scholarly journals The diffuse ionized gas (DIG) in star-forming galaxies: the influence of aperture effects on local H ii regions

2021 ◽  
Vol 508 (2) ◽  
pp. 1582-1589
Author(s):  
F Mannucci ◽  
F Belfiore ◽  
M Curti ◽  
G Cresci ◽  
R Maiolino ◽  
...  
Keyword(s):  
Emission Line ◽  
Strong Line ◽  
H Ii Regions ◽  
Line Flux ◽  
Ionized Gas ◽  
Star Forming ◽  
Distant Galaxies ◽  
Diffuse Ionized Gas ◽  
Large Correction ◽  
Nearby Galaxies

ABSTRACT The diffuse ionized gas (DIG) contributes to the nebular emission of galaxies, resulting in emission line flux ratios that can be significantly different from those produced by H ii regions. Comparing the emission of [SII]λ6717,31 between pointed observations of H ii regions in nearby galaxies and integrated spectra of more distant galaxies, it has been recently claimed that the DIG can also deeply affect the emission of bright, star-forming galaxies, and that a large correction must be applied to observed line ratios to recover the genuine contribution from H ii regions. Here, we show instead that the e?ect of DIG on the integrated spectra of star-forming galaxies is lower than assumed in previous work. Here we show that, in contrast, aperture effects on the spectroscopy of nearby H ii regions are largely responsible for the observed difference: When spectra of local H ii regions are extracted using large enough apertures while still avoiding the DIG, the observed line ratios are the same as in more distant galaxies. This result is highly relevant for the use of strong-line methods to measure metallicity.

scholarly journals Diffuse ionized gas and its effects on nebular metallicity estimates of star-forming galaxies

2019 ◽  
Vol 489 (4) ◽  
pp. 4721-4733 ◽  
Author(s):  
N Vale Asari ◽  
G S Couto ◽  
R Cid Fernandes ◽  
G Stasińska ◽  
A L de Amorim ◽  
...  
Keyword(s):  
Formation Rate ◽  
Sloan Digital Sky Survey ◽  
Emission Lines ◽  
Strong Line ◽  
Galactocentric Distance ◽  
Ionized Gas ◽  
Star Forming ◽  
Diffuse Ionized Gas ◽  
Stellar Masses ◽  
The Impact

ABSTRACT We investigate the impact of the diffuse ionized gas (DIG) on abundance determinations in star-forming (SF) galaxies. The DIG is characterized using the H α equivalent width (WH α). From a set of 1 409 SF galaxies from the Mapping Nearby Galaxies at APO (MaNGA) survey, we calculate the fractional contribution of the DIG to several emission lines using high-S/N data from SF spaxels (instead of using noisy emission-lines in DIG-dominated spaxels). Our method is applicable to spectra with observed WH α ≳ 10 Å (which are not dominated by DIG emission). Since the DIG contribution depends on galactocentric distance, we provide DIG-correction formulae for both entire galaxies and single aperture spectra. Applying those to a sample of $\, \gt 90\, 000$ SF galaxies from the Sloan Digital Sky Survey, we find the following. (1) The effect of the DIG on strong-line abundances depends on the index used. It is negligible for the ([O iii]/H β)/([N ii]/H α) index, but reaches ∼0.1 dex at the high-metallicity end for [N ii]/H α. (2) This result is based on the ∼kpc MaNGA resolution, so the real effect of the DIG is likely greater. (3) We revisit the mass–metallicity–star formation rate (SFR) relation by correcting for the DIG contribution in both abundances and SFR. The effect of DIG removal is more prominent at higher stellar masses. Using the [N ii]/Hα index, O/H increases with SFR at high stellar mass, contrary to previous claims.

scholarly journals The importance of the diffuse ionized gas for interpreting galaxy spectra

2020 ◽  
Vol 15 (S359) ◽  
pp. 371-380
Author(s):  
Natalia Vale Asari ◽  
Grażyna Stasińska
Keyword(s):  
Star Formation ◽  
Emission Line ◽  
Active Galactic Nucleus ◽  
Early Type ◽  
Late Type ◽  
Chemical Abundances ◽  
Ionized Gas ◽  
Star Forming ◽  
Diffuse Ionized Gas ◽  
Emission Line Spectrum

AbstractDiffuse ionized gas (DIG) in galaxies can be found in early-type galaxies, in bulges of late-type galaxies, in the interarm regions of galaxy disks, and outside the plane of such disks. The emission-line spectrum of the DIG can be confused with that of a weakly active galactic nucleus. It can also bias the inference of chemical abundances and star formation rates in star forming galaxies. We discuss how one can detect and feasibly correct for the DIG contribution in galaxy spectra.

scholarly journals Diffuse Ionized Gas in Nearby Galaxies

1991 ◽  
Vol 144 ◽  
pp. 223-232
Author(s):  
R.A.M. Walterbos
Keyword(s):  
Interstellar Medium ◽  
Spectral Characteristics ◽  
High Ratio ◽  
Radio Continuum ◽  
Ionized Gas ◽  
Star Forming ◽  
Star Forming Regions ◽  
Diffuse Ionized Gas ◽  
External Galaxies ◽  
Nearby Galaxies

We discuss the distribution and spectral characteristics of diffuse ionized gas in nearby galaxies. The existence of this elusive component of the interstellar medium (ISM), also referred to as the Warm Ionized Medium, is by now well established from deep imaging and spectroscopic surveys in several emission lines in external galaxies. Diffuse ionized gas is characterized by a relatively high ratio of [SII] over Hα intensities, typically twice as high as for discrete HII regions. The diffuse gas has been mapped in both edge-on and more face-on galaxies providing information on the radial and vertical distribitions. Emission from diffuse ionized gas is strongest around star forming regions. The vertical distribution appears related to the radio continuum thick-disk emission. We also briefly discuss ionization mechanisms, and the connection between star formation characteristics and morphology of the interstellar medium.

scholarly journals 3D optical spectroscopic study of NGC 3344 with SITELLE: I. Identification and confirmation of supernova remnants

2019 ◽  
Vol 488 (1) ◽  
pp. 803-829 ◽  
Author(s):  
I Moumen ◽  
C Robert ◽  
D Devost ◽  
R P Martin ◽  
L Rousseau-Nepton ◽  
...  
Keyword(s):  
Supernova Remnants ◽  
Flux Ratio ◽  
Large Magellanic Cloud ◽  
Emission Lines ◽  
Ionization Mechanism ◽  
H Ii Regions ◽  
Nearby Galaxy ◽  
Galactocentric Distance ◽  
Ionized Gas ◽  
Diffuse Ionized Gas

ABSTRACT We present the first optical identification and confirmation of a sample of supernova remnants (SNRs) in the nearby galaxy NGC 3344. Using high spectral and spatial resolution data, obtained with the CFHT imaging Fourier transform spectrograph SITELLE, we identified about 2200 emission line regions, many of which are H ii regions, diffuse ionized gas regions, and also SNRs. Considering the stellar population and diffuse ionized gas background, which are quite important in NGC 3344, we have selected 129 SNR candidates based on four criteria for regions where the emission lines flux ratio [S ii]/H α ≥ 0.4. Emission lines of [O ii] λ3727, H β, [O iii] λλ4959,5007, H α, [N ii] λλ6548,6583, and [S ii] λλ6716,6731 have been measured to study the ionized gas properties of the SNR candidates. We adopted a self-consistent spectroscopic analysis, based on Sabbadin plots and Baldwin, Phillips & Terlevich diagrams, to confirm the shock-heated nature of the ionization mechanism in the candidates sample. With this analysis, we end up with 42 Confirmed SNRs, 45 Probable SNRs, and 42 Less likely SNRs. Using shock models, the confirmed SNRs seem to have a metallicity ranging between Large Magellanic Cloud and 2×solar. We looked for correlations between the size of the confirmed SNRs and their emission lines ratios, their galaxy environment, and their galactocentric distance: We see a trend for a metallicity gradient among the SNR population, along with some evolutionary effects.

scholarly journals H ii regions in the CALIFA survey: I. catalogue presentation

2020 ◽  
Vol 494 (2) ◽  
pp. 1622-1646 ◽  
Author(s):  
C Espinosa-Ponce ◽  
S F Sánchez ◽  
C Morisset ◽  
J K Barrera-Ballesteros ◽  
L Galbany ◽  
...  
Keyword(s):  
Stellar Populations ◽  
Spectroscopic Properties ◽  
Emission Lines ◽  
H Ii Regions ◽  
Ionized Gas ◽  
New Approach ◽  
Integral Field Spectroscopy ◽  
Diffuse Ionized Gas ◽  
Spectroscopic Information ◽  
Selection Of

ABSTRACT We present a new catalogue of H ii regions based on the integral field spectroscopy (IFS) data of the extended CALIFA and PISCO samples. The selection of H ii regions was based on two assumptions: a clumpy structure with high contrast of H α emission and an underlying stellar population comprising young stars. The catalogue provides the spectroscopic information of 26 408 individual regions corresponding to 924 galaxies, including the flux intensities and equivalent widths of 51 emission lines covering the wavelength range between 3745 and 7200 Å. To our knowledge, this is the largest catalogue of spectroscopic properties of H ii regions. We explore a new approach to decontaminate the emission lines from diffuse ionized gas contribution. This diffuse gas correction was estimated to correct every emission line within the considered spectral range. With the catalogue of H ii regions corrected, new demarcation lines are proposed for the classical diagnostic diagrams. Finally, we study the properties of the underlying stellar populations of the H ii regions. It was found that there is a direct relationship between the ionization conditions on the nebulae and the properties of stellar populations besides the physicals condition on the ionized regions.

scholarly journals Chemodynamics of green pea galaxies – I. Outflows and turbulence driving the escape of ionizing photons and chemical enrichment

2020 ◽  
Vol 494 (3) ◽  
pp. 3541-3561 ◽  
Author(s):  
L Hogarth ◽  
R Amorín ◽  
J M Vílchez ◽  
G F Hägele ◽  
M Cardaci ◽  
...  
Keyword(s):  
Emission Line ◽  
Indirect Evidence ◽  
Young Star ◽  
High Dispersion ◽  
H Ii Regions ◽  
Ionized Gas ◽  
Narrow Component ◽  
Radiation Fields ◽  
Hard Radiation ◽  
Green Pea

ABSTRACT We investigate the ionized gas kinematics, physical properties, and chemical abundances of Sloan Digital Sky Survey J142947, a Green Pea galaxy at redshift z∼ 0.17 with strong, double-peak Ly α emission and indirect evidence of Lyman continuum (LyC) leakage. Using high-dispersion spectroscopy, we perform a multicomponent analysis of emission-line profiles. Our model consistently fits all lines as a narrow component with intrinsic velocity dispersion σ ∼ 40 km s−1, and two broader blue-shifted components with σ ∼ 90 and ∼ 250 km s−1. We find electron densities and temperatures, ionization conditions, and direct O/H and N/O abundances for each component. A highly ionized, metal-poor, young and compact starburst dominates narrow emission, showing evidence of hard radiation fields and elevated N/O. The blue-shifted broader components are consistent with highly turbulent, possibly clumpy ionized gas at the base of a strong photoionized outflow, which accounts for ≳50 per cent of the integrated emission-line fluxes. The outflow is dense and metal-enriched compared to the H ii regions, with expansion velocities larger than those obtained from UV interstellar absorption lines under standard assumptions. Some of these metals may be able to escape, with outflows loading factors comparable to those found in high-z galaxies of similar SFR/Area. Our findings depict a two-stage starburst picture; hard radiation fields from young star clusters illuminate a turbulent and clumpy ISM that has been eroded by SNe feedback. Whilst UV data suggest an extended Ly α halo with high average H i column density, LyC photons could only escape from SDSS J142947 through low H i density channels or filaments in the ISM approaching density-bounded conditions, traced by outflowing gas.

scholarly journals The UM/CTIO Magellanic Cloud Emission-line Survey

1999 ◽  
Vol 190 ◽  
pp. 28-31 ◽  
Author(s):  
R. Chris Smith ◽  
Keyword(s):  
Interstellar Medium ◽  
Emission Line ◽  
Supernova Remnants ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
H Ii Regions ◽  
Deep Imaging ◽  
Small Scales ◽  
Nearby Galaxies ◽  
Line Survey

The Magellanic Clouds are unique in providing sites to study the interstellar medium (ISM) and its components at all scales. To promote the pursuit of such studies, we have begun the Magellanic Cloud Emission-line Survey (MCELS), a deep imaging survey of both of these nearby galaxies in the emission of Hα, [S II], and [O III]. The emission-line images will be used in detailed optical and multiwavelength studies of H II regions, supernova remnants, planetary nebulae, superbubbles, and supergiant shells. Together with parallel surveys at other wavelengths, this survey will provide the foundation upon which to build a deeper understanding of the ISM in the Clouds and other galaxies, from small scales (~1 pc) all the way up to global scales. We present a sample of recent and current work using the MCELS dataset.

scholarly journals First detection of [13C II] in the Large Magellanic Cloud

2019 ◽  
Vol 631 ◽  
pp. L12 ◽  
Author(s):  
Yoko Okada ◽  
Ronan Higgins ◽  
Volker Ossenkopf-Okada ◽  
Cristian Guevara ◽  
Jürgen Stutzki ◽  
...  
Keyword(s):  
Optical Depth ◽  
Line Profile ◽  
Large Magellanic Cloud ◽  
Abundance Ratio ◽  
Magellanic Cloud ◽  
Star Forming ◽  
Star Forming Regions ◽  
Distant Galaxies ◽  
Nearby Galaxies ◽  
Galactic Sources

Context. [13C II] observations in several Galactic sources show that the fine-structure [12C II] emission is often optically thick (the optical depths around 1 to a few). Aims. Our goal was to test whether this also affects the [12C II] emission from nearby galaxies like the Large Magellanic Cloud (LMC). Methods. We observed three star-forming regions in the LMC with upGREAT on board SOFIA at the frequency of the [C II] line. The 4 GHz bandwidth covers all three hyperfine lines of [13C II] simultaneously. For the analysis, we combined the [13C II] F = 1−0 and F = 1−1 hyperfine components as they do not overlap with the [12C II] line in velocity. Results. Three positions in N159 and N160 show an enhancement of [13C II] compared to the abundance-ratio-scaled [12C II] profile. This is likely due to the [12C II] line being optically thick, supported by the fact that the [13C II] line profile is narrower than [12C II], the enhancement varies with velocity, and the peak velocity of [13C II] matches the [O I] 63 μm self-absorption. The [12C II] line profile is broader than expected from a simple optical depth broadening of the [13C II] line, supporting the scenario of several PDR components in one beam having varying [12C II] optical depths. The derived [12C II] optical depth at three positions (beam size of 14″, corresponding to 3.4 pc) is 1−3, which is similar to values observed in several Galactic sources shown in previous studies. If this also applies to distant galaxies, the [C II] intensity will be underestimated by a factor of approximately 2.

scholarly journals Stellar populations and physical properties of starbursts in the antennae galaxy from self-consistent modelling of MUSE spectra

2020 ◽  
Vol 497 (3) ◽  
pp. 3860-3895
Author(s):  
M L P Gunawardhana ◽  
J Brinchmann ◽  
P M Weilbacher ◽  
P Norberg ◽  
A Monreal-Ibero ◽  
...  
Keyword(s):  
High Resolution ◽  
Emission Line ◽  
Stellar Populations ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Full Spectrum ◽  
Star Forming ◽  
Self Consistent ◽  
Spectrum Fitting ◽  
Overlap Region

ABSTRACT We have modelled the stellar and nebular continua and emission-line intensity ratios of massive stellar populations in the Antennae galaxy using high resolution and self-consistent libraries of model H ii regions around central clusters of ageing stars. The model libraries are constructed using the stellar population synthesis code, starburst99, and photoionization model, and cloudy. The Geneva and PARSEC stellar evolutionary models are plugged into starburst99 to allow comparison between the two models. Using a spectrum-fitting methodology that allows the spectral features in the stellar and nebular continua [e.g. Wolf–Rayet (WR) features, Paschen jump], and emission-line diagnostics to constrain the models, we apply the libraries to the high-resolution Multi-Unit Spectroscopic Explorer spectra of the starbursting regions in the Antennae galaxy. Through this approach, we were able to model the continuum emission from WR stars and extract stellar and gas metallicities, ages, electron temperatures, and densities of starbursts by exploiting the full spectrum. From the application to the Antennae galaxy, we find that (1) the starbursts in the Antennae galaxy are characterized by stellar and gas metallicities of around solar, (2) the star-forming gas in starbursts in the Western loop of NGC 4038 appears to be more enriched, albeit slightly, than the rest of galaxy, (3) the youngest starbursts are found across the overlap region and over parts of the western-loop, though in comparison, the regions in the western-loop appear to be at a slightly later stage in star formation than the overlap region, and (4) the results obtained from fitting the Geneva and Parsec models are largely consistent.

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