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Register a new userThe SAMI Galaxy Survey: understanding observations of large-scale outflows at low redshift with EAGLE simulations
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This work presents a study of galactic outflows driven by stellar feedback. We extract main sequence disc galaxies with stellar mass $10^9le$ M$_{star}/$M$_{odot} le 5.7times10^{10}$ at redshift $z=0$ from the highest resolution cosmological simulation of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) set. Synthetic gas rotation velocity and velocity dispersion ($sigma$) maps are created and compared to observations of disc galaxies obtained with the Sydney-AAO Multi-object Integral field spectrograph (SAMI), where $sigma$-values greater than $150$ km s$^{-1}$ are most naturally explained by bipolar outflows powered by starburst activity. We find that the extension of the simulated edge-on (pixelated) velocity dispersion probability distribution depends on stellar mass and star formation rate surface density ($Sigma_{rm SFR}$), with low-M$_{star}/$low-$Sigma_{rm SFR}$ galaxies showing a narrow peak at low $sigma$ ($sim30$ km s$^{-1}$) and more active, high-M$_{star}/$high-$Sigma_{rm SFR}$ galaxies reaching $sigma>150$ km s$^{-1}$. Although supernova-driven galactic winds in the EAGLE simulations may not entrain enough gas with T $<10^5$ K compared to observed galaxies, we find that gas temperature is a good proxy for the presence of outflows. There is a direct correlation between the thermal state of the gas and its state of motion as described by the $sigma$-distribution. The following equivalence relations hold in EAGLE: $i)$ low-$sigma$ peak $,Leftrightarrow,$ disc of the galaxy $,Leftrightarrow,$ gas with T $<10^5$ K; $ii)$ high-$sigma$ tail $,Leftrightarrow,$ galactic winds $,Leftrightarrow,$ gas with T $ge 10^5$ K.
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We investigate the Tully-Fisher Relation (TFR) for a morphologically and kine- matically diverse sample of galaxies from the SAMI Galaxy Survey using 2 dimensional spatially resolved Halpha velocity maps and find a well defined relation across the stellar mass range of 8.0 < log(M*) < 11.5. We use an adaptation of kinemetry to parametrise the kinematic Halpha asymmetry of all galaxies in the sample, and find a correlation between scatter (i.e. residuals off the TFR) and asymmetry. This effect is pronounced at low stellar mass, corresponding to the inverse relationship between stellar mass and kinematic asymmetry found in previous work. For galaxies with log(M*) < 9.5, 25 +/- 3% are scattered below the root mean square (RMS) of the TFR, whereas for galaxies with log(M*) > 9.5 the fraction is 10 +/- 1% We use simulated slits to directly compare our results with those from long slit spectroscopy and find that aligning slits with the photometric, rather than the kinematic, position angle, increases global scatter below the TFR. Further, kinematic asymmetry is correlated with misalignment between the photometric and kinematic position angles. This work demonstrates the value of 2D spatially resolved kinematics for accurate TFR studies; integral field spectroscopy reduces the underestimation of rotation velocity that can occur from slit positioning off the kinematic axis.
Cosmological hydrodynamical simulations are rich tools to understand the build-up of stellar mass and angular momentum in galaxies, but require some level of calibration to observations. We compare predictions at $zsim0$ from the Eagle, Hydrangea, Horizon-AGN, and Magneticum simulations with integral field spectroscopic (IFS) data from the SAMI Galaxy Survey, ATLAS3D, CALIFA and MASSIVE surveys. The main goal of this work is to simultaneously compare structural, dynamical, and stellar population measurements in order to identify key areas of success and tension. We have taken great care to ensure that our simulated measurement methods match the observational methods as closely as possible. We find that the Eagle and Hydrangea simulations reproduce many galaxy relations but with some offsets at high stellar masses. There are moderate mismatches in $R_e$ (+), $epsilon$ (-), $sigma_e$ (-), and mean stellar age (+), where a plus sign indicates that quantities are too high on average, and minus sign too low. The Horizon-AGN simulations qualitatively reproduce several galaxy relations, but there are a number of properties where we find a quantitative offset to observations. Massive galaxies are better matched to observations than galaxies at low and intermediate masses. Overall, we find mismatches in $R_e$ (+), $epsilon$ (-), $sigma_e$ (-) and $(V/sigma)_e$ (-). Magneticum matches observations well: this is the only simulation where we find ellipticities typical for disk galaxies, but there are moderate differences in $sigma_e$ (-), $(V/sigma)_e$ (-) and mean stellar age (+). Our comparison between simulations and observational data has highlighted several areas for improvement, such as the need for improved modelling resulting in a better vertical disk structure, yet our results demonstrate the vast improvement of cosmological simulations in recent years.
We describe the selection of galaxies targeted in eight low redshift clusters (APMCC0917, A168, A4038, EDCC442, A3880, A2399, A119 and A85; $0.029 < z < 0.058$) as part of the Sydney-AAO Multi-Object integral field Spectrograph Galaxy Survey (SAMI-GS). We have conducted a redshift survey of these clusters using the AAOmega multi-object spectrograph on the 3.9m Anglo-Australian Telescope. The redshift survey is used to determine cluster membership and to characterise the dynamical properties of the clusters. In combination with existing data, the survey resulted in 21,257 reliable redshift measurements and 2899 confirmed cluster member galaxies. Our redshift catalogue has a high spectroscopic completeness ($sim 94%$) for $r_{rm petro} leq 19.4$ and clustercentric distances $R< 2rm{R}_{200}$. We use the confirmed cluster member positions and redshifts to determine cluster velocity dispersion, $rm{R}_{200}$, virial and caustic masses, as well as cluster structure. The clusters have virial masses $14.25 leq {rm log }({rm M}_{200}/rm{M}_{odot}) leq 15.19$. The cluster sample exhibits a range of dynamical states, from relatively relaxed-appearing systems, to clusters with strong indications of merger-related substructure. Aperture- and PSF-matched photometry are derived from SDSS and VST/ATLAS imaging and used to estimate stellar masses. These estimates, in combination with the redshifts, are used to define the input target catalogue for the cluster portion of the SAMI-GS. The primary SAMI-GS cluster targets have $R< rm{R}_{200}$, velocities $|v_{rm pec}| < 3.5sigma_{200}$ and stellar masses $9.5 leq {rm log(M}^*_{approx}/rm{M}_{odot}) leq 12$. Finally, we give an update on the SAMI-GS progress for the cluster regions.
The existence of a kinematic morphology-density relation remains uncertain, and instead stellar mass appears the more dominant driver of galaxy kinematics. We investigate the dependence of the stellar spin parameter proxy $lambda_{R_e}$ on environment using a marked cross-correlation method with data from the SAMI Galaxy Survey. Our sample contains 710 galaxies with spatially resolved stellar velocity and velocity dispersion measurements. By utilising the highly complete spectroscopic data from the GAMA survey, we calculate marked cross-correlation functions for SAMI galaxies using a pair count estimator and marks based on stellar mass and $lambda_{R_e}$. We detect an anti-correlation of stellar kinematics with environment at the 3.2$sigma$ level, such that galaxies with low $lambda_{R_e}$ values are preferably located in denser galaxy environments. However, a significant correlation between stellar mass and environment is also found (correlation at 2.4$sigma$), as found in previous works. We compare these results to mock-observations from the cosmological EAGLE simulations, where we find a similar significant $lambda_{R_e}$ anti-correlation with environment, and a mass and environment correlation. We demonstrate that the environmental correlation of $lambda_{R_e}$ is not caused by the mass-environment relation. The significant relationship between $lambda_{R_e}$ and environment remains when we exclude slow rotators. The signals in SAMI and EAGLE are strongest on small scales (10-100 kpc) as expected from galaxy interactions and mergers. Our work demonstrates that the technique of marked correlation functions is an effective tool for detecting the relationship between $lambda_{R_e}$ and environment.
The 2dF Galaxy Redshift Survey is the first to measure more than 100,000 redshifts. This allows precise measurements of many of the key statistical measures of galaxy clustering, in particular redshift-space distortions and the large-scale power spectrum. This paper presents the current 2dFGRS results in these areas. Redshift-space distortions are detected with a high degree of significance, confirming the detailed Kaiser distortion from large-scale infall velocities, and measuring the distortion parameter beta = 0.43 +/- 0.07. The power spectrum is measured to < 10% accuracy for k > 0.02 h Mpc^-1, and is well fitted by a CDM model with Omega_m h = 0.20 +/- 0.03 and a baryon fraction of 0.15 +/- 0.07.
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