The SAMI Galaxy Survey: understanding observations of large-scale outflows at low redshift with EAGLE simulations

This work presents a study of galactic outflows driven by stellar feedback. We extract main-sequence disc galaxies with stellar mass 10^9 ≤ M⋆/ M⊙ ≤ 5.7 × 10^(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 (σ) maps are created and compared to observations of disc galaxies obtained with the Sydney-AAO (Australian Astronomical Observatory) Multi-object Integral field spectrograph (SAMI), where σ-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 (Σ_(SFR)), with low-M⋆/low-Σ_(SFR) galaxies showing a narrow peak at low σ (∼30 km s^(−1)) and more active, high-M⋆/high-Σ_(SFR) galaxies reaching σ > 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 σ-distribution. The following equivalence relations hold in EAGLE: (i) low-σ peak  ⇔ disc of the galaxy  ⇔ gas with T <10^5 K; (ii) high-σ tail  ⇔ galactic winds  ⇔ gas with T ≥10^5 K

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

KROSS–SAMI: a direct IFS comparison of the Tully–Fisher relation across 8 Gyr since z ≈ 1

We construct Tully–Fisher relations (TFRs), from large samples of galaxies with spatially resolved H α emission maps from the K-band Multi-Object Spectrograph (KMOS) Redshift One Spectroscopic Survey (KROSS) at z ≈ 1. We compare these to data from the Sydney-Australian-Astronomical-Observatory Multi-object Integral-Field Spectrograph (SAMI) Galaxy Survey at z ≈ 0. We stringently match the data quality of the latter to the former, and apply identical analysis methods and sub-sample selection criteria to both to conduct a direct comparison of the absolute K-band magnitude and stellar mass TFRs at z ≈ 1 and 0. We find that matching the quality of the SAMI data to that of KROSS results in TFRs that differ significantly in slope, zero-point, and (sometimes) scatter in comparison to the corresponding original SAMI relations. These differences are in every case as large as or larger than the differences between the KROSS z ≈ 1 and matched SAMI z ≈ 0 relations. Accounting for these differences, we compare the TFRs at z ≈ 1 and 0. For disc-like, star-forming galaxies we find no significant difference in the TFR zero-points between the two epochs. This suggests the growth of stellar mass and dark matter in these types of galaxies is intimately linked over this ≈8 Gyr period

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

Using an artificial neural network to classify multicomponent emission lines with integral field spectroscopy from SAMI and S7

Integral field spectroscopy (IFS) surveys are changing how we study galaxies and are creating vastly more spectroscopic data available than before. The large number of resulting spectra makes visual inspection of emission line fits an infeasible option. Here, we present a demonstration of an artificial neural network (ANN) that determines the number of Gaussian components needed to describe the complex emission line velocity structures observed in galaxies after being fit with LZIFU. We apply our ANN to IFS data for the S7 survey, conducted using the Wide Field Spectrograph on the ANU 2.3 m Telescope, and the SAMI Galaxy Survey, conducted using the SAMI instrument on the 4 m Anglo-Australian Telescope. We use the spectral fitting code LZIFU (Ho et al. 2016a) to fit the emission line spectra of individual spaxels from S7 and SAMI data cubes with 1-, 2- and 3-Gaussian components. We demonstrate that using an ANN is comparable to astronomers performing the same visual inspection task of determining the best number of Gaussian components to describe the physical processes in galaxies. The advantage of our ANN is that it is capable of processing the spectra for thousands of galaxies in minutes, as compared to the years this task would take individual astronomers to complete by visual inspection

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&

The SAMI Galaxy Survey: understanding observations of large-scale outflows at low redshift with EAGLE simulations

This work presents a study of galactic outflows driven by stellar feedback. We extract main-sequence disc galaxies with stellar mass 10^9 ≤ M⋆/ M⊙ ≤ 5.7 × 10^(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 (σ) maps are created and compared to observations of disc galaxies obtained with the Sydney-AAO (Australian Astronomical Observatory) Multi-object Integral field spectrograph (SAMI), where σ-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 (Σ_(SFR)), with low-M⋆/low-Σ_(SFR) galaxies showing a narrow peak at low σ (∼30 km s^(−1)) and more active, high-M⋆/high-Σ_(SFR) galaxies reaching σ > 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 σ-distribution. The following equivalence relations hold in EAGLE: (i) low-σ peak  ⇔ disc of the galaxy  ⇔ gas with T <10^5 K; (ii) high-σ tail  ⇔ galactic winds  ⇔ gas with T ≥10^5 K

Shocked Gas in IRAS F17207-0014: ISM Collisions and Outflows

We combine optical and near-infrared AO-assisted integral field observations of the merging ULIRG IRAS F17207-0014 from the Wide-Field Spectrograph (WiFeS) and Keck/OSIRIS. The optical emission line ratios [N II]/H$\alpha$, [S II]/H$\alpha$, and [O I]/H$\alpha$ reveal a mixing sequence of shocks present throughout the galaxy, with the strongest contributions coming from large radii (up to 100% at $\sim$5 kpc in some directions), suggesting galactic-scale winds. The near-infrared observations, which have approximately 30 times higher spatial resolution, show that two sorts of shocks are present in the vicinity of the merging nuclei: low-level shocks distributed throughout our field-of-view evidenced by an H$_{2}$/Br$\gamma$ line ratio of $\sim$0.6-4, and strong collimated shocks with a high H$_{2}$/Br$\gamma$ line ratio of $\sim$4-8, extending south from the two nuclear disks approximately 400 pc ($\sim$0.5 arcsec). Our data suggest that the diffuse shocks are caused by the collision of the interstellar media associated with the two progenitor galaxies and the strong shocks trace the base of a collimated outflow coming from the nucleus of one of the two disks.Comment: accepted to MNRA

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