Classification parameters for the emission-line spectra of extragalactic objects

Baldwin, J. A.; Phillips, M. M.; Terlevich, Elena

doi:10.1086/130766

Cited by 4,681 publications

(4,549 citation statements)

References 7 publications

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“…We note that most of high-redshift emission-line galaxies satisfy the criterion [O iii]λ4959/Hβ 1.0, and hence have similar excitation conditions in their H ii regions; 4) galaxies with AGN activity are excluded. We used obvious AGN spectral characteristics: broad emission lines (QSOs and Sy1 galaxies), the presence of strong high-ionisation [Ne v] λ3426 and He ii Baldwin et al (1981) (BPT diagram, Fig. 1).…”

Section: The Samplementioning

confidence: 99%

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On the universality of luminosity–metallicity and mass–metallicity relations for compact star-forming galaxies at redshifts 0 < z < 3

Izotov

Гусева

Fricke

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We study relations between global characteristics of low-redshift (0 < z < 1) compact star-forming galaxies, including absolute optical magnitudes, Hβ emission-line luminosities (or equivalently star-formation rates), stellar masses, and oxygen abundances. The sample consists of 5182 galaxies with high-excitation H ii regions selected from the SDSS DR7 and SDSS/BOSS DR10 surveys adopting a criterion [O iii]λ4959/Hβ 1. These data were combined with the corresponding data for high-redshift (2 z 3) star-forming galaxies. We find that in all diagrams low-z and high-z star-forming galaxies are closely related indicating a very weak dependence of metallicity on stellar mass, redshift, and star-formation rate. This finding argues in favour of the universal character of the global relations for compact star-forming galaxies with high-excitation H ii regions over redshifts 0 < z < 3.

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Section: The Samplementioning

confidence: 99%

“…Furthermore, excitation conditions in those H ii regions are similar to those in high-z galaxies. (Baldwin et al 1981). Selected SDSS compact starforming galaxies with [O iii]λ4959/Hβ 1.0, corresponding to log [O iii]λ5007/Hβ 0.5, and detected [N ii]λ6584 line are shown by blue filled circles.…”

Section: Introductionmentioning

confidence: 99%

On the universality of luminosity–metallicity and mass–metallicity relations for compact star-forming galaxies at redshifts 0 < z < 3

Izotov

Гусева

Fricke

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…In the optical band, we considered a galaxy as an AGN if its emission-line ratios places it in the AGN region of the standard BPT diagram (Baldwin et al 1981). While in the X-rays, we used the rest-frame hard X-ray (i.e.…”

Section: X-ray and Optically Selected Agnmentioning

confidence: 99%

A new sample of X-ray selected narrow emission-line galaxies

Pons

Watson

2016

A&A

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A sample of X-ray and optically selected narrow emission-line galaxies (769 sources) from the 3XMM catalogue cross-correlated with SDSS (DR9) catalogue has been studied. Narrow-emission line active galactic nuclei (AGN; type-2) have been selected on the basis of their emission line ratios and/or X-ray luminosity. We have looked for X-ray unobscured type-2 AGN. As X-ray spectra were not available for our whole sample, we have checked the reliability of using the X-ray hardness ratio (HR) as a probe of the level of obscuration and we found a very good agreement with full spectral fitting results, with only 2% of the sources with apparently unobscured HR turning out to have an obscured spectrum. Despite the fact that type-2 AGN are supposed to be absorbed based on the Unified Model, about 60% of them show no sign or very low level of X-ray obscuration. After subtraction of contaminants to the sample, that is Narrow-Line Seyfert 1 and Compton-thick AGN, the fraction of unobscured Sy2 drops to 47%. For these sources, we were able to rule out dust reddening and variability for most of them as an explanation of the absence of optical broad emission-lines. The main explanations remaining are the dilution of weak/very broad emission-lines by the host galaxy and the intrinsic absence of the broad-line region (BLR) due to low accretion rates (i.e. True Sy2). However, the number of True Sy2 strongly depends on the method used to verify the intrinsic lack of broad lines. Indeed using the optical continuum luminosity to predict the BLR properties gives a much larger fraction of True Sy2 (about 90% of the unobscured Sy2 sample) than the use of the X-ray 2 keV luminosity (about 20%). Nevertheless the number of AGN we securely detected as True Sy2 is at least three times larger that the previously confirmed number of True Sy2.

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“…These IFU surveys will facilitate statistical analysis of the radial variations in star-formation histories, SFRs and the relative fraction of starburst to AGN power in AGN host galaxies. (Baldwin, Phillips & Terlevich 1981;Veilleux & Osterbrock 1987) is commonly used to separate star-formation from AGN activity. The emission line pairs used in each ratio ([N II] λ 6548 and Hα λ 6583, [O III] λ 5007 and Hβ λ 4861) are very close in wavelength, making the diagnostic virtually insensitive to reddening.…”

Section: Introductionmentioning

confidence: 99%

Starburst–AGN mixing – II. Optically selected active galaxies

Davies

Kewley

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We use 4 galaxies from the Calar Alto Legacy Integral Field Area (CALIFA) survey with clear signs of accretion onto supermassive black holes to investigate the relative contribution of star-formation and active galactic nucleus (AGN) activity to the lineemission of each galaxy as a function of radius. The combination of star-formation and AGN activity produces curved "mixing sequences" on standard optical diagnostic diagrams, and the fraction of emission due to AGN activity decreases smoothly with distance from the centre of the galaxy. We use the AGN activity profiles to calculate the size of the AGN narrow line regions, which have radii of ∼ 6.3 kpc. We calculate the fractional contribution of the star-formation and the AGN activity to the global Hα, [O II] λλ 3727,3729 and [O III] λ 5007 luminosities of each galaxy, and show that both ionization sources contribute significantly to the emission in all three lines. We use weighted combinations of stellar and AGN photoionization models to produce mixing models, which are consistent with observations for 85 percent of spaxels across the galaxies in our sample. We also present a new diagnostic for starburst-AGN mixing which requires only the [O II], [O III] and Hβ emission lines, and can therefore be used to calculate AGN fractions up to z ∼ 0.85 in the optical and z ∼ 3.5 in the nearinfrared. We anticipate that this diagnostic will facilitate studies of the properties of AGN ionizing radiation fields and the relative optical contribution of star-formation and AGN activity over cosmic time.

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Classification parameters for the emission-line spectra of extragalactic objects

Cited by 4,681 publications

References 7 publications

On the universality of luminosity–metallicity and mass–metallicity relations for compact star-forming galaxies at redshifts 0 < z < 3

On the universality of luminosity–metallicity and mass–metallicity relations for compact star-forming galaxies at redshifts 0 < z < 3

A new sample of X-ray selected narrow emission-line galaxies

Starburst–AGN mixing – II. Optically selected active galaxies

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