metallicity groups, we estimated their dependence on metallicity. Simultaneously, we identified those exhibiting stronger correlations with time. We found that the stronger chemical-age relations ([Zr/α]) are not necessarily the ratios with the smaller dependence on metallicity ([Ce/α] and [Ce/Eu]). Conclusions. We confirm the [n-capture/α]-age trends for evolved stars, wherein the most significant correlation is evident in stars with solar metallicity, gradually diminishing in stars with lower iron content. The lack of homogeneity within the metallicity range highlights the intricate nature of our Galaxy’s star formation history and yield production. The dependence on metallicity of the yields involving s-process elements and the influence of radial stellar migration pose challenges to relying solely on chemical abundances for dating stars. These findings contest the feasibility of establishing universally applicable chemical clocks that are valid across the entire Galaxy and across various metallicity ranges.

The cosmic-ray positron excess and its imprint in the Galactic gamma-ray sky

We study the origin of the positron excess observed in the local cosmic-ray spectrum at high energies, and relate it to the cosmic rays and gamma-ray emission across the entire Galaxy. In particular, we explore the hypothesis of a single, dominant source accountable for primary electron-positron pairs. Since we are agnostic about the physical nature of the underlying source population, we consider four models that are representative of young pulsars, old stars (as a tracer of millisecond pulsars), and annihilating dark matter particles. In the dark matter hypothesis, we consider both a cored and a cuspy model for the halo in the Milky Way. Then, we compare the associated gamma-ray sky maps with Fermi-LAT data. We find that the emission arising from pulsar wind nebulae is fairly concentrated near the mid plane, and therefore additional cosmic-ray sources must be invoked to explain the emission at the center of the Galaxy. If the local positron excess were mainly due to millisecond pulsars, inverse Compton scattering by the particles injected would naturally account for a non-negligible fraction of the central gamma-ray emission. The same process would lead to a tension for a standard NFW dark matter profile, exceeding the gamma-ray data by almost a factor of 2 in some regions of the Galaxy. Although the results for an isothermal, cored profile are in agreement with these data, the cross section needed in both cases is around 2 orders of magnitude above the thermal cross-section, disfavouring the dark matter interpretation.

Experimental observation of violent relaxation

Structures in the Universe, ranging from globular clusters to entire galaxies, are not described by standard statistical mechanics at equilibrium. Instead, they are formed through a process of a very different nature, called violent relaxation that is now known to be possible also in other systems that exhibit long-range interactions. This mechanism was proposed theoretically and modelled numerically, but never directly observed in any physical system. Here, we develop a table-top experiment allowing us to directly observe violent relaxation in an optical setting. The resulting optical dynamics can also be likened to the formation of an analogue 2D-galaxy through the analogy of the underlying equations, where we can control a range of parameters, including the nonlocal interacting potential, allowing us to emulate the physics of gravitational quantum and classical dark matter models.

Revisiting the accretion disc spectra of dwarf novae and nova-like variables: implications for the standard disc model

ABSTRACT Accretion discs are fundamental to much of astronomy. They can occur around stars, both young and old, around compact objects they provide a window into the extremes of physics, and around supermassive black holes in galaxy centres, they generate spectacular luminosities that can outshine the entire galaxy. However, our understanding of the inner workings of accretion discs remains far from complete. Here, we revisit a conundrum in the observations of some of the simplest accreting systems: the cataclysmic variables (CVs). The high-accretion-rate states of (non-magnetic) CVs can be divided into the short-lived outbursts (∼a week), typical of dwarf novae (DNe), and the long-lived (and sometimes perpetual) high states of nova-like (NL) CVs. Since both sorts of high-state occur in approximately steady-state accretion discs with similar properties and accretors, we would expect them to display similar spectral energy distributions. However, previous analyses based on UV spectra from the International Ultraviolet Explorer have shown that their spectral energy distributions are different. We perform a re-analysis of the data using up to date calibrations and distance (and thus dereddening) estimates to test whether this difference persists and whether it is statistically significant over the sample. We find that it does persist, and it is statistically significant. We propose routes to investigating this discrepancy further and discuss the implications this has for other accreting systems, such as X-ray binaries, active galactic nuclei, and protoplanetary discs.

Cosmic evolution of radio-excess active galactic nuclei in quiescent and star-forming galaxies across 0 < z < 4

Context. Radio-excess active galactic nuclei (radio-AGNs) are essential to our understanding of both the physics of black hole (BH) accretion and the interaction between BHs and host galaxies. Recent deep and wide radio continuum surveys have made it possible to study radio-AGNs down to lower luminosities and up to higher redshifts than previous studies, and are providing new insights into the abundance and physical origin of radio-AGNs. Aims. Here we focus on the cosmic evolution, physical properties, and AGN-host galaxy connections of radio-AGNs selected from a total sample of ∼400 000 galaxies at 0 < z < 4 in the GOODS-N and COSMOS fields. Methods. Combining the deep radio continuum data with multi-band, de-blended far-infrared, and submillimeter data, we were able to identify 983 radio-AGNs out of the entire galaxy sample through radio excess relative to the far-infrared–radio relation. Results. We studied the cosmic evolution of 1.4 GHz radio luminosity functions (RLFs) for both star-forming galaxies (SFGs) and radio-AGNs, which can be well described by a pure luminosity evolution of L⋆ ∝ (1 + z)−0.34 × z + 3.57 and a pure density evolution of Φ⋆ ∝ (1 + z)−0.77 × z + 2.69, respectively. We derived the turnover luminosity, above which the number density of radio-AGNs surpasses that of SFGs. We show that this crossover luminosity increases with increasing redshifts, from 1022.9 W Hz−1 at z ∼ 0 to 1025.2 W Hz−1 at z ∼ 4. At the full redshift range of 0 < z < 4, we further derive the probability (pradio) of SFGs and quiescent galaxies (QGs) hosting a radio-AGN, as a function of stellar mass (M⋆), radio luminosity (LR), and redshift (z), which yields pradio ∝ (1+z)3.08 M⋆1.06 LR−0.77 for SFGs, and pradio ∝ (1+z)2.47 M⋆1.41 LR−0.60 for QGs, respectively. Conclusions. The quantitative relation for the probabilities of galaxies hosting a radio-AGN indicates that radio-AGNs in QGs prefer to reside in more massive galaxies with higher LR than those in SFGs. The fraction of radio-AGN increases toward higher redshift in both SFGs and QGs, with a more rapid increase in SFGs.

The MAGPI survey: evolution of radial trends in star formation activity across cosmic time

ABSTRACT Using adaptive optics with the Multi-Unit Spectroscopic Explorer on the Very Large Telescope, the Middle Ages Galaxy Properties with Integral Field Spectroscopy survey allows us to study the spatially resolved Universe at a crucial time of ∼4 Gyr ago (z ∼ 0.3) when simulations predict the greatest diversity in evolutionary pathways for galaxies. We investigate the radial trends in the star formation (SF) activity and luminosity-weighted stellar ages as a function of offset from the star-forming main sequence (SFMS) for a total of 294 galaxies. Using both Hα emission and the 4000 Å break (i.e. D4000) as star formation rate (SFR) tracers, we find overall flat radial profiles for galaxies lying on and above the SFMS, suggestive of physical processes that enhance/regulate SF throughout the entire galaxy disc. However, for galaxies lying below the SFMS, we find positive gradients in SF suggestive of inside–out quenching. Placing our results in context with results from other redshift regimes suggests an evolution in radial trends at z ∼ 0.3 for SF galaxies above the SFMS, from uniformly enhanced SF at z ∼ 1 and ∼ 0.3 to centrally enhanced SF at z ∼ 0 (when averaged over a wide range of mass). We also capture higher local SFRs for galaxies below the SFMS compared to that of z ∼ 0, which can be explained by a larger population of quenched satellites in the local Universe and/or different treatments of limitations set by the D4000–sSFR relation.

SuperCAM CO(3-2) APEX survey at a 6 pc resolution in the Small Magellanic Clouds

The Small Magellanic Cloud (SMC) is an ideal laboratory for studying the properties of star-forming regions thanks to its low metallicity, which has an impact on the molecular gas abundance. However, a small number of molecular gas surveys of the entire galaxy have been carried out in the last few years, limiting the measurements of interstellar medium (ISM) properties in a homogeneous manner. We present the CO($3-2$) APEX survey at a $6$ pc resolution of the bar of the SMC, observed with the SuperCAM receiver attached to the APEX telescope. This high-resolution survey has allowed us to study certain properties of the ISM and to identify CO clouds in the innermost parts of the H$_2$ envelopes. We black adopted the CO analysis in the SMC bar comparing the CO($3-2$) survey with that of the CO($2-1$) of a similar resolution. We studied the CO($3-2$)-to-CO($2-1$) ratio ($R_ $), which is very sensitive to the environment properties (e.g., star-forming regions). We analyzed the correlation of this ratio with observational quantities that trace the star formation such as the local CO emission, the Spitzer color $ $, and the total IR surface brightness measured from the Spitzer and Herschel bands. For the identification of the CO($3-2$) clouds, we used the CPROPS algorithm, which allowed us to measure the physical properties of the clouds. We analyzed the scaling relationships of such physical properties. black We obtained $R_ 0.02$ for the SW bar and a slightly higher ratio 0.1,$ for N66 in the SMC. We found that $R_ $ varies from region to region, depending on the star formation activity. In regions dominated by HII and photo-dissociated regions (e.g., N22, N66) $R_ $ tends to be higher than the median values. Meanwhile, lower values were found toward quiescent clouds. We also found that $R_ black is correlated with the IR color $ $ and the total IR surface brightness. This finding indicates that $R_ $ increases with environmental properties, such as the dust temperature, total gas density, and radiation field. We identified $225$ molecular clouds with sizes of $R > 1.5$ pc and signal-to-noise ratios (S/N) of $> 3$ black of which only $17$ black are well resolved CO($3-2$) clouds black with S/N $ 5$. These $17$ clouds follow consistent scaling relationships to the inner Milky Way clouds but with some departures. For instance, CO($3-2$) tends to be less turbulent and less luminous than the inner Milky Way clouds of similar sizes. Finally, we estimated a median virial-based CO($3-2$)-to-H$_2$ conversion factor of for the total sample.

How time weathers galaxies: The temporal impact of the cluster environment on galaxy formation and evolution

Abstract We illuminate the altered evolution of galaxies in clusters compared to central galaxies by tracking galaxies in the IllustrisTNG300 simulation as they enter isolated clusters of mass 1013 < M200, mean/M⊙ < 1015 (at z = 0). We demonstrate significant trends in galaxy properties with residence time (time since first infall) and that there is a population of galaxies that remain star-forming even many Gyrs after their infall. By comparing the properties of galaxies at their infall time to their properties at z = 0, we show how scaling relations, like the stellar-to-halo mass ratio, shift as galaxies live in the cluster environment. Galaxies with a residence time of 10 Gyr increase their stellar-to-halo mass ratio, by around 1 dex. As measurements of the steepest slope of the galaxy cluster number density profile (Rst), frequently used as a proxy for the splashback radius, have been shown to depend strongly on galaxy selection, we show how Rst depends on galaxy residence time. Using galaxies with residence times less than one cluster crossing time (≈5 Gyr) to measure Rst leads to significant offsets relative to using the entire galaxy population. Galaxies must have had the opportunity to ‘splash back’ to the first caustic to trace out a representative value of Rst, potentially leading to issues for galaxy surveys using UV-selected galaxies. Our work demonstrates that the evolution of cluster galaxies continues well into their lifetime in the cluster and departs from a typical central galaxy evolutionary path.

Retarded Gravity in Disk Galaxies

Disk galaxies have a typical dimension of a few tens of kiloparsecs. It follows from the theory of general relativity that any signal originating from the galactic center will be noticed at the outskirts of the galaxy only tens of thousands of years later. This retardation effect, however, is absent in modelling used to calculate rotation curves throughout entire galaxies and their external gas. The considerable differences between Newtonian predictions and observed velocities are currently removed either by assuming dark matter or by suggesting various modifications to the laws of gravity, MOND being a long standing alternative to Newtonian gravity. In previous papers we have shown that by applying general relativity in a rigorous fashion, without neglecting retardation, one can explain the rotational velocities of galactic matter without modifying gravity or adding dark matter. Moreover, it was shown that dark matter effects, as they appear in gravitational lensing, the Tully-Fisher relation, and mass estimations based on the virial theorem could also be explained as retarded-gravity effects. It must be noted, however, that the proposed theory relies on the existence of a mass flow (of a changing rate) into the galaxy; a requirement that was not directly observed. In the original paper on the subject only one galaxy (M33) was analysed in detail. This was later amended with a published study of eleven galaxies. Here we give a more comprehensive retardation analysis of 143 galaxies of different types from the SPARC Galaxy collection. We show that in most cases we obtain very accurate fits to the data.

Merging galaxies in isolated environments. I. Multiband photometry, classification, stellar masses, and star formation rates

Extragalactic surveys provide significant statistical data for the study of crucial galaxy parameters (e.g. stellar mass, M$_*$, and star formation rate ,SFR) used to constrain galaxy evolution under different environmental conditions. These quantities are derived using manual or automatic methods for galaxy detection and flux measurement in imaging data at different wavelengths. The reliability of these automatic measurements, however, is subject to mis-identification and poor fitting due to the morphological irregularities present in resolved nearby galaxies (e.g. clumps, tidal disturbances, star- forming regions) and its environment (galaxies in overlap). Our aim is to provide accurate multi-wavelength photometry (from the UV to the IR, including GALEX, SDSS, and WISE) in a sample of $ 600$ nearby (z<0.1) isolated mergers, as well as estimations of M$_*$ and SFR. We performed photometry following a semi-automated approach using SExtractor, confirming by visual inspection that we successfully extracted the light from the entire galaxy, including tidal tails and star-forming regions. We used the available SED fitting code MAGPHYS in order to estimate M$_*$ and SFR. We provide the first catalogue of isolated merging galaxies of galaxy mergers including aperture-corrected photometry in 11 bands (FUV, NUV, u, g, r, i, z, W1, W2, W3, and W4), morphological classification, merging stage, M$_*$, and SFR. We found that SFR and M$_*$ derived from automated catalogues can be wrong by up to three orders of magnitude as a result of incorrect photometry. Contrary to previous methods, our semi-automated method can reliably extract the flux of a merging system completely. Even when the SED fitting often smooths out some of the differences in the photometry, caution using automatic photometry is suggested as these measurements can lead to large differences in M$_*$ and SFR estimations.

The epoch of the Milky Way’s bar formation: dynamical modelling of Mira variables in the nuclear stellar disc

ABSTRACT A key event in the history of the Milky Way is the formation of the bar. This event affects the subsequent structural and dynamical evolution of the entire Galaxy. When the bar formed, gas was likely rapidly funnelled to the centre of the Galaxy settling in a star-forming nuclear disc. The Milky Way bar formation can then be dated by considering the age distribution of the oldest stars in the formed nuclear stellar disc. In this highly obscured and crowded region, reliable age tracers are limited, but bright, high-amplitude Mira variables make useful age indicators as they follow a period–age relation. We fit dynamical models to the proper motions of a sample of Mira variables in the Milky Way’s nuclear stellar disc region. Weak evidence for inside-out growth and both radial and vertical dynamical heating with time of the nuclear stellar disc is presented, suggesting that the nuclear stellar disc is dynamically well-mixed. Furthermore, for Mira variables around a ∼350-d period, there is a clear transition from nuclear stellar disc-dominated kinematics to background bar-bulge-dominated kinematics. Using a Mira variable period–age relation calibrated in the solar neighbourhood, this suggests the nuclear stellar disc formed in a significant burst in star formation $(8\pm 1)\, \mathrm{Gyr}$ ago, although the data are also weakly consistent with a more gradual formation of the nuclear stellar disc at even earlier epochs. This implies a relatively early formation time for the Milky Way bar ($\gtrsim 8\, \mathrm{Gyr}$), which has implications for the growth and state of the young Milky Way and its subsequent history.

The Reliability of Accretion Disk Inclination Derived from X-Ray Spectroscopy of Active Galaxies

The inclination angle of substructures in active galaxies gives insights into physical components from scales of the vicinity of the central black hole to the entire host galaxy. We use the self-consistent reflection spectral model RELXILL to measure the inclination of the inner region of accretion disks with broadband (0.3–78 keV) X-ray observations, systematically studying the reliability of this methodology. To test the capability of the model to return statistically consistent results, we analyze multiepoch joint XMM-Newton and NuSTAR data of the narrow-line Seyfert 1 galaxy I Zwicky 1 and the broad-line radio galaxy 3C 382, which exhibit different degrees of spectral complexity and reflection features. As expected, we find that adding more data for analysis narrows the confidence interval and that multiepoch joint observations return optimal measurements; however, even single-epoch data can be well fitted if the reflection component is sufficiently dominant. Mock spectra are used to test the capability of RELXILL to recover input parameters from typical single-epoch joint observations. We find that inclination is well recovered at 90% confidence, with improved constraints at higher reflection fraction and higher inclination. Higher iron abundance and corona temperature tighten the constraints as well, but the effect is not as significant as a higher reflection fraction. The spin, however, has little effect in reflection-based inclination measurements. We conclude that broadband reflection spectroscopy can reliably measure inner accretion disk inclination.