Frédéric Galliano - Academia.edu (original) (raw)
Papers by Frédéric Galliano
EPJ Web of Conferences, 2022
The mm-to-cm range of the Spectral Energy Distribution of spiral galaxies remains largely unexplo... more The mm-to-cm range of the Spectral Energy Distribution of spiral galaxies remains largely unexplored. Its coverage is required to disentangle the contribution of dust emission, free-free and synchrotron radiation and can provide constraints on dust models, star-formation rates and ISM properties. We present the case for a synergy between NIKA2 observations of nearby spirals and those from planned and current instrumentation at the Sardinia Radio Telescope, and report on a pilot K-band program to search for Anomalous Microwave Emission, an elusive emission component which is presumably related to dust.
We present the severe, systematic uncertainties currently facing our understanding of dust emissi... more We present the severe, systematic uncertainties currently facing our understanding of dust emission, which stymie our ability to truly exploit dust as a tool for studying galaxy evolution. We propose a program of study to tackle these uncertainties, describe the necessary facilities, and discuss the potential science gains that would result.
Monthly Notices of the Royal Astronomical Society, 2021
The objective of this paper is to understand the variance of the far-infrared (FIR) spectral ener... more The objective of this paper is to understand the variance of the far-infrared (FIR) spectral energy distribution (SED) of the DustPedia galaxies, and its link with the stellar and dust properties. An interesting aspect of the dust emission is the inferred FIR colours which could inform us about the dust content of galaxies, and how it varies with the physical conditions within galaxies. However, the inherent complexity of dust grains as well as the variety of physical properties depending on dust, hinder our ability to utilize their maximum potential. We use principal component analysis (PCA) to explore new hidden correlations with many relevant physical properties such as the dust luminosity, dust temperature, dust mass, bolometric luminosity, star formation rate (SFR), stellar mass, specific SFR, dust-to-stellar mass ratio, the fraction of absorbed stellar luminosity by dust (fabs), and metallicity. We find that 95 per cent of the variance in our sample can be described by two pri...
Proceedings of The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments — PoS(LCDU2013), 2014
Publications of the Astronomical Society of Japan, 2019
The anomalous microwave emission (AME) still lacks a conclusive explanation. This excess of emiss... more The anomalous microwave emission (AME) still lacks a conclusive explanation. This excess of emission, roughly between 10 and 50 GHz, tends to defy attempts to explain it as synchrotron or free–free emission. The overlap with frequencies important for cosmic microwave background explorations, combined with a strong correlation with interstellar dust, drive cross-disciplinary collaboration between interstellar medium and observational cosmology. The apparent relationship with dust has prompted a “spinning dust” hypothesis. The typical peak frequency range of the AME profile implicates spinning grains on the order of 1 nm. This points to polycyclic aromatic hydrocarbons (PAHs). We use data from the AKARI/Infrared Camera (IRC), due to its thorough PAH-band coverage, to compare AME from the Planck Collaboration astrophysical component separation product with infrared dust emission in the λ Orionis AME-prominent region. We look also at infrared dust emission from other mid-infrared and fa...
Astronomy & Astrophysics, 2020
Context. Dust in late-type galaxies in the local Universe is responsible for absorbing approximat... more Context. Dust in late-type galaxies in the local Universe is responsible for absorbing approximately one third of the energy emitted by stars. It is often assumed that dust heating is mainly attributable to the absorption of ultraviolet and optical photons emitted by the youngest (≤100 Myr) stars. Consequently, thermal re-emission by dust at far-infrared wavelengths is often linked to the star-formation activity of a galaxy. However, several studies argue that the contribution to dust heating by much older stellar populations might be more significant than previously thought. Advances in radiation transfer simulations finally allow us to actually quantify the heating mechanisms of diffuse dust by the stellar radiation field. Aims. As one of the main goals in the DustPedia project, we have developed a framework to construct detailed 3D stellar and dust radiative transfer models for nearby galaxies. In this study, we analyse the contribution of the different stellar populations to the...
Astronomy & Astrophysics, 2019
Aims. Within the framework of the DustPedia project we investigate the properties of cosmic dust ... more Aims. Within the framework of the DustPedia project we investigate the properties of cosmic dust and its interaction with stellar radiation (originating from different stellar populations) for 814 galaxies in the nearby Universe, all observed by the Herschel Space Observatory. Methods. We take advantage of the widely used fitting code CIGALE, properly adapted to include the state-of-the-art dust model THEMIS. For comparison purposes, an estimation of the dust properties is provided by approximating the emission at far-infrared and sub-millimeter wavelengths with a modified blackbody. Using the DustPedia photometry we determine the physical properties of the galaxies, such as the dust and stellar mass, the star-formation rate, the bolometric luminosity, the unattenuated and the absorbed by dust stellar light, for both the old (> 200 Myr) and young (≤200 Myr) stellar populations. Results. We show how the mass of stars, dust, and atomic gas, as well as the star-formation rate and th...
Monthly Notices of the Royal Astronomical Society, 2018
This article presents a new dust spectral energy distribution (SED) model, named HerBIE, aimed at... more This article presents a new dust spectral energy distribution (SED) model, named HerBIE, aimed at eliminating the noise-induced correlations and large scatter obtained when performing least-squares fits. The originality of this code is to apply the hierarchical Bayesian approach to full dust models, including realistic optical properties, stochastic heating, and the mixing of physical conditions in the observed regions. We test the performances of our model by applying it to synthetic observations. We explore the impact on the recovered parameters of several effects: signal-to-noise ratio, SED shape, sample size, the presence of intrinsic correlations, the wavelength coverage, and the use of different SED model components. We show that this method is very efficient: the recovered parameters are consistently distributed around their true values. We do not find any clear bias, even for the most degenerate parameters, or with extreme signal-to-noise ratios.
Annual Review of Astronomy and Astrophysics, 2018
This article gives an overview of the constitution, physical conditions, and observables of dust ... more This article gives an overview of the constitution, physical conditions, and observables of dust in the interstellar medium of nearby galaxies. We first review the macroscopic, spatial distribution of dust in these objects and its consequences for our ability to study grain physics. We also discuss the possibility of using dust tracers as diagnostic tools. We then survey the current understanding of the microscopic, intrinsic properties of dust in different environments, derived from different observables: emission, extinction, polarization, and depletions, over the whole electromagnetic spectrum. Finally, we summarize the clues about grain evolution, evidenced either on local scales or over cosmic time. We put in perspective the different evolution scenarios. We attempt a comprehensive presentation of the main observational constraints, analysis methods, and modeling frameworks of the distinct processes. We discuss neither the dust properties of the Milky Way and distant galaxies, ...
EAS Publications Series, 2002
We are modeling the spectra of dwarf galaxies from infrared to submillimeter wavelengths to under... more We are modeling the spectra of dwarf galaxies from infrared to submillimeter wavelengths to understand the nature of the various dust components in low-metallicity environments, which may be comparable to the ISM of galaxies in their early evolutionary state. The overall nature of the dust in these environments appears to differ from those of higher metallicity starbursting systems. Here, we present a study of one of our sample of dwarf galaxies, NGC 1569, which is a nearby, well-studied starbursting dwarf. Using ISOCAM, IRAS, ISOPHOT and SCUBA data with the DéΓΓsertetal(1990)model, wef indconsistencywithlittlecontributionf romP AHsandV erySm
Planetary and Space Science, 2017
Nearby galaxies are particularly relevant laboratories to study dust evolution due to the diversi... more Nearby galaxies are particularly relevant laboratories to study dust evolution due to the diversity of physical conditions they harbor and to the wealth of data at our disposal. In this paper, we review several recent advances in this field, mainly based on Herschel observations. We first discuss the problems linked with our ignorance of grain emissivities, and show that it can be constrained in some cases. New models are starting to incorporate these constraints. We then present methodological issues encountered when fitting spectral energy distributions, leading to biases in derived dust properties, and some attempts to solve them. Subsequently, we review studies scrutinizing dust evolution: (i) from a global point of view, inferring long term cosmic dust evolution; (ii) from a local point of view, looking for indices of dust processing in the ISM.
AIP Conference Proceedings, 2005
I present a simple self-consistent dust spectral energy distribution (SED) model that has been ap... more I present a simple self-consistent dust spectral energy distribution (SED) model that has been applied to fit the well-sampled observed UV-to-radio SED of four nearby starbursting dwarf galaxies. The main originality of this model is that numerous multi-wavelength observations, from UV to millimeter (mm), constrain in a self-consistent manner, both the local radiation field and the grain size distribution. I finally present the results of our model and discuss the average dust properties in these dwarf galaxies.
Astronomy & Astrophysics, 2015
We investigate the physical properties of the molecular and ionized gas, and their relationship t... more We investigate the physical properties of the molecular and ionized gas, and their relationship to the star formation and dust properties in M 83, based on submillimeter imaging spectroscopy from within the central 3.5 (∼4 kpc in diameter) around the starburst nucleus. The observations use the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) onboard the Herschel Space Observatory. The newly observed spectral lines include [CI] 370 µm, [CI] 609 µm, [NII] 205 µm, and CO transitions from J = 4−3 to J = 13−12. Combined with previously observed J = 1−0 to J = 3−2 transitions, the CO spectral line energy distributions are translated to spatially resolved physical parameters, column density of CO, N(CO), and molecular gas thermal pressure, P th , with a non-local thermal equilibrium (non-LTE) radiative transfer model, RADEX. Our results show that there is a relationship between the spatially resolved intensities of [NII] 205 µm and the surface density of the star formation rate (SFR), Σ SFR. This relation, when compared to integrated properties of ultra-luminous infrared galaxies (ULIRGs), exhibits a different slope, because the [NII] 205 µm distribution is more extended than the SFR. The spatially resolved [CI] 370 µm, on the other hand, shows a generally linear relationship with Σ SFR and can potentially be a good SFR tracer. Compared with the dust properties derived from broad-band images, we find a positive trend between the emissivity of CO in the J = 1−0 transition with the average intensity of interstellar radiation field (ISRF), U. This trend implies a decrease in the CO-to-H 2 conversion factor, X CO , when U increases. We estimate the gas-to-dust mass ratios to be 77 ± 33 within the central 2 kpc and 93 ± 19 within the central 4 kpc of M 83, which implies a Galactic dust-to-metal mass ratio within the observed region of M 83. The estimated gas-depletion time for the M 83 nucleus is 1.13 ± 0.6 Gyr, which is shorter than the values for nearby spiral galaxies found in the literature (∼2.35 Gyr), most likely due to the young nuclear starbursts. A linear relationship between P th and the radiation pressure generated by U , P rad , is found to be P th ≈ 30 P rad , which signals that the ISRF alone is insufficient to sustain the observed CO transitions. The spatial distribution of P th reveals a pressure gradient, which coincides with the observed propagation of starburst activities and the alignment of (possibly background) radio sources. We discover that the off-centered (from the optical nucleus) peak of the molecular gas volume density coincides well with a minimum in the relative aromatic feature strength, indicating a possible destruction of their carriers. We conclude that the observed CO transitions are most likely associated with mechanical heating processes that are directly or indirectly related to very recent nuclear starbursts.
Proceedings of the International Astronomical Union, 2011
The low metallicity interstellar medium of dwarf galaxies gives a different picture in the far in... more The low metallicity interstellar medium of dwarf galaxies gives a different picture in the far infrared(FIR)/submillimetre(submm)wavelengths than the more metal-rich galaxies. Excess emission is often found in the submm beginning at or beyond 500 μm. Even without taking this excess emission into account as a possible dust component, higher dust-to-gas mass ratios (DGR) are often observed compared to that expected from their metallicity for moderately metal-poor galaxies. The Spectral Energy Distributions (SEDs) of the lowest metallicity galaxies, however, give very low dust masses and excessively low values of DGR, inconsistent with the amount of metals expected to be captured into dust if we presume the usual linear relationship holding for all metallicities, including the more metal-rich galaxies. This transition seems to appear near metalllicities of 12 + log(O/H) 8.0 - 8.2. These results rely on accurately quantifying the total molecular gas reservoir, which is uncertain in low ...
Proceedings of the International Astronomical Union, 2012
The wide variety of low metallicity galaxies of the local universe serve as convenient laboratori... more The wide variety of low metallicity galaxies of the local universe serve as convenient laboratories to study the evolution of gas and dust and conditions for star formation in environments which may resemble those of the early universe. The Herschel Dwarf Galaxy Survey is studying the far infrared (FIR) and submillimeter (submm) properties of the gas and dust in galaxies with metallicity values as low as 1/45 that of solar. With complementary Spitzer, Laboca/APEX, Scuba/JCMT data, the dust spectral energy distributions are well constrained now, providing more accurate dust masses. We find a steep drop in dust-to-gas mass ratio (D/G) when the metallicity is below 12+log(O/H) ∼ 8. A submillimeter excess can be found in some low metallicity galaxies, which, when present, becomes apparent at wavelengths at or longer than 500 μm. While CO is difficult to observe in low metallicity gas, the FIR fine structure lines, on the other hand, are very luminous and highlight a potentially importan...
Clefs CEA, 2009
Comme toutes les galaxies spirales, notre Voie lactee est active: de nouvelles etoiles y naissent... more Comme toutes les galaxies spirales, notre Voie lactee est active: de nouvelles etoiles y naissent encore aujourd'hui. Meme si elles ne representent pas, et de loin, la totalite de la matiere d'une galaxie, les etoiles en constituent le principal « moteur ».
Proceedings of the International Astronomical Union, 2008
This paper presents the results of a study aimed at understanding the evolution of the dust prope... more This paper presents the results of a study aimed at understanding the evolution of the dust properties, as a function of both the environmental conditions and the metal enrichment of the system. I first review the peculiar dust properties of dwarf galaxies, and discuss attempts to understand their origin. Then, I discuss the evolution of the PAH and dust abundances, constrained by the UV-to-radio SED of nearby galaxies, comparing the properties of low-metallicity environments and more evolved systems. I discuss the long term evolution of dust in galaxies, comparing the grain production by various stellar progenitors to their destruction by SN blast waves and in Hiiregions. Finally, I will show how these models explain the paucity of PAHs in low-metallicity environments.
Proceedings of the International Astronomical Union, 2011
In a recent study based on the modelling of spatially resolved Spitzer and Herschel observations ... more In a recent study based on the modelling of spatially resolved Spitzer and Herschel observations of the Large Magellanic Cloud (LMC), we have shown that the infrared (IR) to submillimetre (submm) grain opacities are systematically higher in the LMC than in our Galaxy. This discovery demonstrates an evolution of the dust properties with environment. Here, we discuss the consequences of this evolution on the modelling of SEDs of galaxies, emphasizing that the uncertainties on the grain properties can lead to erroneous interpretations of the structure of the interstellar medium (ISM) of galaxies, if no additional independent constraints are used.
EPJ Web of Conferences, 2022
The mm-to-cm range of the Spectral Energy Distribution of spiral galaxies remains largely unexplo... more The mm-to-cm range of the Spectral Energy Distribution of spiral galaxies remains largely unexplored. Its coverage is required to disentangle the contribution of dust emission, free-free and synchrotron radiation and can provide constraints on dust models, star-formation rates and ISM properties. We present the case for a synergy between NIKA2 observations of nearby spirals and those from planned and current instrumentation at the Sardinia Radio Telescope, and report on a pilot K-band program to search for Anomalous Microwave Emission, an elusive emission component which is presumably related to dust.
We present the severe, systematic uncertainties currently facing our understanding of dust emissi... more We present the severe, systematic uncertainties currently facing our understanding of dust emission, which stymie our ability to truly exploit dust as a tool for studying galaxy evolution. We propose a program of study to tackle these uncertainties, describe the necessary facilities, and discuss the potential science gains that would result.
Monthly Notices of the Royal Astronomical Society, 2021
The objective of this paper is to understand the variance of the far-infrared (FIR) spectral ener... more The objective of this paper is to understand the variance of the far-infrared (FIR) spectral energy distribution (SED) of the DustPedia galaxies, and its link with the stellar and dust properties. An interesting aspect of the dust emission is the inferred FIR colours which could inform us about the dust content of galaxies, and how it varies with the physical conditions within galaxies. However, the inherent complexity of dust grains as well as the variety of physical properties depending on dust, hinder our ability to utilize their maximum potential. We use principal component analysis (PCA) to explore new hidden correlations with many relevant physical properties such as the dust luminosity, dust temperature, dust mass, bolometric luminosity, star formation rate (SFR), stellar mass, specific SFR, dust-to-stellar mass ratio, the fraction of absorbed stellar luminosity by dust (fabs), and metallicity. We find that 95 per cent of the variance in our sample can be described by two pri...
Proceedings of The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments — PoS(LCDU2013), 2014
Publications of the Astronomical Society of Japan, 2019
The anomalous microwave emission (AME) still lacks a conclusive explanation. This excess of emiss... more The anomalous microwave emission (AME) still lacks a conclusive explanation. This excess of emission, roughly between 10 and 50 GHz, tends to defy attempts to explain it as synchrotron or free–free emission. The overlap with frequencies important for cosmic microwave background explorations, combined with a strong correlation with interstellar dust, drive cross-disciplinary collaboration between interstellar medium and observational cosmology. The apparent relationship with dust has prompted a “spinning dust” hypothesis. The typical peak frequency range of the AME profile implicates spinning grains on the order of 1 nm. This points to polycyclic aromatic hydrocarbons (PAHs). We use data from the AKARI/Infrared Camera (IRC), due to its thorough PAH-band coverage, to compare AME from the Planck Collaboration astrophysical component separation product with infrared dust emission in the λ Orionis AME-prominent region. We look also at infrared dust emission from other mid-infrared and fa...
Astronomy & Astrophysics, 2020
Context. Dust in late-type galaxies in the local Universe is responsible for absorbing approximat... more Context. Dust in late-type galaxies in the local Universe is responsible for absorbing approximately one third of the energy emitted by stars. It is often assumed that dust heating is mainly attributable to the absorption of ultraviolet and optical photons emitted by the youngest (≤100 Myr) stars. Consequently, thermal re-emission by dust at far-infrared wavelengths is often linked to the star-formation activity of a galaxy. However, several studies argue that the contribution to dust heating by much older stellar populations might be more significant than previously thought. Advances in radiation transfer simulations finally allow us to actually quantify the heating mechanisms of diffuse dust by the stellar radiation field. Aims. As one of the main goals in the DustPedia project, we have developed a framework to construct detailed 3D stellar and dust radiative transfer models for nearby galaxies. In this study, we analyse the contribution of the different stellar populations to the...
Astronomy & Astrophysics, 2019
Aims. Within the framework of the DustPedia project we investigate the properties of cosmic dust ... more Aims. Within the framework of the DustPedia project we investigate the properties of cosmic dust and its interaction with stellar radiation (originating from different stellar populations) for 814 galaxies in the nearby Universe, all observed by the Herschel Space Observatory. Methods. We take advantage of the widely used fitting code CIGALE, properly adapted to include the state-of-the-art dust model THEMIS. For comparison purposes, an estimation of the dust properties is provided by approximating the emission at far-infrared and sub-millimeter wavelengths with a modified blackbody. Using the DustPedia photometry we determine the physical properties of the galaxies, such as the dust and stellar mass, the star-formation rate, the bolometric luminosity, the unattenuated and the absorbed by dust stellar light, for both the old (> 200 Myr) and young (≤200 Myr) stellar populations. Results. We show how the mass of stars, dust, and atomic gas, as well as the star-formation rate and th...
Monthly Notices of the Royal Astronomical Society, 2018
This article presents a new dust spectral energy distribution (SED) model, named HerBIE, aimed at... more This article presents a new dust spectral energy distribution (SED) model, named HerBIE, aimed at eliminating the noise-induced correlations and large scatter obtained when performing least-squares fits. The originality of this code is to apply the hierarchical Bayesian approach to full dust models, including realistic optical properties, stochastic heating, and the mixing of physical conditions in the observed regions. We test the performances of our model by applying it to synthetic observations. We explore the impact on the recovered parameters of several effects: signal-to-noise ratio, SED shape, sample size, the presence of intrinsic correlations, the wavelength coverage, and the use of different SED model components. We show that this method is very efficient: the recovered parameters are consistently distributed around their true values. We do not find any clear bias, even for the most degenerate parameters, or with extreme signal-to-noise ratios.
Annual Review of Astronomy and Astrophysics, 2018
This article gives an overview of the constitution, physical conditions, and observables of dust ... more This article gives an overview of the constitution, physical conditions, and observables of dust in the interstellar medium of nearby galaxies. We first review the macroscopic, spatial distribution of dust in these objects and its consequences for our ability to study grain physics. We also discuss the possibility of using dust tracers as diagnostic tools. We then survey the current understanding of the microscopic, intrinsic properties of dust in different environments, derived from different observables: emission, extinction, polarization, and depletions, over the whole electromagnetic spectrum. Finally, we summarize the clues about grain evolution, evidenced either on local scales or over cosmic time. We put in perspective the different evolution scenarios. We attempt a comprehensive presentation of the main observational constraints, analysis methods, and modeling frameworks of the distinct processes. We discuss neither the dust properties of the Milky Way and distant galaxies, ...
EAS Publications Series, 2002
We are modeling the spectra of dwarf galaxies from infrared to submillimeter wavelengths to under... more We are modeling the spectra of dwarf galaxies from infrared to submillimeter wavelengths to understand the nature of the various dust components in low-metallicity environments, which may be comparable to the ISM of galaxies in their early evolutionary state. The overall nature of the dust in these environments appears to differ from those of higher metallicity starbursting systems. Here, we present a study of one of our sample of dwarf galaxies, NGC 1569, which is a nearby, well-studied starbursting dwarf. Using ISOCAM, IRAS, ISOPHOT and SCUBA data with the DéΓΓsertetal(1990)model, wef indconsistencywithlittlecontributionf romP AHsandV erySm
Planetary and Space Science, 2017
Nearby galaxies are particularly relevant laboratories to study dust evolution due to the diversi... more Nearby galaxies are particularly relevant laboratories to study dust evolution due to the diversity of physical conditions they harbor and to the wealth of data at our disposal. In this paper, we review several recent advances in this field, mainly based on Herschel observations. We first discuss the problems linked with our ignorance of grain emissivities, and show that it can be constrained in some cases. New models are starting to incorporate these constraints. We then present methodological issues encountered when fitting spectral energy distributions, leading to biases in derived dust properties, and some attempts to solve them. Subsequently, we review studies scrutinizing dust evolution: (i) from a global point of view, inferring long term cosmic dust evolution; (ii) from a local point of view, looking for indices of dust processing in the ISM.
AIP Conference Proceedings, 2005
I present a simple self-consistent dust spectral energy distribution (SED) model that has been ap... more I present a simple self-consistent dust spectral energy distribution (SED) model that has been applied to fit the well-sampled observed UV-to-radio SED of four nearby starbursting dwarf galaxies. The main originality of this model is that numerous multi-wavelength observations, from UV to millimeter (mm), constrain in a self-consistent manner, both the local radiation field and the grain size distribution. I finally present the results of our model and discuss the average dust properties in these dwarf galaxies.
Astronomy & Astrophysics, 2015
We investigate the physical properties of the molecular and ionized gas, and their relationship t... more We investigate the physical properties of the molecular and ionized gas, and their relationship to the star formation and dust properties in M 83, based on submillimeter imaging spectroscopy from within the central 3.5 (∼4 kpc in diameter) around the starburst nucleus. The observations use the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) onboard the Herschel Space Observatory. The newly observed spectral lines include [CI] 370 µm, [CI] 609 µm, [NII] 205 µm, and CO transitions from J = 4−3 to J = 13−12. Combined with previously observed J = 1−0 to J = 3−2 transitions, the CO spectral line energy distributions are translated to spatially resolved physical parameters, column density of CO, N(CO), and molecular gas thermal pressure, P th , with a non-local thermal equilibrium (non-LTE) radiative transfer model, RADEX. Our results show that there is a relationship between the spatially resolved intensities of [NII] 205 µm and the surface density of the star formation rate (SFR), Σ SFR. This relation, when compared to integrated properties of ultra-luminous infrared galaxies (ULIRGs), exhibits a different slope, because the [NII] 205 µm distribution is more extended than the SFR. The spatially resolved [CI] 370 µm, on the other hand, shows a generally linear relationship with Σ SFR and can potentially be a good SFR tracer. Compared with the dust properties derived from broad-band images, we find a positive trend between the emissivity of CO in the J = 1−0 transition with the average intensity of interstellar radiation field (ISRF), U. This trend implies a decrease in the CO-to-H 2 conversion factor, X CO , when U increases. We estimate the gas-to-dust mass ratios to be 77 ± 33 within the central 2 kpc and 93 ± 19 within the central 4 kpc of M 83, which implies a Galactic dust-to-metal mass ratio within the observed region of M 83. The estimated gas-depletion time for the M 83 nucleus is 1.13 ± 0.6 Gyr, which is shorter than the values for nearby spiral galaxies found in the literature (∼2.35 Gyr), most likely due to the young nuclear starbursts. A linear relationship between P th and the radiation pressure generated by U , P rad , is found to be P th ≈ 30 P rad , which signals that the ISRF alone is insufficient to sustain the observed CO transitions. The spatial distribution of P th reveals a pressure gradient, which coincides with the observed propagation of starburst activities and the alignment of (possibly background) radio sources. We discover that the off-centered (from the optical nucleus) peak of the molecular gas volume density coincides well with a minimum in the relative aromatic feature strength, indicating a possible destruction of their carriers. We conclude that the observed CO transitions are most likely associated with mechanical heating processes that are directly or indirectly related to very recent nuclear starbursts.
Proceedings of the International Astronomical Union, 2011
The low metallicity interstellar medium of dwarf galaxies gives a different picture in the far in... more The low metallicity interstellar medium of dwarf galaxies gives a different picture in the far infrared(FIR)/submillimetre(submm)wavelengths than the more metal-rich galaxies. Excess emission is often found in the submm beginning at or beyond 500 μm. Even without taking this excess emission into account as a possible dust component, higher dust-to-gas mass ratios (DGR) are often observed compared to that expected from their metallicity for moderately metal-poor galaxies. The Spectral Energy Distributions (SEDs) of the lowest metallicity galaxies, however, give very low dust masses and excessively low values of DGR, inconsistent with the amount of metals expected to be captured into dust if we presume the usual linear relationship holding for all metallicities, including the more metal-rich galaxies. This transition seems to appear near metalllicities of 12 + log(O/H) 8.0 - 8.2. These results rely on accurately quantifying the total molecular gas reservoir, which is uncertain in low ...
Proceedings of the International Astronomical Union, 2012
The wide variety of low metallicity galaxies of the local universe serve as convenient laboratori... more The wide variety of low metallicity galaxies of the local universe serve as convenient laboratories to study the evolution of gas and dust and conditions for star formation in environments which may resemble those of the early universe. The Herschel Dwarf Galaxy Survey is studying the far infrared (FIR) and submillimeter (submm) properties of the gas and dust in galaxies with metallicity values as low as 1/45 that of solar. With complementary Spitzer, Laboca/APEX, Scuba/JCMT data, the dust spectral energy distributions are well constrained now, providing more accurate dust masses. We find a steep drop in dust-to-gas mass ratio (D/G) when the metallicity is below 12+log(O/H) ∼ 8. A submillimeter excess can be found in some low metallicity galaxies, which, when present, becomes apparent at wavelengths at or longer than 500 μm. While CO is difficult to observe in low metallicity gas, the FIR fine structure lines, on the other hand, are very luminous and highlight a potentially importan...
Clefs CEA, 2009
Comme toutes les galaxies spirales, notre Voie lactee est active: de nouvelles etoiles y naissent... more Comme toutes les galaxies spirales, notre Voie lactee est active: de nouvelles etoiles y naissent encore aujourd'hui. Meme si elles ne representent pas, et de loin, la totalite de la matiere d'une galaxie, les etoiles en constituent le principal « moteur ».
Proceedings of the International Astronomical Union, 2008
This paper presents the results of a study aimed at understanding the evolution of the dust prope... more This paper presents the results of a study aimed at understanding the evolution of the dust properties, as a function of both the environmental conditions and the metal enrichment of the system. I first review the peculiar dust properties of dwarf galaxies, and discuss attempts to understand their origin. Then, I discuss the evolution of the PAH and dust abundances, constrained by the UV-to-radio SED of nearby galaxies, comparing the properties of low-metallicity environments and more evolved systems. I discuss the long term evolution of dust in galaxies, comparing the grain production by various stellar progenitors to their destruction by SN blast waves and in Hiiregions. Finally, I will show how these models explain the paucity of PAHs in low-metallicity environments.
Proceedings of the International Astronomical Union, 2011
In a recent study based on the modelling of spatially resolved Spitzer and Herschel observations ... more In a recent study based on the modelling of spatially resolved Spitzer and Herschel observations of the Large Magellanic Cloud (LMC), we have shown that the infrared (IR) to submillimetre (submm) grain opacities are systematically higher in the LMC than in our Galaxy. This discovery demonstrates an evolution of the dust properties with environment. Here, we discuss the consequences of this evolution on the modelling of SEDs of galaxies, emphasizing that the uncertainties on the grain properties can lead to erroneous interpretations of the structure of the interstellar medium (ISM) of galaxies, if no additional independent constraints are used.