A Multiwavelength Optical Emission Line Survey of Warm Ionized Gas in the Galaxy

Madsen, G. J.; Reynolds, R. J.; Haffner, L. M.

doi:10.1086/508441

Cited by 171 publications

(306 citation statements)

References 74 publications

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“…2) display an increase on the line ratio in those areas with low Hα surface brightness. Similar results have been observed in other environments, like our Galaxy (Madsen et al 2006;Reynolds et al 1999), or other spiral galaxies (Collins & Rand 2001;Miller & Veilleux 2003;Blanc et al 2009) in the so-called diffuse ionized gas (DIG) or warm interstellar medium (WIM). In this section we further explore this result by looking at the relation between the ionization degree and surface brightness for the different interaction groups.…”

Section: Anti-correlation Between Excitation and Hα Luminositysupporting

confidence: 86%

“…Hα surface brightness. We estimated our observational limit by looking at the typical values and uncertainties measured for our Madsen et al (2006). Note that because its [S ii]/Hα line ratio only includes the λ6717 sulfur line, we added an offset of 0.25 dex to their values to take into account the contribution from the λ6731 line.…”

Section: Anti-correlation Between Excitation and Hα Luminositymentioning

confidence: 99%

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VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies

Monreal-Ibero

Arribas

Colina

et al. 2010

A&A

101

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Context. Luminous infrared galaxies (LIRGs) are an important class of objects in the low-z universe bridging the gap between normal spirals and the strongly interacting and starbursting ultraluminous infrared galaxies (ULIRGs). Since a large fraction of the stars in the Universe have been formed in these objects, LIRGs are also relevant in a high-z context. Studies of the two-dimensional physical properties of LIRGs are still lacking. Aims. We aim to understand the nature and origin of the ionization mechanisms operating in the extra-nuclear regions of LIRGs as a function of the interaction phase and infrared luminosity. Methods. This study uses optical integral field spectroscopy (IFS) data obtained with VIMOS. Our analysis is based on over 25 300 spectra of 32 LIRGs covering all types of morphologies (isolated galaxies, interacting pairs, and advanced mergers), and the entire 10 11 −10 12 L infrared luminosity range. Results. We found strong evidence for shock ionization, with a clear trend with the dynamical status of the system. Specifically, we quantified the variation with interaction phase of several line ratios indicative of the excitation degree. While the [N ii]λ6584/Hα ratio does not show any significant change, the [S ii]λλ6717,6731/Hα and [O i]λ6300/Hα ratios are higher for more advanced interaction stages. Velocity dispersions are higher than in normal spirals and increase with the interaction class (medians of 37, 46, and 51 km s −1 for class 0−2, respectively). We constrained the main mechanisms causing the ionization in the extra-nuclear regions (typically for distances ranging from ∼0.2−2.1 kpc to ∼0.9−13.2 kpc) using diagnostic diagrams. Isolated systems are mainly consistent with ionization caused by young stars. Large fractions of the extra-nuclear regions in interacting pairs and more advanced mergers are consistent with ionization caused by shocks of v s < ∼ 200 km s −1 . This is supported by the relation between the excitation degree and the velocity dispersion of the ionized gas, which we interpret as evidence for shock ionization in interacting galaxies and advanced mergers but not in isolated galaxies. This relation does not show any dependence with the infrared luminosity (i.e. the level of star formation). All this indicates that tidal forces play a key role in the origin of the ionizing shocks in the extra-nuclear regions. We also showed for the first time what appears to be a common log([O i]λ6300/Hα) − log(σ) relation for the extranuclear ionized gas in interacting (U)LIRGs (i.e. covering the entire 10 11.0 −10 12.3 L luminosity range). This preliminary result needs to be investigated further with a larger sample of ULIRGs.

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Section: Anti-correlation Between Excitation and Hα Luminositysupporting

confidence: 86%

Section: Anti-correlation Between Excitation and Hα Luminositymentioning

confidence: 99%

VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies

Monreal-Ibero

Arribas

Colina

et al. 2010

A&A

101

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“…Much information regarding the source(s) of ionization has come from optical emission line ratios in the Milky Way and external galaxies (e.g., Rand 1997Rand , 1998bGreenawalt et al 1997;Collins & Rand 2001;Otte et al 2002;Haffner et al 1999;Hoopes & Walterbos 2003;Madsen et al 2006). Studies of the spatial behavior of several diagnostic line ratios have supported the idea that photoionization by massive stars is the primary ionization mechanism, but crucial aspects of the data require a more complex picture.…”

Section: Emission Lines From Digmentioning

confidence: 99%

“…He i k5876 is difficult to detect, but He i/H traces the relative ionization fractions of helium and hydrogen and thus is a useful measure of the hardness of the radiation field. In the Milky Way, Madsen et al (2006) have detected the line in a few diverse environments, finding a range of helium ionization fractions, but in general the diffuse gas is in a lower ionization state than in H ii regions. The line is detected in M33 with large uncertainties ( Hoopes & Walterbos 2003;Voges & Walterbos 2006), while in the halo of NGC 891 helium is about 70% ionized ( Rand 1997).…”

Section: Emission Lines From Digmentioning

confidence: 99%

Infrared Spectroscopy of the Diffuse Ionized Halo of NGC 891

Rand

Wood

Benjamin

2008

ApJ

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We present infrared spectroscopy from the Spitzer Space Telescope at one disk position and two positions at a height of 1 kpc from the disk in the edge-on spiral NGC 891, with the primary goal of studying halo ionization. Our main result is that the [Ne iii]/[Ne ii] ratio, which provides a measure of the hardness of the ionizing spectrum free from the major problems plaguing optical line ratios, is enhanced in the extraplanar pointings relative to the disk pointing. Using a 2D Monte Carlo-based photoionization code that accounts for the effects of radiation field hardening, we find that this trend cannot be reproduced by any plausible photoionization model and that a secondary source of ionization must therefore operate in gaseous halos. We also present the first spectroscopic detections of extraplanar PAH features in an external normal galaxy. If they are in an exponential layer, very rough emission scale heights of 330-530 pc are implied for the various features. Extinction may be nonnegligible in the midplane and reduce these scale heights significantly. There is little significant variation in the relative emission from the various features between disk and extraplanar environment. Only the 17.4 m feature is significantly enhanced in the extraplanar gas compared to the other features, possibly indicating a preference for larger PAHs in the halo.

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“…The Galactic measurements of Madsen et al (2006) give an average electron temperature T e of about 1000 K higher in diffuse ionized gas (DIG) than in HII regions. Assuming that the same difference occurs in M 31, and taking an HII region (DIG) contribution of 60%(40%) to the total Hα emission (e.g.…”

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confidence: 99%

Multi-scale radio-infrared correlations in M 31 and M 33: The role of magnetic fields and star formation

Tabatabaei

Berkhuijsen

Frick

et al. 2013

A&A

101

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Interstellar magnetic fields and the propagation of cosmic ray electrons have an important impact on the radio-infrared (IR) correlation in galaxies. This becomes evident when studying different spatial scales within galaxies. We investigate the correlation between the IR and free-free/synchrotron radio continuum emission at 20 cm from the two local group galaxies M 31 and M 33 on spatial scales between 0.4 and 10 kpc. The multi-scale radio-IR correlations have been carried out using a wavelet analysis. The free-free and IR emission are correlated on all scales, but on some scales the synchrotron emission is only marginally correlated with the IR emission. The synchrotron-IR correlation is stronger in M 33 than in M 31 on small scales (<1 kpc), but it is weaker than in M 31 on larger scales. Taking the smallest scale on which the synchrotron-IR correlation exists as the propagation length of cosmic ray electrons, we show that the difference on small scales can be explained by the smaller propagation length in M 33 than in M 31. On large scales, the difference is due to the thick disk/halo in M 33, which is absent in M 31. A comparison of our data with data on NGC 6946, the LMC and M 51 suggests that the propagation length is determined by the ratio of ordered-to-turbulent magnetic field strength, which is consistent with diffusion of CR electrons in the ISM. As the diffusion length of CR electrons influences the radio-IR correlation, this dependence is a direct observational evidence of the importance of magnetic fields for the radio-IR correlation within galaxies. The star-formation rate per surface area only indirectly influences the diffusion length as it increases the strength of the turbulent magnetic field.

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A Multiwavelength Optical Emission Line Survey of Warm Ionized Gas in the Galaxy

Cited by 171 publications

References 74 publications

VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies

VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies

Infrared Spectroscopy of the Diffuse Ionized Halo of NGC 891

Multi-scale radio-infrared correlations in M 31 and M 33: The role of magnetic fields and star formation

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