We review the use of emission lines for understanding galaxy evolution, focusing on excitation source, metallicity, ionization parameter, ISM pressure, and electron density. We discuss the physics, ...benefits, and caveats of emission line diagnostics, including the effects of theoretical model uncertainties, diffuse ionized gas, and sample selection bias. In anticipation of upcoming telescope facilities, we provide new self-consistent emission line diagnostic calibrations for complete spectral coverage from the UV to the IR. These diagnostics can be used in concert to understand how fundamental galaxy properties have changed across cosmic time. We conclude the following:
The UV, optical, and IR contain complementary diagnostics that can probe the conditions within different nebular ionization zones.
Accounting for complex density gradients and temperature profiles is critical for reliably estimating the fundamental properties of H
ii
regions and galaxies.
Diffuse ionized gas can raise metallicity estimates, flatten metallicity gradients, and introduce scatter in ionization parameter measurements.
New 3D emission line diagnostics successfully separate the contributions from star formation, AGN, and shocks using integral field spectroscopy.
We summarize with a discussion of the challenges and major opportunities for emission line diagnostics in the coming years.
In this paper we treat the preionization problem in shocks over the velocity range 10 < vs < 1500 km s−1 in a self-consistent manner. We identify four distinct classes of solutions controlled by the ...value of the shock-precursor parameter, , where is the ionization parameter of the UV photons escaping upstream. This parameter determines both the temperature and the degree of ionization of the gas entering the shock. In increasing velocity, the shock solution regimes are cold neutral precursors (vs 40 km s−1), warm neutral precursors (40 vs 75 km s−1), warm partly ionized precursors (75 vs 120 km s−1), and fast shocks in which the preshock gas is in photoionization equilibrium and is fully ionized. The main effect of a magnetic field is to push these velocity ranges to higher values and to limit the postshock compression. In order to facilitate comparison with observations of shocks, we provide a number of convenient scaling relationships for parameters, such as postshock temperature, compression factors, cooling lengths, and Hβ and X-ray luminosity.
Abstract
We propose that Gigahertz Peak Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources are the signposts of relativistic jet feedback in evolving galaxies. Our simulations of ...relativistic jets interacting with a warm, inhomogeneous medium, utilizing cloud densities and velocity dispersions in the range derived from optical observations, show that free–free absorption can account for the ∼ GHz peak frequencies and low-frequency power laws inferred from the radio observations. These new computational models replace a power-law model for the free–free optical depth a more fundamental model involving disrupted log-normal distributions of warm gas. One feature of our new models is that at early stages, the low-frequency spectrum is steep but progressively flattens as a result of a broader distribution of optical depths, suggesting that the steep low-frequency spectra discovered by Callingham et al. may possibly be attributed to young sources. We also investigate the inverse correlation between peak frequency and size and find that the initial location on this correlation is determined by the average density of the warm ISM. The simulated sources track this correlation initially but eventually fall below it, indicating the need for a more extended ISM than presently modelled. GPS and CSS sources can potentially provide new insights into the phenomenon of AGN feedback since their peak frequencies and spectra are indicative of the density, turbulent structure, and distribution of gas in the host galaxy.
Relativistic jet feedback – III. Feedback on gas discs Mukherjee, Dipanjan; Bicknell, Geoffrey V; Wagner, Alexander Y ...
Monthly notices of the Royal Astronomical Society,
10/2018, Letnik:
479, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We study the interactions of a relativistic jet with a dense turbulent gaseous disc of radius ∼2 kpc. We have performed a suite of simulations with different mean density, jet power, and orientation. ...Our results show that: (A) The relativistic jet couples strongly with the gas in the inner kpc, creating a cavity and launching outflows. (B) The high pressure bubble inflated by the jet and its back-flow compresses the disc at the outer edges, driving inflows within the disc. (C) Jets inclined towards the disc affect the disc more and launch sub-relativistic, wide-angled outflows along the minor axis. (D) Shocks driven directly by the jet and the jet-driven energy bubble raise the velocity dispersion throughout the disc by several times its initial value. (E) Compression by the jet-driven shocks can enhance the star formation rate in the disc, especially in a ring-like geometry close to the axis. However, enhanced turbulent dispersion in the disc also leads to quenching of star formation. Whether positive or negative feedback dominates depends on jet power, ISM density, jet orientation with respect to the disc, and the time-scale under consideration. Qualitatively, our simulations compare favourably with kinematic and morphological signatures of several observed galaxies such as NGC 1052, NGC 3079, 3C 326, and 3C 293.
In this paper we examine the Direct Method for measuring electron temperatures in H ii regions, and the extent to which such measurements can provide meaningful information on the physical conditions ...in these regions. We discuss the limits to what can be inferred about electron temperatures from nebular emission line fluxes. We provide a new simplified method for estimating electron temperatures, including parameters that can be used to determine this from UV O iii and O ii oxygen lines observable in high-redshift objects using ground-based telescopes. We test this method on published UV high redshift observations and compare the results with reported electron temperatures.
This
Letter
presents a new, remarkably simple diagnostic specifically designed to derive chemical abundances for high redshift galaxies. It uses only the
H
α
, N
ii
and S
ii
emission lines, which ...can usually be observed in a single grating setting, and is almost linear up to an abundance of
12
+
log
(
O
/
H
)
=
9.05
. It can be used over the full abundance range encountered in high redshift galaxies. By its use of emission lines located close together in wavelength, it is also independent of reddening. Our diagnostic depends critically on the calibration of the N/O ratio. However, by using realistic stellar atmospheres combined with the N/O vs. O/H abundance calibration derived locally from stars and H
ii
regions, and allowing for the fact that high-redshift H
ii
regions have both high ionisation parameters
and
high gas pressures, we find that the observations of high-redshift galaxies can be simply explained by the models without having to invoke arbitrary changes in N/O ratio, or the presence of unusual quantities of Wolf-Rayet stars in these galaxies.
Abstract
The photoionization model of narrow-line regions in active galactic nuclei (AGNs) has been investigated for decades. Many published models are restricted to simple linear scaling abundance ...relations, dust-free assumption, uniform AGN radiation field, and using one specific photoionization code, which restricts them from providing a satisfactory prediction on a broad range of AGN observations. Through a comprehensive investigation, here we present how the choice of abundance scaling relations, dust inclusion, AGN radiation fields, and different photoionization codes CLOUDY and MAPPINGS affect the predictions on the strength of strong UV, optical, and infrared emission lines. We find the dust-depleted radiation-pressure-dominated AGN model built with the latest nonlinear abundance sets and photoionization code MAPPINGS V are consistent with AGN observations across a broad range of wavelengths. We also assess new potential H
ii
-AGN separation diagrams in the optical and UV wavelengths.
In an earlier paper we treated the preionization problem in shocks over the velocity range 20 km s−1 km s−1 in a fully self-consistent manner. Here we investigate in detail the effect of the upstream ...UV photon field generated in the radiative zone of shocks in the range in which hydrogen is only partly ionized 20 km s−1 ( km s−1). We show that, as a result of superheating in the nonequilibrium preshock plasma, both the magnetic parameter and the Mach number of the shock are strongly affected by the preionization state of the gas, which controls to a large extent the radiative spectrum of the shock. We use these models to provide specific line diagnostics for Herbig-Haro objects, which allow us to solve for both the preshock density and shock velocity, and we present detailed models of the HH 34 jet, which allows us to derive the shock conditions, mass-loss rate, momentum flux, and chemical abundances in the jet. We show that the refractory elements Mg, Ca, Fe, and Ni are enhanced by 0.22 dex over the solar values, which provides interesting clues about the jet-launching mechanism in pre-main-sequence evolution.
The jet–ISM interactions in IC 5063 Mukherjee, Dipanjan; Wagner, Alexander Y; Bicknell, Geoffrey V ...
Monthly notices of the Royal Astronomical Society,
05/2018, Letnik:
476, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
The interstellar medium of the radio galaxy IC 5063 is highly perturbed by an AGN jet expanding in the gaseous disc of the galaxy. We model this interaction with relativistic hydrodynamic ...simulations and multiphase initial conditions for the interstellar medium and compare the results with recent observations. As the jets flood through the intercloud channels of the disc, they ablate, accelerate, and disperse clouds to velocities exceeding 400 km s−1. Clouds are also destroyed or displaced in bulk from the central regions of the galaxy. Our models with jet powers of 1044 and 1045 erg s−1 are capable of reproducing many of the observed features in the position velocity diagram of IC 5063, and confirm the notion that the jet is responsible for the strongly perturbed gas dynamics seen in the ionized, neutral, and molecular gas phases. In our simulations, we also see strong venting of the jet plasma perpendicular to the disc, which entrains clumps and diffuse filaments into the halo of the galaxy. Our simulations are the first 3D hydrodynamic simulations of the jet and interstellar matter of IC 5063.
Recently, Nicholls et al., inspired by in situ observations of solar system astrophysical plasmas, suggested that the electrons in H II regions are characterized by a Kappa -distribution of energies ...rather than a simple Maxwell-Boltzmann distribution. Here, we have collected together new atomic data within a modified photoionization code to explore the effects of both the new atomic data and the Kappa -distribution on the strong-line techniques used to determine chemical abundances in H II regions. By comparing the recombination temperatures (T sub(rec)) with the forbidden line temperatures (T sub(FL)), we conclude that Kappa ~ 20. While representing only a mild deviation from equilibrium, this result is sufficient to strongly influence abundances determined using methods that depend on measurements of the electron temperature from forbidden lines. We present a number of new emission line ratio diagnostics that cleanly separate the two parameters determining the optical spectrum of H II regions-the ionization parameter q or U and the chemical abundance, 12+log(O/H). An automated code to extract these parameters is presented. Using the homogeneous data set from van Zee et al., we find self-consistent results between all of these different diagnostics. The systematic errors between different line ratio diagnostics are much smaller than those found in the earlier strong-line work. Overall, the effect of the Kappa -distribution on the strong-line abundances derived solely on the basis of theoretical models is rather small.
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