Hα Emission Research Articles

An Hα view of galaxy buildup in the first 2 Gyr: Luminosity functions at z∼4-6.5 from NIRCam/grism spectroscopy

The Hα nebular emission line is an optimal tracer for recent star formation in galaxies. With the advent of JWST this line has recently become observable at z>3 for the first time. We present a catalog of $1,050$ Hα emitters at $3.7<z<6.7$ in the GOODS fields obtained from a blind search in JWST NIRCam/grism data. We made use of the FRESCO survey's 124 arcmin^2 of observations in GOODS-North and GOODS-South with the F444W filter, probing Hα at $4.9<z<6.7$, and the CONGRESS survey's 62 arcmin^2 of observations in GOODS-North with F356W, probing Hα at $3.8<z<5.1$. We found an overdensity with 98 sources at z∼4.4 in GOODS-N, and confirmed previously reported overdensities at z∼5.2 in GOODS-N and at z∼5.4 and z∼ 5.9 in GOODS-S. We computed the observed Hα luminosity functions (LFs) in three bins centered at z∼4.45, $5.30$, and $6.15$, which are the first such measurements at z>3 obtained based purely on spectroscopic data, robustly tracing galaxy star formation rates (SFRs) beyond the peak of the cosmic star formation history. We compared our results with theoretical predictions from three different simulations and found good agreement at z∼4-6. The UV LFs of this spectroscopically confirmed sample are in good agreement with pre- JWST measurements obtained with photometrically selected objects. Finally, we derived SFR functions and integrated them to compute the evolution of the cosmic SFR densities across z∼4-6, finding values in good agreement with recent UV estimates from Lyman-break galaxies, which imply a continuous decrease in SFR density by a factor of three over z∼4 to z∼6. Our work shows the power of NIRCam grism observations to efficiently provide new tests for early galaxy formation models based on emission line statistics.

Physical properties of circumnuclear ionising clusters II. NGC 7469

Circumnuclear star-forming regions (CNSFRs) found close to galactic nuclei are ionised by massive clusters. These entities give us an excellent opportunity to study star formation in environments with high metallicity, and to relate it with active galactic nuclei. Our principal aim is to derive the physical properties and dynamical masses of the CNSFRs in the two rings of the spiral NGC 7469, categorised as a luminous infrared galaxy (LIRG) and hosting a Seyfert 1 nucleus. We used archival data obtained with the MUSE spectrograph. The galaxy shows two prominent star-forming rings, one of them very close to their active galactic nucleus, within 1.5 arcsec from the galaxy centre. We constructed 2D flux maps of the different emission lines and two continuum bands. A map of the EW(Hα) emission shows the circumnuclear regions within the rings having EW(Hα) > 50 Å, consistent with the presence of recent star formation. All emission lines appear to have at least two kinematical components. We ascribe the most intense and narrow component to the emission lines originated by the ionising star-forming complexes (SFC) since they follow the radial velocity of the galaxy disc. For each HII region, we derived the number rate of Lyman continuum photons; the gas electron density; the ionisation parameter; the filling factor; and the mass of ionised hydrogen. We used sulphur as a tracer for chemical abundances with the temperature-sensitive SIII λ 6312 Å emission line having been measured in ∼ 50 % of the total, allowing the derivation of abundances by the direct method. The evolutionary state of the SFC was inferred with the help of population synthesis models yielding mean ages of 5.7 Ma, agreeing with the presence of the broad Wolf--Rayet (WR) carbon feature at λ 5800 Å detected in all the regions. Ionising (lower limits) and photometric SFC masses were estimated from the number of Lyman continuum photons and absolute r-magnitudes using stellar population synthesis techniques, and give median values of 2.3 times 10^6 and 6.9 times 10^6, respectively. The dynamical masses (upper limit) were derived from the measured absorption CaT velocity dispersion and the sizes of each cluster were measured on continuum light, assuming virialisation, and yield a median value of 6.7 times 10^8. Regions in the studied galaxy show sizes larger than implied by simple photo-ionisation models, which can be explained by the stellar winds produced by WR stars. The inner ring regions seem to be more compact than the outer ones. The young stellar population of the clusters has contributions of ionising populations with ages around 5 Ma, and its masses constitute less than 1% of the total dynamical mass of each SFC. Finally, the comparison between the characteristics of the inner and outer ring ionising clusters, together with their derived dynamical masses, point to circumnuclear regions close to the active galactic nucleus being more compact and having higher gas density.

A Be star that turned bright and blue during a major outburst

Classical Be stars are rapidly rotating B-type stars exhibiting Balmer emission lines originating from circumstellar Keplerian gaseous disks, which likely form through episodic mass-ejection events. The currently favored model for Be star disks is the viscous decretion disk (VDD) model. However, the mechanism behind the mass ejection process during the formation of a VDD is a mystery. We present peculiar behavior of the Be star KIC 9715425, which exhibited several minor outbursts (MIBs) and one major outburst (MAB) observed as brightenings in broadband photometry, as well as transient H line emission. The variability may provide valuable keys to understanding the nature of Be outbursts. Based on Kepler the All-Sky Automated Survey for Supernovae (ASAS-SN) and the Transiting Exoplanet Survey Satellite (TESS) time-series photometry, the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopy, multi-wavelength observations in the near-ultraviolet (NUV) from the Galaxy Evolution Explorer (GALEX) and optical from Gaia Xinglong 2.16m telescope and Isaac Newton Telescope (INT) of KIC,9715425 covering its outbursts, we determined fundamental parameters of the central star and the circumstellar disk. A frequency analysis and spectral modeling were carried out to characterize the events. During the major outburst, we find a 36% flux increase in the GALEX NUV band compared to 25% in the Kepler band, suggesting that whatever produced the flux increase should be hotter than the central B-type star. This is contradictory to the conventional scenario that the VDD should be cooler. In addition, such a high flux increase can only be accounted for by a luminous disk, which should produce a much stronger Hα emission than observed. The origin of this anomalously hot component remains unexplained. Except for the bluing, the available observations of KIC 9715425 are perfectly compatible with being a normal Be star. If the bluing was physically related to the MAB, the most economical effort to identify the nature of the underlying process could be adaptive NUV and far-ultraviolet (FUV) monitoring of Be stars with cyclically repeating MABs.

An infrared and far-UV study of jet-induced star formation in the halo of Centaurus A

Centaurus A (Cen A) is the nearest galaxy hosting an active galactic nucleus (AGN), which produces powerful radio and X-ray jets extending to hundreds of kiloparsecs from the center. At 15 kpc northeast (NE) and 12 kpc southwest (SW) in the halo along the jet from the nucleus of Cen A, dust clouds accompanying the Hα emission are detected. For both NE and SW clouds, past studies suggested that star formation may have been induced through interactions between the AGN jet and the surrounding intergalactic media. For these clouds, we performed dust model fitting of infrared (IR) spectral energy distributions (SEDs) created from the archival data of WISE, Spitzer, and Herschel. Then we compare the IR emission properties of the dust clouds with the far-ultraviolet (UV) emission using the archival data of GALEX/FUV. As a result, we find that the interstellar radiation field intensity G0 (and thus the dust temperature) in the NE cloud suggests star formation activity, while that in the SW cloud does not. The local far-UV intensity and G0 in the NE region are significantly larger than those expected for the far-UV radiation originating from the central region of Cen A and its dust-scattered component, respectively. In contrast, the local far-UV intensity and G0 in the SW region are compatible with them. The polycyclic aromatic hydrocarbon (PAH) emission is detected for both NE and SW clouds. The mass abundance ratios of PAH to dust are similar for both clouds and significantly lower than that in the central region of Cen A. We suggest that the dust clouds and the PAHs in the clouds are associated with the broken ring-like structure of H I gas which is thought to be a remnant of the past gas-rich merger and that shocks by the jet responsible for the middle lobe on the north side may have triggered the star formation in the NE cloud.

Spectroscopic confirmation of the galaxy clusters CARLA J0950+2743 at z = 2.363 and CARLA-Ser J0950+2743 at z = 2.243

Galaxy clusters are the largest gravitationally bound structures in the Universe and therefore are a powerful tool for studying mass assembly at different epochs. At z > 2, they provide the unique opportunity to place solid constraints not only on the growth of the dark matter halo, but also on the mechanisms of galaxy quenching and morphological transformation when the Universe was younger than 3.3 Gyr. However, the currently available sample of confirmed z > 2 clusters remains very limited. We present the spectroscopic confirmation of the galaxy cluster CARLA J0950+2743 at z = 2.363 ± 0.005 and a new serendipitously discovered cluster, CARLA-Ser J0950+2743 at z = 2.243 ± 0.008, in the same region. We confirm eight star-forming galaxies in the first and five in the second cluster by detecting [OII], [OIII], and Hα emission lines. The analysis of an archival X-ray Chandra dataset that covers the cluster position revealed a counterpart with a total luminosity of L0.5−5keV = 2.9 ± 0.6 × 1045 erg s−1. Because the depth of the X-ray observations is limited, we cannot distinguish the 1D profile of the source from a point spread function model, but our statistical analysis of the 2D profile favors an extended component that might be associated with a thermal contribution from the intracluster medium. If the extended X-ray emission is due to the hot intracluster medium, the total combined dark matter mass for the two clusters would be M200 ≈ 3.0−0.23(stat)+0.20 −0.85(sys)+1.13 × 1014 M⊙, assuming a ∼30% contribution from the active galactic nucleus. Our two clusters are therefore interesting targets for studies of the structure growth in the cosmological context. However, future investigation will require deeper high-resolution X-ray and spectroscopic observations to rule out the hypotheses that the emission is entirely due to the active galactic nucleus or that it originates from other contaminating radio galaxies and structures.

A dormant overmassive black hole in the early Universe

Recent observations have found a large number of supermassive black holes already in place in the first few hundred million years after the Big Bang, many of which seem to be overmassive relative to their host galaxy stellar mass when compared with local relation1, 2, 3, 4, 5, 6, 7, 8–9. Several different models have been proposed to explain these findings, ranging from heavy seeds to light seeds experiencing bursts of high accretion rate10, 11, 12, 13, 14, 15–16. Yet, current datasets are unable to differentiate between these various scenarios. Here we report the detection, from the JADES survey, of broad Hα emission in a galaxy at z = 6.68, which traces a black hole with a mass of about 4 × 108M⊙ and accreting at a rate of only 0.02 times the Eddington limit. The black hole to host galaxy stellar mass ratio is about 0.4—that is, about 1,000 times above the local relation—whereas the system is closer to the local relations in terms of dynamical mass and velocity dispersion of the host galaxy. This object is most likely an indication of a much larger population of dormant black holes around the epoch of reionization. Its properties are consistent with scenarios in which short bursts of super-Eddington accretion have resulted in black hole overgrowth and massive gas expulsion from the accretion disk; in between bursts, black holes spend most of their life in a dormant state.

The Solar Neighborhood. LII. M Dwarf Twin Binaries—Presumed Identical Twins Appear Fraternal in Variability, Rotation, Hα, and X-Rays

We present an investigation into the rotation and stellar activity of four fully convective M dwarf “twin” wide binaries. Components in each pair have (1) astrometry confirming they are common-proper-motion binaries, (2) Gaia BP, RP, and 2MASS J, H, and K s magnitudes matching within 0.10 mag, and (3) presumably the same age and composition. We report long-term photometry, rotation periods, multiepoch Hα equivalent widths, X-ray luminosities, time series radial velocities, and speckle observations for all components. Although it might be expected for the twin components to have matching magnetic attributes, this is not the case. Decade-long photometry of GJ 1183 AB indicates consistently higher spot activity on A than B, a trend matched by A appearing 58% ± 9% stronger in L X and 26% ± 9% stronger in Hα on average—this is despite similar rotation periods of A = 0.86 day and B = 0.68 day, thereby informing the range in activity for otherwise identical and similarly rotating M dwarfs. The young β Pic Moving Group member 2MA 0201+0117 AB displays a consistently more active B component that is 3.6 ± 0.5 times stronger in L X and 52% ± 19% stronger in Hα on average, with distinct rotation at A = 6.01 days and B = 3.30 days. Finally, NLTT 44989 AB displays remarkable differences with implications for spindown evolution—B has sustained Hα emission while A shows absorption, and B is ≥39 ± 4 times stronger in L X, presumably stemming from the surprisingly different rotation periods of A = 38 days and B = 6.55 days. The last system, KX Com, has an unresolved radial velocity companion, and is therefore not a twin system.

JWST/NIRCam Paβ Narrowband Imaging Reveals Ordinary Dust Extinction for Hα Emitters within the Spiderweb Protocluster at z = 2.16

We combine JWST/NIRCam and Subaru/MOIRCS dual Paβ+Hα narrowband imaging to trace the dust attenuation and the star formation activities of a sample of 43 Hα emitters at the core of one of the most massive and best-studied clusters in formation at the cosmic noon: the Spiderweb protocluster at z = 2.16. We find that most Hα emitters display Paβ/Hα ratios compatible with Case B recombination conditions, which translates into nebular extinction values ranging at AV ≈ 0–3 mag, and dust corrected Paβ star formation rates consistent with coeval main sequence field galaxies at fixed stellar mass ( 9.4<logM*/M⊙<11.0 ) during this cosmic epoch. Furthermore, we investigate possible environmental impacts on dust extinction across the protocluster large-scale structure and find no correlation between the dustiness of its members and environmental proxies such as phase-space position, clustercentric radius, or local density. These results support the scenario for which dust production within the main galaxy population of this protocluster is driven by secular star formation activities fueled by smooth gas accretion across its large-scale structure. This downplays the role of gravitational interactions in boosting star formation and dust production within the Spiderweb protocluster, in contrast with observations in higher redshift and less evolved protocluster cores.

First Comparison of FLARIX Simulations with MSDP Observation of the C1.6 Solar Flare in the Hα Line of Hydrogen

The primary objective of this study is to develop a time-dependent model of the flaring atmosphere based on observational data. Here, we present, for the first time, a comparison between numerical simulations of the flaring emission, specifically focusing on the hydrogen Hα line, utilizing the FLARIX code and spectral observations of a compact C1.6 GOES-class flare observed on 2012 September 10, by the MSDP imaging spectrograph installed at the Białków Observatory. The Multichannel Subtractive Double Pass imaging spectrograph spectral data, collected with a temporal resolution as fine as 50 ms, enabled a comprehensive analysis of Hα line profiles and light curves measured within an area of the flare’s emission. An initial atmospheric model close to VAL-C, with a modified temperature in the upper chromosphere, was employed in simulations. To enhance temporal resolution, modulations of the nonthermal electron (NTE) beam’s parameters were introduced based on variations in observed hard X-ray (HXR) flux (using RHESSI data). The synthesized Hα line profiles were compared with the observed spectra. During the impulsive phase of the flare, the evolution of the observed and synthetic Hα line intensity agrees, but discrepancies were found in intensities at specific wavelengths of the Hα line profile. Fluctuations in the energy flux of NTEs exhibited a strong correlation with the Hα emission during the HXR pulse. After considering various effects (such as the filling factor FF = 0.20) that could influence observed emissions, relatively good agreement between theoretical and observed lines was achieved.

Gleeok’s Fire-breathing: Triple Flares of AT 2021aeuk within Five Years from the Active Galaxy SDSS J161259.83+421940.3

We present a noteworthy transient AT 2021aeuk exhibiting three distinct optical flares between 2018 and 2023. It is hosted in a radio-loud narrow-line Seyfert 1 galaxy, with an optical image showing a minor tidal morphology and a red mid-infrared color (W1 − W2 = 1.1). Flares II and III exhibit rapid rises, and long-term decays (≳1000 days) with recurring after-peak bumps. The g − r color after subtracting the reference magnitude exhibited a rapid drop and recovery during Flare II, followed by a minor after-peak evolution in blue colors. We applied a canonical tidal disruption event (TDE) fitting on the light curves, which gives a decay index p of −2.99−0.14+0.13 for Flare II and −1.61−0.65+0.34 for Flare III. The blackbody fitting shows lower temperatures (∼103.8 K) with minor after-peak evolution. The blackbody radius (≳1016 cm) and luminosity (∼1045 erg s−1) are larger than the typical TDE sample’s. The time lag (in rest frame) between the ZTF g and r bands ( τg,r=3.4−0.9+1.0 days) significantly exceeds the prediction from the standard accretion disk. Pre-burst spectra reveal prominent Bowen fluorescence lines, indicating a vigorous or potentially long-lasting process that enriches the local metallicity. Additionally, we derived black hole masses of logM•=7.09−0.31+0.18M⊙ and logM•=7.52−0.10+0.08M⊙ using Hβ and Hα emission lines. The variation and recurring features of AT 2021aeuk are not likely induced by the radio-beaming effect or Type II superluminous supernova; however, we cannot rule out the possibility of TDE or enhanced active galactic nuclei accretion process. The unusually high occurrence of three flares within 5 yr may also induced by the complex local environment.

Mass evolution of broad-line regions to explain the luminosity variability of broad Hα in the tidal disruption event ASASSN-14li

We propose an oversimplified model to explain the different variability trends in the observed broad Hα emission line luminosity, LHα(t), and the tidal disruption event (TDE) model-determined bolometric luminosity, Lbol(t), of the TDE ASASSN-14li. Assuming that broad emission line regions (BLRs) in the central accretion disk are related to materials accreted onto the central black hole of a TDE, the mass evolution of central BLRs, MBLRs(t), can be determined as the maximum mass, MBLRs, 0, of central BLRs minus the corresponding accreted mass in a TDE. Meanwhile, through the simple linear dependence of broad Balmer emission line luminosity on the mass of BLRs, the mass evolution of central BLRs, MBLRs(t), can be applied to describe the observed LHα(t). Although our proposed model is oversimplified – with only one free model parameter, MBLRs, 0 – with MBLRs, 0 ∼ 0.02 M⊙, it describes the observed LHα(t) in the TDE ASASSN-14li well. Meanwhile, the oversimplified model also roughly describes the observed LHα(t) in the TDE ASASSN-14ae. The reasonable descriptions of the observed LHα(t) in ASASSN-14li and ASASSN-14ae indicate that our oversimplified model is probably efficient enough to describe mass evolutions of MBLRs related to central accreted debris in TDEs.

Revealing the Quiescent Galaxy Population in the Spiderweb Protocluster at z = 2.16 with Deep HST/WFC3 Slitless Spectroscopy

We report the Hubble Space Telescope Wide Field Camera 3 G141 grism slitless spectroscopy observation of the core region of the Spiderweb protocluster at z = 2.16. We analyzed the spectra of all objects in a ∼2×2arcmin2 field of view and identified 40 protocluster members, recovering 19 previously identified Hα emitters in addition to revealing 21 new members. The spectra allowed us to identify 11 galaxies with quiescent spectra. In all, 3 galaxies with quiescent spectra are possibly still star forming according to spectral energy distribution fitting, indicating a possible leftover or dust-obscured star formation. We estimate a quiescent fraction of ∼50% for M ⋆ > 1011 M ⊙. About half of the quiescent galaxies possibly host an active galactic nucleus (AGN), hinting at AGN’s key role in quenching galaxies in the protocluster environment. These quiescent galaxies have relatively more compact and concentrated light profiles than the star-forming members, but they are not yet as bulge dominated as local ellipticals. These results are consistent with previous studies that indicate the Spiderweb protocluster is in the maturing stage, with a red sequence that has begun forming.

JWST/NIRCam Narrowband Survey of Paβ Emitters in the Spiderweb Protocluster at z = 2.16

We report the initial result of our Paβ narrowband imaging on a protocluster with the JWST Near Infrared Camera (NIRCam). As NIRCam enables deep narrowband imaging of rest-frame near-infrared lines at z > 1, we target one of the most studied protoclusters, the Spiderweb protocluster at z = 2.16, in which previous studies have confirmed more than a hundred member galaxies. The NIRCam F405N narrowband filter covers in the Paβ line the protocluster redshift given by known protocluster members, allowing for the search for new member candidates. The weight-corrected color–magnitude diagram obtained 57 sources showing narrowband excesses, 41 of which satisfy further color selection criteria for limiting the sample to Paβ emitter candidates at z ∼ 2.16, and 24 of them do not have Hα emitter counterparts. The Paβ emitter candidates appear to follow the spatial distribution of known protocluster members; however, follow-up spectroscopic confirmation is required. Only 17 out of 58 known Hα-emitting cluster members are selected as Paβ emitters in the current data, albeit the rest fall out of the narrowband selection owing to their small Paβ equivalent widths. We derive the Paβ luminosity function in the Spiderweb protocluster, showing a normalization density of logϕ*=−2.53±0.15 at a characteristic Paβ luminosity of logL*=42.33±0.17 . Furthermore, we examine the possibility of detecting faint line emitters visible only in the narrowband image but find no promising candidates.

Extreme ionizing properties of a metal-poor, MUV ≃ −12 star complex in the first gigayear

We report the serendipitous discovery of a faint (MUV &gt; −12.2), low-metallicity (Z ∼ 0.02 Z⊙) ionizing source, dubbed T2c, with a spectroscopic redshift of z = 6.146. T2c is part of a larger structure amplified by the Hubble Frontier Field galaxy cluster MACSJ0416 and was observed with the James Webb Space Telescope (JWST) NIRSpec integral field unit. Stacking the short-wavelength NIRCam data reveals no stellar continuum detection down to a magnitude limit of mUV ≃ 31.0 (3σ). However, prominent Hβ, [O III]λλ4959, 5007, and Hα emissions are detected, with equivalent widths exceeding 200 Å, 800 Å, and 1300 Å (3σ), respectively. The corresponding intrinsic (magnification-corrected ×23 ± 3) ultraviolet and optical rest-frame magnitudes exceed 34.4 and 33.9 (corresponding to MUV and Mopt fainter than −12.2 and −12.8 at λrest ∼ 2000 Å and ∼5000 Å, respectively), suggesting a stellar mass lower than a few 104 M⊙ under an instantaneous burst scenario. The inferred ionizing photon production efficiency (ξion) is high: ξion ≳ 26.08(25.86) 3(5)σ, assuming no dust attenuation and no Lyman continuum leakage. This indicates the presence of massive stars despite the low mass of the object. The very poor sampling of the initial mass function in such a low-mass star-forming complex suggests that the formation of very massive stars might be favored in very low-metallicity environments. T2c is surrounded by Balmer and weak oxygen emission on a spatial scale of a few hundred parsecs, after correcting for lensing effects. This system resembles a H II region potentially powered by currently undetected, extremely efficient, low-metallicity star complexes or clusters. We propose that massive O-type stars populate these low-mass, low-metallicity, high-redshift satellites, likely observed in an early and short formation phase, and contribute to the ionization of the surrounding medium.

The First Combined Hα and Rest-UV Spectroscopic Probe of Galactic Outflows at High Redshift

We investigate the multiphase structure of gas flows in galaxies. We study 80 galaxies during the epoch of peak star formation (1.4 ≤ z ≤ 2.7) using data from the Keck/Low-Resolution Imaging Spectrometer (LRIS) and the Very Large Telescope/K-Band Multi-Object Spectrograph (KMOS). Our analysis provides a simultaneous probe of outflows using UV emission and absorption features and Hα emission. With this unprecedented data set, we examine the properties of gas flows estimated from LRIS and KMOS in relation to other galaxy properties, such as star formation rate (SFR), SFR surface density (ΣSFR), stellar mass (M *), and main-sequence offset (ΔMS). We find no strong correlations between outflow velocity measured from rest-UV line centroids and galaxy properties. However, we find that galaxies with detected outflows show higher averages in SFR, ΣSFR, and ΔMS than those lacking outflow detections, indicating a connection between outflow and galaxy properties. Furthermore, we find a lower average outflow velocity than previously reported, suggesting greater absorption at the systemic redshift of the galaxy. Finally, we detect outflows in 49% of our LRIS sample and 30% in the KMOS sample and find no significant correlation between outflow detection and inclination. These results may indicate that outflows are not collimated and that Hα outflows have a lower covering fraction than low-ionization interstellar absorption lines. Additionally, these tracers may be sensitive to different physical scales of outflow activity. A larger sample size with a wider dynamic range in galaxy properties is needed to further test this picture.

Silencing the Giant: Evidence of Active Galactic Nucleus Feedback and Quenching in a Little Red Dot at z = 4.13

The James Webb Space Telescope (JWST) has uncovered a ubiquitous population of dust-obscured compact sources at z ≳ 4. Many of these objects exhibit signs of active galactic nucleus (AGN) activity, making their study crucial for understanding the formation of supermassive black holes (SMBHs) and their growth with host galaxies. In this work, we examine low and medium-resolution JWST/NIRSpec spectra from the JADES GTO public data release in the GOODS-N field of a red, luminous (M B ∼ −22.2 mag) and compact (<500 pc) source at z = 4.13. The rest-optical (λ rest > 4000 Å) continuum of this source is strongly dominated by a massive (log10[M */M ⊙] ∼ 10.6), quenched (log10[sSFR/yr−1] < −11) galaxy, as indicated by the clear presence of a Balmer break and stellar absorption lines. Star formation history modeling reveals a starburst episode followed by rapid quenching about 200 Myr ago. The spectrum shows extremely broad (FWHM ∼2500 km s−1) Hα emission and elevated optical line ratios, indicating an actively accreting SMBH. Moreover, our work has potentially revealed clear AGN signatures in the rest-UV in little red dots for the first time via the detection of a strong Lyα emission and a broad Mg ii doublet. The derived black hole mass of log10(M BH/M ⊙) ∼ 7.3 results in M BH/M * ∼ 0.04%, consistent with the local relations, unlike the elevated ratios in other high-z reddened AGN. Finally, we use JWST data from AGN at z = 4–10 to explore an evolutionary link between high-z reddened AGN, early quiescent galaxies, and local ellipticals.

Spatially Resolved Comparison of SFRs from UV and Hα in GASP Gas-stripped Galaxies

Star formation rates (SFRs) in galaxies offer a view of various physical processes across them, and are measured using various tracers, such as Hα and ultraviolet (UV). Different physical mechanisms can affect Hα and UV emission, resulting in a discrepancy in the corresponding SFR estimates (ΔSFR). We investigate the effects of ram pressure on the SFR measurements and ΔSFR across five galaxies from the GASP survey caught in the late stages of gas stripping due to ram pressure. We probe spatially resolved ΔSFR at pixel scales of 0.5 kpc, and compare disks to tails and regions dominated by the dense gas to diffuse ionized gas (DIG) regions. The regions dominated by dense gas show similar SFR values for UV and Hα tracers, while the regions dominated by the DIG show up to 0.5 dex higher SFR(UV). There is a large galaxy-by-galaxy variation in ΔSFR, with no difference between the disks and the tails. We discuss the potential causes of variations in ΔSFR between the dense gas and DIG areas. We conclude that the dominant cause of discrepancy are recent variations in star formation histories, where star formation recently dropped in the DIG-dominated regions leading to changes in ΔSFR. The areal coverage of the tracers shows areas with Hα and no UV emission; these areas have LINER-like emission (excess in [O i λ6300]/Hα line ratio), indicating that they are ionized by processes other than star formation.

Widespread Rapid Quenching at Cosmic Noon Revealed by JWST Deep Spectroscopy

Massive quiescent galaxies in the young Universe are expected to be quenched rapidly, but it is unclear whether they all experience starbursts before quenching and what physical mechanism drives rapid quenching. We study 14 massive quiescent galaxies ( log(M⋆/M⊙)>10 ) at z ∼ 2 selected from a representative sample of the Blue Jay survey. We reconstruct their star formation histories (SFHs) by fitting spectral energy distribution models to the JWST/NIRSpec R ∼ 1000 spectra. We find that massive quiescent galaxies can be split into three categories with roughly equal numbers of galaxies according to their SFHs: (1) relatively old galaxies quenched at early epochs; (2) galaxies that are rapidly and recently quenched after a flat or bursty formation history (depending on the assumed prior); and (3) galaxies that are rapidly and recently quenched after a major starburst. Most recently quenched galaxies show neutral gas outflows, probed by blueshifted Na i D absorption, and ionized gas emission, with line ratios consistent with active galactic nucleus (AGN) diagnostics. This suggests that AGN activity drives multiphase gas outflows, leading to rapid quenching. By tracing back the SFHs of the entire sample, we predict the number density of massive quiescent galaxies at z = 4–6: n = (1.5–6.0) × 10−5 Mpc−3. The two old massive quiescent galaxies in our sample appear to have extremely early formation and quenching (z ≳ 6) and are possibly descendants of early post-starbursts at z > 3. These galaxies still show neutral gas reservoirs and weak Hα emission, perhaps because the ejective AGN feedback that caused rapid quenching has weakened over time.

ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY)

Context. Accretion among planetary mass companions is a poorly understood phenomenon, due to the lack of both observational and theoretical studies. The detection of emission lines from accreting gas giants facilitates detailed investigations into this process. Aims. This work presents a detailed analysis of Balmer lines from one of the few known young, planetary-mass objects with observed emission, the isolated L2γ dwarf 2MASS J11151597+1937266 with a mass between 7 and 21 MJup and an age of 5–45 Myr, located at 45 ± 2 pc. Methods. We obtained the first high-resolution (R ~ 50 000) spectrum of the target with VLT/UVES, an echelle spectrograph operating in the near-ultraviolet to visible wavelengths (3200–6800 Å). Results. We report several resolved hydrogen (H I; H3–H6) and helium (He I; λ5875.6) emission lines in the spectrum. Based on the asymmetric line profiles of Hα and Hβ, the 10% width of Hα (199 ± 1 km s−1), tentative He I λ6678 emission, and indications of a disk from mid-infrared excess, we confirm ongoing accretion at this object. Using the Gaia update of the parallax, we revise its temperature to 1816 ± 63 K and radius to 1.5 ± 0.1 RJup. Analysis of observed H I profiles using a 1D planet-surface shock model implies a pre-shock gas velocity, v0 = 120−40+ 80 km s−1, and a pre-shock density, log(n0/cm−3) = 14−5+ 0. The pre-shock velocity points to a mass, Mp = 6−4+ 8 MJup, for the target. Combining H I line luminosities (Lline) and planetary Lline−Lacc (accretion luminosity) scaling relations, we derived a mass accretion rate, Ṁacc = 1.4−0.9+ 2.8 × 10−8 MJup yr−1. Conclusions. The line-emitting area predicted from the planet-surface shock model is very small (~0.03%), and points to a shock at the base of a magnetospherically induced funnel. The Hα profile exhibits a much stronger flux than predicted by the model that best fits the rest of the H I profiles, indicating that another mechanism than shock emission contributes to the Hα emission. Comparison of line fluxes and Ṁacc from archival moderate-resolution SDSS spectra indicate variable accretion at 2MASS J11151597+1937266.

Fundamental Parameters of a Binary System Consisting of a Red Dwarf and a Compact Star

TIC 157365951 has been classified as a δ Scuti type by the International Variable Star Index. Through the spectra from Large Sky Area Multi-Object Fiber Spectroscopic Telescope and its light curve, we further discovered that it is a binary system. This binary system comprises a red-dwarf star and a compact star. Through the spectral energy distribution fitting, we determined the mass of the red dwarf star as M 1 = 0.31 ± 0.01M ⊙ and its radius as R 1 = 0.414 ± 0.004R ⊙. By fitting the double-peaked Hα emission, we derived the mass ratio of q = 1.76 ± 0.04, indicating a compact star mass of M 2 = 0.54 ± 0.01M ⊙. Using Phoebe to model the light curve and radial velocity curve for the detached binary system, we obtained a red dwarf star mass of M 1 = 0.29 ± 0.02M ⊙, a radius of R 1 = 0.39 ± 0.04R ⊙, and a Roche–lobe filling factor of f = 0.995 ± 0.129, which is close to the f = 1 expected for a semidetached system. The Phoebe model gives a compact star mass M 2 = 0.53 ± 0.05M ⊙. Constraining the system to be semidetached gives M 1 = 0.34 ± 0.02M ⊙, R 1 = 0.41 ± 0.01R ⊙, and M 2 = 0.62 ± 0.03M ⊙. The consistency of the models is encouraging. The value of the Roche–lobe filling factor suggests that there might be ongoing mass transfer. The compact star mass is as massive as a typical white dwarf.