Context. Active galactic nuclei (AGNs) have been observed in dwarf galaxies, yet the impact of black hole feedback in these low-mass systems remains unclear. Aims. To uncover the potential effects of AGNs in the low-mass galaxy regime, we study the properties and demographics of active dwarf galaxies at z = 0, using IllustrisTNG simulations. Methods. We used data from the TNG50-1 simulation, selecting central galaxies with stellar masses in the range 8 ≤ log( M * /M ⊙ )≤9.5, along with a selection of AGNs based on their Eddington ratios ( λ Edd ). We analyzed the properties and environment of AGN host galaxies and compared them with inactive control galaxies. Results. The AGN fractions found in the simulation depend strongly on the threshold for λ Edd in the AGN selection, ranging from ∼1% ( λ Edd ≥ 0.05) to ∼24% ( λ Edd ≥ 0.01). In comparison with non-AGN galaxies of similar stellar and halo mass, dwarf AGN hosts are deficient in neutral gas, having ∼3.9 times less neutral mass, in qualitative agreement with observations. The dearth in neutral gas is stronger beyond two stellar half-mass radii ( r ≳ 3 kpc), and AGN hosts have more extended gas components than non-AGN galaxies, with a gas half-mass radius that is ≳10 kpc larger, on average. AGN hosts also display slightly less star-forming activity, but there are no differences seen in terms of the local environment. Conclusions. We found that AGNs can significantly decrease the neutral gas component of dwarf galaxies, which is a direct effect of the high-accretion feedback mode employed in IllustrisTNG. However, it is important to test our findings with observations to unveil the complete role of AGNs in dwarf galaxies. In TNG50, dwarf AGN fractions are an order of magnitude larger than those observed, motivating a detailed investigation to precisely quantify the mismatch between simulations and observations.

Thanks to Integral Field Unit survey data, it is possible to explore in detail the link between the formation of the stellar content in galaxies and the drivers of evolution. Traditionally, scaling relations have connected galaxy-wide parameters such as stellar mass (Ms), morphology or average velocity dispersion (sigma) to the star formation histories (SFHs). We study a high quality sample of SDSS-MaNGA spectra to test the possibility that sub-galaxy (less than or similar to 2 kpc) scales are dominant, instead of galaxy-wide parameters. We find a strong correlation between local velocity dispersion and key line strengths that depend on the SFHs, allowing us to make the ansatz that this indicator-that maps the local gravitational potential-is the major driver of star formation in galaxies, whereas larger scales play a role of a secondary nature. Galactocentric distance has a weaker correlation, suggesting that the observed radial gradients effectively reflect local variations of velocity dispersion. In our quest for a cause, instead of a correlation, we contrast sigma with local stellar mass (or surface mass density), that appears less correlated with population properties. We conclude that the inherently higher uncertainty in M-s (or Sigma(M))may explain its lower correlation with respect to sigma, but the extra uncertainty needed for sigma to have similar correlations as stellar mass is rather high. Therefore, we posit local velocity dispersion as the major driver of evolution, a result that should be reproduced by hydrodynamical models at the proper resolution.

Thanks to Integral Field Unit survey data it is possible to explore in detail the link between the formation of the stellar content in galaxies and the drivers of evolution. Traditionally, scaling relations have connected galaxy-wide parameters such as stellar mass (M_s), morphology or average velocity dispersion (σ) to the star formation histories (SFHs). We study a high quality sample of SDSS-MaNGA spectra to test the possibility that sub-galaxy (∼2 kpc) scales are dominant, instead of galaxy-wide parameters. We find a strong correlation between local velocity dispersion and key line strengths that depend on the SFHs, allowing us to make the ansatz that this indicator - that maps the local gravitational potential - is the major driver of star formation in galaxies, whereas larger scales play a role of a secondary nature. Galactocentric distance has a weaker correlation, suggesting that the observed radial gradients effectively reflect local variations of velocity dispersion. In our quest for a cause, instead of a correlation, we contrast σ with local stellar mass, that appears less correlated with population properties. We conclude that the inherently higher uncertainty in M_s may explain its lower correlation with respect to σ, but the extra uncertainty needed for σ to have similar correlations as M_s is rather high. Therefore we posit local velocity dispersion as the major driver of evolution, a result that should be reproduced by hydrodynamical models at the proper resolution.

The influence of Active Galactic Nuclei (AGN) on star formation within their host galaxies remains a topic of intense debate. One of the primary challenges in quantifying the star formation rate (SFR) within AGN hosts arises from the prevalent assumption in most methodologies, which attribute gas excitation to young stars alone. However, this assumption does not consider the contribution of the AGN to the ionization of the gas in their environment. To address this issue, we evaluate the use of strong optical emission lines to obtain the SFR surface density (Sigma SFRAGN) in regions predominantly ionized by an AGN, using a sample of 293 AGN hosts from the MaNGA survey, with SFR measurements available through stellar population fitting. We propose calibrations involving the H alpha and [OIII]lambda 5007 emission lines, which can be used to determine Sigma SFRAGN, resulting in values consistent with those estimated through stellar population fitting.

We investigated the stellar population properties of a sample of 1858 massive compact galaxies (MCGs) extracted from the Sloan Digital Sky Survey (SDSS). Motivated by previous results showing that older compact galaxies tend to have larger velocity dispersion at fixed stellar mass, we used the distance to the sigma(e) versus R-e and M-star versus sigma(e) relations as selection criteria. We found that MCGs are old (greater than or similar to 10 Gyr), alpha-enhanced ([alpha/Fe] similar to 0.2), and have solar to supersolar stellar metallicities. Metallicity increases with sigma(e), while age and [alpha/Fe] do not vary significantly. Moreover, at fixed sigma(e), metallicity and stellar mass are correlated. Compared with a control sample of typical quiescent galaxies, MCGs have, on average, lower metallicities than control sample galaxies (CSGs) of similar sigma(e). For sigma(e) less than or similar to 225 km s(-1), MCGs are older and more alpha-enhanced than CSGs, while for higher sigma(e) ages and alpha-enhancement are similar. The differences in age and alpha-enhancement can be explained by lower sigma(e) CSGs being an amalgam of quiescent galaxies with a variety of ages. The origin of the differences in metallicity, however, is not clear. Lastly, we compared the stellar mass within the region probed by the SDSS fibre finding that, at fixed fibre velocity dispersion, MCGs have lower stellar masses on average. Since the velocity dispersion is a tracer of the dynamical mass, this raises the possibility that MCGs have, on average, a bottom-heavier initial mass function or a larger dark matter fraction within the inner similar to 1-2 kpc.

As galáxias compactas massivas (MCGs) são galáxias quiescentes caracterizadas, neste trabalho, com altos valores de dispersão de velocidades efetiva, massa estelar e pequenos valores de raio efetivo. Com o objetivo de investigar a formação e evolução das MCGs, nós determinamos as propriedades das populações estelares de 1858 MCGs derivadas do levantamento Sloan Digital Sky Survey. Comparamos os resultados com uma amostra de galáxias controle (CSGs) (galáxias quiescentes com tamanhos médios) pareada em redshift com as MCGs. Comparamos os resultados à dispersão de velocidades fixa e encontramos diferenças entre as propriedades das populações estelares, especialmente para a metalicidade estelar: MCGs apresentam menor metalicidade que CSGs à dispersão de velocidades fixa. Os resultados apresentados ainda não são suficientes para determinar o caminho evolutivo das MCGs, mas podem indicar diferenças associadas à função de massa inicial ou da fração de matéria escura dentro de 1 raio efetivo nas MCGs.

ABSTRACT Compact groups of dwarf galaxies (CGDs) have been observed at low redshifts (z < 0.1) and are direct evidence of hierarchical assembly at low masses. To understand the formation of CGDs and the galaxy assembly in the low-mass regime, we search for analogues of compact (radius ≤100 kpc) groups of dwarfs (7 ≤ log [M*/M⊙] ≤ 9.5) in the IllustrisTNG highest resolution simulation. Our analysis shows that TNG50-1 can successfully produce CGDs at z = 0 with realistic total and stellar masses. We also find that the CGD number density decreases towards the present, especially at z ≲ 0.26, reaching $n \approx 10^{-3.5} \ \rm cMpc^{-3}$ at z = 0. This prediction can be tested observationally with upcoming surveys targeting the faint end of the galaxy population and is essential to constrain galaxy evolution models in the dwarf regime. The majority of simulated groups at z ∼ 0 formed recently ($\lesssim 1.5 \ \rm Gyr$), and CGDs identified at z ≤ 0.5 commonly take more than 1 Gyr to merge completely, giving origin to low- to intermediate-mass (8 ≤ log [M*/M⊙] ≤ 10) normally star-forming galaxies at z = 0. We find that haloes hosting CGDs at z = 0 formed later when compared to haloes of similar mass, having lower stellar masses and higher total gas fractions. The simulations suggest that CGDs observed at z ∼ 0 arise from a late hierarchical assembly in the last ∼3 Gyr, producing rapid growth in total mass relative to stellar mass and creating dwarf groups with median halo masses of $\sim 10^{11.3} \ \rm M_\odot$ and B-band mass-to-light ratios mostly in the range 10 ≲ M/L ≲ 100, in agreement with previous theoretical and observational studies.

We studied the ionized gas in the inner region ( <^> 680 x 470 pc(2)) ) of the galaxy NGC 6868 using Gemini/GMOS (Gemini Multi- Object Spectrograph) integral field unit observations. Channel maps reveal complex kinematics and morphology, indicating multiple processes at work in NGC 6868. Through emission-line fitting, we identified two ubiquitous components in our data: a narrow ( delta <^> 110 km s (- 1) ) tracing an ionized gas disc and a broad component ( delta <^> 300 km s( - 1 )) mainly associated with inflo wing/out flowing gas. The deri ved V-band reddening sho ws a spatial distribution consistent with that obtained from stellar population synthesis, although with generally higher values. For the first time, we measured the electron temperature in NGC 6868, finding values ranging from <^> 14 000 K in the central region to >= 20000 K with an outward increasing temperature gradient. The electron density map exhibits an inverse relationship, with central values reaching N-e <^> 4000 cm( -3) for the broad component decreasing to N-e <^> 100 cm( -3) towards the edges of the field of view. Using BPT diagrams, we found that all spaxels are consistent with both active galactic nucleus (AGN) and shock ionization. Ho we ver, when this information is combined with our kinematic and temperature findings, and further supported by the WHAN diagram, we argue that an AGN is the dominant ionization mechanism in the central region of NGC 6868, while the extended outer component is ionized by a combination of hot lo w-mass e volved stars and shocks. According to our findings, shocks play a significant role in the ionization balance of this galaxy.

ABSTRACT Near-infrared long-slit spectroscopy has been used to study the stellar population (SP) of the low luminosity active galactic nuclei (AGNs) and matched analogues (LLAMA) sample. To perform the SP fits we have employed the X-shooter simple stellar population models together with the starlight code. Our main conclusions are: The star formation history of the AGNs is very complex, presenting many episodes of star formation during their lifetimes. In general, AGN hosts have higher fractions of intermediate-age SP (light-weighted mean ages, L ≲ 4.5 Gyr) when compared with their analogues ( L ≲ 8.0 Gyr). AGNs are more affected by reddening and require significant fractions of featureless continuum and hot dust components. The ratio between the AGN radiated energy and the gravitational potential energy of the molecular gas (ERad/EPG) for the AGN is compared with the L and a possible anticorrelation is observed. This suggests that the AGN is affecting the star formation in these galaxies, in the sense that more energetic AGN [log(ERad/EPG) ≳ 3] tend to host nuclear younger SP ( L ≲4 Gyr). We found that the recent (t <2 Gyr) returned (recycled) stellar mass is higher in AGN than in the controls. We also provide evidence that the mass-loss of stars would be enough to feed the AGN, thus providing observational constraints for models that predict that AGN feeding is partially due to the recycled gas from dying stars.

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$\mu$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.

We investigate the formation and evolution of z = 0 massive compact galaxies (MCGs) in the IllustrisTNG cosmological simulation. We found that, as in observations, MCGs are mainly old (median age similar to 10.8 Gyr), have supersolar metallicities (median log Z/Z(circle dot) similar to 0.35), and are alpha-enhanced (median [alpha/Fe] similar to 0.25). The age distribution extends to younger ages, however, and a few MCGs are as young as similar to 7 Gyr. In general, MCGs assemble their mass early and accrete low angular momentum gas, significantly increasing their mass while growing their size much slower. A small fraction of MCGs follow another evolutionary path, going through a compaction event, with their sizes shrinking by 40 per cent or more. The accretion of low angular momentum gas leads to enhanced supermassive black hole (SMBH) growth, and MCGs reach the threshold SMBH mass of log M-BH similar to 10(8.5) M-circle dot - when kinetic active galactic nucleus feedback kicks in and quenches the galaxy - earlier than non-compact galaxies. Comparing MCGs to a sample of median-sized quiescent galaxies matched in effective velocity dispersion, we find that their accretion histories are very different. 71 per cent of MCGs do not merge after quenching compared to 37 per cent of median-sized quiescent galaxies. Moreover, tracing these populations back in time, we find that at least a third of median-sized quiescent galaxies do not have a compact progenitor, underscoring that both dry mergers and progenitor bias effects are responsible for the differences in the kinematics and stellar population properties of MCGs and median-sized quiescent galaxies.

We use Gemini integral field unit observations to map the stellar population properties in the inner region (∼680×470 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_⊙) with a negative metallicity gradient. We also found a recent (∼63 Myr) metal-rich (1.6 Z_⊙) 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<100pc and R>220pc, Mg_2, Mg_b anti correlate with respect to Fe3 and [MgFe]', and for 100 pc

We discuss the role of planetary nebulae and their progeny in galaxy context in terms of ionization of the galaxy interstellar medium. This regards ionized gas outside the disk of spiral galaxies, the diffuse ionized medium in spiral galaxies, and the weak line emission of elliptical galaxies.

We characterized the kinematics, morphology, and stellar population (SP) properties of a sample of massive compact quiescent galaxies (MCGs, 10 less than or similar to log M-*/M-circle dot less than or similar to 11 and r(e) similar to 1-3 kpc) in theMaNGA Survey, with the goal of constraining their formation, assembly history, and assessing their relation with non-compact quiescent galaxies. We compared their properties with those of a control sample of median-sized quiescent galaxies (re similar to 4-8 kpc) with similar effective velocity dispersions. MCGs have elevated rotational support, as evidenced by a strong anticorrelation between the Gauss-Hermite moment h(3) and V/sigma. In contrast, 30 per cent of control sample galaxies (CSGs) are slow rotators, and fast-rotating CSGs generally show a weak h(3)-V/sigma anticorrelation. MCGs and CSGs have similar ages, but MCGs are more metal-rich and alpha-enhanced. Both MCGs and CSGs have shallow negative metallicity gradients and flat [alpha/Fe] gradients. On average, MCGs and CSGs have flat age gradients, but CSGs have a significantly larger dispersion of gradient values. The kinematics and SP properties of MCGs suggest that they experienced highly dissipative gas-rich events, such as mergers, followed by an intense, short, and centrally concentrated burst of star formation, between 4 and 10 Gyr ago ( z similar to 0.4-2), and had a quiet accretion history since then. This sequence of events might be analogous to, although less extreme than, the compaction events that formed compact quiescent galaxies at z similar to 2. The small sizes of MCGs, and the high efficiency and short duration of their last star formation episode suggest that they are descendants of compact post-starburst galaxies.

We analyse the globular cluster (GC) systems of a sample of 15 massive, compact early-type galaxies (ETGs), 13 of which have already been identified as good relic galaxy candidates on the basis of their compact morphologies, old stellar populations and stellar kinematics. These relic galaxy candidates are likely the nearby counterparts of high redshift red nugget galaxies. Using F814W ( I) and F160W ( H) data from the WFC3 camara onboard the Hubble Space Telescope we determine the total number, luminosity function, specific frequency, colour and spatial distribution of the GC systems. We find lower specific frequencies (SN<2.5 with a median of SN=1) than ETGs of comparable mass. This is consistent with a scenario of rapid, early dissipative formation, with relatively low levels of accretion of low-mass, high-SN satellites. The GC half-number radii are compact, but follow the relations found in normal ETGs. We identify an anticorrelation between the specific angular momentum (lambda_R) of the host galaxy and the (I-H) colour distribution width of their GC systems. Assuming that lambda_R provides a measure of the degree of dissipation in massive ETGs, we suggest that the (I-H) colour distribution width can be used as a proxy for the degree of complexity of the accretion histories in these systems.

ABSTRACT In the local Universe, there are a handful of dwarf compact star-forming galaxies with extremely low oxygen abundances. It has been proposed that they are young, having formed a large fraction of their stellar mass during their last few hundred Myr. However, little is known about the fraction of young stellar populations in more massive galaxies. In a previous article, we analysed 404 000 Sloan Digital Sky Survey spectra to identify a surprisingly large sample of more massive very young galaxies (VYGs), defined to have formed at least $50{{\ \rm per\ cent}}$ of their stellar mass within the last 1 Gyr. Here, we investigate in detail the properties of a subsample of 207 galaxies that are VYGs according to all three of our spectral models. We compare their properties with those of control sample galaxies (CSGs). We find that VYGs tend to have higher surface brightness and to be more compact, dusty, asymmetric, and clumpy than CSGs. Analysis of a subsample with H i detections reveals that VYGs are more gas rich than CSGs. VYGs tend to reside more in the inner parts of low-mass groups and are twice as likely as CSGs to be interacting with a neighbour galaxy. On the other hand, VYGs and CSGs have similar gas metallicities and large-scale environments (relative to filaments and voids). These results suggest that gas-rich interactions and mergers are the main mechanisms responsible for the recent triggering of star formation in low-redshift VYGs, except for the lowest mass VYGs, where the starbursts would arise from a mixture of mergers and gas infall.

We investigate how the stellar populations of the inner regions of the first and the second brightest group galaxies (respectively BGGs and SBGGs) vary as a function of magnitude gap, using a Sloan Digital Sky Survey-based sample of 550 groups with elliptical BGGs. The sample is complete in redshift, luminosity, and for Delta M-12 up to 2.5 mag, and contains 59 large-gap groups (LGGs, with Delta M-12 > 2.0 mag). We determine ages, metallicities, and star formation histories (SFHs) of BGGs and SBGGs using the STARLIGHT code with two different single stellar population models (which lead to important disagreements in SFHs), and also compute [alpha/Fe] from spectral indices. After removing the dependence with galaxy velocity dispersion or with stellar mass, there is no correlation with magnitude gap of BGG ages, metallicities, [alpha/Fe], and SFHs. The lack of trends of BGG SFHs with magnitude gap suggests that BGGs in LGGs have undergone more mergers than those in small-gap groups, but these mergers are either dry or occurred at very high redshift, which in either case would leave no detectable imprint in their spectra. We show that SBGGs in LGGs lie significantly closer to the BGGs (in projection) than galaxies with similar stellar masses in normal groups, which appears to be a sign of the earlier entry of the former into their groups. Nevertheless, the stellar population properties of the SBGGs in LGGs are compatible with those of the general population of galaxies with similar stellar masses residing in normal groups.