David Glass
Gather.town id
CSF04
Poster Title
The Evolutionary History of Dusty Early-Type Galaxies From ALMA-Observed Cool ISM Content and Distribution
Institution
Jeremiah Horrocks Institute, University of Central Lancashire
Abstract (short summary)
The spatial distribution and kinematics of cool interstellar medium (dust and molecular gas) within early-type galaxies (ETGs) can be used to highlight mechanisms causing galaxy evolution. For example, asymmetries and spatial or kinematic misalignments of cool ISM compared to stellar discs can be used to indicate recent merger activity. High-resolution mm-wavelength observations can reveal the spatial distribution of cool ISM, and allow ISM kinematics to be explored.
ALMA observations were obtained in 2016 of continuum and 12CO(2-1) line emission for a sample of five ETGs in the GAMA equatorial fields with redshifts ~0.04, drawn from a clean and complete sample of visually-classified ETGs. The sample was chosen to have relatively high dust content (10^7.5 – 10^8 Mʘ) determined using Herschel-ATLAS data. The observations revealed massive (~few x 10^9 Mʘ) extended molecular gas reservoirs in three ETGs.
This poster presents the findings from the modelling of molecular gas kinematics for the three ETGs with massive gas reservoirs, using the KINematic Molecular Simulation (KinMS) package. Axisymmetric single-component models are fitted to ALMA data to highlight additional structural components and any asymmetry. The models also allow examination of potential star formation in the cool molecular gas. Kinematic alignments of molecular gas, stars and ionised gas are also compared, using data from the SAMI galaxy survey. Scenarios for the evolutionary history of these ETGs are discussed using the findings. Future work based on results from these observations is also discussed, along with the possibilities for further observations.
ALMA observations were obtained in 2016 of continuum and 12CO(2-1) line emission for a sample of five ETGs in the GAMA equatorial fields with redshifts ~0.04, drawn from a clean and complete sample of visually-classified ETGs. The sample was chosen to have relatively high dust content (10^7.5 – 10^8 Mʘ) determined using Herschel-ATLAS data. The observations revealed massive (~few x 10^9 Mʘ) extended molecular gas reservoirs in three ETGs.
This poster presents the findings from the modelling of molecular gas kinematics for the three ETGs with massive gas reservoirs, using the KINematic Molecular Simulation (KinMS) package. Axisymmetric single-component models are fitted to ALMA data to highlight additional structural components and any asymmetry. The models also allow examination of potential star formation in the cool molecular gas. Kinematic alignments of molecular gas, stars and ionised gas are also compared, using data from the SAMI galaxy survey. Scenarios for the evolutionary history of these ETGs are discussed using the findings. Future work based on results from these observations is also discussed, along with the possibilities for further observations.
Plain text (extended) Summary
Cool interstellar medium content and distribution in early-type galaxies can indicate mechanisms involved in their evolution. For example, kinematic alignment between cool molecular gas and stars suggests recent accretion or merger activity (Davis et al. 2011). To test this for dusty early-type galaxies in the nearby Universe, five ETGs in the GAMA equatorial field (Driver et al. 2009) were observed by ALMA in 2016 (Sansom et al. 2019). Three ETGs (GAMA64646, 272990 and 622429) were found to have massive molecular gas reservoirs. This work is to fit kinematic models to the ALMA data for the three ETGs, to reveal any additional structures in the molecular gas that indicate mechanisms for these ETGs. Models were constructed using the KINematic Molecular Simulation (KinMS) package (Davis et al. 2013).
ALMA data for GAMA64646 and GAMA272990 were fitted with a single axisymmetric disc with a Sérsic surface brightness profile. The residual zeroth order moment map (data minus model) for GAMA64646 shows a bright central feature, an inner ring and an outer ring. These features are also apparent in a plot of azimuthally-averaged surface brightness versus radius. The position-velocity diagram and spectra show that the molecular gas is largely symmetric. For GAMA272990, a bright central feature and inner ring are apparent in the residual map, with asymmetric molecular gas distribution. The spectrum also shows asymmetry, with more molecular gas at positive velocity than negative.
GAMA622429 was modelled with an axisymmetric gas disc and a smaller edge-on disc representing a bar-like feature. The residual zeroth order moment map shows a bright central feature, residual asymmetric spiral features not visible in optical images, and a patch of molecular gas on one side.
Maps of the Toomre stability criterion (Q, Toomre 1964) were created from deprojected zeroth order moment maps and fitted model parameters. Locations of likely star formation are in general agreement with IFU observations from the SAMI Galaxy Survey DR3 (Croom et al. 2021) for GAMA64646 and 272990. For GAMA622429, the SAMI data shows star formation in the asymmetric patch of molecular gas, but not along the opposite spiral arm as could be expected from the Q map.
Kinematic position angles are also available from SAMI for stars and ionised gas. These align well for the kinematic position angles for molecular gas for the three ETGs, suggesting that no major disturbance to these galaxies happened within the last 100 Myr (Tohline et al. 1982). Evidence from optical images does indicate some past disturbances to the galaxies.
In conclusion, GAMA64646 and GAMA272990 appear to have undergone a disturbance which caused molecular gas to reconfigure. GAMA622429 appears to have acquired additional molecular gas. We now have 31 dusty ETGs observed for molecular gas with the IRAM 30m telescope (Glass et al. in prep.), and we can draw from these to design a more detailed survey of the evolution of dusty ETGs with ALMA.
ALMA data for GAMA64646 and GAMA272990 were fitted with a single axisymmetric disc with a Sérsic surface brightness profile. The residual zeroth order moment map (data minus model) for GAMA64646 shows a bright central feature, an inner ring and an outer ring. These features are also apparent in a plot of azimuthally-averaged surface brightness versus radius. The position-velocity diagram and spectra show that the molecular gas is largely symmetric. For GAMA272990, a bright central feature and inner ring are apparent in the residual map, with asymmetric molecular gas distribution. The spectrum also shows asymmetry, with more molecular gas at positive velocity than negative.
GAMA622429 was modelled with an axisymmetric gas disc and a smaller edge-on disc representing a bar-like feature. The residual zeroth order moment map shows a bright central feature, residual asymmetric spiral features not visible in optical images, and a patch of molecular gas on one side.
Maps of the Toomre stability criterion (Q, Toomre 1964) were created from deprojected zeroth order moment maps and fitted model parameters. Locations of likely star formation are in general agreement with IFU observations from the SAMI Galaxy Survey DR3 (Croom et al. 2021) for GAMA64646 and 272990. For GAMA622429, the SAMI data shows star formation in the asymmetric patch of molecular gas, but not along the opposite spiral arm as could be expected from the Q map.
Kinematic position angles are also available from SAMI for stars and ionised gas. These align well for the kinematic position angles for molecular gas for the three ETGs, suggesting that no major disturbance to these galaxies happened within the last 100 Myr (Tohline et al. 1982). Evidence from optical images does indicate some past disturbances to the galaxies.
In conclusion, GAMA64646 and GAMA272990 appear to have undergone a disturbance which caused molecular gas to reconfigure. GAMA622429 appears to have acquired additional molecular gas. We now have 31 dusty ETGs observed for molecular gas with the IRAM 30m telescope (Glass et al. in prep.), and we can draw from these to design a more detailed survey of the evolution of dusty ETGs with ALMA.
URL
dhwglass@uclan.ac.uk
Poster file