A New Diagnostic Diagram of Ionization Sources for High-redshift Emission Line Galaxies

Zhang, Kai; Hao, Lei

doi:10.3847/1538-4357/aab207

Cited by 14 publications

(31 citation statements)

References 159 publications

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“…3 and 5) suggests a very high [O iii]/Hβ ratio, as expected in the case of ionisation by AGN (e.g., Kewley et al 2001;Kauffmann et al 2003). This ionisation mechanism is further supported by the large velocity dispersion, FWHM ∼ 600 km s −1 , of the extended [O iii] emission (see e.g., Zhang & Hao 2018).…”

Section: The Extended Emission From Ionised Gassupporting

confidence: 60%

Down-the-barrel observations of a multi-phase quasar outflow at high redshift

Noterdaeme

Balashev

Krogager

et al. 2021

A&A

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We present ultraviolet to near infrared spectroscopic observations of the quasar SDSS J001514+184212 and its proximate molecular absorber at z = 2.631. The [O III] emission line of the quasar is composed of a broad (FWHM ∼ 1600 km s−1), spatially unresolved component, blueshifted by about 600 km s−1 from a narrow, spatially-resolved component (FWHM ∼ 650 km s−1). The wide, blueshifted, unresolved component is consistent with the presence of outflowing gas in the nuclear region. The narrow component can be further decomposed into a blue and a red blob with a velocity width of several hundred km s−1 each, seen ∼5 pkpc on opposite spatial locations from the nuclear continuum emission, indicating outflows on galactic scales. The presence of ionised gas on kpc scales is also seen from a weak C IV emission component, detected in the trough of a saturated C IV absorption that removes the strong nuclear emission from the quasar. Towards the nuclear emission, we observe absorption lines from atomic species in various ionisation and excitation stages and confirm the presence of strong H2 lines originally detected in the SDSS spectrum. The overall absorption profile is very wide, spread over ∼600 km s−1, and it roughly matches the velocities of the narrow blue [O III] blob. From a detailed investigation of the chemical and physical conditions in the absorbing gas, we infer densities of about nH ∼ 104 − 105 cm−3 in the cold (T ∼ 100 K) H2-bearing gas, which we find to be located at ∼10 kpc distances from the central UV source. We conjecture that we are witnessing different manifestations of a same AGN-driven multi-phase outflow, where approaching gas is intercepted by the line of sight to the nucleus. We corroborate this picture by modelling the scattering of Ly-α photons from the central source through the outflowing gas, reproducing the peculiar Ly-α absorption-emission profile, with a damped Ly-α absorption in which red-peaked, spatially offset, and extended Ly-α emission is seen. Our observations open up a new way to investigate quasar outflows at high redshift and shed light on the complex issue of AGN feedback.

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Section: The Extended Emission From Ionised Gassupporting

confidence: 60%

Down-the-barrel observations of a multi-phase quasar outflow at high redshift

Noterdaeme

Balashev

Krogager

et al. 2021

A&A

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“…We chose the stellar mass derived using the Maraston et al (2011) templates. The RF classification results are quite consistent with the KEx and MEx demarcation lines from Zhang & Hao (2018) and Juneau et al (2011), respectively. In terms of accuracy, the KEx diagram gives classification accuracies of 89%, 75.6%, and 81% for SFGs, composites, and AGNs, respectively.…”

Section: Classification Using Only Spectroscopic Featuressupporting

confidence: 86%

Machine-learning Classifiers for Intermediate Redshift Emission-line Galaxies

Zhang

Schlegel

Andrews

et al. 2019

ApJ

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Classification of intermediate redshift (z = 0.3-0.8) emission line galaxies as star-forming galaxies, composite galaxies, active galactic nuclei (AGN), or low-ionization nuclear emission regions (LINERs) using optical spectra alone was impossible because the lines used for standard optical diagnostic diagrams: [N II], Hα, and [S II] are redshifted out of the observed wavelength range. In this work, we address this problem using four supervised machine learning classification algorithms: k-nearest neighbors (KNN), support vector classifier (SVC), random forest (RF), and a multi-layer perceptron (MLP) neural network. For input features, we use properties that can be measured from optical galaxy spectra out to z < 0.8-[O III]/Hβ, [O II]/Hβ, [O III] line width, and stellar velocity dispersion-and four colors (u − g, g − r, r − i, and i − z) corrected to z = 0.1. The labels for the low redshift emission line galaxy training set are determined using standard optical diagnostic diagrams. RF has the best area under curve (AUC) score for classifying all four galaxy types, meaning highest distinguishing power. Both the AUC scores and accuracies of the other algorithms are ordered as MLP>SVC>KNN. The classification accuracies with all eight features (and the four spectroscopicallydetermined features only) are 93.4% (92.3%) for star-forming galaxies, 69.4% (63.7%) for composite galaxies, 71.8% (67.3%) for AGNs, and 65.7% (60.8%) for LINERs. The stacked spectrum of galaxies of the same type as determined by optical diagnostic diagrams at low redshift and RF at intermediate redshift are broadly consistent. Our publicly available code a and trained models will be instrumental for classifying emission line galaxies in upcoming wide-field spectroscopic surveys.

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“…This ionisation mechanism is further supported by the large velocity dispersion, FWHM ∼ 600 km s −1 , of the extended [O iii] emission (see e.g. Zhang & Hao 2018).…”

Section: The Extended Emission From Ionised Gasmentioning

confidence: 72%

Down-the-barrel observations of a multiphase quasar outflow at high redshift: VLT/X-shooter spectroscopy of the proximate molecular absorber at z=2.631 towards SDSS J001514+184212

Noterdaeme,

Balashev,

Krogager

et al. 2020

Preprint

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A New Diagnostic Diagram of Ionization Sources for High-redshift Emission Line Galaxies

Cited by 14 publications

References 159 publications

Down-the-barrel observations of a multi-phase quasar outflow at high redshift

Down-the-barrel observations of a multi-phase quasar outflow at high redshift

Machine-learning Classifiers for Intermediate Redshift Emission-line Galaxies

Down-the-barrel observations of a multiphase quasar outflow at high redshift: VLT/X-shooter spectroscopy of the proximate molecular absorber at z=2.631 towards SDSS J001514+184212

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