Observations of galaxy isophotes, long-slit kinematics, and high-resolution photometry suggested a possible dichotomy between two distinct classes of elliptical galaxies. But these methods are ...expensive for large galaxy samples. Instead, integral field spectroscopy can efficiently recognize the shape, dynamics, and stellar population of complete samples of early-type galaxies (ETGs). These studies showed that the two main classes, the fast and slow rotators, can be separated using stellar kinematics. I show that there is a dichotomy in the dynamics of the two classes. The slow rotators are weakly triaxial and dominate above
. Below
M
crit
, the structure of fast rotators parallels that of spiral galaxies. There is a smooth sequence along which the age, the metal content, the enhancement in α-elements, and the weight of the stellar initial mass function all increase with the central mass density slope, or bulge mass fraction, while the molecular gas fraction correspondingly decreases. The properties of ETGs on galaxy scaling relations, in particular the
diagram, and their dependence on environment, indicate two main independent channels for galaxy evolution. Fast-rotator ETGs start as star-forming disks and evolve through a channel dominated by gas accretion, bulge growth, and quenching, whereas slow rotators assemble near the centers of massive halos via intense star formation at high redshift and remain as such for the rest of their evolution via a channel dominated by gas poor mergers. This is consistent with independent studies of the galaxies redshift evolution.
We present a simple and efficient anisotropic generalization of the semi-isotropic (two-integral) axisymmetric Jeans formalism, which is used to model the stellar kinematics of galaxies. The ...following is assumed: (i) a constant mass-to-light ratio (M/L) and (ii) a velocity ellipsoid that is aligned with cylindrical coordinates (R, z) and characterized by the classic anisotropy parameter . Our simple models are fit to SAURON integral-field observations of the stellar kinematics for a set of fast-rotator early-type galaxies. With only two free parameters (βz and the inclination), the models generally provide remarkably good descriptions of the shape of the first (V) and second () velocity moments, once a detailed description of the surface brightness is given. This is consistent with previous findings on the dynamical structure of these objects. With the observationally motivated assumption that βz≳ 0, the method is able to recover the inclination. The technique can be used to determine the dynamical M/L and angular momenta of early-type fast-rotators and spiral galaxies, especially when the quality of the data does not justify more sophisticated modelling approaches. This formalism allows for the inclusion of dark matter, supermassive black holes, spatially varying anisotropy and multiple kinematic components.
I start by providing an updated summary of the penalized pixel-fitting (ppxf) method that is used to extract the stellar and gas kinematics, as well as the stellar population of galaxies, via full ...spectrum fitting. I then focus on the problem of extracting the kinematics when the velocity dispersion ... is smaller than the velocity sampling Delta V that is generally, by design, close to the instrumental dispersion sigma sub( inst). The standard approach consists of convolving templates with a discretized kernel, while fitting for its parameters. This is obviously very inaccurate when sigma ... Delta V/2, due to undersampling. Oversampling can prevent this, but it has drawbacks. Here I present a more accurate and efficient alternative. It avoids the evaluation of the undersampled kernel and instead directly computes its well-sampled analytic Fourier transform, for use with the convolution theorem. A simple analytic transform exists when the kernel is described by the popular Gauss-Hermite parametrization (which includes the Gaussian as special case) for the line-of-sight velocity distribution. I describe how this idea was implemented in a significant upgrade to the publicly available ppxf software. The key advantage of the new approach is that it provides accurate velocities regardless of ... This is important e.g. for spectroscopic surveys targeting galaxies with sigma << sigma sub( inst), for galaxy redshift determinations or for measuring line-of-sight velocities of individual stars. The proposed method could also be used to fix Gaussian convolution algorithms used in today's popular software packages. (ProQuest: ... denotes formulae/symbols omitted.)
We study trends in the slope of the total mass profiles and dark matter fractions within the central half-light radius of 258 early-type galaxies, using data from the volume-limited ATLAS3D survey. ...We use three distinct sets of dynamical models, which vary in their assumptions and also allow for spatial variations in the stellar mass-to-light ratio, to test the robustness of our results. We confirm that the slopes of the total mass profiles are approximately isothermal, and investigate how the total mass slope depends on various galactic properties. The most statistically significant correlations we find are a function of either surface density, Σe, or velocity dispersion, σe. However there is evidence for a break in the latter relation, with a nearly universal logarithmic slope above log10σe/(km s−1) ∼ 2.1 and a steeper trend below this value. For the 142 galaxies above that critical σe value, the total mass–density logarithmic slopes have a mean value 〈γ΄〉 = −2.193 ± 0.016 (1σ error) with an observed rms scatter of only $\sigma _{\gamma ^\prime }=0.168\pm 0.015$. Considering the observational errors, we estimate an intrinsic scatter of $\sigma _{\gamma ^\prime }^\mathrm{intr} \approx 0.15$. These values are broadly consistent with those found by strong lensing studies at similar radii and agree, within the tight errors, with values recently found at much larger radii via stellar dynamics or H i rotation curves (using significantly smaller samples than this work).
We investigate the accuracy of the parametric recovery of the line‐of‐sight velocity distribution (LOSVD) of the stars in a galaxy while working in pixel space. Problems appear when the data have a ...low signal‐to‐noise ratio or the observed LOSVD is not well sampled by the data. We propose a simple solution based on maximum penalized likelihood, and we apply it to the common situation in which the LOSVD is described by a Gauss‐Hermite series. We compare different techniques by extracting the stellar kinematics from observations of the barred lenticular galaxy NGC 3384 obtained with the SAURON integral‐field spectrograph.
ABSTRACT
I present a flexible solution for the axisymmetric Jeans equations of stellar hydrodynamics under the assumption of an anisotropic (three-integral) velocity ellipsoid aligned with the ...spherical polar coordinate system. I describe and test a robust and efficient algorithm for its numerical computation. I outline the evaluation of the intrinsic velocity moments and the projection of all first and second velocity moments, including both the line-of-sight velocities and the proper motions. This spherically aligned Jeans anisotropic modelling (JAMsph) method can describe in detail the photometry and kinematics of real galaxies. It allows for a spatially varying anisotropy, or stellar mass-to-light ratio gradients, as well as for the inclusion of general dark matter distributions and supermassive black holes. The JAMsph method complements my previously derived cylindrically aligned JAMcyl and spherical Jeans solutions, which I also summarize in this paper. Comparisons between results obtained with either JAMsph or JAMcyl can be used to assess the robustness of inferred dynamical quantities. As an illustration, I modelled the ATLAS3D sample of 260 early-type galaxies with high-quality integral-field spectroscopy, using both methods. I found that they provide statistically indistinguishable total density logarithmic slopes. This may explain the previously reported success of the JAM method in recovering density profiles of real or simulated galaxies. A reference software implementation of JAMsph is included in the publicly available jam software package.
SDSS-IV MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is the largest integral-field unit (IFU) spectroscopy survey to date, aiming to observe a statistically representative sample of ...10,000 low-redshift galaxies. In this paper, we study the reliability of the emission-line fluxes and kinematic properties derived by the MaNGA Data Analysis Pipeline (DAP). We describe the algorithmic choices made in the DAP with regards to measuring emission-line properties, and the effect of our adopted strategy of simultaneously fitting the continuum and line emission. The effects of random errors are quantified by studying various fit-quality metrics, idealized recovery simulations, and repeat observations. This analysis demonstrates that the emission lines are well fit in the vast majority of the MaNGA data set and the derived fluxes and errors are statistically robust. The systematic uncertainty on emission-line properties introduced by the choice of continuum templates is also discussed. In particular, we test the effect of using different stellar libraries and simple stellar-population models on the derived emission-line fluxes and the effect of introducing different tying prescriptions for the emission-line kinematics. We show that these effects can generate large (>0.2 dex) discrepancies at low signal-to-noise ratio and for lines with low equivalent width (EW); however, the combined effect is noticeable even for H EW > 6 . We provide suggestions for optimal use of the data provided by SDSS data release 15 and propose refinements on the DAP for future MaNGA data releases.
ABSTRACT
I introduce some improvements to the ppxf method, which measures the stellar and gas kinematics, star formation history (SFH) and chemical composition of galaxies. I describe the new ...optimization algorithm that ppxf uses and the changes I made to fit both spectra and photometry simultaneously. I apply the updated ppxf method to a sample of 3200 galaxies at redshift 0.6 < z < 1 (median z = 0.76, stellar mass $M_\ast \gtrsim 3\times 10^{10}$ M⊙), using spectroscopy from the LEGA-C survey (DR3) and 28-bands photometry from two different sources. I compare the masses from new JAM dynamical models with the ppxf stellar population M* and show the latter are more reliable than previous estimates. I use three different stellar population synthesis (SPS) models in ppxf and both photometric sources. I confirm the main trend of the galaxies’ global ages and metallicity M/H with stellar velocity dispersion σ* (or central density), but I also find that M/H depends on age at fixed σ*. The SFHs reveal a sharp transition from star formation to quenching for galaxies with $\lg (\sigma _\ast /\mathrm{km}\, s^{-1})\gtrsim 2.3$ ($\sigma _\ast \gtrsim 200$$\mathrm{km}\, s^{-1}$), or average mass density within 1 kpc $\lg (\Sigma _1^{\rm JAM}/\mathrm{\mathrm{M}_{\odot }kpc^{-2}})\gtrsim 9.9$ ($\Sigma _1^{\rm JAM}\gtrsim 7.9\times 10^9\, \mathrm{\mathrm{M}_{\odot }\ kpc^{-2}}$), or with $M/H\gtrsim -0.1$, or with Sersic index $\lg n_{\rm Ser}\gtrsim 0.5$ ($n_{\rm Ser}\gtrsim 3.2$). However, the transition is smoother as a function of M*. These results are consistent for two SPS models and both photometric sources, but they differ significantly from the third SPS model, which demonstrates the importance of comparing model assumptions.
We demonstrate that the comparison of Tully–Fisher relations (TFRs) derived from global H i linewidths to TFRs derived from the circular-velocity profiles of dynamical models (or stellar kinematic ...observations corrected for asymmetric drift) is vulnerable to systematic and uncertain biases introduced by the different measures of rotation used. We therefore argue that to constrain the relative locations of the TFRs of spiral and S0 galaxies, the same tracer and measure must be used for both samples. Using detailed near-infrared imaging and the circular velocities of axisymmetric Jeans models of 14 nearby edge-on Sa–Sb spirals and 14 nearby edge-on S0s drawn from a range of environments, we find that S0s lie on a TFR with the same slope as the spirals, but are on average 0.53 ± 0.15 mag fainter at KS band at a given rotational velocity. This is a significantly smaller offset than that measured in earlier studies of the S0 TFR, which we attribute to our elimination of the bias associated with using different rotation measures and our use of earlier-type spirals as a reference. Since our measurement of the offset avoids systematic biases, it should be preferred to previous estimates. A spiral stellar population in which star formation is truncated would take ≈1 Gyr to fade by 0.53 mag at KS band. If S0s are the products of a simple truncation of star formation in spirals, then this finding is difficult to reconcile with the observed evolution of the spiral/S0 fraction with redshift. Recent star formation could explain the observed lack of fading in S0s, but the offset of the S0 TFR persists as a function of both stellar and dynamical mass. We show that the offset of the S0 TFR could therefore be explained by a systematic difference between the total mass distributions of S0s and spirals, in the sense that S0s need to be smaller or more concentrated than spirals.
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