arXiv subjects

Susanne Aalto

Publications and source records attributed to Susanne Aalto.

At least 19 recordsLinked to original sources

arXiv2026

Efficient Interstellar Grain Growth from High Sticking Coefficients on Amorphous Carbon Dust

Cosmic dust is the solid phase of the interstellar medium (ISM), classically assumed to be composed of carbonaceous and silicate grains with size distributions spanning $\sim 5~Å$ to $\sim 1~μ$m (Weingartner & Draine 2001, Draine & Li 2007, Hensley & Draine 2023). While it constitutes at most order-of-magnitude $\mathbf{1\%}$ of the ISM mass, dust is second only to stars in importance for the observable properties of galaxies (Zavala et al. 2021). Large uncertainties in the efficiency of grain growth obfuscate the relative contribution of the two dominant sources of dust in the Universe: direct production from evolved stars versus gas-phase accretion in the ambient ISM (Feldmann 2015, Esmerian & Gnedin 2022, Esmerian & Gnedin 2024). Advances in supercomputers have only recently allowed us to move beyond simple, idealized predictions of dust grain growth efficiencies (Leitch-Devlin & Williams 1985) with atomistic dynamical calculations (Bossion et al. 2024). We show that small carbon dust grains can grow significantly on timescales much shorter than the age of the universe and, in some ISM phases, comparable to the lifetimes of giant molecular clouds. Specifically, we perform molecular dynamics simulations of an amorphous carbon (a-C) grain surface impacted by gas-phase atoms of cosmologically abundant elements with realistic interstellar conditions, finding high ($\gtrsim 0.2$) sticking coefficients for all non-inert elements at all relevant gas and grain temperatures. We present the results of experiments conducted on similar dust candidate materials that support our theoretical calculations. Our results therefore confirm that the process of gas-phase accretion onto grains is likely an efficient mechanism for the growth of interstellar dust mass on astrophysical timescales, and plausibly central to the evolutionary life-cycle of interstellar grains at all cosmic epochs. (abridged)

astro-ph.GA↗

arXiv2026

The Millimeter/X-ray Relation in Rapidly Accreting Supermassive Black Holes at $z < 0.16$

A tight correlation between nuclear millimeter and X-ray emission has recently been found in nearby ($z < 0.01$) and low-Eddington ratio ($\rm λ_{Edd} < 0.1$) radio-quiet Active Galactic Nuclei (AGN), suggesting a common origin in the hot X-ray corona. We test this relation in nine more distant RQ AGN ($z \sim 0.06-0.16$) with higher bolometric luminosities ($\log(L_{\rm bol}/\mathrm{erg\,s^{-1}})=45.3-46.3$), Eddington ratios ($\rm λ_{Edd} = 0.19-0.85$), and X-ray bolometric corrections ($κ_{2-10}=29-194$), selected from the Burst Alert Telescope (BAT) survey. We obtained quasi-simultaneous observations with Swift at 2-10 keV and the Atacama Large Millimeter/submillimeter Array (ALMA) at 100 GHz and with high angular resolution ($<0.14$"). We find that these high-luminosity AGN lie above the millimeter/X-ray correlation defined by lower-luminosity sources. A joint fit to both samples yields a second-degree polynomial with an intrinsic scatter of 0.32 dex. Furthermore, the millimeter emission correlates linearly with both the UV disk luminosity and $L_{\rm bol}$, with intrinsic scatters of 0.45 and 0.35 dex, respectively. We propose that the deviation from the linear millimeter/X-ray relation arises from a two-component coronal electron population: thermal electrons that produce X-rays, but become less efficient at higher luminosities, and nonthermal electrons that produce millimeter emission and remain tied to $L_{\rm bol}$. Additional millimeter emission from outflow-driven shocks may also contribute, though spectral energy distribution modeling and spectral index studies favor a coronal origin.

astro-ph.HE↗

arXiv2026

The PARADIGM Project II: Characterising Nuclear and Diffuse Radio Components in Local U/LIRGs

Disentangling SF and AGN emission is essential for understanding galaxy evolution, yet remains challenging in merging systems where both processes are enhanced and spatially intertwined. Galaxy mergers drive gas inflows that simultaneously fuel nuclear SBs and BH accretion, shaping morphology from nuclear ($\lesssim 250$~pc) to large-scale ($\gtrsim 500$~pc) regions. Radio interferometry provides an unobscured view, but separating compact nuclear SBs, AGN, and diffuse SF requires multiscale, multi-frequency observations. We present a systematic method to characterise multiscale radio properties in 15 local ($z\lesssim 0.1$) U/LIRGs ($L_{\mathrm{IR}} > 10^{11}\mathrm{L}_{\odot}$). Using \emph{e}-MERLIN and VLA at 1.4, 6.0 and 33.0~GHz, we probe physical scales from $\sim 10$--$250$~pc to $\sim 0.5$--$3.0$~kpc. We decompose radio emission into nuclear (compact cores and nuclear extended) and large-scale (total and diffuse) components, comparing morphological properties (emission fractions, sizes, luminosities, surface densities) and investigating correlations with source classes, merger stages, and $L_{\mathrm{IR}}$. We find: i) nuclear emission contributes $\sim$50\% of total radio emission on average; ii) total multiscale diffuse emission (SF-related) contributes $\sim$80\% to total power; iii) nuclear emission components act together to correlate with total radio and infrared luminosities, which increase with merger stage, whilst diffuse emission at larger scales shows no clear dependence on nuclear processes; iv) sources with radio excess (lower $q_{\mathrm{IR}}$) show lower nuclear luminosity ratios $L_{\mathrm{R,33}}^{\mathrm{N}}/L_{\mathrm{R,6}}^{\mathrm{N}}$, indicating a deficit of high-$ν$ radio emission; since 33.0~GHz traces recent SF, this suggests the radio excess is dominated by non-thermal emission at lower $ν$, likely AGN-related, rather than enhanced SF.

astro-ph.GA↗

arXiv2025

Clumpy, dense gas in the outflow of NGC 1266

Outflows are one of the most spectacular mechanisms through which active galactic nuclei (AGN) impact their host galaxy, though the role of AGN-driven outflows in global star formation regulation across the galaxy population is unclear. NGC 1266 is an excellent case study for investigating the outflows and star formation quenching because it is a nearby (D\sim30 Mpc) AGN host galaxy with an outflow driving shocks through the interstellar medium (ISM) and has recently quenched its star formation outside the nucleus. While previous works have studied the molecular outflow from its CO emission, to fully characterize the impact the outflow has on the ISM observations probing the dense, cold gas are necessary. Our ALMA cycle 0 observations do not detect a molecular outflow in 13CO(2-1) and yield a lower limit 12CO/13CO \geq 250, suggesting a highly optically thin CO outflow with low 13CO abundance. In contrast, we detect substantial HCN(1-0) emission in the outflow, with an HCN(1-0)/12CO(1-0) ratio of 0.09, consistent with global measurements of many star-forming galaxies and Luminous InfraRed Galaxies (LIRGs). We conclude that the CO emission traces a diffuse component of the molecular gas with a low optical depth, whereas the HCN(1-0) traces dense clumps of gas entrained in the outflow. We measure an upper limit molecular outflow rate of < 85 Msun/yr. Assuming the ongoing nuclear star formation and outflow continue at the same rates, NGC 1266 will deplete its gas reservoirs in 450 Myr or longer, indicating that relatively low-level AGN feedback is capable of gradually expelling the molecular gas reservoir after a rapid quenching event.

astro-ph.GA↗

arXiv2025

Probing Infrared eXcess to Investigate Early-Universe Dust (PIXIEDust)

Despite the implied presence of dust through reddened UV emission in high-redshift galaxies, no dust emission has been detected in the (sub)millimetre regime beyond $z > 8.3$. This study combines around two hundred hours of Atacama Large Millimeter/submillimeter Array (ALMA) and Northern Extended Millimeter Array (NOEMA) observations on ten $z > 8$ galaxies, revealing no significant dust emission down to a $1 σ$ depth of $2.0$, $2.0$, and $1.5 \,μ$Jy at rest-frame 158, 88 $μ$m, and across all the data, respectively. This constrains average dust masses to be below $< 10^{5}$ M$_{\odot}$ at $3 σ$ and dust-to-stellar mass ratios to be below $3.7 \times{} 10^{-4}$ (assuming $T_{\rm dust} = 50$ K and $β_{\rm dust} = 2.0$). Binning by redshift ($8 < z < 9.5$ and $9.5 < z < 15$), UV-continuum slope ($β_{\rm UV} \lessgtr -2$) and stellar mass ($\log_{10} M_{\ast}/{\rm M_{\odot}} \lessgtr 9$) yields similarly stringent constraints. Combined with other studies, these results are consistent with inefficient dust build-up in the $z > 8$ Universe, likely due to inefficient supernova production, limited interstellar grain growth and/or ejection by outflows. We provide data and tools online to facilitate community-wide high-redshift dust searches.

astro-ph.GA↗

arXiv2025

An empirical view of the extended atmosphere and inner envelope of the asymptotic giant branch star R Doradus. II. Constraining the dust properties with radiative transfer modelling

Mass loss in oxygen-rich asymptotic giant branch (AGB) stars remains poorly understood, as the dust detected around them appears too transparent to drive winds through absorption alone. The current paradigm invokes outflows driven by photon scattering on relatively large grains ($\sim0.3\,μ$m), but whether such grains exist in sufficient quantities remains uncertain. We test whether the dust around the oxygen-rich AGB star R~Doradus can drive its wind by combining polarimetric constraints, elemental abundance limits, and force-balance calculations. We examine Fe-free silicates (MgSiO$_3$), alumina (Al$_2$O$_3$), and Fe-bearing silicates (MgFeSiO$_4$) to evaluate whether any species can produce enough radiative pressure under realistic conditions. Using high-angular-resolution polarimetric observations from SPHERE/ZIMPOL at the VLT, we model the circumstellar dust with RADMC-3D and explore a broad parameter space in grain size, density structure, and wavelength-dependent stellar radius. For models consistent with the observations, we assess wind feasibility using updated gas-density profiles, elemental depletion constraints, and radiation-pressure thresholds. Although several dust configurations reproduce the observed scattering patterns, none generate sufficient radiative force at realistic gas-to-dust ratios, even under maximal elemental depletion. Our results for R~Doradus indicate that photon scattering on dust cannot by itself launch the wind, implying that additional mechanisms must contribute.

astro-ph.SR↗

arXiv2025

A warm ultra-luminous infrared galaxy just 600 million years after the Big Bang

We present an Atacama Large Millimeter/submillimeter Array (ALMA) Band 9 continuum detection ($3.3 σ$) of MACS0416_Y1 that confirms the suspected warm dust (91$^{+62}_{-35}$ K) of this Lyman-Break Galaxy (LBG) at $z = 8.3$ with $\log_{10} M_{\ast}/$M$_{\odot} = 9.0 \pm 0.1$. A modified black-body fit to the ALMA Bands 3 through 9 data of MACS0416_Y1 finds an intrinsic infrared luminosity of 1.0$^{+1.8}_{-0.6} \times{} 10^{12}\ \mathrm{L_{\odot}}$, placing this UV-selected LBG in the regime of Ultra Luminous Infrared Galaxies (ULIRGs). Its luminous but modest dust reservoir (1.4$^{+1.3}_{-0.5} \times{} 10^{6}\ \mathrm{M_{\odot}}$) is co-spatial to regions with a UV-continuum slope $β_{\rm UV} \approx -1.5$ as seen by James Webb Space Telescope (JWST) imaging. Although this implies some dust obscuration, the JWST photometry implies less obscured star formation than seen in the complete characterization by ALMA, implying some spatial separation of dust and stars on scales below 200 pc, i.e., smaller than those probed by JWST and ALMA. This source is an extreme example of dust-obscured star formation contributing strongly to the cosmic build-up of stellar mass, which can only be revealed through direct and comprehensive observations in the (sub)mm regime.

astro-ph.GA↗

arXiv2025

The Binding Energies of Atoms on Amorphous Silicate Dust: A Computational Study

Context. We investigate the binding energies of atoms to interstellar dust particles, which play a key role in their growth and evolution, as well as for the chemical reactions on their surfaces. Aims. We aim to compute the binding energies of abundant atoms in the interstellar medium (C, N, O, Mg, Al, Si, S, Ca, Fe, and Ni) to silicate dust. Methods. We used the Geometries, Frequencies, and Non-covalent Interactions Tight Binding (GFN1-xTB) method to compute the binding energies. An FeMgSiO$_4$ periodic surface model, containing 81 local minima on the surface, was used. Results. A range of binding energies was found for each element. The median of the binding energies follows the order Si (14.8 eV) > Al (12.8 eV) > Ca (12.7 eV) > C (9.5 eV) > O (8.1 eV) > N (6.2 eV) > Fe (6.0 eV) > S (5.2 eV) > Mg (2.4 eV). The probability distribution of binding energies for each element except Ca is statistically consistent with a log-normal distribution. Conclusions. In general, Si, Ca, and Al atoms have large binding energies. Thus, these atoms can stay on the silicate dust particles at high temperatures. The binding energies of the other atoms, C, N, O, Mg, S, Fe and Ni, are relatively weak. However, the computed binding energies for these elements are still far stronger than the energies associated with dust temperatures typical of the ambient interstellar medium (ISM), suggesting that silicate grains are generally stable against sublimation. We estimate sublimation temperatures for silicate grains to range from 1600 K to 3000K depending on assumed grain size and lifetime. These binding energies on silicate dust grains, estimated from first principles for the first time, provide invaluable input to models of dust evolution and dust-catalyzed chemical reactions in the interstellar medium.

astro-ph.GA↗

arXiv2025

GOALS-JWST: The Warm Molecular Outflows of the Merging Starburst Galaxy NGC 3256

We present James Webb Space Telescope (JWST) Integral Field Spectrograph observations of NGC 3256, a local infrared-luminous late-stage merging system with two nuclei roughly 1$\;\rm{kpc}$ apart, both of which have evidence of cold molecular outflows. Using JWST/NIRSpec and MIRI datasets, we investigate this morphologically complex system on spatial scales of $<$100$\;\rm{pc}$, where we focus on the warm molecular H$_2$ gas surrounding the nuclei. We detect collimated outflowing warm H$_2$ gas originating from the southern nucleus, though we do not find significant outflowing H$_2$ gas surrounding the northern nucleus. We measure maximum intrinsic outflow velocities of $\sim$1,000$\;\rm{km}\;\rm{s}^{-1}$, which extend out to a distance of 0.7$\;\rm{kpc}$. Based on H$_2$ S(7)/S(1) ratios, we find a larger fraction of warmer gas near the S nucleus, which decreases with increasing distance from the nucleus, signifying the southern nucleus as a primary source of H$_2$ heating. The gas mass of the warm H$_2$ outflow component is estimated to be $M\rm{_{warm,out}}=(1.4\pm0.2)\times10^6\;\rm{M}_{\odot}$, as much as 6$\%$ of the cold H$_2$ mass estimated using ALMA CO data. The outflow time scale is about $7\times10^5\;\rm{yr}$, resulting in a mass outflow rate $\dot{M}\rm{_{warm,out}}=2.0\pm0.8\;\rm{M}_{\odot}\;\rm{yr}^{-1}$ and kinetic power $P\rm{_{warm,out}}\;\sim\;4\times10^{41}\;\rm{erg}\;\rm{s}^{-1}$. Lastly, regions within our 3.0"x3.0" NIRSpec data where the outflowing gas reside show high [Fe II]/Pa$β$ and H$_2$/Br$γ$ line ratios, indicate enhanced mechanical heating caused by the outflows. The fluxes and ratios of Polycyclic Aromatic Hydrocarbons (PAH) in these regions are not significantly different compared to those elsewhere in the disk, suggesting the outflows may not significantly alter the PAH ionization state or grain size.

astro-ph.GA↗

arXiv2025

A Census of the Most Obscured Galaxy Nuclei over Cosmic Time to be revealed by PRIMA

Characterizing the growth of supermassive Black Holes (SMBHs) is critical to the evolution of galaxies, however the majority of this activity is obscured, rendering traditional tracers of active SMBHs, such as in the restframe optical/UV, ineffective. The mid-infrared has been particularly successful in revealing obscured AGN activity however much of this work is confined to the local universe due to the lack of a far-IR telescope with the required sensitivity and wavelength coverage. In this work we demonstrate the effectiveness of PRIMA (PRobe far-Infrared Mission for Astrophysics), a concept 1.8m far-IR observatory, to detect and characterize deeply obscured galaxy nuclei over cosmic time. With the PRIMAger instrument covering 25 - 235 $μ$m, we find that we can accurately detect obscured nuclei via the deep silicate absorption at restframe $9.8 μ$m between $z=2-7$. Additionally, the FIRESS spectrograph can produce R$\sim$100 spectra of obscured nuclei out to $z\sim7$, detecting Polycyclic Aromatic Hydrocarbons (PAHs), ices, ionized and molecular gas. With the large number of deeply obscured nuclei PRIMA can detect and characterize, such a mission is critical to understanding the growth of SMBHs.

astro-ph.GA↗

arXiv2024

A High-resolution Far-infrared Survey to Probe Black Hole-Galaxy Co-evolution

Far-infrared (FIR) surveys are critical to probing the co-evolution of black holes and galaxies, since of order half the light from accreting black holes and active star formation is emitted in the rest-frame infrared over $0.5\lesssim z \lesssim 10$. For deep fields with areas of 1 deg$^2$ or less, like the legacy surveys GOODS, COSMOS, and CANDELS, source crowding means that sub-arcsecond resolution is essential. In this paper, we show with a simulation of the FIR sky that observations made with a small telescope (2 m) at low angular resolution preferentially detect the brightest galaxies, and we demonstrate the scientific value of a space mission that would offer sub-arcsecond resolution. We envisage a facility that would provide high-resolution imaging and spectroscopy over the wavelength range $25-400\,μm$, and we present predictions for an extragalactic survey covering $0.5\,\hbox{deg}^2$. Such a survey is expected to detect tens of thousands of star-forming galaxies and thousands of Active Galactic Nuclei (AGN), in multiple FIR lines (e.g. [CII], [OI], [CI]) and continuum. At the longest wavelengths (200-400$\,μ$m), it would probe beyond the reionization epoch, up to $z\sim 7$-8. A combination of spectral resolution, line sensitivity, and broad spectral coverage would allow us to learn about the physical conditions (temperature, density, metallicity) characterizing the interstellar medium of galaxies over the past $\sim 12$ billion years and to investigate galaxy-AGN co-evolution.

astro-ph.GA↗

arXiv2024

Accurate sticking coefficient calculation for carbonaceous dust growth through accretion and desorption in astrophysical environments

Context. Cosmic dust is ubiquitous in astrophysical environments, where it significantly influences the chemistry and the spectra. Dust grains are likely to grow through the accretion of atoms and molecules from the gas-phase onto them. Despite their importance, only a few studies compute sticking coefficients for relevant temperatures and species, and their direct impact on grain growth. Overall, the formation of dust and its growth are processes not well understood. Aims. To calculate sticking coefficients, binding energies, and grain growth rates over a wide range of temperatures, for various gas species interacting with carbonaceous dust grains. Methods. We perform molecular dynamics simulations with a reactive force field algorithm to compute accurate sticking coefficients and obtain binding energies. The results are included in an astrophysical model of nucleation regions to study dust growth. Results. We present, for the first time, sticking coefficients of H, H2, C, O, and CO on amorphous carbon structures for temperatures ranging from 50 K to 2250 K. In addition, we estimate the binding energies of H, C, and O in carbonaceous dust to calculate the thermal desorption rates. Combining accretion and desorption allows us to determine an effective accretion rate and sublimation temperature for carbonaceous dust. Conclusions. We find that sticking coefficients can differ substantially from what is commonly used in astrophysical models and this gives new insight on carbonaceous dust grain growth via accretion in dust-forming regions.

astro-ph.GA↗

arXiv2024

Components of star formation in NGC 253 : Non-negative Matrix Factorization Analysis with the ALCHEMI integrated intensity images

It is essential to examine the physical or chemical properties of molecular gas in starburst galaxies to reveal the underlying mechanisms characterizing starbursts. We used non-negative matrix factorization (NMF) to extract individual molecular or physical components involved in the star formation process in NGC\,253. We used images of 148 transitions from 44 different species of the ALMA large program ALCHEMI. Additionally, we included the continuum images at ALMA Bands 3 and 7 from the same dataset. For the five NMF components (NF1--5), we obtained that their distributions correspond to various basic phenomena related to star formation: i) low-density gas extended through the galactic central molecular zone (NF2), ii) shocks (NF3), iii) starburst regions (NF4), and iv) young star-forming regions (NF5). The other component (NF1) is related to excitation; three components obtained by NMF (NF3, 1, and 5) show a strong dependence upon the upper state energies of transitions, and represent low-, intermediate-, and high-excitation, respectively. We also compared our results using principal component analysis (PCA) previously applied to the same dataset. Molecular components extracted from NMF are similar to the ones obtained from PCA. However, NMF is better at extracting components associated with a single physical component, while a single component in PCA usually contains information on multiple physical components. This is especially true for features with weak intensities like emission from outflows. Our results suggest that NMF can be one of promising methods interpreting molecular line survey data, especially in the upcoming era of wide-band receivers.

astro-ph.GA↗

arXiv2024

Pulling back the curtain on shocks and star-formation in NGC 1266 with Gemini-NIFS

We present Gemini near-infrared integral field spectrograph (NIFS) K-band observations of the central 400 pc of NGC 1266, a nearby (D$\approx$30 Mpc) post-starburst galaxy with a powerful multi-phase outflow and a shocked ISM. We detect 7 H$_2$ ro-vibrational emission lines excited thermally to $T$$\sim$2000 K, and weak Br$γ$ emission, consistent with a fast C-shock. With these bright H$_2$ lines, we observe the spatial structure of the shock with an unambiguous tracer for the first time. The Br$γ$ emission is concentrated in the central $\lesssim$100 pc, indicating that any remaining star-formation in NGC 1266 is in the nucleus while the surrounding cold molecular gas has little on-going star-formation. Though it is unclear what fraction of this Br$γ$ emission is from star-formation or the AGN, assuming it is entirely due to star-formation we measure an instantaneous star-formation rate of 0.7 M$_\odot$ yr$^{-1}$, though the star-formation rate may be significantly higher in the presence of additional extinction. NGC 1266 provides a unique laboratory to study the complex interactions between AGN, outflows, shocks, and star-formation, all of which are necessary to unravel the evolution of the post-starburst phase.

astro-ph.GA↗

arXiv2024

GOALS-JWST: Constraining the Emergence Timescale for Massive Star Clusters in NGC 3256

We present the results of a James Webb Space Telescope (JWST) NIRCam and NIRSpec investigation into the young massive star cluster (YMC) population of NGC 3256, the most cluster-rich luminous infrared galaxy (LIRG) in the Great Observatories All Sky LIRG Survey. We detect 3061 compact YMC candidates with a $S/N \geq 3$ at F150W, F200W, and F335M. Based on yggdrasil stellar population models, we identify 116/3061 sources with F150W - F200W $> 0.47$ and F200W - F355M $> -1.37$ colors suggesting they are young (t $\leq 5$ Myr), dusty ($A_{V} = 5 - 15$), and massive ($M_{\odot} > 10^{5}$). This increases the sample of dust-enshrouded YMCs detected in this system by an order of magnitude relative to previous HST studies. With NIRSpec IFU pointings centered on the northern and southern nucleus, we extract the Pa$α$ and 3.3$μ$m PAH equivalent widths for 8 bright and isolated YMCs. Variations in both the F200W - F335M color and 3.3$μ$m PAH emission with the Pa$α$ line strength suggest a rapid dust clearing ($< 3 - 4$ Myr) for the emerging YMCs in the nuclei of NGC 3256. Finally, with both the age and dust emission accurately measured we use yggdrasil to derive the color excess (E(B - V)) for all 8 YMCs. We demonstrate that YMCs with strong 3.3$μ$m PAH emission (F200W - F335M $> 0$) correspond to sources with E(B - V) $> 3$, which are typically missed in UV-optical studies. This underscores the importance of deep near-infrared imaging for finding and characterizing these very young and dust-embedded sources.

astro-ph.GA↗

arXiv2024

The fountain of the luminous infrared galaxy Zw049.057 as traced by its OH megamaser

High resolution (0."037-0."13 [10-35 pc]) e-MERLIN ($\lambda6-18$ cm) and (0."024 [6.5 pc]) ALMA ($λ1.1$ mm) observations have been used to image OH (hydroxyl) and H$_2$CO (formaldehyde) megamaser emission, and HCN 3->2 emission towards the nuclear (<100 pc) region of the luminous infrared galaxy Zw049.057. Zw049.057 hosts a compact obscured nucleus (CON), thus representing a class of galaxies that are often associated with inflow and outflow motions. Formaldehyde megamaser emission is detected towards the nuclear region, <30 pc (<0."1), and traces a structure along the disk major axis. OH megamaser (OHM) emission is detected along the minor axis of the disk, ~30 pc (0."1) from the nucleus, where it exhibits a velocity gradient with extrema of -20 km/s south-east (SE) of the disk and -110 km/s north-west (NW) of the disk. HCN 3->2 emission reveals extended emission, along the disk minor axis out to ~60 pc (0."2). Analysis of the minor axis HCN emission reveals high-velocity features, extending out to 600 km/s, redshifted on the SE side and blueshifted on the NW side. We propose that the high-velocity HCN emission traces a fast >250 km/s and collimated outflow, that is enveloped by a wide-angle and slow ~50 km/s outflow that is traced by the OHM emission. Analysis of the outflow kinematics suggests that the slow wide-angle outflow will not reach escape velocity and instead will fall back to the galaxy disk, evolving as a so-called fountain flow, while the fast collimated outflow traced by HCN emission will likely escape the nuclear region. We suggest that the absence of OHM emission in the nuclear region is due to high densities there. Even though OHMs associated with outflows are an exception to conventional OHM emission, we expect them to be common in CON sources that host both OHM and H$_2$CO megamasers.

astro-ph.GA↗

arXiv2024

GOALS-JWST: Mid-Infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the AGN in the LIRG VV 114

The enormous increase in mid-IR sensitivity and spatial and spectral resolution provided by the JWST spectrographs enables, for the first time, detailed extragalactic studies of molecular vibrational bands. This opens an entirely new window for the study of the molecular interstellar medium in luminous infrared galaxies (LIRGs). We present a detailed analysis of rovibrational bands of gas-phase CO, H$_2$O, C$_2$H$_2$ and HCN towards the heavily-obscured eastern nucleus of the LIRG VV 114, as observed by NIRSpec and MIRI MRS. Spectra extracted from apertures of 130 pc in radius show a clear dichotomy between the obscured AGN and two intense starburst regions. We detect the 2.3 $μ$m CO bandheads, characteristic of cool stellar atmospheres, in the star-forming regions, but not towards the AGN. Surprisingly, at 4.7 $\mathrmμ$m we find highly-excited CO ($T_\mathrm{ex} \approx 700-800$ K out to at least rotational level $J = 27$) towards the star-forming regions, but only cooler gas ($T_\mathrm{ex} \approx 200$ K) towards the AGN. We conclude that only mid-infrared pumping through the rovibrational lines can account for the equilibrium conditions found for CO and H$_2$O in the deeply-embedded starbursts. Here the CO bands probe regions with an intense local radiation field inside dusty young massive star clusters or near the most massive young stars. The lack of high-excitation molecular gas towards the AGN is attributed to geometric dilution of the intense radiation from the bright point source. An overview of the relevant excitation and radiative transfer physics is provided in an appendix.

astro-ph.GA↗

arXiv2024

GOALS-JWST: Gas Dynamics and Excitation in NGC7469 revealed by NIRSpec

We present new JWST-NIRSpec IFS data for the luminous infrared galaxy NGC7469: a nearby (70.6Mpc) active galaxy with a Sy 1.5 nucleus that drives a highly ionized gas outflow and a prominent nuclear star-forming ring. Using the superb sensitivity and high spatial resolution of the JWST instrument NIRSpec-IFS, we investigate the role of the Seyfert nucleus in the excitation and dynamics of the circumnuclear gas. Our analysis focuses on the [Fe ii], H2, and hydrogen recombination lines that trace the radiation/shocked-excited molecular and ionized ISM around the AGN. We investigate the gas excitation through H2/Brγ and [Fe ii]/Pa\b{eta} emission line ratios and find that photoionization by the AGN dominates within the central 300 pc of the galaxy and together with a small region show ing signatures of shock-heated gas; these shock-heated regions are likely associated with a compact radio jet. In addition, the velocity field and velocity dispersion maps reveal complex gas kinematics. Rotation is the dominant feature, but we also identify non-circular motions consistent with gas inflows as traced by the velocity residuals and the spiral pattern in the Paα velocity dispersion map. The inflow is consistent with the mass outflow rate and two orders of magnitude higher than the AGN accretion rate. The compact nuclear radio jet has enough power to drive the highly ionized outflow. This scenario suggests that the inflow and outflow are in a self-regulating feeding-feedback process, with a contribution from the radio jet helping to drive the outflow.

astro-ph.GA↗