Constraints on the minor merging and star formation history of the Wolf–Rayet galaxy NGC 5430 through observations

Abstract

We used multi-wavelength analysis of the newly observed molecular gas ( 12 CO and 13 CO (1-0)) with interferometer CARMA and archival star formation tracers to constrain the interaction, merging, and star formation history of an off-center minor merger, a three-spiral barred galaxy NGC 5430 and its satellite embedded in the bar. Morphology of the molecular gas in the bar of NGC 5430 shows minimal signs of recent interactions in our resolution. The apparent morphological remnant of the past galaxy interaction is an asymmetric spiral arm, containing more molecular gas and exhibiting higher star formation rate (SFR) surface density than the two primary arms. Rotation curve analysis suggests that NGC 5430 and its satellite collided several Gyr ago. History of star formation was constrained by using SFRs that trace different timescales (infrared, radio continuum, and Hα). The collision occurred 5 -10 Myr ago, triggering a transient off-center starburst of Wolf-Rayet stars at the eastern bar end. In the past, the global SFR during the Wolf-Rayet starburst peaked at 35 M ⊙ yr −1 . At present, the merger-driven starburst is rapidly decaying and the current global SFR has decreased to the Galactic value. The SFR will continue to decay as suggested by the present amount of dense gas (traced by HCN (1-0)). Nonetheless, the global SFR is still dominated by the Wolf-Rayet region rather than the circumnuclear region. Compared with other barred galaxies, the circumnuclear region exhibits particularly low dense gas fraction, low star formation activity and high concentration of gas. Physical properties of the molecular gas are inferred by using the large velocity gradient (LVG) calculations. The initial mass ratio of the NGC 5430 and its satellite are suggested to be in the intermediate ratio range of 7:1-20:1.

SDSS-IV MaNGA: Spatial Evolution of Star Formation Triggered by Galaxy Interactions

“…Finally, it is worth noting that the SFR in this work is calculated by Hα luminosity, tracing the ongoing star formation (<100 Myr), while the extension and enhancement of star formation can occur in different timescales. We refer the reader to Pan et al (2015) and Davies et al (2015) for the comparisons of interaction-triggered SFRs using observational tracers which probe different star formation timescales and Cortijo-Ferrero et al (2017a, 2017c for the constraints onto interaction-triggered star formation history using population synthesis. Galaxies in pairs or mergers (p/m) are defined as galaxies with a spectroscopic companion.…”

CO Multi-line Imaging of Nearby Galaxies (COMING). III. Dynamical effect on molecular gas density and star formation in the barred spiral galaxy NGC 4303

“…It cannot be estimated from only one emission line because one intensive variable such as an intensity of a line cannot constrain extensive variables such as density and temperature of molecular gas. Thus, it is necessary to observe multiple lines Unfortunately, since molecular emission lines excluding low-excitation line of 12 CO are usually weak, this confines observation targets to luminous (e.g., starburst galaxies; Iono et al 2007, Pan et al 2015 or very near galaxies (e.g., galaxies in the Local Group; Minamidani et al 2011, Muraoka et al 2012. Therefore, molecular gas density in the bar of barred spiral galaxies is not yet clear.…”

SDSS-IV MaNGA: Spatial Evolution of Star Formation Triggered by Galaxy Interactions

“…Finally, it is worth noting that the star formation rate in this work is calculated by Hα luminosity, tracing the ongoing star formation (< 100 Myr), while the extension and enhancement of star formation can occur in different time-scales. We refer the reader to Pan et al (2015) and Davies et al (2015) for the comparisons of interactiontriggered SFRs using observational tracers which probe different star formation time-scales and Cortijo-Ferrero et al (2017a,b,c) for the constraints onto interactiontriggered star formation history using population synthesis.…”