Integral Field Spectroscopy Observations Research Articles

From particles to pixels: How many particles do I really need to construct stellar kinematic mock observational measurements?

Abstract This work considers the impact of resolution in the construction of mock observations of simulated galaxies. In particular, when building mock integral field spectroscopic observations from galaxy formation models in cosmological simulations, we investigate the possible systematics that may arise given the assumption that all galaxies above some stellar mass limit will provide unbiased and meaningful observable stellar kinematics. We build a catalogue of N-body simulations to sample the range of stellar particle resolutions within the Eagle Ref0050N0752 simulation box and examine how their observable kinematics vary relative to a higher-resolution N-body control. We use these models to compile a table of the minimum number of particles-per-pixel to reach a given uncertainty in the fitted line-of-sight velocity distribution parameters. Further, we introduce a Voronoi-binning module to the mock observation code, SimSpin, in order to meet these minimum numbers. Using Eagle, we show the impact of this shot noise on the observed spin-ellipticity plane and the recovery of this space when observations are binned with increasing numbers of particles. In conclusion, we advise binning mock images to meet at least 200 particles-per-pixel to avoid systematically under-estimating the velocity dispersion along a given line-of-sight. We demonstrate that this is important for comparing galaxies extracted from the same simulation, as well as between simulations of varying mass resolution and observations of real galaxies.

Recovering chemical bimodalities in observed edge-on stellar disks: Insights from AURIGA simulations

The well-known bimodal distribution of Milky Way disk stars in the [α/Fe]–metallicity plane is often used to define thick and thin disks. In external edge-on galaxies, there have been attempts to identify this type of bimodality using integral field spectroscopy (IFS) data. However, for unresolved stellar populations, observations only contain integrated information, making these studies challenging. We assessed the ability to recover chemical bimodalities in IFS observations of edge-on galaxies, using 24 Milky Way-mass galaxies from the AURIGA zoom-in cosmological simulations. We first analyzed the distribution of single stellar particles in the [Mg/Fe]–[Fe/H] plane, finding that bimodality is frequent but not ubiquitous and often unclear. Then we produced mock IFS [Mg/Fe] and [Fe/H] maps of galaxies seen edge on, and considered integrated stellar-population properties (projected and spatially binned). We investigated how the distribution of stars in the [Mg/Fe]–[Fe/H] plane is affected by edge-on projection and spatial binning. Bimodality is preserved, while distributions change their shapes. Naturally, broad distributions of individual star particles are narrowed into smaller [Mg/Fe] and [Fe/H] ranges for spatial bins. We observe continuous distributions from high [Mg/Fe] and low [Fe/H], to lower [Mg/Fe] values and higher [Fe/H]. Despite being continuous, these distributions are bimodal in most cases. The overlap in [Fe/H] is small, and different [Mg/Fe] components show up as peaks instead of sequences (even when the latter are present for individual particles). The larger the spatial bins, the narrower the [Mg/Fe]–[Fe/H] distribution. This narrowing helps amplify the density of different [Mg/Fe] peaks, often leading to a clearer bimodality in mock IFS observations than for original star particles. We also assessed the correspondence of chemical bimodalities with the distinction between geometric thick and thin disks. Their individual particles have different distributions, but mostly overlap in [Mg/Fe] and [Fe/H]. However, integrated properties of geometric thick and thin disks in mock maps do mostly segregate into different regions of the [Mg/Fe]–[Fe/H] plane. In bimodal distributions, they correspond to the two distinct peaks. Our results show that this approach can be used for bimodality studies in future IFS observations of edge-on external galaxies.

No evidence of active galactic nucleus features in the nuclei of Arp 220 from JWST/NIRSpec IFS

Context. Arp 220 is the nearest ultra-luminous infrared galaxy. It shows evidence of 100 pc scale molecular outflows that are likely connected with galaxy-scale outflows traced by ionised and neutral gas. The two highly obscured nuclei of Arp 220 are sites of intense star formation, with extreme (far-infrared based) star formation rate surface densities, ΣSFR ≳ 103 M⊙ yr−1 kpc−2. Despite extensive investigations that searched for active galactic nucleus (AGN) activity in the Arp 220 nuclei, direct evidence remains elusive. Aims. We present JWST/NIRSpec integral field spectroscopy (IFS) observations covering the 0.9 − 5.1 μm wavelength range of the innermost (5″ × 4″, i.e. 1.8 × 1.5 kpc) regions of Arp 220. The primary goal is to investigate the potential presence of AGN signatures in the nuclear regions by analysing the spectra extracted from circular apertures with a radius of 55 pc (0.15″) around each of the two nuclei. Methods. The analysis aims to identify highly ionised gas emission lines (with ionisation potential > 54 eV) and other spectral features indicative of AGN activity. Atomic and molecular gas kinematics were also taken into account to study the outflow signatures at < 60 pc scales. Results. We identify ∼70 atomic and ∼50 molecular emission lines in the nuclear spectra of Arp 220. We used recombination line ratios to measure optical extinctions in the range AV ∼ 11 − 14 mag. High-ionisation lines are not detected, except for the [Mg IV] line at 4.49 μm, which we interpret as due to shocks rather than to AGN ionisation. We identify broadening and multiple kinematic components in the H I and H2 lines caused by outflows and shocks, with velocities up to ∼550 km s−1. Significantly higher velocities (up to ∼900 km s−1) are detected in the off-nuclear regions, but they do not conclusively represent direct evidence for AGN activity. Broad-line region components are not detected in any permitted emission line within the NIRSpec wavelength range. Conclusions. Even with the unprecedented sensitivity of JWST/NIRSpec IFS, achieving an unambiguous identification or exclusion of the presence of an AGN in the Arp 220 system remains challenging because of its extreme dust obscuration.

A fast-rotator post-starburst galaxy quenched by supermassive black-hole feedback at z = 3

AbstractThe most massive galaxies in the Universe stopped forming stars due to the time-integrated feedback from central supermassive black holes (SMBHs). However, the exact quenching mechanism is not yet understood, because local massive galaxies were quenched billions of years ago. Here we present JWST/NIRSpec integral-field spectroscopy observations of GS-10578, a massive, quiescent galaxy at redshift z = 3.064 ± 0.002. From its spectrum, we measure a stellar mass M⋆ = 1.6 ± 0.2 × 1011 M⊙ and a dynamical mass Mdyn = 2.0 ± 0.5 × 1011 M⊙. Half of its stellar mass formed at z = 3.7–4.6, and the system is now quiescent, with a current star-formation rate of less than 19 M⊙ yr−1. We detect ionized- and neutral-gas outflows traced by [O iii] emission and Na i absorption, with mass outflow rates 0.14–2.9 and 30–100 M⊙ yr−1, respectively. Outflow velocities reach vout ≈ 1,000 km s−1, comparable to the galaxy escape velocity. GS-10578 hosts an active galactic nucleus, evidence that these outflows are due to SMBH feedback. The neutral outflow rate is higher than the star-formation rate. Hence, this is direct evidence for ejective SMBH feedback, with a mass loading capable of interrupting star formation by rapidly removing its fuel. Stellar kinematics show ordered rotation, with spin parameter $${\lambda }_{{{{R}}}_{{\rm{e}}}}=0.62\pm 0.07$$ λ R e = 0.62 ± 0.07 , meaning GS-10578 is rotation-supported. This study presents direct evidence for ejective active galactic nucleus feedback in a massive, recently quenched galaxy, thus helping to clarify how SMBHs quench their hosts. The high value of $${\lambda }_{{{{R}}}_{{\rm{e}}}}$$ λ R e implies that quenching can occur without destroying the stellar disk.

GA-NIFS: the interplay between merger, star formation and chemical enrichment in MACS1149-JD1 at z=9.11 with JWST/NIRSpec

Abstract We present JWST/NIRSpec integral-field spectroscopy observations of the z ∼ 9.11 lensed galaxy MACS1149-JD1, as part of the GA-NIFS programme. The data was obtained with both the G395H grating (R∼ 2700) and the prism (R∼ 100). This target shows a main elongated UV-bright clump and a secondary component detected in continuum emission at a projected distance of 2 kpc. The R2700 data trace the ionised-gas morpho-kinematics in between the two components, showing an elongated emission mainly traced by [O iii] λ5007. We spatially resolve [O ii] λλ3726,3729, [O iii] λλ4959,5007, and [O iii] λ4363, which enable us to map the electron density (ne ∼ 1.0 × 103 cm−3), temperature (Te ∼ 1.6 × 104 K), and direct-method gas-phase metallicity (-1.2 to -0.7 dex solar). A spatially resolved full-spectrum modelling of the prism indicates a north-south gas metallicity and stellar age gradient between the two components. We found 3-σ evidence of a spatially resolved anti-correlation of the gas-phase metallicity and the star formation rate density, which is likely driven by gas inflows, enhancing the star formation in JD1. We employ high-z sensitive diagnostic diagrams to rule out the presence of a strong AGN in the main component. These findings show the unambiguous presence of two distinct stellar populations, with the majority of the mass ascribed to an old star formation burst, as suggested by previous works. We disfavour the possibility of a rotating-disc nature for MACS1149-JD1; we favour a merger event that has led to a recent burst of star formation in two separate regions, as supported by high values of [O iii] λ5007/Hβ, ionised gas velocity dispersion, and gas-phase metallicity.

Ionized and Cold Gas Components in Low Surface Brightness Galaxy AGC 102004

Abstract We present the integral field spectroscopic observations of ionized gas (Hα and [N II]) using the PCWI, along with deep CO(2–1) observations by the ‵ U ¯ ‵ u ¯ receiver on JCMT for AGC 102004. The velocity field of Hα shows an anomalous distribution in the northwestern (NW) disk. The Hα spectrum is well-fitted by two Gaussian components, and the weak Gaussian component is dominated by the anomalous Hα in the NW disk. The Gaussian fit center of Hα emission is offset by +24.2 km s−1 from the systemic velocity obtained from the H i emission. We derive the gas-phase metallicity, 12+log(O/H), using [N II]λ6583/Hα ratio as a proxy. The mean value of 12+log(O/H) is 8.30 ± 0.19 over the whole galaxy. The metallicity in the outer disk is lower than the detection limit of 7.72, indicating the metallicity gradient exists in AGC 102004. We speculate a minor/mini-merger event could have happened to the NW disk. CO(2–1) emission has nondetection in AGC 102004, reaching a noise level of 0.33 mK smoothed to 30 km s−1. The upper limit of molecular gas mass in AGC 102004 is 2.1 × 107 M ⊙ with X CO = 3.02 × 1020 cm−2 (K km s−1)−1. The M H 2 /M H I corr of AGC 102004 is lower than 0.0037 and lower than that of normal galaxies.

Kaleidoscope of irradiated disks: MUSE observations of proplyds in the Orion Nebula Cluster

In the Orion Nebula Cluster (ONC), protoplanetary disks exhibit ionized gas clouds in the form of a striking teardrop shape as massive stars irradiate the disk material. We present the first spatially and spectrally resolved observations of 12 such objects, known as proplyds, using integral field spectroscopy observations performed with the Multi-Unit Spectroscopic Explorer (MUSE) instrument in Narrow Field Mode (NFM) on the Very Large Telescope (VLT). We present the morphology of the proplyds in seven emission lines and measure the radius of the ionization front (I-front) of the targets in four tracers, covering transitions of different ionization states for the same element. We also derive stellar masses for the targets. The measurements follow a consistent trend of increasing I-front radius for a decreasing strength of the far-UV radiation as expected from photoevaporation models. By analyzing the ratios of the I-front radii as measured in the emission lines of Hα, [O I] 6300 A, [O II] 7330 A, and [O III] 5007 A, we observe the ionization stratification, that is, the most ionized part of the flow being the furthest from the disk (and closest to the UV source). The ratios of ionization front radii scale in the same way for all proplyds in our sample regardless of the incident radiation. We show that the stratification can help constrain the densities near the I-front by using a 1D photoionization model. We derive the upper limits of photoevaporative mass-loss rates (Ṁloss) by assuming ionization equilibrium, and estimate values in the range 1.07–94.5 × 10−7 M⊙ yr−1, with Ṁloss values decreasing towards lower impinging radiation. We do not find a correlation between the mass-loss rate and stellar mass. The highest mass-loss rate is for the giant proplyd 244–440. These values of Ṁloss, combined with recent estimates of the disk mass with ALMA, confirm previous estimates of the short lifetime of these proplyds. This work demonstrates the potential of this MUSE dataset and offers a new set of observables to be used to test current and future models of external photoevaporation.

O iii] λ5007 emissions in extremely red quasars (ERQs) are compact

ABSTRACT ‘Extremely red quasars’ (ERQs) are a non-radio-selected, intrinsically luminous population of quasars at cosmic noon selected by their extremely red colour from rest-frame UV to mid-IR. ERQs are uniquely associated with exceptionally broad and blueshifted [O iii] $\lambda$5007 emission reaching speeds $\gt $6000 km s$^{-1}$. We obtained adaptive optics integral-field spectroscopic observations using Keck/OSIRIS and Gemini/NIFS of a sample of 10 ERQs with bolometric luminosities (10$^{47.0}$–10$^{47.9}$) erg s$^{-1}$ at $z\sim$ (2.3–3.0). The goal is to measure the sizes and spatially resolved kinematics of the [O iii]-emitting regions. We study the surface brightness maps and aperture-extracted spectra and model the point-spread functions. We identify signs of merger activities in the continuum emissions. We identify physically distinct [O iii] kinematic components that are bimodal and respectively trace ERQ-driven outflows of velocity dispersion $\gtrsim$250 km s$^{-1}$ and dynamically quiescent interstellar media. We find that the ERQ-driven ionized outflows are typically at $\sim$1 kpc scales whereas the quiescent ionized gas extend to a few kpc. Compared to normal quasars the extremely fast ERQ-driven [O iii] outflows tend to be more compact, supporting the notion that ERQs are in a young stage of quasar/galaxy evolution and represent unique physical conditions beyond orientation differences with normal quasar populations. The kinematically quiescent [O iii] emissions in ERQs tend to be spatially resolved but less extended than in normal quasars, which can be explained by global and patchy dust obscuration. The hint of ionization cones suggests some of the obscuration can be partially explained by a patchy torus.

JADES

Finding the first generation of stars formed out of pristine gas in the early Universe, known as Population III (PopIII) stars, is one of the most important goals of modern astrophysics. Recent models have suggested that PopIII stars may form in pockets of pristine gas in the halo of more evolved galaxies. We present NIRSpec integral field spectroscopy and micro-shutter array spectroscopic observations of the region around GN-z11, an exceptionally luminous galaxy at z = 10.6, that reveal a greater than 5σ detection of a feature consistent with being HeIIλ1640 emission at the redshift of GN-z11. The very high equivalent width of the putative HeII emission in this clump (log(EWrest(HeII)/Å) = 1.79−0.25+0.15) and a lack of metal lines can be explained in terms of photoionisation by PopIII stars, while photoionisation by PopII stars is inconsistent with the data. The high equivalent width would also indicate that the putative PopIII stars likely have an initial mass function with an upper cutoff reaching at least 500 M⊙. The PopIII bolometric luminosity inferred from the HeII line would be ∼7 × 109 L⊙, which would imply a total stellar mass formed in the burst of ∼2 × 105 M⊙. We find that photoionisation by the active galactic nucleus (AGN) in GN-z11 cannot account for the HeII luminosity observed in the clump but can potentially be responsible for an additional HeII emission observed closer to GN-z11. We also consider the possibility of in situ photoionisation by an accreting direct collapse black hole hosted by the HeII clump. We find that this scenario is less favoured, but it remains a possible alternative interpretation. We also report the detection of a Lyα halo stemming out of GN-z11 and extending out to ∼2 kpc as well as resolved funnel-shaped CIII emission likely tracing the ionisation cone of the AGN.

Understanding stellar populations in thin and thick discs of edge-on galaxies with MUSE – I. The case of the reignited S0 galaxy ESO 544-27

ABSTRACT Edge-on galaxies act as the best laboratories to understand the origin of thin and thick discs in galaxies. Measurement of spatially resolved stellar population properties in such galaxies, particularly age, metallicity, and [α/Fe], are crucial to understanding the formation and evolution of disc galaxies. Such measurements are made possible from stellar population model fits to deep integral field spectroscopic (IFU) observations of resolved galaxies. We utilize archival MUSE IFU observations of the edge-on galaxy ESO 544-27 to uncover the formation history of its thin and thick discs through its stellar populations. We find the thin disc of the galaxy is dominated by an old (>9 Gyr) low [α/Fe] metal-rich stellar population. Its outer thick disc is dominated by an old (>9 Gyr) high [α/Fe] metal-rich component that should have formed with higher star formation efficiency than the Milky Way thick disc. We thus find [α/Fe] dichotomy in ESO 544-27 with its thin and thick discs dominated by low and high [α/Fe] stellar populations, respectively. However, we also find a metal-rich younger (<2 Gyr old) stellar population in ESO 544-27. The galaxy was nearly quenched until its star formation was reignited recently first in the outer and inner thick disc (∼1 Gyr ago) and then in the thin disc (∼600 Myr ago). We thus find that both the low [α/Fe] thin and high [α/Fe] thick discs of ESO 544-27 are inhabited primarily by similarly old metal-rich stellar populations, a contrast to that of other galaxies with known thin and thick disc stellar population properties.

MUSE view of PDS 456: Kiloparsec-scale wind, extended ionized gas, and close environment

PDS 456 is the most luminous (Lbol ∼ 1047 erg s−1) radio-quiet quasar at z < 0.3 and can be regarded as a local counterpart of the powerful quasars shining at Cosmic Noon. It hosts a strong nuclear X-ray ultra-fast (∼0.3c) outflow, and a massive and clumpy CO (3–2) molecular outflow extending up to ∼5 kpc from the nucleus. We analyzed the first MUSE Wide Field Mode (WFM) and Adaptive-Optics Narrow Field Mode (AO-NFM) optical integral field spectroscopic observations of PDS456. The AO-NFM observations provide an unprecedented spatial resolution, reaching up to ∼280 pc. Our findings reveal a complex circumgalactic medium around PDS 456, extending to a maximum projected size of ≈46 kpc. This includes a reservoir of gas with a mass of ∼107 − 108 M⊙, along with eight companion galaxies and a multi-phase outflow. WFM and NFM MUSE data reveal an outflow on a large scale (≈12 kpc from the quasar) in [O III], and on smaller scales (within 3 kpc) with higher resolution (about 280 pc) in Hα, respectively. The [O III] outflow mass rate is 2.3 ± 0.2 M⊙ yr−1 which is significantly lower than those typically found in other luminous quasars. Remarkably, the Hα outflow shows a similar scale, morphology, and kinematics to the CO (3–2) molecular outflow, with the latter dominating in terms of kinetic energy and mass outflow rate by two and one orders of magnitude, respectively. Our results therefore indicate that mergers, powerful active galactic nucleus (AGN) activity, and feedback through AGN-driven winds collectively contribute to shaping the host galaxy evolution of PDS 456, and likely that of similar objects at the brightest end of the AGN luminosity function across all redshifts. Moreover, the finding that the momentum boost of the total outflow deviates from the expected energy-conserving expansion for large-scale outflows highlights the need of novel AGN-driven outflow models to comprehensively interpret these phenomena.

Feedback and ionized gas outflows in four low-radio power AGN at z ∼ 0.15

An increasing number of observations and simulations suggests that low-power (< 1044 erg s−1) jets may be a significant channel of feedback produced by active galactic nuclei (AGN), but little is known about their actual effect on their host galaxies from the observational point of view. We targeted four luminous type 2 AGN hosting moderately powerful radio emission (∼1044 erg s−1), two of which and possibly a third are associated with jets, with optical integral field spectroscopy observations from the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT) to analyze the properties of their ionized gas as well as the properties and effects of ionized outflows. We combined these observations with Very Large Array (VLA) and e-MERLIN data to investigate the relations and interactions between the radio jets and host galaxies. We detected ionized outflows as traced by the fast bulk motion of the gas. The outflows extended over kiloparsec scales in the direction of the jet, when present. In the two sources with resolved radio jets, we detected a strong enhancement in the emission-line velocity dispersion (up to 1000 km s−1) perpendicular to the direction of the radio jets. We also found a correlation between the mass and the energetics of this high-velocity dispersion gas and the radio power, which supports the idea that the radio emission may cause the enhanced turbulence. This phenomenon, which is now being observed in an increasing number of objects, might represent an important channel for AGN feedback on galaxies

Integral field spectroscopy supports atmospheric optics to reveal the finite outer scale of the turbulence

The spatial coherence wavefront outer scale ( characterizes the size of the largest turbulence eddies in Earth's atmosphere, determining low spatial frequency perturbations in the wavefront of the light captured by ground-based telescopes. Advances in adaptive optics (AO) techniques designed to compensate for atmospheric turbulence emphasize the crucial role of this parameter for the next generation of large telescopes. The motivation of this work is to introduce a novel technique for estimating \ from seeing-limited integral field spectroscopic (IFS) data. This approach is based on the impact of a finite \ on the light collected by the pupil entrance of a ground-based telescope. We take advantage of the homogeneity of IFS observations to generate band filter images spanning a wide wavelength range, enabling the assessment of image quality (IQ) at the telescope's focal plane. Comparing the measured wavelength-dependent IQ variation with predictions derived from a first-order analytical approach based on turbulence statistics simplifications using the von Kármán model provides valuable insights into the prevailing \ parameter during the observations. We applied the proposed technique to observations from the Multi-Unit Spectroscopic Explorer (MUSE) in the wide-field mode obtained at the Paranal Observatory. Our analysis successfully validates the first-order analytical expression, which combines the seeing ($ $) and the \ parameters, to predict the IQ variations with the wavelength in ground-based astronomical data. However, we observed some discrepancies between the measured and predictions of the IQ that are analyzed in terms of uncertainties in the estimated $ $ and dome-induced turbulence contributions. This work constitutes the empirical validation of the analytical expression for estimating IQ at the focal plane of ground-based telescopes under specific $ $ and finite \ conditions. Additionally, we provide a simple methodology to characterize the \ and dome-seeing ($ dome $) as by-products of IFS observations routinely conducted at major ground-based astronomical observatories.

Optical tomography of the born-again ejecta of A 58

In a born-again planetary nebula (PN), processed H-deficient material has been injected inside the old, H-rich nebula as a result of a very late thermal pulse (VLTP) event. Long-slit spectra have been used to unveil the chemical and physical differences between these two structures, but the ejection and shaping processes still remain unclear. To peer into the morpho-kinematics of the H-deficient ejecta in the born-again PN A 58, we present the first integral field spectroscopic observations of a born-again PN as obtained with GTC MEGARA. We detect emission from the Hα, He I, [O III], [N II] and [S II] emission lines, which help us unveil the expansion patterns of the different structures. In combination with ALMA and Hubble Space Telescope data we have been able to produce a complete view of the H-deficient ionized and molecular ejecta in A 58. We propose an hourglass structure for the ionized material, which embraces molecular high-velocity polar components and is simultaneously bisected by an expanding toroidal molecular and dusty structure. Our results leverage the role of a companion in shaping the VLTP ejecta in this born-again PN.

Stellar populations and the origin of thick disks in AURIGA simulations

Context. Recent integral-field spectroscopy observations of edge-on galaxies have led to significant progress in our knowledge of the ages and chemical compositions of thick disks. However, the origin of thick disks and their evolutionary connection with thin disks is still a matter of debate. Aims. We provide new insights into this topic by connecting the stellar populations of thick disks at redshift z = 0 with their past formation and growth in 24 Milky Way-mass galaxies from the AURIGA zoom-in cosmological simulations. We assess the role played by mergers of satellite galaxies in the mass assembly of geometrically defined thick disks. Methods. We projected each galaxy edge on and decomposed it morphologically into two disk components in order to geometrically define the thin and thick disks, as is usually done in observations of external galaxies. We produced age, metallicity, and [Mg/Fe] edge-on maps of the 24 galaxies. We quantified the impact of satellite mergers by mapping the distribution of ex situ stars. Results. Thick disks are on average ∼3 Gyr older, ∼0.25 dex more metal poor, and ∼0.06 dex more [Mg/Fe]-enhanced than thin disks. Their average ages range from ∼6 to ∼9 Gyr, metallicities from ∼ − 0.15 to ∼0.1 dex, and [Mg/Fe] from ∼0.12 to ∼0.16 dex. These properties are the result of an early initial in situ formation, followed by a later growth driven by the combination of direct accretion of stars, some in situ star formation fueled by mergers, and dynamical heating of stars. The balance between these processes varies from galaxy to galaxy and impacts thick-disk ages and metallicities. The oldest thick disks (older than 8 Gyr) are hosted by galaxies with a low mass fraction of accreted stars (below 8%), while the youngest thick disks (younger than 7 Gyr) are found in galaxies with higher accreted fractions (larger than 25%). Mergers play a key role in the mass assembly of thick disks, contributing an average accreted mass fraction of ∼22% in the analyzed thick-disk-dominated regions. In two galaxies, about half of the geometric thick-disk mass was directly accreted. The mass fraction of accreted stars is lower than 10% only in four thick disks. While primordial thick disks form at high redshifts in all galaxies, young metal-rich thin disks, with much lower [Mg/Fe] abundances, start to form later but at different times (at higher or lower redshifts) depending on the galaxy. Conclusions. We conclude that thick disks, although mostly formed in situ, grow thanks to the significant contribution of satellite mergers, especially through the direct accretion of stars. They result from the interplay of external processes with the internal evolution of the galaxy.

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.

Galaxy kinematics and mass estimates at z ∼ 1 from ionized gas and stars

ABSTRACT We compare ionized gas and stellar kinematics of 16 star-forming galaxies (log (M⋆/M⊙) = 9.7–11.2, SFR =6 − 86 M⊙ yr−1) at z ∼ 1 using near-infrared integral field spectroscopy (IFS) of Hα emission from the KMOS3D (the K-band Multi-Object Spectrograph 3D) survey and optical slit spectroscopy of stellar absorption and gas emission from the LEGA-C (Large Early Galaxy Astrophysics Census) survey. Hα is dynamically colder than stars, with higher disc rotation velocities (by ∼45 per cent) and lower disc velocity dispersions (by a factor ∼2). This is similar to trends observed in the local Universe. We find higher rotational support for Hα relative to [O ii], potentially explaining systematic offsets in kinematic scaling relations found in the literature. Regarding dynamical mass measurements, for six galaxies with cumulative mass profiles from Jeans Anisotropic Multi-Gaussian Expansion (JAM) models the Hα dynamical mass models agree remarkably well out to ∼10 kpc for all but one galaxy (average $\Delta M_{\rm dyn}(R_{e,\rm F814W})\lt 0.1$ dex). Simpler dynamical mass estimates based on integrated stellar velocity dispersion are less accurate (standard deviation 0.24 dex). Differences in dynamical mass estimates are larger, for example, for galaxies with stronger misalignments of the Hα kinematic major axis and the photometric position angle, highlighting the added value of IFS observations for dynamics studies. The good agreement between the JAM and the dynamical models based on Hα kinematics at z ∼ 1 corroborates the validity of dynamical mass measurements from Hα IFS observations, which can be more easily obtained for higher redshift galaxies.

CAHA/PPAK Integral-field Spectroscopic Observations of M81. II. Testing Photoionization Models in a Spatially Resolved LINER

The origin of the low-ionization nuclear emission-line region (LINER) prevalent in local galaxies and its relationship with supermassive black holes have been debated for decades. We perform a comprehensive evaluation of traditional photoionization models against the circumnuclear ionized gas in M81, for which recent CAHA/PPAK integral-field spectroscopic observations reveal a LINER characteristic out to a galactocentric radius of ∼1 kpc. Constructed with the photoionization code cloudy, the models have the novel aspect of their primary parameters being well constrained by extensive observations of a prototypical low-luminosity active galactic nucleus (LLAGN) and an old stellar bulge in M81. Additionally, these models incorporate a reasonably broad range of uncertain nebular properties. It is found that the integrated photoionization by the LLAGN and hot, low-mass stars distributed in the bulge can roughly reproduce the observed radial intensity distributions of the Hα, Hβ, and [N ii] lines, with the bulge stars dominating the ionizing flux at radii ≳200 pc. However, the models generally fail to reproduce a similarly declining profile of the [O iii] line or an accordingly flat profile of the [O iii]/Hβ ratio. This clearly points to a deficiency of ionizing photons in the outer regions despite an extended photoionization source. The discrepancy might be alleviated if much of the observed [O iii] line arose from a bulge-filling, low-density gas surrounding a denser, Hα-emitting disk, or by a higher AGN luminosity in the recent past. The case of M81 has important implications for the ionization mechanism of LINERs and low-ionization emission-line regions in general.

Supermassive black hole mass in the massive elliptical galaxy M87 from integral-field stellar dynamics using OASIS and MUSE with adaptive optics: assessing systematic uncertainties

ABSTRACT The massive elliptical galaxy M87 has been the subject of several supermassive black hole mass measurements from stellar dynamics, gas dynamics, and recently the black hole shadow by the Event Horizon Telescope. This uniquely positions M87 as a benchmark for alternative black hole mass determination methods. Here, we use stellar kinematics extracted from integral-field spectroscopy observations with adaptive optics using Multi Unit Spectroscopic Explorer (MUSE) and Optically Adaptive System for Imaging Spectroscopy (OASIS). We exploit our high-resolution integral field spectroscopy to spectrally decompose the central actice galactic nuclei (AGNs) from the stars. We derive an accurate inner stellar-density profile and find it is flatter than previously assumed. We also use the spectrally extracted AGNs as a reference to accurately determine the observed MUSE and OASIS AO PSF. We then perform Jeans anisotropic modelling, with a new flexible spatially variable anisotropy, and measure the anisotropy profile, stellar mass-to-light variations, inner dark matter fraction, and black hole mass. Our preferred black hole mass is MBH = (8.7 ± 1.2[random] ± 1.3[systematic]) × 109 M⊙. However, using the inner stellar density from previous studies, we find a preferred black hole mass of $M_{\rm BH} = (5.5^{+0.5}_{-0.3}) \times 10^9 \ M_\odot$, consistent with previous work. We find that this is the primary cause of the difference between our results and previous work, in addition to smaller contributions due to kinematics and modelling method. We conduct numerous systematic tests of the kinematics and model assumptions and conclude that uncertainties in the black hole mass of M87 from previous determinations may have been underestimated and further analyses are needed.

Complex AGN feedback in the Teacup galaxy

Context. The z ∼ 0.1 type-2 QSO J1430+1339, known as the “Teacup”, is a complex galaxy showing a loop of ionised gas ∼10 kpc in diameter, co-spatial radio bubbles, a compact (∼1 kpc) jet, and outflow activity. Its closeness offers the opportunity to study in detail the intricate interplay between the central supermassive black hole (SMBH) and the material in and around the galaxy, both the interstellar medium (ISM) and circumgalactic medium (CGM). Aims. We characterise the spatially resolved properties and effects of the galactic ionised gas outflow and compare them with those of the radio jet and with theoretical predictions to infer its acceleration mechanism. Methods. We used VLT/MUSE optical integral field spectroscopic observations to obtain flux, kinematic, and excitation maps of the extended (up to ∼100 kpc) ionised gas and to characterise the properties of stellar populations. We built radial profiles of the outflow properties as a function of distance from the active nucleus, from kiloparsec up to tens of kiloparsec scales, at ∼1 kpc resolution. Results. We detect a velocity dispersion enhancement (≳300 km s−1) elongated over several kiloparsecs perpendicular to the radio jet, the active galactic nucleus (AGN) ionisation lobes, and the fast outflow, similar to what is found in other galaxies hosting compact, low-power jets, indicating that the jet strongly perturbs the host ISM during its passage. We observe a decreasing trend with distance from the nucleus for the outflow properties (mass outflow rate, kinetic rate, momentum rate). The mass outflow rate drops from around 100 M⊙ yr−1 in the inner 1–2 kpc to ≲0.1 M⊙ yr−1 at 30 kpc. The mass outflow rate of the ionised outflow is significantly higher (∼1–8 times) than the molecular one, in contrast with what is often quoted in AGN. Based on energetic and morphological arguments, the driver of the multi-phase outflow is likely a combination of AGN radiation and the jet, or AGN radiation pressure on dust alone. The outflow mass-loading factor is ∼5–10 and the molecular gas depletion time due to the multi-phase outflow is ≲108 yr, indicating that the outflow can significantly affect the star formation and the gas reservoir in the galaxy. However, the fraction of the ionised outflow that is able to escape the dark matter halo potential is likely negligible. We detect blue-coloured continuum emission co-spatial with the ionised gas loop. Here, stellar populations are younger (≲100–150 Myr) than in the rest of the galaxy (∼0.5–1 Gyr). This constitutes possible evidence for star formation triggered at the edge of the bubble due to the compressing action of the jet and outflow (“positive feedback”), as predicted by theory. All in all, the Teacup constitutes a rich system in which AGN feedback from outflows and jets, in both its negative and positive flavours, co-exist.