Extranuclear Hα-emitting complexes in low-z(U)LIRGs: precursors of tidal dwarf galaxies?

Abstract

This paper characterizes the physical and kinematic properties of external massive star-forming regions in a sample of (U)LIRGs. We use high angular resolution ACS images from the Hubble Space Telescope (HST) in F435W (∼B) and F814W (∼I) bands, as well as Hα-line emission maps obtained with integral field spectroscopy. We find 31 external Hα-emitting (i.e., young star-forming) complexes in 11 (U)LIRGs. These complexes have in general similar sizes (from few hundreds of pc to about 2 kpc), luminosities (M F435W < -10.65 and L(Hα) > 10 39 L ), and metallicities (12 + log (O/H) ∼ 8.5-8.7) to extragalactic giant HII regions and TDG candidates found in less luminous mergers and compact groups of galaxies. We assess the mass content and the likelihood of survival as TDGs of the 22 complexes with simple structures in the HST images based on their photometric, structural, and kinematic properties. The dynamical tracers used (radius-σ and luminosity-σ diagrams) indicate that most of the complexes might be self-gravitating entities. The resistance to forces from the parent galaxy is studied by considering the tidal mass of the candidate and its relative velocity with respect to the parent galaxy. After combining the results of previous studies of TDG searches in ULIRGs a total of 9 complexes satisfy most of the applied criteria and thus show a high-medium or high likelihood of survival, their total mass likely being compatible with that of dwarf galaxies. They are defined as TDG candidates. We propose that they probably formed more often during the early phases of the interaction. Combining all data for complexes with IFS data where a significant fraction of the system is covered, we infer a TDG production rate of 0.3 candidates with the highest probabilities of survival per system for the (U)LIRGs class. This rate, though, might decrease to 0.1 after the systems in (U)LIRGs have evolved for 10 Gyr, for long-lived TDGs, which would imply that no more than 5-10% of the overall dwarf population could be of tidal origin.

Ionized gas outflows and global kinematics of low-zluminous star-forming galaxies

“…1) show a wide range of physical properties (see Table B.1 for specific values) with a median size (half-light radius), velocity dispersion, and (observed Hα-based) star formation surface density of 0.43 kpc, 39 km s −1 , and 0.13 M yr −1 kpc −2 , respectively. Their sizes are similar to those of giant HII regions (0.1-1 kpc diameter; Kennicutt 1998;Mayya 1994), and the external Hα clumps located mostly in the tidal tails of U/LIRGs (Monreal-Ibero et al 2007;Miralles-Caballero et al 2012). The largest clumps, with (light) diameters of 2 kpc and above (see Table B.1) cover the range of sizes measured only in high-z clumps (Wisnioski et al 2012, Fig.…”

“…In addition to the nuclear starburst, many interacting and merger galaxies exhibit extranuclear knots of star formation, which are more massive than star clusters in normal spiral galaxies (e.g., Super Star Clusters, SSC; Whitmore et al 2007;Miralles-Caballero et al 2012). It has been proposed that this extranuclear star formation is triggered by an increase of the ISM turbulence as a consequence of the tidal interaction A14, page 6 of 36 (Elmegreen et al 2000;Struck et al 2005;Bournaud et al 2010).…”

Properties of ionized outflows in MaNGA DR2 galaxies

“…(20 − 100 pc;Miralles-Caballero, Colina & Arribas 2012), the values of Σ L(Hα) estimated here should be considered lower limits. The parameter Vmax = |∆V | + F W HM broad /2 corresponds to the maximum velocity of the ionized gas, with ∆V being the velocity difference in km/s between the narrow and broad kinematic components.…”

VLT-SINFONI sub-kpc study of the star formation in local LIRGs and ULIRGs

“…Subsequent ground-based optical integral field spectroscopy of the same sample, detected large Hα-emitting regions identified with star-forming clumps (Miralles-Caballero et al 2012). Owing to the higher angular resolution of the HST images, the structure of these Hα clumps consisted of few star-forming knots, with an average of 2.2 per clump.…”

“…Only a few clumps show a more complex knot structure, with several bright blue knots spread inside the area of the clump (see Fig. 2 and Table 1 in Miralles-Caballero et al 2012). …”