Edvige Corbelli

Bio: Edvige Corbelli is an academic researcher from INAF. The author has contributed to research in topics: Galaxy & Star formation. The author has an hindex of 55, co-authored 139 publications receiving 8705 citations.

The CO-to-H2 Conversion Factor from Infrared Dust Emission across the Local Group

Abstract: We estimate the conversion factor relating CO emission to H2 mass, αCO, in five Local Group galaxies that span approximately an order of magnitude in metallicity—M 31, M 33, the Large Magellanic Cloud (LMC), NGC 6822, and the Small Magellanic Cloud (SMC). We model the dust mass along the line of sight from infrared (IR) emission and then solve for the αCO that best allows a single gas-to-dust ratio (δGDR) to describe each system. This approach remains sensitive to CO-dark envelopes H2 surrounding molecular clouds. In M 31, M 33, and the LMC we find αCO 3-9 M ☉ pc–2 (K km s–1)–1, consistent with the Milky Way value within the uncertainties. The two lowest metallicity galaxies in our sample, NGC 6822 and the SMC (12 + log (O/H) 8.2 and 8.0), exhibit a much higher αCO. Our best estimates are αNGC6822 CO 30 M ☉ pc–2 (K km s–1)–1 and αSMC CO 70 M ☉ pc–2 (K km s–1)–1. These results are consistent with the conversion factor becoming a strong function of metallicity around 12 + log (O/H) ~ 8.4-8.2. We favor an interpretation where decreased dust shielding leads to the dominance of CO-free envelopes around molecular clouds below this metallicity.

The CO-to-H2 Conversion Factor From Infrared Dust Emission Across the Local Group

Abstract: We estimate the conversion factor relating CO emission to H2 mass, alpha_CO, in five Local Group galaxies that span approximately an order of magnitude in metallicity - M31, M 33, the Large Magellanic Cloud (LMC), NGC 6822, and the Small Magellanic Cloud (SMC). We model the dust mass along the line of sight from infrared (IR) emission and then solve for the alpha_CO that best allows a single gas-to-dust ratio (delta_GDR) to describe each system. This approach remains sensitive to CO-dark envelopes of H2 surrounding molecular clouds. In M 31, M 33, and the LMC we find alpha_CO \approx 3-9 M_sun pc^-2 (K km s^-1)^-1, consistent with the Milky Way value within the uncertainties. The two lowest metallicity galaxies in our sample, NGC 6822 and the SMC (12 + log(O/H) \approx 8.2 and 8.0), exhibit a much higher alpha_CO. Our best estimates are \alpha_NGC6822 \approx 30 M_sun/pc^-2 (K km s^-1)^-1 and \alpha_SMC \approx 70 M_sun/pc^-2 (K km s-1)-1. These results are consistent with the conversion factor becoming CO a strong function of metallicity around 12 + log(O/H) \sim 8.4 - 8.2. We favor an interpretation where decreased dust-shielding leads to the dominance of CO-free envelopes around molecular clouds below this metallicity.

The initial mass function 50 years later

Abstract: Preface,List of Participants,Part I The IMF Concept through Time, Introduction to IMF@50, Ed, me, and the Insterstellar Medium,The IMF challenge - 25 questions, Fifty years of IMF variation: the intermediate-mass stars, The Initial Mass Function: from Salpeter 1955 to 2005, Part II The IMF in our Galaxy: Clusters and field stars, The field IMF across the H-burning, The 0.03-10M.mass function of young open clusters, The time spread of star formation in the Pleiades, Age spreads in clusters and associations: the lithium test, The Initial Mass Function of three galactic open clusters, The stellar IMF of galactic clusters and its evolution, Two stages of star formation in globular clusters and the IMF, The stellar Initial Mass Function in the Galactic Center, The Initial Mass Function in the Galactic Bulge, Halo mass function 101, Part III The IMF in our Galaxy: Star forming regions, Embedded clusters and the IMF, The IMF of stars and brown dwarfs in star forming regions, The substellar IMF of the Taurus cloud, The low-mass end of the IMF in Chamaeleon I, Limitations of the IR-excess method for identifying young stars, The IMF of Class II objects in the active Serpens cloud core, Orionis: a 0.02-50M. IMF, Does the "stellar" IMF extend to planetary masses?, Estimating the low-mass IMF in OB associations: Orionis, Young brown dwarfs in Orion, The formation of free-floating brown dwarves & planetary-mass objects by photo-erosion of prestellar cores, IMF in small young embedded star clusters, The Arches cluster - a case for IMF variations?, The IMF and mass segregation in young galactic starburst clusters, A 2.2 micron catalogue of stars in NGC 3603, The IMF of the massive star forming region NGC 3603 from VLT adaptive optics observations, X-rays and young clusters, NGC 2264: a Chandra view, Part IV The Extragalactic IMF, Variations of the IMF, On the form of the IMF: upper-mass cutoff and slope, Evidence for a fundamental stellar upper mass limit from clustered star formation, Monte Carlo experiments on star cluster induced integrated-galaxy IMF variations, The initial conditions to star formation: low-mass stars at low metallicity, Stellar associations in the LMC, The IMF long ago and far away, The massive star IMF at high metallicity, The Initial Mass Function in disc galaxies and in galaxy clusters: the chemo-photometric picture, Steeper, flatter, or just Salpeter? Evidence from galaxy evolution and galaxy clusters, Initial mass function and galactic chemical evolution models, New database of SSPs with different IMFs, The starburst IMF n An impossible measurement?, Gould's Belt to starburst galaxies: the IMF of extreme star formation, Mid-IR observations at high spatial resolution: constraints on the IMF in very young embedded super star clusters, Wolf-Rayet stars as IMF probes, Part V The Origin of the IMF: Atomic and molecular gas tracers, Smidgens of fuel for star formation, The Initial Mass Function in the context of warm ionized gas in disk galaxies, Tracing the star formation cycle through the diffuse Interstellar Medium, Examining the relationship between interstellar turbulence and star formation, The IMF of Giant Molecular Clouds, Multiphase molecular gas and star forming sites in M33, How does star formation build a galactic disk?, Mapping extragalactic molecular clouds: Centaurus A (NGC 5128), Tiny HI clouds in the local ISM, Submm observations of prestellar condensations: probing the initial conditions for the IMF, How well determined is the core mass function of Oph?, From dense cores to protostars in low-mass star forming regions, Fragmentation of a high-mass star forming core, Part VI The Origin of the IMF: Cloud fragmentation and collapse, Understanding the IMF, Flows, filaments and fragmentation, Minimum mass for opacity-limited fragmentation in dynamically triggered star formation, Origin of the core mass function, The connection between the core mass function and the IMF in Taurus, The stellar IMF as a property of turbulence, The stellar mass spectrum from non-isothermal gravoturbulent fragmentation, Turbulent control of the star formation efficiency, Thermal condensation in a turbulent atomic hydrogen flow, The formation of molecular clouds, Turbulence-accelerated star formation in magnetized clouds, Cluster density and the IMF, Part VII The Origin of the IMF: From gas to stars, A theory of the IMF, A class of IMF theories, An effective Initial Mass Function for galactic disks, Competitive accretion and the IMF, The dependence of the IMF on initial conditions, A minimum hypothesis explanation for an IMF with a lognormal body and power law tail, Feedback and the Initial Mass Function, Feedback in star formation simulations: implications for the IMF, Massive star feedback on the IMF, Discussion: Turbulence and magnetic fields in clouds, Part VIII The "Initial" IMF, The primordial IMF, Cosmic relevance of the first stars, Star formation triggered by first supernovae, Detecting primordial stars, Constraints on the IMF in low metallicity and PopIII environments, Thermal evolution of star forming clouds in low metallicity environment, Observational evidence for a different IMF in the early Galaxy, The role of the IMF in the cosmic metal production, From Population III stars to (super)massive black holes, Gamma-ray burst afterglows as probes of high-z star formation, Part IX Chuzpah talks, Electrostatic screening of nuclear reactions 50 years later, The life and death of Planetary Nebulae, Early results from the infrared spectrograph on the Spitzer Space Telescope, Future observational opportunities, Author Index

The extended rotation curve and the dark matter halo of M33

Abstract: We present the 21-cm rotation curve of the nearby galaxy M33 out to a galactocentric distance of 16 kpc (13 disk scale-lengths). The rotation curve keeps rising out to the last measured point and implies a dark halo mass larger than 5 10^{10} solar masses. The stellar and gaseous disks provide virtually equal contributions to the galaxy gravitational potential at large galactocentric radii but no obvious correlation is found between the radial distribution of dark matter and the distribution of stars or gas. Results of the best fit to the mass distribution in M33 picture a dark halo which controls the gravitational potential from 3 kpc outward, with a matter density which decreases radially as R^{-1.3}. The density profile is consistent with the theoretical predictions for structure formation in hierarchical clustering cold dark matter models but mass concentrations are lower than those expected in the standard cosmogony.

Dark matter and visible baryons in M33

Abstract: In this paper we present new measurements of the gas kinematics in M33 using the CO J = 1 - 0 line. The resulting rotational velocities complement previous 21-cm line data for a very accurate and extended rotation curve of this nearby galaxy. The implied dark matter mass, within the total gaseous extent, is a factor of 5 higher than the visible baryonic mass. Dark matter density profiles with an inner cusp as steep as R - 1 , suggested by some numerical simulation of structures formation, are compatible with the actual data. The dark matter concentrations required for fitting the M33 rotation curve are very low but still marginally consistent with haloes forming in a standard cold dark matter cosmology. The M33 virialized dark halo is at least 50 times more massive than the visible baryons and its size is comparable with the M33-M31 separation. Inner cusps as steep as R - 1 . 5 are ruled out, while halo models with a large size core of constant density are consistent with the M33 data. A central excess of stars is needed and we evaluate its dynamical mass range. Using accurate rotational velocity gradients and the azimuthally averaged baryonic surface densities, we show that a disc instability can regulate the star formation activity in M33. Considering the gaseous surface density alone, the predicted outer star formation threshold radius is consistent with the observed drop of the Ha surface brightness if a shear rate criterion is used with the lowest possible value of velocity dispersion. The classical Toomre criterion predicts the size of the unstable region correctly only when the stellar or dark halo gravity, derived in this paper, is added to that of the gaseous disc.

Star Formation in the Milky Way and Nearby Galaxies

Abstract: We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star-formation rates are discussed, and updated prescriptions for calculating star-formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.

Theory of Star Formation

Abstract: We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation—turbulence, magnetic fields, and self-gravity— are highly nonlinear and multidimensional. Physical arguments are used to identify and explain the features and scalings involved in star formation, and results from numerical simulations are used to quantify these effects. We divide star formation into large-scale and small-scale regimes and review each in turn. Large scales range from galaxies to giant molecular clouds (GMCs) and their substructures. Important problems include how GMCs form and evolve, what determines the star formation rate (SFR), and what determines the initial mass function (IMF). Small scales range from dense cores to the protostellar systems they beget. We discuss formation of both low- and high-mass stars, including ongoing accretion. The development of winds and outflows is increasingly well understood, as are the mechanisms governing angular momentum transport in disks. Although outstanding questions remain, the framework is now in place to build a comprehensive theory of star formation that will be tested by the next generation of telescopes.

Dwarf galaxies of the local group

Abstract: ▪ Abstract The Local Group dwarf galaxies offer a unique window to the detailed properties of the most common type of galaxy in the Universe. In this review, I update the census of Local Group dwarfs based on the most recent distance and radial velocity determinations. I then discuss the detailed properties of this sample, including (a) the integrated photometric parameters and optical structures of these galaxies, (b) the content, nature, and distribution of their interstellar medium (ISM), (c) their heavy-element abundances derived from both stars and nebulae, (d) the complex and varied star-formation histories of these dwarfs, (e) their internal kinematics, stressing the relevance of these galaxies to the “dark matter problem” and to alternative interpretations, and (f) evidence for past, ongoing, and future interactions of these dwarfs with other galaxies in the Local Group and beyond. To complement the discussion and to serve as a foundation for future work, I present an extensive set of basic observ...

The CO-to-H2 Conversion Factor

Abstract: CO line emission represents the most accessible and widely used tracer of the molecular interstellar medium. This renders the translation of observed CO intensity into total H2 gas mass critical to understand star formation and the interstellar medium in our Galaxy and beyond. We review the theoretical underpinning, techniques, and results of efforts to estimate this CO-to-H2 “conversion factor,” XCO, in different environments. In the Milky Way disk, we recommend a conversion factor XCO = 2×10 20 cm −2 (K km s −1 ) −1 with ±30% uncertainty. Studies of other “normal galaxies” return similar values in Milky Way-like disks, but with greater scatter and systematic uncertainty. Departures from this Galactic conversion factor are both observed and expected. Dust-based determinations, theoretical arguments, and scaling relations all suggest that XCO increases with decreasing metallicity, turning up sharply below metallicity ≈ 1/3–1/2 solar in a manner consistent with model predictions that identify shielding as a key parameter. Based on spectral line modeling and dust observations, XCO appears to drop in the central, bright regions of some but not all galaxies, often coincident with regions of bright CO emission and high stellar surface density. This lower XCO is also present in the overwhelmingly molecular interstellar medium of starburst galaxies, where several lines of evidence point to a lower CO-to-H2 conversion factor. At high redshift, direct evidence regarding the conversion factor remains scarce; we review what is known based on dynamical modeling and other arguments. Subject headings: ISM: general — ISM: molecules — galaxies: ISM — radio lines: ISM

The Star Formation Law in Nearby Galaxies on Sub-Kpc Scales

Abstract: We present a comprehensive analysis of the relationship between star formation rate surface density, ΣSFR, and gas surface density, Σgas, at sub-kpc resolution in a sample of 18 nearby galaxies. We use high-resolution H I data from The H I Nearby Galaxy Survey, CO data from HERACLES and the BIMA Survey of Nearby Galaxies, 24 μm data from the Spitzer Space Telescope, and UV data from the Galaxy Evolution Explorer. We target seven spiral galaxies and 11 late-type/dwarf galaxies and investigate how the star formation law differs between the H2 dominated centers of spiral galaxies, their H I dominated outskirts and the H I rich late-type/dwarf galaxies. We find that a Schmidt-type power law with index N = 1.0 ± 0.2 relates ΣSFR and ΣH2 across our sample of spiral galaxies, i.e., that H2 forms stars at a constant efficiency in spirals. The average molecular gas depletion time is ~2 × 109 years. The range of ΣH2 over which we measure this relation is ~3-50 M ☉ pc–2, significantly lower than in starburst environments. We find the same results when performing a pixel-by-pixel analysis, averaging in radial bins, or when varying the star formation tracer used. We interpret the linear relation and constant depletion time as evidence that stars are forming in giant molecular clouds with approximately uniform properties and that ΣH2 may be more a measure of the filling fraction of giant molecular clouds than changing conditions in the molecular gas. The relationship between total gas surface density (Σgas) and ΣSFR varies dramatically among and within spiral galaxies. Most galaxies show little or no correlation between ΣHI and ΣSFR. As a result, the star formation efficiency (SFE), ΣSFR/Σgas, varies strongly across our sample and within individual galaxies. We show that this variation is systematic and consistent with the SFE being set by local environmental factors: in spirals the SFE is a clear function of radius, while the dwarf galaxies in our sample display SFEs similar to those found in the outer optical disks of the spirals. We attribute the similarity to common environments (low density, low metallicity, H I dominated) and argue that shear (which is typically absent in dwarfs) cannot drive the SFE. In addition to a molecular Schmidt law, the other general feature of our sample is a sharp saturation of H I surface densities at ΣHI ≈ 9 M ☉ pc–2 in both the spiral and dwarf galaxies. In the case of the spirals, we observe gas in excess of this limit to be molecular.