Abstract
The fraction of galaxies supported by internal rotation compared to galaxies stabilized by internal pressure provides a strong constraint on galaxy formation models. In integral field ...spectroscopy surveys, this fraction is biased because survey instruments typically only trace the inner parts of the most massive galaxies. We present aperture corrections for the two most widely used stellar kinematic quantities V/σ and λR (spin parameter proxy). Our demonstration involves integral field data from the SAMI (Sydney-AAO Multi-object Integral-field spectrograph) Galaxy Survey and the ATLAS3D survey. We find a tight relation for both V/σ and λR when measured in different apertures that can be used as a linear transformation as a function of radius, i.e. a first-order aperture correction. In degraded seeing, however, the aperture corrections are more significant as the steeper inner profile is more strongly affected by the point spread function than the outskirts. We find that V/σ and λR radial growth curves are well approximated by second-order polynomials. By only fitting the inner profile (0.5Re), we successfully recover the profile out to one Re if a constraint between the linear and quadratic parameter in the fit is applied. However, the aperture corrections for V/σ and λR derived by extrapolating the profiles perform as well as applying a first-order correction. With our aperture-corrected λR measurements, we find that the fraction of slow rotating galaxies increases with stellar mass. For galaxies with log M*/M⊙ > 11, the fraction of slow rotators is 35.9 ± 4.3 per cent, but is underestimated if galaxies without coverage beyond one Re are not included in the sample (24.2 ± 5.3 per cent). With measurements out to the largest aperture radius, the slow rotator fraction is similar as compared to using aperture-corrected values (38.3 ± 4.4 per cent). Thus, aperture effects can significantly bias stellar kinematic integral field spectrograph studies, but this bias can now be removed with the method outlined here.
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 the Sydney-AAO Multi-object Integral field spectrograph (SAMI) and the Wide Field Spectrograph, we study the nature of an isolated disc galaxy, SDSS J090005.05+000446.7 (z = 0.053 86). In the integral field data sets, 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 H ii regions, (2) a broad kinematic component consistent with shock excitation, and (3) an intermediate component consistent with shock excitation and photoionization 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 photoionization 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 photoionization 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.
Abstract
We investigate the energy sources of random turbulent motions of ionized gas from H α emission in eight local star-forming galaxies from the Sydney-AAO Multi-object Integral field ...spectrograph (SAMI) Galaxy Survey. These galaxies satisfy strict pure star-forming selection criteria to avoid contamination from active galactic nuclei (AGNs) or strong shocks/outflows. Using the relatively high spatial and spectral resolution of SAMI, we find that – on sub-kpc scales, our galaxies display a flat distribution of ionized gas velocity dispersion as a function of star formation rate (SFR) surface density. A major fraction of our SAMI galaxies shows higher velocity dispersion than predictions by feedback-driven models, especially at the low SFR surface density end. Our results suggest that additional sources beyond star formation feedback contribute to driving random motions of the interstellar medium in star-forming galaxies. We speculate that gravity, galactic shear and/or magnetorotational instability may be additional driving sources of turbulence 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 |$z$| ∼ 0 from the eagle, hydrangea, horizon-agn, and magneticum simulations with integral field spectroscopic (IFS) data from the SAMI (Sydney-AAO Multi-object Integral field spectrograph) Galaxy Survey, ATLAS^3D, CALIFA (Calar Alto Legacy Integral Field Area), 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, and we construct samples that match the observed stellar mass distribution for the combined IFS sample. 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 (+), ε (−), σ_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 (+), ε (−), σ_e (−), and (V/σ)_e (−). magneticum matches observations well: this is the only simulation where we find ellipticities typical for disc galaxies, but there are moderate differences in σ_e (−), (V/σ)_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 disc structure, yet our results demonstrate the vast improvement of cosmological simulations in recent years.
We use data from the Galaxy And Mass Assembly (GAMA) survey in the redshift range 0.01 < z < 0.1 (8399 galaxies in g to Ks bands) to derive the stellar mass-half-light radius relations for various ...divisions of 'early'- and 'late'-type samples. We find that the choice of division between early and late (i.e. colour, shape, morphology) is not particularly critical; however, the adopted mass limits and sample selections (i.e. the careful rejection of outliers and use of robust fitting methods) are important. In particular, we note that for samples extending to low stellar mass limits (...) the Sersic index bimodality, evident for high-mass systems, becomes less distinct and no-longer acts as a reliable separator of early- and late-type systems. The final set of stellar mass-half-light radius relations are reported for a variety of galaxy population subsets in 10 bands (ugrizZY JHKs) and are intended to provide a comprehensive low-z benchmark for the many ongoing high-z studies. Exploring the variation of the stellar mass-half-light radius relations with wavelength, we confirm earlier findings that galaxies appear more compact at longer wavelengths albeit at a smaller level than previously noted: at ... both spiral systems and ellipticals show a decrease in size of 13 per cent from g to Ks (which is near linear in log wavelength). Finally, we note that the sizes used in this work are derived from 2D Sersic light profile fitting (using galfit3), i.e. elliptical semimajor half-light radii, improving on earlier low-z benchmarks based on circular apertures. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
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 (∇) and central value of the fits (evaluated at Re/4) are compared against a set of six observables that may act as drivers of the trends. We find that velocity dispersion (σ) – 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 ∇Mg/Fe with increasing σ is contrasted by a rather shallow dependence of ∇Z/H with σ (although this radial gradient is overall rather steep). This result, along with a shallow age slope at the massive end, imposes a substantial constraint on the progenitors of the populations that contribute to the formation of the outer envelopes of ETGs. The SAMI sample is split, by design, between ‘field’ and cluster galaxies. Only weak environment-related differences are found, most notably a stronger dependence of central total metallicity (Z/He4) with σ, along with a marginal trend of ∇Z/H to steepen in cluster galaxies, a result that is not followed by Mg/Fe. The results presented here serve as stringent constraints on numerical models of the formation and evolution of ETGs.
ABSTRACT Recent cosmological hydrodynamical simulations suggest that integral field spectroscopy can connect the high-order stellar kinematic moments h3 (∼skewness) and h4 (∼kurtosis) in galaxies to ...their cosmological assembly history. Here, we assess these results by measuring the stellar kinematics on a sample of 315 galaxies, without a morphological selection, using two-dimensional integral field data from the SAMI Galaxy Survey. Proxies for the spin parameter ( ) and ellipticity ( ) are used to separate fast and slow rotators; there exists a good correspondence to regular and non-regular rotators, respectively, as also seen in earlier studies. We confirm that regular rotators show a strong h3 versus anti-correlation, whereas quasi-regular and non-regular rotators show a more vertical relation in h3 and . Motivated by recent cosmological simulations, we develop an alternative approach to kinematically classify galaxies from their individual h3 versus signatures. Within the SAMI Galaxy Survey, we identify five classes of high-order stellar kinematic signatures using Gaussian mixture models. Class 1 corresponds to slow rotators, whereas Classes 2-5 correspond to fast rotators. We find that galaxies with similar values can show distinctly different signatures. Class 5 objects are previously unidentified fast rotators that show a weak h3 versus anti-correlation. From simulations, these objects are predicted to be disk-less galaxies formed by gas-poor mergers. From morphological examination, however, there is evidence for large stellar disks. Instead, Class 5 objects are more likely disturbed galaxies, have counter-rotating bulges, or bars in edge-on galaxies. Finally, we interpret the strong anti-correlation in h3 versus as evidence for disks in most fast rotators, suggesting a dearth of gas-poor mergers among fast rotators.
We examine the kinematic morphology of early-type galaxies (ETGs) in three galaxy clusters Abell 85, 168 and 2399. Using data from the Sydney-AAO Multi-object Integral field spectrograph we measure ...spatially resolved kinematics for 79 ETGs in these clusters. We calculate λ
R
, a proxy for the projected specific stellar angular momentum, for each galaxy and classify the 79 ETGs in our samples as fast or slow rotators. We calculate the fraction of slow rotators in the ETG populations (f
SR) of the clusters to be 0.21 ± 0.08, 0.08 ± 0.08 and 0.12 ± 0.06 for Abell 85, 168 and 2399, respectively, with an overall fraction of 0.15 ± 0.04. These numbers are broadly consistent with the values found in the literature, confirming recent work asserting that the fraction of slow rotators in the ETG population is constant across many orders of magnitude in global environment. We examine the distribution of kinematic classes in each cluster as a function of environment using the projected density of galaxies: the kinematic morphology–density relation. We find that in Abell 85 f
SR increases in higher density regions but in Abell 168 and 2399 this trend is not seen. We examine the differences between the individual clusters to explain this. In addition, we find slow rotators on the outskirts of two of the clusters studied, Abell 85 and 2399. These galaxies reside in intermediate to low density regions and have clearly not formed at the centre of a cluster environment. We hypothesize that they formed at the centres of groups and are falling into the clusters for the first time.
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.
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