7 research outputs found
MĂ©canismes Ă©teignant la formation des Ă©toiles au sein de galaxies proches
Astronomical data become more and more precise and help the refining of our understanding of the processes that drive galaxy evolution, but we still do not have a global paradigm to explain some physical mechanisms. Especially, the triggering and regulation of star formation quenching are not understood in detail given the numerous processes that it can be resulting from and the different timescales that are involved.The aim of this thesis project is to study the gas content, star formation activity and quenching within galaxies using integral field spectroscopic data from the SDSS-IV MaNGA survey, as well as single-dish observations of molecular and atomic gas.Firsly, I describe the sample of nearby galaxies that I decided to focus on. It consists of 29 nearby galaxies that show complex kinematic features in their optical spectra. It is drawn from the cross-identification between the MaNGA data release DR15 and a catalogue comprising massive, isolated, bulge-dominated galaxies exhibiting a central excess of star formation.In the second part, I present an analysis of this sample in terms of galaxy structural parameters and star formation activity. I conclude that these objects enable us to sample different phases of galaxy evolution, that result from minor-merger events.In the third part, I detail the results that I obtained by applying an innovative fitting procedure to the data from one peculiar MaNGA galaxy. This approach helps reveal a minor-merger event by disentangling the optical spectral features, both in gas and stellar components.In the fourth part, I focus on the analysis of the cold gas content through molecular and atomic gas observations. I infer the molecular and atomic gas masses as well as a Kennicutt-Schmidt relation so as to estimate the star formation efficiency of the studied galaxies.Les donnĂ©es astronomiques deviennent de plus en plus prĂ©cises et permettent dâaffiner notre comprĂ©hension des processus qui rĂ©gissent lâĂ©volution des galaxies, mais nous ne disposons toujours pas dâun paradigme global pour expliquer certains mĂ©canismes physiques. En particulier, le dĂ©clenchement et la rĂ©gulation de lâextinction de la formation stellaire ne sont pas compris en dĂ©tail Ă©tant donnĂ© les nombreux processus dont elle peut rĂ©sulter et les diffĂ©rentes Ă©chelles de temps qui sont impliquĂ©es.Le but de ce projet de thĂšse est dâĂ©tudier le contenu en gaz, lâactivitĂ© de formation dâĂ©toiles et lâextinction des Ă©toiles dans les galaxies en utilisant les donnĂ©es spectroscopiques du relevĂ© SDSS-IV MaNGA, ainsi que des observations de gaz molĂ©culaire et atomique.Tout dâabord, je dĂ©cris lâĂ©chantillon de galaxies proches sur lequel jâai dĂ©cidĂ© de me concentrer. Il sâagit de 29 galaxies proches qui prĂ©sentent des caractĂ©ristiques cinĂ©matiques complexes dans leurs spectres dans le domaine visible. Dans la deuxiĂšme partie, je prĂ©sente une analyse de cet Ă©chantillon en termes de paramĂštres structurels des galaxies et dâactivitĂ© de formation dâĂ©toiles. Je conclus que ces objets nous permettent dâĂ©chantillonner diffĂ©rentes phases de lâĂ©volution des galaxies, qui rĂ©sultent dâĂ©vĂ©nements de fusions mineures. Dans la troisiĂšme partie, je dĂ©taille les rĂ©sultats que jâai obtenus en appliquant une procĂ©dure dâajustement de spectres innovante aux donnĂ©es dâune galaxie MaNGA particuliĂšre. Cette approche permet de mettre en Ă©vidence une fusion mineure en dĂ©composant les caractĂ©ristiques spectrales optiques, Ă la fois dans les raies dâĂ©mission du gaz et dans le continuum stellaire. Dans la quatriĂšme partie, je me concentre sur lâanalyse du contenu en gaz froid Ă travers des observations de gaz molĂ©culaire et atomique. Je dĂ©duis les masses de gaz molĂ©culaire ainsi quâune relation de Kennicutt-Schmidt afin dâestimer lâefficacitĂ© de la formation dâĂ©toiles des galaxies Ă©tudiĂ©es
Mechanisms of star formation quenching in local galaxies
Les donnĂ©es astronomiques deviennent de plus en plus prĂ©cises et permettent dâaffiner notre comprĂ©hension des processus qui rĂ©gissent lâĂ©volution des galaxies, mais nous ne disposons toujours pas dâun paradigme global pour expliquer certains mĂ©canismes physiques. En particulier, le dĂ©clenchement et la rĂ©gulation de lâextinction de la formation stellaire ne sont pas compris en dĂ©tail Ă©tant donnĂ© les nombreux processus dont elle peut rĂ©sulter et les diffĂ©rentes Ă©chelles de temps qui sont impliquĂ©es.Le but de ce projet de thĂšse est dâĂ©tudier le contenu en gaz, lâactivitĂ© de formation dâĂ©toiles et lâextinction des Ă©toiles dans les galaxies en utilisant les donnĂ©es spectroscopiques du relevĂ© SDSS-IV MaNGA, ainsi que des observations de gaz molĂ©culaire et atomique.Tout dâabord, je dĂ©cris lâĂ©chantillon de galaxies proches sur lequel jâai dĂ©cidĂ© de me concentrer. Il sâagit de 29 galaxies proches qui prĂ©sentent des caractĂ©ristiques cinĂ©matiques complexes dans leurs spectres dans le domaine visible. Dans la deuxiĂšme partie, je prĂ©sente une analyse de cet Ă©chantillon en termes de paramĂštres structurels des galaxies et dâactivitĂ© de formation dâĂ©toiles. Je conclus que ces objets nous permettent dâĂ©chantillonner diffĂ©rentes phases de lâĂ©volution des galaxies, qui rĂ©sultent dâĂ©vĂ©nements de fusions mineures. Dans la troisiĂšme partie, je dĂ©taille les rĂ©sultats que jâai obtenus en appliquant une procĂ©dure dâajustement de spectres innovante aux donnĂ©es dâune galaxie MaNGA particuliĂšre. Cette approche permet de mettre en Ă©vidence une fusion mineure en dĂ©composant les caractĂ©ristiques spectrales optiques, Ă la fois dans les raies dâĂ©mission du gaz et dans le continuum stellaire. Dans la quatriĂšme partie, je me concentre sur lâanalyse du contenu en gaz froid Ă travers des observations de gaz molĂ©culaire et atomique. Je dĂ©duis les masses de gaz molĂ©culaire ainsi quâune relation de Kennicutt-Schmidt afin dâestimer lâefficacitĂ© de la formation dâĂ©toiles des galaxies Ă©tudiĂ©es.Astronomical data become more and more precise and help the refining of our understanding of the processes that drive galaxy evolution, but we still do not have a global paradigm to explain some physical mechanisms. Especially, the triggering and regulation of star formation quenching are not understood in detail given the numerous processes that it can be resulting from and the different timescales that are involved.The aim of this thesis project is to study the gas content, star formation activity and quenching within galaxies using integral field spectroscopic data from the SDSS-IV MaNGA survey, as well as single-dish observations of molecular and atomic gas.Firsly, I describe the sample of nearby galaxies that I decided to focus on. It consists of 29 nearby galaxies that show complex kinematic features in their optical spectra. It is drawn from the cross-identification between the MaNGA data release DR15 and a catalogue comprising massive, isolated, bulge-dominated galaxies exhibiting a central excess of star formation.In the second part, I present an analysis of this sample in terms of galaxy structural parameters and star formation activity. I conclude that these objects enable us to sample different phases of galaxy evolution, that result from minor-merger events.In the third part, I detail the results that I obtained by applying an innovative fitting procedure to the data from one peculiar MaNGA galaxy. This approach helps reveal a minor-merger event by disentangling the optical spectral features, both in gas and stellar components.In the fourth part, I focus on the analysis of the cold gas content through molecular and atomic gas observations. I infer the molecular and atomic gas masses as well as a Kennicutt-Schmidt relation so as to estimate the star formation efficiency of the studied galaxies
MĂ©canismes Ă©teignant la formation des Ă©toiles au sein de galaxies proches
Astronomical data become more and more precise and help the refining of our understanding of the processes that drive galaxy evolution, but we still do not have a global paradigm to explain some physical mechanisms. Especially, the triggering and regulation of star formation quenching are not understood in detail given the numerous processes that it can be resulting from and the different timescales that are involved.The aim of this thesis project is to study the gas content, star formation activity and quenching within galaxies using integral field spectroscopic data from the SDSS-IV MaNGA survey, as well as single-dish observations of molecular and atomic gas.Firsly, I describe the sample of nearby galaxies that I decided to focus on. It consists of 29 nearby galaxies that show complex kinematic features in their optical spectra. It is drawn from the cross-identification between the MaNGA data release DR15 and a catalogue comprising massive, isolated, bulge-dominated galaxies exhibiting a central excess of star formation.In the second part, I present an analysis of this sample in terms of galaxy structural parameters and star formation activity. I conclude that these objects enable us to sample different phases of galaxy evolution, that result from minor-merger events.In the third part, I detail the results that I obtained by applying an innovative fitting procedure to the data from one peculiar MaNGA galaxy. This approach helps reveal a minor-merger event by disentangling the optical spectral features, both in gas and stellar components.In the fourth part, I focus on the analysis of the cold gas content through molecular and atomic gas observations. I infer the molecular and atomic gas masses as well as a Kennicutt-Schmidt relation so as to estimate the star formation efficiency of the studied galaxies.Les donnĂ©es astronomiques deviennent de plus en plus prĂ©cises et permettent dâaffiner notre comprĂ©hension des processus qui rĂ©gissent lâĂ©volution des galaxies, mais nous ne disposons toujours pas dâun paradigme global pour expliquer certains mĂ©canismes physiques. En particulier, le dĂ©clenchement et la rĂ©gulation de lâextinction de la formation stellaire ne sont pas compris en dĂ©tail Ă©tant donnĂ© les nombreux processus dont elle peut rĂ©sulter et les diffĂ©rentes Ă©chelles de temps qui sont impliquĂ©es.Le but de ce projet de thĂšse est dâĂ©tudier le contenu en gaz, lâactivitĂ© de formation dâĂ©toiles et lâextinction des Ă©toiles dans les galaxies en utilisant les donnĂ©es spectroscopiques du relevĂ© SDSS-IV MaNGA, ainsi que des observations de gaz molĂ©culaire et atomique.Tout dâabord, je dĂ©cris lâĂ©chantillon de galaxies proches sur lequel jâai dĂ©cidĂ© de me concentrer. Il sâagit de 29 galaxies proches qui prĂ©sentent des caractĂ©ristiques cinĂ©matiques complexes dans leurs spectres dans le domaine visible. Dans la deuxiĂšme partie, je prĂ©sente une analyse de cet Ă©chantillon en termes de paramĂštres structurels des galaxies et dâactivitĂ© de formation dâĂ©toiles. Je conclus que ces objets nous permettent dâĂ©chantillonner diffĂ©rentes phases de lâĂ©volution des galaxies, qui rĂ©sultent dâĂ©vĂ©nements de fusions mineures. Dans la troisiĂšme partie, je dĂ©taille les rĂ©sultats que jâai obtenus en appliquant une procĂ©dure dâajustement de spectres innovante aux donnĂ©es dâune galaxie MaNGA particuliĂšre. Cette approche permet de mettre en Ă©vidence une fusion mineure en dĂ©composant les caractĂ©ristiques spectrales optiques, Ă la fois dans les raies dâĂ©mission du gaz et dans le continuum stellaire. Dans la quatriĂšme partie, je me concentre sur lâanalyse du contenu en gaz froid Ă travers des observations de gaz molĂ©culaire et atomique. Je dĂ©duis les masses de gaz molĂ©culaire ainsi quâune relation de Kennicutt-Schmidt afin dâestimer lâefficacitĂ© de la formation dâĂ©toiles des galaxies Ă©tudiĂ©es
MĂ©canismes Ă©teignant la formation des Ă©toiles au sein de galaxies proches
Astronomical data become more and more precise and help the refining of our understanding of the processes that drive galaxy evolution, but we still do not have a global paradigm to explain some physical mechanisms. Especially, the triggering and regulation of star formation quenching are not understood in detail given the numerous processes that it can be resulting from and the different timescales that are involved.The aim of this thesis project is to study the gas content, star formation activity and quenching within galaxies using integral field spectroscopic data from the SDSS-IV MaNGA survey, as well as single-dish observations of molecular and atomic gas.Firsly, I describe the sample of nearby galaxies that I decided to focus on. It consists of 29 nearby galaxies that show complex kinematic features in their optical spectra. It is drawn from the cross-identification between the MaNGA data release DR15 and a catalogue comprising massive, isolated, bulge-dominated galaxies exhibiting a central excess of star formation.In the second part, I present an analysis of this sample in terms of galaxy structural parameters and star formation activity. I conclude that these objects enable us to sample different phases of galaxy evolution, that result from minor-merger events.In the third part, I detail the results that I obtained by applying an innovative fitting procedure to the data from one peculiar MaNGA galaxy. This approach helps reveal a minor-merger event by disentangling the optical spectral features, both in gas and stellar components.In the fourth part, I focus on the analysis of the cold gas content through molecular and atomic gas observations. I infer the molecular and atomic gas masses as well as a Kennicutt-Schmidt relation so as to estimate the star formation efficiency of the studied galaxies.Les donnĂ©es astronomiques deviennent de plus en plus prĂ©cises et permettent dâaffiner notre comprĂ©hension des processus qui rĂ©gissent lâĂ©volution des galaxies, mais nous ne disposons toujours pas dâun paradigme global pour expliquer certains mĂ©canismes physiques. En particulier, le dĂ©clenchement et la rĂ©gulation de lâextinction de la formation stellaire ne sont pas compris en dĂ©tail Ă©tant donnĂ© les nombreux processus dont elle peut rĂ©sulter et les diffĂ©rentes Ă©chelles de temps qui sont impliquĂ©es.Le but de ce projet de thĂšse est dâĂ©tudier le contenu en gaz, lâactivitĂ© de formation dâĂ©toiles et lâextinction des Ă©toiles dans les galaxies en utilisant les donnĂ©es spectroscopiques du relevĂ© SDSS-IV MaNGA, ainsi que des observations de gaz molĂ©culaire et atomique.Tout dâabord, je dĂ©cris lâĂ©chantillon de galaxies proches sur lequel jâai dĂ©cidĂ© de me concentrer. Il sâagit de 29 galaxies proches qui prĂ©sentent des caractĂ©ristiques cinĂ©matiques complexes dans leurs spectres dans le domaine visible. Dans la deuxiĂšme partie, je prĂ©sente une analyse de cet Ă©chantillon en termes de paramĂštres structurels des galaxies et dâactivitĂ© de formation dâĂ©toiles. Je conclus que ces objets nous permettent dâĂ©chantillonner diffĂ©rentes phases de lâĂ©volution des galaxies, qui rĂ©sultent dâĂ©vĂ©nements de fusions mineures. Dans la troisiĂšme partie, je dĂ©taille les rĂ©sultats que jâai obtenus en appliquant une procĂ©dure dâajustement de spectres innovante aux donnĂ©es dâune galaxie MaNGA particuliĂšre. Cette approche permet de mettre en Ă©vidence une fusion mineure en dĂ©composant les caractĂ©ristiques spectrales optiques, Ă la fois dans les raies dâĂ©mission du gaz et dans le continuum stellaire. Dans la quatriĂšme partie, je me concentre sur lâanalyse du contenu en gaz froid Ă travers des observations de gaz molĂ©culaire et atomique. Je dĂ©duis les masses de gaz molĂ©culaire ainsi quâune relation de Kennicutt-Schmidt afin dâestimer lâefficacitĂ© de la formation dâĂ©toiles des galaxies Ă©tudiĂ©es
Central star formation in double-peak, gas-rich radio galaxies
International audienceThe respective contributions of gas accretion, galaxy interactions, and mergers to the mass assembly of galaxies, as well as the evolution of their molecular gas and star-formation activity are still not fully understood. In a recent work, a large sample of double-peak (DP) emission-line galaxies have been identified from the SDSS. While the two peaks could represent two kinematic components, they may be linked to the large bulges that their host galaxies tend to have. Star-forming DP galaxies display a central star-formation enhancement and have been discussed as compatible with a sequence of recent minor mergers. In order to probe merger-induced star-formation mechanisms, we conducted observations of the molecular-gas content of 35 star-forming DP galaxies in the upper part of the main sequence (MS) of star formation (SF) with the IRAM 30 m telescope. Including similar galaxies 0.3 dex above the MS and with existing molecular-gas observations from the literature, we finally obtained a sample of 52 such galaxies. We succeeded in fitting the same kinematic parameters to the optical ionised- and molecular-gas emission lines for ten (19%) galaxies. We find a central star-formation enhancement resulting most likely from a galaxy merger or galaxy interaction, which is indicated by an excess of gas extinction found in the centre. This SF is traced by radio continuum emissions at 150 MHz, 1.4 GHz, and 3 GHz, all three of which are linearly correlated in log with the CO luminosity with the same slope. The 52 DP galaxies are found to have a significantly larger amount of molecular gas and longer depletion times, and hence a lower star-formation efficiency, than the expected values at their distance of the MS. The large bulges in these galaxies might be stabilising the gas, hence reducing the SF efficiency. This is consistent with a scenario of minor mergers increasing the mass of bulges and driving gas to the centre. We also excluded the inwards-directed gas migration and central star-formation enhancement as the origin of a bar morphology. Hence, these 52 DP galaxies could be the result of recent minor mergers that funnelled molecular gas towards their centre, triggering SF, but with moderate efficiency
Central star formation in double-peak gas rich radio galaxies
In a recent work, a large sample of double-peak (DP) emission line galaxies
have been identified from the SDSS. While the two peaks could represent two
kinematic components, they may be linked to the large bulges which their host
galaxies tend to have. Star-forming DP galaxies display a central star
formation enhancement and have been discussed to be compatible with a sequence
of recent minor mergers. In order to probe merger induced star formation
mechanisms, we conducted observations of the molecular gas content of 35
star-forming DP galaxies in the upper part of the main sequence (MS) of star
formation with the IRAM 30m telescope. Including similar galaxies 0.3 dex above
MS and with existing molecular gas observations from the literature, we finally
obtain a sample of 52 such galaxies. We succeed in fitting the same kinematic
parameters to the optical ionised and molecular gas emission lines for 10 (19%)
galaxies. We find a central star formation enhancement resulting most likely
from a galaxy merger or galaxy interaction, which is indicated by an excess of
gas extinction found in the centre. This star formation is traced by radio
continuum emissions at 150MHz, 1.4 and 3GHz, which are all three linearly
correlated in log with the CO luminosity with the same slope. The 52 DP
galaxies are found to have a significantly larger amount of molecular gas and
larger depletion times, hence a lower star formation efficiency, than the
expected values at their distance of the MS. This is consistent with a scenario
of minor mergers increasing the mass of bulges and driving gas to the centre.
We also exclude the inwards directed gas migration and central star formation
enhancement to be the origin of a bar morphology. Hence, these 52 DP galaxies
could be the results of recent minor mergers that funnelled molecular gas
towards their centre, triggering star formation, but with a moderate
efficiency.Comment: 33 pages, 19 figures, accepted by A&
Two interacting galaxies hiding as one, revealed by MaNGA
International audienceGiven their prominent role in galaxy evolution, it is of paramount importance to unveil galaxy interactions and merger events and to investigate the underlying mechanisms. The use of high-resolution data makes it easier to identify merging systems, but it can still be challenging when the morphology does not show any clear galaxy pair or gas bridge. Characterising the origin of puzzling kinematic features can help reveal complicated systems. Here, we present a merging galaxy, MaNGA 1-114955, in which we highlighted the superimposition of two distinct rotating discs along the line of sight. These counter-rotating objects both lie on the star-forming main sequence but display perturbed stellar velocity dispersions. The main galaxy presents off-centred star formation as well as off-centred high-metallicity regions, supporting the scenario of recent starbursts, while the secondary galaxy hosts a central starburst that coincides with an extended radio emission, in excess with respect to star formation expectations. Stellar mass as well as dynamical mass estimates agree towards a mass ratio within the visible radius of 9:1 for these interacting galaxies. We suggest that we are observing a pre-coalescence stage of a merger. The primary galaxy accreted gas through a past first pericentre passage about 1 Gyr ago and more recently from the secondary gas-rich galaxy, which exhibits an underlying active galactic nucleus. Our results demonstrate how a galaxy can hide another one and the relevance of a multi-component approach for studying ambiguous systems. We anticipate that our method will be efficient at unveiling the mechanisms taking place in a sub-sample of galaxies observed by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, all of which exhibit kinematic features of a puzzling origin in their gas emission lines