Leyes pioneras en la lucha contra el odio en redes sociales.

4.12.1. Temperature-sensitive line ratio data

The tables in this appendix give the wavelengths, transition probabilities and line ratio multipliers (Equations4.29and4.31), for transitions of thep2,p4andp3 lines of nebular interest. For the meanings of the wavelength and transition probability symbols, see Sections 6.2 and 6.3.

4.12 Appendix: Supplementary Data Tables 107

Table 4.7 Line wavelengths (Å) (in air) and line strengths and line ratio multipliers for thep2andp4ions

Species O i N ii O iii S iii Ne iii Ar iii Ar v

λa(Å) 5577.3 5754.6 4363.2 6312.1 3342.2 5191.8 4625.4

λo2(Å) 6363.8 6548.0 4958.9 9068.6 3968.5 7751.1 6435.1

λo3(Å) 6300.3 6583.4 5006.8 9530.6 3868.8 7135.8 7005.8

λu2(Å) 2972.3 3062.8 2321.0 3721.6 1814.6 3109.2 2691.1

λu3(Å) 2958.4 3070.6 2331.4 3797.2 1823.7 3005.2 2786.0

Aa 1.26E+00 1.14E+00 1.71E+00 2.08E+00 2.65E+00 3.10E+00 3.80E+00

Ao2 1.82E-03 9.84E-04 6.21E-03 1.85E-02 5.40E-02 8.31E-02 2.26E-01

Ao3 5.65E-03 2.91E-03 1.81E-02 4.80E-02 1.74E-01 3.35E-02 5.20E-01

Au2 7.54E-02 3.18E-02 2.15E-01 6.61E-01 2.06E+00 4.02E+00 6.80E+00

Au3 2.42E-04 1.55E-04 6.34E-04 8.82E-03 4.00E-03 4.30E-02 8.10E-02

f1(A,λ) 1.06824 1.11132 1.01650 1.12615 0.65458 0.63050 0.52476

f1(A,λ)uv? 0.12034 0.05853 0.24096 0.61492 0.93727 1.38038 1.63260

?

The final line in this table shows thef1(A,λ) line ratio multiplier for the UV-to-optical line ratios. They are related to the auroral-to-optical line ratios via the wavelength weighted branching ratios.

Table 4.8 Line wavelengths (Å) (in air) and line strengths and line ratio multi- pliers for thep3ions

Species N i S ii O ii Ne iv Ar iv λa1 10407.6 10370.5 7330.7 4725.6 7332.2 λa2 10407.2 10336.4 7329.7 4724.2 7263.3 λa3 10398.1 10320.5 7320.0 4715.7 7237.8 λa4 10397.7 10286.7 7318.9 4714.2 7170.7 λo1 5200.3 6730.8 3728.8 2424.4 4740.1 λo2 5197.9 6716.4 3726.0 2421.8 4711.3 λu1 3466.5 4076.3 2470.3 1601.1 2868.2 λu2 3466.5 4068.6 2470.2 1600.9 2853.7

Aa1 5.31E-02 6.81E-02 5.34E-02 3.89E-01 1.22E-01

Aa2 2.74E-02 1.42E-01 8.67E-02 4.36E-01 6.78E-01

Aa3 3.45E-02 1.57E-01 9.91E-02 1.10E-01 6.70E-01

Aa4 6.12E-02 1.15E-01 5.19E-02 3.01E-01 9.08E-01

Ao1 7.56E-06 6.84E-04 3.06E-05 5.80E-04 7.71E-02

Ao2 2.03E-05 2.02E-04 1.78E-04 5.47E-03 9.60E-03

Au1 6.50E-03 7.72E-02 5.22E-02 5.30E-01 9.70E-01

Au2 2.60E-03 1.92E-01 2.12E-02 1.33E+00 2.55E+00

f2(A,λ) 0.47521 0.41815 0.40631 0.20480 0.26438

f2(A,λ)uv? 0.07365 0.59216 0.30377 0.90891 0.98929

?_{Alternative flux ratios can be used for thep}3

ions, using the UV lines in place of the “auroral”. This is done, for example, in the IRAF/temden routine for S ii, Ne iv and Ar iv. The final line in this table shows thef2(A,λ) line ratio multiplier for the UV-to-optical line ratios. They are related to the auroral-to-optical line ratios via the wavelength weighted branching ratios.

109

CHAPTER 5

Nebular metallicities in two isolated Local

Void dwarf galaxies

. . . the Chaotic Voids outside of the Stars are measured by the Stars William Blake,Milton, A Poem, Book 2

This chapter was previously published as‘Nebular metallicities in two isolated Local Void dwarf galaxies’,

Nicholls, D. C., Jerjen, H., Dopita, M. A., and Basurah, H., ApJ, 780, 88. The work is entirely my own, taking into account suggestions from my co-authors. Minor typographical errors have been corrected, and sections, tables and figures have been renumbered to conform with the layout of the thesis.

5.1.

Chapter summary

Isolated dwarf galaxies, especially those situated in voids, may provide insight into prim- ordial conditions in the universe and the physical processes that govern star formation in undisturbed stellar systems. The metallicity of H ii regions in such galaxies is key to investig- ating this possibility. From the SIGRID sample of isolated dwarf galaxies, we have identified two exceptionally isolated objects, the Local Void galaxy [KK98]246 (ESO 461-G036) and another somewhat larger dwarf irregular on the edge of the Local Void, MCG-01-41-006 (HIPASS J1609-04). We report our measurements of the nebular metallicities in these ob- jects. The first object has a single low luminosity H ii region, while the second is in a more vigorous star forming phase with several bright H ii regions. We find that the metallicities in both galaxies are typical for galaxies of this size, and do not indicate the presence of any primordial gas, despite (for [KK98]246) the known surrounding large reservoir of neutral hydrogen.

5.2.

Introduction

The physical isolation of a dwarf galaxy is often argued to be a major contributor in pre- serving evidence of intergalactic H i gas in its primordial condition. Isolated dwarf galaxies

are thought to be very slow to enrich their neutral gas clouds, compared to the much more rapid evolution of larger galaxies (e.g.,Mateo 1998). Their relatively shallow potential wells are argued to be inefficient in retaining the heavy element abundances generated by supernovae (e.g.,Kunth & Östlin 2000). This picture is consistent with the mass-metallicity relation (e.g.,Lee et al. 2003;Tremonti et al. 2004;Lee et al. 2006), which shows that smaller galaxies generally exhibit lower nebular metallicity than larger ones. Investigating the nature of this relation was one of the motivations behind the SIGRID sample of isolated gas-rich dwarf galaxies (Nicholls et al. 2011), which,inter alia, seeks to clarify the behaviour of the mass-metallicity relation at low galactic masses. It has also been suggested that dwarf galaxies residing in low density environments (e.g., in voids) have lower metallicities, and in some cases, very low mass-to-light ratios, compared to similar objects in higher density regions (Pustilnik & Kniazev 2007;Pustilnik et al. 2011b,a). Therefore it is useful to investigate whether spatially isolated galaxies in voids are in any way unusual, in terms of mass-to-light ratio or metallicity, compared to similar objects in denser environments.

We have identified two isolated gas-rich dwarf galaxies in the SIGRID sample located within the Local Void for investigation, [KK98]246 (ESO 461-G036), hereafter “KK246” and MCG- 01-41-006 (HIPASS J1609-04), hereafter “J1609”. KK246 is relatively nearby (6.4 Mpc, Tully

et al. 2008). J1609-04 is somewhat more massive and luminous, but is over twice as distant,

at 14.82 Mpc (Nicholls et al. 2011). We present the spectra and nebular metallicity results for the two galaxies, and compare them with data from other investigations of void galaxies.

This paper is organised as follows. In Sections 5.3 and 5.4 we provide a summary of what is known about the two galaxies. In Section 5.5 we detail our observations. In Section 5.6 we present the flux-calibrated spectra from 3600Å to 7000Å at resolutions of 3000 (blue) and 7000 (red). In Section 5.7 we present the methods and results for our metallicity analyses; we list the observed line fluxes; and nebular metallicities and ionisation parameters using the revised strong line methods described inDopita et al.(2013). In Section 5.8 we present comparisons with other surveys of similar galaxies for mass-to-light ratios and mass-metallicities. In Section 5.9 we discuss the implications for dwarf galaxy evolution of these observations. Section 5.10 presents our conclusions.