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Register a new userThe SAMI Galaxy Survey: Detection of Environmental Dependence of Galaxy Spin in Observations and Simulations Using Marked Correlation Functions
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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.
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We explore the radial distribution of star formation in galaxies in the SAMI Galaxy Survey as a function of their local group environment. Using a sample of galaxies in groups (with halo masses less than $ simeq 10^{14} , mathrm{M_{odot}}$) from the Galaxy And Mass Assembly Survey, we find signatures of environmental quenching in high-mass groups ($M_{G} > 10^{12.5} , mathrm{M_{odot}}$). The mean integrated specific star formation rate of star-forming galaxies in high-mass groups is lower than for galaxies in low-mass groups or that are ungrouped, with $Delta log(sSFR/mathrm{yr^{-1}}) = 0.45 pm 0.07$. This difference is seen at all galaxy stellar masses. In high-mass groups, star-forming galaxies more massive than $M_{*} sim 10^{10} , mathrm{M_{odot}}$ have centrally-concentrated star formation. These galaxies also lie below the star-formation main sequence, suggesting they may be undergoing outside-in quenching. Lower mass galaxies in high-mass groups do not show evidence of concentrated star formation. In groups less massive than $M_{G} = 10^{12.5} , mathrm{M_{odot}}$ we do not observe these trends. In this regime we find a modest correlation between centrally-concentrated star formation and an enhancement in total star formation rate, consistent with triggered star formation in these galaxies.
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.
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.
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 ($sigma$) 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 $sigma$ 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 $sigma$ 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 $lambda_R$ 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.
We investigate how different galaxy properties - luminosities in u, g, r, J, K-bands, stellar mass, star formation rate and specific star formation rate trace the environment in the local universe. We also study the effect of survey flux limits on galaxy clustering measurements. We measure the two-point correlation function (2pCF) and marked correlation functions (MCFs) using the aforementioned properties as marks. We use nearly stellar-mass-complete galaxy sample in the redshift range 0.1 < z < 0.16 from the Galaxy And Mass Assembly (GAMA) survey with a flux limit of r < 19.8. Further, we impose a brighter flux limit of r < 17.8 to our sample and repeat the measurements to study how this affects galaxy clustering analysis. We compare our results to measurements from the Sloan Digital Sky Survey (SDSS) with flux limits of r < 17.8 and r < 16.8. We show that the stellar mass is the best tracer of galaxy environment, the K-band luminosity being a good substitute, although such a proxy sample misses close pairs of evolved, red galaxies. We also confirm that the u-band luminosity is a good, but not a perfect proxy of star formation rate in the context of galaxy clustering. We observe an effect of the survey flux limit on clustering studies - samples with a higher flux limit (smaller magnitude) miss some information about close pairs of starburst galaxies.
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