Kinemetry of SINS High‐Redshift Star‐Forming Galaxies: Distinguishing Rotating Disks from Major Mergers

Abstract

We present a simple set of kinematic criteria that can distinguish between galaxies dominated by ordered rotational motion and those involved in major merger events. Our criteria are based on the dynamics of the warm ionized gas (as traced by H) within galaxies, making this analysis accessible to high-redshift systems, whose kinematics are primarily traceable through emission features. Using the method of kinemetry (developed by Krajnović and coworkers), we quantify asymmetries in both the velocity and velocity dispersion maps of the warm gas, and the resulting criteria enable us to empirically differentiate between nonmerging and merging systems at high redshift. We apply these criteria to 11 of our best-studied rest-frame UV/optical-selected z $ 2 galaxies for which we have near-infrared integralfield spectroscopic data from SINFONI on the VLT. Of these 11 systems, we find that >50% have kinematics consistent with a single rotating disk interpretation, while the remaining systems are more likely undergoing major mergers. This result, combined with the short formation timescales of these systems, provides evidence that rapid, smooth accretion of gas plays a significant role in galaxy formation at high redshift.

Dusty star-forming galaxies at high redshift

“…Collectively, they observe 16 SMGs at 2.0 < z < 2.5 and present strong evidence for merger-driven histories−many at an early stage first pass, where multiple components are seen separated by ∼8 kpc and 200 km s −1 , while others are later stage single-component systems with high-dispersion and buried AGN. Figure 29 illustrates the line-profile characteristics of these SMGs with respect to local starbursts from the SINGS sample, the z ∼ 2 SINS sample of star-forming galaxies (Shapiro et al, 2008), some simulated SMGs Davé et al (2010), and simulated disk and merger templates (also from Shapiro et al, 2008). The divide between mergers and disks is quite clear and narrow in this sample, with ∼8.5/10 of SMGs lying in the unambiguous merger-driven region of the plot.…”

“…This figure is reproduced with permission from Alaghband-Zadeh et al (2012). Blue background points represent regions dominated by smoothly rotating disk galaxies while red points are expected to be dominated by merger-driven templates (Shapiro et al, 2008). The triangles represent local samples: both normal star-forming galaxies from SINGS (blue) and ULIRGs (yellow).…”

“…SFGs exclude ULIRGs, SMGs, or other extreme starburst populations summarized in this review. Although the definition of SFG is not strictly defined in observational terms, several works have claimed that SFGs can be broadly described as sitting on the normal galaxy 'main sequence' (Noeske et al, 2007b) and are mostly not made up of secularly evolving, disk galaxies (Shapiro et al, 2008;Förster Schreiber et al, 2009;Tacconi et al, 2010;Daddi et al, 2010a;Genzel et al, 2010). …”

The rise and fall of stellar across the peak of cosmic star formation history: effects of mergers versus diffuse stellar mass acquisition

“…Forster Schreiber et al 2006;Shapiro et al 2008;Genzel & Burkert 2008;Mancini et al 2011;). In addition, many primordial spheroids that are forming the bulk of their stellar mass at z ∼ 2 do not show the tidal features that would be expected from recent major mergers ).…”

Galaxy Growth at Early Times from 3D Studies

“…The SINS/zC-SINF and other near-IR IFU surveys of kinematics revealed that > 50% of z ∼ 1−3 SFGs are fairly regular rotation-dominated disks, whereas a minority consists of disturbed (major) merging systems or more compact, velocity dispersion-dominated objects (e.g., Shapiro et al 2008;Förster Schreiber et al 2009;Law et al 2009;Jones et al 2010b;Gnerucci et al 2011a;Épinat et al 2012;Newman et al 2013). The rotation velocity v rot scales roughly linearly with galaxy size, consistent with centrifugally-supported baryonic disks of constant angular momentum parameter within virialized dark matter halos.…”