[Paper Review] 3D spectroscopy with VLT/GIRAFFE: I- the true Tully Fisher relationship at z~0.6

H. Flores, F. Hammer+3 more|arXiv (Cornell University)|Mar 21, 2006

Astronomy and Astrophysical Research98 citations

TL;DR

This study uses 3D integral field spectroscopy with VLT/GIRAFFE to measure the Tully-Fisher relation at z ~ 0.6, revealing that only 35% of galaxies are rotating disks. The apparent evolution in the Tully-Fisher relation reported in prior slit-spectroscopy studies is shown to stem from kinematic disturbances in 65% of galaxies, not cosmological evolution, with the true Tully-Fisher relation showing no evolution in slope, zero point, or scatter when only relaxed disks are considered.

ABSTRACT

A precise derivation of the evolution of the Tully Fisher is crucial to understand the interplay between dark matter and baryonic matter in cosmological models, Using 15 deployable integral field units of FLAMES/GIRAFFE at VLT, we have recovered the velocity fields of 35 galaxies at intermediate redshift (0.4 < z < 0.75). This facility is able to recover the velocity fields of almost all the emission line galaxies with Iab <=22.5 and W_0(OII)>=15A In our sample, we find only 35% rotating disks. These rotating disks produce a Tully-Fisher relationship (stellar mass or M_K versus V_max) which has apparently not evolved in slope, zero point and scatter since z=0.6. The only evolution found is a brightening of the B band luminosity of a third of the disks, possibly due to an enhancement of the star formation. The very large scatters found in previously reported Tully-Fisher relationships at moderate redshifts are caused by the numerous (65%) galaxies with perturbed or complex kinematics. Those galaxies include minor or major mergers, merger remnants and/or inflow/outflows and their kinematics can be easily misidentified by slit spectroscopy. Their presence suggests a strong evolution in the dynamical properties of galaxies during the last 7 Gyrs.

Motivation & Objective

• To resolve the conflicting results on Tully-Fisher relation evolution at intermediate redshift (z ~ 0.6) by using 3D spectroscopy to accurately measure galaxy kinematics.
• To determine whether the Tully-Fisher relation—linking luminosity or mass to rotational velocity—has evolved since z ~ 0.6, as suggested by previous slit-spectroscopy studies.
• To identify the cause of the large scatter observed in prior Tully-Fisher relations at moderate redshift, particularly whether it arises from instrumental limitations or intrinsic galaxy dynamics.
• To assess the dynamical state of high-redshift galaxies and quantify the fraction of non-rotating or perturbed systems that contaminate traditional slit-based measurements.

Proposed method

• 3D spectroscopy was performed using 15 deployable integral field units (IFUs) of the FLAMES/GIRAFFE instrument at the VLT, enabling spatially resolved velocity field and velocity dispersion mapping.
• Galaxy samples were selected based on I_AB ≤ 22.5 and W₀(OII) ≥ 15 Å to ensure detectable emission lines and sufficient signal-to-noise.
• Velocity fields and σ-maps were reconstructed from the 3D datacubes to classify galaxies into kinematic categories: rotating disks, perturbed rotation, or complex/random motions.
• Galaxy kinematics were classified using visual inspection and structural criteria, including peak offset of velocity dispersion and alignment between optical and kinematic axes.
• The Tully-Fisher relation was reconstructed using stellar mass and K-band absolute magnitude (M_K) as functions of maximum rotational velocity (V_max), restricted to galaxies with relaxed, disk-like kinematics.
• Statistical analysis excluded galaxies with disturbed kinematics (e.g., mergers, inflows, outflows) to isolate the true Tully-Fisher relation from contamination by dynamical non-equilibrium systems.

Experimental results

Research questions

• RQ1 Does the Tully-Fisher relation exhibit evolution in slope, zero point, or scatter between z ~ 0.6 and the local universe when measured with 3D spectroscopy?
• RQ2 What causes the large scatter in previously reported Tully-Fisher relations at moderate redshift—instrumental limitations or intrinsic dynamical complexity?
• RQ3 What fraction of high-redshift galaxies (z ~ 0.6) are rotating disks in dynamical equilibrium, and how do their kinematics compare to local galaxies?
• RQ4 To what extent do mergers, inflows, or outflows distort rotation curves and lead to misclassification in slit-spectroscopy-based studies?
• RQ5 Does the Tully-Fisher relation in stellar mass or K-band luminosity remain unchanged from z ~ 0.6 to z = 0 when only relaxed rotating disks are considered?

Key findings

• Only 35% of the 35 galaxies observed at z ~ 0.6 are rotating disks in dynamical equilibrium, indicating that a majority (65%) exhibit perturbed or complex kinematics.
• The large scatter in prior Tully-Fisher relations at moderate redshift is primarily due to contamination by galaxies with disturbed kinematics, not cosmological evolution.
• When restricted to rotating disks, the Tully-Fisher relation shows no evolution in slope, zero point, or scatter when compared to the local relation in both stellar mass and M_K magnitude.
• The B-band luminosity of rotating disks at z ~ 0.6 is on average 0.3 mag brighter than at z = 0, suggesting a 1/3 enhancement in star formation activity.
• Galaxies with compact morphologies and low stellar masses are more likely to show complex kinematics, including inflows/outflows, which can dominate over rotational motion.
• The fraction of non-rotating or non-equilibrium systems at z ~ 0.6 is significantly higher (36% of galaxies with MB < -19.5) than in the local universe, indicating strong dynamical evolution over the last 7 Gyr.