Herve Wozniak | Université de Montpellier (original) (raw)

Papers by Herve Wozniak

Astronomy and Astrophysics, 2008

Context. Intermediate mass galaxies (>10 10 M ⊙ ) at z∼0.6 are the likeliest progenitors of the p... more Context. Intermediate mass galaxies (>10 10 M ⊙ ) at z∼0.6 are the likeliest progenitors of the present-day, numerous population of spirals. There is growing evidence that they have evolved rapidly since the last 6 to 8 Gyr ago, and likely have formed a significant fraction of their stellar mass, often showing perturbed morphologies and kinematics. Aims. We have gathered a representative sample of 88 such galaxies and have provided robust estimates of their gas phase metallicity. Methods. For doing so, we have used moderate spectral resolution spectroscopy at VLT/FORS2 with unprecedented high S/N allowing to remove biases coming from interstellar absorption lines and extinction to establish robust values of R 23 = ([OII]λ3727 + [OIII]λλ4959, 5007)/Hβ. Results. We definitively confirm that the predominant population of z∼ 0.6 starbursts and luminous IR galaxies (LIRGs) are on average, two times less metal rich than the local galaxies at a given stellar mass. We do find that the metal abundance of the gaseous phase of galaxies is evolving linearly with time, from z=1 to z=0 and after comparing with other studies, from z=3 to z=0. Combining our results with the reported evolution of the Tully Fisher relation, we do find that such an evolution requires that ∼30% of the stellar mass of local galaxies have been formed through an external supply of gas, thus excluding the close box model. Distant starbursts & LIRGs have properties (metal abundance, star formation efficiency & morphologies) similar to those of local LIRGs. Their underlying physics is likely dominated by gas infall probably through merging or interactions. Conclusions. Our study further supports the rapid evolution of z∼0.4 -1 galaxies. Gas exchanges between galaxies is likely the main cause of this evolution.

Eas Publications Series, 2011

We have recently identified a new radial migration mechanism resulting from the overlap of spiral... more We have recently identified a new radial migration mechanism resulting from the overlap of spiral and bar resonances in galactic disks. Here we confirm the efficiency of this mechanism in fully self-consistent, Tree-SPH simulations, as well as high-resolution pure N-body simulations. In all barred cases we clearly identify the effect of spiral-bar resonance overlap by measuring a bimodality in the changes of angular momentum in the disk, dL, whose maxima are near the bar's corotation and outer Lindblad resonance. This contrasts with the smooth distribution of dL for a simulation with no stable bar present, where strong radial migration is induced by multiple spirals. The presence of a disk gaseous component appears to increase the rate of angular momentum exchange by about 20%. The efficiency of this mechanism is such that galactic stellar disks can extend to over 10 scale-lengths within 1-3 Gyr in both Milky Way size and low-mass galaxies (circular velocity ~100 km/s). We also show that metallicity gradients can flatten in less than 1 Gyr rendering mixing in barred galaxies an order of magnitude more efficient than previously thought.

Eso Astrophysics Symposia, 2007

We present some preliminary results obtained with a new galactic chemodynamical tool under develo... more We present some preliminary results obtained with a new galactic chemodynamical tool under development. In the framework of non-instantaneous recycling approach, we follow the interactions due to star formation and feedback processes. One of the main original features of our code is that we record the abundance evolution of several chemical elements. This allows us to build cooling functions dependent on the real abundances of individual elements. We illustrate the need for such metal-dependent cooling functions using a toy model made of a star cluster embedded in a two-phase gas cloud. Our results suggest that computing cooling rates according to individual abundances of chemical elements can influence the star formation rate.

Astronomy and Astrophysics Supplement Series, Apr 29, 1991

Detailed CCD surface photometry was obtained of 10 early-type barred galaxies which are a part of... more Detailed CCD surface photometry was obtained of 10 early-type barred galaxies which are a part of the sample used by Athanassoula et al. (1990), in order to investigate morphological properties of SBO galaxies. The data analysis procedures used are discussed and the results of observations, obtained in three colors (B Jonson, I and R Kron-Cousins bandpasses), are presented. These include the semimajor axis length, the surface brightness and its mean error, the ellipticity, and position-angle profiles for each galaxy.

Dynamics of Galaxies from the Early Universe to the Present, 2000

I show that the counter-rotating core of the barred galaxy NGC 5728 could be explained by the int... more I show that the counter-rotating core of the barred galaxy NGC 5728 could be explained by the internal dynamics of the bar. This supports the idea that the nuclear bar is counter-rotating.

We compare the dense molecular gas content in two barred spiral galaxies, NGC 6764 (classified LI... more We compare the dense molecular gas content in two barred spiral galaxies, NGC 6764 (classified LINER) and NGC 5430 (a Wolf-Rayet galaxy). We find a significant difference in the proportion of dense molecular gas between the two galaxies. CS(3-2) is detected in NGC 6764 but not in NGC 5430, even though the intensities of CO(2-1) and HCN(1-0) are higher in the latter galaxy. The non detection in NGC 5430 indicates that the CS abundance in that galaxy is unusually low, or that HCN is subthermally excited. To complement these observations, we discuss the ionization source in the nucleus of the LINER galaxy NGC 6764.

We report a preliminary study of the evolution of the central region of barred galaxies using a s... more We report a preliminary study of the evolution of the central region of barred galaxies using a self-consistent N-body code including stars, gas and star formation. The results of our simulations are calibrated with spectrophotometric evolution models of Bruzual & Charlot (GISSEL2000). This technique allows to study simultaneously the dynamical, kinematical and photometric evolution of both the stellar and gaseous components, in particular the regions of star formation.

Impact of Modern Dynamics in Astronomy, 1999

The properties of chaos in 2D self-consistent models of barred galaxies are investigated using Ko... more The properties of chaos in 2D self-consistent models of barred galaxies are investigated using Kolmogorov-Sinai entropy hKS. These models are constructed with Schwarzschild's method which c o m bines orbits as elementary building blocks.

This note describes the main technical achievements of the IVOA for the last year as well as the ... more This note describes the main technical achievements of the IVOA for the last year as well as the updated roadmaps for each Working Groups and Interest Groups for the upcoming year, detailing plans and associated milestones. Furthermore, it identifies specific issues that may require more focus coordination between some working groups and interest groups.

This note describes the main technical achievements of the IVOA for the last year as well as the ... more This note describes the main technical achievements of the IVOA for the last year as well as the updated roadmaps for each Working Group and Interest Group for the upcoming year, detailing plans and associated milestones. Furthermore, it identifies specific issues that may require more focus coordination between some working groups and interest groups.

Proceedings of the International Astronomical Union, 2006

The Astrophysical Journal, 2005

The relevance of the Tremaine-Weinberg (TW) method is tested to measure the bar, spiral and inner... more The relevance of the Tremaine-Weinberg (TW) method is tested to measure the bar, spiral and inner structure pattern speeds using a gaseous velocity field. The TW method is applied to

Astronomy & Astrophysics

Context. Double-barred galaxies account for almost one third of all barred galaxies, suggesting t... more Context. Double-barred galaxies account for almost one third of all barred galaxies, suggesting that secondary stellar bars, which are embedded in large-scale primary bars, are long-lived structures. However, up to now it has been hard to self-consistently simulate a disc galaxy that sustains two nested stellar bars for longer than a few rotation periods.
Aims: The dynamical and physical requirements for long-lived triaxiality in the central region of galaxies still need to be clarified.
Methods: N-body/hydrodynamical simulations including star formation recipes have been performed. Their properties (bar lengths, pattern speeds, age of stellar population, and gas content) have been compared with the most recent observational data in order to prove that they are representative of double-barred galaxies, even SB0. Overlaps in dynamical resonances and bar modes have been looked for using Fourier spectrograms.
Results: Double-barred galaxies have been successfully simulated with lifetimes as long as 7 Gyr. The stellar and gaseous distributions in the central regions are time dependent and display many observed morphological features (circumnuclear rings, pseudo-bulges, triaxial bulges, ovals, etc.) typical of barred galaxies, even early-type. The stellar population of the secondary bar is younger on average than for the primary large-scale bar. An important feature of these simulations is the absence of any resonance overlap for several Gyr. In particular, there is no overlap between the primary bar inner Lindblad resonance and the secondary bar corotation. Therefore, mode coupling cannot sustain the secondary bar mode. Star formation is identified here as possibly being responsible for bringing energy to the nuclear mode. Star formation is also responsible for limiting the amount of gas in the central region which prevents the orbits sustaining the secondary bar from being destroyed. Therefore, the secondary bar can dissolve but reappear after ≈1 Gyr as the associated wave is persistent as long as central star formation is active. When star formation is switched off the dynamical perturbation associated with the secondary bar needs several Gyr to fully vanish, although the central morphological signature is almost undetectable after 2 Gyr.
Conclusions: Double-bars can be long-lived in numerical simulations with a gaseous component, even in the absence of overlap of resonances or mode coupling, provided that star formation remains active, even moderately, in the central region where the nuclear bar lies.

Astronomy & Astrophysics, 2010

We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC6822 observe... more We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC6822 observed from 70 to 500 mu and clearly resolve the HII regions with PACS and SPIRE. We find that the ratio 250/500 is dependent on the 24 mu surface brightness in NGC6822, which would locally link the heating processes of the coldest phases of dust in the ISM to the star formation activity. We model the SEDs of some regions HII regions and less active regions across the galaxy and find that the SEDs of HII regions show warmer ranges of dust temperatures. We derive very high dust masses when graphite is used in our model to describe carbon dust. Using amorphous carbon, instead, requires less dust mass to account for submm emission due to its lower emissivity properties. This indicates that SED models including Herschel constraints may require different dust properties than commonly used.

Astronomy & Astrophysics, 2010

We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC6822 observe... more We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC6822 observed from 70 to 500 mu and clearly resolve the HII regions with PACS and SPIRE. We find that the ratio 250/500 is dependent on the 24 mu surface brightness in NGC6822, which would locally link the heating processes of the coldest phases of dust in the ISM to the star formation activity. We model the SEDs of some regions HII regions and less active regions across the galaxy and find that the SEDs of HII regions show warmer ranges of dust temperatures. We derive very high dust masses when graphite is used in our model to describe carbon dust. Using amorphous carbon, instead, requires less dust mass to account for submm emission due to its lower emissivity properties. This indicates that SED models including Herschel constraints may require different dust properties than commonly used.

Astronomy & Astrophysics, 2010

The standard method of mapping the interstellar medium in a galaxy, by observing the molecular ga... more The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies.

Astronomy & Astrophysics, 2010

The standard method of mapping the interstellar medium in a galaxy, by observing the molecular ga... more The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies.

Astronomy and Astrophysics, 2008

Context. Intermediate mass galaxies (>10 10 M ⊙ ) at z∼0.6 are the likeliest progenitors of the p... more Context. Intermediate mass galaxies (>10 10 M ⊙ ) at z∼0.6 are the likeliest progenitors of the present-day, numerous population of spirals. There is growing evidence that they have evolved rapidly since the last 6 to 8 Gyr ago, and likely have formed a significant fraction of their stellar mass, often showing perturbed morphologies and kinematics. Aims. We have gathered a representative sample of 88 such galaxies and have provided robust estimates of their gas phase metallicity. Methods. For doing so, we have used moderate spectral resolution spectroscopy at VLT/FORS2 with unprecedented high S/N allowing to remove biases coming from interstellar absorption lines and extinction to establish robust values of R 23 = ([OII]λ3727 + [OIII]λλ4959, 5007)/Hβ. Results. We definitively confirm that the predominant population of z∼ 0.6 starbursts and luminous IR galaxies (LIRGs) are on average, two times less metal rich than the local galaxies at a given stellar mass. We do find that the metal abundance of the gaseous phase of galaxies is evolving linearly with time, from z=1 to z=0 and after comparing with other studies, from z=3 to z=0. Combining our results with the reported evolution of the Tully Fisher relation, we do find that such an evolution requires that ∼30% of the stellar mass of local galaxies have been formed through an external supply of gas, thus excluding the close box model. Distant starbursts & LIRGs have properties (metal abundance, star formation efficiency & morphologies) similar to those of local LIRGs. Their underlying physics is likely dominated by gas infall probably through merging or interactions. Conclusions. Our study further supports the rapid evolution of z∼0.4 -1 galaxies. Gas exchanges between galaxies is likely the main cause of this evolution.

Eas Publications Series, 2011

We have recently identified a new radial migration mechanism resulting from the overlap of spiral... more We have recently identified a new radial migration mechanism resulting from the overlap of spiral and bar resonances in galactic disks. Here we confirm the efficiency of this mechanism in fully self-consistent, Tree-SPH simulations, as well as high-resolution pure N-body simulations. In all barred cases we clearly identify the effect of spiral-bar resonance overlap by measuring a bimodality in the changes of angular momentum in the disk, dL, whose maxima are near the bar's corotation and outer Lindblad resonance. This contrasts with the smooth distribution of dL for a simulation with no stable bar present, where strong radial migration is induced by multiple spirals. The presence of a disk gaseous component appears to increase the rate of angular momentum exchange by about 20%. The efficiency of this mechanism is such that galactic stellar disks can extend to over 10 scale-lengths within 1-3 Gyr in both Milky Way size and low-mass galaxies (circular velocity ~100 km/s). We also show that metallicity gradients can flatten in less than 1 Gyr rendering mixing in barred galaxies an order of magnitude more efficient than previously thought.

Eso Astrophysics Symposia, 2007

We present some preliminary results obtained with a new galactic chemodynamical tool under develo... more We present some preliminary results obtained with a new galactic chemodynamical tool under development. In the framework of non-instantaneous recycling approach, we follow the interactions due to star formation and feedback processes. One of the main original features of our code is that we record the abundance evolution of several chemical elements. This allows us to build cooling functions dependent on the real abundances of individual elements. We illustrate the need for such metal-dependent cooling functions using a toy model made of a star cluster embedded in a two-phase gas cloud. Our results suggest that computing cooling rates according to individual abundances of chemical elements can influence the star formation rate.

Astronomy and Astrophysics Supplement Series, Apr 29, 1991

Detailed CCD surface photometry was obtained of 10 early-type barred galaxies which are a part of... more Detailed CCD surface photometry was obtained of 10 early-type barred galaxies which are a part of the sample used by Athanassoula et al. (1990), in order to investigate morphological properties of SBO galaxies. The data analysis procedures used are discussed and the results of observations, obtained in three colors (B Jonson, I and R Kron-Cousins bandpasses), are presented. These include the semimajor axis length, the surface brightness and its mean error, the ellipticity, and position-angle profiles for each galaxy.

Dynamics of Galaxies from the Early Universe to the Present, 2000

I show that the counter-rotating core of the barred galaxy NGC 5728 could be explained by the int... more I show that the counter-rotating core of the barred galaxy NGC 5728 could be explained by the internal dynamics of the bar. This supports the idea that the nuclear bar is counter-rotating.

We compare the dense molecular gas content in two barred spiral galaxies, NGC 6764 (classified LI... more We compare the dense molecular gas content in two barred spiral galaxies, NGC 6764 (classified LINER) and NGC 5430 (a Wolf-Rayet galaxy). We find a significant difference in the proportion of dense molecular gas between the two galaxies. CS(3-2) is detected in NGC 6764 but not in NGC 5430, even though the intensities of CO(2-1) and HCN(1-0) are higher in the latter galaxy. The non detection in NGC 5430 indicates that the CS abundance in that galaxy is unusually low, or that HCN is subthermally excited. To complement these observations, we discuss the ionization source in the nucleus of the LINER galaxy NGC 6764.

We report a preliminary study of the evolution of the central region of barred galaxies using a s... more We report a preliminary study of the evolution of the central region of barred galaxies using a self-consistent N-body code including stars, gas and star formation. The results of our simulations are calibrated with spectrophotometric evolution models of Bruzual & Charlot (GISSEL2000). This technique allows to study simultaneously the dynamical, kinematical and photometric evolution of both the stellar and gaseous components, in particular the regions of star formation.

Impact of Modern Dynamics in Astronomy, 1999

The properties of chaos in 2D self-consistent models of barred galaxies are investigated using Ko... more The properties of chaos in 2D self-consistent models of barred galaxies are investigated using Kolmogorov-Sinai entropy hKS. These models are constructed with Schwarzschild's method which c o m bines orbits as elementary building blocks.

This note describes the main technical achievements of the IVOA for the last year as well as the ... more This note describes the main technical achievements of the IVOA for the last year as well as the updated roadmaps for each Working Groups and Interest Groups for the upcoming year, detailing plans and associated milestones. Furthermore, it identifies specific issues that may require more focus coordination between some working groups and interest groups.

This note describes the main technical achievements of the IVOA for the last year as well as the ... more This note describes the main technical achievements of the IVOA for the last year as well as the updated roadmaps for each Working Group and Interest Group for the upcoming year, detailing plans and associated milestones. Furthermore, it identifies specific issues that may require more focus coordination between some working groups and interest groups.

Proceedings of the International Astronomical Union, 2006

The Astrophysical Journal, 2005

The relevance of the Tremaine-Weinberg (TW) method is tested to measure the bar, spiral and inner... more The relevance of the Tremaine-Weinberg (TW) method is tested to measure the bar, spiral and inner structure pattern speeds using a gaseous velocity field. The TW method is applied to

Astronomy & Astrophysics

Context. Double-barred galaxies account for almost one third of all barred galaxies, suggesting t... more Context. Double-barred galaxies account for almost one third of all barred galaxies, suggesting that secondary stellar bars, which are embedded in large-scale primary bars, are long-lived structures. However, up to now it has been hard to self-consistently simulate a disc galaxy that sustains two nested stellar bars for longer than a few rotation periods.
Aims: The dynamical and physical requirements for long-lived triaxiality in the central region of galaxies still need to be clarified.
Methods: N-body/hydrodynamical simulations including star formation recipes have been performed. Their properties (bar lengths, pattern speeds, age of stellar population, and gas content) have been compared with the most recent observational data in order to prove that they are representative of double-barred galaxies, even SB0. Overlaps in dynamical resonances and bar modes have been looked for using Fourier spectrograms.
Results: Double-barred galaxies have been successfully simulated with lifetimes as long as 7 Gyr. The stellar and gaseous distributions in the central regions are time dependent and display many observed morphological features (circumnuclear rings, pseudo-bulges, triaxial bulges, ovals, etc.) typical of barred galaxies, even early-type. The stellar population of the secondary bar is younger on average than for the primary large-scale bar. An important feature of these simulations is the absence of any resonance overlap for several Gyr. In particular, there is no overlap between the primary bar inner Lindblad resonance and the secondary bar corotation. Therefore, mode coupling cannot sustain the secondary bar mode. Star formation is identified here as possibly being responsible for bringing energy to the nuclear mode. Star formation is also responsible for limiting the amount of gas in the central region which prevents the orbits sustaining the secondary bar from being destroyed. Therefore, the secondary bar can dissolve but reappear after ≈1 Gyr as the associated wave is persistent as long as central star formation is active. When star formation is switched off the dynamical perturbation associated with the secondary bar needs several Gyr to fully vanish, although the central morphological signature is almost undetectable after 2 Gyr.
Conclusions: Double-bars can be long-lived in numerical simulations with a gaseous component, even in the absence of overlap of resonances or mode coupling, provided that star formation remains active, even moderately, in the central region where the nuclear bar lies.

Astronomy & Astrophysics, 2010

We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC6822 observe... more We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC6822 observed from 70 to 500 mu and clearly resolve the HII regions with PACS and SPIRE. We find that the ratio 250/500 is dependent on the 24 mu surface brightness in NGC6822, which would locally link the heating processes of the coldest phases of dust in the ISM to the star formation activity. We model the SEDs of some regions HII regions and less active regions across the galaxy and find that the SEDs of HII regions show warmer ranges of dust temperatures. We derive very high dust masses when graphite is used in our model to describe carbon dust. Using amorphous carbon, instead, requires less dust mass to account for submm emission due to its lower emissivity properties. This indicates that SED models including Herschel constraints may require different dust properties than commonly used.

Astronomy & Astrophysics, 2010

We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC6822 observe... more We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC6822 observed from 70 to 500 mu and clearly resolve the HII regions with PACS and SPIRE. We find that the ratio 250/500 is dependent on the 24 mu surface brightness in NGC6822, which would locally link the heating processes of the coldest phases of dust in the ISM to the star formation activity. We model the SEDs of some regions HII regions and less active regions across the galaxy and find that the SEDs of HII regions show warmer ranges of dust temperatures. We derive very high dust masses when graphite is used in our model to describe carbon dust. Using amorphous carbon, instead, requires less dust mass to account for submm emission due to its lower emissivity properties. This indicates that SED models including Herschel constraints may require different dust properties than commonly used.

Astronomy & Astrophysics, 2010

The standard method of mapping the interstellar medium in a galaxy, by observing the molecular ga... more The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies.

Astronomy & Astrophysics, 2010

The standard method of mapping the interstellar medium in a galaxy, by observing the molecular ga... more The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies.