arXiv subjects

Jon S. Lawrence

Publications and source records attributed to Jon S. Lawrence.

At least 19 recordsLinked to original sources

arXiv2026

Exploration of small footprint stick-slip piezoelectric actuators for use in the FLEX fibre positioner system for the Wide-field Spectroscopic Telescope (WST)

This work presents a novel stick-slip piezoelectric actuator for the FLEX fibre positioner, addressing the challenge of reducing footprint while maintaining precision in next-generation multi-object spectroscopic instruments such as the Wide-field Spectroscopic Telescope (WST). The actuator combines compact geometry (3.2 mm diameter, sub 70 mm length) with high-resolution incremental motion, low power consumption, and high reliability. Three actuators can be integrated into a sub 7 mm diameter circle, enabling a simplified, single-plane assembly. This design offers a promising solution for miniaturized, accurate fibre positioning in wide-field spectroscopic applications.

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arXiv2026

The SAMI Galaxy Survey: Quenching of Star Formation in Clusters III. Ram-Pressure-Affected Galaxy Populations

Cluster environments influence galaxy evolution by curtailing star formation activity, notably through ram-pressure stripping (RPS). In this study, using spatially resolved spectroscopic data from the SAMI Galaxy Survey, we identify galaxies undergoing or recently affected by RPS in eight nearby clusters ($0.029 < z < 0.058$), through a visual classification scheme based on the ionised gas ($\rm Hα+ [NII]λ6584$) morphologies, split into unperturbed, asymmetric, and truncated. The projected phase-space analysis shows that asymmetric galaxies are found in a narrow region in cluster-centric distance ($\rm 0.1 < R/R_{200} < 0.6$) and have a larger dispersion in line-of-sight velocity ($σ(|v_{pec}|)_\mathrm{Asym} = 0.71^{+0.09}_{-0.07}\ σ_{200}$) compared to the truncated and unperturbed samples. In terms of star formation activity, RPS candidates yield a much steeper resolved star-forming main sequence (rSFMS; $Σ_\mathrm{SFR} - Σ_\ast$) relation compared to the unperturbed counterparts, primarily emerging from having lower $Σ_\mathrm{SFR}$ values for the low mass density regime, with the steepest gradient deriving from the truncated sample. Moreover, radial star formation profiles reveal that star formation in RPS candidates is suppressed in the outskirts relative to unperturbed galaxies and is more prominent for the truncated sample. In contrast, central ($\rm r/r_{eff}<0.5$) star formation activity in RPS candidates is comparable with that in their unperturbed and field counterparts, suggesting no elevated activity. Taken together, this suggests an evolutionary trend linked to the RPS stage, where unperturbed galaxies likely represent recently accreted systems (pre-RPS), while asymmetric and truncated galaxies may correspond to populations undergoing RPS and post-RPS phases, respectively, favouring outside-in quenching.

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arXiv2024

The SAMI Galaxy Survey: On the importance of applying multiple selection criteria for finding Milky Way Analogues

Milky Way Analogues (MWAs) provide an alternative insight into the various pathways that lead to the formation of disk galaxies with similar properties to the Milky Way. In this study, we explore different selection techniques for identifying MWAs in the SAMI Galaxy Survey. We utilise a nearest neighbours method to define MWAs using four selection parameters including stellar mass ($M_{\star}$), star formation rate ($SFR$), bulge-to-total ratio ($B/T$) and disk effective radius ($R_{\rm{e}}$). Based on 15 different selection combinations, we find that including $M_{\star}$ and SFR is essential for minimising biases in the average MWA properties as compared to the Milky Way. Furthermore, given the Milky Way's smaller-than-average size, selection combinations without $R_{\rm{e}}$ result in MWAs being too large. Lastly, we find that $B/T$ is the least important parameter out of the four tested parameters. Using all four selection criteria, we define the top 10 most Milky Way-like galaxies in the GAMA and Cluster regions of the SAMI survey. These most Milky-Way-like galaxies are typically barred spirals, with kinematically cold rotating disks and reside in a wide range of environments. Surprisingly, we find no significant differences between the MWAs selected from the GAMA and Cluster regions. Our work highlights the importance of using multiple selection criteria for finding MWAs and also demonstrates potential biases in previous MWA studies.

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arXiv2023

The SAMI Galaxy Survey: Environmental analysis of the orbital structures of passive galaxies

Most dynamical models of galaxies to date assume axisymmetry, which is not representative of a significant fraction of massive galaxies. We have built triaxial orbit-superposition Schwarzschild models of galaxies observed by the SAMI Galaxy Survey, in order to reconstruct their inner orbital structure and mass distribution. The sample consists of 153 passive galaxies with total stellar masses in the range $10^{9.5}$ to $10^{12} M_{\odot}$. We present an analysis of the internal structures and intrinsic properties of these galaxies as a function of their environment. We measure their environment using three proxies: central or satellite designation, halo mass and local $5^{th}$ nearest neighbour galaxy density. We find that although these intrinsic properties correlate most strongly with stellar mass, environment does play a secondary role: at fixed stellar mass, galaxies in the densest regions are more radially anisotropic. In addition, central galaxies, and galaxies in high local densities show lower values of edge-on spin parameter proxy \lam. We also find suggestions of a possible trend of the fractions of orbits with environment for lower-mass galaxies (between $10^{9.5}$ and $10^{11} M_{\odot}$) such that, at fixed stellar mass, galaxies in higher local densities and halo mass have higher fractions of hot orbits and lower fractions of warm orbits. Our results demonstrate that after stellar mass, environment does play a role in shaping present-day passive galaxies.

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arXiv2022

The SAMI Galaxy Survey: flipping of the spin-filament alignment correlates most strongly with growth of the bulge

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 M_bulge=M_star x (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_star 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. Focusing 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.

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arXiv2022

The SAMI Galaxy Survey: The relationship between galaxy rotation and the motion of neighbours

Using data from the SAMI Galaxy Survey, we investigate the correlation between the projected stellar kinematic spin vector of 1397 SAMI galaxies and the line-of-sight motion of their neighbouring galaxies. We calculate the luminosity-weighted mean velocity difference between SAMI galaxies and their neighbours in the direction perpendicular to the SAMI galaxies angular momentum axes. The luminosity-weighted mean velocity offsets between SAMI and neighbours, which indicates the signal of coherence between the rotation of the SAMI galaxies and the motion of neighbours, is 9.0 $\pm$ 5.4 km s$^{-1}$ (1.7 $σ$) for neighbours within 1 Mpc. In a large-scale analysis, we find that the average velocity offsets increase for neighbours out to 2 Mpc. However, the velocities are consistent with zero or negative for neighbours outside 3 Mpc. The negative signals for neighbours at distance around 10 Mpc are also significant at $\sim 2$ $σ$ level, which indicate that the positive signals within 2 Mpc might come from the variance of large-scale structure. We also calculate average velocities of different subsamples, including galaxies in different regions of the sky, galaxies with different stellar masses, galaxy type, $λ_{Re}$ and inclination. Although low-mass, high-mass, early-type and low-spin galaxies subsamples show 2 - 3 $σ$ signal of coherence for the neighbours within 2 Mpc, the results for different inclination subsamples and large-scale results suggest that the $\sim 2 σ$ signals might result from coincidental scatter or variance of large-scale structure. Overall, the modest evidence of coherence signals for neighbouring galaxies within 2 Mpc needs to be confirmed by larger samples of observations and simulation studies.

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arXiv2022

The SAMI Galaxy Survey: The Link Between [$α$/Fe] and Kinematic Morphology

We explore a sample of 1492 galaxies with measurements of the mean stellar population properties and the spin parameter proxy, $λ_{R_{\rm{e}}}$, drawn from the SAMI Galaxy Survey. We fit a global $\left[α/\rm{Fe}\right]$-$σ$ relation, finding that $\left[α/\rm{Fe}\right]=(0.395\pm0.010)\rm{log}_{10}\left(σ\right)-(0.627\pm0.002)$. We observe an anti-correlation between the residuals $Δ\left[α/\rm{Fe}\right]$ and the inclination-corrected $λ_{\,R_{\rm{e}}}^{\rm{\,eo}}$, which can be expressed as $Δ\left[α/\rm{Fe}\right]=(-0.057\pm0.008)λ_{\,R_{\rm{e}}}^{\rm{\,eo}}+(0.020\pm0.003)$. The anti-correlation appears to be driven by star-forming galaxies, with a gradient of $Δ\left[α/\rm{Fe}\right]\sim(-0.121\pm0.015)λ_{\,R_{\rm{e}}}^{\rm{\,eo}}$, although a weak relationship persists for the subsample of galaxies for which star formation has been quenched. We take this to be confirmation that disk-dominated galaxies have an extended duration of star formation. At a reference velocity dispersion of 200 km s$^{-1}$, we estimate an increase in half-mass formation time from $\sim$0.5 Gyr to $\sim$1.2 Gyr from low- to high-$λ_{\,R_{\rm{e}}}^{\rm{\,eo}}$ galaxies. Slow rotators do not appear to fit these trends. Their residual $α$-enhancement is indistinguishable from other galaxies with $λ_{\,R_{\rm{e}}}^{\rm{\,eo}}\lessapprox0.4$, despite being both larger and more massive. This result shows that galaxies with $λ_{\,R_{\rm{e}}}^{\rm{\,eo}}\lessapprox0.4$ experience a similar range of star formation histories, despite their different physical structure and angular momentum.

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arXiv2022

The LEGA-C and SAMI Galaxy Surveys: Quiescent Stellar Populations and the Mass-Size Plane across 6 Gyr

We investigate the change in mean stellar population age and metallicity ([Z/H]) scaling relations for quiescent galaxies from intermediate redshift ($0.60\leq z\leq0.76$) using the LEGA-C Survey, to low redshift ($0.014\leq z\leq0.10$) using the SAMI Galaxy Survey. We find that, similarly to their low-redshift counterparts, the stellar metallicity of quiescent galaxies at $0.60\leq z\leq 0.76$ closely correlates with $M_*/R_\mathrm{e}$ (a proxy for the gravitational potential or escape velocity), in that galaxies with deeper potential wells are more metal-rich. This supports the hypothesis that the relation arises due to the gravitational potential regulating the retention of metals, by determining the escape velocity required by metal-rich stellar and supernova ejecta to escape the system and avoid being recycled into later stellar generations. On the other hand, we find no correlation between stellar age and $M_*/R_\mathrm{e}^2$ (stellar mass surface density $Σ$) in the LEGA-C sample, despite this being a strong relation at low redshift. We consider this change in the age--$Σ$ relation in the context of the redshift evolution of the star-forming and quiescent populations in the mass--size plane, and find our results can be explained as a consequence of galaxies forming more compactly at higher redshifts, and remaining compact throughout their evolution. Furthermore, galaxies appear to quench at a characteristic surface density that decreases with decreasing redshift. The $z\sim 0$ age--$Σ$ relation is therefore a result of building up the quiescent and star-forming populations with galaxies that formed at a range of redshifts and so a range of surface densities.

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arXiv2022

The SAMI Galaxy Survey: The internal orbital structure and mass distribution of passive galaxies from triaxial orbit-superposition Schwarzschild models

Dynamical models are crucial for uncovering the internal dynamics of galaxies, however, most of the results to date assume axisymmetry, which is not representative for a significant fraction of massive galaxies. Here, we build triaxial Schwarschild orbit-superposition models of galaxies taken from the SAMI Galaxy Survey, in order to reconstruct their inner orbital structure and mass distribution. The sample consists of 161 passive galaxies with total stellar masses in the range $10^{9.5}$ to $10^{12} M_{\odot}$. We find that the changes in internal structures within 1$R_{\rm e}$ are correlated with the total stellar mass of the individual galaxies. The majority of the galaxies in the sample ($73\% \pm 3\%$) are oblate, while $19\% \pm 3\%$ are mildly triaxial and $8\% \pm 2\%$ have triaxial/prolate shape. Galaxies with $\log M_{\star}/M_{\odot} > 10.50$ are more likely to be non-oblate. We find a mean dark matter fraction of $f_{\rm{DM}} = 0.28 \pm 0.20$, within 1$R_{\rm e}$. Galaxies with higher intrinsic ellipticity (flatter) are found to have more negative velocity anisotropy $β_r$ (tangential anisotropy). $β_r$ also shows an anti-correlation with the edge-on spin parameter \lam, so that $β_r$ decreases with increasing \lam. We see evidence of an increasing fraction of hot orbits with increasing stellar mass, while warm and cold orbits show a decreasing trend. We also find that galaxies with different ($V/σ$ - $h_3$) kinematic signatures have distinct combinations of orbits. These results are in agreement with a formation scenario in which slow- and fast-rotating galaxies form through two main channels.

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arXiv2022

The SAMI Galaxy Survey: the difference between ionised gas and stellar velocity dispersions

We investigate the mean locally-measured velocity dispersions of ionised gas ($σ_{\rm gas}$) and stars ($σ_*$) for 1090 galaxies with stellar masses $\log\,(M_*/M_{\odot}) \geq 9.5$ from the SAMI Galaxy Survey. For star-forming galaxies, $σ_*$ tends to be larger than $σ_{\rm gas}$, suggesting that stars are in general dynamically hotter than the ionised gas (asymmetric drift). The difference between $σ_{\rm gas}$ and $σ_*$ ($Δσ$) correlates with various galaxy properties. We establish that the strongest correlation of $Δσ$ is with beam smearing, which inflates $σ_{\rm gas}$ 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 ionised gas emission, implying the gas velocity dispersion is strongly affected by the power source. In contrast, using the velocity dispersion measured from integrated spectra ($σ_{\rm aper}$) results in less correlation between the aperture-based $Δσ$ ($Δσ_{\rm aper}$) 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 $Δσ_{\rm aper}$ is much smaller than that of $Δσ$, a correlation between $Δσ_{\rm aper}$ and gas velocity gradient is still detected, implying there is a small bias in dynamical masses derived from stellar and ionised gas velocity dispersions.

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arXiv2021

The SAMI Galaxy Survey: Trends in [α/Fe] as a Function of Morphology and Environment

We present a new set of index-based measurements of [$α$/Fe] for a sample of 2093 galaxies in the SAMI Galaxy Survey. Following earlier work, we fit a global relation between [$α$/Fe] and the galaxy velocity dispersion $σ$ for red sequence galaxies, [$α$/Fe]=(0.378$\pm$0.009)log($σ$/100)+(0.155$\pm$0.003). We observe a correlation between the residuals and the local environmental surface density, whereas no such relation exists for blue cloud galaxies. In the full sample, we find that elliptical galaxies in high-density environments are $α$-enhanced by up to 0.057$\pm$0.014 dex at velocity dispersions $σ$<100 km/s, compared with those in low-density environments. This $α$-enhancement is morphology-dependent, with the offset decreasing along the Hubble sequence towards spirals, which have an offset of 0.019$\pm$0.014 dex. At low velocity dispersion and controlling for morphology, we estimate that star formation in high-density environments is truncated $\sim1$ Gyr earlier than in low-density environments. For elliptical galaxies only, we find support for a parabolic relationship between [$α$/Fe] and $σ$, with an environmental $α$-enhancement of at least 0.03 dex. This suggests strong contributions from both environment and mass-based quenching mechanisms. However, there is no evidence for this behaviour in later morphological types.

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arXiv2021

The SAMI Galaxy Survey: a statistical approach to an optimal classification of stellar kinematics in galaxy surveys

Large galaxy samples from multi-object IFS surveys now allow for a statistical analysis of the z~0 galaxy population using resolved kinematics. However, the improvement in number statistics comes at a cost, with multi-object IFS survey more severely impacted by the effect of seeing and lower S/N. We present an analysis of ~1800 galaxies from the SAMI Galaxy Survey and investigate the spread and overlap in the kinematic distributions of the spin parameter proxy $λ_{Re}$ as a function of stellar mass and ellipticity. For SAMI data, the distributions of galaxies identified as regular and non-regular rotators with \textsc{kinemetry} show considerable overlap in the $λ_{Re}$-$\varepsilon_e$ diagram. In contrast, visually classified galaxies (obvious and non-obvious rotators) are better separated in $λ_{Re}$ space, with less overlap of both distributions. Then, we use a Bayesian mixture model to analyse the observed $λ_{Re}$-$\log(M_*/M_{\odot})$ distribution. Below $\log(M_{\star}/M_{\odot})\sim10.5$, a single beta distribution is sufficient to fit the complete $λ_{Re}$ distribution, whereas a second beta distribution is required above $\log(M_{\star}/M_{\odot})\sim10.5$ to account for a population of low-$λ_{Re}$ galaxies. While the Bayesian mixture model presents the cleanest separation of the two kinematic populations, we find the unique information provided by visual classification of kinematic maps should not be disregarded in future studies. Applied to mock-observations from different cosmological simulations, the mixture model also predicts bimodal $λ_{Re}$ distributions, albeit with different positions of the $λ_{Re}$ peaks. Our analysis validates the conclusions from previous smaller IFS surveys, but also demonstrates the importance of using kinematic selection criteria that are dictated by the quality of the observed or simulated data.

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arXiv2021

Building hybridized 28-baseline pupil-remapping photonic interferometers for future high resolution imaging

One key advantage of single-mode photonic technologies for interferometric use is their ability to easily scale to an ever increasing number of inputs without a major increase in the overall device size, compared to traditional bulk optics. This is particularly important for the upcoming ELT generation of telescopes currently under construction. We demonstrate the fabrication and characterization of a novel hybridized photonic interferometer, with 8 simultaneous inputs, forming 28 baselines, the largest amount to-date. Utilizing different photonic fabrication technologies, we combine a 3D pupil remapper with a planar 8-port ABCD pairwise beam combiner, along with the injection optics necessary for telescope use, into a single integrated monolithic device. We successfully realized a combined device called Dragonfly, which demonstrates a raw instrumental closure-phase stability down to $0.9^{\circ}$ over $8π$ phase piston error, relating to a detection contrast of $\sim6.5\times 10^{-4}$ on an Adaptive-Optics corrected 8-m telescope. This prototype successfully demonstrates advanced hybridization and packaging techniques necessary for on-sky use for high-contrast detection at small inner working angles, ideally complementing what can currently be achieved using coronagraphs.

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arXiv2021

The SAMI Galaxy Survey: stellar population and structural trends across the Fundamental Plane

We study the Fundamental Plane (FP) for a volume- and luminosity-limited sample of 560 early-type galaxies from the SAMI survey. Using r-band sizes and luminosities from new Multi-Gaussian Expansion (MGE) photometric measurements, and treating luminosity as the dependent variable, the FP has coefficients a=1.294$\pm$0.039, b= 0.912$\pm$0.025, and zero-point c= 7.067$\pm$0.078. We leverage the high signal-to-noise of SAMI integral field spectroscopy, to determine how structural and stellar-population observables affect the scatter about the FP. The FP residuals correlate most strongly (8$σ$ significance) with luminosity-weighted simple-stellar-population (SSP) age. In contrast, the structural observables surface mass density, rotation-to-dispersion ratio, Sérsic index and projected shape all show little or no significant correlation. We connect the FP residuals to the empirical relation between age (or stellar mass-to-light ratio $Υ_\star$) and surface mass density, the best predictor of SSP age amongst parameters based on FP observables. We show that the FP residuals (anti-)correlate with the residuals of the relation between surface density and $Υ_\star$. This correlation implies that part of the FP scatter is due to the broad age and $Υ_\star$ distribution at any given surface mass density. Using virial mass and $Υ_\star$ we construct a simulated FP and compare it to the observed FP. We find that, while the empirical relations between observed stellar population relations and FP observables are responsible for most (75%) of the FP scatter, on their own they do not explain the observed tilt of the FP away from the virial plane.

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arXiv2020

The SAMI Galaxy Survey: A Range in S0 Properties Indicating Multiple Formation Pathways

It has been proposed that S0 galaxies are either fading spirals or the result of galaxy mergers. The relative contribution of each pathway, and the environments in which they occur remains unknown. Here we investigate stellar and gas kinematics of 219 S0s in the SAMI Survey to look for signs of multiple formation pathways occurring across the full range of environments. We identify a large range of rotational support in their stellar kinematics, which correspond to ranges in their physical structure. We find that pressure-supported S0s with $v/σ$ below 0.5 tend to be more compact and feature misaligned stellar and gas components, suggesting an external origin for their gas. We postulate that these S0s are consistent with being formed through a merger process. Meanwhile, comparisons of ellipticity, stellar mass and Sérsic index distributions with spiral galaxies shows that the rotationally supported S0s with $v/σ$ above 0.5 are more consistent with a faded spiral origin. In addition, a simulated merger pathway involving a compact elliptical and gas-rich satellite results in an S0 that lies within the pressure-supported group. We conclude that two S0 formation pathways are active, with mergers dominating in isolated galaxies and small groups, and the faded spiral pathway being most prominent in large groups ($10^{13} < M_{halo} < 10^{14}$).

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arXiv2020

The SAMI Galaxy Survey: Gas velocity dispersions in low-$z$ star-forming galaxies and the drivers of turbulence

We infer the intrinsic ionised gas kinematics for 383 star-forming galaxies across a range of integrated star-formation rates (SFR $\in [10^{-3}, 10^2]$ M$_\odot$ yr$^{-1}$) at $z \lesssim 0.1$ using a consistent 3D forward-modelling technique. The total sample is a combination of galaxies from the SAMI Galaxy Survey and DYNAMO survey. For typical low-$z$ galaxies taken from the SAMI Galaxy Survey, we find the vertical velocity dispersion ($σ_{v, z}$) to be positively correlated with measures of star-formation rate, stellar mass, HI gas mass, and rotational velocity. The greatest correlation is with star-formation rate surface density ($Σ_\text{SFR}$). Using the total sample, we find $σ_{v, z}$ increases slowly as a function of integrated star-formation rate in the range SFR $\in$ [$10^{-3}$, 1] M$_\odot$ yr$^{-1}$ from $17\pm3$ km s$^{-1}$ to $24\pm5$ km s$^{-1}$ followed by a steeper increase up to $σ_{v, z}$ $\sim 80$ km s$^{-1}$ for SFR $\gtrsim 1$ M$_\odot$ yr$^{-1}$. This is consistent with recent theoretical models that suggest a $σ_{v, z}$ floor driven by star-formation feedback processes with an upturn in $σ_{v, z}$ at higher SFR driven by gravitational transport of gas through the disc.

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arXiv2020

The SAMI Galaxy Survey: Decomposed Stellar Kinematics of Galaxy Bulges and Disks

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 (SAMI) 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 $λ_R$ indicates bulges are pressure-dominated systems and disks are supported by rotation; (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.

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arXiv2020

The SAMI Galaxy Survey: stellar population gradients of central galaxies

We examine the stellar population radial gradients (age, metallicity and [$α/$Fe]) of $\sim$ 100 passive central galaxies up to $\sim 2 R_e$. The targeted groups have a halo mass range spanning from $11 < \log(M_{200}/M_{\odot}) < 15$, in the SAMI Galaxy Survey. The main goal of this work is to determine whether central galaxies have different stellar population properties when compared to similarly massive satellite galaxies. We find negative metallicity radial gradients, which become shallower with increasing stellar mass. The age and [$α$/Fe] gradients are consistent with zero or slightly positive. [$α$/Fe] gradients become more negative with increasing mass, while age gradients do not show any significant trend with mass. We do not observe a significant difference between the stellar population gradients of central and satellite galaxies, at fixed stellar mass. The mean metallicity gradients are $\overline{Δ[Z/H]/Δ\log(r/R_e)} = -0.25 \pm 0.03$ for central galaxies and $\overline{Δ[Z/H]/Δ\log(r/R_e)} = -0.30 \pm 0.01$ for satellites. The mean age and [$α$/Fe] gradients are consistent between central and satellite galaxies, within the uncertainties, with a mean value of $\overline{Δ\textrm{log (Age/Gyr)}/Δ\log(r/R_e)} = 0.13 \pm 0.03$ for centrals and $\overline{Δ\textrm{log (Age/Gyr)}/Δ\log(r/R_e)} = 0.17 \pm 0.01$ for satellite and $\overline{Δ[α/Fe]/Δ\log(r/R_e)} = 0.01 \pm 0.03$ for centrals and $\overline{Δ[α/Fe]/Δ\log(r/R_e)} = 0.08 \pm 0.01$ for satellites. This evidence suggests that the central region of central passive galaxies form in a similar fashion to satellite passive galaxies, in agreement with a two-phase formation scenario.

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