arXiv subjects

A. E. Watkins

Publications and source records attributed to A. E. Watkins.

At least 19 recordsLinked to original sources

arXiv2026

Isophote shape analysis and the unfortunate subtlety of dwarf galaxy structure

Dwarf galaxies ($M_{*}/M_{\odot} \lesssim 10^{9.5}$), being sensitive to key evolutionary drivers like baryonic feedback and tidal perturbation, are crucial for understanding galaxy evolution as a whole. Their abundance and faintness, however, ensures that most will be studied primarily via broadband imaging for the foreseeable future. It is thus crucial to identify the most informative broadband-derivable quantities in the dwarf regime. As studies of widely used morphological parameters like concentration, asymmetry, and smoothness suggest these lack discriminatory power among dwarfs, we assess alternatives derived from isophotes: position angle twists, ellipticity, deviations from pure ellipses, and residuals to single-Sérsic profile fits. Using these parameters, we compare dwarf populations with massive galaxies of the same morphological class, and among themselves by morphological class. Only dwarf spirals may differ from their massive counterparts, being structurally simpler; dwarf and massive early type galaxy (ETG) isophotal similarity suggests all dwarf ETGs may be triaxial. Among only dwarfs, morphological classes are indistinguishable in this parameter space. A principal component analysis (PCA) using all available morphological, isophotal, and physical parameters expands on this: no PC explains more than $\sim$26% of the population variance, and no clear multimodality appears in any pairwise PC projection. We find similarly moderate spectral clustering, with a silhouette score of only 0.35. Given this self-similarity, parsing dwarf galaxy evolution from photometric parameters alone will likely require detailed statistical analysis of large dwarf populations in a high-dimensional parameter space, a task suitable for up-coming large-scale surveys like the Legacy Survey of Space and Time.

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arXiv2026

Multi-wavelength morphology and dust emission in low-redshift dwarf galaxies in COSMOS-Web with HST and JWST

Low-mass or dwarf galaxies (M$_{\ast}<10^{9}$ M${\odot}$) are abundant in the Universe, yet their formation and evolution remain poorly understood. Their enhanced sensitivity to feedback from star formation and active galactic nuclei (AGN) make them excellent laboratories to test whether feedback prescriptions in cosmological simulations accurately reproduce their interstellar medium (ISM) properties. We present JWST/NIRCam and MIRI imaging of nine dwarf galaxies from COSMOS-Web survey at redshift $z<0.08$, with star formation rates ranging from 0.003-0.3 M${\odot}$ yr$^{-1}$ and stellar masses of log M$_{\ast}\sim8-9$ M$_{\odot}$. The detection rate with both NIRCam and MIRI is 100\%, indicating that these dwarfs possess substantial ISM content. The detected sample includes a roughly equal mix of early-type and late-type dwarfs, suggesting that it is representative of the broader dwarf galaxy population in low-density environments. We find that the observed MIRI flux distributions are comparable to forward-modelled flux distributions of mass-matched simulated galaxies in TNG50. We further conduct a multi-wavelength morphological analysis complementing the JWST NIRCam and MIRI imaging with archival HST/ACS data, employing the CAS (concentration, asymmetry, smoothness) framework. Among the multi-wavelength images, MIRI exhibits the largest variation in CAS parameters, likely due to dust lanes and clumps in several galaxies, also suggested by Spectral Energy Distribution (SED) fitting. This suggests that the dust content in these systems may be higher than those implied by rest-frame optical or near-infrared observations alone. Upcoming UV/optical and mid-infrared spectroscopic follow-up will be critical for constraining the gas kinematics and dust grain properties of dwarf galaxies in low-density environments such as COSMOS.

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arXiv2025

Variability-selected AGN in dwarf galaxies: the incidence of AGN in dwarf and massive galaxies is similar

We use the VST-COSMOS survey to identify, via their optical broadband variability, 30 AGN in nearby (z<0.4) dwarf (10^8 MSun < M < 10^10 MSun) galaxies. VST-COSMOS offers a 1 deg^2 survey footprint, a single visit depth of 24.6 mag and 68 r-band visits spanning an eleven-year temporal baseline. Compared to a control sample matched in stellar mass and redshift, the dwarf AGN population shows an elevated fraction of early-type galaxies but a similar fraction of interacting objects, suggesting that interactions do not play a significant role in triggering these AGN. Dwarf AGN hosts do not show strong differences in their distances to nodes, filaments and massive galaxies compared to the controls, which indicates that AGN triggering, at least in this sample, is not strongly correlated with environment. Finally, by combining the true number of galaxies, the detectability of AGN and the measured numbers of variable sources in dwarf and massive (M > 10^10 MSun) galaxies, we estimate the relative frequency of AGN in these two mass regimes. Our results suggest that the incidence of AGN in dwarfs and massive galaxies is similar (within less than a factor of 2 of each other), with some evidence that the AGN fraction increases with stellar mass in the dwarf population.

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arXiv2025

Cosmic reflections I: the structural diversity of simulated and observed low-mass galaxy analogues

Dwarf galaxies serve as powerful laboratories for investigating the underlying physics of galaxy evolution including the impact of baryonic feedback processes and environmental influences. We compare the visual and structural properties of dwarf galaxies in ultra-deep HSC-SSP imaging of the COSMOS field with those measured from realistic HSC-like synthetic observations of dwarfs generated by the Illustris TNG50 and NewHorizon simulations. Using Sérsic profile fitting and non-parametric morphological metrics (Gini, $M_{20}$, asymmetry, and concentration), we evaluate the diversity of structural properties in observed and simulated galaxies. Our analysis shows that NewHorizon and TNG50 galaxies lie at opposite extremes of observed structural trends: NewHorizon produces diffuse, extended galaxies with shallow Sérsic indices, while TNG50 yields compact, concentrated systems with steep indices. Both simulations reproduce observed structural trends more closely at higher stellar masses ($M_{\star}\sim10^{9.5} {\rm M_{\odot}}$) but fail to capture the full diversity of COSMOS dwarfs at lower masses. Non-parametric metrics further show that NewHorizon galaxies exhibit more uneven, clumpy light distributions while TNG50 galaxies have smoother but excessively concentrated profiles. These structural differences reflect underlying differences in their physical prescriptions and are likely driven by differing approaches to ISM physics, supernova feedback and star formation in addition to differences in numerical resolution. Our findings highlight the unique power of low-mass galaxies to constrain differences in simulation physics, especially star formation and feedback. Upcoming surveys from facilities like the Vera C. Rubin Observatory and Euclid will enable more rigorous comparisons with simulations, offering deeper insights into the physical processes shaping galaxy evolution.

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arXiv2025

Nearby dwarf galaxies with extreme star formation rates: a window into dwarf-galaxy evolution in the early Universe

We study a sample of nearby (z~0.2) low-luminosity dwarf (10^7 MSun < M* < 10^8 MSun) galaxies which have extreme (0.1 - 3 MSun/yr) star formation rates (SFRs) for this mass regime, making them plausible analogues of dwarfs at z~5.5. We compare the properties of these analogues to control samples of 'normal' dwarfs, which reside on the star formation main sequence (SFMS) at z~0.2 and are matched in their stellar mass and redshift distributions to the analogue population. The analogue and normal populations do not show differences, either in their half-light radii or the projected distances to nodes, filaments and massive galaxies. This suggests that the comparatively extreme SFRs in the analogues are not driven by them being anomalously compact or because they reside in specific environments which might provide a larger gas supply. However, the fractions of interacting galaxies and those that have early-type morphology are significantly elevated (by factors of ~5.6 and ~9 respectively) in the analogues compared to the normal population. Extrapolation of the redshift evolution of the star formation main sequence into our mass range of interest appears to underestimate the SFRs of observed dwarfs at z~5.5. Since current SFMS measurements remain dominated by low and intermediate redshift data (especially at low stellar masses), our study suggests that this underestimation may be driven by interactions (which are more frequent at earlier epochs) boosting the SFRs in the high-redshift dwarf population. Our results are consistent with a picture where higher gas availability, augmented by interactions, drives much of the stellar mass assembly of dwarf galaxies in the early Universe.

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arXiv2025

The Complete Spitzer Survey of Stellar Structure in Galaxies (CS$^4$G)

The Spitzer Survey of Stellar Structure in Galaxies (S$^4$G), together with its Early Type Galaxy (ETG) extension, stand as the most extensive dataset of deep, uniform mid-infrared (mid-IR; 3.6 and 4.5$\,μ$m) imaging for a sample of $2817$ nearby ($d<40 \,$Mpc) galaxies. However, the velocity criterion used to select the original sample results in an additional 422 galaxies without HI detection that ought to have been included in the S$^4$G on the basis of their optical recession velocities. In order to create a complete magnitude-, size- and volume-limited sample of nearby galaxies, we collect $3.6\,μ$m and $i$-band images using archival data from different surveys and complement it with new observations for the missing galaxies. We denote the sample of these additional galaxies as Disc Galaxy (DG) extension. We present the Complete Spitzer Survey of Stellar Structure in Galaxies (CS$^4$G), encompassing a sample of $3239$ galaxies with consistent imaging, surface brightness profiles, photometric parameters, and revised morphological classification. Following the original strategy of the S$^4$G survey, we produce masks, surface brightness profiles, and curves of growth using masked $3.6\,μ$m and $i$-band images. From these profiles, we derive the integrated quantities: total magnitude, stellar mass, concentration parameter, and galaxy size, converting to $3.6\,μ$m. We re-measure these parameters also for the S$^4$G and ETG to create a homogenous sample. We present new morphological revised $T$-types, and we showcase mid-IR scaling relations for the photometric parameters. We complete the S$^4$G sample by incorporating 422 galaxies. The CS$^4$G includes at least 99.94\% of the complete sample of nearby galaxies, meeting the original selection criteria, and it will enable a wide set of investigations into galaxy structure and evolution.

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arXiv2025

The quenching of star formation in dwarf galaxies: new perspectives from deep-wide surveys

Dwarf galaxies dominate the galaxy number density, making them critical to our understanding of galaxy evolution. However, typical dwarfs are too faint to be visible outside the very local Universe in past surveys like the SDSS, which offer large footprints but are shallow. Dwarfs in such surveys have relatively high star formation rates, which boost their luminosity, making them detectable in shallow surveys, but also biased and potentially unrepresentative of dwarfs as a whole. Here, we use deep data to perform an unbiased statistical study of ~7,000 nearby (z<0.25) dwarfs (10^8 MSun < M < 10^9.5 MSun) in the COSMOS field which, at these redshifts, is a relatively low-density field. At z~0.05, ~40 per cent of dwarfs in low-density environments are red/quenched, falling to ~30 per cent by z~0.25. Red dwarfs reside closer to nodes, filaments and massive galaxies. Proximity to a massive galaxy appears to be more important in determining whether a dwarf is red, rather than simply its distance from nodes and filaments or the mean density of its local environment. Interestingly, around half of the red dwarfs reside outside the virial radii of massive galaxies and around a third of those also inhabit regions in the lower 50 per cent in density percentile (i.e. regions of very low ambient density). Around half of the red dwarf population is, therefore, quenched by mechanisms unrelated to environment, which are likely to be internal processes such as stellar and AGN feedback.

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arXiv2024

Cloudy modeling suggests a diversity of ionization mechanisms for diffuse extraplanar gas

The ionization of diffuse gas located far above the energetic midplane OB stars poses a challenge to the commonly accepted notion that radiation from OB stars is the primary ionization source for gas in galaxies. We investigated the sources of ionizing radiation, specifically leaking midplane HII regions and/or in situ hot low-mass evolved stars (HOLMES), in extraplanar diffuse ionized gas (eDIG) in a sample of eight nearby (17-52 Mpc) edge-on disk galaxies observed with the Multi Unit Spectroscopic Explorer (MUSE). We constructed a model for the photoionization of eDIG clouds and the propagation of ionizing radiation through the eDIG using subsequent runs of Cloudy photoionization code. Our model includes radiation originating both from midplane OB stars and in situ evolved stars and its dilution and processing as it propagates in the eDIG. We fit the model to the data using the vertical line ratio profiles of our sample galaxies, and find that while the ionization by in situ evolved stars is insignificant for most of the galaxies in our sample, it may be able to explain the enhanced high-ionization lines in the eDIG of the green valley galaxy ESO 544-27. Our results show that while leaking radiation from midplane HII regions is the primary ionization source for eDIG, in situ evolved stars can play a significant part in ionizing extraplanar gas in galaxies with low star forming rates.

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arXiv2024

The properties of AGN in dwarf galaxies identified via SED fitting

Given their dominance of the galaxy number density, dwarf galaxies are central to our understanding of galaxy formation. While the incidence of AGN and their impact on galaxy evolution has been extensively studied in massive galaxies, much less is known about the role of AGN in the evolution of dwarfs. We search for radiatively-efficient AGN in the nearby (0.1 < z < 0.3) dwarf (10^8 MSun < M < 10^10 MSun) population, using SED fitting (via Prospector) applied to deep ultraviolet to mid-infrared photometry of 508 dwarf galaxies. Around a third (32 +/- 2 per cent) of our dwarfs show signs of AGN activity. We compare the properties of our dwarf AGN to control samples, constructed from non-AGN, which have the same distributions of redshift and stellar mass as their AGN counterparts. KS tests between the AGN and control distributions indicates that the AGN do not show differences in their distances to nodes, filaments and nearby massive galaxies from their control counterparts. This indicates that AGN triggering in the dwarf regime is not strongly correlated with local environment. The fraction of AGN hosts with early-type morphology and those that are interacting are also indistinguishable from the controls within the uncertainties, suggesting that interactions do not play a significant role in inducing AGN activity in our sample. Finally, the star formation activity in dwarf AGN is only slightly lower than that in their control counterparts, suggesting that the presence of radiatively-efficient AGN does not lead to significant, prompt quenching of star formation in these systems.

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arXiv2024

Implications on star-formation-rate indicators from HII regions and diffuse ionised gas in the M101 Group

We examine the connection between diffuse ionised gas (DIG), HII regions, and field O and B stars in the nearby spiral M101 and its dwarf companion NGC 5474 using ultra-deep H$α$ narrow-band imaging and archival GALEX UV imaging. We find a strong correlation between DIG H$α$ surface brightness and the incident ionising flux leaked from the nearby HII regions, which we reproduce well using simple Cloudy simulations. While we also find a strong correlation between H$α$ and co-spatial FUV surface brightness in DIG, the extinction-corrected integrated UV colours in these regions imply stellar populations too old to produce the necessary ionising photon flux. Combined, this suggests that HII region leakage, not field OB stars, is the primary source of DIG in the M101 Group. Corroborating this interpretation, we find systematic disagreement between the H$α$- and FUV-derived star formation rates (SFRs) in the DIG, with SFR$_{{\rm H}α} < $SFR$_{\rm FUV}$ everywhere. Within HII regions, we find a constant SFR ratio of 0.44 to a limit of $\sim10^{-5}$ M$_{\odot}$~yr$^{-1}$. This result is in tension with other studies of star formation in spiral galaxies, which typically show a declining SFR$_{{\rm H}α}/$SFR$_{\rm FUV}$ ratio at low SFR. We reproduce such trends only when considering spatially averaged photometry that mixes HII regions, DIG, and regions lacking H$α$ entirely, suggesting that the declining trends found in other galaxies may result purely from the relative fraction of diffuse flux, leaky compact HII regions, and non-ionising FUV-emitting stellar populations in different regions within the galaxy.

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arXiv2024

Strategies for optimal sky subtraction in the low surface brightness regime

The low surface brightness (LSB) regime ($μ_{g} \gtrsim 26$ mag arcsec$^{-2}$) comprises a vast, mostly unexplored discovery space, from dwarf galaxies to the diffuse interstellar medium. Accessing this regime requires precisely removing instrumental signatures and light contamination, including, most critically, night sky emission. This is not trivial, as faint astrophysical and instrumental contamination can bias sky models at the precision needed to characterize LSB structures. Using idealized synthetic images, we assess how this bias impacts two common LSB-oriented sky-estimation algorithms: 1.) masking and parametric modelling, and 2.) stacking and smoothing dithered exposures. Undetected flux limits both methods by imposing a pedestal offset to all derived sky models. Careful, deep masking of fixed sources can mitigate this, but source density always imposes a fundamental limit. Stellar scattered light can contribute $\sim28$--$29$ mag arcsec$^{-2}$ of background flux even in low-density fields; its removal is critical prior to sky estimation. For complex skies, image combining is an effective non-parametric approach, although it strongly depends on observing strategy and adds noise to images on the smoothing kernel scale. Preemptive subtraction of fixed sources may be the only practical approach for robust sky estimation. We thus tested a third algorithm, subtracting a preliminary sky-subtracted coadd from exposures to isolate sky emission. Unfortunately, initial errors in sky estimation propagate through all subsequent sky models, making the method impractical. For large-scale surveys like LSST, where key science goals constrain observing strategy, masking and modelling remains the optimal sky estimation approach, assuming stellar scattered light is removed first.

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arXiv2023

Constraining the top-light initial mass function in the extended ultraviolet disk of M83

The universality or non-universality of the initial mass function (IMF) has significant implications for determining star formation rates and star formation histories from photometric properties of stellar populations. We reexamine whether the IMF is deficient in high-mass stars (top-light) in the low-density environment of the outer disk of M83 and constrain the shape of the IMF therein. Using archival Galaxy Evolution Explorer (GALEX) far ultraviolet (FUV) and near ultraviolet (NUV) data and new deep OmegaCAM narrowband H$α$ imaging, we constructed a catalog of FUV-selected objects in the outer disk of M83. We counted H$α$-bright clusters and clusters that are blue in FUV$-$NUV in the catalog, measured the maximum flux ratio $F_{\mathrm{H}α}/f_{λ\mathrm{FUV}}$ among the clusters, and measured the total flux ratio $ΣF_{\mathrm{H}α}/Σf_{λ\mathrm{FUV}}$ over the catalog. We then compared these measurements to predictions from stellar population synthesis models made with a standard Salpeter IMF, truncated IMFs, and steep IMFs. We also investigated the effect of varying the assumed internal extinction on our results. We are not able to reproduce our observations with models using the standard Salpeter IMF or the truncated IMFs. It is only when assuming an average internal extinction of $0.10 < A_{\mathrm{V}} < 0.15$ in the outer disk stellar clusters that models with steep IMFs ($α> 3.1$) simultaneously reproduce the observed cluster counts, the maximum observed $F_{\mathrm{H}α}/f_{λ\mathrm{FUV}}$, and the observed $ΣF_{\mathrm{H}α}/Σf_{λ\mathrm{FUV}}$. Our results support a non-universal IMF that is deficient in high-mass stars in low-density environments.

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arXiv2023

A possible signature of the influence of tidal perturbations in dwarf galaxy scaling relations

Dwarf galaxies are excellent cosmological probes, because their shallow potential wells make them very sensitive to the key processes that drive galaxy evolution, including baryonic feedback, tidal interactions, and ram pressure stripping. However, some of the key parameters of dwarf galaxies, which help trace the effects of these processes, are still debated, including the relationship between their sizes and masses. We re-examine the Fornax Cluster dwarf population from the point of view of isomass-radius--stellar mass relations (IRSMRs) using the Fornax Deep Survey Dwarf galaxy Catalogue, with the centrally located (among dwarfs) $3.63 \mathcal{M}_{\odot}$~pc$^{-2}$ isodensity radius defining our fiducial relation. This relation is a powerful diagnostic tool for identifying dwarfs with unusual structure, as dwarf galaxies' remarkable monotonicity in light profile shapes, as a function of stellar mass, reduces the relation's scatter tremendously. By examining how different dwarf properties (colour, tenth-nearest-neighbour distance, etc.) correlate with distance from our fiducial relation, we find a significant population of structural outliers with comparatively lower central mass surface density and larger half-light-radii, residing in locally denser regions in the cluster, albeit with similar red colours. We propose that these faint, extended outliers likely formed through tidal disturbances, which make the dwarfs more diffuse, but with little mass loss. Comparing these outliers with ultra-diffuse galaxies (UDGs), we find that the term UDG lacks discriminatory power; UDGs in the Fornax Cluster lie both on and off of IRSMRs defined at small radii, while IRSMR outliers with masses below $\sim 10^{7.5} \mathcal{M}_{\odot}$ are excluded from the UDG classification due to their small effective radii.

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arXiv2022

Preparing for low surface brightness science with the Vera C. Rubin Observatory: characterisation of tidal features from mock images

Tidal features in the outskirts of galaxies yield unique information about their past interactions and are a key prediction of the hierarchical structure formation paradigm. The Vera C. Rubin Observatory is poised to deliver deep observations for potentially of millions of objects with visible tidal features, but the inference of galaxy interaction histories from such features is not straightforward. Utilising automated techniques and human visual classification in conjunction with realistic mock images produced using the NEWHORIZON cosmological simulation, we investigate the nature, frequency and visibility of tidal features and debris across a range of environments and stellar masses. In our simulated sample, around 80 per cent of the flux in the tidal features around Milky Way or greater mass galaxies is detected at the 10-year depth of the Legacy Survey of Space and Time (30-31 mag / sq. arcsec), falling to 60 per cent assuming a shallower final depth of 29.5 mag / sq. arcsec. The fraction of total flux found in tidal features increases towards higher masses, rising to 10 per cent for the most massive objects in our sample (M*~10^{11.5} Msun). When observed at sufficient depth, such objects frequently exhibit many distinct tidal features with complex shapes. The interpretation and characterisation of such features varies significantly with image depth and object orientation, introducing significant biases in their classification. Assuming the data reduction pipeline is properly optimised, we expect the Rubin Observatory to be capable of recovering much of the flux found in the outskirts of Milky Way mass galaxies, even at intermediate redshifts (z<0.2).

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arXiv2022

Stellar masses, sizes, and radial profiles for 465 nearby early-type galaxies: an extension to the Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G)

The Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G) is a detailed study of over 2300 nearby galaxies in the near-infrared (NIR), which has been critical to our understanding of the detailed structures of nearby galaxies. Because the sample galaxies were selected only using radio-derived velocities, however, the survey favored late-type disk galaxies over lenticulars and ellipticals. A follow-up Spitzer survey was conducted to rectify this bias, adding 465 early-type galaxies (ETGs) to the original sample, to be analyzed in a manner consistent with the initial survey. We present the data release of this ETG extension, up to the third data processing pipeline (P3): surface photometry. We produce curves of growth and radial surface brightness profiles (with and without inclination corrections) using reduced and masked Spitzer IRAC 3.6$μ$m and 4.5$μ$m images produced through Pipelines 1 and 2, respectively. From these profiles, we derive the following integrated quantities: total magnitudes, stellar masses, concentration parameters, and galaxy size metrics. We showcase NIR scaling relations for ETGs among these quantities. We examine general trends across the whole S$^{4}$G and ETG extension among our derived parameters, highlighting differences between ETGs and late-type galaxies (LTGs). ETGs are, on average, more massive and more concentrated than LTGs, and also show subtle distinctions among ETG morphological sub-types. We also derive the following scaling relations and compare with previous results in visible light: mass--size (both half-light and isophotal), mass--concentration, mass--surface brightness (central, effective, and within 1 kpc), and mass--color. We find good agreement with previous works, though some relations (e.g., mass--central surface brightness) will require more careful multi-component decompositions to be fully understood.

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arXiv2022

The multifarious ionization sources and disturbed kinematics of extraplanar gas in five low-mass galaxies

We investigate the origin of the extraplanar diffuse ionized gas (eDIG) and its predominant ionization mechanisms in five nearby (17-46 Mpc) low-mass ($10^9\text{-}10^{10}$ $M_{\odot}$) edge-on disk galaxies: ESO 157-49, ESO 469-15, ESO 544-27, IC 217, and IC 1553. We acquired Multi Unit Spectroscopic Explorer (MUSE) integral field spectroscopy and deep narrowband H$α$ imaging of our sample galaxies. To investigate the connection between in-plane star formation and eDIG, we perform a photometric analysis of our narrowband H$α$ imaging. We measure eDIG scale heights of $h_{z\text{eDIG}} = 0.59 \text{-} 1.39$ kpc and find a positive correlation between them and specific star formation rates. In all galaxies, we also find a strong correlation between extraplanar and midplane radial H$α$ profiles. Using our MUSE data, we investigate the origin of eDIG via kinematics. We find ionized gas rotation velocity lags above the midplane with values between 10 and 27 km s$^{-1}$ kpc$^{-1}$. While we do find hints of an accretion origin for the ionized gas in ESO 157-49, IC 217, and IC 1553, overall the ionized gas kinematics of our galaxies do not match a steady galaxy model or any simplistic model of accretion or internal origin for the gas. We also construct standard diagnostic diagrams and emission-line maps (EW(H$α$), [NII]/H$α$, [SII]//H$α$, [OIII]/H$β$) and find regions consistent with mixed OB star and hot low-mass evolved stars (HOLMES) ionization, and mixed OB-shock ionization. Our results suggest that OB stars are the primary driver of eDIG ionization, while both HOLMES and shocks may locally contribute to the ionization of eDIG to a significant degree. Despite our galaxies' similar structures and masses, we find a surprisingly composite image of ionization mechanisms and a multifarious origin for the eDIG.

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arXiv2021

The complex multi-component outflow of the Seyfert galaxy NGC 7130

AGN are a key ingredient for understanding galactic evolution. AGN-driven outflows are one of the manifestations of feedback. The AO mode for MUSE at the VLT permits to study the innermost tens of parsecs of nearby AGN in the optical. We present a detailed analysis of the ionised gas in the central regions of NGC 7130, an archetypical composite Seyfert and nuclear starburst galaxy. We achieve an angular resolution of 0.17$^{\prime\prime}$ (50 pc). We performed a multi-component analysis of the main ISM lines and identified nine kinematic components, six of which correspond to the outflow. The outflow is biconic and has velocities of a few $100\,{\rm km\,s^{-1}}$ with respect to the disc. We decompose the approaching side of the outflow into a broad and a narrow component with typical velocity dispersions below and above $\sim200\,{\rm km\,s^{-1}}$, respectively. The blueshifted narrow component has substructure, in particular a collimated plume aligned with the radio jet, indicating that it may be jet-powered. The redshifted lobe is composed of two Narrow Components and a Broad Component. An additional redshifted component is seen outside the main outflow axis. Line ratio diagnostics indicate that the outflow gas in the main axis is AGN-powered whereas the off-axis component has LINER properties. The ionised gas mass outflow rate is $\dot{M}=1.2\pm0.7\,M_{\odot}\,{\rm yr^{-1}}$ and the kinetic power is $\dot{E}_{\rm kin}=(2.7\pm2.0)\times10^{41}\,{\rm erg\,s^{-1}}$, which corresponds to $F_{\rm kin}=0.12\pm0.09\%$ of the bolometric AGN power. The combination of high angular resolution integral field spectroscopy and a careful multi-component decomposition allows a uniquely detailed view of the outflow in NGC 7130, illustrating that AGN kinematics are more complex than traditionally derived from less sophisticated data and analyses. (abridged)

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arXiv2019

The Fornax Deep Survey with VST. VII. Evolution and Structure of Late Type Galaxies inside the Virial Radius of the Fornax Cluster

We present the study of a magnitude limited sample (mB < 16.6 mag) of 13 late type galaxies (LTGs), observed inside the virial radius, Rvir 0.7 Mpc, of the Fornax cluster within the Fornax Deep Survey (FDS). The main objective is to use surface brightness (SB) profiles and g-i colour maps to obtain information on the internal structure of these galaxies and find signatures of the mechanisms that drive their evolution in high-density environment, which is inside the virial radius of the cluster. By modelling galaxy isophotes, we extract the azimuthally averaged surface brightness profiles in four optical bands. We also derive g-i colour profiles, and structural parameters like total magnitude and effective radius. For 10 of the galaxies in this sample, we observe a clear discontinuity in their SB profiles, derive their break radius (Br), and classify their disc-breaks into Type-II (down-bending) or Type-III (up-bending). We find that Type-II galaxies have bluer average (g-i) colour in their outer discs while Type-III galaxies are redder. Br increases with stellar mass and molecular gas mass while decreases with molecular gas-fractions. The inner and outer scale-lengths increase monotonically with absolute magnitude, as found in other works. In Fornax, galaxies with morphological type 5< T< 9 (~60 % of the sample) are located beyond the high-density, ETG-dominated regions, but no correlation found between T and the disc-break type. The main results of this work suggest that the disc-breaks of LTGs inside the virial radius of the Fornax cluster seem to have arisen through a variety of mechanisms, which is evident in their outer-disc colours and the absence of molecular gas beyond their break radius in some cases. This can result in a variety of stellar populations inside and outside the break radii.

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