ORCID Profile
0000-0003-1645-0543
Current Organisation
Universität Hamburg
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Publisher: EDP Sciences
Date: 08-2022
DOI: 10.1051/0004-6361/202142935
Abstract: Aims. We present the capabilities of G alapagos -2 and G alfitm in the context of fitting two-component profiles – bulge–disk decompositions – to galaxies, with the ultimate goal of providing complete multi-band, multi-component fitting of large s les of galaxies in future surveys. We also release both the code and the fit results to 234 239 objects from the DR3 of the GAMA survey, a s le significantly deeper than in previous works. Methods. We use stringent tests on both simulated and real data, as well as comparison to public catalogues to evaluate the advantages of using multi-band over single-band data. Results. We show that multi-band fitting using G alfitm provides significant advantages when trying to decompose galaxies into their in idual constituents, as more data are being used, by effectively being able to use the colour information buried in the in idual exposures to its advantage. Using simulated data, we find that multi-band fitting significantly reduces deviations from the real parameter values, allows component sizes and Sérsic indices to be recovered more accurately, and – by design – constrains the band-to-band variations of these parameters to more physical values. On both simulated and real data, we confirm that the spectral energy distributions (SEDs) of the two main components can be recovered to fainter magnitudes compared to using single-band fitting, which tends to recover ‘disks’ and ‘bulges’ with – on average – identical SEDs when the galaxies become too faint, instead of the different SEDs they truly have. By comparing our results to those provided by other fitting codes, we confirm that they agree in general, but measurement errors can be significantly reduced by using the multi-band tools developed by the MEGAMORPH project. Conclusions. We conclude that the multi-band fitting employed by G alapagos -2 and G alfitm significantly improves the accuracy of structural galaxy parameters and enables much larger s les to be be used in a scientific analysis.
Publisher: Oxford University Press (OUP)
Date: 18-08-2022
Abstract: We derive single Sérsic fits and bulge-disc decompositions for 13 096 galaxies at redshifts z & 0.08 in the GAMA II equatorial survey regions in the Kilo-Degree Survey (KiDS) g, r, and i bands. The surface brightness fitting is performed using the Bayesian two-dimensional profile fitting code ProFit. We fit three models to each galaxy in each band independently with a fully automated Markov chain Monte Carlo analysis: a single Sérsic model, a Sérsic plus exponential and a point source plus exponential. After fitting the galaxies, we perform model selection and flag galaxies for which none of our models are appropriate (mainly mergers/Irregular galaxies). The fit quality is assessed by visual inspections, comparison to previous works, comparison of independent fits of galaxies in the overlap regions between KiDS tiles and bespoke simulations. The latter two are also used for a detailed investigation of systematic error sources. We find that our fit results are robust across various galaxy types and image qualities with minimal biases. Errors given by the MCMC underestimate the true errors typically by factors 2–3. Automated model selection criteria are accurate to $\\gt 90{{\\ \\rm per\\ cent}}$ as calibrated by visual inspection of a subs le of galaxies. We also present g−r component colours and the corresponding colour–magnitude diagram, consistent with previous works despite our increased fit flexibility. Such reliable structural parameters for the components of a erse s le of galaxies across multiple bands will be integral to various studies of galaxy properties and evolution. All results are integrated into the GAMA database.
Publisher: Oxford University Press (OUP)
Date: 25-11-2022
Abstract: The star-formation rate in galaxies is well known to correlate with stellar mass (the ‘star-forming main sequence’). Here, we extend this further to explore any additional dependence on galaxy surface brightness, a proxy for stellar mass surface density. We use a large s le of low-redshift (z ≤ 0.08) galaxies from the Galaxy And Mass Assembly survey which have both spectral energy distribution (SED) derived star-formation rates and photometric bulge-disc decompositions, the latter providing measures of disc surface brightness and disc masses. Using two s les, one of galaxies fitted by a single component with Sérsic index below 2 and one of the discs from two-component fits, we find that once the overall mass dependence of star-formation rate is accounted for, there is no evidence in either s le for a further dependence on stellar surface density.
Publisher: Oxford University Press (OUP)
Date: 02-2021
Abstract: We have entered a new era where integral-field spectroscopic surveys of galaxies are sufficiently large to adequately s le large-scale structure over a cosmologically significant volume. This was the primary design goal of the SAMI Galaxy Survey. Here, in Data Release 3, we release data for the full s le of 3068 unique galaxies observed. This includes the SAMI cluster s le of 888 unique galaxies for the first time. For each galaxy, there are two primary spectral cubes covering the blue (370–570 nm) and red (630–740 nm) optical wavelength ranges at spectral resolving power of R = 1808 and 4304, respectively. For each primary cube, we also provide three spatially binned spectral cubes and a set of standardized aperture spectra. For each galaxy, we include complete 2D maps from parametrized fitting to the emission-line and absorption-line spectral data. These maps provide information on the gas ionization and kinematics, stellar kinematics and populations, and more. All data are available online through Australian Astronomical Optics Data Central.
Publisher: Oxford University Press (OUP)
Date: 23-02-2018
DOI: 10.1093/MNRAS/STY440
Publisher: Oxford University Press (OUP)
Date: 12-09-2023
Publisher: Oxford University Press (OUP)
Date: 26-02-2022
Abstract: We investigate the mean locally measured velocity dispersions of ionized gas (σgas) and stars (σ*) for 1090 galaxies with stellar masses $\\log \\, (M_{\\!\\ast }/M_{\\odot }) \\ge 9.5$ from the SAMI Galaxy Survey. For star-forming galaxies, σ* tends to be larger than σgas, suggesting that stars are in general dynamically hotter than the ionized gas (asymmetric drift). The difference between σgas and σ* (Δσ) correlates with various galaxy properties. We establish that the strongest correlation of Δσ is with beam smearing, which inflates σgas more than σ*, introducing a dependence of Δσ on both the effective radius relative to the point spread function and velocity gradients. The second strongest correlation is with the contribution of active galactic nuclei (AGN) (or evolved stars) to the ionized gas emission, implying that the gas velocity dispersion is strongly affected by the power source. In contrast, using the velocity dispersion measured from integrated spectra (σap) results in less correlation between the aperture-based Δσ (Δσap) and the power source. This suggests that the AGN (or old stars) dynamically heat the gas without causing significant deviations from dynamical equilibrium. Although the variation of Δσap is much smaller than that of Δσ, a correlation between Δσap and gas velocity gradient is still detected, implying that there is a small bias in dynamical masses derived from stellar and ionized gas velocity dispersions.
Publisher: Oxford University Press (OUP)
Date: 14-05-2020
Abstract: We investigate the stellar kinematics of the bulge and disk components in 826 galaxies with a wide range of morphology from the Sydney-AAO Multi-object Integral-field spectroscopy Galaxy Survey. The spatially resolved rotation velocity (V) and velocity dispersion (σ) of bulge and disk components have been simultaneously estimated using the penalized pixel fitting (ppxf) method with photometrically defined weights for the two components. We introduce a new subroutine of ppxf for dealing with degeneracy in the solutions. We show that the V and σ distributions in each galaxy can be reconstructed using the kinematics and weights of the bulge and disk components. The combination of two distinct components provides a consistent description of the major kinematic features of galaxies over a wide range of morphological types. We present Tully–Fisher and Faber–Jackson relations showing that the galaxy stellar mass scales with both V and σ for both components of all galaxy types. We find a tight Faber–Jackson relation even for the disk component. We show that the bulge and disk components are kinematically distinct: (1) the two components show scaling relations with similar slopes, but different intercepts (2) the spin parameter λR indicates bulges are pressure-dominated systems and disks are supported by rotation and (3) the bulge and disk components have, respectively, low and high values in intrinsic ellipticity. Our findings suggest that the relative contributions of the two components explain, at least to first order, the complex kinematic behaviour of galaxies.
Publisher: Oxford University Press (OUP)
Date: 02-03-2022
Abstract: In Galaxy And Mass Assembly Data Release 4 (GAMA DR4), we make available our full spectroscopic redshift s le. This includes 248 682 galaxy spectra, and, in combination with earlier surveys, results in 330 542 redshifts across five sky regions covering ∼250 deg2. The redshift density, is the highest available over such a sustained area, has exceptionally high completeness (95 per cent to rKiDS = 19.65 mag), and is well-suited for the study of galaxy mergers, galaxy groups, and the low redshift (z & 0.25) galaxy population. DR4 includes 32 value-added tables or Data Management Units (DMUs) that provide a number of measured and derived data products including GALEX, ESO KiDS, ESO VIKING, WISE, and HerschelSpace Observatory imaging. Within this release, we provide visual morphologies for 15 330 galaxies to z & 0.08, photometric redshift estimates for all 18 million objects to rKiDS ∼ 25 mag, and stellar velocity dispersions for 111 830 galaxies. We conclude by deriving the total galaxy stellar mass function (GSMF) and its sub- ision by morphological class (elliptical, compact-bulge and disc, diffuse-bulge and disc, and disc only). This extends our previous measurement of the total GSMF down to 106.75 M$_{\\odot } \\, h_{70}^{-2}$ and we find a total stellar mass density of ρ* = (2.97 ± 0.04) × 108 M$_{\\odot } \\, h_{70}$ Mpc−3 or $\\Omega _*=(2.17 \\pm 0.03) \\times 10^{-3} \\, h_{70}^{-1}$. We conclude that at z & 0.1, the Universe has converted 4.9 ± 0.1 per cent of the baryonic mass implied by big bang Nucleosynthesis into stars that are gravitationally bound within the galaxy population.
Publisher: Oxford University Press (OUP)
Date: 26-08-2022
Abstract: We study the alignments of galaxy spin axes with respect to cosmic web filaments as a function of various properties of the galaxies and their constituent bulges and discs. We exploit the SAMI Galaxy Survey to identify 3D spin axes from spatially resolved stellar kinematics and to decompose the galaxy into the kinematic bulge and disc components. The GAMA survey is used to reconstruct the cosmic filaments. The mass of the bulge, defined as the product of stellar mass and bulge-to-total flux ratio Mbulge = M⋆ × (B/T), is the primary parameter of correlation with spin–filament alignments: galaxies with lower bulge masses tend to have their spins parallel to the closest filament, while galaxies with higher bulge masses are more perpendicularly aligned. M⋆ and B/T separately show correlations, but they do not fully unravel spin–filament alignments. Other galaxy properties, such as visual morphology, stellar age, star formation activity, kinematic parameters, and local environment, are secondary tracers. Focussing on S0 galaxies, we find preferentially perpendicular alignments, with the signal dominated by high-mass S0 galaxies. Studying bulge and disc spin–filament alignments separately reveals additional information about the formation pathways of the corresponding galaxies: bulges tend to have more perpendicular alignments, while discs show different tendencies according to their kinematic features and the mass of the associated bulge. The observed correlation between the flipping of spin–filament alignments and the growth of the bulge can be explained by mergers, which drive both alignment flips and bulge formation.
Publisher: American Astronomical Society
Date: 20-07-2020
No related grants have been discovered for Sarah Casura.