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Rogério Riffel

Publications and source records attributed to Rogério Riffel.

At least 37 records · Page 2Linked to original sources
arXiv2024

Blowing star formation away in AGN Hosts (BAH) -- I. Observation of Warm Molecular Outflows with JWST MIRI

We use the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) medium-resolution spectrometer (MRS) observations of the radio loud AGN host UGC 8782 to map the warm molecular and ionized gas kinematics. The data reveal spatially resolved outflows in the inner 2 kpc, seen in low ionization (traced by the [Ar ii] 6.99um emission) and in warm molecular gas (traced by the H2 rotational transitions). We find a maximum mass-outflow rate of 4.90 (2.04) M/yr at ~900 pc from the nucleus for the warm outflow (198 K< T< 1000 K) and estimate and outflow rate of up to 1.22 (0.51) M/yr for the hotter gas phase (T > 1000 K). These outflows can clear the entire nuclear reservoir of warm molecular gas in about 1 Myr. The derived kinetic power of the molecular outflows lead to coupling efficiencies of 2-5 percent of the AGN luminosity, way above the minimum expected to the AGN feedback be effective quenching the star formation.

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arXiv2024

Determining star-formation rates in Active Galactic Nuclei hosts via stellar population synthesis

The effect of active galactic nuclei (AGN) feedback on the host galaxy, and its role in quenching or enhancing star-formation, is still uncertain due to the fact that usual star-formation rate (SFR) indicators -- emission-line luminosities based on the assumption of photoionisation by young stars -- cannot be used for active galaxies as the ionising source is the AGN. We thus investigate the use of SFR derived from the stellar population and its relation with that derived from the gas for a sample of 170 AGN hosts and a matched control sample of 291 galaxies. We compare the values of SFR densities obtained via the Ha emission line (SFRg) for regions ionised by hot stars according to diagnostic diagrams with those obtained from stellar population synthesis (SFRstars) over the last 1 to 100~Myr. We find that the SFRstars over the last 20~Myrs closely reproduces the SFRg, although a better match is obtained via the transformation: log(SFRstars) = (0.870+/-0.004) log(SFRg) +(0.007+/-0.006), which is valid for both AGN hosts and non-active galaxies. We also compare the reddening obtained via the gas Ha/Hb ratio with that derived via the full spectral fitting in the stellar population synthesis. We find that the ratio between the gas and stellar extinction is in the range 2.64 < A_Vgas/A_Vstar} < 2.85, in approximate agreement with previous results from the literature, obtained for smaller samples. We interpret the difference as being due to the fact that the reddening of the stars is dominated by that affecting the less obscured underlying older population, while the reddening of the gas is larger as it is associated to a younger stellar population buried deeper in the dust.

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arXiv2024

Systematic analysis of jellyfish galaxy candidates in Fornax, Antlia, and Hydra from the S-PLUS survey: A self-supervised visual identification aid

We study 51 jellyfish galaxy candidates in the Fornax, Antlia, and Hydra clusters. These candidates are identified using the JClass scheme based on the visual classification of wide-field, twelve-band optical images obtained from the Southern Photometric Local Universe Survey. A comprehensive astrophysical analysis of the jellyfish (JClass > 0), non-jellyfish (JClass = 0), and independently organized control samples is undertaken. We develop a semi-automated pipeline using self-supervised learning and similarity search to detect jellyfish galaxies. The proposed framework is designed to assist visual classifiers by providing more reliable JClasses for galaxies. We find that jellyfish candidates exhibit a lower Gini coefficient, higher entropy, and a lower 2D Sérsic index as the jellyfish features in these galaxies become more pronounced. Jellyfish candidates show elevated star formation rates (including contributions from the main body and tails) by $\sim$1.75 dex, suggesting a significant increase in the SFR caused by the ram-pressure stripping phenomenon. Galaxies in the Antlia and Fornax clusters preferentially fall towards the cluster's centre, whereas only a mild preference is observed for Hydra galaxies. Our self-supervised pipeline, applied in visually challenging cases, offers two main advantages: it reduces human visual biases and scales effectively for large datasets. This versatile framework promises substantial enhancements in morphology studies for future galaxy image surveys.

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arXiv2024

A study of interacting galaxies from the Arp-Madore Catalogue: Triggering of star formation and nuclear activity

We present Gemini Multi-Object Spectrograph (GMOS) spectroscopic observations of 95 galaxies from the Arp & Madore (1987) catalogue of peculiar galaxies. These galaxies have been selected because they appear to be in pairs and small groups. These observations have allowed us to confirm that 60 galaxies are indeed interacting systems. For the confirmed interacting sample, we have built a matched control sample of isolated galaxies. We present an analysis of the stellar populations and nuclear activity in the interacting galaxies and compare them with the isolated galaxies. We find a median light (mass) fraction of 55% (10%) in the interacting galaxies coming from stellar populations younger than 2 Gyr and 28% (3%) in the case of the isolated galaxies. More than half of the interacting galaxies are dominated by this young stellar population, while the isolated ones have most of their light coming from older stellar populations. We used a combination of diagnostic diagrams (BPTs and WHAN) to classify the main ionization mechanisms of the gas. The interacting galaxies in our sample consistently show a higher fraction of active galactic nuclei (AGN) relative to the control sample, which ranges between 1.6 and 4 depending on the combination of diagnostic diagrams employed to classify the galaxies and the number of galaxies considered. Our study provides further observational evidence that interactions drive star formation and nuclear activity in galaxies and can have a significant impact on galaxy evolution.

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arXiv2024

SMARTY: The mileS Moderate resolution neAr-infRared sTellar librarY

Most of the observed galaxies cannot be resolved into individual stars and are studied through their integrated spectrum using simple stellar populations (SSPs) models, with stellar libraries being a key ingredient in building them. Spectroscopic observations are increasingly being directed towards the near-infrared (NIR), where much is yet to be explored. SSPs in the NIR are still limited, and there are inconsistencies between different sets of models. One of the ways to minimize this problem is to have reliable NIR stellar libraries. The main goal of this work is to present SMARTY (mileS Moderate resolution neAr-infRared sTellar librarY) a ~0.9-2.4$μ$m stellar spectral library composed of 31 stars observed with the Gemini Near-IR Spectrograph (GNIRS) at the 8.1m Gemini North telescope and make it available to the community. The stars were chosen from the SMARTY library, for which the atmospheric parameters are reliable (and well tested), to populate different regions of the Hertzsprung-Russell (HR) diagram. Furthermore, five of these stars have NIR spectra available that we use to assess the quality of SMARTY. The remaining 26 stars are presented for the first time in the NIR. We compared the observed SMARTY spectra with synthetic and interpolated spectra, finding a mean difference of ~20% in the equivalent widths and ~1% in the overall continuum shape in both sets of comparisons. We computed the spectrophotometric broadband magnitudes and colours and compared them with the 2MASS ones, resulting in mean differences up to 0.07 and 0.10mag in magnitudes and colours, respectively. In general, a small difference was noted between the SMARTY spectra corrected using the continuum from the interpolated and the theoretical stars.

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arXiv2024

The extent and power of "maintainance mode" feedback in MaNGA AGN

We study the ionised gas kinematics of 293 Active Galactic Nuclei (AGN) hosts as compared to that of 485 control galaxies from the MaNGA-SDSS survey using measurements of the [OIII]$λ$5007Åemission-line profiles, presenting flux, velocity and W$_{80}$ maps. In 45% of the AGN, a broad component was needed to fit the line profiles wings within the inner few kpc, that we have identified with an outflow. But in most AGN, the profiles are broader than that of their controls over a much more extended region, identified as the "kinematically disturbed regions" (KDRs). We find a positive correlation between the mean $\langle$W$_{80}\rangle$ and L[OIII], supporting that the KDR is due to heating and turbulence of the ISM by outflows and radiation from the AGN. The extent R$_{KDR}$ reaches up to 24kpc, with a mean ratio to that of the ENLR of 57%. We estimate ionised gas mass flow rates ($\dot{M}_{\rm out}$) and kinetic powers ($\dot{E}_{\rm out}$) both from the AGN broad components and from the W$_{80}$ values, that can be obtained for the whole AGN sample. We find values for $\dot{M}_{\rm out}$ and $\dot{E}_{\rm out}$ that correlate with the AGN luminosity $L_{bol}$, populating the low luminosity end of these known correlations. The mean coupling efficiency between $\dot{E}_{\rm out}$ and AGN luminosity is $\approx$ 0.02% from the W$_{80}$ values and lower from the broad component. But the large extent of the KDR shows that even low-luminosity AGN can impact the host galaxy along several kpc in a "maintenance mode" feedback.

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arXiv2023

Mapping the stellar population and gas excitation of MaNGA galaxies with MEGACUBES. Results for AGN versus control sample

We present spaxel-by-spaxel stellar population fits for the $\sim$10 thousand MaNGA datacubes. We provide multiple extension fits files, nominated as MEGACUBES, with maps of several properties as well as emission-line profiles that are provided for each spaxel. All the MEGACUBES are available through a web interface (\url{https://manga.linea.org.br/} or \url{http://www.if.ufrgs.br/~riffel/software/megacubes/}). We also defined a final Active Galactic Nuclei (AGN) sample, as well as a control sample matching the AGN host galaxy properties. We have analysed the stellar populations and spatially resolved emission-line diagnostic diagrams of these AGNs and compared them with the control galaxies sample. We find that the relative fractions of young ($t \leq $56 Myr) and intermediate-age (100 Myr $\leq t \leq$ 2 Gyr) show predominantly a positive gradient for both AGNs and controls. The relative fraction of intermediate-age stellar population is higher in AGN hosts when compared to the control sample, and this difference becomes larger for higher [O III] luminosity AGNs. We attribute this to the fact that extra gas is available in these more luminous sources and that it most likely originates from mass-loss from the intermediate-age stars. The spatially resolved diagnostic diagrams reveal that the AGN emission is concentrated in the inner 0.5 $R_e$ (effective radius) region of the galaxies, showing that the AGN classification is aperture dependent and that emission-line ratios have to be taken together with the H$α$ equivalent width for proper activity classification. We present a composite ``BPT+WHAN" diagram that produces a more comprehensive mapping of the gas excitation.

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arXiv2023

BASS XXXV. The $M_\rm{BH}$-$σ_\rm{\star}$ Relation of 105-Month Swift-BAT Type 1 AGNs

We present two independent measurements of stellar velocity dispersions ( $σ_\rm{\star}$ ) from the Ca\,H+K \& Mg\,\textsc{i} region (3880--5550~Å) and the Calcium Triplet region (CaT, 8350--8750~Å) for 173 hard X-ray-selected Type 1 AGNs ($z \leq$ 0.08) from the 105-month Swift-BAT catalog. We construct one of the largest samples of local Type 1 AGNs that have both single-epoch (SE) 'virial' black hole mass ($M_\rm{BH}$) estimates and $σ_\rm{\star}$ measurements obtained from high spectral resolution data, allowing us to test the usage of such methods for SMBH studies. We find that the two independent $σ_\rm{\star}$ measurements are highly consistent with each other, with an average offset of only $0.002\pm0.001$ dex. Comparing $M_\rm{BH}$ estimates based on broad emission lines and stellar velocity dispersion measurements, we find that the former is systematically lower by $\approx$0.12 dex. Consequently, Eddington ratios estimated through broad-line $M_\rm{BH}$ determinations are similarly biased (but in the opposite way). We argue that the discrepancy is driven by extinction in the broad-line region (BLR). We also find an anti-correlation between the offset from the $M_\rm{BH}$ - $σ_\rm{\star}$ relation and the Eddington ratio. Our sample of Type 1 AGNs shows a shallower $M_\rm{BH}$ - $σ_\rm{\star}$ relation (with a power law exponent of $\approx$3.5) compared with that of inactive galaxies (with a power-law exponent of $\approx$4.5), confirming earlier results obtained from smaller samples.

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arXiv2023

Spatially resolved self-consistent spectral modelling of jellyfish galaxies from MUSE with FADO: trends with mass and stripping intensity

We present a spatially resolved stellar population analysis of 61 jellyfish galaxies and 47 control galaxies observed with ESO/MUSE attempting to understand the general trends of the stellar populations as a function of the stripping intensity and mass. This is the public sample from the GASP programme, with $0.01 < z < 0.15$ and $8.9 <\log(M_{\star}/M_{\odot}) < 12.0$. We apply the spectral population synthesis code FADO to fit self-consistently both the stellar and nebular contributions to the spectra of the sources. We present 2D morphological maps for mean stellar ages, metallicities, gas-phase oxygen abundances, and star formation rates for the galaxies with Integrated Nested Laplace Approximation (INLA), which is efficient in reconstructing spatial data of extended sources. We find that "extreme stripping" and "stripping" galaxies are typically younger than the other types. Regarding stellar and nebular metallicities, the "stripping" and "control passive" galaxies are the most metal-poor. Based on the phase space for jellyfish cluster members we find trends in ages, metallicities, and abundances with different regions of the diagram. We also compute radial profiles for the same quantities. We find that both the stripping and the stellar masses seem to influence the profiles, and we see differences between various groups and distinct mass bins. The radial profiles for different mass bins present relations already shown in the literature for undisturbed galaxies, i.e., profiles of ages and metallicities tend to increase with mass. However, beyond $\sim0.75$ effective radius, the ages of the most massive galaxies become similar to or lower than the ages of the lower mass ones.

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arXiv2023

A Decade of Near-Infrared Variability in NGC4388: Insights into the AGN Structure

Variability studies have proven to be a powerful diagnostic tool for understanding the physics and properties of of Active Galactic Nuclei (AGNs). They provide insights into the spatial and temporal distribution of the emitting regions, the structure and dynamics of the accretion disk, and the properties of the central black hole. Here, we have analysed the K-band spectral variability of the Seyfert 1.9/2 galaxy NGC4388 spanning five epochs over a period of ten years. We have performed spectral synthesis of the nuclear region and found that the contribution of warm dust (T~800K) declined by 88% during these 10 years. In the same period, the [CaVIII] coronal line decreased 61%, whereas BrG emission declined 35%. For the HeI and H2, we did not detect any significant variation beyond their uncertainties. Based on the time span of these changes, we estimate that the region where the warm dust is produced is smaller than 0.6pc, which suggests that this spectral feature comes from the innermost part of the region sampled, directly from the AGN torus. On the other hand, the bulk of [CaVIII] is produced in the inner ~2pc and the nuclear BrG region is more extended, spanning a region larger than 3pc. Lastly, HeI and H2 are even more external, with most of the emission probably being produced in the host galaxy rather than in the AGN. This is the first spectroscopic variability study in the NIR for an AGN where the central source is not directly visible.

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arXiv2023

Digging deeper into NGC\,6868 I: stellar population

We use Gemini integral field unit observations to map the stellar population properties in the inner region ($\sim680\times470$ pc$^2$) of the galaxy NGC 6868. In order to understand the physical and chemical properties of the stellar content of this galaxy, we performed stellar population synthesis using the starlight code with the MILES simple stellar population models. We measured the absorption line indices Fe4383, Mg$_2$, Mg$_b$, Fe5270, Fe5335 for the whole FoV, and used them to derive Fe3 and [MgFe]'. These indices were used to derive [$α$/Fe]. This galaxy is dominated by old metal-rich populations (12.6 Gyr; 1.0 and 1.6 Z$_\odot$) with a negative metallicity gradient. We also found a recent ($\sim63$ Myr) metal-rich (1.6 Z$_{\odot}$) residual star formation in the centre of the galaxy. A dust lane with a peak extinction in the V band of 0.65 mag is seen. No signs of ordered stellar motion are found and the stellar kinematics is dispersion dominated. All indices show a spatial profile varying significantly along the FoV. Mg$_2$ shows a shallow gradient, compatible with the occurrence of mergers in the past. Mg$_b$ and Fe3 profiles suggest different enrichment processes for these elements. We observe three distinct regions: for $R<100$pc and $R>220$pc, Mg$_2$, Mg$_b$ anti correlate with respect to Fe3 and [MgFe]', and for $100 \text{pc}<R<220 \text{pc}$, they correlate, hinting at different enrichment histories. The [$α$/Fe] profile is really complex and has a central value of $\sim 0.2$ dex. We interpret this as the result of a past merger with another galaxy with a different [$α$/Fe] history, thus explaining the [$α$/Fe] maps.

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arXiv2023

Spatially resolved observations of outflows in the radio loud AGN of UGC 8782

We use optical Integral Field Spectroscopy (IFU) to study the gas emission structure and kinematics in the inner 3.4$\times$4.9 kpc$^2$ region of the galaxy UGC 8782 (3C 293), host of a radio loud Active Galactic Nucleus (AGN). The observations were performed with the GMOS-IFU on the Gemini North telescope, resulting in a spatial resolution of $\sim725$ pc at the distance of the galaxy. While the stars present ordered rotation following the orientation of the large scale disc, the gas shows a disturbed kinematics. The emission-line profiles present two kinematic components: a narrow ($σ\lesssim200$ km s$^{-1}$) component associated with the gas in the disc of the galaxy and a broad ($σ\gtrsim200$ km s$^{-1}$) component produced by gas outflows. Emission-line ratio diagrams indicate that the gas in the disc is excited by the AGN radiation field, while the emission of the outflow includes additional contribution of shock excitation due to the interaction of the radio jet with the environment gas. Deviations from pure rotation, of up to 30 km s$^{-1}$, are observed in the disc component and likely produced by a previous merger event. The broad component is blueshifted by $\sim150-500$ km s$^{-1}$ relative to the systemic velocity of the galaxy in all locations. We construct radial profiles of the mass outflow rate and kinetic power of the ionized gas outflows, which have the maximum values at $\sim1$ kpc from the nucleus with peak values of $\dot{M}_{\rm out,ΔR}=0.5\pm0.1$ M$_\odot$ yr$^{-1}$ and $\dot{K}_{\rm out,ΔR} =$(6.8$\pm$1.1)$\times$10$^{41}$ erg s$^{-1}$. The kinetic coupling efficiency of these outflows is in the range of 1$-$3 per cent, indicating that they could be powerful enough to affect the star formation in the host galaxy as predicted by theoretical simulations.

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arXiv2023

The need for multicomponent dust attenuation in modeling nebular emission: Constraints from SDSS-IV MaNGA

A fundamental assumption adopted in nearly every extragalactic emission-line study is that the attenuation of different emission lines can be described by a single attenuation curve. Here we show this assumption fails in many cases with important implications for derived results. We developed a new method to measure the differential nebular attenuation among three kinds of transitions: the Balmer lines of hydrogen, high-ionization transitions, and low-ionization transitions. This method bins the observed data in a multidimensional space spanned by attenuation-insensitive line ratios. Within each small bin, the variations in line ratios are mainly driven by the variations in the nebular attenuation. This allows us to measure the nebular attenuation using both forbidden lines and Balmer lines. We applied this method to a sample of 2.4 million star-forming spaxels from SDSS-IV MaNGA. We found that the attenuation of high ionization lines and Balmer lines can be well described by a single Fitzpatrick (1999) extinction curve with $R_V=3.1$. However, no single attenuation curve can simultaneously account for all three transitions. This strongly suggests that different lines have different effective attenuations, likely because spectroscopy at kiloparsec resolutions mixes multiple regions with different intrinsic line ratios and different levels of attenuation. As a result, the assumption that different lines follow the same attenuation curve breaks down. Using a single attenuation curve determined by Balmer lines to correct attenuation-sensitive forbidden line ratios could bias the nebular parameters derived by 0.06--0.25 dex at $A_V = 1$, depending on the details of the dust attenuation model. Observations of a statistically large sample of H II regions with high spatial resolutions and large spectral coverage are vital for improved modeling and deriving accurate corrections for this effect.

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arXiv2023

Oxygen abundances in the narrow line regions of Seyfert galaxies and the metallicity-luminosity relation

We present oxygen abundances relative to hydrogen (O/H) in the narrow line regions (NLRs) gas phases of Seyferts 1 (Sy 1s) and Seyferts 2 (Sy 2s) Active Galactic Nuclei (AGNs). We used fluxes of the optical narrow emission line intensities [$3\,500<λ($Å$)<7\,000$] of 561 Seyfert nuclei in the local universe ($z\lesssim0.31$) from the second catalog and data release (DR2) of the BAT AGN Spectroscopic Survey, which focuses on the \textit{Swift}-BAT hard X-ray ($\gtrsim10$ keV) detected AGNs. We derived O/H from relative intensities of the emission lines via the strong-line methods. We find that the AGN O/H abundances are related to their hosts stellar masses and that they follow a downward redshift evolution. The derived O/H together with the hard X-ray luminosity ($L_{\rm X}$) were used to study the X-ray luminosity-metallicity ($L_{\rm X}$-$Z_{\rm NLR}$) relation for the first time in Seyfert galaxies. In contrast to the broad-line focused ($L_{\rm X}$-$Z_{\rm BLR}$) studies, we find that the $L_{\rm X}$-$Z_{\rm NLR}$ exhibit significant anti-correlations with the Eddington ratio ($λ_{\rm Edd}$) and these correlations vary with redshifts. This result indicates that the low-luminous AGNs are more actively undergoing Interstellar Medium (ISM) enrichment through star formation in comparison with the more luminous X-ray sources. Our results suggest that the AGN is somehow driving the galaxy chemical enrichment, as a result of the inflow of pristine gas that is diluting the metal rich gas, together with a recent cessation on the circumnuclear star-formation.

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arXiv2023

Gas metallicity distributions in SDSS-IV MaNGA galaxies: what drives gradients and local trends?

The gas metallicity distributions across individual galaxies and across galaxy samples can teach us much about how galaxies evolve. Massive galaxies typically possess negative metallicity gradients, and mass and metallicity are tightly correlated on local scales over wide range of galaxy masses; however, the precise origins of such trends remain elusive. Here, we employ data from SDSS-IV MaNGA to explore how gas metallicity depends on local stellar mass density and on galactocentric radius within individual galaxies. We also consider how the strengths of these dependencies vary across the galaxy mass-size plane. We find that radius is more predictive of local metallicity than stellar mass density in extended lower mass galaxies, while we find density and radius to be almost equally predictive in higher-mass and more compact galaxies. Consistent with previous work, we find a mild connection between metallicity gradients and large-scale environment; however, this is insufficient to explain variations in gas metallicity behaviour across the mass-size plane. We argue our results to be consistent with a scenario in which extended galaxies have experienced smooth gas accretion histories, producing negative metallicity gradients over time. We further argue that more compact and more massive systems have experienced increased merging activity that disrupts this process, leading to flatter metallicity gradients and more dominant density-metallicity correlations within individual galaxies.

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arXiv2022

The HI Content of Red Geyser Galaxies

Red geysers are a specific type of quiescent galaxy, denoted by twin jets emerging from their galactic centers. These bisymmetric jets possibly inject energy and heat into the surrounding material, effectively suppressing star formation by stabilizing cool gas. In order to confirm the presence and evolutionary consequences of these jets, this paper discusses the scaling, stacking, and conversion of 21-cm HI flux data sourced from the HI-MaNGA survey into HI gas-to-stellar mass (G/S) spectra. Our samples were dominated by non-detections, or galaxies with weak HI signals, and consequently by HI upper limits. The stacking technique discussed successfully resolved emission features in both the red geyser G/S spectrum and the control sample G/S spectrum. From these stacked spectra, we find that on average, red geyser galaxies have G/S of 0.086 $\pm$ 0.011(random)+0.029(systematic), while non-red geyser galaxies of similar stellar mass have a G/S ratio of 0.039 $\pm$ 0.018(random)+0.013(systematic). Therefore, we find no statistically significant evidence that the HI content of red geysers is different from the general quiescent population.

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arXiv2022

BASS XXXIX: Swift-BAT AGN with changing-look optical spectra

Changing-look (CL) AGN are unique probes of accretion onto supermassive black holes (SMBHs), especially when simultaneous observations in complementary wavebands allow investigations into the properties of their accretion flows. We present the results of a search for CL behaviour in 412 Swift-BAT detected AGN with multiple epochs of optical spectroscopy from the BAT AGN Spectroscopic Survey (BASS). 125 of these AGN also have 14-195 keV ultra-hard X-ray light-curves from Swift-BAT which are contemporaneous with the epochs of optical spectroscopy. Eight CL events are presented for the first time, where the appearance or disappearance of broad Balmer line emission leads to a change in the observed Seyfert type classification. Combining with known events from the literature, 21 AGN from BASS are now known to display CL behaviour. Nine CL events have 14-195 keV data available, and five of these CL events can be associated with significant changes in their 14-195 keV flux from BAT. The ultra-hard X-ray flux is less affected by obscuration and so these changes in the 14-195 keV band suggest that the majority of our CL events are not due to changes in line-of-sight obscuration. We derive a CL rate of 0.7-6.2 per cent on 10-25 year time-scales, and show that many transitions happen within at most a few years. Our results motivate further multi-wavelength observations with higher cadence to better understand the variability physics of accretion onto SMBHs.

astro-ph.HE↗
arXiv2022

Multiple gas acquisition events in galaxies with dual misaligned gas disks

Frequent accretion of external cold gas is thought to play an important role in galaxy assembly. However, almost all known kinematically misaligned galaxies identify only one gas disk that is misaligned with the stellar disk, implying a single gas acquisition event. Here we report a new configuration in two galaxies where both contain two gas disks misaligned with each other and also with the stellar disk. Such systems are not expected to be stable or long-lasting, challenging the traditional picture of gas accretion of galaxies and their angular momentum build-up. The differences in kinematic position angles are larger than 120° between the two gas disks, and 40° between each gas disk and the stellar component. The star formation activity is enhanced at the interface of the two gas disks compared with the other regions within the same galaxy. Such systems illustrate that low-redshift galaxies can still experience multiple gas acquisition events, and provide a new view into the origins of galactic gas.

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