arXiv subjects

Ashley Barnes

Publications and source records attributed to Ashley Barnes.

At least 19 recordsLinked to original sources

arXiv2026

Low cosmic-ray ionisation at parsec scales in G035.39-00.33

Cosmic rays (CRs) regulate the chemical evolution of the gas and its coupling to the magnetic field in the densest and coldest regions of the interstellar medium (ISM). However, the CR ionisation rate of H$_2$ ($\zeta_2$) is one of the most debated parameters characterising molecular clouds due to the uncertainties in its estimation. We developed a new analytical framework based on the chemistry of N$_2$H$^+$, N$_2$D$^+$ and DCO$^+$ to overcome observational limitations in current estimates of $\zeta_2$ and to probe the latter and the electron fraction, $x(e)$, in the gas across multiple density regimes. We applied this method towards the parsec-scale filament of the infrared dark cloud (IRDC) G035.39-00.33 with new observations from the NOrthern Extended Array (NOEMA) at a resolution of $3''$ (or $\sim9000$ au). Ancillary observations of C$^{18}$O complete this survey to measure $x(e)$ and $\zeta_2$ in G035.39-00.33. CO depletion is widespread in G035.39-00.33 with factors, $f_\mathrm{D}$, positively correlated with column and number densities of H$_2$ in the cloud. The deuterium fractions ($R_\mathrm{D}$) are enhanced towards these same sites in which the corresponding electron fraction values cluster below $\lesssim10^{-8}$. $\zeta_2$ varies by three orders of magnitude in G035.39-00.33 ($\sim10^{-18}-10^{-15}$ s$^{-1}$) with a median of $\sim2.3\times10^{-18}$ s$^{-1}$, consistent with those reported for other IRDCs and giant filaments, but on average lower than the typical $\zeta_2$ for the ISM. $\zeta_2$ shows a functional dependence on $N(\mathrm{H_2})$, but with absolute values lower compared to those predicted by theoretical models. This behaviour suggests the presence of an overall attenuation of the CR flux taking place in G035.39-00.33. The CR flux appears to be reduced by the change in magnetic field strength and morphology previously reported in the region.

astro-ph.GA↗

arXiv2026

Surveying the Whirlpool at Arcseconds with NOEMA (SWAN). IV. Extent of active galactic nucleus feedback on the interstellar medium

Active Galactic Nuclei (AGN) are intertwined with galaxy evolution, injecting energy into the interstellar medium (ISM) that could regulate star formation as a galaxy evolves. However, the phenomena through which we observe AGN are multiphase and multiscale, which can lead to conflicting results for how significantly AGN influence the ISM. We endeavor to characterize the spatial extent and dominant modes of AGN feedback in M51, which hosts a low-luminosity Seyfert nucleus and multi-phase outflow. We identified regions dominated by AGN ionization using an emission line ratio (ELR) function constructed from VENGA integral field spectroscopy. We then investigated how AGN feedback influences the ISM using cloud-scale mapping of dense molecular gas tracers HCN(1-0), HNC(1-0), HCO+(1-0), and N2H+(1-0) provided by SWAN. This combined dataset has a resolution of 180pc, providing a clear demarcation of where AGN feedback dominates the ISM. If we assume that N2H+ is the best tracer of dense, cold gas in SWAN, then AGN-dominated regions defined by the ELR all have greater emission in (1-0) transitions in HCN, HNC, and HCO+ than expected if they traced dense gas alone, implying excitation of these lines from the AGN. The ELR better selects these regions than molecular tracers of AGN activity like HCN/HCO+. The highest ELR values are also associated with optical and molecular shock tracers (HNCO/CO), indicating a potential dense molecular outflow in the nucleus that agrees with the heightened N2H+ emission in this limited region. All tracers of AGN activity point to a "two-stage" feedback scenario, whereby mechanical feedback from the jet-ISM interaction spurs soft X-ray emission that excites molecules such as HCN. Dense gas entrenched in a molecular outflow may also lead to a greater chemical abundance of multiple tracers measured with SWAN, but to a lesser extent than excitation from AGN feedback.

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arXiv2026

The Structure of Molecular Gas in PHANGS-ALMA Galaxies: Cloud Spacing, Two-Point Correlation and Stacked Intensity Profiles

The sub-kpc scale gas structure encodes key information of giant molecular cloud (GMC) formation. Therefore, we aim for a quantitative description of molecular gas structure across 150-1000 pc using a sample of 8984 GMCs from 40 galaxies observed by PHANGS-ALMA. We homogenize our data to a fixed resolution of 150 pc and mass sensitivity of 2.5 M$_{\odot}$ pc$^{-2}$ to remove observational bias. We then calculate nearest neighbour distances, neighbour number density, and two-point correlation functions for the catalogued GMCs. When analysing the two-point correlation function, we generate several control samples that reflect different null hypotheses on large spatial scales. We stack integrated intensity CO emission profiles around the position of catalogued GMCs to probe the gas distribution on scales between the resolution limit and the typical GMC-GMC spacing. Our measurements of cloud spacing and number of neighbours show that GMC clustering follows the large-scale gas distribution. Once we account for this contribution, the peak excess clustering in the two-point correlation function drops from 1+$\omega$ of 2.3 to 1.3, with the power-law slope flattened from -0.25 to 0. We show that the stacked CO intensity profiles around CO peaks can be recovered by the "GMC size" measured by CPROPS, with an additional 20% of the flux in an extended component beyond 500 pc. We find that our stacked profiles can be fit with a double Gaussian function plus a constant offset. The broad Gaussian component accounts for 70% of the over-density power above the constant offset, and is stronger around massive and gravitationally bound GMCs. Our results indicate that galactic structure regulates the GMC distribution in galaxy disks, and the formation of massive, gravitationally bound GMCs is related to strong local gas clustering.

astro-ph.GA↗

arXiv2026

Constraining the Sub-Galactic Relationship Between Star Formation and the Hot Interstellar Medium in NGC 4254

We investigate the relationship between star formation and X-ray emission from the hot interstellar medium (ISM) on $\sim$kpc scales in NGC 4254 (M99) by combining spatially resolved star formation histories (SFHs) and Bayesian X-ray spectral fitting. We measure sub-galactic star formation rates (SFR) by modeling spectrophotometric UV-IR data with flexible SFHs, and we produce point-source-subtracted maps of the diffuse X-ray emission using Chandra data. We extract and fit the spectra of 5 regions selected by their SFR density $\Sigma_{\rm SFR}$, deriving hot gas luminosities and plasma temperatures. We examine the sub-galactic $kT-\Sigma_{\rm SFR}$ and $L^{\rm gas}_X-\Sigma_{\rm SFR}$ scaling relations in NGC 4254, and compare to predictions from simple models of the feedback into the ISM from core collapse supernovae (CCSNe). The hot gas emission from NGC 4254 is consistent with thermalization of $\approx 40-50\%$ of the energy from CCSNe in the ISM, and mass-loading of the CCSNe ejecta which decreases as $\Sigma_{\rm SFR}^{-1/3}$. Our optimized model implies a temperature and X-ray production efficiency that scale as $kT = (0.72^{+0.26}_{-0.18}~{\rm keV}) \Sigma_{\rm SFR}^{0.34\pm0.10}$ and $\eta = (0.03^{+0.02}_{-0.01}) \Sigma_{\rm SFR}^{0.34\pm0.18}$, respectively, for $\Sigma_{\rm SFR} = 0.01-0.13~{\rm M_{\odot}~yr^{-1}~kpc^{-2}}$. We also compare the properties of the hot ISM to other ISM phases using data from the PHANGS program. The diffuse X-ray emission of a given region is on average 200 times fainter than the H$\alpha$ emission, and we see evidence that the hot ISM is over-pressurized compared to the large-scale dynamical equilibrium pressure of the galaxy, consistent with expansion of the hot ISM into the ambient medium.

astro-ph.GA↗

arXiv2025

Discovery of a Giant Molecular Cloud at the Midpoint of the Galactic Bar Dust Lanes: M4.7-0.8

We present the detection of a previously unknown giant molecular cloud (GMC) located at the midpoint of the Galactic Bar Dust Lanes (M4.7--0.8), using spectral line observations taken with the Green Bank Telescope (GBT). This $\sim$60 pc long GMC is associated with accreting material that is transitioning from the quieter Galactic disk environment to the more extreme central molecular zone (CMZ) environment. Our 24 GHz single-dish radio observations targeted the NH$_3$ (1,1)$-$(4,4) and HC$_5$N (9$-$8), known dense gas tracers. The observations reveal the main features of the GMC, which we have dubbed the `Nexus' and `Filament', covering a 0$.\!\!^\circ$5$\times$0$.\!\!^\circ$25 area at 31$''$ angular resolution. In this publication we investigate the gas kinematics within the observed region and compare the distribution of molecular emission to previous infrared surveys to better understand the dust component. The observed gas tracers show centrally condensed cores corresponding to the positions of high dust column densities and low dust temperatures. We report the detection of a previously unknown NH$_3$ (3,3) maser, along with a 70$\mu$m source association, which supports the identification of this region as being actively star-forming. Gas emission in this region shows broad linewidths, comparable to values seen in CMZ clouds. The overall description of this cloud that we present is that of a highly dynamic region comprising dense gas and dust. This encapsulates a wide range of features associated with star formation, in addition to material transport related to the CMZ.

astro-ph.GA↗

arXiv2025

Linking stellar populations to HII regions across nearby galaxies. II. Infrared Reprocessed and UV Direct Radiation Pressure in HII Regions

Radiation pressure is a key mechanism by which stellar feedback disrupts molecular clouds and drives HII region expansion. This includes direct radiation pressure exerted by UV photons on dust grains, pressure associated with photoionization, and infrared (IR) radiation pressure on grains due to dust-reprocessed IR photons. We present a new method that combines high resolution mid-IR luminosities from JWST-MIRI, optical attenuation and nebular line measurements from VLT-MUSE, and HST H$\alpha$-based region sizes to estimate the strength of radiation pressure in $\approx 18,000$ HII regions across 19 nearby star-forming galaxies. This is the most extensive and direct estimate of these terms beyond the Local Group to date. In the disks of galaxies, we find that the total reprocessed IR pressure is on average 5% of the direct UV radiation pressure. This fraction rises to 10% in galaxy centers. We expect reprocessed IR radiation pressure to dominate over UV radiation pressure in regions where $L_{\rm F2100W}/L_{\rm H\alpha}^{\rm corr} \gtrsim 75$. Radiation pressure due to H ionizations is lower than pressure on dust in our sample, but appears likely to dominate the radiation pressure budget in dwarf galaxies similar to the Small Magellanic Cloud. The contribution from all radiation pressure terms appears to be subdominant compared to thermal pressure from ionized gas, reinforcing the view that radiation pressure is most important in compact, heavily embedded, and young regions.

astro-ph.GA↗

arXiv2024

Dense gas scaling relations at kiloparsec scales across nearby galaxies with the ALMA ALMOND and IRAM 30m EMPIRE surveys

Dense, cold gas is the key ingredient for star formation. Over the last two decades, HCN(1-0) emission has been utilised as the most accessible dense gas tracer to study external galaxies. We present new measurements tracing the relationship between dense gas tracers, bulk molecular gas tracers, and star formation in the ALMA ALMOND survey, the largest sample of resolved (1-2 kpc resolution) HCN maps of galaxies in the local universe (d < 25 Mpc). We measure HCN/CO, a line ratio sensitive to the physical density distribution, and SFR/HCN, a proxy for the dense gas star formation efficiency, as a function of molecular gas surface density, stellar mass surface density, and dynamical equilibrium pressure across 31 galaxies, increasing the number of galaxies by a factor of > 3 over the previous largest such study (EMPIRE). HCN/CO increases (slope of ~ 0.5 and scatter of ~ 0.2 dex), while SFR/HCN decreases (slope of ~ -0.6 and scatter of ~ 0.4 dex) with increasing molecular gas surface density, stellar mass surface density and pressure. Galaxy centres with high stellar mass surface density show a factor of a few higher HCN/CO and lower SFR/HCN compared to the disc average, but both environments follow the same average trend. Our results emphasise that molecular gas properties vary systematically with the galactic environment and demonstrate that the scatter in the Gao-Solomon relation (SFR against HCN) is of physical origin.

astro-ph.GA↗

arXiv2024

3-D CMZ III: Constraining the 3-D structure of the Central Molecular Zone via molecular line emission and absorption

The Milky Way's Central Molecular Zone (CMZ) is the largest concentration of dense molecular gas in the Galaxy, the structure of which is shaped by the complex interplay between Galactic-scale dynamics and extreme physical conditions. Understanding the 3-D geometry of this gas is crucial as it determines the locations of star formation and subsequent feedback. We present a catalogue of clouds in the CMZ using Herschel data. Using archival data from the APEX and MOPRA CMZ surveys, we measure averaged kinematic properties of the clouds at 1mm and 3mm. We use archival ATCA data of the H$_{2}$CO (1$_{1,0}$ - 1$_{1,1}$) 4.8 GHz line to search for absorption towards the clouds, and 4.85 GHz GBT C-band data to measure the radio continuum emission. We measure the absorption against the continuum to provide new constraints for the line-of-sight positions of the clouds relative to the Galactic centre, and find a highly asymmetric distribution, with most clouds residing in front of the Galactic centre. The results are compared with different orbital models, and we introduce a revised toy model of a vertically-oscillating closed elliptical orbit. We find that most models describe the PPV structure of the gas reasonably well, but find significant inconsistencies in all cases regarding the near vs. far placement of individual clouds. Our results highlight that the CMZ is likely more complex than can be captured by these simple geometric models, along with the need for new data to provide further constraints on the true 3-D structure of the CMZ.

astro-ph.GA↗

arXiv2024

3-D CMZ II: Hierarchical Structure Analysis of the Central Molecular Zone

The Central Molecular Zone (CMZ) is the way station at the heart of our Milky Way Galaxy, connecting gas flowing in from Galactic scales with the central nucleus. Key open questions remain about its 3-D structure, star formation properties, and role in regulating this gas inflow. In this work, we identify a hierarchy of discrete structures in the CMZ using column density maps from Paper I (Battersby et al., submitted). We calculate the physical ($N$(H$_2$), $T_{\rm{dust}}$, mass, radius) and kinematic (HNCO, HCN, and HC$_3$N moments) properties of each structure as well as their bolometric luminosities and star formation rates (SFRs). We compare these properties with regions in the Milky Way disk and external galaxies. Despite the fact that the CMZ overall is well below the Gao-Solomon dense gas star-formation relation (and in modest agreement with the Schmidt-Kennicutt relation), individual structures on the scale of molecular clouds generally follow these star-formation relations and agree well with other Milky Way and extragalactic regions. We find that individual CMZ structures require a large external pressure ($P_e$/k$_B$ $> 10^{7-9}$ K cm$^{-3}$) to be considered bound, however simple estimates suggest that most CMZ molecular-cloud-sized structures are consistent with being in pressure-bounded virial equilibriuim. We perform power-law fits to the column density probability distribution functions (N-PDFs) of the inner 100 pc, SgrB2, and the outer 100 pc of the CMZ as well as several individual molecular cloud structures and find generally steeper power-law slopes ($-9<\alpha<-2$) compared with the literature ($-6 < \alpha < -1$).

astro-ph.GA↗

arXiv2024

3-D CMZ I: Central Molecular Zone Overview

The Central Molecular Zone (CMZ) is the largest reservoir of dense molecular gas in the Galaxy and is heavily obscured in the optical and near-IR. We present an overview of the far-IR dust continuum, where the molecular clouds are revealed, provided by Herschel in the inner 40\deg($|l| <$ 20\deg) of the Milky Way with a particular focus on the CMZ. We report a total dense gas ($N$(H$_2$) $> 10^{23}$ cm$^{-2}$) CMZ mass of M=$2\substack{+2 \\ -1} \times 10^7$ M$_{\odot}$ and confirm that there is a highly asymmetric distribution of dense gas, with about 70-75% at positive longitudes. We create and publicly release complete fore/background-subtracted column density and dust temperature maps in the inner 40\deg ($|l| <$ 20\deg) of the Galaxy. We find that the CMZ clearly stands out as a distinct structure, with an average mass per longitude that is at least $3\times$ higher than the rest of the inner Galaxy contiguously from 1.8\deg $> \ell >$ -1.3\deg. This CMZ extent is larger than previously assumed, but is consistent with constraints from velocity information. The inner Galaxy's column density peaks towards the SgrB2 complex with a value of about 2 $\times$ 10$^{24}$ cm$^{-2}$, and typical CMZ molecular clouds are about N(H$_2$)=10$^{23}$ cm$^{-2}$. Typical CMZ dust temperatures range from about $12-35$ K with relatively little variation. We identify a ridge of warm dust in the inner CMZ that potentially traces the base of the northern Galactic outflow seen with MEERKAT.

astro-ph.GA↗

arXiv2024

3-D CMZ IV: Distinguishing Near vs. Far Distances in the Galactic Center Using Spitzer and Herschel

A comprehensive 3-D model of the central 300 pc of the Milky Way, the Central Molecular Zone (CMZ) is of fundamental importance in understanding energy cycles in galactic nuclei, since the 3-D structure influences the location and intensity of star formation, feedback, and black hole accretion. Current observational constraints are insufficient to distinguish between existing 3-D models. Dust extinction is one diagnostic tool that can help determine the location of dark molecular clouds relative to the bright Galactic Center emission. By combining Herschel and Spitzer observations, we developed three new dust extinction techniques to estimate the likely near/far locations for each cloud in the CMZ. We compare our results to four geometric CMZ orbital models. Our extinction methods show good agreement with each other, and with results from spectral line absorption analysis from Walker et al. (submitted). Our near/far results for CMZ clouds are inconsistent with a projected version of the Sofue (1995) two spiral arms model, and show disagreement in position-velocity space with the Molinari et al. (2011) closed elliptical orbit. Our results are in reasonable agreement with the Kruijssen et al. (2015) open streams. We find that a simplified toy-model elliptical orbit which conserves angular momentum shows promising fits in both position-position and position-velocity space. We conclude that all current CMZ orbital models lack the complexity needed to describe the motion of gas in the CMZ, and further work is needed to construct a complex orbital model to accurately describe gas flows in the CMZ.

astro-ph.GA↗

arXiv2024

New methods for ALMA angular-scale based observation scheduling, quality assessment, and beam shaping II: refinements

The Atacama Large Millimeter/submillimeter Array remains the largest mm radio interferometer observatory world-wide. It is now conducting its 11th observing cycle. In our previous paper presented at this conference series in 2020, we outlined a number of possible improvements to the ALMA end-to-end observing and data processing procedures which could further optimize the uv coverage and thus the image quality while at the same time improving the observing efficiency. Here we report an update of our results refining our proposed adjustments to the scheduling and quality assurance processes. In particular we present new results on ways to assess the uv coverage of a given observation efficiently, methods to define and measure the maximum recoverable angular scale, and on the robustness of the deconvolution in the final interferometric imaging process w.r.t. defects in the uv coverage. Finally we present the outline of a design for integrating uv coverage assessment into the control and processing loop of observation scheduling. The results are applicable to all radio interferometers with more than approx. 10 antennas.

astro-ph.IM↗

arXiv2024

Spectrum and polarization of the Galactic center radio transient ASKAP J173608.2-321635 from THOR-GC and VLITE

The radio transient ASKAP J173608.2-321735, at the position (l,b)= (356.0872,-0.0390), was serendipitously observed by The HI/OH/Recombination Line Survey of the Galactic Center (THOR-GC) at three epochs in March 2020, April 2020 and February 2021. The source was detected only on 2020 April 11 with flux density 20.6 +/- 1.1 mJy at 1.23 GHz and in-band spectral index alpha = -3.1 +/- 0.2. The commensal VLA Low-band Ionsophere and Transient Experiment (VLITE) simultaneously detected the source at 339 MHz with a flux density 122.6 +/- 20.4 mJy, indicating a spectral break below 1 GHz. The rotation measure in April 2020 was 63.9 +/- 0.3rad/m2, which almost triples the range of the variable rotation measure observed by Wang et al. (2021) to ~130 rad/m2. The polarization angle, corrected for Faraday rotation, was 97 +/- 6 degrees. The 1.23 GHz linear polarization was 76.7% +/- 3.9% with wavelength-dependent depolarization indicating Faraday depth dispersion sigma_phi = 4.8^{+0.5}_{-0.7} rad/m2. We find an upper limit to circular polarization |V|/I < 10.1%. Interpretation of the data in terms of diffractive scattering of radio waves by a plasma near the source indicates electron density and line-of-sight magnetic field strength within a factor 3 of n_e ~2 cm^{-3} and B_par ~2 x 10^5 microgauss. Combined with causality limits to the size of the source, these parameters are consistent with the low-frequency spectral break resulting from synchrotron self-absorption, not free-free absorption. A possible interpretation of the source is a highly supersonic neutron star interacting with a changing environment.

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arXiv2024

PHANGS-HST catalogs for $\sim$100,000 star clusters and compact associations in 38 galaxies: I. Observed properties

We present the largest catalog to-date of star clusters and compact associations in nearby galaxies. We have performed a V-band-selected census of clusters across the 38 spiral galaxies of the PHANGS-HST Treasury Survey, and measured integrated, aperture-corrected NUV-U-B-V-I photometry. This work has resulted in uniform catalogs that contain $\sim$20,000 clusters and compact associations which have passed human inspection and morphological classification, and a larger sample of $\sim$100,000 classified by neural network models. Here, we report on the observed properties of these samples, and demonstrate that tremendous insight can be gained from just the observed properties of clusters, even in the absence of their transformation into physical quantities. In particular, we show the utility of the UBVI color-color diagram, and the three principal features revealed by the PHANGS-HST cluster sample: the young cluster locus, the middle-age plume, and the old globular cluster clump. We present an atlas of maps of the 2D spatial distribution of clusters and compact associations in the context of the molecular clouds from PHANGS-ALMA. We explore new ways of understanding this large dataset in a multi-scale context by bringing together once-separate techniques for the characterization of clusters (color-color diagrams and spatial distributions) and their parent galaxies (galaxy morphology and location relative to the galaxy main sequence). A companion paper presents the physical properties: ages, masses, and dust reddenings derived using improved spectral energy distribution (SED) fitting techniques.

astro-ph.GA↗

arXiv2023

Surveying the Whirlpool at Arcseconds with NOEMA (SWAN)- I. Mapping the HCN and N$_2$H$^+$ 3mm lines

We present the first results from "Surveying the Whirlpool at Arcseconds with NOEMA" (SWAN), an IRAM Northern Extended Millimetre Array (NOEMA)+30m large program that maps emission from several molecular lines at 90 and 110 GHz in the iconic nearby grand-design spiral galaxy M~51 at cloud-scale resolution ($\sim$3\arcsec=125\,pc). As part of this work, we have obtained the first sensitive cloud-scale map of N$_2$H$^+$(1-0) of the inner $\sim5\,\times 7\,$kpc of a normal star-forming galaxy, which we compare to HCN(1-0) and CO(1-0) emission to test their ability in tracing dense, star-forming gas. The average N$_2$H$^+$-to-HCN line ratio of our total FoV is $0.20\pm0.09$, with strong regional variations of a factor of $\gtrsim 2$ throughout the disk, including the south-western spiral arm and the center. The central $\sim1\,$kpc exhibits elevated HCN emission compared to N$_2$H$^+$, probably caused by AGN-driven excitation effects. We find that HCN and N$_2$H$^+$ are strongly super-linearily correlated in intensity ($\rho_\mathrm{Sp}\sim 0.8$), with an average scatter of $\sim0.14\,$dex over a span of $\gtrsim 1.5\,$dex in intensity. When excluding the central region, the data is best described by a power-law of exponent $1.2$, indicating that there is more N$_2$H$^+$ per unit HCN in brighter regions. Our observations demonstrate that the HCN-to-CO line ratio is a sensitive tracer of gas density in agreement with findings of recent Galactic studies which utilize N$_2$H$^+$. The peculiar line ratios present near the AGN and the scatter of the power-law fit in the disk suggest that in addition to a first-order correlation with gas density, second-order physics (such as optical depth, gas temperature) or chemistry (abundance variations) are encoded in the N$_2$H$^+$/CO, HCN/CO and N$_2$H$^+$/HCN ratios.

astro-ph.GA↗

arXiv2023

The impact of HII regions on Giant Molecular Cloud properties in nearby galaxies sampled by PHANGS ALMA and MUSE

We identify giant molecular clouds (GMCs) associated with HII regions for a sample of 19 nearby galaxies using catalogs of GMCs and H regions released by the PHANGS-ALMA and PHANGS-MUSE surveys, using the overlap of the CO and H{\alpha} emission as the key criterion for physical association. We compare the distributions of GMC and HII region properties for paired and non-paired objects. We investigate correlations between GMC and HII region properties among galaxies and across different galactic environments to determine whether GMCs that are associated with HII regions have significantly distinct physical properties to the parent GMC population. We identify trends between the H{\alpha} luminosity of an HII region and the CO peak brightness and the molecular mass of GMCs that we tentatively attribute to a direct physical connection between the matched objects, and which arise independently of underlying environmental variations of GMC and HII region properties within galaxies. The study of the full sample nevertheless hides a large variability galaxy by galaxy. Our results suggests that at the ~100 pc scales accessed by the PHANGS-ALMA and PHANGS-MUSE data, pre-supernova feedback mechanisms in HII regions have a subtle but measurable impact on the properties of the surrounding molecular gas, as inferred from CO observations.

astro-ph.GA↗

arXiv2023

Kinematic analysis of the super-extended HI disk of the nearby spiral galaxy M83

We present new HI observations of the nearby massive spiral galaxy M83, taken with the VLA at $21^{\prime\prime}$ angular resolution ($\approx500$ pc) of an extended ($\sim$1.5 deg$^2$) 10-point mosaic combined with GBT single dish data. We study the super-extended HI disk of M83 (${\sim}$50 kpc in radius), in particular disc kinematics, rotation and the turbulent nature of the atomic interstellar medium. We define distinct regions in the outer disk ($r_{\rm gal}>$central optical disk), including ring, southern area, and southern and northern arm. We examine HI gas surface density, velocity dispersion and non-circular motions in the outskirts, which we compare to the inner optical disk. We find an increase of velocity dispersion ($\sigma_v$) towards the pronounced HI ring, indicative of more turbulent HI gas. Additionally, we report over a large galactocentric radius range (until $r_{\rm gal}{\sim}$50 kpc) that $\sigma_v$ is slightly larger than thermal (i.e. $>8$km s$^{-1}$ ). We find that a higher star formation rate (as traced by FUV emission) is not always necessarily associated with a higher HI velocity dispersion, suggesting that radial transport could be a dominant driver for the enhanced velocity dispersion. We further find a possible branch that connects the extended HI disk to the dwarf irregular galaxy UGCA365, that deviates from the general direction of the northern arm. Lastly, we compare mass flow rate profiles (based on 2D and 3D tilted ring models) and find evidence for outflowing gas at r$_{\rm gal}$ $\sim$2 kpc, inflowing gas at r$_{\rm gal}$ $\sim$5.5 kpc and outflowing gas at r$_{\rm gal}$ $\sim$14 kpc. We caution that mass flow rates are highly sensitive to the assumed kinematic disk parameters, in particular, to the inclination.

astro-ph.GA↗

arXiv2023

Sub-kiloparsec empirical relations and excitation conditions of HCN and HCO+ J=3-2 in nearby star-forming galaxies

We present new HCN and HCO$^+$ ($J$=3-2) images of the nearby star-forming galaxies (SFGs) NGC 3351, NGC 3627, and NGC 4321. The observations, obtained with the Morita ALMA Compact Array, have a spatial resolution of $\sim$290-440 pc and resolve the inner $R_\textrm{gal} \lesssim$ 0.6-1 kpc of the targets, as well as the southern bar end of NGC 3627. We complement this data set with publicly available images of lower excitation lines of HCN, HCO$^+$, and CO and analyse the behaviour of a representative set of line ratios: HCN(3-2)/HCN(1-0), HCN(3-2)/HCO$^+$(3-2), HCN(1-0)/CO(2-1), and HCN(3-2)/CO(2-1). Most of these ratios peak at the galaxy centres and decrease outwards. We compare the HCN and HCO$^+$ observations with a grid of one-phase, non-local thermodynamic equilibrium (non-LTE) radiative transfer models and find them compatible with models that predict subthermally excited and optically thick lines. We study the systematic variations of the line ratios across the targets as a function of the stellar surface density ($\Sigma_\textrm{star}$), the intensity-weighted CO(2-1) ($\langle I_\text{CO}\rangle$), and the star formation rate surface density ($\Sigma_\text{SFR}$). We find no apparent correlation with $\Sigma_\text{SFR}$, but positive correlations with the other two parameters, which are stronger in the case of $\langle I_\text{CO}\rangle$. The HCN/CO-$\langle I_\text{CO}\rangle$ relations show $\lesssim$0.3 dex galaxy-to-galaxy offsets, with HCN(3-2)/CO(2-1)-$\langle I_\text{CO}\rangle$ being $\sim$2 times steeper than HCN(1-0)/CO(2-1). In contrast, the HCN(3-2)/HCN(1-0)-$\langle I_\text{CO}\rangle$ relation exhibits a tighter alignment between galaxies. We conclude that the overall behaviour of the line ratios cannot be ascribed to variations in a single excitation parameter (e.g. density or temperature).

astro-ph.GA↗