[Paper Review] SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution

N. M. Förster Schreiber, R. Genzel+15 more|HAL (Le Centre pour la Communication Scientifique Directe)|Mar 21, 2006

Astrophysics and Star Formation Studies4 citations

TL;DR

This study presents high-resolution near-infrared integral field spectroscopy of 14 z~2 UV-selected galaxies using SINFONI at the VLT, revealing spatially resolved rotation curves and kinematics consistent with rotating disks. The key finding is that these high-redshift galaxies have dynamical masses and specific angular momenta similar to local late-type spirals, with virial masses of ~10^11.7 M☉, supporting a scenario of inside-out disk growth via gas accretion and clump-driven bulge formation over ~1 Gyr.

ABSTRACT

We present 0.5" resolution near-IR integral field spectroscopy of the Ha line emission of 14 z~2 UV-selected BM/BX galaxies obtained with SINFONI at ESO/VLT. The mean Ha half-light radius r_1/2 is about 4kpc and line emission is detected over > ~20kpc in several sources. In 9 sources, we detect spatially-resolved velocity gradients, from 40 to 410 km/s over ~10kpc. The observed kinematics of the larger systems are consistent with orbital motions. Four galaxies are well described by rotating disks with clumpy morphologies and we extract rotation curves out to radii > ~10kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities v_c of 180+-90 km/s and dynamical masses of (0.5-25)x10^10 Msun within r_1/2. On average, the dynamical masses are consistent with photometric stellar masses assuming a Chabrier/Kroupa IMF but too small for a 0.1-100 Msun Salpeter IMF. The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. The specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average v_c at 10kpc, the virial mass of the typical halo of a galaxy in our sample is 10^(11.7+-0.5) Msun. Kinematic modeling of the 3 best cases implies a ratio of v_c to local velocity dispersion of order 2-4 and accordingly a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ~500Myr. We also argue that if our BM/BX galaxies were initially gas rich, their clumpy disks will subsequently lose their angular momentum and form compact bulges on a timescale of ~1 Gyr. [ABRIDGED]

Motivation & Objective

• To investigate the kinematic structure and dynamical masses of z~2 UV-selected BM/BX galaxies using high-resolution integral field spectroscopy.
• To determine whether these high-redshift galaxies are consistent with rotating disk models or merger-driven dynamics.
• To estimate the specific angular momentum of baryons and compare it to that of dark matter halos to constrain formation mechanisms.
• To infer the timescale of gas accretion or exhaustion based on kinematic properties such as v_c/σ ratios.
• To explore the evolutionary path of clumpy, gas-rich disks toward compact bulge formation over ~1 Gyr.

Proposed method

• Acquired ~0.5 arcsecond resolution near-infrared integral field spectroscopy of Hα emission in 14 z~2 BM/BX galaxies using SINFONI on the VLT.
• Measured spatially resolved velocity gradients and constructed two-dimensional kinematic maps to assess rotational vs. merger-like kinematics.
• Extracted rotation curves out to radii >10 h₇₀⁻¹ kpc in four galaxies with well-resolved kinematics.
• Calculated inclination- and beam-corrected maximum circular velocities (v_c) and dynamical masses within the Hα half-light radius.
• Used the average v_c at 10 h₇₀⁻¹ kpc as a proxy for halo virial mass, estimating M_vir ~ 10^11.7±0.5 M☉.
• Conducted kinematic modeling to derive v_c/σ ratios (~2–4), inferring gas accretion or exhaustion timescales of ~200–800 Myr.

Experimental results

Research questions

• RQ1 Are the kinematics of z~2 UV-selected galaxies consistent with rotating disk models or merger-induced dynamics?
• RQ2 What are the dynamical masses and virial masses of these high-redshift galaxies, and how do they compare to photometric stellar mass estimates?
• RQ3 How do the specific angular momenta of baryons in these galaxies compare to those of their dark matter halos?
• RQ4 What is the inferred gas accretion or exhaustion timescale based on kinematic properties such as v_c/σ?
• RQ5 Can the observed clumpy morphologies and kinematics be explained by a scenario of clump-driven bulge formation over ~1 Gyr?

Key findings

• Nine of the 14 galaxies show spatially resolved velocity gradients, with peak-to-peak velocity differences ranging from 40 to 410 km s⁻¹ over ~10 h₇₀⁻¹ kpc.
• The average inclination- and beam-corrected maximum circular velocity is v_c ~ 180 ± 90 km s⁻¹ within the Hα half-light radius.
• Dynamical masses within r₁/₂ range from ~0.5 to 25 × 10¹⁰ h₇₀⁻¹ M☉, consistent with photometric stellar masses assuming a Chabrier or Kroupa IMF but too low for a Salpeter IMF.
• The virial mass of the typical dark matter halo is estimated at 10^11.7±0.5 h₇₀⁻¹ M☉, in good agreement with clustering-based estimates.
• The v_c/σ ratio of 2–4 in the three best-fit cases implies a gas accretion or exhaustion timescale of ~200–800 Myr, consistent with stellar ages.
• The object with the reddest J-K color and brightest K-band magnitude shows a central peak in [N II]/Hα and minimum Hα equivalent width, indicating an inside-out metallicity and age gradient consistent with evolved, bulge-forming systems.