arXiv subjects

Edvige Corbelli

Publications and source records attributed to Edvige Corbelli.

At least 19 recordsLinked to original sources

arXiv2026

DustPedia and Local Volume Legacy samples as benchmarks for dust evolution in galaxies

DustPedia and LVL are two samples representative of the local galaxy population, including in total 1011 unique objects of all morphological types, with a wide range of stellar masses ($M_*$) and star-formation activity, and a spectral coverage from the FUV to the FIR. The purpose of this work is to show that these samples cover two complementary ranges in $M_*$ and morphology, making them an ideal set for constraining the dominant processes in the evolution of the galactic dust content. Using the multiwavelength data provided by the two surveys, we fitted the galaxies' spectral energy distribution and estimated their physical properties, in particular the $M_*$, $sM_\mathrm{dust}=M_\mathrm{dust}/M_*$, and sSFR = SFR$/M_*$. By combining DustPedia and LVL, we highlight that the $\log_{10}(sM_{\rm dust})$-$\log_{10}(M_*)$ trend is not monotonic. Thanks to a large number of objects across a wide range of $M_*$, we have been able to fit two smoothly-joined linear correlations: a positive for $\log_{10}(M_{*}/$M$_\odot)\lesssim9.5$ (mainly LVL late spirals and irregulars), and a negative one for larger-mass, mainly DustPedia spirals (early types are distinct and more dispersed in the same mass regime). For $\log_{10}(M_{*}/$M$_\odot)>9.5$, we confirm a strong sM_{\rm dust}-sSFR correlation; dwarf galaxies, instead, lie below this trend, with a large scatter of $sM_{\rm dust}$, for -10.5<$\log_{10}$(sSFR/yr$^{-1}$)<-9.0. By using chemical evolution models we find that the observed $\log_{10}(sM_{\rm dust})$-$\log_{10}(M_{*})$ and $\log_{10}(sM_{\rm dust})$-$\log_{10}$(sSFR) trends can be interpreted mainly by variations in the initial gas mass budget and the galaxy ages, respectively. Low-mass Sm-Irr galaxies with low $sM_{\rm dust}$ and high sSFR can only be reproduced by the models by assuming high photofragmentation rate of large grains, and/or low grain-growth in clouds.

astro-ph.GA↗

arXiv2026

Luminosity functions and IMF variations from large samples of HII regions and molecular clouds

Large high-quality samples of HII regions and their parent Giant Molecular Clouds (GMC) are now available for local galaxies. It is therefore possible to investigate links between the CO and H$\alpha$ luminosity functions and whether massive stars form in GMCs of all masses. The CO luminosity functions (LF), representing the distribution of GMC masses, are consistently steeper than the H$\alpha$ luminosity functions. The CO LF invariably steepens in the outer disk where fewer massive GMCs are present beyond the median cloud galactocentric distance. The H$\alpha$ LF also steepens in the outer disk for most of the galaxies examined. Using Salpeter, Kroupa, and Chabrier Initial Mass Functions (IMF) along with stellar mass-luminosity-radius relations, we compute numerically the bolometric luminosity and H$\alpha$ emission from young star clusters. The cluster masses are linked to the GMC mass by assuming that the cluster mass is a constant fraction (3\%) of the parent cloud mass. In particular, results for a fully stochastic IMF are compared to suggestions that very massive stars only form in massive clusters or clouds. Within the limits of the observations -- no small molecular clouds or low-luminosity HII regions can be detected at the typical $\sim 10$~Mpc distance of the sample galaxies -- we find no evidence for a maximum stellar mass which varies with cloud or cluster mass.

astro-ph.GA↗

arXiv2026

WALLABY pilot survey: Blinded by the light -- discovery of a fourth member in the ESO 179-013 system

We present new ASKAP/WALLABY HI observations of the nearby dwarf galaxy system ESO 179-013 (Kathryn's Wheel), the nearest known collisional ring galaxy, located 10 Mpc away in the Local Void. The system is composed of three previously known dwarf galaxies embedded in a large HI envelope, with a newly discovered fourth member identified through HI and radio continuum emission behind a bright foreground binary. Galaxy D exhibits the highest star formation rate in the group and deviates from the HI mass-diameter relation, suggesting it is a compact, gas-rich dwarf missed due to stellar foreground contamination. The HI data reveal for the first time an extended HI envelope around the whole system, the neutral gas counterpart of the star-forming ring and gas bridges among members, suggesting a more complex interaction history than the previously proposed collisional ring scenario. ESO 179-013 thus provides a rare opportunity to study hierarchical assembly and gas dynamics in underdense environments and demonstrates the power of blind HI surveys in identifying faint members of low-mass compact groups.

astro-ph.GA↗

arXiv2025

Pressure and Star Formation in LITTLE THINGS Dwarf Irregular Galaxies

The surface densities of star formation, Sigma_SFR, in 24 dwarf irregular (dIrr) galaxies from the LITTLE THINGS survey are combined with gas surface densities and midplane pressures to examine the correlations found previously for spiral galaxies. The pressure is the weight of the disk inside the gas layer, including gas, stars, and dark matter, which usually dominates disk gravity in dIrrs. We compare the results to the outer part of M33, which has similar local properties but a slightly higher metallicity, enabling the detection of CO. All the data are convolved to the HI beam, but to study the effects of resolution, the galaxies are examined first with average radial profiles, and then with maps having 1.5" pixels and 244 pc pixels. The correlations are found to be independent of resolution from 24 pc to 424 pc. The average ratio of molecular to atomic surface density is estimated to be 0.23+-0.1, from the H_2 surface density in M33 compared to the HI surface density at the same Sigma_SFR in the dIrrs. With this ratio, the average star formation rate per molecule is about the same for all the dIrrs, and a factor of 2 less than the rate in M33. The pressure in dIrrs is so low that CO is essentially a dense gas tracer, with the same surface density threshold at the low metallicities of dIrrs as HCN has in spiral galaxies. As a result, CO regions in dIrrs should be strongly self-gravitating.

astro-ph.GA↗

arXiv2025

Star formation drivers across the M33 disk

We investigate the star formation process across the disk of M33 using a multiwavelength dataset and disk dynamics. We computed numerically equilibrium values of gas densities and scale heights across the disk, taking into account dark matter and testing several analytic approximations that are often used to estimate these variables and the hydrostatic pressure. Orthogonal regressions and hierarchical Bayesian models, as well as random forest (RF) analyses, were used to establish the fundamental relations at physical scales from 160~pc to 1~kpc. The gas pressure, is the main driver of the star formation rate (SFR) surface density throughout the whole star-forming disk of M33. High-pressure regions enhance the atomic-to-molecular gas conversion, with the molecular hydrogen mass surface density being tightly correlated to pressure and a uniform scaling law throughout the M33 disk. The relation between pressure and SFR surface density differs, showing a change in slope from the inner to the outer disk. Scaling laws do not depend on the physical scale and brings out an intrinsic scatter linked to variations in the efficiency and relative age of the molecular gas-to-stars conversion. In the inner disk, where spiral arms are present and the stellar surface density dominates gravity, the pressure and SFR surface densidy establish an almost linear correlation with a smaller dispersion than that of the molecular gas -- SFR surface density relation. In the atomic gas-dominated outer disk, the SFR density has a steeper dependence on pressure, which we propose could be the result of an increasing fraction of diffuse molecular gas that does not form stars.

astro-ph.GA↗

arXiv2025

Exploring the interplay of dust and gas phases in DustPedia star-forming galaxies

Molecular gas is the key ingredient of the star formation cycle, and tracing its dependencies on other galaxy properties is essential for understanding galaxy evolution. In this work, we explore the relation between the different phases of the interstellar medium (ISM), namely molecular gas, atomic gas, and dust, and galaxy properties using a sample of nearby late-type galaxies. To this goal, we collect CO maps for 121 galaxies from the DustPedia project, ensuring an accurate determination of $M_{H2}$, the global molecular gas mass. We investigate which scaling relations provide the best description of $M_{H2}$, based on the strength of the correlation and its intrinsic dispersion. Commonly used correlations between $M_{H2}$ and star formation rate (SFR) and stellar mass ($M_{\star}$) are affected by large scatter, which accounts for galaxies that are experiencing quenching of their star formation activity. This issue can be partially mitigated by considering a "fundamental plane" of star formation, fitting together $M_{H2}$, $M_{\star}$, and SFR. We confirm previous results from the DustPedia collaboration that the total gas mass has the tightest connection with the dust mass and that the molecular component also establishes a good correlation with dust. Although dust grains are necessary for the formation of hydrogen molecules, the strength of gravitational potential driven by the stellar component plays a key role in driving density enhancements and the atomic-to-molecular phase transition. Eventually, we investigated the correlations between ISM components and monochromatic luminosities at different wavelengths: we proposed mid and far-IR luminosities as reliable proxies of $L^{\prime}_{CO}$ for sources lacking dedicated millimeter observations. Luminosities in mid-IR photometric bands collecting PAH emission can be used to trace molecular gas and dust masses.

astro-ph.GA↗

arXiv2024

The lunar eclipse and the dawn of astrophysics in van Gogh's masterpieces

When visiting the Museum of Modern Art's special exhibit ''van Gogh and the Colors of the Night (New York, USA, 2008)'' I was impressed by the artist's effort to paint and write about landscapes and life scenes at night. At the same time a clear contrast emerged between the colored Starry Night paint and the darkness or twilight in his earlier production. Since then, while revising van Gogh's artistic production and reading his letters I have come to the conclusion that his work was not only driven by the poetry of the night but also by his awareness of the dawn of astrophysics in the 19th century. A change in the way the artist conceived the sky after his stay in Paris is evident in his later work with the skies becoming more dynamic and rich in colors. In this paper I am presenting new elements in van Gogh's masterpieces that refer to astronomical events visible from France in 1889 and 1890, such as a lunar eclipse and planetary conjunctions. I discuss these elements in addition to the structured and colorful stars and to the large neutral central swirl in the Starry Night, which all suggest the artist's profound attention to celestial phenomena and knowledge of the new wonders and discoveries of astrophysics in 19th century.

physics.hist-ph↗

arXiv2024

The outskirts of M33: Tidally induced distortions versus signatures of gas accretion

We investigate a possible close encounter between M33 and M31 in the past to understand the role of galaxy-galaxy interactions in shaping the matter distribution in galaxy outskirts. We recovered possible orbital trajectories of M33, M31 and the Milky Way in the past, which are compatible with the Early Third Data Release of the Gaia mission and with mass estimates of Local Group spirals, after tuning mass losses and the dynamical friction term with the help of N-body numerical simulations. A close encounter of M33 and M31 in the past has a low but non-negligible probability. If the two galaxies had been closer in the past, their minimum distance would be of the order of 100 kpc or larger, and this happened earlier than 3 Gyr ago. During this encounter, 35-40% of the dark matter mass of M33 might have been removed from the halo due to tidal stripping. A detailed comparison of the results of test-particle simulations with the observed disk warp or with the spatial distribution of candidate dark satellites of M33 suggests that a closer passage of M33 around M31 cannot, however, be responsible for the observed morphological features. We suggest that more recent gas accretion events, possibly from a cosmic filament, might cause the misalignment of the outer disk of M33 after the rapid inner disk formation.

astro-ph.GA↗

arXiv2023

The ALMaQUEST Survey XI: A strong but non-linear relationship between star formation and dynamical equilibrium pressure

We present the extended ALMA MaNGA QUEnching and STar formation survey, a combination of the original 46 ALMaQUEST galaxies plus new ALMA observations for a further 20 interacting galaxies. Three well-studied scaling relations are fit to the 19,999 star-forming spaxels in the extended sample, namely the resolved Schmidt-Kennicutt (rSK) relation, the resolved star forming main sequence (rSFMS) and the resolved molecular gas main sequence (rMGMS). We additionally investigate the relationship between the dynamical equilibrium pressure (PDE) and star formation rate surface density (Sigma_SFR), which we refer to as the resolved PDE (rPDE) relation. Contrary to previous studies that have focussed on normal star-forming galaxies and found an approximately linear rPDE relation, the presence of more vigourously star-forming galaxies in the extended ALMaQUEST sample reveals a marked turnover in the relation at high pressures. Although the scatter around the linear fit to the rPDE relation is similar to the other three relations, a random forest analysis, which can extract non-linear dependences, finds that PDE is unambiguously more important than either Sigma_H2 or Sigma_star for predicting Sigma_SFR. We compare the observed rPDE relation to the prediction of the pressure-regulated feedback-modulated (PRFM) model of star formation, finding that galaxies residing on the global SFMS do indeed closely follow the rPDE relation predicted by the PRFM theory. However, galaxies above and below the global SFMS show significant deviations from the model. Galaxies with high SFR are instead consistent with models that include other contributions to turbulence in addition to the local star formation feedback.

astro-ph.GA↗

arXiv2022

Exploring extreme conditions for star formation: a deep search for molecular gas in the Leo ring

We carry out sensitive searches for the CO J=1-0 and J=2-1 lines in the giant extragalactic HI ring in Leo to investigate the star formation process within environments where gas metallicities are close to solar but physical conditions are different than those typical of bright galaxy disks. Our aim is to check the range of validity of known scaling relations. We use the IRAM-30m telescope to observe eleven regions close to HI gas peaks or where sparse young massive stars have been found. For all pointed observations we reached a spectral noise between 1 and 5~mK for at least one observed frequencies at 2~km/s spectral resolution. We marginally detect two CO J=1-0 lines in the star forming region Clump~1 of the Leo ring, whose radial velocities are consistent with those of Halpha lines but line widths are much smaller than observed for virialized molecular clouds of similar mass in galaxies. The low signal-to-noise ratio, the small line widths and the extremely low number densities suggest that a more standard population of molecular clouds, still undetected, might be in place. Using upper limits to the CO lines, the most sensitive pointed observations show that the molecular gas mass surface density is lower than expected from the extrapolation of the molecular Kennicutt-Schmidt relation established in the disk of galaxies. The sparse stellar population in the ring, possibly forming ultra diffuse dwarf galaxies, might then be the result of a short molecular gas depletion time in this extreme environment.}

astro-ph.GA↗

arXiv2022

The resolved scaling relations in DustPedia: Zooming in on the local Universe

We perform a homogeneous analysis of an unprecedented set of spatially resolved scaling relations (SRs) between ISM components and other properties in the range of scales 0.3-3.4 kpc. We also study some ratios: dust-to-stellar, dust-to-gas, and dust-to-metal. We use a sample of 18 large, spiral, face-on DustPedia galaxies. All the SRs are moderate/strong correlations except the dust-HI SR that does not exist or is weak for most galaxies. The SRs do not have a universal form but each galaxy is characterized by distinct correlations, affected by local processes and galaxy peculiarities. The SRs hold starting from 0.3 kpc, and if a breaking down scale exists it is < 0.3 kpc. By evaluating all galaxies at 3.4 kpc, differences due to peculiarities of individual galaxies are cancelled out and the corresponding SRs are consistent with those of whole galaxies. By comparing subgalactic and global scales, the most striking result emerges from the SRs involving ISM components: the dust-total gas SR is a good correlation at all scales, while the dust-H2 and dust-HI SRs are good correlations at subkpc/kpc and total scales, respectively. For the other explored SRs, there is a good agreement between small and global scales and this may support the picture where the main physical processes regulating the properties and evolution of galaxies occur locally. Our results are consistent with the hypothesis of self-regulation of the SF process. The analysis of subgalactic ratios shows that they are consistent with those derived for whole galaxies, from low to high z, supporting the idea that also these ratios could be set by local processes. Our results highlight the heterogeneity of galaxy properties and the importance of resolved studies on local galaxies in the context of galaxy evolution. They also provide observational constraints to theoretical models and updated references for high-z studies.

astro-ph.GA↗

arXiv2021

Gaseous nebulae and massive stars in the giant HI ring in Leo

Chemical abundances in the Leo ring, the largest HI cloud in the local Universe, have recently been determined to be close or above solar, incompatible with a previously claimed primordial origin of the ring. The gas, pre-enriched in a galactic disk and tidally stripped, did not manage to form stars very efficiently in intergalactic space. We map nebular lines in 3 dense HI clumps of the Leo ring and complement these data with archival stellar continuum observations to investigate the slow building up of a sparse population of stars in localized areas of the ring. Individual young stars as massive as O7-types are powering some HII regions. The average star formation rate density is of order of 10^{-5} Msun/yr/kpc^2 and proceeds with local bursts a few hundred parsecs in size, where loose stellar associations of 500-1000 Msun occasionally host massive outliers. The far ultraviolet-to-Halpha emission ratio in nebular regions implies recent stellar bursts, from 2 to 7 Myr ago. The relation between the local HI gas density and the star formation rate in the ring is similar to what is found in dwarfs and outer disks with gas depletion times as long as 100~Gyrs. We find a candidate planetary nebula in a compact and faint Halpha region with [OIII]/Halpha line enhancement, consistent with the estimated mean stellar surface brightness of the ring. The presence of 1 kpc partial ring emitting weak Halpha lines around the brightest and youngest HII region suggests that local shocks might be the triggers of new star forming events.

astro-ph.GA↗

arXiv2021

Heavy elements unveil the non primordial origin of the giant HI ring in Leo

The origin and fate of the most extended extragalactic neutral cloud known in the local Universe, the Leo ring, is still debated 38 years after its discovery. Its existence is alternatively attributed to leftover primordial gas with some low level of metal pollution versus enriched gas stripped during a galaxy-galaxy encounter. Taking advantage of MUSE (Multi Unit Spectroscopic Explorer) operating at the VLT, we performed optical integral field spectroscopy of 3 HI clumps in the Leo ring where ultraviolet continuum emission has been found. We detected, for the first time, ionized hydrogen in the ring and identify 4 nebular regions powered by massive stars. These nebulae show several metal lines ([OIII],[NII],[SII]) which allowed reliable measures of metallicities, found to be close to or above the solar value. Given the faintness of the diffuse stellar counterparts, less than 3 percent of the observed heavy elements could have been produced locally in the main body of the ring and not much more than 15 percent in the HI clump towards M96. This inference, and the chemical homogeneity among the regions, convincingly demonstrates that the gas in the ring is not primordial, but has been pre-enriched in a galaxy disk, then later removed and shaped by tidal forces and it is forming a sparse population of stars.

astro-ph.GA↗

arXiv2020

A panchromatic spatially resolved analysis of nearby galaxies -- II. The main sequence - gas relation at sub-kpc scale in grand-design spirals

In the second work of this series, we analyse the connection between the availability of gas and the position of a region with respect to the spatially resolved main sequence (MS) relation. Following the procedure presented in Paper I we obtain 500pc scales estimates of stellar mass and star formation rate surface densities ($Σ_{\star}$ and $Σ_{\rm{SFR}}$). Our sample consists of five face-on, grand design spiral galaxies located on the MS. Thanks to HI 21cm and $^{12}$CO(2-1) maps, we connect the gas surface densities and gas fractions to the observed star formation properties of each region. We find that the spatially resolved MS ($σ=0.23$ dex) is the combination of two relations: the Kennicutt-Schmidt law ($σ=0.19$ dex) and the molecular gas MS (MGMS, $σ=0.22$ dex); $Σ_{\star}$, $Σ_{\rm{SFR}}$ and the surface density of the molecular gas, $Σ_{\rm{H_2}}$, define a 3D relation as proposed by \citet{2019ApJ...884L..33L}. We find that $Σ_{\rm{H_2}}$ steadily increases along the MS relation, varies little towards higher $Σ_{\rm{SFR}}$ at fixed stellar surface densities (not enough to sustain the change in SFR), and it is almost constant perpendicular to the relation. The surface density of neutral gas ($Σ_{\rm{HI}}$) is constant along the MS, and increases in its upper envelop. $Σ_{\rm{SFR}}$ can be expressed as a function of $Σ_{\star}$ and $Σ_{\rm{HI}}$, following the Equation: $\logΣ_{\rm{SFR}}$ = 0.97$\logΣ_{\star}$ + 1.99$\logΣ_{\rm{HI}}$ - 11.11. Finally, we show that f$_{\rm{gas}}$ increases significantly towards the starburst region in the $\logΣ_{\star}$ - $\logΣ_{\rm{SFR}}$ plane, accompanied by a slight increase in SFE.

astro-ph.GA↗

arXiv2020

Radio emission during the formation of stellar clusters in M33

We investigate thermal and non-thermal radio continuum associated with the early formation and evolution of Young Stellar Clusters (YSCs) selected by their MIR emission in M33. For the first time in an external galaxy it has been possible to identify radio counterparts to more than 300 star forming regions. We proof the nature of candidate YSCs fully embedded in molecular clouds, by recovering their associated faint radio continuum luminosities. Using the Halpha line to identify free-free radio emission at 5 GHz in the more evolved, partially exposed YSCs, we retrieve information on the relevance of magnetic fields and cosmic rays across the M33 disk at 25 pc spatial scales. A cross-correlation of MIR and radio continuum luminosities is established from bright to very faint YSCs, with MIR-to-radio emission ratio showing a gradual decline towards the outer disk, while the magnetic field is pervasive at all radii. We establish and discuss the tight relation between radio continuum and other star formation indicators, such as Halpha. This relation holds for individual YSCs over four orders of magnitude as well as for molecular clouds hosting YSCs. On average about half of radio emission at 5 GHz in YSCs is non-thermal. For exposed but compact YSCs the non-thermal radio fraction increases with source brightness, while for large HII regions the fraction is lower and shows no clear trend. This has been found for YSCs with and without identified SNRs and underlines the possible role of massive stars in triggering particle acceleration through winds and shocks: these particles diffuse throughout the native molecular cloud prior to cloud dispersal.

astro-ph.GA↗

arXiv2019

The ISM scaling relations in DustPedia late-type galaxies: A benchmark study for the Local Universe

The purpose of this work is the characterization of the main scaling relations between all the ISM components (dust, atomic/molecular/total gas), gas-phase metallicity, and other galaxy properties, such as Mstar and galaxy morphology, for late-type galaxies in the Local Universe. This study is performed by extracting late-type galaxies from the entire DustPedia sample and by exploiting the large and homogeneous dataset available thanks to the DustPedia project. The sample consists of 436 galaxies with morphological stage from T = 1 to 10, Mstar from 6 x 10^7 to 3 x 10^11 Msun, SFR from 6 x 10^(-4) to 60 Msun/yr, and 12 + log(O/H) from 8 to 9.5. The scaling relations involving the molecular gas are studied by assuming both a constant and a metallicity-dependent XCO. The analysis has been performed by means of the survival analysis technique. We confirm that the dust mass correlates very well with the total gas mass, and find -- for the first time -- that the dust mass correlates better with the atomic gas mass than the molecular one. We characterize important mass ratios such as gas fraction, molecular-to-atomic gas mass ratio, dust-to-total gas mass ratio (DGR), and dust-to-stellar mass ratio. Only the assumption of a metallicity-dependent XCO reproduces the expected decrease of the DGR with increasing morphological stage and decreasing gas-phase metallicity, with a slope of about 1. DGR, gas-phase metallicity, and the dust-to-stellar mass ratio are, for our galaxy sample, directly linked to the galaxy morphology. The molecular-to-atomic gas mass ratio and the DGR show a positive correlation for low molecular gas fractions, but for molecular gas rich galaxies this trend breaks down. This trend has never been found previously, to our knowledge. It provides new constraints for theoretical models of galaxy evolution and a reference for high-redshift studies.

astro-ph.GA↗

arXiv2019

Rise and fall of molecular clouds across the M33 disk

We carried out deep searches for CO line emission in the outer disk of M33, at R>7 kpc, and examined the dynamical conditions that can explain variations in the mass distribution of the molecular cloud throughout the disk of M33. We used the IRAM-30~m telescope to search for CO lines in the outer disk toward 12 faint mid-infrared (MIR) selected sources and in an area of the southern outer disk hosting MA1, a bright HII region. We detect narrow CO lines at the location of two MIR sources at galactocentric distances of about 8 kpc that are associated with low-mass young stellar clusters, and at four locations in the proximity of MA1. The paucity of CO lines at the location of weak MIR-selected sources probably arises because most of them are not star-forming sites in M33, but background sources. Although very uncertain, the total molecular mass of the detected clouds around MA1 is lower than expected given the stellar mass of the cluster, because dispersal of the molecular gas is taking place as the HII region expands. The mean mass of the giant molecular clouds (GMCs) in M33 decreases radially by a factor 2 from the center out to 4 kpc, then it stays constant until it drops at R>7 kpc. We suggest that GMCs become more massive toward the center because of the fast rotation of the disk, which drives mass growth by coalescence of smaller condensations as they cross the arms. The analysis of both HI and CO spectral data gives the consistent result that corotation of the two main arms in this galaxy is at a radius of 4.7+-0.3 kpc, and spiral shock waves become subsonic beyond 3.9 kpc. Perturbations are quenched beyond 6.5 kpc, where CO lines have been detected only around sporadic condensations associated with UV and MIR emission.

astro-ph.GA↗

arXiv2018

The Probability Distribution Function of Gas Surface Density in M33

The probability distribution functions (PDFs) for atomic, molecular, and total gas surface densities of M33 are determined at a resolution of about 50~pc over regions that share coherent morphological properties to unveil fingerprints of self-gravity across the star-forming disk. Most of the total gas PDFs from the central region to the edge of the star-forming disk are well-fitted by log-normal functions whose width decreases radially outwards. Because the HI velocity dispersion is approximately constant across the disk, the decrease of the PDF width is consistent with a lower Mach number for the turbulent ISM at large galactocentric radii where a higher fraction of HI is in the warm phase. The atomic gas is found mostly at face-on column densities below N$_{H}^{lim}$=2.5 10$^{21}$~cm$^{-2}$, with small radial variations of N$_{H}^{lim}$. The molecular gas PDFs do not show strong deviations from log-normal functions in the central region where molecular fractions are high. Here the high pressure and rate of star formation shapes the PDF as a log-normal function dispersing self-gravitating complexes with intense feedback at all column densities that are spatially resolved. Power law PDFs for the molecules are found near and above N$_H^{lim}$, in the well defined southern spiral arm and in a continuous dense filament extending at larger galactocentric radii; this is evident in cloud samples at different evolutionary stages along the star formation cycle. In the filament nearly half of the molecular gas departs from a log-normal PDF and power laws are also observed in pre-star forming molecular complexes. The slope of the power law is between -1 and -2. This slope, combined with maps showing where the different parts of the power law PDFs come from, suggest a power-law stratification of density within molecular cloud complexes, which is consistent with the dominance of self-gravity.

astro-ph.GA↗