The Limitations of Optical Spectroscopic Diagnostics in Identifying Active Galactic Nuclei in the Low-mass Regime

Cann, Jenna M.; Satyapal, S.; Abel, N. P.; Blecha, Laura; Mushotzky, R. F.; Reynolds, C. S.; Secrest, Nathan J.

doi:10.3847/2041-8213/aaf88d

Cited by 57 publications

(51 citation statements)

References 49 publications

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“…However, the colours clearly show that most of the objects found here are higher mass galaxies, with the lower mass points favouring the star-forming and composite regions. The behaviour exhibited by these low mass galaxies mirrors what we found in Birchall et al (2020) and is consistent with a growing body of work suggesting that these optical spectroscopic measurements are less effective at identifying AGN in lower mass galaxies (Agostino & Salim 2019;Cann et al 2019).…”

Section: Bpt Classificationsupporting

confidence: 88%

The Incidence of X-ray selected AGN in Nearby Galaxies

Birchall,

Watson,

Aird

et al. 2021

Preprint

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We present the identification and analysis of an unbiased sample of AGN that lie within the local galaxy population. Using the MPA-JHU catalogue (based on SDSS DR8) and 3XMM DR7 we define a parent sample of 25,949 local galaxies (𝑧 ≤ 0.33). After confirming that there was strictly no AGN light contaminating stellar mass and star-formation rate calculations, we identified 917 galaxies with central, excess X-ray emission likely originating from an AGN. We analysed their optical emission lines using the BPT diagnostic and confirmed that such techniques are more effective at reliably identifying sources as AGN in higher mass galaxies: rising from 30% agreement in the lowest mass bin to 93% in the highest. We then calculated the growth rates of the black holes powering these AGN in terms of their specific accretion rates (∝ 𝐿 𝑋 /𝑀 * ). Our sample exhibits a wide range of accretion rates, with the majority accreting at rates ≤ 0.5% of their Eddington luminosity. Finally, we used our sample to calculate the incidence of AGN as a function of stellar mass and redshift. After correcting for the varying sensitivity of 3XMM, we split the galaxy sample by stellar mass and redshift and investigated the AGN fraction as a function of X-ray luminosity and specific black hole accretion rate. From this we found the fraction of galaxies hosting AGN above a fixed specific accretion rate limit of 10 −3.5 is constant (at ≈ 1%) over stellar masses of 8 < log M * /M < 12 and increases (from ≈ 1% to 10%) with redshift.

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Section: Bpt Classificationsupporting

confidence: 88%

The Incidence of X-ray selected AGN in Nearby Galaxies

Birchall,

Watson,

Aird

et al. 2021

Preprint

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“…The lack of a positive classification in the remaining sources might be due to contamination from nearby, bright star-forming regions, stellar dilution, or to changes in the line ratios in the IMBH regime, as predicted by Trump et al (2015). In fact, optical spectroscopic diagnostics such as the BPT diagrams are expected to fail for low-mass BHs (Cann et al 2019 Astronomy Observatory (Prop. 2015A/14A-0608 and F. Förster), which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation.…”

Section: Discussionmentioning

confidence: 99%

Introducing the Search for Intermediate-mass Black Holes in Nearby Galaxies (SIBLING) Survey

Martínez-Palomera

Lira

Bhalla-Ladd

et al. 2020

ApJ

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Intermediate mass black holes (IMBHs) have masses between the 10 2 −10 6 M and are key to our understanding of the formation of massive black holes. The known population of IMBH remains small, with a few hundred candidates and only a handful of them confirmed as bona-fide IMBHs. Until now, the most widely used selection method is based on spectral analysis. Here we present a methodology to select IMBH candidates via optical variability analysis of the nuclear region of local galaxies (z 0.35). Active IMBH accreting at low rates show small amplitude variability with time scales of hours, as it is seen in one of the known IMBH NGC4395. We found a sample of ∼ 500 galaxies evidencing fast and small amplitude variation in their weekly based light curves. We estimate an average occupancy fraction of 4% and a surface density of ∼ 3 deg −2 , which represent an increase by a factor of ∼ 40 compared to previous searches. A large fraction (78%) of the candidates are in spiral galaxies. We preliminary confirm the AGN nature of 22 sources via BPT diagrams using SDSS legacy spectra. Further confirmation of these candidates will require multiwavelength observations, especially in X-ray and radio bands.

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“…A concern in this study is the extension of regular optical AGN diagnostic in to dwarf mass regime -a concern explored in detail in e.g Cann et al (2019) -and studies like Trump et al (2015), Penny et al (2018), andMackay Dickey et al (2019) does bring into question whether AGNs in dwarf galaxies are robustly identified in regular diagnostic tools.…”

Section: On Selection Methods Biasmentioning

confidence: 99%

Environments of dwarf galaxies with optical AGN characteristics

Kristensen

Pimbblet

2020

Monthly Notices of the Royal Astronomical Society

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ABSTRACT This study aims to explore the relation between dwarf galaxies (M* ≤ 5 × 109 M⊙) with active galactic nuclei (AGNs) and their environment by comparing neighbourhood parameters of AGN and non-AGN samples. Using the NASA-Sloan Atlas, both the local environment and the immediate environment of dwarf galaxies with z ≤ 0.055 are analysed. Of the 145 155 galaxies in the catalogue, 62 258 of them are classified as dwarf galaxies, and by employing two AGN selection methods based on emission-line fluxes (BPT and WHAN), 4476 are found to have AGN characteristics in their optical spectra. Regardless of selection method, this study finds no discernible differences in environment between AGN and non-AGN host dwarf galaxies and these results indicate that environment is not an important factor in triggering AGN activity in dwarf galaxies. This is in line with existing literature on environments of regular galaxies with AGNs and suggests universality in terms of reaction to environment across the mass regime. The biases of AGN selection in low-mass galaxies, and the biases of different measures of environment are also considered. It is found that there are several mass trends in emission-line ratios and that the SDSS fibre covers galaxies non-uniformly with redshift. These biases should be accounted for in future work by possibly including other wavelength regimes or mass weighting of emission-line ratios. Lastly, a discussion of the environment estimation methods is included since they may not gauge the desired properties due to factors such as time delay or using loosely constrained proxy parameters.

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The Limitations of Optical Spectroscopic Diagnostics in Identifying Active Galactic Nuclei in the Low-mass Regime

Cited by 57 publications

References 49 publications

The Incidence of X-ray selected AGN in Nearby Galaxies

The Incidence of X-ray selected AGN in Nearby Galaxies

Introducing the Search for Intermediate-mass Black Holes in Nearby Galaxies (SIBLING) Survey

Environments of dwarf galaxies with optical AGN characteristics

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