Abstract
We present the first major release of data from the SAMI Galaxy Survey. This data release focuses on the emission-line physics of galaxies. Data Release One includes data for 772 galaxies, ...about 20 per cent of the full survey. Galaxies included have the redshift range 0.004 < z < 0.092, a large mass range (7.6 < log M*/ M⊙ < 11.6), and star formation rates of ∼10−4 to ∼101M⊙ yr−1. For each galaxy, we include two spectral cubes and a set of spatially resolved 2D maps: single- and multi-component emission-line fits (with dust-extinction corrections for strong lines), local dust extinction, and star formation rate. Calibration of the fibre throughputs, fluxes, and differential atmospheric refraction has been improved over the Early Data Release. The data have average spatial resolution of 2.16 arcsec (full width at half-maximum) over the 15 arcsec diameter field of view and spectral (kinematic) resolution of R = 4263 (σ = 30 km s−1) around H α. The relative flux calibration is better than 5 per cent, and absolute flux calibration has an rms of 10 per cent. The data are presented online through the Australian Astronomical Observatory's Data Central.
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.
We present SAMI-HI, a survey of the atomic hydrogen content of 296 galaxies
with integral field spectroscopy available from the SAMI Galaxy Survey. The
sample spans nearly 4 dex in stellar mass ...($M_\star = 10^{7.4}-10^{11.1}~ \rm
M_\odot$), redshift $z<0.06$, and includes new Arecibo observations of 153
galaxies, for which we release catalogues and HI spectra. We use these data to
compare the rotational velocities obtained from optical and radio observations
and to show how systematic differences affect the slope and scatter of the
stellar-mass and baryonic Tully-Fisher relations. Specifically, we show that
H$\alpha$ rotational velocities measured in the inner parts of galaxies (1.3
effective radii in this work) systematically underestimate HI global
measurements, with HI/H$\alpha$ velocity ratios that increase at low stellar
masses, where rotation curves are typically still rising and H$\alpha$
measurements do not reach their plateau. As a result, the H$\alpha$ stellar
mass Tully-Fisher relation is steeper (when $M_\star$ is the independent
variable) and has larger scatter than its HI counterpart. Interestingly, we
confirm the presence of a small fraction of low-mass outliers of the H$\alpha$
relation that are not present when HI velocity widths are used and are not
explained by "aperture effects". These appear to be highly disturbed systems
for which H$\alpha$ widths do not provide a reliable estimate of the rotational
velocity. Our analysis reaffirms the importance of taking into account
differences in velocity definitions as well as tracers used when interpreting
offsets from the Tully-Fisher relation, at both low and high redshifts and when
comparing with simulations.
In this work, we investigate how the central stellar metallicity (Z/H) of 1363 galaxies from the SAMI galaxy survey is related to their stellar mass and a proxy for the gravitational potential, ...\(\Phi\) = log10(M/M*) - log10(\(r_e\)/kpc). In agreement with previous studies, we find that passive and star-forming galaxies occupy different areas of the Z/H-M* plane, with passive galaxies having higher Z/H than star-forming galaxies at fixed mass (a difference of 0.23 dex at log10(M/M*)=10.3). We show for the first time that all galaxies lie on the same relation between Z/H and \(\Phi\), and show that the offset in Z/H between passive and star-forming galaxies at fixed \(\Phi\) is smaller than or equal to the offset in Z/H at fixed mass (an average \(\Delta\)Z/H of 0.11 dex at fixed \(\Phi\) compared to 0.21 dex at fixed mass). We then build a simple model of galaxy evolution to explain and understand our results. By assuming that Z/H traces \(\Phi\) over cosmic time and that the probability that a galaxy quenches depends on both its mass and size, we are able to reproduce these offsets in stellar metallicity with a model containing instantaneous quenching. We therefore conclude that an offset in metallicity at fixed mass cannot by itself be used as evidence of slow quenching processes, in contrast to previous studies. Instead, our model implies that metal-rich galaxies have always been the smallest objects for their mass in a population. Our findings reiterate the need to consider galaxy size when studying stellar populations.
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 \(\sigma\)) 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 \(\sim 2\) \(\sigma\) 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, \(\lambda_{Re}\) and inclination. Although low-mass, high-mass, early-type and low-spin galaxies subsamples show 2 - 3 \(\sigma\) signal of coherence for the neighbours within 2 Mpc, the results for different inclination subsamples and large-scale results suggest that the \(\sim 2 \sigma\) 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.
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 \(\beta_r\) (tangential anisotropy). \(\beta_r\) also shows an anti-correlation with the edge-on spin parameter \lam, so that \(\beta_r\) 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 (\(V/\sigma\) - \(h_3\)) 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.
Recent integral field spectroscopy observations have found that about 11% of galaxies show star-gas misalignment. The misalignment possibly results from external effects such as gas accretion, ...interaction with other objects, and other environmental effects, hence providing clues to these effects. We explore the properties of misaligned galaxies using Horizon-AGN, a large-volume cosmological simulation, and compare the result with the result of the Sydney-AAO Multi-object integral field spectrograph (SAMI) Galaxy Survey. Horizon-AGN can match the overall misalignment fraction and reproduces the distribution of misalignment angles found by observations surprisingly closely. The misalignment fraction is found to be highly correlated with galaxy morphology both in observations and in the simulation: early-type galaxies are substantially more frequently misaligned than late-type galaxies. The gas fraction is another important factor associated with misalignment in the sense that misalignment increases with decreasing gas fraction. However, there is a significant discrepancy between the SAMI and Horizon-AGN data in the misalignment fraction for the galaxies in dense (cluster) environments. We discuss possible origins of misalignment and disagreement.
The kinematic morphology-density relation of galaxies is normally attributed to a changing distribution of galaxy stellar masses with the local environment. However, earlier studies were largely ...focused on slow rotators; the dynamical properties of the overall population in relation to environment have received less attention. We use the SAMI Galaxy Survey to investigate the dynamical properties of \(\sim\)1800 early and late-type galaxies with \(\log(M_*/M_{\odot})>9.5\) as a function of mean environmental overdensity (\(\Sigma_{5}\)) and their rank within a group or cluster. By classifying galaxies into fast and slow rotators, at fixed stellar mass above \(\log(M_*/M_{\odot})>10.5\), we detect a higher fraction (\(\sim3.4\sigma\)) of slow rotators for group and cluster centrals and satellites as compared to isolated-central galaxies. Focusing on the fast-rotator population, we also detect a significant correlation between galaxy kinematics and their stellar mass as well as the environment they are in. Specifically, by using inclination-corrected or intrinsic \(\lambda_{R_e}\) values, we find that, at fixed mass, satellite galaxies on average have the lowest \(\lambda_{\,R_e,intr}\), isolated-central galaxies have the highest \(\lambda_{\,R_e,intr}\), and group and cluster centrals lie in between. Similarly, galaxies in high-density environments have lower mean \(\lambda_{\,R_e,intr}\) values as compared to galaxies at low environmental density. However, at fixed \(\Sigma_{5}\), the mean \(\lambda_{\,R_e,intr}\) differences for low and high-mass galaxies are of similar magnitude as when varying \(\Sigma_{5}\) {(\(\Delta \lambda_{\,R_e,intr} \sim 0.05\). Our results demonstrate that after stellar mass, environment plays a significant role in the creation of slow rotators, while for fast rotators we also detect an independent, albeit smaller, impact of mass and environment on their kinematic properties.
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\(\sigma\) 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 \(\Upsilon_\star\)) 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 \(\Upsilon_\star\). This correlation implies that part of the FP scatter is due to the broad age and \(\Upsilon_\star\) distribution at any given surface mass density. Using virial mass and \(\Upsilon_\star\) 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.
We examine the stellar population radial gradients (age, metallicity and \(\alpha/\)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 \(\alpha\)/Fe gradients are consistent with zero or slightly positive. \(\alpha\)/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 \(\overline{\Delta Z/H/\Delta \log(r/R_e)} = -0.25 \pm 0.03\) for central galaxies and \(\overline{\Delta Z/H/\Delta \log(r/R_e)} = -0.30 \pm 0.01\) for satellites. The mean age and \(\alpha\)/Fe gradients are consistent between central and satellite galaxies, within the uncertainties, with a mean value of \(\overline{\Delta \textrm{log (Age/Gyr)}/\Delta \log(r/R_e)} = 0.13 \pm 0.03\) for centrals and \(\overline{\Delta \textrm{log (Age/Gyr)}/\Delta \log(r/R_e)} = 0.17 \pm 0.01\) for satellite and \(\overline{\Delta \alpha/Fe/\Delta \log(r/R_e)} = 0.01 \pm 0.03\) for centrals and \(\overline{\Delta \alpha/Fe/\Delta \log(r/R_e)} = 0.08 \pm 0.01\) 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.
PDF