We investigate a sample of 40 local, main-sequence, edge-on disc galaxies using integral field spectroscopy with the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey to ...understand the link between properties of the extraplanar gas and their host galaxies. The kinematics properties of the extraplanar gas, including velocity asymmetries and increased dispersion, are used to differentiate galaxies hosting large-scale galactic winds from those dominated by the extended diffuse ionized gas. We find rather that a spectrum of diffuse gas-dominated to wind-dominated galaxies exist. The wind-dominated galaxies span a wide range of star formation rates (SFRs; −1 ≲ log (SFR/M⊙ yr−1) ≲ 0.5) across the whole stellar mass range of the sample (8.5 ≲ log (M
*/M⊙) ≲ 11). The wind galaxies also span a wide range in SFR surface densities (10− 3–10− 1.5 M⊙ yr− 1 kpc− 2) that is much lower than the canonical threshold of 0.1 M⊙ yr− 1 kpc− 2. The wind galaxies on average have higher SFR surface densities and higher HδA values than those without strong wind signatures. The enhanced HδA indicates that bursts of star formation in the recent past are necessary for driving large-scale galactic winds. We demonstrate with Sloan Digital Sky Survey data that galaxies with high SFR surface density have experienced bursts of star formation in the recent past. Our results imply that the galactic winds revealed in our study are indeed driven by bursts of star formation, and thus probing star formation in the time domain is crucial for finding and understanding galactic winds.
We use integral-field spectroscopy from the SAMI Galaxy Survey to identify galaxies that show evidence of recent quenching of star formation. The galaxies exhibit strong Balmer absorption in the ...absence of ongoing star formation in more than 10% of their spectra within the SAMI field of view. These -strong (HDS) galaxies (HDSGs) are rare, making up only ∼2% (25/1220) of galaxies with stellar mass > 10. The HDSGs make up a significant fraction of nonpassive cluster galaxies (15%; 17/115) and a smaller fraction (2.0%; 8/387) of the nonpassive population in low-density environments. The majority (9/17) of cluster HDSGs show evidence of star formation at their centers, with the HDS regions found in the outer parts of the galaxy. Conversely, the HDS signal is more evenly spread across the galaxy for the majority (6/8) of HDSGs in low-density environments and is often associated with emission lines that are not due to star formation. We investigate the location of the HDSGs in the clusters, finding that they are exclusively within 0.6R200 of the cluster center and have a significantly higher velocity dispersion relative to the cluster population. Comparing their distribution in projected phase space to those derived from cosmological simulations indicates that the cluster HDSGs are consistent with an infalling population that has entered the central 0.5r200,3D cluster region within the last ∼1 Gyr. In the eight of nine cluster HDSGs with central star formation, the extent of star formation is consistent with that expected of outside-in quenching by ram pressure stripping. Our results indicate that the cluster HDSGs are currently being quenched by ram pressure stripping on their first passage through the cluster.
Abstract
We present the ∼800 star formation rate maps for the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey based on H α 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/H β, N ii/H α, S ii/H α, and O i/H α 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 >3σ 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.
ABSTRACT
Dwarf ellipticals are the most common galaxy type in cluster environments; however, the challenges associated with their observation mean that their formation mechanisms are still poorly ...understood. To address this, we present deep integral field observations of a sample of 31 low-mass (107.5 < M⋆ < 109.5 M⊙) early-type galaxies in the Fornax cluster with the SAMI instrument. For 21 galaxies, our observations are sufficiently deep to construct spatially resolved maps of the stellar velocity and velocity dispersion – for the remaining galaxies, we extract global velocities and dispersions from aperture spectra only. From the kinematic maps, we measure the specific stellar angular momentum λR of the lowest mass dE galaxies to date. Combining our observations with early-type galaxy data from the literature spanning a large range in stellar mass, we find that λR decreases towards lower stellar mass, with a corresponding increase in the proportion of slowly rotating galaxies in this regime. The decrease of λR with mass in our sample dE galaxies is consistent with a similar trend seen in somewhat more massive spiral galaxies from the CALIFA survey. This suggests that the degree of dynamical heating required to produce dEs from low-mass starforming progenitors may be relatively modest and consistent with a broad range of formation mechanisms.
ABSTRACT
We study the Fundamental Plane (FP) for a volume- and luminosity-limited sample of 560 early-type galaxies from the SAMI survey. Using r-band sizes and luminosities from new multi-Gaussian ...expansion photometric measurements, and treating luminosity as the dependent variable, the FP has coefficients a = 1.294 ± 0.039, b = 0.912 ± 0.025, and zero-point c = 7.067 ± 0.078. We leverage the high signal-to-noise ratio of SAMI integral field spectroscopy, to determine how structural and stellar population observables affect the scatter about the FP. The FP residuals correlate most strongly (8σ significance) with luminosity-weighted simple stellar population (SSP) age. In contrast, the structural observables surface mass density, rotation-to-dispersion ratio, Sérsic index, and projected shape all show little or no significant correlation. We connect the FP residuals to the empirical relation between age (or stellar mass-to-light ratio Υ⋆ ) and surface mass density, the best predictor of SSP age amongst parameters based on FP observables. We show that the FP residuals (anti)correlate with the residuals of the relation between surface density and Υ⋆ . This correlation implies that part of the FP scatter is due to the broad age and Υ⋆ distribution at any given surface mass density. Using virial mass and Υ⋆, we construct a simulated FP and compare it to the observed FP. We find that, while the empirical relations between observed stellar population relations and FP observables are responsible for most (75 per cent) of the FP scatter, on their own they do not explain the observed tilt of the FP away from the virial plane.
Abstract
Dynamical models are crucial for uncovering the internal dynamics of galaxies; however, most of the results to date assume axisymmetry, which is not representative of a significant fraction ...of massive galaxies. Here, we build triaxial Schwarzschild orbit-superposition models of galaxies taken from the SAMI Galaxy Survey, in order to reconstruct their inner orbital structure and mass distribution. The sample consists of 161 passive galaxies with total stellar masses in the range 10
9.5
–10
12
M
⊙
. We find that the changes in internal structures within 1
R
e
are correlated with the total stellar mass of the individual galaxies. The majority of the galaxies in the sample (73% ± 3%) are oblate, while 19% ± 3% are mildly triaxial and 8% ± 2% have triaxial/prolate shape. Galaxies with
log
M
⋆
/
M
⊙
>
10.50
are more likely to be non-oblate. We find a mean dark matter fraction of
f
DM
= 0.28 ± 0.20, within 1
R
e
. Galaxies with higher intrinsic ellipticity (flatter) are found to have more negative velocity anisotropy
β
r
(tangential anisotropy).
β
r
also shows an anticorrelation with the edge-on spin parameter
λ
Re
,
EO
, so that
β
r
decreases with increasing
λ
Re
,
EO
, reflecting the contribution from disk-like orbits in flat, fast-rotating galaxies. We see evidence of an increasing fraction of hot orbits with increasing stellar mass, while warm and cold orbits show a decreasing trend. We also find that galaxies with different (
V
/
σ
–
h
3
) kinematic signatures have distinct combinations of orbits. These results are in agreement with a formation scenario in which slow- and fast-rotating galaxies form through two main channels.
ABSTRACT
We investigate changes in stellar population age and metallicity (Z/H) scaling relations for quiescent galaxies from intermediate redshift (0.60 ≤ $z$ ≤ 0.76) using the LEGA-C Survey to low ...redshift (0.014 ≤ $z$ ≤ 0.10) using the SAMI Galaxy Survey. Specifically, we study how the spatially integrated global age and metallicity of individual quiescent galaxies vary in the mass–size plane, using the stellar mass M* and a dynamical mass proxy derived from the virial theorem MD ∝ σ2 Re. We find that, similarly to at low redshift, the metallicity of quiescent galaxies at 0.60 ≤ $z$ ≤ 0.76 closely correlates with M/Re (a proxy for the gravitational potential or escape velocity), in that galaxies with deeper potential wells are more metal-rich. This supports the hypothesis that the relation arises due to the gravitational potential regulating the retention of metals by determining the escape velocity for metal-rich stellar and supernova ejecta to escape the system and avoid being recycled into later stellar generations. Conversely, we find no correlation between age and surface density ($M/R_\mathrm{e}^2$) at 0.60 ≤ $z$ ≤ 0.76, despite this relation being strong at low redshift. We consider this change in the age–$M/R_\mathrm{e}^2$ relation in the context of the redshift evolution of the star-forming and quiescent mass–size relations, and find our results are consistent with galaxies forming more compactly at higher redshifts and remaining compact throughout their evolution. Furthermore, galaxies appear to quench at a characteristic surface density that decreases with decreasing redshift. The $z$ ∼ 0 age–$M/R_\mathrm{e}^2$ relation is therefore a result of building up the quiescent and star-forming populations with galaxies that formed at a range of redshifts and therefore a range of surface densities.
The well-established correlations between the mass of a galaxy and the properties of its stars are considered to be evidence for mass driving the evolution of the stellar population (SP). However, ...for early-type galaxies (ETGs), we find that g − i color and stellar metallicity Z/H correlate more strongly with gravitational potential Φ than with mass M, whereas SP age correlates best with surface density . Specifically, for our sample of 625 ETGs with integral-field spectroscopy from the Sydney-AAO Multi-object Integral-field Galaxy Survey, compared to correlations with mass, the color-Φ, Z/H-Φ, and age- relations show both a smaller scatter and a lower residual trend with galaxy size. For the star formation duration proxy /Fe, we find comparable results for trends with Φ and , with both being significantly stronger than the /Fe-M relation. In determining the strength of a trend, we analyze both the overall scatter, and the observational uncertainty on the parameters, in order to compare the intrinsic scatter in each correlation. These results lead us to the following inferences and interpretations: (1) the color-Φ diagram is a more precise tool for determining the developmental stage of the SP than the conventional color-mass diagram; and (2) gravitational potential is the primary regulator of global stellar metallicity, via its relation to the gas escape velocity. Furthermore, we propose the following two mechanisms for the age and /Fe relations with : (a) the age- and /Fe- correlations arise as results of compactness-driven quenching mechanisms; and/or (b) as fossil records of the relation in their disk-dominated progenitors.
ABSTRACT
We use the SAMI Galaxy Survey to examine the drivers of galaxy spin, $\lambda _{R_{\rm e}}$, in a multidimensional parameter space including stellar mass, stellar population age (or specific ...star formation rate), and various environmental metrics (local density, halo mass, satellite versus central). Using a partial correlation analysis, we consistently find that age or specific star formation rate is the primary parameter correlating with spin. Light-weighted age and specific star formation rate are more strongly correlated with spin than mass-weighted age. In fact, across our sample, once the relation between light-weighted age and spin is accounted for, there is no significant residual correlation between spin and mass, or spin and environment. This result is strongly suggestive that the present-day environment only indirectly influences spin, via the removal of gas and star formation quenching. That is, environment affects age, then age affects spin. Older galaxies then have lower spin, either due to stars being born dynamically hotter at high redshift, or due to secular heating. Our results appear to rule out environmentally dependent dynamical heating (e.g. galaxy–galaxy interactions) being important, at least within 1 Re where our kinematic measurements are made. The picture is more complex when we only consider high-mass galaxies (M* ≳ 1011 M⊙). While the age-spin relation is still strong for these high-mass galaxies, there is a residual environmental trend with central galaxies preferentially having lower spin, compared to satellites of the same age and mass. We argue that this trend is likely due to central galaxies being a preferred location for mergers.
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