[Paper Review] Dynamical Properties of z~2 Star Forming Galaxies and a Universal Star Formation Relation

N. Bouché, G. Cresci+18 more|SPIRE - Sciences Po Institutional REpository|Jun 19, 2007

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy75 references147 citations

TL;DR

This study analyzes the dynamical properties of z~2 star-forming galaxies using SINFONI/VLT integral field spectroscopy and IRAM CO interferometry, comparing UV-, optically-, and submillimeter-selected samples. It finds that UV/optically bright galaxies follow a universal velocity-size relation consistent with rotating disks, while compact, high-density SMGs indicate dissipative major mergers, supporting a universal Schmidt-Kennicutt relation with a slope of ~1.7 at z~2.

ABSTRACT

We present the first comparison of the dynamical properties of different samples of z~1.4-3.4 star forming galaxies from spatially resolved imaging spectroscopy from SINFONI/VLT integral field spectroscopy and IRAM CO millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16 rest-frame optically-selected and 13 submillimeter galaxies (SMGs). We find that restframe UV- and optically bright (K<20) z~2 star forming galaxies are dynamically similar, and follow the same velocity-size relation as disk galaxies at z~0. In the theoretical framework of rotating disks forming from dissipative collapse in dark matter halos, the two samples require a spin parameter ranging from 0.06 to 0.2. In contrast bright SMGs have larger velocity widths and are much more compact. Hence, SMGs have lower angular momenta and higher matter densities than either of the UV- or optically selected populations. This indicates that dissipative major mergers may dominate the SMGs population, resulting in early spheroids, and that the majority of UV/optically bright galaxies have evolved less violently [...]. These early disks may later evolve into spheroids via disk instabilities or mergers. Because of their small sizes and large densities, SMGs lie at the high surface density end of a universal (out to z=2.5) "Schmidt-Kennicutt" relation between gas surface density and star formation rate surface density with a slope of ~1.7.

Motivation & Objective

• To compare the dynamical properties of z~2 star-forming galaxies across different selection criteria: UV, optical, and submillimeter.
• To determine whether UV- and optically bright galaxies at z~2 follow the same kinematic relations as local disk galaxies.
• To investigate the origin of high surface density in submillimeter galaxies (SMGs) and their dynamical evolution.
• To test the universality of the Schmidt-Kennicutt relation at z~2 across diverse galaxy populations.
• To constrain the spin parameters and angular momentum content of high-redshift star-forming galaxies.

Proposed method

• Spatially resolved integral field spectroscopy with SINFONI/VLT to measure velocity fields and dynamical masses in 16 UV-selected, 16 optically-selected, and 13 SMGs at z~1.4–3.4.
• Millimeter-wave CO interferometry with IRAM to measure molecular gas content and kinematics in the same samples.
• Derivation of velocity-size relations and dynamical mass estimates from kinematic modeling of emission line profiles.
• Calculation of spin parameters using the relation λ = V_max / (2V_circular), assuming rotational support.
• Construction of the Schmidt-Kennicutt relation by plotting gas surface density versus star formation rate surface density across the samples.
• Comparison of observed kinematics with theoretical expectations from dissipative collapse in dark matter halos.

Experimental results

Research questions

• RQ1 Do UV- and optically selected z~2 star-forming galaxies exhibit similar dynamical properties?
• RQ2 What is the spin parameter of z~2 disk-like galaxies, and how does it compare to theoretical expectations?
• RQ3 How do the dynamical properties of submillimeter galaxies (SMGs) differ from those of UV- and optically selected galaxies?
• RQ4 Is the Schmidt-Kennicutt relation universal at z~2, and what is its slope across diverse galaxy populations?
• RQ5 What physical processes—such as mergers or disk instabilities—explain the observed kinematic differences?

Key findings

• UV- and optically bright z~2 galaxies (K<20) follow the same velocity-size relation as local disk galaxies, indicating similar rotational dynamics.
• These galaxies require spin parameters between 0.06 and 0.2, consistent with dissipative collapse in dark matter halos.
• Submillimeter galaxies (SMGs) are significantly more compact and have larger velocity widths than UV/optically selected galaxies, indicating lower angular momentum and higher matter densities.
• The dynamical properties of SMGs are best explained by dissipative major mergers, leading to early spheroid formation.
• All three populations lie on a universal Schmidt-Kennicutt relation out to z=2.5, with a slope of approximately 1.7.
• SMGs occupy the high surface density end of the Schmidt-Kennicutt relation, consistent with intense, compact star formation.