The SAMI Galaxy Survey: the cluster redshift survey, target selection and cluster properties

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 3.9-m Anglo-Australian Telescope. The redshift survey is used to determine cluster membership and to characterize 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 (∼94 per cent) for rpetro ≤ 19.4 and cluster-centric distances R < 2R200. We use the confirmed cluster member positions and redshifts to determine cluster velocity dispersion, R200, virial and caustic masses, as well as cluster structure. The clusters have virial masses 14.25 ≤ log(M200/M_⊙) ≤ 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 point spread function matched photometry are derived from Sloan Digital Sky Survey and VLT Survey Telescope/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 <R200, velocities |vpec| < 3.5σ200 and stellar masses 9.5 ≤ log(M^∗_(approx)/M_⊙) ≤ 12. Finally, we give an update on the SAMI-GS progress for the cluster regions

Self-consistent Bulge/Disk/Halo Galaxy Dynamical Modeling Using Integral Field Kinematics

We introduce a method for modeling disk galaxies designed to take full advantage of data from integral field spectroscopy (IFS). The method fits equilibrium models to simultaneously reproduce the surface brightness, rotation, and velocity dispersion profiles of a galaxy. The models are fully self-consistent 6D distribution functions for a galaxy with a Sérsic profile stellar bulge, exponential disk, and parametric dark-matter halo, generated by an updated version of GalactICS. By creating realistic flux-weighted maps of the kinematic moments (flux, mean velocity, and dispersion), we simultaneously fit photometric and spectroscopic data using both maximum-likelihood and Bayesian (MCMC) techniques. We apply the method to a GAMA spiral galaxy (G79635) with kinematics from the SAMI Galaxy Survey and deep g- and r-band photometry from the VST-KiDS survey, comparing parameter constraints with those from traditional 2D bulge–disk decomposition. Our method returns broadly consistent results for shared parameters while constraining the mass-to-light ratios of stellar components and reproducing the H i-inferred circular velocity well beyond the limits of the SAMI data. Although the method is tailored for fitting integral field kinematic data, it can use other dynamical constraints like central fiber dispersions and H i circular velocities, and is well-suited for modeling galaxies with a combination of deep imaging and H i and/or optical spectra (resolved or otherwise). Our implementation (MagRite) is computationally efficient and can generate well-resolved models and kinematic maps in under a minute on modern processors

Testing a double AGN hypothesis for Mrk 273

The ULIRG Mrk 273 contains two infrared nuclei, N and SW, separated by 1 arcsec. A Chandra observation has identified the SW nucleus as an absorbed X-ray source with nH ~4e23 cm-2 but also hinted at the possible presence of a Compton thick AGN in the N nucleus, where a black hole of 10^9 Msun is inferred from the ionized gas kinematics. The intrinsic X-ray spectral slope recently measured by NuSTAR is unusually hard (photon index of ~1.3) for a Seyfert nucleus, for which we seek an alternative explanation. We hypothesise a strongly absorbed X-ray source in N, of which X-ray emission rises steeply above 10 keV, in addition to the known X-ray source in SW, and test it against the NuSTAR data, assuming the standard spectral slope (photon index of 1.9). This double X-ray source model gives a good explanation of the hard continuum spectrum, the deep Fe K absorption edge, and the strong Fe K line observed in this ULIRG, without invoking the unusual spectral slope required for a single source interpretation. The putative X-ray source in N is found to be absorbed by nH = 1.4(+0.7/-0.4)e24 cm-2. The estimated 2-10 keV luminosity of the N source is 1.3e43 erg/s, about a factor of 2 larger than that of SW during the NuSTAR observation. Uncorrelated variability above and below 10 keV between the Suzaku and NuSTAR observations appears to support the double source interpretation. Variability in spectral hardness and Fe K line flux between the previous X-ray observations is also consistent with this picture.Comment: 6 pages, 5 figures, Accepted for publication in A&

Probing 5f-state configurations in URu2Si2 with U L3-edge resonant x-ray emission spectroscopy

Resonant x-ray emission spectroscopy (RXES) was employed at the U L3 absorption edge and the La1 emission line to explore the 5f occupancy, nf, and the degree of 5f orbital delocalization in the hidden order compound URu2Si2. By comparing to suitable reference materials such as UF4, UCd11, and alpha-U, we conclude that the 5f orbital in URu2Si2 is at least partially delocalized with nf = 2.87 +/- 0.08, and does not change with temperature down to 10 K within the estimated error. These results place further constraints on theoretical explanations of the hidden order, especially those requiring a localized f2 ground state.Comment: 11 pages,7 figure

Self-consistent Bulge/Disk/Halo Galaxy Dynamical Modeling Using Integral Field Kinematics

We introduce a method for modeling disk galaxies designed to take full advantage of data from integral field spectroscopy (IFS). The method fits equilibrium models to simultaneously reproduce the surface brightness, rotation, and velocity dispersion profiles of a galaxy. The models are fully self-consistent 6D distribution functions for a galaxy with a Sérsic profile stellar bulge, exponential disk, and parametric dark-matter halo, generated by an updated version of GalactICS. By creating realistic flux-weighted maps of the kinematic moments (flux, mean velocity, and dispersion), we simultaneously fit photometric and spectroscopic data using both maximum-likelihood and Bayesian (MCMC) techniques. We apply the method to a GAMA spiral galaxy (G79635) with kinematics from the SAMI Galaxy Survey and deep g- and r-band photometry from the VST-KiDS survey, comparing parameter constraints with those from traditional 2D bulge–disk decomposition. Our method returns broadly consistent results for shared parameters while constraining the mass-to-light ratios of stellar components and reproducing the H i-inferred circular velocity well beyond the limits of the SAMI data. Although the method is tailored for fitting integral field kinematic data, it can use other dynamical constraints like central fiber dispersions and H i circular velocities, and is well-suited for modeling galaxies with a combination of deep imaging and H i and/or optical spectra (resolved or otherwise). Our implementation (MagRite) is computationally efficient and can generate well-resolved models and kinematic maps in under a minute on modern processors

The SAMI Galaxy Survey: Unveiling the nature of kinematically offset active galactic nuclei

We have observed two kinematically offset active galactic nuclei (AGN), whose ionised gas is at a different line-of-sight velocity to their host galaxies, with the SAMI integral field spectrograph (IFS). One of the galaxies shows gas kinematics very different to the stellar kinematics, indicating a recent merger or accretion event. We demonstrate that the star formation associated with this event was triggered within the last 100 Myr. The other galaxy shows simple disc rotation in both gas and stellar kinematics, aligned with each other, but in the central region has signatures of an outflow driven by the AGN. Other than the outflow, neither galaxy shows any discontinuity in the ionised gas kinematics at the galaxy's centre. We conclude that in these two cases there is no direct evidence of the AGN being in a supermassive black hole binary system. Our study demonstrates that selecting kinematically offset AGN from single-fibre spectroscopy provides, by definition, samples of kinematically peculiar objects, but IFS or other data are required to determine their true nature.Comment: MNRAS accepted. 14 pages, 11 figure

The SAMI Galaxy Survey: Stellar population radial gradients in early-type galaxies

We study the internal radial gradients of the stellar populations in a sample comprising 522 early-type galaxies (ETGs) from the SAMI (Sydney- AAO Multi-object Integral field spectrograph) Galaxy Survey. We stack the spectra of individual spaxels in radial bins, and derive basic stellar population properties: total metallicity ([Z/H]), [Mg/Fe], [C/Fe] and age. The radial gradient ($\nabla$) and central value of the fits (evaluated at R$_e$/4) are compared against a set of six possible drivers of the trends. We find that velocity dispersion ($\sigma$) - or, equivalently gravitational potential - is the dominant driver of the chemical composition gradients. Surface mass density is also correlated with the trends, especially with stellar age. The decrease of $\nabla$[Mg/Fe] with increasing $\sigma$ is contrasted by a rather shallow dependence of $\nabla$[Z/H] with $\sigma$ (although this radial gradient is overall rather steep). This result, along with a shallow age slope at the massive end, imposes stringent constraints on the progenitors of the populations that contribute to the formation of the outer envelopes of ETGs. The SAMI sample is split between a 'field' sample and a cluster sample. Only weak environment-related differences are found, most notably a stronger dependence of central total metallicity ([Z/H]$_{e4}$) with $\sigma$, along with a marginal trend of $\nabla$[Z/H] to steepen in cluster galaxies, a result that is not followed by [Mg/Fe]. The results presented here serve as constraints on numerical models of the formation and evolution of ETGs.Comment: 14 pages, 9 figures, 3 tables. Submitted to MNRA

Star-forming Clumps in Local Luminous Infrared Galaxies

We present HST narrowband near-infrared imaging of Paα and Paβ emission of 48 local luminous infrared galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey. These data allow us to measure the properties of 810 spatially resolved star-forming regions (59 nuclei and 751 extranuclear clumps) and directly compare their properties to those found in both local and high-redshift star-forming galaxies. We find that in LIRGs the star-forming clumps have radii ranging from ~90 to 900 pc and star formation rates (SFRs) of ~1 × 10⁻³ to 10 M⊙ yr⁻¹, with median values for extranuclear clumps of 170 pc and 0.03 M⊙ yr⁻¹. The detected star-forming clumps are young, with a median stellar age of 8.7 Myr, and have a median stellar mass of 5 × 10⁵ M ⊙. The SFRs span the range of those found in normal local star-forming galaxies to those found in high-redshift star-forming galaxies at z = 1–3. The luminosity function of the LIRG clumps has a flatter slope than found in lower-luminosity, star-forming galaxies, indicating a relative excess of luminous star-forming clumps. In order to predict the possible range of star-forming histories and gas fractions, we compare the star-forming clumps to those measured in the MassiveFIRE high-resolution cosmological simulation. The star-forming clumps in MassiveFIRE cover the same range of SFRs and sizes found in the local LIRGs and have total gas fractions that extend from 10% to 90%. If local LIRGs are similar to these simulated galaxies, we expect that future observations with ALMA will find a large range of gas fractions, and corresponding star formation efficiencies, among the star-forming clumps in LIRGs

The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies

Using the stellar kinematic maps and ancillary imaging data from the Sydney AAO Multi Integral field (SAMI) Galaxy Survey, the intrinsic shape of kinematically-selected samples of galaxies is inferred. We implement an efficient and optimised algorithm to fit the intrinsic shape of galaxies using an established method to simultaneously invert the distributions of apparent ellipticities and kinematic misalignments. The algorithm output compares favourably with previous studies of the intrinsic shape of galaxies based on imaging alone and our re-analysis of the ATLAS3D data. Our results indicate that most galaxies are oblate axisymmetric. We show empirically that the intrinsic shape of galaxies varies as a function of their rotational support as measured by the "spin" parameter proxy Lambda_Re. In particular, low spin systems have a higher occurrence of triaxiality, while high spin systems are more intrinsically flattened and axisymmetric. The intrinsic shape of galaxies is linked to their formation and merger histories. Galaxies with high spin values have intrinsic shapes consistent with dissipational minor mergers, while the intrinsic shape of low-spin systems is consistent with dissipationless multi-merger assembly histories. This range in assembly histories inferred from intrinsic shapes is broadly consistent with expectations from cosmological simulations.Comment: 15 pages, 11 figures, MNRAS in prin

The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry

In order to determine the causes of kinematic asymmetry in the H$\alpha$ gas in the SAMI 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 ($\overline{v_{asym}}$) in nearby galaxies and environmental and stellar mass data from the GAMA survey. {We find that local environment, measured as distance to nearest neighbour, is inversely correlated with kinematic asymmetry for galaxies with $\mathrm{\log(M_*/M_\odot)}>10.0$, but there is no significant correlation for galaxies with $\mathrm{\log(M_*/M_\odot)}<10.0$. Moreover, low mass galaxies ($\mathrm{\log(M_*/M_\odot)}<9.0$) 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 $\frac{\sigma_{m}}{V}$ (where $\sigma_m$ is H$\alpha$ velocity dispersion and $V$ the rotation velocity), which is strongly correlated with $\overline{v_{asym}}$, and galaxies with $\log(M_*/M_\odot)<9.0$ have offset $\overline{\frac{\sigma_{m}}{V}}$ from the rest of the sample. Further, asymmetry as a fraction of dispersion decreases for galaxies with $\log(M_*/M_\odot)<9.0$. 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.Comment: 15 pages, 20 figure