Full stellar kinematical profiles of central parts of nearby galaxies

Abstract

Context. We present the largest catalog of detailed stellar kinematics of the central parts of nearby galaxies, which includes higher moments of the line-of-sight velocity distribution (LOSVD) function represented by the Gauss-Hermite series. The kinematics is measured on a sample of galaxies selected from the Arecibo Legacy Fast ALFA (Alfalfa) survey using spectroscopy from the Sloan Digital Sky Survey (SDSS DR7). Aims. The SDSS DR7 offers measurements of the LOSVD based on the assumption of a pure Gaussian shape of the broadening function caused by the combination of rotational and random motion of the stars in galaxies. We discuss the consequences of this oversimplification since the velocity dispersion, one of the measured quantities, often serves as the proxy to important modeling parameters such as the black-hole mass and the virial mass of galaxies. Methods. The publicly available pPXF code is used to calculate the full kinematical profile for the sample galaxies including higher moments of their LOSVD. Both observed and synthetic stellar libraries were used and the related template mismatch problem is discussed. Results. For the whole sample of 2180 nearby galaxies reflecting morphological distribution characteristic for the local Universe, we successfully recovered stellar kinematics of their central parts, including higher order moments of the LOSVD function, for signal-to-noise above 50. Conclusions. We show the consequences of the oversimplification of the LOSVD function with Gaussian function on the velocity dispersion for the empirical and the synthetic stellar library. For the empirical stellar library, this approximation leads to an increase in the virial mass of 13% on average, while for the synthetic library the effect is weaker, with an increase of 9% on average. Systematic erroneous estimates of the velocity dispersion comes from the use of the synthetic stellar library instead of the empirical one and is much larger than the value imposed by the use of the Gaussian function. Only after a careful analysis of the template mismatch problem does one need to address the issue of the deviation of the LOSVD from the Gaussian function. We also show that the kurtotic parameter describing symmetrical departures from the Gaussian seems to increase along the continuous morphological sequence from late-to early-type galaxies.

Dark matter in massive early-type galaxies: 100 years of the jeans equations

“…Among other things, they discovered that the luminosity-weighted average h 4 parameter, < h 4 > e , is positive for all 41 ETGs in their sample. This is in agreement with the study of Vudragović et al (2016) who found that radial anisotropies with h 4 > 0 dominate in the innermost parts of ETGs (and especially ellipticals). In the subsequent paper Veale et al (2018) studied the stellar velocity dispersion profiles and environmental dependence of 90 ETGs.…”

“…2. Two largest samples of ETGs of comparable sizes for which the h 4 parameters were measured are given in Vudragović et al (2016) who presented 84 ellipticals and 183 lenticulars galaxies (only their innermost regions are analyzed because the SDSS (Sloan Digital Sky Survey) spectra used provided only the innermost parts of ETGs) and in Cappellari et al (2011) where 260 nearby ETGs were analyzed (see below). In Vudragović et al (2016) the sample of 2180 galaxies (267 ETGs and 1788 spirals taken from the SDSS DR7 database) it was shown that we have a hint of an increase of the h 4 parameter from spirals to ETGs which indicates the increase of radial anisotropies; on the other hand, it was found that the h 3 parameter remains approximately constant over all morphological types.…”

Simple interpolation functions for the galaxy-wide stellar initial mass function and its effects in early-type galaxies

“…Moreover, Chae et al (2019) use exactly the same parametrization of the gradient in the mass-to-light ratio as we do (Section 3.5). Thus, in consequence, assuming that the random motion in ETGs is completely isotropic is perhaps not as far from the truth, as it would appear from Vudragović et al (2016).…”

“…If the mass-to-light ratios are constant, the observed line-of-sight velocity distributions of over 2000 ETGs studied by Vudragović et al (2016) indicate that radial orbits are preferred over tangential orbits in them. Consequently, Vudragović et al (2016) find for their sample of ETGs that more realistic mass estimates based on the internal dynamics are on average about 10 per cent higher than expected under the assumption of isotropy.…”

“…If the mass-to-light ratios are constant, the observed line-of-sight velocity distributions of over 2000 ETGs studied by Vudragović et al (2016) indicate that radial orbits are preferred over tangential orbits in them. Consequently, Vudragović et al (2016) find for their sample of ETGs that more realistic mass estimates based on the internal dynamics are on average about 10 per cent higher than expected under the assumption of isotropy. The noted discrepancy between mass estimates based on the internal dynamics of ETGs and mass estimates based on the amount of baryons detected in them is usually interpreted as a presence of non-baryonic dark matter.…”