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M. Hayes

Publications and source records attributed to M. Hayes.

At least 19 recordsLinked to original sources
arXiv2026

Not So Isolated: Green Pea Galaxies in Overdense Environments revealed by VLT/MUSE

Context. Green Pea galaxies (GPs) are local starburst galaxies serving as analogues for high-redshift star-forming galaxies, particularly Lyman continuum leakers. It remains debated whether their starbursts are driven by internal secular processes or external triggers. Aims. We aim to constrain the role of environment in this triggering, testing whether external influence comes from close interactions or diffuse processes like gas accretion. Methods. We analyse VLT/MUSE observations of 24 GPs at $z \sim 0.2$ to identify companions via spectral line features. We derive key physical properties (extinction, SFR, stellar mass, age, metallicity) for GPs and companions, and estimate group dynamical masses. Results. We identify 22 emission-line galaxies, 11 being companions ($|\Delta v| \leq 500$ km s$^{-1}$). We find a high companion fraction ($33^{+11}_{-8}$%) and a $\sim$1 dex number density excess compared to the field, confirming GPs reside in overdense environments. Companions typically lie at projected separations of $\sim$100 kpc with no evidence of ongoing interactions. Physically, GPs form a homogeneous class of young (mass-weighted age $\sim$230 Myr), metal-poor, high-sSFR starbursts with elevated velocity dispersions. In contrast, companions are more evolved ($\sim$1.6 Gyr) and heterogeneous in stellar mass, metallicity, and dust attenuation. Inferred group dynamical masses are $\sim$3 dex higher than total stellar masses, suggesting significant dark matter and neutral gas. Conclusions. GPs do not appear triggered by ongoing major mergers with close (10-30 kpc) companions. Results favor a scenario where GPs are transient starbursts in overdense regions, plausibly sustained by gas accretion. Limited spatial resolution prevents ruling out very close mergers ($\lesssim 10$ kpc). High dynamical-to-stellar mass ratios imply substantial non-stellar mass in these systems.

astro-ph.GA↗
arXiv2026

X-ray stellar feedback in low-metallicity starbursts: Insights from the template starburst galaxy ESO 338-IG04 and its halo

The X-ray output of low-metallicity starburst galaxies is a key component of stellar feedback, tracing the processes responsible for gas ionization and chemical enrichment. The integrated X-ray luminosity ($L_X$) from high-mass X-ray binaries in star-forming galaxies scales with both the star formation rate (SFR) and host-galaxy metallicity $Z$. Due to the inverse correlation between $L_X/\mathrm{SFR}$ and $Z$, the contribution of X-ray binaries to the ionizing photon budget is enhanced in metal-poor systems and may ionize He II in the surrounding interstellar medium, powering nebular He II $\lambda4686$ emission. The blue compact dwarf galaxy ESO 338-IG04 (ESO 338-4) provides a nearby laboratory for studying stellar feedback in a low-metallicity starburst, combining vigorous recent star formation, low metallicity ($12+\log(\mathrm{O/H})\approx7.9$), and a rich population of massive stellar clusters. We characterize the X-ray emission of ESO 338-4 and its halo using new deep Chandra and XMM-Newton observations. We analyze X-ray spectra, light curves, and images to constrain the nature of its X-ray sources. We identify five ultra-luminous X-ray sources (ULXs) and diffuse hot gas surrounding the galaxy. Two ULXs are spatially associated with stellar clusters. The total X-ray luminosity exceeds $10^{41}\,\mathrm{erg\,s^{-1}}$. The brightest source, ULX1, shows variability on day timescales and lacks a stellar-cluster counterpart. Photoionization modeling shows that X-ray sources significantly impact the ionizing photon budget; models with ULX1 as the ionizing source predict nebular He II $\lambda4686$ luminosities of $\sim10^{39}\,\mathrm{erg\,s^{-1}}$.

astro-ph.HE↗
arXiv2024

CLASSY X: Highlighting Differences Between Partial Covering and Semi-Analytic Modeling in the Estimate of Galactic Outflow Properties

Feedback driven massive outflows play a crucial role in galaxy evolution by regulating star formation and influencing the dynamics of surrounding media. Extracting outflow properties from spectral lines is a notoriously difficult process for a number of reasons, including the possibility that a substantial fraction of the outflow is carried by dense gas in a very narrow range in velocity. This gas can hide in spectra with insufficient resolution. Empirically motivated analysis based on the Apparent Optical Depth method, commonly used in the literature, neglects the contribution of this gas, and may therefore underestimate the true gas column density. More complex semi-analytical line transfer (e.g., SALT) models, on the other hand, allow for the presence of this gas by modeling the radial density and velocity of the outflows as power laws. Here we compare the two approaches to quantify the uncertainties in the inferences of outflow properties based on 1-D "down-the-barrel" using the UV spectra of the CLASSY galaxy sample. We find that empirical modeling may significantly underestimate the column densities relative to SALT analysis, particularly in the optically thick regime. We use simulations to show that the main reason for this discrepancy is the presence of large amount of dense material at low velocities, which can be hidden by the finite spectral resolution of the data. The SALT models in turn could over-estimate the column densities if the assumed power laws of the density profiles strong are not a property of actual outflows.

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arXiv2024

On the universal validity of Case B recombination theory

In an ongoing search for low-mass extreme emission line galaxies, we identified a galaxy with a Ha/Hb Balmer line ratio of 2.620 +- 0.078. Ha/Hb Balmer ratios lower than the dust-free Case~B value appear relatively frequently in extreme emission line galaxies. These low values suggest that the Case~B assumption may not be valid in these objects. After ruling out the possibility that the low Ha/Hb ratio is due to systematic errors introduced by observational effects, we use constraints from the total Hb luminosity, the [OIII]/[OII] line ratio and the Balmer line equivalent widths, to suggest that the gas is optically thick to both Ha and Lya photons, and the geometry and orientation of the scattering gas causes Ha photons to be preferentially removed from the line of sight with respect to higher order Balmer series photons. Finally, we use data from the SDSS survey to show that Balmer self-absorption may be more important than previously assumed in high excitation emission line galaxies, where Lya pumping of the hydrogen excited state can be effective. If not recognized, Balmer self-absorption could lead to inaccurate estimates of galaxy physical properties. As an example, the effect of dust extinction could be over-estimated, for spherically symmetric scattering medium, or under-estimated, for a not spherically-symmetric distribution.

astro-ph.GA↗
arXiv2024

The Sunburst Arc with JWST: I. Detection of Wolf-Rayet stars injecting nitrogen into a low-metallicity, $z=2.37$ proto-globular cluster leaking ionizing photons

We report the detection of a population of Wolf-Rayet (WR) stars in the Sunburst Arc, a strongly gravitationally lensed galaxy at redshift $z=2.37$. As the brightest known lensed galaxy, the Sunburst Arc has become an important cosmic laboratory for studying star and cluster formation, Lyman $\alpha$ radiative transfer, and Lyman Continuum (LyC) escape. Here, we present the first results of JWST/NIRSpec IFU observations of the Sunburst Arc, focusing on a stacked spectrum of the 12-fold imaged LyC-emitting (Sunburst LCE) cluster. In agreement with previous studies, we find that the cluster is massive and compact, with $M_{\text{dyn}} = (9\pm1) \times 10^{6} M_{\odot}$, Our age estimate of 4.2--4.5 Myr is much larger than the crossing time of $t_{\text{cross}} = 183 \pm 9 $ kyr, indicating that the cluster is dynamically evolved and consistent with being gravitationally bound. We find a significant nitrogen enhancement of the low ionization state ISM, with $\log(N/O) = -0.74 \pm 0.09$, which is $\approx 0.8$ dex above typical values for H II regions of similar metallicity in the local Universe. We find broad stellar emission complexes around He II$\lambda 4686$ and C IV$\lambda 5808$ with associated nitrogen emission -- this is the first time WR signatures have been directly observed at redshifts above $\sim 0.5$. The strength of the WR signatures cannot be reproduced by stellar population models that only include single-star evolution. While models with binary evolution better match the WR features, they still struggle to reproduce the nitrogen-enhanced WR features. JWST reveals the Sunburst LCE to be a highly ionized, proto-globular cluster with low oxygen abundance and extreme nitrogen enhancement that hosts a population of Wolf-Rayet stars, and possibly Very Massive stars (VMSs), which are rapidly enriching the surrounding medium.

astro-ph.GA↗
arXiv2024

Polarimetry of the Ly-alpha envelope of the radio-quiet quasar SDSS J124020.91+145535.6

The radio-quiet quasar SDSS J1240+1455 lies at a redshift of z=3.11, is surrounded by a Ly-alpha blob (LAB), and is absorbed by a proximate damped Ly-alpha system. In order to better define the morphology of the blob and determine its emission mechanism, we gathered deep narrow-band images isolating the Ly-alpha line of this object in linearly polarized light. We provide a deep intensity image of the blob, showing a filamentary structure extending up to 16'' (or ~122 physical kpc) in diameter. No significant polarization signal could be extracted from the data, but 95% probability upper limits were defined through simulations. They vary between ~3% in the central 0.75'' disk (after subtraction of the unpolarized quasar continuum) and ~10% in the 3.8-5.5'' annulus. The low polarization suggests that the Ly-alpha photons are emitted mostly in situ, by recombination and de-excitation in a gas largely ionized by the quasar ultraviolet light, rather than by a central source and scattered subsequently by neutral hydrogen gas. This blob shows no detectable polarization signal, contrary to LAB1, a brighter and more extended blob that is not related to the nearby active galactic nucleus (AGN) in any obvious way, and where a significant polarization signal of about 18% was detected.

astro-ph.GA↗
arXiv2024

MUSE-ALMA Haloes X: The stellar masses of gas-rich absorbing galaxies

The physical processes by which gas is accreted onto galaxies, transformed into stars and then expelled from galaxies are of paramount importance to galaxy evolution studies. Observationally constraining each of these baryonic components in the same systems however, is challenging. Furthermore, simulations indicate that the stellar mass of galaxies is a key factor influencing CGM properties. Indeed, absorption lines detected against background quasars offer the most compelling way to study the cold gas in the circumgalactic medium (CGM). The MUSE-ALMA Haloes survey is composed of quasar fields covered with VLT/MUSE observations, comprising 32 \ion{H}{i} absorbers at 0.2 $<$ $z$ $<$ 1.4 and 79 associated galaxies, with available or upcoming molecular gas measurements from ALMA. We use a dedicated 40-orbit HST UVIS and IR WFC3 broad-band imaging campaign to characterise the stellar content of these galaxies. By fitting their spectral energy distribution, we establish they probe a wide range of stellar masses: 8.1 $<$ log($M_*$/M$_{\odot}$) $<$ 12.4. Given their star-formation rates, most of these objects lie on the main sequence of galaxies. We also confirm a previously reported anti-correlation between the stellar masses and CGM hydrogen column density N(\ion{H}{i}), indicating an evolutionary trend where higher mass galaxies are less likely to host large amounts of \ion{H}{i} gas in their immediate vicinity up to 120 kpc. Together with other studies from the MUSE-ALMA Haloes survey, these data provide stellar masses of absorber hosts, a key component of galaxy formation and evolution, and observational constraints on the relation between galaxies and their surrounding medium.

astro-ph.GA↗
arXiv2023

A MUSE/VLT spatially resolved study of the emission structure of Green Pea galaxies

Green Pea galaxies are remarkable for their intense star formation and serve as a window into the early universe. In our study, we used integral field spectroscopy to examine 24 of these galaxies in the optical spectrum. We focused on the interaction between their ionized interstellar medium and the star formation processes within them. Our research generated spatial maps of emission lines and other properties like ionization structures and chemical conditions. These maps showed that areas with higher levels of excitation are usually located where starbursts are occurring. Continuum maps displayed more intricate structures than emission line maps and hinted at low brightness ionized gas in the galaxies' outer regions. We also analyzed integrated spectra from selected areas within these galaxies to derive physical properties like electron densities and temperatures. In some galaxies, we were able to determine metallicity levels. Our observations revealed the presence of high-ionizing lines in three galaxies, two of which had extremely high rates of star formation. Our findings provide valuable insights into the properties and star-forming processes in Green Pea galaxies, contributing to our broader understanding of galactic evolution in the early universe.

astro-ph.GA↗
arXiv2022

A $\sim$15 kpc outflow cone piercing through the halo of the blue compact metal-poor galaxy SBS0335-052

Context: Outflows from low-mass star-forming galaxies are a fundamental ingredient for models of galaxy evolution and cosmology. Aims: The onset of kpc-scale ionised filaments in the halo of the metal-poor compact dwarf SBS 0335-052E was previously not linked to an outflow. We here we investigate whether these filaments provide evidence for an outflow. Methods: We obtained new VLT/MUSE WFM and deep NRAO/VLA B-configuration 21cm data of the galaxy. The MUSE data provide morphology, kinematics, and emission line ratios H$\beta$/H$\alpha$ and [\ion{O}{iii}]$\lambda5007$/H$\alpha$ of the low surface-brightness filaments, while the VLA data deliver morphology and kinematics of the neutral gas in and around the system. Both datasets are used in concert for comparisons between the ionised and the neutral phase. Results: We report the prolongation of a lacy filamentary ionised structure up to a projected distance of 16 kpc at $\mathrm{SB}_\mathrm{H\alpha} = 1.5\times10^{-18}$erg s$^{-1}$ cm$^{-2}$arcsec$^{-2}$. The filaments exhibit unusual low H$\alpha$/H$\beta \approx 2.4$ and low [\ion{O}{iii}]/H$\alpha \sim 0.4 - 0.6$ typical of diffuse ionised gas. They are spectrally narrow ($\sim 20$ km s$^{-1}$) and exhibit no velocity sub-structure. The filaments extend outwards of the elongated \ion{H}{I} halo. On small scales the $N_\mathrm{HI}$ peak is offset from the main star-forming sites. Morphology and kinematics of \ion{H}{I} and \ion{H}{II} reveal how star-formation driven feedback interacts differently with the ionised and the neutral phase. Conclusions: We reason that the filaments are a large scale manifestation of star-formation driven feedback, namely limb-brightened edges of a giant outflow cone that protrudes through the halo of this gas-rich system. A simple toy model of such a conical-structure is found to be commensurable with the observations.

astro-ph.GA↗
arXiv2022

CLusters in the Uv as EngineS (CLUES): I. Survey presentation \& FUV spectral analysis of the stellar light

The CLusters in the Uv as EngineS (CLUES) survey is a Cosmic Origins Spectrograph (COS) campaign aimed at acquiring the 1130 to 1770 {\AA}, restframe spectroscopy of very young (<20 Myr) and massive (>10^4 solar masses) star clusters in galaxies that are part of the Hubble treasury program Legacy ExtraGalactic Uv Survey (LEGUS). In this first paper of a series, we describe the CLUES sample consisting of 20 young star clusters and report their physical properties as derived by both multi-wavelength photometry and far-UV (FUV) spectroscopy with Hubble Space Telescope (HST). Thanks to the synergy of the two different datasets we build a coherent picture of the diverse stellar populations found in each region (with sizes of 40 to 160 pc). We associate the FUV-brightest stellar population to the central targeted star cluster and the other modeled population to the diffuse stars that are included in the COS aperture. We observe better agreement between photometric and spectroscopic ages for star clusters younger than 5 Myr. For clusters older than 5 Myr, photometry and spectroscopy measurements deviate, with the latter producing older ages, due to the degeneracy of photometric models. FUV spectroscopy enables us to better constrain the stellar metallicities, a parameter that optical colors are insensitive to. Finally, the derived E(B-V) are quite similar, with a tendency for FUV spectroscopy to favor solutions with higher extinctions. The recovered masses are in agreement within a factor of 2 for all the clusters.

astro-ph.GA↗
arXiv2022

The Far-Ultraviolet Continuum Slope as a Lyman Continuum Escape Estimator at High-redshift

Most of the hydrogen in the intergalactic medium (IGM) was rapidly ionized at high-redshifts. While observations have established that reionization occurred, observational constraints on the emissivity of ionizing photons at high-redshift remains elusive. Here, we present a new analysis of the Low-redshift Lyman Continuum Survey (LzLCS) and archival observations, a combined sample of 89 star-forming galaxies at z~0.3 with Hubble Space Telescope observations of their ionizing continua (or Lyman Continuum, LyC). We find a strong (6$\sigma$ significant) inverse correlation between the continuum slope at 1550\r{A} (defined as F$_\lambda\propto\lambda^{\beta}$) and both the LyC escape fraction (f$_{esc}$) and f$_{esc}$ times the ionizing photon production efficiency ($\xi_{ ion}$). On average, galaxies with redder continuum slopes have smaller f$_{esc}$ than galaxies with bluer slopes due to higher dust attenuation. More than 5% (20%) of the LyC emission escapes galaxies with $\beta$<-2.1 (-2.6). We find strong correlations between $\beta$ and the gas-phase ionization ([OIII]/[OII] flux ratio; at 7.5$\sigma$ significance), galaxy stellar mass (at 5.9$\sigma$), the gas-phase metallicity (at 4.6$\sigma$), and the observed FUV absolute magnitude (M$_{UV}$ at 3.4$\sigma$). Using previous observations of $\beta$ at high-redshift, we estimate the evolution of f$_{esc}$ with both $z$ and M$_{UV}$. The LzLCS suggest that fainter and lower mass galaxies dominate the ionizing photon budget at higher redshift, possibly due to their rapidly evolving metal and dust content. Finally, we use our correlation between $\beta$ and f$_{ esc}\times\xi_{ion}$ to predict the ionizing emissivity of galaxies during the epoch of reionization. Our estimated emissivities match IGM observations, and suggest that star-forming galaxies emit sufficient LyC photons into the IGM to exceed recombinations near redshifts of 7-8.

astro-ph.GA↗
arXiv2022

The Lyman Alpha Reference Sample XIII: High-Angular Resolution 21cm HI observations of Ly$\alpha$ emitting galaxies

The Ly$\alpha$ emission line is one of the main observables of galaxies at high redshift, but its output depends strongly on the neutral gas distribution and kinematics around the star-forming regions where UV photons are produced. We present observations of Ly$\alpha$ and 21-cm HI emission at comparable scales with the goal to qualitatively investigate how the neutral interstellar medium (ISM) properties impact Ly$\alpha$ transfer in galaxies. We have observed 21-cm HI at the highest angular resolution possible (~ 3" beam) with the VLA in two local galaxies from the Lyman Alpha Reference Sample. We contrast this data with HST Ly$\alpha$ imaging and spectroscopy, and MUSE and PMAS ionized gas observations. In LARS08, high intensity Ly$\alpha$ emission is co-spatial with high column density HI where dust content is the lowest. The Ly$\alpha$ line is strongly redshifted, consistent with velocity redistribution which allows Ly$\alpha$ escape from high column density neutral medium with low dust content. In eLARS01, high intensity Ly$\alpha$ emission is located in regions of low column density HI, below the HI data sensitivity limit ($<2\times10^{20}\,$cm$^{-2}$). The perturbed ISM distribution with low column density gas in front of the Ly$\alpha$ emission region plays an important role in the escape. In both galaxies, the faint Ly$\alpha$ emission ($\sim 1\times10^{-16}$erg.s$^{-1}$cm$^{-2}$arcsec$^{-2}$) traces intermediate H$\alpha$ emission regions where HI is found, regardless of the dust content. Dust seems to modulate, but not prevent, the formation of a faint Ly$\alpha$ halo. This study suggests the existence of scaling relations between dust, H$\alpha$, HI, and Ly$\alpha$ emission in galaxies.

astro-ph.GA↗
arXiv2022

Haro 11 -- Untying the knots of the nuclear starburst

Star formation is a clustered process that regulates the structure and evolution of galaxies. We investigate this process in the dwarf galaxy Haro 11, forming stars in three knots (A, B, C). The exquisite resolution of HST imaging allows us to resolve the starburst into tens of bright star clusters. We derive masses between $10^5$ and $10^7\,\rm M_{\odot}$ and ages younger than 20 Myr, using photometric modeling. We observe that the clustered star formation has propagated from knot C (the oldest) through knot A (in between) towards knot B (the youngest). We use aperture-matched ultraviolet and optical spectroscopy (HST + MUSE) to independently study the stellar populations of Haro 11 and determine the physical properties of the stellar populations and their feedback in 1 kpc diameter regions. We discuss these results in light of the properties of the ionised gas within the knots. We interpret the broad blue-shifted components of the optical emission lines as outflowing gas ($v_{max} \sim 400$ km/s). The strongest outflow is detected in knot A with a mass-rate of $\dot{M}_{out}\sim 10\,\rm M_{\odot}/yr$, ten times higher than the star-formation in the same region. Knot B hosts a young and not fully developed outflow, whereas knot C has likely been already evacuated. Because Haro 11 has properties similar to high-redshift unresolved galaxies, our work can additionally aid the understanding of star formation at high redshift, a window that will be opened by upcoming facilities.

astro-ph.GA↗
arXiv2021

Ionized gas properties of the extreme starburst galaxy Haro 11. Temperature and metal abundance discrepancies

We use high quality VLT/MUSE data to study the kinematics and the ionized gas properties of Haro 11, a well known starburst merger system and the closest confirmed Lyman continuum leaking galaxy. We present results from integrated line maps, and from maps in three velocity bins comprising the blueshifted, systemic and redshifted emission. The kinematic analysis reveals complex velocities resulting from the interplay of virial motions and momentum feedback. Star formation happens intensively in three compact knots (knots A, B and C), but one, knot C, dominates the energy released in supernovae. The halo is characterised by low gas density and extinction, but with large temperature variations, coincident with fast shock regions. Moreover, we find large temperature discrepancies in knot C, when using different temperature-sensitive lines. The relative impact of the knots in the metal enrichment differs. While knot B is strongly enriching its closest surrounding, knot C is likely the main distributor of metals in the halo. In knot A, part of the metal enriched gas seems to escape through low density channels towards the south. We compare the metallicities from two methods and find large discrepancies in knot C, a shocked area, and the highly ionized zones, that we partially attribute to the effect of shocks. This work shows, that traditional relations developed from averaged measurements or simplified methods, fail to probe the diverse conditions of the gas in extreme environments. We need robust relations that include realistic models where several physical processes are simultaneously at work.

astro-ph.GA↗
arXiv2020

Stars and gas in the most metal-poor galaxies I: COS and MUSE observations of SBS 0335-052E

Among the nearest most metal-poor starburst-dwarf galaxies known, SBS 0335-052E is the most luminous in integrated nebular He II {\lambda}4686 emission. This makes it a unique target to test spectral synthesis models and spectral interpretation tools of the kind that will be used to interpret future rest-frame UV observations of primeval galaxies. Previous attempts to reproduce its He II {\lambda}4686 emission luminosity found that X-ray sources, shocks, and single Wolf-Rayet stars are not main contributors to the He II-ionizing budget; and that only metal-free single rotating stars or binary stars with a top-heavy IMF and an unphysically-low metallicity can reproduce it. We present new UV (COS) and optical (MUSE) spectra which integrate the light of four super star clusters in SBS 0335-052E. Nebular He II, [C III], C III], C IV, and O III] UV emission lines with equivalent widths between 1.7 and 5 {\AA}, and a C IV {\lambda}{\lambda}1548, 1551 P-Cygni like profile are detected. Recent extremely-metal poor shock + precursor models and binary models fail to reproduce the observed optical emission-line ratios. We use different sets of UV and optical observables to test models of constant star formation with single non-rotating stars which account for very massive stars, as blueshifted O V {\lambda}1371 absorption is present. Simultaneously fitting the fluxes of all high-ionization UV lines requires an unphysically-low metallicity. Fitting the P-Cygni like + nebular components of C IV {\lambda}{\lambda}1548, 1551 does not constrain the stellar metallicity and time since the beginning of star formation. We obtain 12+log(O/H)=7.45\pm0.04 and log(C/O)=-0.45(+0.03)(-0.04) for the galaxy. Model-testing would benefit from higher spatial resolution UV and optical spectroscopy of the galaxy.

astro-ph.GA↗
arXiv2020

On bivectors and jay-vectors

A combination $\mathbf{a}+\mathrm{i}\mathbf{b}$ where ${\mathrm i}^2=-1$ and $\mathbf{a}, \, \mathbf{b}$ are real vectors is called a bivector. Gibbs developed a theory of bivectors, in which he associated an ellipse with each bivector. He obtained results relating pairs of conjugate semi-diameters and in particular considered the implications of the scalar product of two bivectors being zero. This paper is an attempt to develop a similar formulation for hyperbolas by the use of jay-vectors - a jay-vector is a linear combination $\mathbf{a}+\mathrm{j}\mathbf{b}$ of real vectors $\mathbf{a}$ and $\mathbf{b}$, where ${\mathrm j}^2=+1$ but ${\mathrm j}$ is not a real number, so ${\mathrm j}\neq\pm1$. The implications of the vanishing of the scalar product of two jay-vectors is also considered. We show how to generate a triple of conjugate semi-diameters of an ellipsoid from any orthonormal triad. We also see how to generate in a similar manner a triple of conjugate semi-diameters of a hyperboloid and its conjugate hyperboloid. The role of complex rotations (complex orthogonal matrices) is discussed briefly. Application is made to second order elliptic and hyperbolic partial differential equations. Keywords: Split complex numbers, Hyperbolic numbers, Coquaternions, Conjugate semi-diameters, Hyperboloids and ellipsoids, Complex rotations, PDEs MSC (2010) 35J05, 35L10, 74J05

math.GM↗
arXiv2020

The Lyman Alpha Reference Sample XI: Efficient Turbulence Driven Ly{\alpha} Escape and the Analysis of IR, CO and [C II]158 {\mu}m

We study the global dust and (molecular) gas content in the Lyman Alpha Reference Sample (LARS), i.e. 14 local star-forming galaxies. We characterize their interstellar medium and relate newly derived properties to quantities relevant for Ly$\alpha$ escape. We observed LARS galaxies with Herschel/PACS, SOFIA/FIFI-LS, the IRAM 30m telescope and APEX, targeting far-infrared (FIR) continuum and emission lines of [C II]158$\mu$m, [O I]63$\mu$m, [O III]88$\mu$m and low-J CO lines. Using Bayesian methods we derive dust model parameters and estimate total gas masses for all LARS galaxies, taking into account a metallicity-dependent gas-to-dust ratio. Star formation rates were estimated from FIR, [C II]158$\mu$m and [O I]63$\mu$m luminosities. LARS covers a wide dynamic range in the derived properties, with FIR-based star formation rates from $\sim$0.5-100 $M_{\odot}\ yr^{-1}$, gas fractions between $\sim$15-80% and gas depletion times ranging from a few hundred Myr up to more than 10 Gyr. The distribution of LARS galaxies in the $\Sigma_{gas}$ vs. $\Sigma_{SFR}$ (Kennicutt-Schmidt plane) is thus quite heterogeneous. However, we find that LARS galaxies with the longest gas depletion times, i.e. relatively high gas surface densities ($\Sigma_{gas}$) and low star formation rate densities ($\Sigma_{SFR}$), have by far the highest Ly$\alpha$ escape fraction. A strong $\sim$linear relation is found between Ly$\alpha$ escape fraction and the total gas (HI+H$_2$) depletion time. We argue that the Ly$\alpha$ escape in those galaxies is driven by turbulence in the star-forming gas that shifts the Ly$\alpha$ photons out of resonance close to the places where they originate. We further report on an extreme [C II]158$\mu$m excess in LARS 5, corresponding to $\sim$14$\pm$3% of the FIR luminosity, i.e. the most extreme [C II]-to-FIR ratio observed in a non-AGN galaxy to date.

astro-ph.GA↗
arXiv2020

Accretion-Driven Sources in Spatially Resolved Ly$\alpha$ Emitters

Ly$\alpha$ emission is a standard tracer of starburst galaxies at high redshift. However, a number of local Ly$\alpha$ emitters (LAEs) are X-ray sources, suggesting a possible origin of Ly$\alpha$ photons other than young, hot stars, and which may be active at much later ages relative to the parent starburst. Resolved, nearby LAEs offer the opportunity to discriminate between diffuse X-ray emission arising from supernova-heated gas, high-mass X-ray binaries (HMXBs), or low-luminosity active galactic nuclei (LLAGN). We examine archival X-ray imaging from Chandra and XMM-Newton for 11 galaxies with spatially resolved Ly$\alpha$ imaging to determine the luminosity, morphology, and spectral hardness of the X-ray sources. The data are consistent with 9 of the 12, bright Ly$\alpha$ sources being driven by luminous, $10^{40}$ erg s$^{-1}$ X-ray sources. Half of the 8 Chandra sources are unresolved. The data suggest that nuclear activity, whether from LLAGN or nuclear starbursts, may play an important role in Ly$\alpha$ emission. Our results also suggest a significant link between Ly$\alpha$ emission and HMXBs, ULXs, and/or LLAGN, which would imply that Ly$\alpha$ may be generated over timescales 1 - 2 orders of magnitude longer than produced by photoionization from OB stars. This highlights a critical need to quantify the relative contributions of different sources across cosmic time, to interpret Ly$\alpha$ observations and the resulting properties of distant galaxies.

astro-ph.GA↗