arXiv subjects

G. J. Ferland

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

At least 37 records · Page 2Linked to original sources

arXiv2021

H, He-like recombination spectra IV; H, He-like recombination spectra IV: clarification and refinement of methodology for $l$-changing collisions

Precise spectral diagnostic modelling of H~{\sc i} and He~{\sc ii} recombination spectra can constrain theoretical models which describe many astrophysical environments. Simple analytic expressions are of interest for collisional $l$-changing rate coefficients that are used by large-scale population modelling codes. We review, clarify and improve-upon the modified Pengelly \& Seaton formulae of Guzmán \etal We show that the recent poor results for it shown by Vrinceanu \etal are due to their misinterpretation of its usage. We also detail efficient numerical algorithms which should enable the full quantum mechanical expression for such rate coefficients to be used much more routinely by modelling codes. We illustrate with some collisional-radiative population modelling for hydrogen.

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arXiv2021

Excitation mechanisms in the intracluster filaments surrounding Brightest Cluster Galaxies

The excitation of the filamentary gas structures surrounding giant elliptical galaxies at the center of cool-core clusters, a.k.a BCGs (brightest cluster galaxies), is key to our understanding of active galactic nucleus feedback, and of the impact of environmental and local effects on star formation. We investigate the contribution of the thermal radiation from the cooling flow surrounding BCGs to the excitation of the filaments. We explore the effects of small levels of extra-heating (turbulence), and of metallicity, on the optical and infrared lines. Using the Cloudy code, we model the photoionization and photodissociation of a slab of gas of optical depth AV{\leq}30mag at constant pressure, in order to calculate self-consistently all of the gas phases, from ionized gas to molecular gas. The ionizing source is the EUV and soft X-ray radiation emitted by the cooling gas. We test these models comparing their predictions to the rich multi-wavelength observations, from optical to submillimeter. These models reproduce most of the multi-wavelength spectra observed in the nebulae surrounding the BCGs, not only the LINER-like optical diagnostics: [O iii]λ 5007 Å/H\b{eta}, [N ii]λ 6583 Å/Hα and ([S ii]λ 6716 Å+[S ii]λ 6731 Å)/Hα but also the infrared emission lines from the atomic gas. The modeled ro-vib H2 lines also match observations, which indicates that near and mid-IR H2 lines are mostly excited by collisions between H2 molecules and secondary electrons produced naturally inside the cloud by the interaction between the X-rays and the cold gas in the filament. However, there is still some tension between ionized and molecular line tracers (i.e. CO), which requires to optimize the cloud structure and the density of the molecular zone.

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arXiv2021

Deciphering the 3-D Orion Nebula-IV: The HH~269 flow emerges from the Orion-S Embedded Molecular Cloud

We have extended the membership and determined the 3-D structure of the large (0.19 pc) HH~269 sequence of shocks in the Orion Nebula. All of the components lie along a track that is highly tilted to the plane-of-the-sky and emerge from within the Orion-S embedded molecular cloud. Their source is probably either the highly obscured mm 9 source associated with a high N2H+ density core (more likely) or the more distant star COUP 632 (less likely). The former must be located in the Photon Dominated Region (PDR) underlying the ionized surface of the Orion South Cloud, while the latter would be embedded within the cloud. The flows seem to be episodic, with intervals of 1900 to 2600 years or 700 to 2600 years if COUP 632 is the source.

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arXiv2021

Role of Polycyclic Aromatic Hydrocarbons on the Cosmic-Ray ionization rate in the Galaxy

The cosmic-ray ionization rate ($ζ$, s$^{-1}$) plays an important role in the interstellar medium. It controls ion-molecular chemistry and provides a source of heating. Here we perform a grid of calculations using the spectral synthesis code CLOUDY along nine sightlines towards, HD 169454, HD 110432, HD 204827, $λ$ Cep, X Per, HD 73882, HD 154368, Cyg OB2 5, Cyg OB2 12. The value of $ζ$ is determined by matching the observed column densities of H$_3^+$ and H$_2$. The presence of polycyclic aromatic hydrocarbons (PAHs) affects the free electron density, which changes the H$_3^+$ density and the derived ionization rate. PAHs are ubiquitous in the Galaxy, but there are also regions where PAHs do not exist. Hence, we consider clouds with a range of PAH abundances and show their effects on the H$_3^+$ abundance. We predict an average cosmic-ray ionization rate for H$_2$ ($ζ$(H$_2$))= (7.88 $\pm$ 2.89) $\times$ 10$^{-16}$ s$^{-1}$ for models with average Galactic PAHs abundances, (PAH/H =10$^{-6.52}$), except Cyg OB2 5 and Cyg OB2 12. The value of $ζ$ is nearly 1 dex smaller for sightlines toward Cyg OB2 12. We estimate the average value of $ζ$(H$_2$)= (95.69 $\pm$ 46.56) $\times$ 10$^{-16}$ s$^{-1}$ for models without PAHs.

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arXiv2021

Deciphering the 3-D Orion Nebula-III: Structure on the NE boundary of the Orion-S Embedded Molecular Cloud

We have extended the work of Papers I and II of this series to determine at higher spatial resolution the properties of the embedded Orion-S Molecular Cloud that lies within the ionized cavity of the Orion Nebula and of the thin ionized layer that lies between the Cloud and the observer. This was done using existing and new [NII](658.3 nm) and [OIII] (500.7 nm) spectra that map the central region of the Orion Nebula (the Huygens Region). However, it remains unclear how the surface brightness of the ionized layer on the Orion-S Molecular Cloud and that of a foreground Nearer Ionized Layer are linked, as the observations show they must be. It is shown that the Cloud modifies the outer parts of the Huygens Region in the direction of the extended hot X-ray gas.

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arXiv2020

Space Telescope and Optical Reverberation Mapping Project. IX. Velocity-Delay Maps for Broad Emission Lines in NGC 5548

We report velocity-delay maps for prominent broad emission lines, Ly_alpha, CIV, HeII and H_beta, in the spectrum of NGC5548. The emission-line responses inhabit the interior of a virial envelope. The velocity-delay maps reveal stratified ionization structure. The HeII response inside 5-10 light-days has a broad single-peaked velocity profile. The Ly_alpha, CIV, and H_beta responses peak inside 10 light-days, extend outside 20 light-days, and exhibit a velocity profile with two peaks separated by 5000 km/s in the 10 to 20 light-day delay range. The velocity-delay maps show that the M-shaped lag vs velocity structure found in previous cross-correlation analysis is the signature of a Keplerian disk with a well-defined outer edge at R=20 light-days. The outer wings of the M arise from the virial envelope, and the U-shaped interior of the M is the lower half of an ellipse in the velocity-delay plane. The far-side response is weaker than that from the near side, so that we see clearly the lower half, but only faintly the upper half, of the velocity--delay ellipse. The delay tau=(R/c)(1-sin(i))=5 light-days at line center is from the near edge of the inclined ring, giving the inclination i=45 deg. A black hole mass of M=7x10^7 Msun is consistent with the velocity-delay structure. A barber-pole pattern with stripes moving from red to blue across the CIV and possibly Ly_alpha line profiles suggests the presence of azimuthal structure rotating around the far side of the broad-line region and may be the signature of precession or orbital motion of structures in the inner disk. Further HST observations of NGC 5548 over a multi-year timespan but with a cadence of perhaps 10 days rather than 1 day could help to clarify the nature of this new AGN phenomenon.

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arXiv2020

Deciphering the 3-D Orion Nebula-II: A low-ionization region of multiple velocity components southwest of Theta1OriC confounds interpretation of low velocity resolution studies of temperature, density, and abundance

We establish that there are two velocity systems along lines-of-sight that contribute to the emission-line spectrum of the the brightest parts of the Orion Nebula. These overlie the Orion-S embedded molecular cloud southwest of the dominant ionizing star (Theta1OriC). Examination of 10x10" samples of high spectral resolution emission-line spectra of this region reveals it to be of low ionization, with velocities and ionization different from the central part of the Nebula. These properties jeopardize earlier determinations of abundance and physical conditions since they indicate that this region is much more complex than has been assumed in analyzing earlier spectroscopic studies and argue for use of very high spectral resolution or known simple regions in future studies.

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arXiv2020

Improved Fe II emission line models for AGN using new atomic datasets

Understanding the Fe II emission from Active Galactic Nuclei (AGN) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving both quasar classification schemes such as "Eigenvector 1" and tracing the chemical evolution of the cosmos. Recently, three large Fe II atomic datasets with radiative and electron collisional rates have become available. We have incorporated these into the spectral synthesis code Cloudy and examine predictions using a new generation of AGN Spectral Energy Distribution (SED), which indicates that the UV emission can be quite different depending on the dataset utilized. The Smyth et al dataset better reproduces the observed Fe II template of the I ZW 1 Seyfert galaxy in the UV and optical regions, and we adopt these data. We consider both thermal and microturbulent clouds and show that a microturbulence of $\approx$ 100 km/s reproduces the observed shape and strength of the so-called Fe II "UV bump". Comparing our predictions with the observed Fe II template, we derive a typical cloud density of $10^{11}$ cm$^{-3}$ and photon flux of $10^{20}$ cm$^{-2}$ s$^{-1}$, and show that these largely reproduce the observed Fe II emission in the UV and optical. We calculate the $I$(Fe II)/$I$(Mg II) emission-line intensity ratio using our best-fitting model and obtain log($I$(Fe II)/$I$(Mg II)) $\sim$ 0.7, suggesting many AGNs have a roughly solar Fe/Mg abundance ratio. Finally, we vary the Eddington ratio and SED shape as a step in understanding the Eigenvector 1 correlation.

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arXiv2020

Space Telescope and Optical Reverberation Mapping Project. XIII. An Atlas of UV and X-ray Spectroscopic Signatures of theDisk Wind in NGC 5548

The unusual behavior of the spectral lines of NGC5548 during the STORM campaign demonstrated a missing piece in the structure of AGNs. For a two-month period in the middle of the campaign, the spectral lines showed a deficit in flux and a reduced response to the variations of the UV continuum. This was the first time that this behavior was unequivocally observed in an AGN. Our previous papers explained this as being due to a variable disk-wind which acts as a shield and alters the SED. Here we use Cloudy to create an atlas of photoionization models for a variety of disk-winds to study their effects on the SED. We show that the winds have three different cases: Case 1 winds are transparent, fully ionized and have minimal effects on the intrinsic SED, although they can produce some line emission, especially HeIIor FeKα. We propose that this is the situation in most of the AGNs. Case 2 winds have a He++-He+ionization-front, block part of the XUV continuum but transmit much of the Lyman continuum. They lead to the observed abnormal behavior. Case 3 winds have H+ionization-front and block much of the Lyman continuum. The results show that the presence of the winds has important effects on the spectral lines of AGNs. They will thus have an effect on the measurements of the black hole mass and the geometry of the AGN. This atlas of spectral simulations can serve as a guide to future reverberation campaigns

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arXiv2020

Cosmic ray dissociation of molecular hydrogen and dense cloud chemistry

Dissociation of molecular hydrogen by secondary electrons produced by cosmic ray or X-ray ionization plays a crucial role in the chemistry of the densest part of molecular clouds. Here we study the effect of the mean kinetic energy of secondary electrons on this process. We compare predictions using a range of secondary electron energies and predictions of the cross-sections with the values in the UMIST database. We find that the predicted column densities change by nearly one dex.

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arXiv2020

Cloudy in the microcalorimeter era: improved energies for K$α$ transitions

X-ray missions with microcalorimeter technology will resolve spectral features with unprecedented detail. In this work, we improve the H-like K$α$ energies for elements between 6 $\leq Z \leq$ 30 for the release version of the spectral simulation code Cloudy to match laboratory energies. We update the ionization potential ($I_{\rm ion}$) for these elements and add a fourth-order polynomial to the level energy difference. This brings the release version of Cloudy into a near-perfect agreement with NIST. The updated energies are $\sim$ 15-4000 times more precise than that of the current release version of Cloudy (C17.02). These new changes will be a part of the next update to the release version, C17.03.

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arXiv2020

Space Telescope and Optical Reverberation Mapping Project. XII. Broad-Line Region Modeling of NGC 5548

We present geometric and dynamical modeling of the broad line region for the multi-wavelength reverberation mapping campaign focused on NGC 5548 in 2014. The dataset includes photometric and spectroscopic monitoring in the optical and ultraviolet, covering the H$β$, C IV, and Ly$α$ broad emission lines. We find an extended disk-like H$β$ BLR with a mixture of near-circular and outflowing gas trajectories, while the C IV and Ly$α$ BLRs are much less extended and resemble shell-like structures. There is clear radial structure in the BLR, with C IV and Ly$α$ emission arising at smaller radii than the H$β$ emission. Using the three lines, we make three independent black hole mass measurements, all of which are consistent. Combining these results gives a joint inference of $\log_{10}(M_{\rm BH}/M_\odot) = 7.64^{+0.21}_{-0.18}$. We examine the effect of using the $V$ band instead of the UV continuum light curve on the results and find a size difference that is consistent with the measured UV-optical time lag, but the other structural and kinematic parameters remain unchanged, suggesting that the $V$ band is a suitable proxy for the ionizing continuum when exploring the BLR structure and kinematics. Finally, we compare the H$β$ results to similar models of data obtained in 2008 when the AGN was at a lower luminosity state. We find that the size of the emitting region increased during this time period, but the geometry and black hole mass remain unchanged, which confirms that the BLR kinematics suitably gauge the gravitational field of the central black hole.

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arXiv2020

X-ray spectroscopy in the microcalorimeter era II: A new Diagnostic on Column Density from the Case A to B Transition in H- and He-like Iron

The Soft X-ray Spectrometer (SXS) on board \textit{Hitomi}, with the unprecedented resolving power of R$\sim$1250, allowed the detection of members of the Fe XXV \ka\ complex emission spectra from the center of the Perseus Cluster. In this paper, we introduce a novel method of measuring the column density using the optically thin (Case A) to optically thick (Case B) transition for one- and two-electron systems. We compare the Fe XXV K$α$ line ratios computed with CLOUDY with that from the \textit{Hitomi} observations in the outer region of the Perseus core using collision strengths from different atomic datasets, and obtain good agreement. We also show the effect of turbulence on Fe XXV K$α$ line ratios and interplay between column density and metallicity. Besides, we discuss the atomic number dependence of transition probabilities for allowed and non-allowed transitions, which causes the highly charged He-like systems, such as Fe XXV, to behave fundamentally differently from He I.

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arXiv2020

X-ray spectroscopy in the microcalorimeter era I: Effects of Fe XXIV Resonance Auger Destruction on Fe XXV K$α$ spectra

We discuss the importance of Fe$^{23+}$ in determining the line intensities of the Fe XXV K$α$ complex in an optically thick cloud, and investigate the prediction of Liedahl (2005) on Resonance Auger Destruction (RAD) with CLOUDY. Although initially motivated by the Perseus cluster, our calculations are extended to the wide range of column densities encountered in astronomy. A Fe XXV line photon can change/lose its identity upon absorption by three-electron iron as a result of "line interlocking". This may lead to the autoionization of the absorbing ion, ultimately destroying the Fe XXV K$α$ photon by RAD. Out of the four members in the Fe XXV K$α$ complex, a significant fraction of the x line photons is absorbed by Fe$^{23+}$ and destroyed, causing the x line intensity to decrease. For example, at a hydrogen column density of 10$^{25}$ cm$^{-2}$, $\sim$ 32\% of x photons are destroyed due to RAD while w is mostly unaffected. The line intensity of y is slightly ($\leq$2\%) reduced. z is not directly affected by RAD, but the contrasting behavior between z and x line intensities points towards the possible conversion of a tiny fraction ($\sim$ 2\%) of x photons into z photons. The change in line intensities due to Electron Scattering Escape (ESE) off fast thermal electrons is also discussed.

astro-ph.HE↗

arXiv2020

Space Telescope and Optical Reverberation Mapping Project. XI. Disk-wind characteristics and contributions to the very broad emission lines of NGC 5548

In 2014 the NGC 5548 Space Telescope and Optical Reverberation Mapping campaign discovered a two-month anomaly when variations in the absorption and emission lines decorrelated from continuum variations. During this time the soft X-ray part of the intrinsic spectrum had been strongly absorbed by a line-of-sight (LOS) obscurer, which was interpreted as the upper part of a disk wind. Our first paper showed that changes in the LOS obscurer produce the decorrelation between the absorption lines and the continuum. A second study showed that the base of the wind shields the BLR, leading to the emission-line decorrelation. In that study, we proposed the wind is normally transparent with no effect on the spectrum. Changes in the wind properties alter its shielding and affect the SED striking the BLR, producing the observed decorrelations. In this work, we investigate the impact of a translucent wind on the emission lines. We simulate the obscuration using XMM-Newton, NuSTAR, and HST observations to determine the physical characteristics of the wind. We find that a translucent wind can contribute a part of the He II and Fe K? emission. It has a modest optical depth to electron scattering, which explains the fainter far-side emission in the observed velocity delay maps. The wind produces the very broad base seen in the UV emission lines and may also be present in the Fe K? line. Our results highlight the importance of accounting for the effects of such winds in the analysis of the physics of the central engine.

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arXiv2020

Deciphering the 3-D Orion Nebula-I: Expanding Shells in the Huygens Region

Based on imaging and spectroscopic data, we develop a 3-D model for the Huygens Region of the Orion Nebula. Theta1OriC , the hottest star in the Trapezium, is surrounded by a wind-blown Central Bubble that opens SW into the Extended Orion Nebula. Outside of this feature lies a layer of ionized gas at about 0.4 pc from Theta1OriC. Both of these features are moving rapidly away from Theta1OriC with an expansion age for the Central Bubble of only 15,000 yrs.

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arXiv2020

Physical conditions in two high-redshift H$_2$-bearing GRB-DLAs, 120815A and 121024A

The gamma-ray burst (GRB) afterglows provide an unique opportunity to study the interstellar medium (ISM) of star-forming galaxies at high-redshift. The GRB-DLAs (damped Lyman-$α$ absorbers) contain a large neutral hydrogen column density, N(H I), and are observed against the GRB afterglow. A large fraction of GRB-DLAs show presence of molecular hydrogen (H$_2$) which is an indicator of star-formation. Hence it is important to study those GRB-DLAs which have H$_2$ lines to decipher and understand their physical conditions. The GRB-DLAs 121024A and 120815A, situated at redshift 2.30 and 2.36 respectively, are two such important H$_2$-bearing GRB-DLAs. Besides H$_2$, these two GRB-DLAs also show many metal lines. In this work we have carried out a detail numerical study on the H$_2$ lines, as well as on those metal lines, in GRB-DLAs 121024A and 120815A self-consistently. We use the spectral synthesis code CLOUDY for this study. This modeling helps us to determine the underlying physical conditions which give rise such lines and hence to understand these two GRB-DLAs in much more detail than any other previous investigation. We find that the hydrogen densities for these two H$_2$-bearing DLAs are $\geq$ 60 cm$^{-3}$. Moreover our study infers that the linear sizes are $\leq 17.7$ pc for these two GRB-DLAs, and the mean gas temperatures averaged over the cloud thickness, are $\leq$ 140 K.

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arXiv2020

Current and future development of the photoionization code Cloudy

The gas that is present in the interstellar medium is usually very far removed from (local) thermodynamic equilibrium, and in some cases may also not be in a steady-state equilibrium with its surroundings. The physics of this material is complex and one needs a sophisticated numerical code to study it. For this purpose the open-source photoionization code Cloudy was created. It models the physical state of the gas and predicts the spectrum that it emits. Cloudy is continually being developed to improve the treatment of the microphysical processes and the database of fundamental data that it uses. In this paper we will discuss how we are developing the code to improve our high-density predictions by implementing better collisional-radiative models for all ions. We will also briefly discuss the experimental mode in Cloudy to model gas that is not in steady-state equilibrium and present a preliminary model of recombining gas in a planetary nebula that is on the cooling track. We finish with a short discussion of how we are speeding up the code by using parallelization.

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