Stellar kinematics and populations out to 1.5 effective radii in the elliptical galaxy NGC 4636

Abstract

We present high quality long slit spectra along the major and minor axes out to 1.5 effective radius (R e ) of the massive galaxy NGC4636 taken by Hobby-Eberly Telescope (HET). Using Fourier Correlation Quotient (FCQ) method, we measured the stellar line-of-sight velocity distribution along the axes. Furthermore, six Lick/IDS indices (Hβ, Mgb, Fe 5015 , Fe 5270 , Fe 5335 , Fe 5406 ) are derived from the clean spectrum. By comparing the measured absorption line strengths with the predictions of Simple Stellar Populations (SSP) models, we derived ages, total metallicity and α abundance profiles of the galaxy. This galaxy presents old and [α/Fe] over abundant stellar populations. Indeed, using the SSP model, we obtained the broadband color profiles. The theoretical colors match well with the measured colors and present red sharp peaks at the galaxy center. The sharp peaks of the colors are mainly shaped by the high metallicity in the galaxy center. Interestingly, the galaxy has steep negative metallicity gradients, but trend flattens outwards. This result likly suggests that the center and outer regions of the galaxy formed through different formation process.

Dynamics of the NGC 4636 globular cluster system II. Improved constraints from a large sample of globular cluster velocities

“…Long slit spectra of NGC 4636 were obtained by Bender et al (1994), andKronawitter et al (2000) presented detailed modelling based on these data. Recently, Pu & Han (2011) presented radial velocities and velocity dispersions derived from deep long-slit spectra along the major and minor axis. Their data reach out to ∼ 2.…”

The Stellar Halos of Massive Elliptical Galaxies. Ii. Detailed Abundance Ratios at Large Radius

“…Despite more than thirty years of effort, most observations of stellar population gradients do not extend much beyond the half-light radius (Spinrad & Taylor 1971;Faber et al 1977;Gorgas et al 1990;Fisher et al 1995;Kobayashi & Arimoto 1999;Ogando et al 2005;Brough et al 2007;Baes et al 2007;Annibali et al 2007;Sánchez-Blázquez et al 2007;Rawle et al 2008;Kuntschner et al 2010;Coccato et al 2010Coccato et al , 2011. While integral-field spectrographs have brought a golden age in the study of spatially resolved galaxy properties Sarzi et al 2006;Cappellari et al 2006Cappellari et al , 2012, there are still few observations that extend beyond the half-light radius in integrated light (Carollo et al 1993;Carollo & Danziger 1994;Mehlert et al 2003;Kelson et al 2006;Weijmans et al 2009;Spolaor et al 2010;Pu et al 2010;Pu & Han 2011). To our knowledge, there are fewer than thirty integrated-light observations in total (using different instruments and techniques) that reach beyond R e in massive elliptical galaxies in the literature.…”

Radial alignment of elliptical galaxies by the tidal force of a cluster of galaxies

“…In the Monte-Carlo simulations, the initial ellipticity distribution and the effective density of the galaxies are chosen as those of field galaxies. There is evidence showing that differences might exist between the density of cluster galaxies and field galaxies (Pu & Han 2011); it is however possible that these differences are caused by the tidal effect we calculated here, which may change the density and ellipticity distributions of the member galaxies of a cluster. Although different initial ellipticity distribution and effective density chosen do not change our conclusion qualitatively, these will become important when analyzing RAD quantitatively.…”