Jesus Gallego

Context. Satellite galaxies in the Local Group exhibit prominent spatially flattened configurations around their hosts, with a significant fraction also sharing coherent orbital motion. However, galaxy formation simulations in the Lambda Cold Dark Matter model have historically struggled to produce similarly planar, kinematically coherent, and stable structures, giving rise to the so-called “planes of satellites problem”. Aims. We investigate the formation of planes of satellites and assess whether their emergence depends on the mass of a major merger at z ∼ 2, comparable to the Gaia-Sausage-Enceladus (GSE) merger in the Milky Way. Methods. We employed the VINTERGATAN-GM suite of five high-resolution cosmological zoom-in realizations of the same Milky Way-mass halo, generated through targeted genetic modifications of a GSE progenitor. The total mass ratio of this z ∼ 2 merger was incrementally increased from 1:10 to 1:2.1, while fixing the galaxy’s final dynamical mass and large-scale environment. We examined whether these simulations produce planes of satellites comparable to those observed in the Local Group and how their properties depend on the GSE progenitor mass. Results. We find a consistent trend that the more massive the GSE progenitor, the more planar and kinematically coherent the satellite population. Simulations with a GSE progenitor with a total mass ratio larger than 1:6 develop long-lived kinematically coherent planes with properties comparable to the one observed in the Milky Way. These structures arise because sufficiently massive mergers, infalling along the direction of maximum compression of the lagrangian volume, produce flattened host halos with anisotropic velocity dispersions. As a result, the minor axis of the resultant host halo aligns with the merger direction and the direction of flattening of the local cosmic web and planes of satellites emerge through two complementary processes: (i) satellites preferentially infall along the stable host’s equatorial plane, and (ii) anisotropic dynamical friction in the nonspherical halo gradually reshape their orbits toward this plane, generating coherent and long-lived planar configurations.

Aims. This paper describes the relationship between the star formation rate and the stellar mass, the so-called main sequence (MS), of low-mass galaxies at three different redshifts from the OTELO survey. In particular, we study H α at z = 0.38, [O III ] at z = 0.83, and [O II ] at z = 1.43 emission line galaxies (ELGs). This is done to characterise the properties of low-mass ELGs. Methods. We fitted the spectral energy distribution (SED) of each emitter and obtained the stellar masses, the total infrared luminosity, and the star formation rate. We found that 100% of the H α emitters and about 90% of the [O III ] and [O II ] emitters are low-mass galaxies (< 10 ¹⁰ M _⊙ ). We generated a MS for each redshift regime, employing all galaxies and binning them in stellar mass. We obtained the parameters of the fit (turnover mass and slope of the low-mass regime) and compared them to results from the literature. Results. We found that the colour–magnitude method employed to select ELGs leaves out a significant number of them. We also found that the whole sample contains few luminous infrared galaxies and no ultra-luminous infrared galaxies. We also found that the lack of infrared constraints in the input SEDs may generate problems when determining the total infrared luminosity. When comparing the MS obtained for our sample of low-mass ELGs with those from the bibliography, we found, in general, very good agreement. We can consider the MS to be almost the same for the relatively unexplored regime of low-mass galaxies. However, the turnover mass obtained by this work is higher for all redshifts compared with the ones from the literature. We suggest that this is an effect of the different methods and samples used in the generation of the MS compared to those of the bibliography.

Aims. We aim to quantify the star formation rate (SFR) from deep optical spectroscopic data and far-infrared (FIR) photometry from a sample of galaxies at z ∼ 0.9 from the OTELO survey and compare the activity estimated by optical tracers and FIR emission. Methods. We used the multi-wavelength OTELO catalogue to construct a sample of FIR sources. We identified and separated galaxies with active nuclei and derived the physical properties of the rest. We analysed their spectral energy distribution, obtaining estimates for stellar mass, dust attenuation, luminosity, and SFR based on infrared luminosity. We also studied H β and [O III ] λ 4959,5007 emission-line galaxies without significant FIR emission from previous works. This approach allowed us to perform a comparative analysis among the SFR obtained through different calibrators, in particular H β presented in a previous work Results. We find that FIR-based SFR estimates uncover a significant fraction of hidden star formation. We determined that the SFR density obtained from the FIR emission is three times larger than that obtained from only emission-line sources. Likely related to the fact that each SFR tracer provides insight into star formation over different timescales, we suggest that such indicators are also more or less suited for different galaxy populations. Specifically, while optical emission lines effectively trace star formation in lower-mass galaxies, FIR-derived SFRs provide a more reliable measure in massive dust-rich systems. By accounting for both optically visible and obscured star formation, we provide a more comprehensive view of the star-forming main sequence at z ∼ 0.9 and reinforce the importance of infrared tracers in studying galaxy evolution.

IZw18 is one of the lowest-metallicity star-forming galaxies known at z ∼ 0, considered a unique local analogue of the first galaxies. The origin of its hard ionizing continuum, expected to be a common feature in the early Universe and traced by He ii emission lines, remains intensely debated and challenging to explain. Here we combine optical Gran Telescopio Canarias MEGARA and mid-infrared (JWST/MIRI) integral field spectroscopic observations for IZw18 to shed new light on the high-ionization phenomenon. This Letter reports the first detection of the high-ionization [Ne v]14.32 μm line in IZw18. Its emission is spatially extended and coincident with the He ii peak, revealing the presence of highly energetic ionizing sources that surpass mechanisms previously proposed on the basis of He ii alone. Our kinematic studies highlight that the He ii λ4686-emitting gas displays higher velocity dispersions and a different velocity pattern compared with the Hβ emission, suggesting the presence of energetic processes such as shocks or stellar-driven feedback. Additionally, integrated spectra show asymmetric blueshifted profiles in the He ii λ4686 line, possibly indicating early-stage stellar-driven outflows potentially facilitating future ionizing photon leakage. Our spatial analysis also reveals differences in structure between the emission of Hβ and He ii λ4686, with the He ii λ4686 peak offset by a projected distance of 140 pc from the peak Hβ emission. This indicates distinct locations for the most extreme ionizing sources compared to moderate ionizing sources. Our findings underscore the complex interplay of physical processes in extremely metal-poor environments with highly ionized gas, offering new insights into the conditions prevailing in the early galaxies.

Context. Satellite galaxies experience multiple physical processes when interacting with their host halos, often leading to the quenching of star formation. In the Local Group, satellite quenching has been shown to be highly efficient, affecting nearly all satellites except the most massive ones. While recent surveys study Milky Way-analogs to assess how representative our Local Group is, the dominant physical mechanisms behind satellite quenching in Milky Way-mass halos remain under debate. Aims. We analyze satellite quenching within the same Milky Way-mass halo simulated using various widely used astrophysical codes, each using different hydrodynamic methods and implementing different supernovae feedback recipes. The goal is to determine whether quenched fractions, quenching timescales, and the dominant quenching mechanisms are consistent across codes or if they show sensitivity to the specific hydrodynamic method and supernovae feedback physics employed. Methods. We used a subset of high-resolution cosmological zoom-in simulations of a Milky Way-mass halo from the multiple-code AGORA CosmoRun suite. Our analysis focuses on comparing satellite quenching across the different models and against observational data. We also analyzed the dominant mechanisms driving satellite quenching in each model. Results. We find that the quenched fraction is consistent with the latest SAGA Survey results within its 1σ host-to-host scatter across all the models. Regarding quenching timescales, all the models reproduce the trend observed in the ELVES survey, Local Group observations, and previous simulations: The less massive the satellite, the shorter its quenching timescale. All of our models converge on the dominant quenching mechanisms: Strangulation halts cold gas accretion in all satellites, while ram pressure stripping is the predominant mechanism for gas removal, and it is particularly effective in satellites with M_*8 M_⊙. Nevertheless, the efficiency of the stripping mechanisms differs among the codes, showing a strong sensitivity to the different supernovae feedback implementations and/or hydrodynamic methods employed.

Aims. We present an analysis of the emitters (Hα, Hβ, and [O II]) from the OTELO survey, in order to characterize the star formation properties of low-mass galaxies (< 10⁹ M_⊙ stellar masses). Methods. We calculated the specific star formation rate function, the stellar mass function, and, by integrating them, the associated densities for both quantities: the specific star formation rate density and the stellar mass density. We obtained the star formation history of our low-mass sample galaxies by fitting the spectral energy distribution of the galaxies. We also compared our results with those from the literature at different mass regimes and redshifts. Results. The specific star formation rate density and the stellar mass density for low-mass galaxies do not depend on the redshift, contrary to the behaviour presented by the high-mass galaxies. We found that the star formation histories of low-mass galaxies are characterized by a constant star formation rate, in contrast to high-mass galaxies. We interpret these results, in the context of the downsizing effect, as representative of the faster evolution of massive galaxies compared with low-mass ones.

Context. The Lockman–SpReSO project is an optical spectroscopic survey of 956 far-infrared (FIR) objects within the Lockman Hole field limited by magnitude R_C(AB) < 24.5. Fe II and Mg II absorption lines have been detected in 21 out of 456 objects with a determined spectroscopic redshift in the catalogue. The redshifts of these objects are in the range 0.5 ≲ z ≲ 1.44. Aims. The aim of this study is to investigate material ejection from star-forming regions and material infall into galaxies by analysing the Fe II and Mg II absorption lines. Additionally, we explore whether the correlations found in previous studies between these galactic wind velocities, line equivalent widths (EWs), and galaxy properties such as stellar mass (M_*), star formation rate (SFR), and specific star formation rate (sSFR) are valid for a sample with FIR-selected objects. The objects analysed span an M_* range of 9.89 < log(M_*/M_⊙) < 11.50 and an SFR range of 1.01 < log(SFR) < 2.70. Methods. We performed measurements of the Mg IIλλ2796, 2803, Mg Iλ2852, Fe IIλλ2374, 82, Fe IIλλ2586, 2600, and Fe IIλ2344 spectral lines present in the spectra of the selected sample to determine the EW and velocity of the flows observed in the star-forming galaxies. Subsequently, we conducted 10⁷ bootstrap simulations using the Spearman’s rank correlation coefficient (ρ_s) to explore correlations with galaxy properties. Furthermore, we calculated the covering factor, gas density, and optical depth for the measured Fe II doublets. Results. Our analysis reveals strong correlations between the EW of Mg II lines and both M_* (ρ_s = 0.43, 4.5σ) and SFR (ρ_s = 0.42, 4.4σ). For the Fe II lines, we observed strong correlations between the EW and SFR (ρ_s ∼ 0.65, > 3.9σ), with a weaker correlation for M_* (ρ_s ∼ 0.35, > 1.9σ). No notable correlations were found between velocity measurements of the Mg II line and M_*, SFR, or sSFR of the objects (ρ_s ∼ 0.1). However, a strong negative correlation was found between the velocity of the Fe II lines and the SFR of the galaxies (ρ_s ∼ −0.45, ∼3σ). Our results align with those of previous studies, although only FIR-selected objects are investigated here. Finally, we detect a candidate ‘loitering outflow’, a recently discovered subtype of the iron low-ionisation broad absorption line (FeLoBAL) quasars, at a redshift of z = 1.4399, exhibiting emission in C III] and low line velocities (|v|≲200 km s⁻¹).

Context.Feedback processes, in particular those driven by outflows, are believed to play a major role in galaxy evolution. Outflows are believed to be ubiquitous in all active galactic nuclei (AGNs), although their presence in low luminosity AGNs, in particular for Low-Ionisation Nuclear Emission line Regions (LINERs), has only started to be explored. Their properties (geometry, mass, and energetics) are still far from being properly characterised.Aims.The main goal is to use integral field spectroscopic data from the MEGARA instrument at the Gran Telescopio Canarias (GTC) to analyse a small sample of nine LINERs, candidates of hosting ionised gas outflows. We aim to study the main emission lines in the optical wavelength range to identify their properties and physical origin.Methods.We obtained data cubes in several bands at the lowest (R ∼ 6000) and highest (R ∼ 20 000) spectral resolution of MEGARA. We modelled and subtracted the stellar continuum to obtain the ionised gas contribution, and then fitted the emission lines to extract their kinematics (velocity and velocity dispersion). We identified outflows as a secondary component in the emission lines and obtained their main properties.Results.The primary component of the emission lines was typically associated with gas in the galactic disc. For some objects, there is an enhanced-σregion typically co-spatial with the secondary component. We associated it to turbulent gas produced due to the interaction with the outflows. We find signatures of outflows in six LINERs, with mass outflow rates ranging from 0.004 to 0.4M_⊙yr⁻¹and energy rates from ∼10³⁸to ∼10⁴⁰erg s⁻¹. Their mean electronic density is 600 cm⁻³, extending to distances of ∼400 pc at an (absolute) velocity of ∼340 km s⁻¹(on average). They tend to be compact and unresolved, although for some sources they are extended with a bubble-like morphology.Conclusions.Our results confirm the existence of outflows in the best LINER candidates identified using previous long-slit spectroscopic and imaging data. These outflows do not follow the scaling relations obtained for more luminous AGNs. For some objects we discuss jets as the main drivers of the outflows.