Starburst Galaxies Research Articles

CGOLS V: Disk-wide Stellar Feedback and Observational Implications of the Cholla Galactic Wind Model

We present the fifth simulation in the Cholla Galactic OutfLow Simulation (CGOLS) project—a set of isolated starburst galaxy simulations modeled over large scales (10 kpc) at uniformly high resolution (Δx ≈ 5 pc). Supernova feedback in this simulation is implemented as a disk-wide distribution of clusters, and we assess the impact of this geometry on several features of the resulting outflow, including the radial profiles of various phases; mass, momentum, and energy outflow rates; covering fraction of cool gas; mock absorption-line spectra; and X-ray surface brightness. In general, we find that the outflow generated by this model is cooler, slower, and contains more mass in the cool phase than a more centrally concentrated outflow driven by a similar number of supernovae. In addition, the energy loading factors in the hot phase are an order of magnitude lower, indicating much larger losses due to radiative cooling in the outflow. However, coupling between the hot and cool phases is more efficient than in the nuclear burst case, with almost 50% of the total outflowing energy flux carried by the cool phase at a radial distance of 5 kpc. These physical differences have corresponding signatures in observable quantities: the covering fraction of cool gas is much larger, and there is greater evidence of absorption in low and intermediate ionization energy lines. Taken together, our simulations indicate that centrally concentrated starbursts are more effective at driving hot, low-density outflows that will expand far into the halo, while galaxy-wide bursts may be more effective at removing cool gas from the disk.

DUVET: Resolved direct metallicity measurements in the outflow of starburst galaxy NGC 1569

Abstract We present the results of direct-method metallicity measurements in the disk and outflow of the low-metallicity starburst galaxy NGC 1569. We use Keck Cosmic Web Imager observations to map the galaxy across 54″ (800 pc) along the major axis and 48″ (700 pc) along the minor axis with a spatial resolution of 1″ (∼15 pc). We detect common strong emission lines ([O iii] λ5007, Hβ, [O ii] λ3727) and the fainter [O iii] λ4363 auroral line, which allows us to measure electron temperature (Te) and metallicity. Theory suggests that outflows drive metals out of the disk driving observed trends between stellar mass and gas-phase metallicity. Our main result is that the metallicity in the outflow is similar to that of the disk, Zout/ZISM ≈ 1. This is consistent with previous absorption line studies in higher mass galaxies. Assumption of a mass-loading factor of $\dot{M}_{\rm out}/{\rm SFR}\sim 3$ makes the metal-loading of NGC 1569 consistent with expectations derived from the mass-metallicity relationship. Our high spatial resolution metallicity maps reveal a region around a supermassive star cluster (SSC-B) with distinctly higher metallicity and higher electron density, compared to the disk. Given the known properties of SSC-B the higher metallicity and density of this region are likely the result of star formation-driven feedback acting on the local scale. Overall, our results are consistent with the picture in which metal-enriched winds pollute the circumgalactic medium surrounding galaxies, and thus connect the small-scale feedback processes to large-scale properties of galaxy halos.

Giant Biconical Dust Filaments in the Starburst Galaxy NGC 1808

We present the results from an analysis of multiwavelength archival data on the multiphase outflow in the starburst galaxy NGC 1808. We report the detection at 70 and 100 μm of dust filaments that extend up to ∼13 kpc from the galactic midplane and trace an edge-brightened biconical structure along the minor axis of the galaxy. The inner filaments are roughly cospatial with previously identified optical dust filaments, extraplanar polycyclic aromatic hydrocarbon emission, and neutral and ionized gaseous outflows. The 70/160 μm flux ratio, a proxy for the dust temperature, is elevated along the edges of the cones, indicating that the dusty medium has been driven out of the central regions of these cones and is possibly shock-heated by a large-scale outflow. We establish lower limits on the extraplanar dust mass and mean height above the stellar disk of log(Md/M⊙)=6.48 and ∣ z ∣ ∼ 5 kpc. The energy requirement of (5.1–9.6) × 1056 erg needed to lift the dusty material, assuming a Milky Way–like dust-to-gas ratio, can be supplied by the current starburst, with a measured star formation rate of 3.5–5.4 M ⊙ yr−1 over a timescale of (4–26) ξ −1 Myr, where ξ is the efficiency of energy transfer. We conclude that a starburst-driven outflow is the most likely mechanism by which the dust features were formed.

A Tale of Three Dwarfs: Cluster-based Star Formation Histories of Blue Compact Dwarf Galaxies

We present a new study of the cluster populations in the blue compact dwarf galaxies (BCD) ESO185-IG13, ESO338-IG04, and Haro11, based on new and archival high-resolution images taken by the Hubble Space Telescope, and the first to probe the populations older than ≈100 Myr. BCDs are believed to experience intense bursts of star formation (including at the present day) after long periods of quiescence, but little is known about the timing, frequency, duration, and strength of these bursts or about their star formation histories in general. We find that the cluster population in each of the three galaxies studied here has its own unique distribution of colors and hence a unique cluster and star formation history. From an assumed correlation between the normalization of the cluster mass function and the star formation rate of the host galaxy, we construct cluster-based star formation histories over the past ≈few × Gyr and find that only Haro11 is currently experiencing a burst (≈factor of 10 increase in the rate of star formation for the last ≈20 Myr), whereas ESO185 experienced enhanced star formation (by a factor ≈4) between 10 and 40 Myr ago, and ESO338 has had a fairly constant SFH over the past few Gyr. These findings indicate that not all BCDs are experiencing a burst of star formation at the present day, and that some have been forming stars and clusters at a fairly steady rate (within a factor of ≈2–3) over the past few Gyr. This scenario is similar to the histories of dwarf irregular and dwarf starburst galaxies, which have star formation rates that are 10–1000 times lower than those in BCDs.

Contribution of γ-Ray Burst Afterglow Emissions to the Isotropic Diffuse γ-Ray Background

The isotropic diffuse γ-ray background (IGRB) serves as a fundamental probe of the evolution of the extreme Universe. Although various astrophysical sources have been proposed as potential contributors to the IGRB, the dominant population is still under debate. γ-ray bursts (GRBs) are among candidate contributors of IGRB, although they are not as frequently discussed as blazars or starburst galaxies. Recent observations of TeV emission from GRB afterglows have provided fresh insights into this subject. This work aims to investigate the potential contribution of GRB afterglows to the IGRB under the standard afterglow model. We carefully examine the influence of each microphysical parameter of the afterglow model on this contribution, with a particular emphasis on the significant role played by the initial kinematic energy. To determine the energy and quantify the contribution of GRB afterglow to IGRBs, we utilize the observed GRB afterglow energy emissions from the Swift X-ray Telescope and Fermi Large Area Telescope instruments. Our calculations, considering the synchrotron self-Compton emission, suggest that GRB afterglows make up less than 10% of the IGRBs. To enhance the precision of our findings, it is crucial to further constrain these parameters by conducting additional ground-based observations of GRB afterglows.

High-dimensional Statistical Analysis and Its Application to an ALMA Map of NGC 253

In astronomy, if we denote the dimension of data as d and the number of samples as n, we often find a case with n ≪ d. Traditionally, such a situation is regarded as ill-posed, and there was no choice but to discard most of the information in data dimensions to let d < n. The data with n ≪ d is referred to as the high-dimensional low sample size (HDLSS). To deal with HDLSS problems, a method called high-dimensional statistics has rapidly developed in the last decade. In this work, we first introduce high-dimensional statistical analysis to the astronomical community. We apply two representative methods in the high-dimensional statistical analysis methods, noise-reduction principal component analysis (NRPCA) and automatic sparse principal component analysis (A-SPCA), to a spectroscopic map of a nearby archetype starburst galaxy NGC 253 taken by the Atacama Large Millimeter/submillimeter Array (ALMA). The ALMA map is an example of a typical HDLSS data set. First, we analyzed the original data, including the Doppler shift due to the systemic rotation. High-dimensional PCA can precisely describe the spatial structure of the rotation. We then applied to the Doppler-shift corrected data to analyze more subtle spectral features. NRPCA and R-SPCA were able to quantify the very complicated characteristics of the ALMA spectra. Particularly, we were able to extract information on the global outflow from the center of NGC 253. This method can also be applied not only to spectroscopic survey data, but also to any type of data with a small sample size and large dimension.

Cosmic-ray induced ionization rates and non-thermal emissions from nuclei of starburst galaxies

ABSTRACT Cosmic rays are the only agent capable of ionizing the interior of dense molecular clouds and, thus, they are believed to play an essential role in determining the physical and chemical evolution of star-forming regions. In this work, we aim to study cosmic-ray induced ionization rates in starburst environments using non-thermal emissions of cosmic rays from starburst nuclei. To this end, we first revisit cosmic-ray models, which could explain data of non-thermal emissions from radio to X-ray and gamma-ray from nuclei of three prototypical starburst galaxies NGC 253, M82, and Arp 220. These models are then applied to predict ionization rates in starburst environments, which gives values around 10−14 s−1. Such a high value of the ionization rate, which is 2 to 3 orders of magnitude higher than the typical values found in the Milky Way, is probably due to relatively high rates of supernova explosions occurring within the nuclei of these starburst galaxies. We also discuss in more detail the case of NGC 253, where our predicted ionization rate is found to be, in most cases, a few times smaller than the values inferred from molecular line observations of clouds in the starburst nucleus. The general framework provided in this work illustrates how the use of non-thermal emission data could help to provide more insights into ionization rates or, more generally, cosmic-ray impact in starburst environments.

The ALCHEMI Atlas: Principal Component Analysis Reveals Starburst Evolution in NGC 253

Molecular lines are powerful diagnostics of the physical and chemical properties of the interstellar medium (ISM). These ISM properties, which affect future star formation, are expected to differ in starburst galaxies from those of more quiescent galaxies. We investigate the ISM properties in the central molecular zone of the nearby starburst galaxy NGC 253 using the ultrawide millimeter spectral scan survey from the Atacama Large Millimeter/submillimeter Array Large Program ALCHEMI. We present an atlas of velocity-integrated images at a 1.″6 resolution of 148 unblended transitions from 44 species, including the first extragalactic detection of HCNH+ and the first interferometric images of C3H+, NO, and HCS+. We conduct a principal component analysis (PCA) on these images to extract correlated chemical species and to identify key groups of diagnostic transitions. To the best of our knowledge, our data set is currently the largest astronomical set of molecular lines to which PCA has been applied. The PCA can categorize transitions coming from different physical components in NGC 253 such as (i) young starburst tracers characterized by high-excitation transitions of HC3N and complex organic molecules versus tracers of on-going star formation (radio recombination lines) and high-excitation transitions of CCH and CN tracing photodissociation regions, (ii) tracers of cloud-collision-induced shocks (low-excitation transitions of CH3OH, HNCO, HOCO+, and OCS) versus shocks from star formation-induced outflows (high-excitation transitions of SiO), as well as (iii) outflows showing emission from HOC+, CCH, H3O+, CO isotopologues, HCN, HCO+, CS, and CN. Our findings show these intensities vary with galactic dynamics, star formation activities, and stellar feedback.

Stochastic star formation in the Milky Way inferred from the unity index of the Kennicutt–Schmidt law

Abstract We performed a correlation analysis between the brightness temperature of the CO line and number density of H ii regions in the longitude–velocity diagram (LVD) of the Milky Way in order to investigate the volumetric star-formation law. We determined the index α of the Kennicut–Schmidt law for the molecular gas defined by $\rho _{\rm SFR}\propto \rho _{\rm H_2}^\alpha$, where ρSFR is the SFR (star-formation rate) density and $\rho _{\rm H_2}$ is the molecular-gas density. We obtained α = 1.053 ± 0.075 and 1.031 ± 0.067 for the CO-line data from the Nobeyama 45 m and Columbia 1.2 m telescope Galactic plane surveys, respectively. This result is consistent with the KS indices currently determined for the molecular gas in the Milky Way as well as in spiral and starburst galaxies. We argue that an index close to 1 is universal in favour of stochastic (spontaneous) star formation, but is inconsistent with the cloud-collision model, which predicts a steeper index of α = 2. We also suggest that the efficiency of star formation in the Galactic Centre is an order of magnitude lower than that in the disc.

X-ray stacking reveals average SMBH accretion properties of star-forming galaxies and their cosmic evolution over 4 ≲ z ≲ 7

ABSTRACT With an X-ray stacking analysis of $\simeq 12\, 000$ Lyman-break galaxies (LBGs) using the Chandra Legacy Survey image, we investigate average supermassive black hole (SMBH) accretion properties of star-forming galaxies (SFGs) at 4 ≲ z ≲ 7. Although no X-ray signal is detected in any stacked image, we obtain strong 3σ upper limits for the average black hole accretion rate (BHAR) as a function of star formation rate (SFR). At z ∼ 4 (5) where the stacked image is deeper, the 3σ BHAR upper limits per SFR are ∼1.5 (1.0) dex lower than the local black hole-to-stellar mass ratio, indicating that the SMBHs of SFGs in the inactive (BHAR $\lesssim 1 \, \mathrm{M}_\odot$ yr−1) phase are growing much more slowly than expected from simultaneous evolution. We obtain a similar result for BHAR per dark halo accretion rate. QSOs from the literature are found to have ∼1 dex higher SFRs and ≳ 2 dex higher BHARs than LBGs with the same dark halo mass. We also make a similar comparison for dusty starburst galaxies and quiescent galaxies from the literature. A duty-cycle corrected analysis shows that for a given dark halo, the SMBH mass increase in the QSO phase dominates over that in the much longer inactive phase. Finally, a comparison with the TNG300, TNG100, SIMBA100, and EAGLE100 simulations finds that they overshoot our BHAR upper limits by ≲ 1.5 dex, possibly implying that simulated SMBHs are too massive.

Flux Contribution and Geometry of Charge Exchange Emission in the Starburst Galaxy M82

Recent X-ray studies of starburst galaxies have found that charge exchange (CX) commonly occurs between outflowing hot plasma and cold gas, possibly from swept-up clouds. However, the total CX flux and the regions where CX occurs have been poorly understood. We present an analysis of XMM-Newton observations of M82, a prototype starburst galaxy, aiming to investigate these key properties of CX emission. We have used a blind source separation method in an image analysis of CCD data, which identified a component with the enhanced O–K lines expected from the CX process. Analyzing the XMM-Newton/RGS spectra from the regions identified by the image analysis, we have detected a high forbidden-to-resonance ratio of the O vii Heα triplet as well as several emission lines from K-shell transitions of C, N, and O that are enhanced by the CX process. CX is less responsible for the emission lines of Ne and Mg, and accurate estimation of the CX contribution is confirmed to be crucial in measuring chemical abundances. The temperature of the plasma acting as an electron receiver in the CX process is significantly lower compared to that of the plasma components responsible for most of the X-rays. From the low temperature and an estimation of the CX-emitting volume, we find that the CX primarily occurs in a limited region at interfaces between plasma and gas whose temperatures rapidly decrease due to thermal conduction.

The galactic bubbles of starburst galaxies

Context. The galactic winds of starburst galaxies (SBGs) give rise to remarkable structures on kiloparsec scales. However, the evolution and shape of these giant wind bubbles, as well as the properties of the shocks they develop, are not yet fully understood. Aims. We aim to understand what shapes the galactic winds of SBGs, with a particular focus on the role of large-scale magnetic fields in the dynamical evolution of galactic wind-inflated bubbles. In addition, we aim to explore where the conditions for efficient particle acceleration are met in these systems. Methods. We performed magnetohydrodynamic simulations with the AMRVAC code (Adaptive Mesh Refinement Versatile Advection Code) with various configurations of the galactic medium density profile and magnetization. Results. We observe that the large-scale magnetic field, in which galactic winds expand, can impact the structure and evolution of inflated bubbles. However, the typical structures observed in starburst galaxies, such as M82, cannot be solely explained by the magnetic field structures that have been considered. This highlights the importance of other factors, such as the galactic disk, in shaping the galactic bubble. Furthermore, in all the magnetized cases we investigated, the forward wave resulting from the expanding bubbles only results in compression waves, whereas the wind termination shock features high Mach numbers, making it a promising site for diffusive shock acceleration up to ∼102 PeV. The synthetic X-ray images generated from our models reveal an envelope surrounding the bubbles that extends up to 2 kpc, which could correspond to the polarized emission observed from planar geometry in M82, as well as a large structure inside the bubble corresponding to the shocked galactic wind. Additionally, our findings indicate that, as observed with the SOFIA instrument, a large ordered magnetic field is associated with the free galactic wind, while a more turbulent magnetic field is present in the shocked region.

The ALMaQUEST Survey. XII. Dense Molecular Gas as Traced by HCN and HCO+ in Green Valley Galaxies

Abstract We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of two dense gas tracers, HCN (1−0) and HCO+ (1-0) for three galaxies in the green valley and two galaxies on the star-forming main sequence with comparable molecular gas fractions as traced by the CO (1−0) emissions, selected from the ALMaQUEST survey. We investigate whether the deficit of molecular gas star formation efficiency (SFEmol) that leads to the low specific star formation rate (sSFR) in these green valley galaxies is due to a lack of dense gas (characterized by the dense gas fraction f dense) or the low star formation efficiency of dense gas (SFEdense). We find that SFEmol as traced by the CO emissions, when considering both star-forming and retired spaxels together, is tightly correlated with SFEdense and depends only weakly on f dense. The sSFR on kiloparsec scales is primarily driven by SFEmol and SFEdense, followed by the dependence on f mol, and is least correlated with f dense or the dense-gas-to-stellar mass ratio (R dense). When compared with other works in the literature, we find that our green valley sample shows lower global SFEmol and lower SFEdense while exhibiting similar dense gas fractions when compared to star-forming and starburst galaxies. We conclude that the star formation of the three green valley galaxies with a normal abundance of molecular gas is suppressed, mainly due to the reduced SFEdense rather than the lack of dense gas.

Detection of Extragalactic Anomalous Microwave Emission in NGC 2903 Using KVN Single-dish Observations

We present the results of the single-dish observations using the Korean VLBI Network to search for anomalous microwave emission (AME) in nearby galaxies. The targets were selected from ‘Mapping the dense molecular gas in the strongest star-forming galaxies' (MALATANG), a legacy survey project of the James Clerk Maxwell Telescope. The MALATANG galaxies are good representatives of local galaxies with enhanced nuclear activity associated with star formation and/or active galactic nuclei (AGNs), providing IR-bright galaxy samples; thus, they are good candidates for AME hosts. Combining with ancillary data, we investigated the radio–IR spectral energy distribution (SED), while searching for AME signals in five galaxies. The AME in NGC 2903 was well detected at a significant confidence level, whereas that in NGC 2146 and M82 was marginal. NGC 1068 and Arp 299 indicated no significant hints, and we provide upper limits for the AME. The best-fit SED exhibited local peaks of the AME components at higher frequencies and with stronger peak fluxes than those in previous studies. This suggested that AME originates from denser environments such as molecular clouds or photodissociation regions rather than warm neutral/ionized medium as commonly suggested by previous studies. Further, our AME-detected targets were observed to exhibit higher specific star formation rates than the other extragalactic AME hosts. Furthermore, AME favored starburst galaxies among our sample rather than AGN hosts. Consequently, this might imply that AGNs are excessively harsh environments for tiny dust to survive.

The ALMA View of Positive Black Hole Feedback in the Dwarf Galaxy Henize 2–10

Henize 2–10 is a dwarf starburst galaxy hosting a ∼106 M ⊙ black hole (BH) that is driving an ionized outflow and triggering star formation within the central ∼100 pc of the galaxy. Here, we present Atacama Large Millimeter/submillimeter Array continuum observations from 99 to 340 GHz, as well as spectral line observations of the molecules CO (1–0, 3–2), HCN (1–0, 3–2), and HCO+ (1–0, 3–2), with a focus on the BH and its vicinity. Incorporating centimeter-wave radio measurements from the literature, we show that the spectral energy distribution of the BH is dominated by synchrotron emission from 1.4 to 340 GHz, with a spectral index of α ≈ − 0.5. We analyze the spectral line data and identify an elongated molecular gas structure around the BH with a velocity distinct from the surrounding regions. The physical extent of this molecular gas structure is ≈130 pc × 30 pc and the molecular gas mass is ∼106 M ⊙. Despite an abundance of molecular gas in this general region, the position of the BH is significantly offset from the peak intensity, which may explain why the BH is radiating at a very low Eddington ratio. Our analysis of the spatially resolved line ratio between CO J = 3–2 and J = 1–0 implies that the CO gas in the vicinity of the BH is highly excited, particularly at the interface between the BH outflow and the regions of triggered star formation. This suggests that the cold molecular gas is being shocked by the bipolar outflow from the BH, supporting the case for positive BH feedback.

Pre-supernova stellar feedback in nearby starburst dwarf galaxies

Stellar feedback in dwarf galaxies remains, to date, poorly explored, yet is crucial to understanding galaxy evolution in the early Universe. In particular, pre-supernova feedback has recently been found to play a significant role in regulating and disrupting star formation in larger spiral galaxies, but it remains uncertain if it also plays this role in dwarfs. We study the ionised gas properties and stellar content of individual star-forming regions across three nearby, low-metallicity ($12+ O/H 7.5$), dwarf ($M_* odot $), starburst ($ SFR -2.8$) galaxies (J0921, KKH046, and Leo P) to investigate how massive stars influence their surroundings and how this influence changes as a function of environment. We extracted integrated spectra of 30 HII regions from archival VLT/MUSE integral field spectroscopic observations of these three dwarf starburst galaxies. We fitted the HII regions' main emission lines with Gaussian profiles to derive their oxygen abundances, electron densities, and luminosities, and we used the Stochastically Ligthing Up Galaxies ( SLUG ) code to derive the stellar mass, age, and bolometric luminosity of the stellar populations driving the HII regions. We quantified two pre-supernova stellar feedback mechanisms, namely the direct radiation pressure and photoionisation feedback, and explored how feedback strength varies with HII region properties. Our findings suggest that stellar feedback has less of an impact on evolved regions, with both the pressure of the ionised gas and the direct radiation pressure decreasing as a function of HII region size (i.e. the evolutionary stage). We find that these stellar feedback mechanisms are also dependent on the metallicity of the HII regions. These findings extend results from stellar feedback studies of more massive star-forming galaxies to the low-mass, low-metallicity regime. In addition, we conclude that the use of stochastic stellar population models significantly affects the relationships found between feedback-related pressure terms and HII region properties, and in particular that non-stochastic models can severely underestimate the bolometric luminosity of low-mass stellar populations.

Neutrino production in starburst galaxies

ABSTRACT Understanding the origin of the diffuse flux of high-energy astrophysical neutrinos detected by IceCube has become a challenging issue within present High Energy Astrophysics. In this work, we present a model to explore the potential neutrino emission of starburst galaxies (SBG) by considering three different neutrino production zones that can be associated to a typical single SBG. The first zone is the starburst nucleus, where due to the high rate of supernova explosions, a significant amount of protons can be accelerated to high energies and undergo pp interactions with cold protons of the interstellar medium. The second zone we consider is the corresponding to the starburst wind, which is formed by the hot gas that emerges from the nucleus and interacts with the intergalactic medium generating shocks. Protons accelerated there can undergo pp interactions with the ambient matter. The third neutrino production zone we consider, is an external one, where we account for the possibility that protons escaping from the whole system interact with the cosmic microwave background. Finally, adding the neutrino contributions of the three zones, we calculate the diffuse neutrino flux and the diffuse photon flux by integration on the redshift range appropriate for SBG. We find that the model behaves well applied to nearby galaxies such as M82 and NGC 253. The contributions made to the diffuse neutrino flux are able to explain part of the data provided by IceCube if typical parameters are considered.

Evolution of gas flows along the starburst to post-starburst to quiescent galaxy sequence

ABSTRACT We measure velocity offsets in the $\rm{Na {}\rm {\small I}}$ λλ5890, 5896 ($\rm{Na {}\rm {\small D}}$) interstellar medium absorption lines to track how neutral galactic winds change as their host galaxies evolve. Our sample of ∼80 000 SDSS spectra at 0.010 &amp;lt; z &amp;lt; 0.325 includes starburst, post-starburst, and quiescent galaxies, forming an evolutionary sequence of declining star formation rate (SFR). We detect bulk flows across this sequence, mostly at higher host stellar masses (log(M*/M⊙)) &amp;gt; 10). Along this sequence, the fraction of outflows decreases (76 ± 2 per cent to 65 ± 4 per cent to a 3σ upper limit of 34 per cent), and the mean velocity offset changes from outflowing to inflowing (−84.6 ± 5.9 to −71.6 ± 11.4 to $76.6\pm 2.3\, \rm km s^{-1}$). Even within the post-starburst sample, wind speed decreases with time elapsed since the starburst ended. These results reveal that outflows diminish as galaxies age. For post-starbursts, there is evidence for an AGN contribution, especially to the speediest outflows: (1) SFR declines faster in time than outflow velocity, a decoupling arguing against massive stellar feedback; (2) of the few outflows strong enough to escape the interstellar medium (9/105), three of the four hosts with measured emission lines are Seyfert galaxies. For discy starburst galaxies, however, the trends suggest flows out of the stellar disc plane (with outflow 1/2-opening angle &amp;gt; 45°) instead of from the nucleus: the wind velocity decreases as the disc becomes more edge-on, and the outflow fraction, constant at $\sim 90~{{\ \rm per\ cent}}$ for disc inclinations i &amp;lt; 45°, steadily decreases from $\sim 90~{{\ \rm per\ cent}}$ to 20 per cent for i &amp;gt; 45°.

GA-NIFS: JWST/NIRSpec integral field unit observations of HFLS3 reveal a dense galaxy group at z ∼ 6.3

Massive, starbursting galaxies in the early Universe represent some of the most extreme objects in the study of galaxy evolution. One such source is HFLS3 (z ∼ 6.34), which was originally identified as an extreme starburst galaxy with mild gravitational magnification (μ ∼ 2.2). Here, we present new observations of HFLS3 with the JWST/NIRSpec integral field unit in both low (PRISM/CLEAR; R ∼ 100) and high spectral resolution (G395H/290LP; R ∼ 2700), with high spatial resolution (∼0.1″) and sensitivity. Using a combination of the NIRSpec data and a new lensing model with accurate spectroscopic redshifts, we find that the 3″ × 3″ field is crowded, with a lensed arc (C, z = 6.3425 ± 0.0002), two galaxies to the south (S1 and S2, z = 6.3592 ± 0.0001), two galaxies to the west (W1, z = 6.3550 ± 0.0001; W2, z = 6.3628 ± 0.0001), and two low-redshift interlopers (G1, z = 3.4806 ± 0.0001; G2, z = 2.00 ± 0.01). We present spectral fits and morpho-kinematic maps for each bright emission line (e.g. [OIII]λ5007, Hα, and [NII]λ6584) from the R2700 data for all sources except G2 (whose spectral lines fall outside the observed wavelengths of the R2700 data). From a line ratio analysis, we find that the galaxies in component C are likely powered by star formation, though we cannot rule out or confirm the presence of active galactic nuclei in the other high-redshift sources. We performed gravitational lens modelling, finding evidence for a two-source composition of the lensed central object and a magnification factor (μ = 2.1 − 2.4) comparable to findings of previous work. The projected distances and velocity offsets of each galaxy suggest that they will merge within the next ∼1 Gyr. Finally, we examined the dust extinction-corrected SFRHα of each z &gt; 6 source, finding that the total star formation (510 ± 140 M⊙ yr−1, magnification-corrected) is distributed across the six z ∼ 6.34 − 6.36 objects over a region of diameter ∼11 kpc. Altogether, this suggests that HFLS3 is not a single starburst galaxy, but instead a merging system of star-forming galaxies in the epoch of reionisation.

An AstroSat/UVIT study of galaxies in the cluster Abell 2199

We present the newly acquired data for an AstroSat/UVIT field centred on a face-on spiral starburst galaxy UGC 10420, located in the X-ray bright cluster Abell 2199 (z = 0.031). We have analysed the FUV BaF2 data for this field along with the archival FUV and NUV data from the GALEX mission, optical photometric data from the SDSS, spectroscopic data from the literature, and low-frequency radio data from the LoTSS survey, respectively. The stars were separated from the galaxies using the SDSS photometric pipeline classification, while the spectroscopic redshifts available for 35% of the detected UVIT sources were used to identify member galaxies of the cluster Abell 2199. We find that (a) the non-cluster galaxies are on average fainter than the cluster galaxies at fixed magnitude, (b) stars and galaxies are indistinguishable in the r vs. NUV–r plane, and (c) bright stars are ∼ 1.5 mag bluer than the galaxies in the FUV–r vs. NUV–r colour-colour plane. Besides UGC 10420 which is the only known cluster galaxy with an extended-UV disk, we identify five more galaxies with asymmetric FUV morphology and extended radio emission in this field. All the asymmetric member galaxies of Abell 2199, lie within the virial boundaries of the cluster. This observation, together with the fact that these asymmetric cluster galaxies have low-frequency radio tails or FUV emission pointing away from the cluster centre leads us to hypothesise that these galaxies are likely undergoing ram-pressure stripping (RPS) under the influence of cluster-environment related mechanisms. A comparison of optical and FUV star formation rate of UVIT detected galaxies shows enhanced star formation in half of the RPS candidates, suggesting that environment-related mechanisms may lead to a burst of star formation in RPS galaxies.Our analysis indicates the presence of at least two more groups or clusters at z ∼ 0.077 and 0.260, coincident with Abell 2199 along the line of sight of the field of view studied here.