arXiv subjects

G. J. Ferland

Publications and source records attributed to G. J. Ferland.

At least 19 recordsLinked to original sources

arXiv2025

A comparison of time-dependent Cloudy astrophysical code simulations with experimental X-ray spectra from keV laser-generated argon plasmas

We have generated strongly photoionized Ar plasmas in experiments designed to use primarily X-ray L-shell line emission generated from Ag foils irradiated by the VULCAN high-power laser at the UK Central Laser Facility. The principle of the experiment is that use of line emission rather than the usual sub-keV quasi-blackbody source allows keV radiation to play a more dominant role compared to softer X-rays and thus mimic the effect of a blackbody with a higher effective spectral temperature. Our aim is to reproduce in the laboratory the extreme photoionization conditions found in accretion-powered astrophysical sources. In this paper, we compare the experimental results on K-$β$ X-ray Ar spectra with modelling using the time-dependent version of the Cloudy astrophysical code. The results indicate that photoionized laboratory plasmas can be successfully modelled with codes such as Cloudy that have been developed for application to astrophysical sources. Our comparison of simulation and experiment shows that the flux of sub-keV photons that photoionize the outer-shell electrons can have a significant effect, and that detailed measurements of the X-ray drive spectrum across all photon energy ranges are crucial for accurate modelling of experiments.

astro-ph.HE↗

arXiv2025

Hidden (absorbed) Cooling Flows V: Groups and Galaxies including Spirals

Cooling flows are observed in X-ray studies of the centres of cool core clusters, galaxy groups and individual elliptical galaxies. They are partly hidden from direct view by embedded cold gas so have been called Hidden Cooling Flows. X-ray spectra from the XMM RGS reveal emission from hot gas modified by photoelectric absorption by cold gas intrinsic to the flow. Here we present the spectral analysis of 6 more low redshift galaxy groups ranging from the nearest fossil group to 2 groups hosting bright radio sources. All reveal absorbed cooling flows. AGN feedback is ineffective in heating the inner cooling gas in groups and elliptical galaxies. We have extended the analysis to include 3 nearby spiral galaxies (the Sombrero, Whirlpool and Sculptor galaxies). They have similar absorbed soft X-ray spectra to elliptical galaxies and may also host cooling flows of 0.3 to 1.1\Msun/yr in their CircumGalactic Medium.

astro-ph.GA↗

arXiv2025

H, He-like recombination spectra VI: Quadrupole $l$-changing collisions

We have developed a simple analytic formula that well describes quadrupole $l$-changing collisions of the form $nl \rightarrow nl'$, as confirmed by comparison with numerical quantal Born calculations obtained with the program autostructure (Badnell 2011). Such formulae could easily be included in models of astrophysical plasma emission, such as the hydrogen and helium-like recombination spectra. When compared with the results of previous quantal calculations based upon an analytic solution of the time-dependent Schrödinger equation by Vrinceanu & Flannery (2001), we find relatively good agreement, with the exception of large $l > n/2$ transitions. We provide a tentative explanation for such discrepancies. However, we also show that the rates for quadrupole $l$-changing collisions are typically two orders of magnitude lower than the dipolar ones. Inclusion of the quadrupolar rates in a hydrogenic collisional-radiative model of nebular plasma shows minimal changes to the level populations, typically within 1% in nebular conditions. Simple and complete theories are now available for $l$-changing collisions suitable for astrophysical applications.

physics.atom-ph↗

arXiv2024

Hidden Cooling Flows in Elliptical Galaxies

The radiative cooling time of hot gas in the cool cores of many galaxy clusters and massive elliptical galaxies drops in the centre to below 100 million years. The mass cooling rates inferred from simple modelling of X-ray observations of these objects are very low, indicating that either AGN feedback is tightly balanced or that soft X-rays from cooling gas are somehow hidden from view. An intrinsic absorption model developed for application to galaxy clusters is used here to search for hidden cooling flows (HCFs) in seven nearby elliptical galaxies. Mass cooling rates of 0.5-8 solar masses per year are found in each galaxy. The absorbed cooling flow luminosity is in agreement with the observed Far Infrared (FIR) luminosity in each case, indicating absorbed emission is energetically capable of emerging in the FIR band. An observed lack of agreement between HCF rates and normal star formation rates suggests the cooled material must have an alternative fate, with low-mass star formation considered as the primary outcome.

astro-ph.GA↗

arXiv2024

Hidden Cooling Flows IV: More Details on Centaurus and the Efficiency of AGN Feedback in Clusters

Cooling flows are common in galaxy clusters which have cool cores. The soft X-ray emission below 1 keV from the flows is mostly absorbed by cold dusty gas within the central cooling sites. Further evidence for this process is presented here through a more detailed analysis of the nearby Centaurus cluster and some additional clusters. Predictions of JWST near and mid-infrared spectra from cooling gas are presented. [NeVI] emission at 7.65 micron should be an important diagnostic of gas cooling between 6 and 1.5 times 10^5 K. The emerging overall picture of hidden cooling flows is explored. The efficiency of AGN feedback in reducing the total cooling rate in cool cores is shown to be above 50 percent for many clusters but is rarely above 90 per cent. The reduction is mostly in outer gas. Cooling dominates in elliptical galaxies and galaxy groups which have mass flow rates below about 15M/yr and in some massive clusters where rates can exceed 1000M/yr.

astro-ph.GA↗

arXiv2024

Consequences of a low-mass, high-pressure, star formation mode in early galaxies

High resolution X-ray spectra reveal hidden cooling flows depositing cold gas at the centres of massive nearby early-type galaxies with little sign of normal star formation. Optical observations are revealing that a bottom-heavy Initial Mass Function is common within the inner kpc of similar galaxies. We revive the possibility that a low-mass star formation mode is operating due to the high thermal pressure in the cooling flow, thus explaining the accumulation of low-mass stars. We further explore whether such a mode operated in early, high-redshift galaxies and has sporadically continued to the present day. The idea links observed distant galaxies with black holes which are ultramassive for their stellar mass, nearby red nuggets and massive early-type galaxies. Nearby elliptical galaxies may be red but they are not dead.

astro-ph.GA↗

arXiv2024

The first spectroscopic IR reverberation programme on Mrk 509

Near IR spectroscopic reverberation of Active Galactic Nuclei (AGN) potentially allows the infrared (IR) broad line region (BLR) to be reverberated alongside the disc and dust continua, while the spectra can also reveal details of dust astro-chemistry. Here, we describe results of a short pilot study (17 near-IR spectra over a 183 d period) for Mrk 509. The spectra give a luminosity-weighted dust radius of $\langle R_{\mathrm{d,lum}} \rangle = 186 \pm 4$ light-days for blackbody (large grain dust), consistent with previous (photometric) reverberation campaigns, whereas carbon and silicate dust give much larger radii. We develop a method of calibrating spectral data in objects where the narrow lines are extended beyond the slit width. We demonstrate this by showing our resultant photometric band light curves are consistent with previous results, with a hot dust lag at >40 d in the K band, clearly different from the accretion disc response at <20 d in the z band. We place this limit of 40 d by demonstrating clearly that the modest variability that we do detect in the H and K band does not reverberate on time-scales of less than 40 d. We also extract the Pa$β$ line light curve, and find a lag which is consistent with the optical BLR H$β$ line of $\sim$70-90 d. This is important as direct imaging of the near-IR BLR is now possible in a few objects, so we need to understand its relation to the better studied optical BLR.

astro-ph.GA↗

arXiv2024

Generation of photoionized plasmas in the laboratory of relevance to accretion-powered x-ray sources using keV line radiation

We describe laboratory experiments to generate X-ray photoionized plasmas of relevance to accretion-powered X-ray sources such as neutron star binaries and quasars, with significant improvements over previous work. A key quantity is referenced, namely the photoionization parameter. This is normally meaningful in an astrophysical steady-state context, but is also commonly used in the literature as a figure of merit for laboratory experiments that are, of necessity, time-dependent. We demonstrate emission-weighted values of ξ > 50 ergcm/s using laser-plasma X-ray sources, with higher results at the centre of the plasma which are in the regime of interest for several astrophysical scenarios. Comparisons of laboratory experiments with astrophysical codes are always limited, principally by the many orders of magnitude differences in time and spatial scales, but also other plasma parameters. However useful checks on performance can often be made for a limited range of parameters. For example, we show that our use of a keV line source, rather than the quasi-blackbody radiation fields normally employed in such experiments, has allowed the generation of the ratio of inner-shell to outer-shell photoionization expected from a blackbody source with ~keV spectral temperature. We compare calculations from our in-house plasma modelling code with those from Cloudy and find moderately good agreement for the time evolution of both electron temperature and average ionisation. However, a comparison of code predictions for a K-beta argon X-ray spectrum with experimental data reveals that our Cloudy simulation overestimates the intensities of more highly ionised argon species. This is not totally surprising as the Cloudy model was generated for a single set of plasma conditions, while the experimental data are spatially integrated.

astro-ph.HE↗

arXiv2023

The 2017 Release of Cloudy

We describe the 2017 release of the spectral synthesis code Cloudy. A major development since the previous release has been exporting the atomic data into external data files. This greatly simplifies updates and maintenance of the data. Many large datasets have been incorporated with the result that we can now predict well over an order of magnitude more emission lines when all databases are fully used. The use of such large datasets is not realistic for most calculations due to the time and memory needs, and we describe the limited subset of data we use by default. Despite the fact that we now predict significantly more lines than the previous Cloudy release, this version is faster because of optimization of memory access patterns and other tuning. The size and use of the databases can easily be adjusted in the command-line interface. We give examples of the accuracy limits using small models, and the performance requirements of large complete models. We summarize several advances in the H- and He-like iso-electronic sequences. We use our complete collisional-radiative models of the ionization of these one and two-electron ions to establish the highest density for which the coronal or interstellar medium (ISM) approximation works, and the lowest density where Saha or local thermodynamic equilibrium can be assumed. The coronal approximation fails at surprisingly low densities for collisional ionization equilibrium but is valid to higher densities for photoionized gas clouds. Many other improvements to the physics have been made and are described. These include the treatment of isotropic continuum sources such as the cosmic microwave background (CMB) in the reported output, and the ability to follow the evolution of cooling non-equilibrium clouds.

astro-ph.GA↗

arXiv2023

Hidden Cooling Flows in Clusters of Galaxies III: Accretion onto the Central Black Hole

Recently, we have uncovered Hidden Cooling Flows (HCF) in the X-ray spectra of the central Brightest Galaxies of 11 clusters, 1 group and 2 elliptical galaxies. Here we report such flows in a further 15 objects, consisting of 8 clusters, 3 groups, 3 ellipticals and 1 Red Nugget. The mass cooling rates are about 1 Msun/yr in the ellipticals, 2 to 20 Msun/yr in the groups and 20 to 100 Msun/yr in regular clusters. The Red Nugget, MRK1216, has an HCF of 10 Msun/yr. We review the fate of the cooled gas and investigate how some of it might accrete onto the central black hole. The gas is likely to be very cold and to have fragmented into low mass stars and smaller objects before being swallowed whole, with little luminous output. If such a scenario is correct and operates at a few Msun/yr then such objects may host the fastest growing black holes in the low redshift Universe. We briefly discuss the relevance of HCF to the growth of early galaxies and black holes.

astro-ph.GA↗

arXiv2022

Hidden Cooling Flows in Clusters of Galaxies II: A Wider Sample

We have recently uncovered Hidden Cooling Flows (HCFs) in the XMM RGS spectra of 3 clusters of galaxies, Centaurus, Perseus and A1835. Here we search for them in a wider sample of objects: the X-ray brightest group NGC5044; 4 moderate X-ray luminosity clusters Sersic 159, A262, A2052 and RXJ0821; and 3 high X-ray luminosity clusters RXJ1532, MACS 1931 and the Phoenix cluster. Finally we examine two Virgo elliptical galaxies, M49 and M84. All statistically allow the addition of an HCF. We find a significant detection of an HCF in 6 clusters and 2 elliptical galaxies. The hidden mass cooling rates are 5 to 40 Solar masses per year for the normal clusters, 1000 Solar masses per year or more for the extreme clusters and 1 to 2 Solar masses per year for the elliptical galaxies. We discuss the implications of the results for the composition of the innermost parts of the massive host galaxies and look forward to future observations.

astro-ph.GA↗

arXiv2022

Backscattering and Line Broadening in Orion

Examination of emission lines in high-velocity resolution optical spectra of the Orion Nebula confirms that the velocity component on the red wing of the main ionization front emission line is due to backscattering in the Photon Dominated Region. This scattered light component has a weak wavelength dependence that is consistent with either general interstellar medium particles or particles in the foreground of the Orion Nebula Cluster. An anomalous line-broadening component that has been known for 60+ years is characterized in unprecedented detail. Although this extra broadening may be due to turbulence along the line-of-sight of our spectra, we explore the possibility that it is due to \alf\ waves in conditions where the ratio of magnetic and thermal energies are about equal and constant throughout the ionized gas.

astro-ph.GA↗

arXiv2022

Radiation pressure-driven outflows from dusty AGN

Radiation pressure-driven outflows from luminous accreting supermassive black holes are an important part of active galactic nucleus (AGN) feedback. The effective Eddington limit, based on absorption of radiation by dust, not electron scattering, is revealed in the plane of AGN absorption column density $N_{\mathrm{H}}$ as a function of Eddington fraction $λ_{\mathrm{Edd}} = L_{\mathrm{bol}}/L_{\mathrm{Edd}}$, where a lack of objects is seen in the region where the effective limit is exceeded. Here, we conduct radiation simulation using the CLOUDY code to deduce the radiative force applied onto dusty gas at the nucleus and compare to the gravitational force to reveal the outflow region and its boundary with long-lived absorption clouds. We also investigate how the outflow condition is affected by various AGN and dust properties and distribution. As expected, the dust abundance has the largest effect on the $N_{\mathrm{H}} - λ_{\mathrm{Edd}}$ diagram since the higher the abundance, the more effective the radiative feedback, while the impact of the inner radius of the dusty gas shell, the shell width and the AGN spectral shape are relatively negligible. The presence of other central masses, such as a nuclear star cluster, can also make the feedback less effective. The AGN spectral energy distribution depends on the mass of the black hole and its spin. Though the effects of the AGN SED on the diagram are relatively small, the fraction of ionizing ultraviolet (UV) photons from the blackbody accretion disc is affected more by black hole mass than spin, and can influence the efficiency of radiation pressure.

astro-ph.GA↗

arXiv2022

Hidden Cooling Flows in Clusters of Galaxies

The radiative cooling time of the hot gas at the centres of cool cores in clusters of galaxies drops down to 10 million years and below. The observed mass cooling rate of such gas is very low, suggesting that AGN feedback is very tightly balanced or that the soft X-ray emission from cooling is somehow hidden from view. We use an intrinsic absorption model in which the cooling and coolest gas are closely interleaved to search for hidden cooling flows in the Centaurus, Perseus and A1835 clusters of galaxies. We find hidden mass cooling rates of between 10 to 500 Msunpyr as the cluster mass increases, with the absorbed emission emerging in the Far Infrared band. Good agreement is found between the hidden cooling rate and observed FIR luminosity in the Centaurus Cluster. The limits on the other two clusters allow for considerable hidden cooling. The implied total mass of cooled gas is much larger than the observed molecular masses. We discuss its fate including possible further cooling and collapse into undetected very cold clouds, low mass stars and substellar objects,

astro-ph.GA↗

arXiv2022

A recent update of gas-phase chemical reactions and molecular lines in CLOUDY: its effects on millimeter and sub-millimeter molecular line predictions

Here we present our current updates of the gas-phase chemical reaction rates and molecular lines in the spectral synthesis code CLOUDY, and its implications in spectroscopic modelling of various astrophysical environments. We include energy levels, radiative and collisional rates for HF, CF$^+$, HC$_3$N, ArH$^+$, HCl, HCN, CN, CH, and CH$_2$. Simultaneously, we expand our molecular network involving these molecules. For this purpose, we have added 561 new reactions and have updated the existing 165 molecular reaction rates involving these molecules. As a result, CLOUDY now predicts all the lines arising from these nine molecules. In addition, we also update H$_2$--H$_2$ collisional data up to rotational levels $J$=31 for $v$=0. We demonstrate spectroscopic simulations of these molecules for a few astrophysical environments. Our existing model for globules in the Crab nebula successfully predicts the observed column density of ArH$^+$. Our model predicts a detectable amount of HeH$^+$, OH$^+$, and CH$^+$ for the Crab nebula. We also model the ISM towards HD185418, W31C, NGC 253, and our predictions match with most of the observed column densities within the observed error bars. Very often molecular lines trace various physical conditions. Hence, this update will be very supportive for spectroscopic modelling of various astrophysical environments, particularly involving sub-millimeter and mid-infrared observations using ALMA and JWST, respectively.

astro-ph.GA↗

arXiv2022

Linking the properties of accreting white dwarfs with the ionization state of their ambient medium

Steadily accreting white dwarfs (WDs) are efficient sources of ionization and thus, are able to create extended ionized nebulae in their vicinity. These nebulae represent ideal tools for the detection of accreting WDs, given that in most cases the source itself is faint. In this work, we combine radiation transfer simulations with known H and He accreting WD models, providing for the first time the ionization state and the emission line spectra of the formed nebulae as a function of the WD mass, the accretion rate and the chemical composition of the accreted material. We find that the nebular optical line fluxes and radial extent vary strongly with the WD's accretion properties, peaking in systems with WD masses of 0.8 - 1.2 $\rm~M_{\odot}$. Projecting our results on the 'BPT' diagnostic diagrams, we show that accreting WDs nebulae possess characteristics distinct from those of H II-like regions, while they share similar line ratios with the galactic low-ionization emission-line regions. Finally, we compare our results to the relevant constraints imposed by the lack of ionized nebulae in the vicinity of supersoft X-ray sources (SSSs) and Type Ia supernova remnants - sources which are related to steadily accreting WDs. The large discrepancies uncovered by our comparison rule out any steadily accreting WD as a potential progenitor of the studied remnants and additionally require the ambient medium around the SSSs to be less dense than 0.2 $\rm~cm^{-3}$. We discuss possible alternatives that could bridge the incompatibility between the theoretical expectations and the relevant observations.

astro-ph.SR↗

arXiv2022

A Practical Guide to the Partition Function of Atoms and Ions

The partition function, $U$, the number of available states in an atom or molecules, is crucial for understanding the physical state of any astrophysical system in thermodynamic equilibrium. There are surprisingly few {\em useful} discussions of the partition function's numerical value. Textbooks often define $U$; some give tables of representative values, while others do a deep dive into the theory of a dense plasma. Most say that it depends on temperature, atomic structure, density, and that it diverges, that is, it goes to infinity, at high temperatures, but few give practical examples. We aim to rectify this. We show that there are two limits, one and two-electron (or closed-shell) systems like H or He, and species with a complicated electronic structure like C, N, O, and Fe. The high-temperature divergence does not occur for one and two-electron systems in practical situations since, at high temperatures, species are collisionally ionized to higher ionization stages and are not abundant. The partition function is then close to the statistical weight of the ground state. There is no such simplification for many-electron species. $U$ is temperature-sensitive across the range of temperatures where an ion is abundant but remains finite at even the highest practical temperatures. The actual value depends on highly uncertain truncation theories in high-density plasmas. We show that there are various theories for continuum lowering but that they are not in good agreement. This remains a long-standing unsolved problem.

astro-ph.IM↗

arXiv2021

Dense Molecular Clouds in the Crab Supernova Remnant

Molecular emission was imaged with ALMA from numerous components near and within bright H2-emitting knots and absorbing dust globules in the Crab Nebula. These observations provide a critical test of how energetic photons and particles produced in a young supernova remnant interact with gas, cleanly differentiating between competing models. The four fields targeted show contrasting properties but within them, seventeen distinct molecular clouds are identified with CO emission; a few also show emission from HCO+, SiO and/or SO. These observations are compared with Cloudy models of these knots. It has been suggested that the Crab filaments present an exotic environment in which H2 emission comes from a mostly-neutral zone probably heated by cosmic rays produced in the supernova surrounding a cool core of molecular gas. Our model is consistent with the observed CO J=3-2 line strength. These molecular line emitting knots in the Crab present a novel phase of the ISM representative of many important astrophysical environments.

astro-ph.GA↗