On the Observability of Optically Thin Coronal Hyperfine Structure Lines

We present Cloudy calculations for the intensity of coronal hyperfine lines in various environments. We model indirect collisional and radiative transitions, and quantify the collisionally-excited line emissivity in the density-temperature phase-space. As an observational aid, we also express the emissivity in units of the continuum in the 0.4--0.7 keV band. For most hyperfine lines, knowledge of the X-ray surface brightness and the plasma temperature is sufficient for rough estimates. We find that the radiation fields of both Perseus A and Virgo A can enhance the populations of highly ionized species within 1 kpc. They can also enhance line emissivity within the cluster core. This could have implications for the interpretation of spectra around bright AGN. We find the intensity of the $^{57}$Fe XXIV {\lambda}3.068 mm to be about two orders of magnitude fainter than previously thought, at about 20 {\mu}K. Comparably bright lines may be found in the infrared. Finally, we find the intensity of hyperfine lines in the Extended Orion Nebula to be low, due to the shallow sightline. Observations of coronal hyperfine lines will likely be feasible with the next generation of radio and sub-mm telescopes.Comment: 48 pages; 13 figures; 9 tables; additional images available at the online journa

Chandra Observation of Abell 2065: An Unequal Mass Merger?

We present an analysis of a 41 ks Chandra observation of the merging cluster Abell 2065 with the ACIS-I detector. Previous observations with ROSAT and ASCA provided evidence for an ongoing merger, but also suggested that there were two surviving cooling cores, which were associated with the two cD galaxies in the center of the cluster. The Chandra observation reveals only one X-ray surface brightness peak, which is associated with the more luminous, southern cD galaxy. The gas related with that peak is cool and displaced slightly from the position of the cD. The data suggest that this cool material has formed a cold front. On the other hand, in the higher spatial resolution Chandra image, the second feature to the north is not associated with the northern cD; rather, it appears to be a trail of gas behind the main cD. We argue that only one of the two cooling cores has survived the merger, although it is possible that the northern cD may not have possessed a cool core prior to the merger. We use the cool core survival to constrain the kinematics of the merger and we find an upper limit of ~< 1900 km/s for the merger relative velocity. A surface brightness discontinuity is found at ~140 kpc from the southern cD; the Mach number for this feature is ${\cal M} = 1.66^{+0.24}_{-0.32}$, although its nature (shock or cold front) is not clear from the data. We argue that Abell 2065 is an example of an unequal mass merger. The more massive southern cluster has driven a shock into the ICM of the infalling northern cluster, which has disrupted the cool core of the latter, if one existed originally. We estimate that core crossing occurred a few hundred Myr ago, probably for the first time.Comment: 15 pages, 10 figures, ApJ in pres

Effects of External Radiation Fields on Line Emission - Application to Star-forming Regions

A variety of astronomical environments contain clouds irradiated by a combination of isotropic and beamed radiation fields. For example, molecular clouds may be irradiated by the isotropic cosmic microwave background (CMB), as well as by a nearby active galactic nucleus (AGN). These radiation fields excite atoms and molecules and produce emission in different ways. We revisit the escape probability theorem and derive a novel expression that accounts for the presence of external radiation fields. We show that when the field is isotropic the escape probability is reduced relative to that in the absence of external radiation. This is in agreement with previous results obtained under ad hoc assumptions or with the two-level system, but can be applied to complex many-level models of atoms or molecules. This treatment is in the development version of the spectral synthesis code Cloudy. We examine the spectrum of a Spitzer cloud embedded in the local interstellar radiation field, and show that about 60 percent of its emission lines are sensitive to background subtraction. We argue that this geometric approach could provide an additional tool toward understanding the complex radiation fields of starburst galaxies.Comment: 12 pages, 7 figures, accepted for publication to Ap

The [CII] 158\u3cem\u3eμ\u3c/em\u3em Line Emission in High-Redshift Galaxies

Gas is a crucial component of galaxies, providing the fuel to form stars, and it is impossible to understand the evolution of galaxies without knowing their gas properties. The [CII] fine structure transition at 158 μm is the dominant cooling line of cool interstellar gas, and is the brightest of emission lines from star forming galaxies from FIR through metre wavelengths, almost unaffected by attenuation. With the advent of ALMA and NOEMA, capable of detecting [CII]-line emission in high-redshift galaxies, there has been a growing interest in using the [CII] line as a probe of the physical conditions of the gas in galaxies, and as a star formation rate (SFR) indicator at z ≥ 4. In this paper, we have used a semi-analytical model of galaxy evolution (G.A.S.) combined with the photoionisation code CLOUDY to predict the [CII] luminosity of a large number of galaxies (25 000 at z ≃ 5) at 4 ≤ z ≤ 8. We assumed that the [CII]-line emission originates from photo-dominated regions. At such high redshift, the CMB represents a strong background and we discuss its effects on the luminosity of the [CII] line. We studied the L[CII]–SFR and L[CII]–Zg relations and show that they do not strongly evolve with redshift from z = 4 and to z = 8. Galaxies with higher [CII] luminosities tend to have higher metallicities and higher SFRs but the correlations are very broad, with a scatter of about 0.5 and 0.8 dex for L[CII]–SFR and L[CII]–Zg, respectively. Our model reproduces the L[CII]–SFR relations observed in high-redshift star-forming galaxies, with [CII] luminosities lower than expected from local L[CII]–SFR relations. Accordingly, the local observed L[CII]–SFR relation does not apply at high-z (z ≳ 5), even when CMB effects are ignored. Our model naturally produces the [CII] deficit (i.e. the decrease of L[CII]/LIR with LIR), which appears to be strongly correlated with the intensity of the radiation field in our simulated galaxies. We then predict the [CII] luminosity function, and show that it has a power law form in the range of L[ CII] probed by the model (1 × 107–2 × 109 L⊙ at z = 6) with a slope α = −1. The slope is not evolving from z = 4 to z = 8 but the number density of [CII]-emitters decreases by a factor of 20×. We discuss our predictions in the context of current observational estimates on both the differential and cumulative luminosity functions

Ανάλυση Πειραματικών Δεδομένων Ηλεκτροδιέγερσης του Πρωτονίου στην Κινηματική Περιοχή του Συντονισμού Δ με W=1232 MeV και Q^2=1 (GeV/c)^2

Σε πειράματα ηλεκτροδιέγερσης το πρωτονίου μέσω της αντίδρασης p(e,e’p)π0 οι μετρούμενες ενεργές διατομές μετρούνται με την βοήθεια της οργανολογίας “Out Of Plane Spectrometry” (OOPS) και συντίθενται από γραμμικούς συνδυασμούς των εγκάρσιων και διαμηκών συναρτήσεων απόκρισης (RL, RT) καθώς και της επαλληλίας αυτών (RLT, RTT). Οι συναρτήσεις αυτές απόκρισης εκφράζονται με τη βοήθεια της θεωρίας CGLN (Chew-Goldberger-Low-Nambu) κάνοντας χρήση της πλειονοπολικής βάσης ηλεκτρομαγνητικών πλατών (Ei, Mi, Ci). Το ζητούμενο της ανάλυσης των πειραματικών δεδομένων είναι ο προσδιορισμός των κυρίαρχων αυτών πλατών στην κινηματική περιοχή των μετρήσεων. Στην παρούσα εργασία αναλύονται μέσα στο πλαίσιο αυτό πειραματικά δεδομένα από το εργαστήριο Jefferson Lab της ηλεκτροδιέγερσης του πρωτονίου στην περιοχή συντονισμού Δ, και ειδικότερα, στην κινηματική περιοχή W=1232 MeV και Q2=1 (GeV/c)2. Αφού εξηγηθεί η σημασία των κινηματικών μεγεθών και των πειραματικών μετρήσεων, επιχειρείται θεωρητική ανάλυση με την οποία υπολογίζονται οι μετρημένες ενεργές διατομές από τη βάση των πλειονοπόλων. Η πολυπλοκότητα των σχέσεων CGLN που συνδέουν τα πλειονόπολα αυτά με τα πειραματικά δεδομένα καθιστά την όλη διαδικασία δύσκολα αναστρέψιμη, αδυνατώντας να προσδιορίσει μονοσήμαντα τις τιμές των πλειονοπόλων. Για την επίλυση του αντιστρόφου προβλήματος, εισάγεται στην ανάλυση το μοντέλο AMIAS (Athens Model Independent Analysis Scheme), το οποίο βασίζεται σε τεχνικές Monte Carlo και δίνει την δυνατότητα υπολογισμού των ζητούμενων πλειονοπόλων από τα πειραματικά δεδομένα και μόνο, χωρίς να εισάγει σφάλμα μοντέλου (model error). Αρχικά, η κατανόηση της αντίστροφης αυτής διαδικασίας δίνεται με απλά παραδείγματα όπου εξαίρεται η σημασία των συσχετισμών των ελεύθερων παραμέτρων του προβλήματος. Στη συνέχεια, βασικά αποτελέσματα της πλειονοπολικής ανάλυσης προσδιορίζονται από τα πειραματικά δεδομένα και συγκρίνονται με την απόκλιση του σχήματος του αδρονίου από την σφαιρικότητα. Τέλος, τα πειραματικά αποτελέσματα του JLab συγκρίνονται με τις ζώνες αβεβαιότητας (error bands) 1σ και 2σ, οι οποίες προκύπτουν λαμβάνοντας υπόψη την κατανομή της πιθανότητας (PDF) των πλειονοπολικών αποτελεσμάτων του AMIAS.In proton elecro-excitation experiments through the process p(e,e’p)π0, the cross sections are calculated by the experimental technique “Out Of Plane Spectrometry” (OOPS) and they are expressed by linear combinations of the transverse and longitudinal Response Functions (RL, RT) as well as their interferences (RLT, RTT). Those Response Functions are connected through the CGLN (Chew-Goldberger-Low-Nambu) notation with the basis of the electromagnetic amplitudes (Ei, Mi, Ci). The ultimate goal of this analysis is to define the number and kind of the amplitudes which dominate the energy region of the experimental data. The current work, focuses on the analysis of experimental data collected in Hall A of the Jefferson Lab, describing the proton electro-excitation at the region of the Δ resonance, and more specifically, at the kinematical variables of W=1232 MeV and Q2=1 (GeV/c)2. Having explained the importance of the kinematic terms and the experimental measurements, the theoretical analysis on how to produce the cross sections from a multipole database is analytically described. The complexity of the CGLN formalism that connects the cross sections to the multipoles, does not permit a unique inversion of the problem, thus making the theoretical determination of the important multipoles ambiquous. In order to solve this irreversible problem, the model AMIAS (Athens Model Independent Analysis Scheme) is introduced to the analysis. AMIAS is based on Monte Carlo techniques and offers the ability to calculate the multipoles from the experimental data only, without inserting any model error. Firstly, the understanding of this reversed procedure can be achieved with simple examples where the importance of the correlations between the free parameters of the problem is conducted. Furthermore, the fundamental results of the multipole analysis are defined and compared to the divergence of the hadron’s shape from the spherical. Last but not least, the experimental data from JLab are compared to the 1σ and 2σ error bands, which are produced by taking under consideration the probability distribution functions (PDF) of the AMIAS multipole results

Accurate determination of the free-free Gaunt factor. II - relativistic Gaunt factors

When modelling an ionised plasma, all spectral synthesis codes need the thermally averaged free-free Gaunt factor defined over a very wide range of parameter space in order to produce an accurate prediction for the spectrum. Until now no data set exists that would meet these needs completely. We have therefore produced a table of relativistic Gaunt factors over a much wider range of parameter space than has ever been produced before. We present tables of the thermally averaged Gaunt factor covering the range log10(gamma^2) = -6 to 10 and log10(u) = -16 to 13 for all atomic numbers Z = 1 through 36. The data were calculated using the relativistic Bethe-Heitler-Elwert (BHE) approximation and were subsequently merged with accurate non-relativistic results in those parts of the parameter space where the BHE approximation is not valid. These data will be incorporated in the next major release of the spectral synthesis code Cloudy. We also produced tables of the frequency integrated Gaunt factor covering the parameter space log10(gamma^2) = -6 to 10 for all values of Z between 1 and 36. All the data presented in this paper are available online.Comment: 8 pages, 8 figures, 2 table

Accurate determination of the free-free Gaunt factor; I - non-relativistic Gaunt factors

Modern spectral synthesis codes need the thermally averaged free-free Gaunt factor defined over a very wide range of parameter space in order to produce an accurate prediction for the spectrum emitted by an ionized plasma. Until now no set of data exists that would meet this need in a fully satisfactory way. We have therefore undertaken to produce a table of very accurate non-relativistic Gaunt factors over a much wider range of parameters than has ever been produced before. We first produced a table of non-averaged Gaunt factors, covering the parameter space log10(epsilon_i) = -20 to +10 and log10(w) = -30 to +25. We then continued to produce a table of thermally averaged Gaunt factors covering the parameter space log10(gamma^2) = -6 to +10 and log10(u) = -16 to +13. Finally we produced a table of the frequency integrated Gaunt factor covering the parameter space log10(gamma^2) = -6 to +10. All the data presented in this paper are available online.Comment: 10 pages, 5 tables, 3 figures. Fixed typo in Eq. 1