MAGNUS I: A MUSE-DEEP sample of early-type galaxies at intermediate redshift

TL;DR

We address how massive early-type galaxies (ETGs) assembled mass and angular momentum over $0.25<z<0.75$. Using MAGNUS, a homogeneous, deep sample of 212 ETGs from MUSE-DEEP with supporting HST imaging, we derive spatially resolved kinematics via $\lambda_R$ and perform robust structural and stellar-population analyses with two SPS models. We find a slow-rotator fraction of about $19\%$, fast and slow rotators showing alignment patterns similar to the local Universe, and global stellar-population properties that scale with central velocity dispersion $\sigma_e$, with slow rotators being more massive, metal-rich, and having higher $M_*/L$. These results imply that the fundamental dynamical and stellar-population scaling relations were already in place by $z\sim0.75$ and have remained stable to the present, underscoring the continuity of ETG evolutionary pathways. The MAGNUS dataset provides a solid platform for future studies of environmental influence and for integrating dynamical constraints into time-delay cosmography.

Abstract

We present a sample of 212 early-type galaxies (ETGs) at redshifts $0.25 < z < 0.75$. We combine deep integral-field spectroscopy from the MUSE-DEEP survey with high-resolution HST imaging to study the structure, kinematics, and stellar populations of these galaxies. We measure spatially resolved stellar kinematics and use the specific angular momentum proxy, $λ_R$, to classify galaxies into fast and slow rotators. We find a slow rotator fraction consistent with local Universe samples, suggesting little evolution in the massive ETG population since $z \sim 1$. The kinematic and photometric axes of fast rotators are generally well-aligned, similar to their local counterparts. We find that global stellar population properties, such as age, metallicity, and mass-to-light ratio ($M_*/L$), correlate strongly with the central velocity dispersion ($σ_\mathrm{e}$), following trends established for local ETGs. Slow rotators are typically more massive, have higher $σ_\mathrm{e}$, and are more metal-rich than fast rotators. Our findings indicate that the fundamental structural, kinematic, and stellar population scaling relations of massive ETGs were already in place by $z \sim 0.75$, suggesting their evolutionary pathways have remained stable over the last $\sim 7$ Gyr.

Figures (20)

• Figure 1: Distribution of MAGNUS sample properties. Left: integrated velocity dispersion, $\sigma_\mathrm{e}$, of the galaxies within the half-light isophote as a function of redshift. Right: average surface brightness in the F814W band, $\langle\mu_e\rangle$, as a function of semi-major axis, $R_{\rm e}^{\rm maj}$. Both quantities were measured within the elliptical half-light isophote and using the HST image of the galaxies. The color map shows the redshifts of the galaxies.
• Figure 2: Example of kinematics extraction from galaxies at different redshifts. The galaxies are A370_8644 ($z=0.371$, top), MACS1149_62 ($z=0.551$, middle) and COSMOSGR83_1251492 ($z=0.7$, bottom). In each case, two extracted spectra (blue) from two different Voronoi bins, one close to the galaxy center and the other close to the edge, are shown with kinematic fitting from pPXF (red). The gray regions mark the excluded wavelength range from the fitting. Besides, the corresponding HST image of the galaxy, extracted velocity (median subtracted), velocity dispersion, and RMS velocity maps are shown. The green circle in each HST image shows the aperture of the extracted kinematic data relative to the observed surface brightness. The red markers in the vrms map shows the luminosity weighted coordinates the of the bins.
• Figure 3: Example of SPS fitting from pPXF. Top-fitting was done using FSPS templates. Bottom-fitting was performed using GaLAXEV templates. In both cases, the blue curve shows the observed galaxy spectrum from A370_8644 (z=0.371), the red curve is the best-fitting model (stellar continuum + gas) from pPXF, the orange curve is the best-fitting gas-only spectrum, and the green diamonds are the residuals. The grey-shaded regions were masked and excluded from fitting.
• Figure 4: Distribution of $\lambda_R$ in the MAGNUS sample. Left: The specific angular momentum proxy $\lambda_R$ is plotted against ellipticity $\epsilon$. $\lambda_R$ was measured within an elliptical aperture with a semi-major axis of 2$R_{\rm e}^{\rm maj}$, and $\epsilon$ is the observed ellipticity from MGE models. Markers indicate visual classifications: blue circles for regular rotators, red squares for non-regular rotators, and green for unclassified galaxies. The solid green line shows the theoretical relation for an edge-on ($i=90^{\circ}$) isotropic rotator Binney2005, using the formula from Cappellari_review_2016, while the dashed green line is at one-third of this value. The magenta line represents the empirical anisotropy limit for edge-on local galaxies Cappellari_2007. Grey dotted lines show this limit for different inclinations (in steps of $\Delta i=10^{\circ}$), and grey dashed lines illustrate how galaxies with given intrinsic ellipticities (in steps of $\Delta\epsilon_{\text{intr}}=0.1$) move on the diagram as inclination changes. The black solid lines, defined by $\lambda_{R_{\mathrm{e}}}<0.08+\varepsilon_e / 4$ and $\varepsilon_e<0.4$Cappellari_review_2016, separate slow from fast rotators, updating the previous criterion by ATLAS_III_Emselem_2011 (green dashed line). Our measured $\lambda_{R}$ values generally confirm the visual classifications. Right: Distribution of LOESS-smoothed velocity dispersion $\sigma_\mathrm{e}$ (see \ref{['sec:result_kin_classifiation']}) on the ($\lambda_R, \epsilon$) plane. This panel shows that non-regular rotators typically have higher $\sigma_\mathrm{e}$ than most regular rotators. The lines are identical to the left panel.
• Figure 5: Misalignment angle between kinematic and photometric PAs as a function of $\epsilon$. $PA_{\text{phot}}$ of the galaxies was measured using the sky-subtracted HST images, and $PA_{\text{kin}}$ was measured from the median-subtracted velocity maps. The blue, red, and green markers denote the same qualitative classification as described in \ref{['fig:lambda_ep']}. The plot is symmetrized about the black solid line along 0$^{\circ}$ to eliminate any indication of bias towards positive or negative misalignments. The dashed lines show $\pm 10^{\circ}, \pm 30^{\circ}$ misalignments. Most of the regular rotators have $\Psi_{\text{mis}} < |10^{\circ}|$.