Spiral Galaxy NGC Research Articles

Large-scale turbulence cascade in the spiral galaxy NGC 6946

ABSTRACT The generation mechanism of compressible fluid turbulence at kiloparsec scales in the interstellar medium is a long-lasting puzzle. In this work, we explore the nature of large-scale turbulence in the external spiral galaxy NGC 6946. We use the visibility moment estimator to measure the H i column density and line-of-sight turbulent velocity power spectra combining the new observations of A array configuration of Karl G. Jansky Very Large Array (VLA) with the VLA B, C, D array observations from The H i Nearby Galaxy Survey. The estimated power spectra are obeying a power law with a slope of −0.96 ± 0.05 in column density and −1.81 ± 0.07 in line-of-sight velocity in length-scales ranging from 6 kpc to 170 pc. This points towards a forward energy cascade in the plane of the disc with a driving scale at least as large as 6 kpc. The values of the power-law indices indicate a combination of solenoidal and compressive force responsible for driving the measured turbulence. The presence of strong regular magnetic fields from the magnetic spiral arms in the galaxy is possibly contributing to the solenoidal part, while self-gravity or gravitational instability can mostly be the input for the compressive part of the forcing in the driving mechanism.

Chandra Observation of NGC 1559: Eight Ultraluminous X-Ray Sources Including a Compact Binary Candidate

Despite the 30 yr history of ultraluminous X-ray sources (ULXs) studies, issues such as the majority of their physical natures (i.e., neutron stars, stellar-mass black holes, or intermediate black holes) as well as the accretion mechanisms are still under debate. Expanding the ULX sample size in the literature is clearly a way to help. To this end, we investigated the X-ray source population, ULXs in particular, in the barred spiral galaxy NGC 1559 using a Chandra observation made in 2016. In this 45 ks exposure, 33 X-ray point sources were detected within the 2.′7 isophotal radius of the galaxy. Among them, eight ULXs were identified with the criterion of the X-ray luminosity L x > 1039 erg s−1 (0.3–7 keV). Both X-ray light curves and spectra of all the sources were examined. Except for some low-count spectra that only provide ambiguous spectral fitting results, all the X-ray sources were basically spectrally hard and therefore likely have nonthermal origins. While no strong X-ray variability was present in most of the sources owing to the relatively short exposure of the observation, we found an intriguing ULX, named X-24, exhibiting a periodicity of ∼7500 s with a detection significance of 2.7σ. We speculate that it is the orbital period of the system. Roche-lobe overflow and Roche limit are consistent with the speculation. Thus, we suggest that X-24 may be one of the rare compact binary ULXs, and hence, a good candidate as a stellar-mass black hole.

Three is the magic number: Distance measurement of NGC 3147 using SN 2021hpr and its siblings

Context. The nearby spiral galaxy NGC 3147 hosted three Type Ia supernovae (SNe Ia) in the past decades that have been the subjects of intense follow-up observations. Simultaneous analysis of their data provides a unique opportunity for testing different methods of light curve fitting and distance estimation. Aims. The detailed optical follow-up of SN 2021hpr allows us to revise the previous distance estimations to NGC 3147 and compare the widely used light curve fitting algorithms to each other. After the combination of the available and newly published data of SN 2021hpr, its physical properties can also be estimated with higher accuracy. Methods. We present and analyse new BV griz and Swift photometry of SN 2021hpr to constrain its general physical properties. Together with its siblings, SNe 1997bq and 2008fv, we cross-compared the individual distance estimates of these three SNe given by the Spectral Adaptive Lightcurve Template (SALT) code, and we also checked their consistency with the results from the Multi-Color Light Curve Shape (MLCS) code. The early spectral series of SN 2021hpr was also fit with the radiative spectral code TARDIS to verify the explosion properties and constrain the chemical distribution of the outer ejecta. Results. After combining the distance estimates for the three SNe, the mean distance to their host galaxy, NGC 3127, is 42.5 ± 1.0 Mpc, which matches with the distance inferred by the most up-to-date light curve fitters, SALT3 and BayeSN. We confirm that SN 2021hpr is a Branch-normal Type Ia SN that ejected ~1.12 ± 0.28 M⊙ from its progenitor white dwarf and synthesized ~0.44 ± 0.14 M⊙ of radioactive 56Ni.

Spatially Resolved Recent Star Formation History in NGC 6946

The nearby face-on star-forming spiral galaxy NGC 6946 is known as the Fireworks Galaxy due to its hosting an unusually large number of supernovae. We analyze its resolved near-ultraviolet stellar photometry measured from images taken with the Hubble Space Telescope’s Wide Field Camera 3 with the F275W and F336W filters. We model the color–magnitude diagrams of the UV photometry to derive the spatially resolved star formation history of NGC 6946 over the last 25 Myr. From this analysis, we produce maps of the spatial distribution of the young stellar population and measure the total recent star formation rate (SFR) of nearly the entire young stellar disk. We find the global SFR(age ≤25 Myr) = . Over this period, the SFR is initially very high ( 16–25 Myr ago), then monotonically decreases to in the last 10 Myr. This decrease in global SFR over the last 25 Myr is consistent with measurements made with other SFR indicators. We discuss in detail two of the most active regions of the galaxy, which we find are responsible for 3% and 5% of the total star formation over the past 6.3 Myr.

Dwarf galaxy discoveries from the KMTNet supernova programme – III. The Milky-Way analogue NGC 2997 group

ABSTRACT We present the discovery of 48 new and the analysis of 55, including seven previously discovered dwarf galaxy candidates (DGCs) around the giant spiral galaxy NGC 2997 using deep BVI images from the Korea Microlensing Telescope Network Supernova Programme. Their V-band central surface brightness and total absolute magnitudes are in the range of 20.3–26.7 mag arcsec−2 and −(8.02–17.69) mag, respectively, while the I-band effective radii are 0.14–2.97 kpc. We obtain $\alpha \, \simeq$ −1.43 ± 0.02 for the faint-end slope of their luminosity function, comparable to previously measured values but shallower than theoretical predictions based on Λ cold dark matter models. The distance-independent distributions of their mass and colour suggest that the group could have recently accreted new massive members from the surrounding fields. The systematically bluer colours of the brighter members indicate younger stellar population and higher star formation activities in them, which appears to be consistent with similar findings from the SAGA or ELVES survey. We suggest that the massive and bluer dwarf galaxies in the group have experienced less environmental quenching due to their recent accretion, while environmental quenching has been more effective for the low-mass members. The interpretation of NGC 2997 being populationally young with recent accretion of massive members is also consistent with the overall morphological distribution of the dwarf galaxies showing a lack of morphologically evolved candidates but a plethora of irregularly shaped ones. Our detection rate of DGCs in the NGC 2997 group and their inferred star formation activities are comparable to those found in Milky Way analogue systems from recent surveys within the magnitude limit M$_{V}\, \lesssim$ −13 mag.

Прояснение природы спиральной структуры в галактиках: такие разные случаи NGC 3686 и M 100

At present, the question remains whether spiral arms are long-lived or not. The two main theories about the nature of the spiral structure (density waves and the theory of dynamical spirals) give different answers to this question. There is a number of evidence in favor of both of them, while convincingly confirming which of them is correct from observations is an extremely non-trivial task. In this paper, using the analysis of the collected sample of corotation radii, we found two spiral galaxies NGC~3686 and M~100, which are expected to have a fundamentally different answer to the question considered. In the first galaxy, a quasi-stationary density wave is clearly detected, and in the second case, the spirals are of a dynamic nature. We validate our analysis independently with model, kinematic, morphological and metallicity distribution analysis. For the first time, such a large number of independent observational evidence collected and convincingly shows that both theories can be valid in real objects.

Composite bulges – IV. Detecting signatures of gas inflows in the IFU data: the MUSE view of ionized gas kinematics in NGC 1097

ABSTRACT Using VLT/MUSE integral-field spectroscopic data for the barred spiral galaxy NGC 1097, we explore techniques that can be used to search for extended coherent shocks that can drive gas inflows in centres of galaxies. Such shocks should appear as coherent velocity jumps in gas kinematic maps, but this appearance can be distorted by inaccurate extraction of the velocity values and dominated by the global rotational flow and local perturbations like stellar outflows. We include multiple components in the emission-line fits, which corrects the extracted velocity values and reveals emission associated with AGN outflows. We show that removal of the global rotational flow by subtracting the circular velocity of a fitted flat disc can produce artefacts that obscure signatures of the shocks in the residual velocities if the inner part of the disc is warped or if gas is moving around the centre on elongated (non-circular) trajectories. As an alternative, we propose a model-independent method which examines differences in the LOSVD moments of H α and [N II]λ6583. This new method successfully reveals the presence of continuous shocks in the regions inward from the nuclear ring of NGC 1097, in agreement with nuclear spiral models.

On the origin of the anomalous gas, non-declining rotation curve, and disc asymmetries in NGC 253

ABSTRACT We present a multiwavelength (from far-ultraviolet to ${\rm H}\, \rm {\small I}$ emission) study of star formation feedback on the kinematics of the interstellar medium in the Sculptor galaxy, NGC 253. Its three well-known features (a disrupted stellar disc, a previously reported declining rotation curve, and anomalous ${\rm H}\, \rm {\small I}$ gas) are studied in a common context of disc asymmetries. About 170 h of on-source ATCA observations are collected and reduced into two versions of ${\rm H}\, \rm {\small I}$ data cubes of different angular resolution (30 arcsec/2 arcmin) and H i column density sensitivity (7.4 × 1019 cm−2/4 × 1018 cm−2). We separate the anomalous gas from the disc using a custom-made line profile fitting toolkit called FMG. Two star formation tracers (H α, FUV emission) are carefully processed and studied. We find that at R > 7.5 kpc, the star formation activity is strongly lopsided (SFRNE > SFRSW), and investigate several other properties (H α/FUV, dust temperature, stellar age, and disc stability parameters). We also find that the declining nature of the rotation curve perceived by previous studies is not intrinsic but a combined effect of kinematical asymmetries at R = 7.5–16 kpc. This is likely the consequence of star formation triggered outflow. The mass distribution and the time-scale of the anomalous gas also imply that it originates from gas outflow, which is perhaps caused by galaxy–galaxy interaction considering the crowded environment of NGC 253.

Constraining the LyC escape fraction from LEGUS star clusters with SIGNALS H ii region observations: a pilot study of NGC 628

ABSTRACT The ionizing radiation of young and massive stars is a crucial form of stellar feedback. Most ionizing (Lyman-continuum; LyC, λ < 912Å) photons are absorbed close to the stars that produce them, forming compact H ii regions, but some escape into the wider galaxy. Quantifying the fraction of LyC photons that escape is an open problem. In this work, we present a seminovel method to estimate the escape fraction by combining broadband photometry of star clusters from the Legacy ExtraGalactic UV Survey (LEGUS) with H ii regions observed by the Star formation, Ionized gas, and Nebular Abundances Legacy Survey (SIGNALS) in the nearby spiral galaxy NGC 628. We first assess the completeness of the combined catalogue, and find that 49 per cent of H ii regions lack corresponding star clusters as a result of a difference in the sensitivities of the LEGUS and SIGNALS surveys. For H ii regions that do have matching clusters, we infer the escape fraction from the difference between the ionizing power required to produce the observed H ii luminosity and the predicted ionizing photon output of their host star clusters; the latter is computed using a combination of LEGUS photometric observations and a stochastic stellar population synthesis code slug (Stochastically Lighting Up Galaxies). Overall, we find an escape fraction of ${f}_{\textrm {esc}}= 0.09^{+0.06}_{-0.06}$ across our sample of 42 H ii regions; in particular, we find H ii regions with high fesc are predominantly regions with low $\operatorname{H\alpha }$-luminosity. We also report possible correlation between fesc and the emission lines $\rm [O\, \rm {\small II}]/[N\, \rm {\small II}]$ and $\rm [O\, \rm {\small II}]/H\beta$.

WISDOM Project – XV. Giant molecular clouds in the central region of the barred spiral galaxy NGC 5806

ABSTRACT We present high spatial resolution (≈24 pc) Atacama Large Millimeter/sub-millimeter Array 12CO(2-1) observations of the central region of the nearby barred spiral galaxy NGC 5806. NGC 5806 has a highly structured molecular gas distribution with a clear nucleus, a nuclear ring, and offset dust lanes. We identify 170 spatially and spectrally resolved giant molecular clouds (GMCs). These clouds have comparable sizes (Rc) and larger gas masses, observed linewidths (σobs, los), and gas mass surface densities than those of clouds in the Milky Way disc. The size–linewidth relation of the clouds is one of the steepest reported so far ($\sigma _{\mathrm{obs,los}}\propto R_{\mathrm{c}}^{1.20}$ ), the clouds are on average only marginally bound (with a mean virial parameter 〈αvir〉 ≈ 2), and high velocity dispersions are observed in the nuclear ring. These behaviours are likely due to bar-driven gas shocks and inflows along the offset dust lanes, and we infer an inflow velocity of ≈120 km s−1 and a total molecular gas mass inflow rate of ≈5 M⊙ yr−1 into the nuclear ring. The observed internal velocity gradients of the clouds are consistent with internal turbulence. The number of clouds in the nuclear ring decreases with azimuthal angle downstream from the dust lanes without clear variation of cloud properties. This is likely due to the estimated short lifetime of the clouds (≈6 Myr), which appears to be mainly regulated by cloud–cloud collision and/or shear processes. Overall, it thus seems that the presence of the large-scale bar and gas inflows to the centre of NGC 5806 affect cloud properties.

Regular Chains of Star Formation Regions in Spiral Arms and Rings of Disk Galaxies

The regularity in the distribution of young stellar groups along the spiral arms of galaxies, first discovered by Bruce and Debra Elmegreen in 1983, was considered a rather rare phenomenon. However, recent studies of the spatial regularities in the distribution of the young stellar populations along the arms of the spiral galaxies NGC 628, NGC 895, NGC 4321, NGC 5474, NGC 6946, as well as along the rings of the spiral galaxy NGC 6217 and the lenticular galaxy NGC 4324, have revealed that this spatial (quasi) regularity and/or the presence of regular chains of star-forming regions is a fairly common phenomenon. Across all galaxies, the characteristic regularity scale is 350–500 pc or a multiple thereof. It should be noted that theoretical models predict an instability scale of a stellar-gas disk on the order of a few kpc, which is several times larger than what has been observed. The paper is partly based on the report presented at the Modern Stellar Astronomy 2022 Conference held at the Caucasian Mountain Observatory of the Sternberg Astronomical Institute, Moscow State University, on November 8–10, 2022.

MIGHTEE-H i: possible interactions with the galaxy NGC 895

ABSTRACT The transformation and evolution of a galaxy is strongly influenced by interactions with its environment. Neutral hydrogen (H i) is an excellent way to trace these interactions. Here, we present H i observations of the spiral galaxy NGC 895, which was previously thought to be isolated. High-sensitivity H i observations from the MeerKAT large survey project MIGHTEE reveal possible interaction features, such as extended spiral arms and the two newly discovered H i companions, that drive us to change the narrative that it is an isolated galaxy. We combine these observations with deep optical images from the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and its companions. We do find an excess of light in the outer parts of the companion galaxy MGTH$\_$J022138.1-052631, which could be an indication of external perturbation and thus possible sign of interactions. Our analysis shows that NGC 895 is an actively star-forming galaxy with a SFR of 1.75 ± 0.09[M⊙/yr], a value typical for high-stellar mass galaxies on the star-forming main sequence. It is reasonable to state that different mechanisms may have contributed to the observed features in NGC 895, and this emphasizes the need to revisit the target with more detailed observations. Our work shows the high potential and synergy of using state-of-the-art data in both H i and optical to reveal a more complete picture of galaxy environments.

The stellar population responsible for a kiloparsec-size superbubble seen in the JWST ‘phantom’ images of NGC 628

ABSTRACT We here study the multiband properties of a kiloparsec-size superbubble in the late-type spiral galaxy NGC 628. The superbubble is the largest of many holes seen in the early release images using James Webb Space Telescope (JWST)/MIRI filters that trace the polycyclic aromatic hydrocarbon (PAH) emissions. The superbubble is located in the interarm region ∼3 kpc from the Galactic Centre in the south-east direction. The shell surrounding the superbubble is detected in H i, CO, and H α with an expansion velocity of 12 km s−1 and contains as much as 2 × 107 M⊙ of mass in gas that is mostly in molecular form. We find a clear excess of blue, bright stars inside the bubble as compared to the surrounding disc on the Hubble Space Telescope/Advanced Camera for Surveys images. These excess blue, bright stars are part of a stellar population of 105 M⊙ mass that is formed over the last 50 Myr in different star formation episodes, as determined from an analysis of colour–magnitude diagrams using a Bayesian technique. The mechanical power injected by the massive stars of these populations is sufficient to provide the energy necessary for the expansion of the shell gas. Slow and steady, rather than violent, injection of energy is probably the reason for the maintenance of the shell structure over the kiloparsec scale. The expanding shell is currently the site for triggered star formation as inferred from the JWST 21 µm (F2100W filter) and the H α images.

MUSE crowded field 3D spectroscopy in NGC 300

Aims. We perform a deep survey of planetary nebulae (PNe) in the spiral galaxy NGC 300 to construct its planetary nebula luminosity function (PNLF). We aim to derive the distance using the PNLF and to probe the characteristics of the most luminous PNe. Methods. We analysed 44 fields observed with MUSE at the VLT, covering a total area of ∼11 kpc2. We find [O III]λ5007 sources using the differential emission line filter (DELF) technique. We identified PNe through spectral classification with the aid of the BPT diagram. The PNLF distance was derived using the maximum likelihood estimation technique. For the more luminous PNe, we also measured their extinction using the Balmer decrement. We estimated the luminosity and effective temperature of the central stars of the luminous PNe based on estimates of the excitation class and the assumption of optically thick nebulae. Results. We identify 107 PNe and derive a most-likely distance modulus $ (m-M)_0 = 26.48^{+0.11}_{-0.26} $ ($ d = 1.98^{+0.10}_{-0.23} $ Mpc). We find that the PNe at the PNLF cutoff exhibit relatively low extinction, with some high-extinction cases caused by local dust lanes. We present the lower limit luminosities and effective temperatures of the central stars for some of the brighter PNe. We also identify a few Type I PNe that come from a young population with progenitor masses > 2.5 M⊙ but do not populate the PNLF cutoff. Conclusions. The spatial resolution and spectral information of MUSE allow precise PN classification and photometry. These capabilities also enable us to resolve possible contamination by diffuse gas and dust, improving the accuracy of the PNLF distance to NGC 300.

PHANGS–JWST First Results: Rapid Evolution of Star Formation in the Central Molecular Gas Ring of NGC 1365

Large-scale bars can fuel galaxy centers with molecular gas, often leading to the development of dense ringlike structures where intense star formation occurs, forming a very different environment compared to galactic disks. We pair ∼0.″3 (30 pc) resolution new JWST/MIRI imaging with archival ALMA CO(2–1) mapping of the central ∼5 kpc of the nearby barred spiral galaxy NGC 1365 to investigate the physical mechanisms responsible for this extreme star formation. The molecular gas morphology is resolved into two well-known bright bar lanes that surround a smooth dynamically cold gas disk (R gal ∼ 475 pc) reminiscent of non-star-forming disks in early-type galaxies and likely fed by gas inflow triggered by stellar feedback in the lanes. The lanes host a large number of JWST-identified massive young star clusters. We find some evidence for temporal star formation evolution along the ring. The complex kinematics in the gas lanes reveal strong streaming motions and may be consistent with convergence of gas streamlines expected there. Indeed, the extreme line widths are found to be the result of inter-“cloud” motion between gas peaks; ScousePy decomposition reveals multiple components with line widths of 〈σ CO,scouse〉 ≈ 19 km s−1 and surface densities of , similar to the properties observed throughout the rest of the central molecular gas structure. Tailored hydrodynamical simulations exhibit many of the observed properties and imply that the observed structures are transient and highly time-variable. From our study of NGC 1365, we conclude that it is predominantly the high gas inflow triggered by the bar that is setting the star formation in its CMZ.

Serendipitous Nebular-phase JWST Imaging of SN Ia SN 2021aefx: Testing the Confinement of 56Co Decay Energy

We present new 0.3–21 μm photometry of SN 2021aefx in the spiral galaxy NGC 1566 at +357 days after B-band maximum, including the first detection of any Type Ia supernova (SN Ia) at >15 μm. These observations follow earlier JWST observations of SN 2021aefx at +255 days after the time of maximum brightness, allowing us to probe the temporal evolution of the emission properties. We measure the fraction of flux emerging at different wavelengths and its temporal evolution. Additionally, the integrated 0.3–14 μm decay rate of Δm 0.3–14 = 1.35 ± 0.05 mag/100 days is higher than the decline rate from the radioactive decay of 56Co of ∼1.2 mag/100 days. The most plausible explanation for this discrepancy is that flux is shifting to >14 μm, and future JWST observations of SNe Ia will be able to directly test this hypothesis. However, models predicting nonradiative energy loss cannot be excluded with the present data.

PHANGS–JWST First Results: Massive Young Star Clusters and New Insights from JWST Observations of NGC 1365

A primary new capability of JWST is the ability to penetrate the dust in star-forming galaxies to identify and study the properties of young star clusters that remain embedded in dust and gas. In this Letter we combine new infrared images taken with JWST with our optical Hubble Space Telescope (HST) images of the starbursting barred (Seyfert2) spiral galaxy NGC 1365. We find that this galaxy has the richest population of massive young clusters of any known galaxy within 30 Mpc, with ∼30 star clusters that are more massive than 106 M ⊙ and younger than 10 Myr. Sixteen of these clusters are newly discovered from our JWST observations. An examination of the optical images reveals that 4 of 30 (∼13%) are so deeply embedded that they cannot be seen in the Hubble I band (A V ≳ 10 mag), and that 11 of 30 (∼37%) are missing in the HST B band, so age and mass estimates from optical measurements alone are challenging. These numbers suggest that massive clusters in NGC 1365 remain completely obscured in the visible for ∼1.3 ± 0.7 Myr and are either completely or partially obscured for ∼3.7 ± 1.1 Myr. We also use the JWST observations to gain new insights into the triggering of star cluster formation by the collision of gas and dust streamers with gas and dust in the bar. The JWST images reveal previously unknown structures (e.g., bridges and overshoot regions from stars that form in the bar) that help us better understand the orbital dynamics of barred galaxies and associated star-forming rings. Finally, we note that the excellent spatial resolution of the NIRCAM F200W filter provides a better way to separate barely resolved compact clusters from individual stars based on their sizes.

The vertical structure of the spiral galaxy NGC 3501: first stages of the formation of a thin metal-rich disc

ABSTRACT We trace the evolution of the edge-on spiral galaxy NGC 3501, making use of its stellar populations extracted from deep integral-field spectroscopy MUSE observations. We present stellar kinematic and population maps, as well as the star formation history, of the south-western half of the galaxy. The derived maps of the stellar line-of-sight velocity and velocity dispersion are quite regular, show disc-like rotation, and no other structural component of the galaxy. However, maps of the stellar populations exhibit structures in the mass-weighted and light-weighted age, total metallicity, and [Mg/Fe] abundance. These maps indicate that NGC 3501 is a young galaxy, consisting mostly of stars with ages between 2 and 8 Gyr. Also, they show a thicker more extended structure that is metal-poor and α-rich, and another inner metal-rich and α-poor one with smaller radial extension. While previous studies revealed that NGC 3501 shows only one morphological disc component in its vertical structure, we divided the galaxy into two regions: an inner metal-rich mid-plane and a metal-poor thicker envelope. Comparing the star formation history of the inner thinner metal-rich disc and the thicker metal-poor disc, we see that the metal-rich component evolved more steadily, while the metal-poor one experienced several bursts of star formation. We propose this spiral galaxy is being observed in an early evolutionary phase, with a thicker disc already in place and an inner thin disc in an early formation stage. So we are probably witnessing the birth of a future massive thin disc, continuously growing embedded in a preexisting thicker disc.

Fountain-driven gas accretion feeding star formation over the disc of NGC 2403

ABSTRACT We use a dynamical model of galactic fountain to study the neutral extraplanar gas (EPG) in the nearby spiral galaxy NGC 2403. We have modelled the EPG as a combination of material ejected from the disc by stellar feedback (i.e. galactic fountain) and gas accreting from the inner circumgalactic medium (CGM). This accretion is expected to occur because of cooling/condensation of the hot CGM (corona) triggered by the fountain. Our dynamical model reproduces the distribution and kinematics of the EPG H i emission in NGC 2403 remarkably well and suggests a total EPG mass of $4.7^{+1.2}_{-0.9}\times 10^8\, \mathrm{M_\odot }$, with a typical scale height of around 1 kpc and a vertical gradient of the rotation velocity of $-10.0\pm 2.7\, \mathrm{km\, s^{-1}\, kpc^{-1}}$. The best-fitting model requires a characteristic outflow velocity of $50\pm 10\, \mathrm{km\, s^{-1}}$. The outflowing gas starts out mostly ionized and only becomes neutral later in the trajectory. The accretion rate from the condensation of the inner hot CGM inferred by the model is 0.8 $\mathrm{M}_\odot \, \mathrm{yr}^{-1}$, approximately equal to the star-formation rate in this galaxy (0.6 $\mathrm{M}_\odot \, \mathrm{yr}^{-1}$). We show that the accretion profile, which peaks at a radius of about 4.5 kpc, predicts a disc growth rate compatible with the observed value. Our results indicate that fountain-driven corona condensation is a likely mechanism to sustain star formation, as well as the disc inside-out growth in local disc galaxies.

Metal-THINGS: Association and optical characterization of supernova remnants with H I holes in NGC 6946

Context. NGC 6946, also known as the “Fireworks Galaxy”, is an unusual galaxy that hosts a total of 225 supernova remnant (SNR) candidates, including 147 optically identified with high [S II]/Hα line ratios. In addition, this galaxy shows prominent H I holes, which have been analyzed in previous studies. Indeed, the connection between SNRs and H I holes along with their physical implications in the surrounding gas are worthy of attention. Aims. This paper explores the connection between the SNRs and the H I holes, including an analysis of their physical link to observational optical properties inside and around the rims of the holes, using new integral field unit (IFU) data from the Metal-THINGS survey. Methods. We present an analysis combining previously identified H I holes, SNR candidates, and new integral field unit (IFU) data from Metal-THINGS of the spiral galaxy NGC 6946. We analyzed the distributions of the oxygen abundance, star formation rate surface density, extinction, ionization, and diffuse ionized gas, as well as the Baldwin-Phillips-Terlevich classification throughout the galaxy. Results. By analyzing the optical properties of the 121 previously identify H I holes in NGC 6946 in detail, we find that the SNRs are concentrated at the rims of the H I holes. Furthermore, our IFU data show that the star formation rate and extinction are enhanced at the rims of the holes. To a lesser degree, the oxygen abundance and ionization parameter show hints of enhancement on the rims of the holes. Altogether, this provides evidence of induced star formation taking place at the rims of the holes, whose origin can be explained by the expansion of superbubbles created by multiple supernova explosions in large stellar clusters dozens of Myr ago.