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An increase in black hole activity in galaxies with kinematically misaligned gas

Abstract

External accretion events such as a galaxy merger or the accretion of gas from the immediate environment of a galaxy can create a large misalignment between the gas and the stellar kinematics. Numerical simulations have suggested that misaligned structures may promote the inflow of gas to the nucleus of the galaxy and the accretion of gas by the central supermassive black hole. We show for the first time that galaxies with a strong misalignment between the ionized gas and stellar kinematic angles have a higher observed fraction of active black holes than galaxies with aligned rotation of gas and stars. The increase in black hole activity suggests that the process of formation and/or the presence of misaligned structures are connected with the fuelling of active supermassive black holes.

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Fig. 1: Distribution of the stellar-to-gas kinematic misalignment.
Fig. 2: Fraction of galaxies with different excitation mechanisms divided per interval of misalignment angle (ΔPA).
Fig. 3: Fraction of AGN and LINERs in galaxies with aligned versus misaligned stellar-to-gas kinematics.

Data availability

The data used in this study are available in the AAO Data Central repository (https://docs.datacentral.org.au/sami/). Additional data can accessed via a persistent repository at https://erda.ku.dk/archives/dcf9b1543592f8fbd824cf1eeb733b4e/published-archive.html. The following lists the availability of the catalogues used in the section ‘Cross matching with AGN catalogues’: the Second ROSAT All-Sky Survey (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/A+A/588/A103); the Swift/Burst Alert Telescope (BAT)AT 70-month AGN X-ray catalogue (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/ApJS/233/17); the Wide-field Infrared Survey Explorer (WISE) AGN catalogue (90% confidence level) based on the AllWISE catalogue (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/ApJS/234/23); the catalogue of ref. 71 (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/ApJ/751/52) and the radio-loud AGN catalogue of ref. 72 (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/MNRAS/421/1569).

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Acknowledgements

The authors would like to thank the referees for their constructive comments. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 891744 (S.I.R.). This research has been financially supported by the Independent Research Fund Denmark via grant number DFF 8021-00130 (M.V.). This paper includes data that have been provided by AAO Data Central (datacentral.org.au). The SAMI Galaxy Survey is based on observations made at the Anglo-Australian Telescope. SAMI was developed jointly by the University of Sydney and the Australian Astronomical Observatory. The SAMI input catalogue is based on data taken from the Sloan Digital Sky Survey, the GAMA Survey and the VST ATLAS Survey. The SAMI Galaxy Survey is funded by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020, and other participating institutions. This research has made use of the VizieR catalogue access tool, CDS (https://doi.org/10.26093/cds/vizier). The original description of the VizieR service was published in ref. 74. This research made use of Astropy (http://www.astropy.org), a community-developed core Python package for Astronomy75.

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S.I.R. conceived the study, carried out the analysis and wrote the paper. M.M. and M.V. wrote the paper, making an equal contribution to the paper. All authors discussed the results and their interpretation and commented on the manuscript at all stages.

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Correspondence to Sandra I. Raimundo.

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Extended data

Extended Data Fig. 1 Kinematic position angle.

Result of the kinematic position angle (PA) determination for one of the galaxies in the sample, J145002.16+003443.6, or ID 93807 in the SAMI catalogue. Left: Map of stellar velocity with title Vstar. The best fit kinematic PA is shown by the green solid line. The value determined is PAstellar = 184.0 ± 1. 5 where the error corresponds to the 3σ uncertainties of the fit. Right: Map of gas velocity with title Vgas. The best fit kinematic PA is shown by the green solid line, PAgas = 4 ± 4. The PA orientation is measured from North (PA = 0, up in the figure) to East and is per our definition oriented from the approaching (blueshifted) to the receding (redshifted) regions of the map. The dashed black line shows the zero velocity line, which is the axis that fit_kinematic_pa uses to create the mirrored bi(anti)symmetric velocity map. The measured misalignment between the stellar and gas kinematic angles for this galaxy, ΔPA = PAstellar - PAgas = 180, corresponds to counter-rotation of gas and stars.

Extended Data Fig. 2 Fraction of AGN, LINER and star forming galaxies for cutoff angle of 30 deg.

Similar to Fig. 3 but using ΔPA = 30 as the cut-off angle. The fraction of AGN is 7 ± 1% in aligned galaxies and 17 ± 3% in misaligned galaxies, the fraction of LINERs is 16 ± 1% in aligned galaxies and 35 ± 4% in misaligned galaxies and the fraction of star forming galaxies is 78 ± 1% in aligned galaxies and 49 ± 4% in misaligned galaxies. The absolute numbers for each bar in the order aligned/misaligned are: top left panel 65+9 − 7, 22+5 − 4; top right panel 150+12 − 11, 46+6 − 5; bottom panel 743+12 − 13, 65+6 − 6, respectively. The error bars correspond to the 68% confidence intervals using a beta distribution quantile technique.

Extended Data Fig. 3 Fraction of galaxies with a specific excitation mechanism divided by morphology.

Fraction of galaxies with a specific excitation mechanism, as a function of the misalignment between the stellar and the gas kinematic angle (ΔPA = PAstars - PAgas) and the galaxy morphology. The histogram bars of each colour add up to 1 across the ΔPA distribution. The top panel shows the total population, the bottom left panel shows the early type galaxies and the bottom right panel shows the late type galaxies in the sample. Each panel is colour coded as a function of the main excitation mechanism in the galaxies. The panels can be understood as, for example how galaxies with emission lines from AGN, LINERs or young stars are distributed as a function of ΔPA. Almost all the late type galaxies in the sample are aligned, while early-type galaxies show a broader distribution in terms of ΔPA. Most of the misaligned galaxies have AGN or LINER as their excitation mechanism. Excitation by star formation only, in early type galaxies tends to occur mostly in aligned ΔPA < 45, with a smaller secondary peak in close to counter-rotating ΔPA ~ 180 galaxies. The fraction of star forming early-type galaxies in the fourth bin (135≤ΔPA ≤180) is marginally higher than the fraction of star forming early-type galaxies in the second and third bins at the 68% and 95% confidence level, respectively.

Extended Data Fig. 4 Pie charts with morphology classification.

Pie charts showing the morphology classification of the sub-samples of galaxies. The top row shows the sub-sample of galaxies with an excitation classification, divided into ‘aligned’ (0≤ΔPA < 45 - top left panel) and ‘misaligned’ (45≤ΔPA ≤180 - top right panel). The bottom row shows the sub-sample of galaxies classified as AGN, divided into AGN in ‘aligned’ galaxies (bottom left panel) and AGN in ‘misaligned’ galaxies (bottom right panel). The morphological classification is divided into early-type and late-type galaxies with ‘Other’ referring to an unknown morphological classification. 75% of all misaligned galaxies are in early-type galaxies while 95% of AGN with misaligned hosts are in early-type galaxies.

Extended Data Fig. 5 Emission line diagrams.

Illustration of the emission line diagrams used in this work and the theoretical regions of62 indicated by the solid and dashed lines. The text labels refer to the fraction of spaxels that fall in each of the different regions of the diagrams. For clarity we use the same names in the figure as in the text (see Methods). The suffixes ‘SF’ stand for star-forming regions, ‘AGN’ for AGN-excitation regions, ‘comp’ for composite regions (likely a combination of excitation by young stars and AGN) and ’LINER’ for low-ionization nuclear emission-line region. The suffixes [N II], [S II] and [O I] refer to each of the corresponding BPT diagrams: [N II]/Hα, [S II]/Hα and [O I]/Hα.

Extended Data Fig. 6 Example of emission line diagram classification.

Illustration of the line diagnostics used. Each figure shows the BPT analysis used to identify the excitation mechanisms: The three top panels show the galaxy spatial maps colour-coded by dominant excitation mechanism, purple for AGN, salmon for composite, grey for star formation and blue for LINER. Bottom panels show the BPT diagrams for each spaxel in the image, colour-coded as a function of distance from centre of the galaxy (shown as position (0,0) in the top panels). Blue symbols correspond to spaxels closest to the nucleus, red symbols to spaxels further away from the nucleus, with the range of colours calibrated for each individual galaxy. For example, the bluest point for each galaxy will be the spaxel with detected emission that is closest to its nucleus. That could be the central spaxel (distance = 0) or a spaxel that is further away from the nucleus if no emission is detected in the central spaxels. The solid and dashed lines are the classification boundaries from62. Each column refers for a specific line ratio, from left to right: [O III]/Hβ vs [N II]/Hα, [O III]/Hβ vs [S II]/Hα and [O III]/Hβ vs [O I]/Hα. The labels in the bottom row refer to the excitation classification in each region of the diagrams: AGN, LINER, SF (star-forming galaxies) or Comp (composite regions). The two figures (from top to bottom) show an example of a galaxy classified as AGN and another as LINER. An example of a star-forming galaxy is shown in Supplementary Information.

Extended Data Fig. 7 Distribution of average gas velocity dispersion.

Histograms of the distribution of average gas velocity dispersion. The y-axis shows the number of galaxies per bin. The dark-coloured histograms at the top show misaligned galaxies while the light-coloured histograms at the bottom show the aligned galaxies. The distribution for AGN are shown in the left panels while the distribution for non-AGN galaxies are shown in the right panels.

Extended Data Fig. 8 Distribution of stellar mass.

Histograms of the distribution of stellar mass in units of solar masses. The y-axis shows the number of galaxies per bin. The dark-coloured histograms at the top show misaligned galaxies while the light-coloured histograms at the bottom show the aligned galaxies. The distribution for AGN are shown in the left panels while the distribution for non-AGN galaxies are shown in the right panels.

Extended Data Table 1 Number of galaxies in the different sub-samples. Numbers for the different galaxy sub-samples used in this work. Note: there is some overlap in the AGN identification, as some AGN are identified both in the BPT diagram and with broad lines or with broad lines and catalogue matching. Text in bold highlights the two most important galaxy sub-samples
Extended Data Table 2 Distribution of galaxies as a function of morphology. Distribution of galaxies that have an excitation classification and PAstellar and PAgas well constrained, divided according to morphology. ‘a/m’ stands for aligned/misaligned numbers in each group of galaxies and ‘SF’ for star-forming galaxies. Numbers in bold show the total number of galaxies in each classification group. The total number of galaxies is different from Table 1 because some of the SAMI galaxies do not have a clear morphological classification

Supplementary information

Supplementary Information

Supplementary Figs. 1–5 and Table 1.

Supplementary Data 1

Supplementary data for Supplementary Table 1. The file contains a .csv table.

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Raimundo, S.I., Malkan, M. & Vestergaard, M. An increase in black hole activity in galaxies with kinematically misaligned gas. Nat Astron (2023). https://doi.org/10.1038/s41550-022-01880-z

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