STELLAR KINEMATICS OFz∼ 2 GALAXIES AND THE INSIDE-OUT GROWTH OF QUIESCENT GALAXIES^,

Abstract

Using stellar kinematics measurements, we investigate the growth of massive, quiescent galaxies from z ∼2 to today. We present X-Shooter spectra from the UV to NIR and dynamical mass measurements of five quiescent massive (> 10 11 M ⊙ ) galaxies at z ∼ 2. This triples the sample of z > 1.5 galaxies with well constrained (δσ < 100km s −1 ) velocity dispersion measurements. From spectral population synthesis modeling we find that these galaxies have stellar ages that range from 0.5-2 Gyr, with no signs of ongoing star formation. We measure velocity dispersions (290-450 km s −1 ) from stellar absorption lines and find that they are 1.6-2.1 times higher than those of galaxies in the Sloan Digital Sky Survey at the same mass. Sizes are measured using GALFIT from Hubble Space Telescope Wide Field Camera 3 H 160 and UDS K-band images. The dynamical masses correspond well to the spectral energy distribution based stellar masses, with dynamical masses that are ∼ 15% higher. We find that M * /M dyn may decrease slightly with time, which could reflect the increase of the dark matter fraction within an increasing effective radius. We combine different stellar kinematic studies from the literature, and examine the structural evolution from z ∼ 2 to z ∼ 0: we confirm that at fixed dynamical mass, the effective radius increases by a factor of ∼ 2.8, and the velocity dispersion decreases by a factor of ∼ 1.7. The mass density within one effective radius decreases by a factor of ∼ 20, while within a fixed physical radius (1 kpc) it decreases only mildly (factor of ∼ 2). When we allow for an evolving mass limit by selecting a population of galaxies at fixed number density, a stronger size growth with time is found (factor of ∼ 4), velocity dispersion decreases by a factor of ∼ 1.4, and interestingly, the mass density within 1 kpc is consistent with no evolution. This finding suggests that massive quiescent galaxies at z ∼ 2 grow inside-out, consistent with the expectations from minor mergers.

Spatially Resolved Kinematics in the Central 1 kpc of a Compact Star-forming Galaxy at z ∼ 2.3 from ALMA CO Observations

“…These galaxies have been identified in sizable numbers and their properties: small stellar sizes, steep radial mass profiles and obscured SFR properties have all been confirmed by multiple studies (e.g., Barro et al 2014a;van Dokkum et al 2015). Moreover, NIR spectroscopic follow-up has allowed a characterization of the kinematic and dynamical properties of their ionized gas from the analysis of rest-frame optical emission lines (e.g., Barro et al 2014b;van Dokkum et al 2015;Nelson et al 2016).…”

“…′′ 12), and the line-of-sight inclination. We estimate the latter from the optical axis-ratio, q = 0.82, following the method of van Dokkum et al (2015), and we obtain i = 62…”

“…The most likely explanation for such large discrepancies are the uncertainties on the dynamical modeling assumptions. For example, the lineof-sight inclination, the ratio between ordered and random motions of the gas (i.e., the amount of rotational support, v rot /σ), the extent of gas profile relative to the stellar mass distribution, or the aperture corrections to scale the measurements within the slit to either galaxywide or effective (r = r e ) values can all contribute to the observed difference (e.g., van Dokkum et al 2015;Price et al 2016).…”

THE MOSFIRE DEEP EVOLUTION FIELD (MOSDEF) SURVEY: REST-FRAME OPTICAL SPECTROSCOPY FOR ∼1500 H -SELECTED GALAXIES AT $1.37\leqslant z\leqslant 3.8$

“…The grism redshifts are derived by fitting the grism spectra and multi-wavelength photometry simultaneously (Brammer et al 2012. Additional spectroscopic redshifts are included as well (Reddy et al 2006;Barger et al 2008;Coil et al 2009Coil et al , 2011Cooper et al 2012;Newman et al 2013;van de Sande et al 2013). When no spectroscopic redshift is available, from either the grism spectra or other spectroscopic campaigns, we use a photometric redshift as derived using EAzY (Brammer et al 2008).…”

“…These galaxies are not simply the younger versions of elliptical and starforming galaxies today, but were smaller and denser at similar mass (e.g., Williams et al 2010). Both populations appear to grow inside out, but the physical mechanism (e.g., minor mergers, progenitor bias, cold streams and in situ star formation) responsible for the growth is still subject to debate (e.g., van de Sande et al 2013;Newman et al 2012a;Carollo et al 2013;Dutton et al 2011;van Dokkum et al 2013).…”