Parallel-sequencing of early-type and spiral galaxies

Since Edwin Hubble introduced his famous tuning fork diagram more than 70 years ago, spiral galaxies and early-type galaxies (ETGs) have been regarded as two distinct families. The spirals are characterized by the presence of disks of stars and gas in rapid rotation, while the early-types are gas poor and described as spheroidal systems, with less rotation and often non-axisymmetric shapes. The separation is physically relevant as it implies a distinct path of formation for the two classes of objects. I will give an overview of recent findings, from independent teams, that motivated a radical revision to Hubble's classic view of ETGs. These results imply a much closer link between spiral galaxies and ETGs than generally assumed.Comment: 1 page, 1 figure, LaTeX. Invited talk to the Special Session 3 "Galaxy Evolution Through Secular Processes". To appear in Highlights of Astronomy, Vol. 16, Proc. of the XXVIII IAU General Assembly, Beijing, China, August 2012, ed. T. Montmerle. Cambridge University Pres

Measuring the inclination and mass-to-light ratio of axisymmetric galaxies via anisotropic Jeans models of stellar kinematics

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 beta_z=1-sigma_z^2/sigma_R^2. 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 (beta_z and the inclination) the models generally provide remarkably good descriptions of the shape of the first (V) and second (V_rms=sqrt{V^2+sigma^2}) velocity moments, once a detailed description of the surface brightness is given. This is consistent with previous findings on the simple dynamical structure of these objects. With the observationally-motivated assumption that beta_z>0, the method is able to recover the inclination. The technique can be used to determine the dynamical mass-to-light ratios and angular momenta of early-type fast-rotators and spiral galaxies, especially when the quality of the data does not justify more sophisticated modeling approaches. This formalism allows for the inclusion of dark matter, supermassive black holes, spatially varying anisotropy, and multiple kinematic components.Comment: 16 pages, 7 figures, LaTeX. Published in MNRAS. Software implementing the JAM method described in this paper is available at http://www-astro.physics.ox.ac.uk/~mxc/idl

Effect of environment on galaxies mass-size distribution: unveiling the transition from outside-in to inside-out evolution

The distribution of galaxies on the mass-size plane as a function of redshift or environment is a powerful test for galaxy formation models. Here we use integral-field stellar kinematics to interpret the variation of the mass-size distribution in two galaxy samples spanning extreme environmental densities. The samples are both identically and nearly mass-selected (stellar mass M*>6e9 Msun) and volume-limited. The first consists of nearby field galaxies from the Atlas3D parent sample. The second consists of galaxies in the Coma Cluster (Abell 1656), one of densest environments for which good resolved spectroscopy can be obtained. The mass-size distribution in the dense environment differs from the field one in two ways: (i) spiral galaxies are replaced by bulge-dominated disk-like fast-rotator early-type galaxies (ETGs), which follow the SAME mass-size relation and have the SAME mass distribution as in the field sample; (ii) the slow rotator ETGs are segregated in mass from the fast rotators, with their size increasing proportionally to their mass. A transition between the two processes appears around the stellar mass M_crit=2e11 Msun. We interpret this as evidence for bulge growth (outside-in evolution) and bulge-related environmental quenching dominating at low masses, with little influence from merging, while significant dry mergers (inside-out evolution) and halo-related quenching driving the mass and size growth at the high-mass end. The existence of these two processes naturally explains the diverse size evolution of galaxies of different masses and the separability of mass and environmental quenching.Comment: 6 pages, 5 figures, LaTeX. Accepted for publication in ApJ Letter

Dynamical masses of early-type galaxies at z~2

The evolution of masses and sizes of passive (early-type) galaxies with redshift provides ideal constraints to galaxy formation models. These parameters can in principle be obtained for large galaxy samples from multi-band photometry alone. However the accuracy of photometric masses is limited by the non-universality of the IMF. Galaxy sizes can be biased at high redshift due to the inferior quality of the imaging data. Both problems can be avoided using galaxy dynamics, and in particular by measuring the galaxies stellar velocity dispersion. Here we provide an overview of the efforts in this direction.Comment: 8 pages, 4 figures, LaTeX. Invited talk to the IAU Symposium 295 "The Intriguing Life of Massive Galaxies". To appear in Proc. of the XXVIII IAU General Assembly, Beijing, China, August 2012, eds. D. Thomas, A. Pasquali & I. Ferreras. Cambridge University Pres

General spherical anisotropic Jeans models of stellar kinematics: including proper motions and radial velocities

Cappellari (2008) presented a flexible and efficient method to model the stellar kinematics of anisotropic axisymmetric and spherical stellar systems. The spherical formalism could be used to model the line-of-sight velocity second moments allowing for essentially arbitrary radial variation in the anisotropy and general luminous and total density profiles. Here we generalize the spherical formalism by providing the expressions for all three components of the projected second moments, including the two proper motion components. A reference implementation is now included in the public JAM package available at http://purl.org/cappellari/softwareComment: 3 pages, 2 figures, LaTeX. Not submitted anywhere but here. Software implementing the update to the JAM method described in this paper is available at http://purl.org/cappellari/softwar

Full spectrum fitting with photometry in ppxf: non-parametric star formation history, metallicity and the quenching boundary from 3200 LEGA-C galaxies at redshift z~0.8

I start by describing some updates to the pPXF method, which has been used to measure stellar and gas kinematics as well as the formation history (SFH) and chemical composition of galaxies. I outline the novel linearly-constrained least-squares optimization algorithm used by pPXF and I illustrate the changes I made to be able to include photometric measurements together with full-spectrum fitting in pPXF. Then I present an application of the revised pPXF method to the study of the non-parametric SFH and metallicity $[M/H]$ of a sample of 3200 galaxies at redshift $0.6<z<1$ (median $z=0.76$), complete above a stellar mass $M_\ast>3\times10^{10}$ M$_\odot$, with spectroscopy from the LEGA-C survey and 28-bands photometry from two alternative catalogues. I extract and compare the stellar population using three independent stellar population synthesis (SPS) methods and both photometric catalogues. I find robust trends in the global light-weighted ages and $[M/H]$ consistent and of similar quality as those from nearby galaxy surveys, with the well-known main dependence on the galaxies' stellar velocity dispersion $\sigma_\ast$ (or alternative measures of central density). The recovered SFH indicate a sharp and strikingly clear boundary from star formation to quenching at $\lg(\sigma_\ast/km s^{-1})\approx2.3$, similar to what is invoked by some models. Equally clear quenching boundaries are seen at $[M/H]\approx-0.1$ and for a Sersic exponent $n_{\rm Ser}\approx0.5$. Results are consistent with two SPS methods and both photometric catalogues, but the third SPS method displays significant differences, highlighting the importance of comparing model assumptions. The pPXF software is available from https://pypi.org/project/ppxf/.Comment: 20 pages, 9 figures, LaTeX. Submitted to MNRAS. The method described in this paper is included in the pPXF software package at https://pypi.org/project/ppxf