Detailed Shapes of the Line-of-sight Velocity Distributions in Massive Early-type Galaxies from Nonparametric Spectral Models

Abstract

We present the first systematic study of the detailed shapes of the line-of-sight velocity distributions (LOSVDs) in nine massive early-type galaxies (ETGs) using the novel nonparametric modeling code WINGFIT. High-signal spectral observations with the Multi-Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope allow us to measure between 40 and 400 individual LOSVDs in each galaxy at a signal-to-noise ratio level better than 100 per spectral bin and to trace the LOSVDs all the way out to the highest stellar velocities. We extensively discuss potential LOSVD distortions due to template mismatch and strategies to avoid them. Our analysis uncovers a plethora of complex, large-scale kinematic structures for the shapes of the LOSVDs. Most notably, in the centers of all ETGs in our sample, we detect faint, broad LOSVD “wings” extending the line-of-sight velocities, v los, well beyond 3σ to v los ∼ ± 1000–1500 km s−1 on both sides of the peak of the LOSVDs. These wings likely originate from point-spread function effects and contain velocity information about the very central unresolved regions of the galaxies. In several galaxies, we detect wings of similar shape also toward the outer parts of the MUSE field of view. We propose that these wings originate from faint halos of loosely bound stars around the ETGs, similar to the cluster-bound stellar envelopes found around many brightest cluster galaxies.

The Isotropic Center of NGC 5419—A Core in Formation?

“…The kinematic structure of NGC 5419 can be well explained by the triaxial models (averaged over both sides we get χ 2 /N data = 0.45). As already visible in the SALT stellar kinematics (Mazzalay et al 2016) but much more clearly revealed by the MUSE observations (Mehrgan et al 2023), the velocity map of NGC 5419 points to a kinematically distinct core (KDC). We will come back to the KDC in Section 4.5.…”

“…Moreover, the 2D velocity pattern resembles a kind of "yin-yang symbol" on the sky caused by an apparent connection between the velocity pattern of the KDC and its surrounding large-scale velocity field. The connections between the red and blue inner and outer velocity structures, which cause the similarity to a yin-yang symbol, become even more apparent with the finer bins of Mehrgan et al (2023).…”

“…NGC 5419 is part of a larger sample 4 of massive ETGs for which we obtained MUSE spectra with high signal-to-noise ratio (S/N). The data analysis and stellar kinematical measurements for the whole program are described in detail in Mehrgan et al (2023). Our kinematic analysis is identical to what is explained in that paper except that we bin for an S/N that is roughly twice as high (to reduce the number of kinematic bins by a factor of two).…”

“…For illustration, we show maps of the velocity, dispersion, and Gauss-Hermite coefficients (Gerhard 1993;Van der Marel & Franx 1993) derived from the nonparametric LOSVDs of NGC 5419 in Figure 1. More details about the kinematics and plots with the entire LOSVDs can be found in Mehrgan et al (2023).…”

“…For comparison, NGC 5419ʼs isophotes are shown in black in the map of model velocity dispersion (top second panel). The MUSE kinematics are aligned along the position angle PA = 78°in agreement with the photometric major axis, i.e., north is at the top and east is to the left (see Mazzalay et al 2016;Mehrgan et al 2023).…”