An atlas of star-forming galaxy equivalent widths

Abstract

We present an atlas of starburst galaxy emission lines spanning 10 orders of magnitude in ionizing flux and 7 orders of magnitude in hydrogen number density. Coupling SEDs from Starburst99 with photoionization calculations from Cloudy, we track 96 emission lines from 977 Å to 205 µm which are common to nebular regions, have been observed in H II regions, and serve as useful diagnostic lines. Each simulation grid displays equivalent widths and contains ~1.5x10 4 photoionization models calculated by supplying a spectral energy distribution, chemical abundances, dust content, and gas metallicity (ranging from 0.2 Z to 5.0 Z ). Our simulations will prove useful in starburst emission line data analysis, especially regarding local starburst galaxies that show high ionization emission lines. One sample application of our atlas predicts that C IV λ1549 will serve as a useful diagnostic emission line of vigorous star formation for coming James Webb Space Telescope observations predicting a peak equivalent width of approximately 316 Å. IntroductionStarburst galaxies, also known as H II galaxies or star-forming galaxies, feature strong emission lines primarily due to newly formed massive stars. As mentioned above, along the extreme "wings" of the BPT diagram, AGN and starforming galaxies are easily distinguished from one another. However, while starlight is often the dominant source of excitation in star-forming galaxies, several other excitation mechanisms can contribute to the production of emission lines. The most intensely star forming galaxies along the far left wing of the BPT diagram are often interacting or merging (Robaina et al. 2009). Strong shocks further contribute to the excitation of the gas in galaxies along the left wing.Similarly, at lower ionization, classifying galaxies as star-forming or AGN becomes difficult. For these galaxies, excitation and ionization of gaseous clouds could likely be the result of starlight, non-thermal sources, or a combination of the two. Historically, the presence of a radiation field hard enough to generate photons higher than 50 eV signified excitation from an AGN. However, modern models of stellar radiation fields that incorporate Wolf-Rayet (WR) stars produce a significant number of EUV photons capable of ionizing heavy elements through many excitation states.

Black Hole Coalescence: Observation and Model Validation

“…Nonetheless, insofar as the models are embedded in the experimental methodology, there is a sense in which this could be understood as a kind of experimenter's regress, spelled out in terms of models rather than detectors. There are also clear similarities here to the related "simulationist's regress"(Gelfert 2012;Meskhidze 2017). …”

Optical and JWST Mid-IR Emission Line Diagnostics for Simultaneous IMBH and Stellar Excitation in z~0 Dwarf Galaxies

“…This has implications for statistical samples of galaxies that are analyzed with photoionization models that implicitly assume a particular geometrical configuration or mixing methodology in Figure 1. Such assumptions can lead to powerful selection effects (Ferguson et al 1997, Meskhidze & Richardson 2017. These assumptions could limit the applicability of simple relationships that scale physical properties (e.g., f AGN , M BH ) with emission lines ratios for large samples of galaxies.…”

Addressing the [O III]/Hβ offset of dwarf galaxies in the RESOLVE survey

“…In reality, H II regions vary drastically in size with a variety of physical conditions. We account for this fact by running suites of models varying φ H and n H to form a parameter space that captures the peak emission for most emission lines in the optical (Meskhidze & Richardson 2017). This approach addresses the restriction mentioned earlier, where clouds with different conditions are responsible for generating the observed emission lines strengths.…”

“…In particular, the left hand "wing" represents a sequence of star forming galaxies that excite clouds via starlight and the right hand "wing" represents a sequence of active galactic nuclei (AGN) that excite clouds via a combination of thermal and non-thermal sources. Variation in the star forming wing is traditionally interpreted as a change in ionization parameter, U, and metallicity, Z (Kewley et al 2001), or changing distributions in ionizing E-mail: crichardson17@elon.edu (CTR) flux and Z (Richardson et al 2016, Meskhidze & Richardson 2017.…”