Misalignment of gas and stellar rotation in galaxies can give clues to the origin and processing of accreted gas. Integral field spectroscopic observations of 1213 galaxies from the SAMI Galaxy Survey show that 11% of galaxies with fitted gas and stellar rotation are misaligned by more than 30 degrees in both field/group and cluster environments. Using SAMI morphological classifications and Sersic indices, the misalignment fraction is 45+/-6% in early-type galaxies, but only 5+/-1% in late-type galaxies. The distribution of position angle offsets is used to test the physical drivers of this difference. Slower dynamical settling time of the gas in elliptical stellar mass distributions accounts for a small increase in misalignment in early-type galaxies. However, gravitational dynamical settling time is insufficient to fully explain the observed differences between early- and late-type galaxies in the distributions of the gas/stellar position angle offsets. LTGs have primarily accreted gas close to aligned rather than settled from misaligned based on analysis of the skewed distribution of PA offsets compared to a dynamical settling model. Local environment density is less important in setting the misalignment fractions than morphology, suggesting that mergers are not the main source of accreted gas in these disks. Cluster environments are found to have gas misalignment driven primarily by cluster processes not by gas accretion.
In order to determine the causes of kinematic asymmetry in the H alpha gas in the SAMI (Sydney-AAO Multi-object IFS) Galaxy Survey sample, we investigate the comparative influences of environment and intrinsic properties of galaxies on perturbation. We use spatially resolved H alpha velocity fields from the SAMI Galaxy Survey to quantify kinematic asymmetry ((upsilon(asym)) over bar) in nearby galaxies and environmental and stellar mass data from the Galaxy And Mass Assembly survey. We find that local environment, measured as distance to nearest neighbour, is inversely correlated with kinematic asymmetry for galaxies with log (M-*/M-circle dot) > 10.0, but there is no significant correlation for galaxies with log (M-*/M-circle dot) < 10.0. Moreover, low-mass galaxies [ log (M-*/M-circle dot) < 9.0] have greater kinematic asymmetry at all separations, suggesting a different physical source of asymmetry is important in low-mass galaxies. We propose that secular effects derived from gas fraction and gas mass may be the primary causes of asymmetry in low-mass galaxies. High gas fraction is linked to high sigma(m)/V (where sigma(m) is H alpha velocity dispersion and V the rotation velocity), which is strongly correlated with (upsilon(asym)) over bar, and galaxies with log (M-*/M-circle dot) < 9.0 have offset <(sigma(m))over bar>/V from the rest of the sample. Further, asymmetry as a fraction of dispersion decreases for galaxies with log (M-*/M-circle dot) < 9.0. Gas mass and asymmetry are also inversely correlated in our sample. We propose that low gas masses in dwarf galaxies may lead to asymmetric distribution of gas clouds, leading to increased relative turbulence.
We present the similar to 800 star formation rate maps for the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey based on II alpha emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1. We mask out spaxels contaminated by non-stellar emission using the [O III]/II beta, [NII]/II alpha, [S II]/II alpha, and [O I]/II alpha line ratios. Using these maps, we examine the global and resolved star-forming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main-sequence population has centrally concentrated star formation similar to late-type galaxies, while galaxies >3 sigma below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions.
We investigate the Tully-Fisher relation (TFR) for a morphologically and kinematically diverse sample of galaxies from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey using two-dimensional spatially resolved Ha velocity maps and find a well-defined relation across the stellar mass range of 8.0 < log (M*/M-circle dot) < 11.5. We use an adaptation of kinemetry to parametrize the kinematic Ha 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*/M-circle dot) < 9.5, 25 +/- 3 per cent are scattered below the root mean square (RMS) of the TFR, whereas for galaxies with log (M*/M-circle dot) > 9.5 the fraction is 10 +/- 1 per cent. 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.
We explore the radial distribution of star formation in galaxies in the Sydney Australian Astronomical Observatory Multi-object Integral Field Spectrograph (SAMI) as a function of their local group environment, and other measures of environment associated with the suspected mechanisms for environmental quenching. We find that the dynamical mass of the parent halo of a galaxy is a good predictor of environmental quenching. Higher mass group environments reduce the specific star formation rates of galaxies, but the spatially-resolved signature of this reduction appears to vary with the stellar mass of each galaxy. Galaxies more massive than M∗ ∼ 10 M have star formation quenched first in their outskirts, while galaxies less massive than this appear to be quenched uniformly across their discs. The dominant star-forming galaxies in groups with mass less than 10 M appear to have their star formation enhanced by ∼ 0.2 ± 0.09 dex over non-group galaxies of the same mass, with weak evidence that this enhancement occurs in the centres of these galaxies.
We study the properties of kinematically disturbed galaxies in the SAMI Galaxy Survey using a quantitative criterion, based on kinemetry (Krajnovic et al.). The approach, similar to the application of kinemetry by Shapiro et al. uses ionised gas kinematics, probed by H{\alpha} emission. By this method 23+/-7% of our 360-galaxy sub-sample of the SAMI Galaxy Survey are kinematically asymmetric. Visual classifications agree with our kinemetric results for 90% of asymmetric and 95% of normal galaxies. We find stellar mass and kinematic asymmetry are inversely correlated and that kinematic asymmetry is both more frequent and stronger in low-mass galaxies. This builds on previous studies that found high fractions of kinematic asymmetry in low mass galaxies using a variety of different methods. Concentration of star forma- tion and kinematic disturbance are found to be correlated, confirming results found in previous work. This effect is stronger for high mass galaxies (log(M*) > 10) and indicates that kinematic disturbance is linked to centrally concentrated star formation. Comparison of the inner (within 0.5Re) and outer H{\alpha} equivalent widths of asymmetric and normal galaxies shows a small but significant increase in inner equivalent width for asymmetric galaxies.
We use data from the Sydney-AAO Multi-Object Integral Field Spectrograph (SAMI) Galaxy Survey and the Galaxy And Mass Assembly (GAMA) survey to investigate the spatially-resolved signatures of the environmental quenching of star formation in galaxies. Using dust-corrected measurements of the distribution of Hα emission we measure the radial profiles of star formation in a sample of 201 star-forming galaxies covering three orders of magnitude in stellar mass (M∗M∗; 108.1-1010.95 M⊙) and in 5th nearest neighbour local environment density (Σ5; 10−1.3- 102.1 Mpc−2). We show that star formation rate gradients in galaxies are steeper in dense (log10(Σ5/Mpc2) > 0.5) environments by 0.58 ± 0.29 dex re−1 in galaxies with stellar masses in the range 1010 1.0). These lines of evidence strongly suggest that with increasing local environment density the star formation in galaxies is suppressed, and that this starts in their outskirts such that quenching occurs in an outside-in fashion in dense environments and is not instantaneous.
Galaxy mergers are important events that can determine the fate of a galaxy by changing its morphology, star formation activity and mass growth. Merger systems have commonly been identified from their disturbed morphologies, and we now can employ integral field spectroscopy to detect and analyze the impact of mergers on stellar kinematics as well. We visually classified galaxy morphology using deep images (mu(r) = 28 mag arcsec(-2)) taken by the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory. In this paper we investigate 63 bright (M-r < - 19.3) spectroscopically selected galaxies in Abell 119, of which 53 are early type and 20 show a disturbed morphology by visual inspection. A misalignment between the major axes in the photometric image and the kinematic map is conspicuous in morphologically disturbed galaxies. Our sample is dominated by early-type galaxies, yet it shows a surprisingly tight Tully-Fisher relation except for the morphologically disturbed galaxies which show large deviations. Three out of the eight slow rotators in our sample are morphologically disturbed. The morphologically disturbed galaxies are generally more asymmetric, visually as well as kinematically. Our findings suggest that galaxy interactions, including mergers and perhaps fly-bys, play an important role in determining the orientation and magnitude of a galaxy's angular momentum.
We investigate the relationship between stellar and gas specific angular momentum j, stellar mass M-* and optical morphology for a sample of 488 galaxies extracted from the Sydney-AAO Multi-object Integral field Galaxy Survey. We find that j, measured within one effective radius, monotonically increases with M-* and that, for M-* > 10(9.5) M-aS (TM), the scatter in this relation strongly correlates with optical morphology (i.e. visual classification and S,rsic index). These findings confirm that massive galaxies of all types lie on a plane relating mass, angular momentum and stellar-light distribution, and suggest that the large-scale morphology of a galaxy is regulated by its mass and dynamical state. We show that the significant scatter in the M-*-j relation is accounted for by the fact that, at fixed stellar mass, the contribution of ordered motions to the dynamical support of galaxies varies by at least a factor of 3. Indeed, the stellar spin parameter (quantified via lambda(R)) correlates strongly with S,rsic and concentration indices. This correlation is particularly strong once slow rotators are removed from the sample, showing that late-type galaxies and early-type fast rotators form a continuous class of objects in terms of their kinematic properties.
The SAMI Galaxy Survey will observe 3400 galaxies with the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) on the Anglo-Australian Telescope (AAT) in a 3-year survey which began in 2013. We present the throughput of the SAMI system, the science basis and specifications for the target selection, the survey observation plan and the combined properties of the selected galaxies. The survey includes four volume limited galaxy samples based on cuts in a proxy for stellar mass, along with low-stellar mass dwarf galaxies all selected from the Galaxy And Mass Assembly (GAMA) survey. The GAMA regions were selected because of the vast array of ancillary data available, including ultraviolet through to radio bands. These fields are on the celestial equator at 9, 12, and 14.5 hours, and cover a total of 144 square degrees (in GAMA-I). Higher density environments are also included with the addition of eight clusters. The clusters have spectroscopy from 2dFGRS and SDSS and photometry in regions covered by the Sloan Digital Sky Survey (SDSS) and/or VLT Survey Telescope/ATLAS. The aim is to cover a broad range in stellar mass and environment, and therefore the primary survey targets cover redshifts 0.004 < z < 0.095, magnitudes r_pet < 19.4, stellar masses 10^7 - 10^12 M_sol, and environments from isolated field galaxies through groups to clusters of 10^15 M_sol.
We present a methodology for the regularization and combination of sparse sampled and irregularly gridded observations from fibre-optic multiobject integral field spectroscopy. The approach minimizes interpolation and retains image resolution on combining subpixel dithered data. We discuss the methodology in the context of the Sydney–AAO multiobject integral field spectrograph (SAMI) Galaxy Survey underway at the Anglo-Australian Telescope. The SAMI instrument uses 13 fibre bundles to perform high-multiplex integral field spectroscopy across a 1° diameter field of view. The SAMI Galaxy Survey is targeting ∼3000 galaxies drawn from the full range of galaxy environments. We demonstrate the subcritical sampling of the seeing and incomplete fill factor for the integral field bundles results in only a 10 per cent degradation in the final image resolution recovered. We also implement a new methodology for tracking covariance between elements of the resulting data cubes which retains 90 per cent of the covariance information while incurring only a modest increase in the survey data volume.
We present the Early Data Release of the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. The SAMI Galaxy Survey is an ongoing integral field spectroscopic survey of 3400 low-redshift (z<0.12) galaxies, covering galaxies in the field and in groups within the Galaxy And Mass Assembly (GAMA) survey regions, and a sample of galaxies in clusters. In the Early Data Release, we publicly release the fully calibrated datacubes for a representative selection of 107 galaxies drawn from the GAMA regions, along with information about these galaxies from the GAMA catalogues. All datacubes for the Early Data Release galaxies can be downloaded individually or as a set from the SAMI Galaxy Survey website. In this paper we also assess the quality of the pipeline used to reduce the SAMI data, giving metrics that quantify its performance at all stages in processing the raw data into calibrated datacubes. The pipeline gives excellent results throughout, with typical sky subtraction residuals in the continuum of 0.9-1.2 per cent, a relative flux calibration uncertainty of 4.1 per cent (systematic) plus 4.3 per cent (statistical), and atmospheric dispersion removed with an accuracy of 0."09, less than a fifth of a spaxel.
We present the discovery of a luminous unresolved H II complex on the edge of dwarf galaxy GAMA J141103.98-003242.3 using data from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. This dwarf galaxy is situated at a distance of similar to 100 Mpc and contains an unresolved region of H II emission that contributes similar to 70 per cent of the galaxy's Ha luminosity, located at the top end of established H II region luminosity functions. For the H II complex, we measure a star formation rate of 0.147 +/- 0.041 M-circle dot yr(-1) and a metallicity of 12+log(O/H) = 8.01 +/- 0.05 that is lower than the rest of the galaxy by similar to 0.2 dex. Data from the HI Parkes All-Sky Survey (HIPASS) indicate the likely presence of neutral hydrogen in the galaxy to potentially fuel ongoing and future star-forming events. We discuss various triggering mechanisms for the intense star formation activity of this H II complex, where the kinematics of the ionized gas are well described by a rotating disc and do not show any features indicative of interactions. We show that SAMI is an ideal instrument to identify similar systems to GAMA J141103.98-003242.3, and the SAMI Galaxy Survey is likely to find many more of these systems to aid in the understanding of their formation and evolution.
We take advantage of the first data from the Sydney-AAOMulti-object Integral field (SAMI) Galaxy Survey to investigate the relation between the kinematics of gas and stars, and stellar mass in a comprehensive sample of nearby galaxies. We find that all 235 objects in our sample, regardless of their morphology, lie on a tight relation linking stellar mass (M∗) to internal velocity quantified by the S0.5 parameter, which combines the contribution of both dispersion (σ) and rotational velocity (Vrot) to the dynamical support of a galaxy (S0.5 = √ 0.5V 2 rot + σ 2). Our results are independent of the baryonic component from which σ and Vrot are estimated, as the S0.5 of stars and gas agree remarkably well. This represents a significant improvement compared to the canonical M∗ vs. Vrot and M∗ vs. σ relations. Not only is no sample pruning necessary, but also stellar and gas kinematics can be used simultaneously, as the effect of asymmetric drift is taken into account once Vrot and σ are combined. Our findings illustrate how the combination of dispersion and rotational velocities for both gas and stars can provide us with a single dynamical scaling relation valid for galaxies of all morphologies across at least the stellar mass range 8.5< log(M∗/M⊙) <11. Such relation appears to be more general and at least as tight as any other dynamical scaling relation, representing a unique tool for investigating the link between galaxy kinematics and baryonic content, and a less biased comparison with theoretical models. Subject headings: galaxies: evolution — galaxies: fundamental parameters — galaxies: kinematics and dynamics
We demonstrate the feasibility and potential of using large integral field spectroscopic surveys to investigate the prevalence of galactic-scale outflows in the local Universe. Using integral field data from SAMI and the Wide Field Spectrograph, we study the nature of an isolated disk galaxy, SDSS J090005.05+000446.7 (z = 0.05386). In the integral field datasets, the galaxy presents skewed line profiles changing with position in the galaxy. The skewed line profiles are caused by different kinematic components overlapping in the line-of-sight direction. We perform spectral decomposition to separate the line profiles in each spatial pixel as combinations of (1) a narrow kinematic component consistent with HII regions, (2) a broad kinematic component consistent with shock excitation, and (3) an intermediate component consistent with shock excitation and photoionisation mixing. The three kinematic components have distinctly different velocity fields, velocity dispersions, line ratios, and electron densities. We model the line ratios, velocity dispersions, and electron densities with our MAPPINGS IV shock and photoionisation models, and we reach remarkable agreement between the data and the models. The models demonstrate that the different emission line properties are caused by major galactic outflows that introduce shock excitation in addition to photoionisation by star-forming activities. Interstellar shocks embedded in the outflows shock-excite and compress the gas, causing the elevated line ratios, velocity dispersions, and electron densities observed in the broad kinematic component. We argue from energy considerations that, with the lack of a powerful active galactic nucleus, the outflows are likely to be driven by starburst activities. Our results set a benchmark of the type of analysis that can be achieved by the SAMI Galaxy Survey on large numbers of galaxies.
We take advantage of the first data from the Sydney-AAO Multi-object Integral field Galaxy Survey to investigate the relation between the kinematics of gas and stars, and stellar mass in a comprehensive sample of nearby galaxies. We find that all 235 objects in our sample, regardless of their morphology, lie on a tight relation linking stellar mass (M-*) to internal velocity quantified by the S-0.5 parameter, which combines the contribution of both dispersion (sigma) and rotational velocity (V-rot) to the dynamical support of a galaxy (S-0.5 = root 0.5 V-rot(2) + sigma(2)). Our results are independent of the baryonic component from which sigma and V-rot are estimated, as the S-0.5 of stars and gas agree remarkably well. This represents a significant improvement compared to the canonical M-* versus Vrot and M-* versus s relations. Not only is no sample pruning necessary, but also stellar and gas kinematics can be used simultaneously, as the effect of asymmetric drift is taken into account once V-rot and sigma are combined. Our findings illustrate how the combination of dispersion and rotational velocities for both gas and stars can provide us with a single dynamical scaling relation valid for galaxies of all morphologies across at least the stellar mass range 8.5 < log (M-*/M-circle dot) < 11. Such relation appears to be more general and at least as tight as any other dynamical scaling relation, representing a unique tool for investigating the link between galaxy kinematics and baryonic content, and a less biased comparison with theoretical models.