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.
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.
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.
The measurement of electron temperatures and metallicities in H II regions and planetary nebulae (PNe) has-for several decades-presented a problem: results obtained using different techniques ...disagree. What is worse, they disagree consistently. There have been numerous attempts to explain these discrepancies, but none has provided a satisfactory solution to the problem. In this paper, we explore the possibility that electrons in H II regions and PNe depart from a Maxwell-Boltzmann equilibrium energy distribution. We adopt a " Kappa -distribution" for the electron energies. Such distributions are widely found in solar system plasmas, where they can be directly measured. This simple assumption is able to explain the temperature and metallicity discrepancies in H II regions and PNe arising from the different measurement techniques. We find that the energy distribution does not need to depart dramatically from an equilibrium distribution. From an examination of data from H II regions and PNe, it appears that Kappa gap 10 is sufficient to encompass nearly all objects. We argue that the kappa-distribution offers an important new insight into the physics of gaseous nebulae, both in the Milky Way and elsewhere, and one that promises significantly more accurate estimates of temperature and metallicity in these regions.
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.
ABSTRACT The Magellanic H i Stream ( 2 × 109 M d/55 kpc2) encircling the Galaxy at a distance d is arguably the most important tracer of what happens to gas accreting onto a disk galaxy. Recent ...observations reveal that the Stream's mass is in fact dominated (3:1) by its ionized component. Here we revisit the origin of the mysterious H recombination emission observed along much of its length that is overly bright (∼150-200 mR) for the known Galactic ultraviolet (UV) background ( 20-40 mR d/55 kpc−2). In an earlier model, we proposed that a slow shock cascade was operating along the Stream due to its interaction with the extended Galactic hot corona. We find that for a smooth coronal density profile, this model can explain the bright H emission if the coronal density satisfies 2 × 10−4 < (n/cm−3) < 4 × 10−4 at d = 55 kpc. But in view of updated parameters for the Galactic halo and mounting evidence that most of the Stream must lie far beyond the Magellanic Clouds (d > 55 kpc), we revisit the shock cascade model in detail. At lower densities, the H i gas is broken down by the shock cascade but mostly mixes with the hot corona without significant recombination. At higher densities, the hot coronal mass (including the other baryonic components) exceeds the baryon budget of the Galaxy. If the H emission arises from the shock cascade, the upper limit on the smooth coronal density constrains the Stream's mean distance to 75 kpc. If, as some models indicate, the Stream is even further out, either the shock cascade is operating in a regime where the corona is substantially mass-loaded with recent gas debris, or an entirely different ionization mechanism is responsible.
We present a new library of fully radiative shock models calculated with the MAPPINGS III shock and photoionization code. The library consists of grids of models with shock velocities in the range ...image km s super(-1) and magnetic parameters image of 10 super(-4) to 10 muG cm super(3/2) for five different atomic abundance sets and for a preshock density of 1.0 cm super(-3). In addition, solar abundance model grids have been calculated for densities of 0.01, 0.1, 10, 100, and 1000 cm super(-3 ) with the same range in image and image. Each model includes components of both the radiative shock and its photoionized precursor, ionized by the extreme ultraviolet (EUV) and soft X- ray radiation generated in the radiative gas. We present the details of the ionization structure, the column densities, and the luminosities of the shock and its precursor. Emission-line ratio predictions are separately given for the shock and its precursor as well as for the composite shock+precursor structure to facilitate comparison with observations in cases in which the shock and its precursor are not resolved. Emission-line ratio grids for shock and shock+precursor are presented on standard line ratio diagnostic diagrams, and we compare these grids to observations of radio galaxies and a sample of AGNs and star-forming galaxies from the Sloan Digital Sky Survey. This library is available online, along with a suite of tools to enable the analysis of the shocks and the easy creation of emission line ratio diagnostic diagrams. These models represent a significant increase in parameter space coverage over previously available models and, therefore, provide a unique tool in the diagnosis of emission by shocks.
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