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Paula R. T. Coelho

Publications and source records attributed to Paula R. T. Coelho.

At least 19 recordsLinked to original sources
arXiv2026

Composite Bulges -- V. Detecting signatures of gas inflows in IFU data: The MUSE view of ionised gas kinematics in nearby galaxies

Using VLT/MUSE data, we study the ionised-gas kinematics in a mass- and volume-limited ($M_* \geq 10^{10} M_\odot$, $D \leq 20$\,Mpc) sample of 21 nearby galaxies to identify signatures of extended shocks within their inner kiloparsec, which appear as coherent velocity jumps in kinematic maps. By removing angular momentum, shocks in gas cause inflows, which can trigger nuclear star formation and fuel AGN activity. To identify the signatures of extended shocks, we examine residual velocity fields after subtracting a modelled rotating disc, and we study velocity difference between various gas tracers. Combining our kinematic analysis with BPT ionisation diagnostic maps and dust morphology, we find that 12 of 21 galaxies ($\sim$57%) show extended shock signatures with velocity jumps consistent with models of bar-driven shocks. This is likely a lower limit, as three additional galaxies ($\sim$14%) exhibit shocks along bars, potentially reaching the nucleus but obscured by AGN outflows. We trace shock signatures inwards close to the resolution limit, which suggests that shocks may be the prevailing mechanism of inflow in the central kpc of galaxies. The only two unbarred galaxies in our sample are also the only systems with unperturbed kinematics and no shocks, strongly linking the perturbed gas dynamics in centres of galaxies to the presence of bars. All galaxies with inner bars show LINER- or Seyfert-like nuclear emission, whereas galaxies without inner bars exhibit all emission types, indicating that regardless of gas supply, inner bars suppress star formation in galactic nuclei.

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arXiv2025

J-PLUS: Turning Off the Bright Stars

Photometric surveys require precise point spread function (PSF) characterization, as it varies across filters and is crucial for accurate photometry and low surface brightness (LSB) studies. However, the small PSF size provided by default pipelines suits only barely resolved objects, making it difficult to analyze regions near bright stars (rendering those regions unusable). These components are then combined to generate a final PSF for each exposure and filter, spanning 15 mag arcsec-2 in surface brightness and 4 arcmin in radius in the broad bands. In narrow-band filters, the J-PLUS PSF exhibits two rings, whereas in broad-band filters, only one ring is observed. Additionally, the position of the ring shifts with filter wavelength: as the filters become redder, the ring radius increases. We find that there is no significant variation in the extended PSF observed as a function of time (within 2.5h) or position in the field of view. The radial profile of NGC 4212 (which is close to a star) is also studied before/after PSF-subtraction. We developed a novel method to determine the central coordinates of saturated stars, and classify stars without using Gaia magnitudes. Additionally, mirror reflections are automatically detected and masked. Furthermore, in combining different stars and various components of the PSF, we avoided the use of a fixed radius by introducing a new method that does not depend on radial measurements. Accurate characterization of the extended PSF and its subtraction improves sky subtraction, increases the effective area of the survey by about 10%, and enables the study of extended large LSB features in wide area surveys like J-PLUS. Our pipeline is published as free software (GNU GPLv3) an can be customized to other surveys such as J-PAS, where its impact will be even greater due to its depth. This paper is fully reproducible and produced from Commit 4860c70.

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arXiv2025

Hidden Figures of Globular Clusters: Integrated Stellar Populations Impacted by Hot Subdwarfs

Globular clusters (GCs) are fundamental for understanding the integrated light of old stellar populations and galaxy assembly processes. However, the role of hot, evolved stars, such as horizontal branch (HB), extreme HB, and blue stragglers, remains poorly constrained. These stars are often underrepresented or entirely excluded from stellar population models, despite their dominant contribution to the ultraviolet (UV) flux. Their presence can bias age estimates by mimicking the spectral signatures of younger populations. We examined the impact of evolved hot stars on the models using two well-studied Galactic GCs with high-quality Hubble Space Telescope photometry and integrated spectra from the International Ultraviolet Explorer and the Blanco Telescope. NGC 2808 and NGC 7089 (M 2) have extended HBs and are proxies for old stellar populations. Integrated spectra were constructed using a color magnitude diagram-based (CMD-based) method, matching observed stars to evolutionary phases and then to appropriate synthetic stellar libraries, enabling the HB morphology to be taken into account. Our findings show that the inclusion of evolved hot stars significantly improves the agreement between the model and observed spectra from the UV to the optical. The inclusion of these phases reduced the residuals in spectral comparisons. Our results reinforce that comprehensive stellar population models incorporating evolved hot components are essential to accurately date unresolved systems and to robustly trace formation histories of extragalactic galaxies.

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arXiv2025

Optimising the analysis of emission lines in galaxies: the case of the MUSE TIMER galaxy NGC 613

Galaxy evolution is driven by spatially distributed processes with varying timescales. Integral field spectroscopy provides spatially-resolved information about these processes. Nevertheless, disentangling these processes, which are related to both the underlying stellar populations and the interstellar medium can be challenging. We present a case study on NGC~613, observed with MUSE (Multi-Unit Spectroscopic Explorer) for the TIMER (Time Inference with MUSE in Extragalactic Rings) project, a local barred galaxy, which shows several gas ionisation mechanisms and is rich in both large and inner-scale stellar structures. We develop a set of steps to overcome fundamental problems in the modelling of emission lines with multiple components, together with the characterisation of the stellar populations. That results in the disentanglement of the gas ionisation mechanisms and kinematics, along with an optimal parametrisation for star formation history recovery. Our analysis reveals evidence of gas inflows, which are associated with the bar dust lanes traced with \textit{Hubble} Space Telescope (HST). In addition, we show the gas kinematics in a central biconical outflow, which is aligned with a radio jet observed with Very Large Array (VLA). The emission line provides estimates of electron density, gas-phase metallicity, and the mass outflow rate, allowing us to distinguish intertwined ionisation mechanisms and to identify a part of the multiphase gas cycle in NGC 613. It traces the gas kinematics from the bar lanes to inner scale gas reservoirs, where it can eventually trigger star formation or AGN activity, as observed in the outflow.

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arXiv2025

Semi-empirical versus Theoretical Stellar Population Models: a comparison with Star Clusters

Stellar population synthesis (SPS) models are a key tool for deriving the age, metallicity, radial velocity and reddening of star clusters from their integrated spectra. Using a sample of 129 star clusters with high-quality spectra, we analyze the uncertainties associated with selecting an empirical versus a theoretical stellar spectral library in the SPS models. We find that the fits from the different models agree on the goodness of fit metrics and inferred reddening. However, the derived age and metallicity can be affected by the choice of the stellar library, with synthetic libraries tending to give lower age and metallicity, especially for spectra with low SNR. Ages and reddening values from SSP-equivalent fits are consistent with the multi-population fits, however, SSP-equivalent metallicities are affected by the coarse coverage of the SPS grid in [Fe/H]. When comparing the spectral fitting results with the literature, we find that (1) all models underestimate age for old and metal-poor systems; (2) on average, SPS models based on synthetic stellar libraries better match the isochrone ages and metallicities from high-resolution stellar spectroscopy.

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arXiv2024

Synthetic stellar spectra to study multiple populations in globular clusters: an extended grid and the effects on the integrated light

Most Galactic Globular Clusters (GCs) harbour multiple populations of stars (MPs), composed of at least two generations: the first characterized by a "standard" $α$-enhanced metal mixture, as observed in field halo stars of the Milky Way, and the second displaying anti-correlated CN--ONa chemical abundance pattern in combination with an enhanced helium fraction. Adequate collections of stellar spectra are needed to characterize the effect of such stellar abundance changes on the integrated light of GCs. We present a grid of synthetic stellar spectra covering the atmospheric parameters relevant to old stellar populations at four subsolar metallicities and two abundance patterns, representative of first- and second-generations of stars in GCs. Integrated spectra of populations were computed using our stellar grid and empirical stellar populations, namely, colour-magnitude diagrams from literature for Galactic GCs. The spectra range from 290 to 1000nm, where we measured the effect on several spectrophotometric indices due to the surface abundance variations attributed to MPs. We find non-negligible effects of the MPs on spectroscopic indices sensitive to C, N, Ca, or Na, and on Balmer indices; we also describe how MPs modify specific regions in the near-UV and near-IR that can be measured with narrow or medium photometric passbands. The effects vary with metallicity. A number of these changes remain detectable even when accounting for the stochastic fluctuations due to the finite nature of the stellar population cluster.

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arXiv2022

J-PLUS: Support Vector Regression to Measure Stellar Parameters

Context. Stellar parameters are among the most important characteristics in studies of stars, which are based on atmosphere models in traditional methods. However, time cost and brightness limits restrain the efficiency of spectral observations. The J-PLUS is an observational campaign that aims to obtain photometry in 12 bands. Owing to its characteristics, J-PLUS data have become a valuable resource for studies of stars. Machine learning provides powerful tools to efficiently analyse large data sets, such as the one from J-PLUS, and enable us to expand the research domain to stellar parameters. Aims. The main goal of this study is to construct a SVR algorithm to estimate stellar parameters of the stars in the first data release of the J-PLUS observational campaign. Methods. The training data for the parameters regressions is featured with 12-waveband photometry from J-PLUS, and is cross-identified with spectrum-based catalogs. These catalogs are from the LAMOST, the APOGEE, and the SEGUE. We then label them with the stellar effective temperature, the surface gravity and the metallicity. Ten percent of the sample is held out to apply a blind test. We develop a new method, a multi-model approach in order to fully take into account the uncertainties of both the magnitudes and stellar parameters. The method utilizes more than two hundred models to apply the uncertainty analysis. Results. We present a catalog of 2,493,424 stars with the Root Mean Square Error of 160K in the effective temperature regression, 0.35 in the surface gravity regression and 0.25 in the metallicity regression. We also discuss the advantages of this multi-model approach and compare it to other machine-learning methods.

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arXiv2022

S-PLUS: Exploring wide field properties of multiple populations in galactic globular clusters at different metallicities

The presence of Multiple Stellar Populations (MSPs) in Galactic Globular Clusters (GCs) is a poorly understood phenomenon. By probing different spectral ranges that are affected by different absorption lines using the multi-band photometric survey S-PLUS, we study four GCs -- NGC 104, NGC 288, NGC 3201 and NGC 7089 -- that span a wide range in metallicities. With the combination of broad and narrow-band photometry in 12 different filters from 3485A (u) to 9114A (z), we identified MSPs along the rectified red-giant branch in colour-magnitude diagrams (CMDs) and separated them using a K-means clustering algorithm. Additionally, we take advantage of the large Field of View of the S-PLUS detector to investigate radial trends in our sample. We report on six colour combinations that can be used to successfully identify two stellar populations in all studied clusters and show that they can be characterized as Na-rich and Na-poor. For both NGC 288 and NGC 7089, their radial profiles show a clear concentration of 2P. This directly supports the formation theories that propose an enrichment of the intra-cluster medium and subsequent star formation in the more dense central regions. However, in the case of NGC 3201, the trend is reversed. The 1P is more centrally concentrated, in direct contradiction with previous literature studies. NGC 104 shows a well-mixed population. We also constructed radial profiles up to 1 half-light radius of the clusters with HST data to highlight that radial differences are lost in the inner regions of the GCs and that wide-field studies are essential when studying this.

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arXiv2022

Revisiting the role of bars in AGN fuelling with propensity score sample matching

The high luminosity displayed by an active galactic nucleus (AGN) requires that gas be transported to the centre of the galaxy by some mechanism. Bar-driven processes are often pointed out in this context and a number of studies have addressed the bar-AGN connection, but with conflicting results. Some of the inconsistencies can be explained by the different spatial- and timescales involved in bar-driven gas inflows, accretion by the central black hole, and AGN emission. However, the discrepant results could also be due to sample biases, because both the AGN activity determination and the bar detection are influenced by the method employed. We revisit the bar-AGN connection in a sample of galaxies from SDSS, looking for evidence of the influence of bars on AGN activity. We determine AGN activity by emission line diagnostics and the properties of the bar were previously estimated with \texttt{BUDDA}, which performs 2D bulge-bar-disk decomposition. Before comparing active and inactive galaxies, we made a careful selection of the sample to minimise selection biases. We created control samples by matching them with the AGN sample using propensity score matching. This technique offers an analytical approach for creating control samples given some object parameters. We find that AGN are preferentially found in barred galaxies and that the accretion rate is higher in barred galaxies, but only when different M-$σ$ relations are used to estimate the black hole mass M$_\bullet$ in barred and unbarred galaxies (from the central velocity dispersion $σ$). On the other hand, we find no correlation between activity level and bar strength. Altogether, our results strengthen theoretical predictions that the bar is an important mechanism in disc galaxies, creating a gas reservoir to feed AGN, but they also indicate that other mechanisms can play a major role, particularly at scales <~100 pc.

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arXiv2022

The DIVING$^{3D}$ Survey -- Deep IFS View of Nuclei of Galaxies -- I. Definition and Sample Presentation

We present the Deep Integral Field Spectrograph View of Nuclei of Galaxies (DIVING$^{3D}$) survey, a seeing-limited optical 3D spectroscopy study of the central regions of all 170 galaxies in the Southern hemisphere with B < 12.0 and |b| > 15 degrees. Most of the observations were taken with the Integral Field Unit of the Gemini Multi-Object Spectrograph, at the Gemini South telescope, but some are also being taken with the Southern Astrophysical Research Telescope (SOAR) Integral Field Spectrograph. The DIVING$^{3D}$ survey was designed for the study of nuclear emission-line properties, circumnuclear (within scales of hundreds of pc) emission-line properties, stellar and gas kinematics and stellar archaeology. The data have a combination of high spatial and spectral resolution not matched by previous surveys and will result in significant contributions for studies related to, for example, the statistics of low-luminosity active galactic nuclei, the ionization mechanisms in Low-Ionization Nuclear Emission-Line Regions, the nature of transition objects, among other topics.

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arXiv2021

A Grid of Synthetic Spectra for Subdwarfs: Non-LTE line-blanketed atmosphere models

A new grid of detailed atmosphere model spectra for hot and moderately cool subdwarf stars is presented. High-resolution spectra and synthetic photometry are calculated in the range from 1000Å to 10,000Å using Non-LTE fully line-blanketed atmosphere structures. Our grid covers eight temperatures within 10,000<Teff [K]<65,000, three surface gravities in the range 4.5<logg [cgs]<6.5, two helium abundances matching two extreme helium-rich and helium-poor scenarios, and two limiting metallicity boundaries regarding both solar ([Fe/H] = 0) and Galactic halo ([Fe/H] = -1.5 and [α/Fe] = +0.4). Besides its application in the determination of fundamental parameters of subdwarfs in isolation and in binaries, the resulting database is also of interest for population synthesis procedures in a wide variety of stellar systems.

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arXiv2020

Clues on the history of early-type galaxies from SDSS spectra and GALEX photometry

Stellar population studies of early-type galaxies (ETGs) based on their optical stellar continuum suggest that these are quiescent systems. However, emission lines and ultraviolet photometry reveal a diverse population. We use a new version of the STARLIGHT spectral synthesis code and state-of-the-art stellar population models to simultaneously fit SDSS spectra and GALEX photometry for a sample of 3453 galaxies at $z < 0.1$ with $NUV-r > 5$ that are classified as elliptical by Galaxy Zoo. We reproduce $FUV$ magnitudes for 80 per cent of UV upturn galaxies selected using criteria from the literature, suggesting that additional stellar population ingredients such as binaries and extreme horizontal branch stars may have a limited contribution to the UV upturn. The addition of ultraviolet data leads to a broadening of the distributions of mean stellar ages, metallicities and attenuation. Stellar populations younger than $1\,$Gyr are required to reproduce the ultraviolet emission in 17 per cent of our sample. These systems represent 43 per cent of the sample at $5<NUV-r<5.5$ and span the same stellar mass range as other ETGs in our sample. ETGs with young stellar components have larger $Hα$ equivalent widths ($W_{Hα}$) and larger dust attenuation. Emission line ratios and $W_{Hα}$ indicate that the ionising source in these systems is a mixture of young and old stellar populations. Their young stellar populations are metal-poor, especially for high-mass galaxies, indicating recent star formation associated with rejuvenation events triggered by external processes, such as minor mergers.

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arXiv2020

High Resolution Spectral Line Indices Useful for the Analysis of Stellar Populations

The well-known age-metallicity-attenuation degeneracy does not permit unique and good estimates of basic parameters of stars and stellar populations. The effects of dust can be avoided using spectral line indices, but current methods have not been able to break the age-metallicity degeneracy. Here we show that using at least two new spectral line indices defined and measured on high-resolution (R= 6000) spectra of a signal-to-noise ratio (S/N) > 10 one gets unambiguous estimates of the age and metallicity of intermediate to old stellar populations. Spectroscopic data retrieved with new astronomical facilities, e.g., X-shooter, MEGARA, and MOSAIC, can be employed to infer the physical parameters of the emitting source by means of spectral line index and index--index diagram analysis.

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arXiv2019

To use or not to use synthetic stellar spectra in population synthesis models?

Stellar population synthesis (SPS) models are invaluable to study star clusters and galaxies. They provide means to extract stellar masses, stellar ages, star formation histories, chemical enrichment and dust content of galaxies from their integrated spectral energy distributions, colours or spectra. As most models, they contain uncertainties which can hamper our ability to model and interpret observed spectra. This work aims at studying a specific source of model uncertainty: the choice of an empirical vs. a synthetic stellar spectral library. Empirical libraries suffer from limited coverage of parameter space, while synthetic libraries suffer from modelling inaccuracies. Given our current inability to have both ideal stellar-parameter coverage with ideal stellar spectra, what should one favour: better coverage of the parameters (synthetic library) or better spectra on a star-by-star basis (empirical library)? To study this question, we build a synthetic stellar library mimicking the coverage of an empirical library, and SPS models with different choices of stellar library tailored to these investigations. Through the comparison of model predictions and the spectral fitting of a sample of nearby galaxies, we learned that: predicted colours are more affected by the coverage effect than the choice of a synthetic vs. empirical library; the effects on predicted spectral indices are multiple and defy simple conclusions; derived galaxy ages are virtually unaffected by the choice of the library, but are underestimated when SPS models with limited parameter coverage are used; metallicities are robust against limited HRD coverage, but are underestimated when using synthetic libraries.

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arXiv2019

Testing Stellar Population Fitting Ingredients with Globular Clusters I: Stellar Libraries

The integrated spectra of stellar systems contain a wealth of information, and its analysis can reveal fundamental parameters such as metallicity, age and star formation history. Widely used methods to analyze these spectra are based on comparing the galaxy spectra to stellar population (SP) models. Despite being a powerful tool, SP models contain many ingredients, each with their assumptions and uncertainties. Among the several possible sources of uncertainties, it is not straightforward to identify which ingredient dominates the errors in the models. In this work we propose a study of one of the SP model ingredients -- the spectral stellar libraries -- independently of the other ingredients. To that aim, we will use the integrated spectra of globular clusters which have color-magnitude diagrams (CMDs) available. From these CMDs it is possible to model the integrated spectra of these objects without having to adopt -- or make assumptions -- on the other two main ingredients of SP models, evolutionary tracks or an IMF. Here we tested four widely used stellar libraries. We found that the libraries are able to reproduce the integrated spectra of 18 of the 30 cluster spectra inside a mean flux uncertainty of 5%. For the larger wavelength range tested, a theoretical library outperforms the empirical ones in the comparison. Without the blue part of the spectra, empirical libraries fare better than the theoretical, in particular when individual features are concerned. However, the results are promising for theoretical libraries, which are equally efficient to reproduce the whole spectrum.

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arXiv2018

J-PLUS: A wide-field multi-band study of the M15 globular cluster. Evidence of multiple stellar populations in the RGB

The Javalambre Photometric Local Universe Survey (J-PLUS) provides wide field-of-view images in 12 narrow, intermediate and broad-band filters optimized for stellar photometry. Here we have applied J-PLUS data for the first time for the study of Galactic GCs using science verification data obtained for the very metal-poor GC M\,15. Our J-PLUS data provide low-resolution spectral energy distributions covering the near-UV to the near-IR, allowing us to search for MPs based on pseudo-spectral fitting diagnostics. J-PLUS CMDs are found to be particularly useful to search for splits in the sequences formed by the upper red giant branch (RGB) and asymptotic giant branch (AGB) stars. We interpret these split sequences as evidence for the presence of MPs. This demonstrates that the J-PLUS survey will have sufficient spatial coverage and spectral resolution to perform a large statistical study of GCs through multi-band photometry in the coming years.

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arXiv2017

A grid of Synthetic Spectra for Hot DA White Dwarfs and Its Application in Stellar Population Synthesis

In this work we present a grid of LTE and non-LTE synthetic spectra of hot DA white dwarfs (WDs). In addition to its usefulness for the determination of fundamental stellar parameters of isolated WDs and in binaries, this grid will be of interest for the construction of theoretical libraries for stellar studies from integrated light. The spectral grid covers both a wide temperature and gravity range, with 17,000 K <= T_eff <= 100,000 K and 7.0 <= log(g) <= 9.5. The stellar models are built for pure hydrogen and the spectra cover a wavelength range from 900 A to 2.5 microns. Additionally, we derive synthetic HST/ACS, HST/WFC3, Bessel UBVRI and SDSS magnitudes. The grid was also used to model integrated spectral energy distributions of simple stellar populations and our modeling suggests that DAs might be detectable in ultraviolet bands for populations older than ~8 Gyr.

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