Hα Equivalent Width Research Articles

Accurate and Model-independent Radius Determination of Single FGK and M Dwarfs Using Gaia DR3 Data

Measuring fundamental stellar parameters is key to fully comprehending the evolution of stars. However, current theoretical models overpredict effective temperatures, and underpredict radii, compared to observations of K and M dwarfs (radius inflation problem). In this work, we have developed a model-independent method to infer precise radii of single FGK and M dwarfs using Gaia DR3 parallaxes and photometry, and used it to study the radius inflation problem. We calibrated nine surface brightness–color relations for the three Gaia magnitudes and colors using a sample of stars with angular diameter measurements. We achieved an accuracy of 4% in our angular diameter estimations, which Gaia’s parallaxes allow us to convert to physical radii. We validated our method by comparing our radius measurements with literature samples and the Gaia DR3 catalog, which confirmed the accuracy of our method and revealed systematic offsets in the Gaia measurements. Moreover, we used a sample with measured Hα equivalent width (Hα EW), a magnetic activity indicator, to study the radius inflation problem. We demonstrated that active stars have larger radii than inactive stars, showing that radius inflation is correlated with magnetic activity. We found a correlation between the radius inflation of active stars and Hα EW for the mass bin 0.5 < M[M ⊙] ≤ 0.6, but we found no correlation for lower masses. This could be due to lack of precision in our radius estimation or a physical reason. Radius measurements with smaller uncertainties are necessary to distinguish between the two scenarios.

GA-NIFS: NIRSpec reveals evidence for non-circular motions and AGN feedback in GN20

ABSTRACT We present rest-frame optical data of the $z\sim 4$ submillimetre galaxy GN20 obtained with the JWST Near Infrared Spectrograph (NIRSpec) in integral field spectroscopy mode. The H$\alpha$ emission is asymmetric and clumpy and extends over a projected distance of &amp;gt;15 kpc. To first order, the large-scale ionized gas kinematics are consistent with a turbulent ($\sigma \sim 90$ km s$^{-1}$), rotating disc ($v_{\rm rot}\sim 500$ km s$^{-1}$), congruent with previous studies of its molecular and ionized gas kinematics. However, we also find clear evidence for non-circular motions in the H$\alpha$ kinematics. We discuss their possible connection with various scenarios, such as external perturbations, accretion, or radial flows. In the centre of GN20, we find broad-line emission (full width at half-maximum $\sim 1000{-}2000$ km s$^{-1}$) in the H$\alpha$ + [N ii] complex, suggestive of fast, active galactic nucleus-driven winds or, alternatively, of the broad-line region of an active black hole. Elevated values of [N ii] $\lambda 6583$/H$\alpha \ \gt\ 0.4$ and of the Hα equivalent width EW(H$\alpha)\ \gt\ 6$ Å throughout large parts of GN20 suggest that feedback from the active black hole is able to photoionize the interstellar medium. Our data corroborate that GN20 offers a unique opportunity to observe key processes in the evolution of the most massive present-day galaxies acting in concert, over 12 billion years ago.

Exploring galaxy properties of eCALIFA with contrastive learning

Contrastive learning (CL) has emerged as a potent tool for building meaningful latent representations of galaxy properties across a broad spectrum of wavelengths, ranging from optical and infrared to radio frequencies. These latent representations facilitate a variety of downstream tasks, including galaxy classification, similarity searches in extensive datasets, and parameter estimation, which is why they are often referred to as foundation models for galaxies. In this study, we employ CL on the latest extended data release from the Calar Alto Legacy Integral Field Area (CALIFA) survey, which encompasses a total of 895 galaxies with enhanced spatial resolution that reaches the limits imposed by natural seeing (FWHMPSF ∼ 1.5). We demonstrate that CL can be effectively applied to Integral Field Unit (IFU) surveys, even with relatively small training sets, to construct meaningful embedding where galaxies are well separated based on their physical properties. We discover that the strongest correlations in the embedding space are observed with the equivalent width of Hα, galaxy morphology, stellar metallicity, luminosity-weighted age, stellar surface mass density, the [NII]/Hα ratio, and stellar mass, in descending order of correlation strength. Additionally, we illustrate the feasibility of unsupervised separation of galaxy populations along the star formation main sequence, successfully identifying the blue cloud and the red sequence in a two-cluster scenario, and the green valley population in a three-cluster scenario. Our findings indicate that galaxy luminosity profiles have minimal impact on the construction of the embedding space, suggesting that morphology and spectral features play a more significant role in distinguishing between galaxy populations. Moreover, we explore the use of CL for detecting variations in galaxy population distributions across different large-scale structures, including voids, clusters, and filaments and walls. Nonetheless, we acknowledge the limitations of the CL framework and our specific training set in detecting subtle differences in galaxy properties, such as the presence of an AGN or other minor scale variations that exceed the scope of primary parameters such as the stellar mass or morphology. Conclusively, we propose that CL can serve as an embedding function for the development of larger models capable of integrating data from multiple datasets, thereby advancing the construction of more comprehensive foundation models for galaxies.

Bidimensional Exploration of the warm-Temperature Ionised gaS (BETIS)

We present the Bidimensional Exploration of the warm-Temperature Ionised gaS (BETIS) project, designed for the spatial and spectral study of the diffuse ionised gas (DIG) in a selection of nearby spiral galaxies observed with the MUSE integral-field spectrograph. Our primary objective is to investigate the various ionisation mechanisms at play within the DIG. We analysed the distribution of high- and low-ionisation species in the optical spectra of the sample on a spatially resolved basis. We introduced a new methodology for spectroscopically defining the DIG, optimised for galaxies of different resolutions. Firstly, we employed an innovative adaptive binning technique on the observed datacube based on the spectroscopic signal-to-noise ratio (S/N) of the collisional [S II] line to increase the S/N of the rest of the lines including [O III], [O I], and He I. Subsequently, we created a DIG mask by eliminating the emissions associated with both bright and faint H II regions. We also examined the suitability of using Hα equivalent width (EWHα) as a proxy for defining the DIG and its associated ionisation regime. Notably, for EWHα &lt; 3 Å – the expected emission from hot low-mass evolved stars (HOLMES) – the measured value is contingent on the chosen population synthesis technique performed. Our analysis of the showcase sample reveals a consistent cumulative DIG fraction across all galaxies in the sample, averaging around 40%–70%. The average radial distribution of the [N II]/Hα, [S II]/Hα, [O I]/Hα, and [O III]/Hβ ratios are enhanced in the DIG regimes (up to 0.2 dex). It follows similar trends between the DIG regime and the H II regions, as well as the Hα surface brightness (ΣHα), indicating a correlation between the ionisation of these species in both the DIG and the H II regions. The DIG loci in typical diagnostic diagrams are found, in general, within the line ratios that correspond to photoionisation due to the star formation. There is a noticeable offset correspondent to ionisation due to fast shocks. However, an individual diagnosis performed for each galaxy reveals that all the DIG in these galaxies can be attributed to photoionisation from star formation. The offset is primarily due to the contribution of Seyfert galaxies in our sample, which is closely aligned with models of ionisation from fast shocks and galactic outflows, thus mimicking the DIG emission. Our results indicate that galaxies exhibiting active galactic nucleus (AGN) activity should be considered separately when conducting a general analysis of the DIG ionisation mechanisms, since this emission is indistinguishable from high-excitation DIG.

MIDIS: Unveiling the Role of Strong Hα Emitters During the Epoch of Reionization with JWST

By using an ultradeep JWST/MIRI image at 5.6 μm in the Hubble eXtreme Deep Field, we constrain the role of strong Hα emitters (HAEs) during “cosmic reionization” at z ≃ 7–8. Our sample of HAEs is comprised of young (<35 Myr) galaxies, except for one single galaxy (≈300 Myr), with low stellar masses (≲109 M ⊙). These HAEs show a wide range of rest-frame UV continuum slopes (β), with a median value of β = −2.15 ± 0.21, which broadly correlates with stellar mass. We estimate the ionizing photon production efficiency (ξ ion,0) of these sources (assuming f esc,LyC = 0%), which yields a median value log10(ξion,0/(Hzerg−1))=25.50−0.12+0.10 . We show that ξ ion,0 positively correlates with Hα equivalent width and specific star formation rate. Instead ξ ion,0 weakly anticorrelates with stellar mass and β. Based on the β values, we predict fesc,LyC=4%−2+3 , which results in log10(ξion/(Hzerg−1))=25.55−0.13+0.11 . Considering this and related findings from the literature, we find a mild evolution of ξ ion with redshift. Additionally, our results suggest that these HAEs require only modest escape fractions (f esc,rel) of 6%–15% to reionize their surrounding intergalactic medium. By only considering the contribution of these HAEs, we estimated their total ionizing emissivity ( Ṅion ) as Ṅion=1050.53±0.45s−1Mpc−3 . When comparing their Ṅion with non-HAE galaxies across the same redshift range, we find that that strong, young, and low-mass emitters may have played an important role during cosmic reionization.

Toward Unveiling Cosmic Reionization: The Ionizing Photon Production Efficiency (ξ ion) of Low-mass Hα Emitters at z ∼ 2.3

We investigate the galaxy properties of ∼400 low-mass (<109 M ⊙) Hα emitters (HAEs) at z ∼ 2.3 in the ZFOURGE survey. The selection of these HAEs is based on the excess in the observed K s broadband flux compared to the stellar continuum estimated from the best-fit spectral energy distribution. These low-mass HAEs have elevated SFR(Hα) above the star formation main sequence, making them potential analogs of the galaxies that reionized the Universe during the Epoch of Reionization. The ionizing photon production efficiencies (ξ ion) of the low-mass HAEs have a median value of log(ξion/erg−1Hz)=25.24−0.13+0.10(25.35−0.15+0.12) , assuming the Calzetti (SMC) curve for the stellar continuum dust correction. This value is higher than that of main-sequence galaxies by ∼0.2 dex at similar redshift, indicating that the low-mass HAEs are more efficient in producing ionizing photons. Our results also consolidate the trend of increasing ξ ion with redshift, but reveal a “downsizing” relationship between ξ ion and stellar mass (M ⊙) with increasing redshift. We further explore the dependence of ξ ion on other galaxy properties, such as the UV spectral slope (β UV), the UV magnitude (M UV), and the equivalent widths of Hα and [O iii] emission lines. Galaxies with bluer UV slopes, fainter UV luminosities, and higher equivalent widths exhibit elevated ξ ion by a factor of ∼2 compared to the median ξ ion of our sample. JWST data will provide an opportunity to extend our method and further investigate the properties of low-mass galaxies at high redshifts.

NGDEEP Epoch 1: Spatially Resolved Hα Observations of Disk and Bulge Growth in Star-forming Galaxies at z ∼ 0.6–2.2 from JWST NIRISS Slitless Spectroscopy

We study the Hα equivalent width (EW(Hα)) maps of 19 galaxies at 0.6 < z < 2.2 in the Hubble Ultra Deep Field using NIRISS slitless spectroscopy as part of the Next Generation Deep Extragalactic Exploratory Public Survey. Our galaxies mostly lie on the star formation main sequence with stellar masses between 109 and 1011 M ⊙, characterized as “typical” star-forming galaxies at these redshifts. Leveraging deep Hubble Space Telescope and JWST images, spanning 0.4–4.8 μm, we perform spatially resolved fitting of the spectral energy distributions for these galaxies and construct specific star formation rate (sSFR) and stellar-mass-weighted age maps with a spatial resolution of ∼1 kpc. The pixel-to-pixel EW(Hα) increases with increasing sSFR and with decreasing age. The average trends are slightly different from the relations derived from integrated fluxes of galaxies from the literature, suggesting complex evolutionary trends within galaxies. We quantify the radial profiles of EW(Hα), sSFR, and age. The majority (84%) of galaxies show positive EW(Hα) gradients, in line with the inside-out quenching scenario. A few galaxies (16%) show inverse (and flat) EW(Hα) gradients, possibly due to merging or starbursts. We compare the distributions of EW(Hα) and sSFR to star formation history (SFH) models as a function of galactocentric radius. We argue that the central regions of galaxies have experienced at least one rapid star formation episode, which leads to the formation of the bulge, while their outer regions (e.g., disks) grow via more smoothly varying SFHs. These results demonstrate the ability to study resolved star formation in distant galaxies with JWST NIRISS.

The Factory and the Beehive. V. Chromospheric and Coronal Activity and Its Dependence on Rotation in Praesepe and the Hyades

Low-mass (≲1.2 M ⊙) main-sequence stars lose angular momentum over time, leading to a decrease in their magnetic activity. The details of this rotation–activity relation remain poorly understood, however. Using observations of members of the ≈700 Myr old Praesepe and Hyades open clusters, we aim to characterize the rotation–activity relation for different tracers of activity at this age. To complement published data, we obtained new optical spectra for 250 Praesepe stars, new X-ray detections for 10, and new rotation periods for 28. These numbers for Hyads are 131, 23, and 137, respectively. The latter increases the number of Hyads with periods by 50%. We used these data to measure the fractional Hα and X-ray luminosities, L Hα /L bol and L X/L bol, and to calculate Rossby numbers R o. We found that at ≈700 Myr almost all M dwarfs exhibit Hα emission, with binaries having the same overall color–Hα equivalent width distribution as single stars. In the R o–L Hα /L bol plane, unsaturated single stars follow a power law with index β = −5.9 ± 0.8 for R o > 0.3. In the R o–L X/L bol plane, we see evidence for supersaturation for single stars with R o ≲ 0.01, following a power law with index βsup=0.5−0.1+0.2 , supporting the hypothesis that the coronae of these stars are being centrifugally stripped. We found that the critical R o value at which activity saturates is smaller for L X/L bol than for L Hα /L bol. Finally, we observed an almost 1:1 relation between L Hα /L bol and L X/L bol, suggesting that both the corona and the chromosphere experience similar magnetic heating.

The star formation histories of galaxies in different stages of pre-processing in the Fornax A group

ABSTRACT We study the recent star formation histories of 10 galaxies in the Fornax A galaxy group, on the outskirts of the Fornax cluster. The group galaxies are gas-rich, and their neutral atomic hydrogen (H i) was studied in detail with observations from the MeerKAT telescope. This allowed them to be classified into different stages of pre-processing (early, ongoing, advanced). We use long-slit spectra obtained with the South African Large Telescope (SALT) to analyse stellar population indicators to constrain quenching time-scales and to compare these to the H i gas content of the galaxies. The H α equivalent width, EW(H α), suggest that the pre-processing stage is closely related to the recent (&amp;lt;10 Myr) specific Star Formation Rate (sSFR). The early-stage galaxy (NGC 1326B) is not yet quenched in its outer parts, while the ongoing-stage galaxies mostly have a distributed population of very young stars, though less so in their outer parts. The galaxies in the advanced stage of pre-processing show very low recent sSFR in the outer parts. Our results suggest that NGC 1326B, FCC 35, and FCC 46 underwent significantly different histories from secular evolution during the last Gyr. The fact that most galaxies are on the secular evolution sequence implies that pre-processing has a negligible effect on these galaxies compared to secular evolution. We find EW(H α) to be a useful tool for classifying the stage of pre-processing in group galaxies. The recent sSFR and H i morphology show that galaxies in the Fornax A vicinity are pre-processing from the outside in.

Probing stellar populations and interstellar medium in early-type central galaxies

ABSTRACT In this study, we analyse the characteristics of stellar populations and the interstellar medium (ISM) in 15 107 early-type central galaxies from the SPIDER survey. Using optical spectra from the Sloan Digital Sky Survey (SDSS), we investigate stellar age (Age), metallicity (Z), visual extinction (AV), and H α equivalent width (EWH α) to understand the evolution of the baryonic content in these galaxies. Our analysis explores the relationship between these properties and central velocity dispersion (σ) and halo mass (Mhalo) for isolated centrals (ICs) and group centrals (GCs). Our results confirm that both ICs and GCs’ stellar populations and gas properties are mainly influenced by σ, with Mhalo playing a secondary role. Higher σ values correspond to older, more metal-rich stellar populations in both ICs and GCs. Moreover, fixed σ values we observe younger Ages at higher values of Mhalo, a consistent trend in both ICs and GCs. Furthermore, we investigate the ionization source of the warm gas and propose a scenario where the properties of ionized gas are shaped by a combination of cooling within the intracluster medium (ICM) and feedback from Active Galactic Nuclei (AGNs) assuming a Bondi accretion regime. We observe inherent differences between ICs and GCs, suggesting that the ratio between AGN kinetic power and ICM thermal energy influences EWH α in ICs. Meanwhile, gas deposition in GCs appears to involve a more complex interplay beyond a singular AGN–ICM interaction.

Disentangling the two sub-populations of early Herbig Be stars using VLT/X-shooter spectra

Context. Early Herbig Be (HBe) stars are massive, young stars accreting through the boundary layer mechanism. However, given the rapid (&lt;2 Myr) evolution of early Herbig stars to the main-sequence phase, studying the evolution of the circumstellar medium around these stars can be a cumbersome exercise. Aims. In this work, we study the sample of early (B0–B5) HBe stars using the correlation between Hα emission strength and near–infrared excess, complemented by the analysis of various emission features in the X-shooter spectra. Methods. We segregate the sample of 37 early HBe stars based on the median values of Hα equivalent width (EW) and near–infrared index (n(J–H)) distributions. The stars with |Hα EW| &gt; 50 Å and n(J–H) &gt; −2 are classified as intense HBe stars and stars with |Hα EW| &lt; 50 Å and n(J–H) &lt; −2 as weak HBe stars. Using the VLT/X–shooter spectra of five intense and eight weak HBe stars, we visually checked for the differences in intensity and profiles of various HI and metallic emission lines commonly observed in Herbig stars. Results. We propose that the intense HBe stars possess an inner disk close to the star (as apparent from the high near-infrared excess) and an active circumstellar environment (as seen from the high Hα EW value and presence of emission lines belonging to FeII, CaII, OI, and [OI]). However, for weak HBe stars, the inner disk has cleared, and the circumstellar environment appears more evolved than for intense HBe stars. Furthermore, we compiled a sample of ~58 000 emission-line stars published in Gaia DR3 to identify more intense HBe candidates. Further spectroscopic studies of these candidates will help us to understand the evolution of the inner (approximately a few au) disk in early HBe stars.

A characterization of ASAS-SN core-collapse supernova environments with VLT+MUSE

Context. The analysis of core-collapse supernova (CCSN) environments can provide important information on the life cycle of massive stars and constrain the progenitor properties of these powerful explosions. The MUSE instrument at the Very Large Telescope (VLT) enables detailed local environment constraints of the progenitors of large samples of CCSNe. Using a homogeneous SN sample from the All-Sky Automated Survey for Supernovae (ASAS-SN) survey, an untargeted and spectroscopically complete transient survey, has enabled us to perform a minimally biased statistical analysis of CCSN environments. Aims. We analyze 111 galaxies observed by MUSE that hosted 112 CCSNe – 78 II, nine IIn, seven IIb, four Ic, seven Ib, three Ibn, two Ic-BL, one ambiguous Ibc, and one superluminous SN – detected or discovered by the ASAS-SN survey between 2014 and 2018. The majority of the galaxies were observed by the All-weather MUse Supernova Integral field Nearby Galaxies (AMUSING) survey. Here we analyze the immediate environment around the SN locations and compare the properties between the different CCSN types and their light curves. Methods. We used stellar population synthesis and spectral fitting techniques to derive physical parameters for all H II regions detected within each galaxy, including the star formation rate (SFR), Hα equivalent width (EW), oxygen abundance, and extinction. Results. We found that stripped-envelope supernovae (SESNe) occur in environments with a higher median SFR, Hα EW, and oxygen abundances than SNe II and SNe IIn/Ibn. Most of the distributions have no statistically significant differences, except between oxygen abundance distributions of SESNe and SNe II, and between Hα EW distributions of SESNe and SNe II. The distributions of SNe II and IIn are very similar, indicating that these events explode in similar environments. For the SESNe, SNe Ic have higher median SFRs, Hα EWs, and oxygen abundances than SNe Ib. SNe IIb have environments with similar SFRs and Hα EWs to SNe Ib, and similar oxygen abundances to SNe Ic. We also show that the postmaximum decline rate, s, of SNe II correlates with the Hα EW, and that the luminosity and the Δm15 parameter of SESNe correlate with the oxygen abundance, Hα EW, and SFR at their environments. This suggests a connection between the explosion mechanisms of these events to their environment properties.

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

ABSTRACT We present spaxel-by-spaxel stellar population fits for the ∼10 000 MaNGA data cubes. We provide multiple extension fits files, nominated as megacubes, with maps of several properties as well as emission-line profiles that are provided for each spaxel. All the megacubes are available through a web interface (https://manga.linea.org.br/ or http://www.if.ufrgs.br/~riffel/software/megacubes/). We also defined a final Active Galactic Nuclei (AGN) sample, as well as a control sample matching the AGN host galaxy properties. We have analysed the stellar populations and spatially resolved emission-line diagnostic diagrams of these AGNs and compared them with the control galaxies sample. We find that the relative fractions of young (t ≤56 Myr) and intermediate-age (100 Myr ≤t ≤ 2 Gyr) show predominantly a positive gradient for both AGNs and controls. The relative fraction of intermediate-age stellar population is higher in AGN hosts when compared to the control sample, and this difference becomes larger for higher [O iii] luminosity AGNs. We attribute this to the fact that extra gas is available in these more luminous sources and that it most likely originates from mass-loss from the intermediate-age stars. The spatially resolved diagnostic diagrams reveal that the AGN emission is concentrated in the inner 0.5 Re (effective radius) region of the galaxies, showing that the AGN classification is aperture dependent and that emission-line ratios have to be taken together with the H α equivalent width for proper activity classification. We present a composite ‘BPT+WHAN’ diagram that produces a more comprehensive mapping of the gas excitation.

Photometric determination of the mass accretion rates of pre-main-sequence stars

Aims. We study the properties of low-mass stars recently formed in the field of the NGC 376 cluster in the Small Magellanic Cloud (SMC). Methods. Using photometric observations acquired with the Hubble Space Telescope (HST) in the V, I, and Hα bands, we identify 244 candidate pre-main-sequence (PMS) stars showing Hα excess emission at the 5σ level and with Hα equivalent width of 20 Å or more. We derive physical parameters for all PMS stars, including masses, ages, and mass accretion rates. We compare the effective mass accretion rate of stars in NGC 376 to that of objects in the NGC 346 cluster, with NGC 346 featuring similar metallicity but higher total mass and gas density. Results. We find a median age of 28 Myr for this population (with 25th and 75th percentiles at about 20 and 40 Myr, respectively), in excellent agreement with previous studies of massive stars in the same field. The PMS stars are rather uniformly distributed across the field, whereas massive stars are more clustered. The spatial distribution of PMS objects is compatible with them having formed in the centre of the cluster and then migrating outwards. We find that in NGC 376 the mass accretion rate is systematically lower than in NGC 346 for stars of the same mass and age. This indicates that, in addition to metallicity, there are other environmental factors affecting the rate of mass accretion onto PMS stars. Our observations suggest that the gas density in the star-forming region might play a role.

Active Stars in the Spectroscopic Survey of Mid-to-late M Dwarfs within 15 pc

We present results from the volume-complete spectroscopic survey of 0.1–0.3 M ⊙ M dwarfs within 15 pc. This work discusses the active sample without close binary companions, providing a comprehensive picture of these 123 stars with Hα emission stronger than −1 Å. Our analysis includes rotation periods (including 31 new measurements), Hα equivalent widths, rotational broadening, inclinations, and radial velocities, determined using high-resolution, multiepoch spectroscopic data from the TRES and CHIRON spectrographs supplemented by photometry from TESS and MEarth. Using this volume-complete sample, we establish that the majority of active, low-mass M dwarfs are very rapid rotators: specifically, 74% ± 4% have rotation periods shorter than 2 days, while 19% ± 4% have intermediate rotation periods of 2–20 days, and the remaining 8% ± 3% have periods longer than 20 days. Among the latter group, we identify a population of stars with very high Hα emission, which we suggest is indicative of dramatic spindown as these stars transition from the rapidly rotating mode to the slowly rotating one. We are unable to determine rotation periods for six stars and suggest that some of the stars without measured rotation periods may be viewed pole-on, as such stars are absent from the distribution of inclinations we measure; this lack notwithstanding, we recover the expected isotropic distribution of spin axes. Our spectroscopic and photometric data sets also allow us to investigate activity-induced radial-velocity variability, which we show can be estimated as the product of rotational broadening and the photometric amplitude of spot modulation.

GaiaData Release 3

GaiaData Release 3 contains a wealth of new data products for the community. Astrophysical parameters are a major component of this release, and were produced by the Astrophysical parameters inference system (Apsis) within theGaiaData Processing and Analysis Consortium (DPAC). The aim of this paper is to describe the overall content of the astrophysical parameters inGaiaDR3 and how they were produced. In Apsis, we use the mean BP/RP and mean RVS spectra along with astrometry and photometry, and we derive the following parameters: source classification and probabilities for 1.6 billion objects; interstellar medium characterisation and distances for up to 470 million sources, including a 2D total Galactic extinction map; 6 million redshifts of quasar candidates; 1.4 million redshifts of galaxy candidates; and an analysis of 50 million outlier sources through an unsupervised classification. The astrophysical parameters also include many stellar spectroscopic and evolutionary parameters for up to 470 million sources. These compriseTeff, logg, and [M/H] (470 million using BP/RP, 6 million using RVS), radius (470 million), mass (140 million), age (120 million), chemical abundances (up to 5 million), diffuse interstellar band analysis (0.5 million), activity indices (2 million), Hαequivalent widths (200 million), and further classification of spectral types (220 million) and emission-line stars (50 000). This paper is the first in a series of three papers, and focusses on describing the global content of the parameters inGaiaDR3. The accompanying Papers II and III focus on the validation and use of the stellar and non-stellar products, respectively. This catalogue is the most extensive homogeneous database of astrophysical parameters to date, and is based uniquely onGaiadata. It will only be superseded byGaiaData Release 4, and will therefore remain a key reference over the next four years, providing astrophysical parameters independent of other ground- and space-based data.

GaiaData Release 3

Context.The thirdGaiadata release (GaiaDR3) contains, beyond the astrometry and photometry, dispersed light for hundreds of millions of sources from theGaiaprism spectra (BP and RP) and the spectrograph (RVS). This data release opens a new window on the chemo-dynamical properties of stars in our Galaxy, essential knowledge for understanding the structure, formation, and evolution of the Milky Way.Aims.To provide insight into the physical properties of Milky Way stars, we used these data to produce a uniformly derived all-sky catalogue of stellar astrophysical parameters: atmospheric properties (Teff, logg, [M/H], [α/Fe], activity index, emission lines, and rotation), 13 chemical abundance estimates, evolution characteristics (radius, age, mass, and bolometric luminosity), distance, and dust extinction.Methods.We developed the astrophysical parameter inference system (Apsis) pipeline to infer astrophysical parameters ofGaiaobjects by analysing their astrometry, photometry, BP/RP, and RVS spectra. We validate our results against those from other works in the literature, including benchmark stars, interferometry, and asteroseismology. Here we assess the stellar analysis performance from Apsis statistically.Results.We describe the quantities we obtained, including the underlying assumptions and the limitations of our results. We provide guidance and identify regimes in which our parameters should and should not be used.Conclusions.Despite some limitations, this is the most extensive catalogue of uniformly inferred stellar parameters to date. They compriseTeff, logg, and [M/H] (470 million using BP/RP, 6 million using RVS), radius (470 million), mass (140 million), age (120 million), chemical abundances (5 million), diffuse interstellar band analysis (half a million), activity indices (2 million), Hαequivalent widths (200 million), and further classifications of spectral types (220 million) and emission-line stars (50 thousand). More precise and detailed astrophysical parameters based on epoch BP, RP, and RVS spectrophotometry are planned for the nextGaiadata release.

Magnetic Activity of Different Types of Variable Stars Observed by TESS Mission

The investigation of the magnetic activity of different types of variable stars holds significant implications for our understanding of the physical processes and evolution of stars. This study’s International Variable Star Index (VSX) variable star catalog was cross-matched with Transiting Exoplanet Survey Satellite (TESS) data, resulting in 26,276 labeled targets from 76,187 light curves. A total of 25,327 stellar flare events were detected, including 245 eclipsing binaries, 2324 rotating stars, 111 pulsating stars, and 629 eruptive stars. The results showed that flares from eclipsing binaries, rotating stars, eruptive stars, and pulsating stars have durations such that 90% are less than 2 h, and 91% of their amplitudes are less than 0.3. Flare events mainly occurred in the temperature range of 2000 K to 3000 K. The power-law indices of different types of variable stars were 1.72±0.025 (eclipsing binaries), 1.82±0.062 (rotating stars), 1.80±0.0116 (eruptive stars), and 1.73±0.060 (pulsating stars). Among them, the flare energy of pulsating stars is more concentrated in the high-energy range. In all samples, flare energies were distributed from 3.99×1031 erg to 6.18×1038 erg. The LAMOST DR9 low-resolution spectral survey has provided Hα equivalent widths for 398 variable stars. By utilizing these Hα equivalent widths, we have determined the stellar activity of the variable stars and confirmed a positive correlation between the flare energy and Hα equivalent width.

The Lyα Reference Sample. XIV. Lyα Imaging of 45 Low-redshift Star-forming Galaxies and Inferences on Global Emission

We present Lyα imaging of 45 low-redshift star-forming galaxies observed with the Hubble Space Telescope. The galaxies have been selected to have moderate to high star formation rates (SFRs) using far-ultraviolet (FUV) luminosity and Hα equivalent width criteria, but no constraints on Lyα luminosity. We employ a pixel stellar continuum fitting code to obtain accurate continuum-subtracted Lyα, Hα, and Hβ maps. We find that Lyα is less concentrated than FUV and optical line emission in almost all galaxies with significant Lyα emission. We present global measurements of Lyα and other quantities measured in apertures designed to capture all of the Lyα emission. We then show how the escape fraction of Lyα relates to a number of other measured quantities (mass, metallicity, star formation, ionization parameter, and extinction). We find that the escape fraction is strongly anticorrelated with nebular and stellar extinction, weakly anticorrelated with stellar mass, but no conclusive evidence for correlations with other quantities. We show that Lyα escape fractions are inconsistent with common dust extinction laws, and discuss how a combination of radiative transfer effects and clumpy dust models can help resolve the discrepancies. We present an SFR calibration based on Lyα luminosity, where the equivalent width of Lyα is used to correct for nonunity escape fraction, and show that this relation provides a reasonably accurate SFR estimate. We also show stacked growth curves of Lyα for the galaxies that can be used to find aperture loss fractions at a given physical radius.

Contemporaneous Observations of Hα Luminosities and Photometric Amplitudes for M Dwarfs

While many M dwarfs are known to have strong magnetic fields and high levels of magnetic activity, we are still unsure about the properties of their starspots and the origin of their magnetic dynamos. Both starspots and chromospheric heating are generated by the surface magnetic field; they produce photometric variability and Hα emission, respectively. Connecting brightness variations to magnetic activity therefore provides a means to examine M-dwarf magnetism. We survey 30 M dwarfs previously identified as fast rotating stars (P rot < 10 days). We present time-series optical photometry from the Transiting Exoplanet Survey Satellite (TESS) and contemporaneous optical spectra obtained using the Ohio State Multi-Object Spectrograph (OSMOS) on the 2.4 m Hiltner telescope at MDM Observatory in Arizona. We measure rotation periods and photometric amplitudes from TESS light curves using Gaussian Processes. From the OSMOS spectra, we calculate the equivalent width of Hα, and L Hα /L bol. We find a weak positive correlation between Hα luminosity and the semiamplitude, R var (). We also observe short-term variability (between 20 and 45 minutes) in Hα equivalent widths and possible enhancement from flares consistent to recent literature.