Integral field observations of the blue compact galaxy Haro14

Abstract

Context. Low-luminosity, gas-rich blue compact galaxies (BCG) are ideal laboratories to investigate the triggering and propagation of star formation in galaxies, the effects of massive stellar feedback within a shallow gravitational potential, and the enrichment of the interstellar medium. Aims. We aim to probe the morphology, stellar content, and kinematics, along with the nebular excitation and ionization mechanism, in the BCG Haro 14 by means of integral field observations. Methods. We observed Haro 14 at the Very Large Telescope, working with the Visible Multi-Object Spectrograph. From these data we build maps in continuum and in the brighter emission lines, produce line-ratio maps (interstellar extinction, density, and diagnosticline ratios), and obtain the velocity and velocity dispersion fields. We also generate the integrated spectrum of the major H ii regions and young stellar clusters identified in the maps to determine reliable physical parameters and oxygen abundances. Results. We find as follows: i) the current star formation in Haro 14 is spatially extended with the major H ii regions placed along a linear (chain-like) structure, elongated in the north-south direction, and in a horseshoe-like curvilinear feature that extends about 760 pc eastward; the continuum emission is more concentrated and peaks close to the galaxy center; ii) two different episodes of star formation are present in the central galaxy regions: the recent starburst, with ages ≤ 6 Myrs and the intermediate-age clusters, with ages between 10 and 30 Myrs; these stellar components rest on a several Gyr old underlying host galaxy; iii) the Hα/Hβ pattern is inhomogeneous, with excess color values varying from E(B − V)=0.04 up to E(B − V)=1.09; iv) shocks play a significant role in the galaxy; and v) the velocity field displays a complicated pattern with regions of material moving toward us in the east and north galaxy areas. Conclusions. The morphology of Haro 14, its irregular velocity field, and the presence of shocks speak in favor of a scenario of triggered star formation. Ages of the knots, i.e., 6 Myr for the starburst and 10-30 Myrs for the central clusters, are consistent with the ongoing burst being triggered by the collective action of stellar winds and supernovae originated in the central clusters.

Probing star formation and feedback in dwarf galaxies

“…The high values of the insterstellar extinction and its significant spatial variability agree with previous results for BCGs investigated by means of IFS (Cairós et al 2009b(Cairós et al ,a, 2015Lagos et al 2009Lagos et al , 2016James et al 2013;Cairós & González-Pérez 2017), and stress the importance of information on the dust spatial distribution, even when dealing with small and metal-poor systems such as BCGs. Assuming a single spatial constant value for the extinction, as is usually done for long-slit spectroscopic observations, can lead to significant errors in the fluxes and magnitudes in different galaxy regions.…”

“…This is consistent with shocks caused by the collective effect of massive stellar winds and SN remnants. The same behavior has been found for the other BCGs studied by means of IFU (Cairós et al 2015;Cairós & González-Pérez 2017).…”

“…(2016) at the northwest and southeast galaxy edges and in the space between the SF knots. Similar patterns have been found in the few other blue compact and dwarf galaxies for which 2D maps of the ionized gas velocity dispersion are available (Bordalo et al 2009;Moiseev & Lozinskaya 2012;Moiseev et al 2015;Cairós et al 2015;Cairós & González-Pérez 2017;Lagos et al 2016). Moiseev et al (2015) argued that the ionized gas turbulent motions in dwarfs do not reflect virial motions, but are instead connected with stellar feedback, that is, with the energy injected into the ISM by stellar winds and SN explosions.…”

“…Integral-field high-sensitivity spectroscopy permits building diagnostic diagrams in terms of spaxels, that is, to plot in the diagram each individual element of spatial resolution, and thus to investigate the existence of distinct mechanims acting in different regions of the galaxy. This technique has been applied in recent years with great success to nearby galaxies (Sharp & Bland-Hawthorn 2010;Rich et al 2011Rich et al , 2012Rich et al , 2015Leslie et al 2014;Belfiore et al 2015Belfiore et al , 2016Cairós & González-Pérez 2017 Figure 13). We also draw in the graphics the maximum starburst line or photoionization line derived by Kewley et al (2001).…”

“…Investigations of large samples are essential to open a new research field, establish general trends and find correlations among fundamental parameters, but detailed analyses of individual objects are needed to better understand the physical processes underlying galaxy parameters and behaviors. This is the second in the series of papers presenting the analysis of individual galaxies; results for the BCG Haro14 have been published recently (Cairós & González-Pérez 2017). Here we investigate the BCG Tololo 1937-423, an object that has not received much attention so far.…”