Understanding star formation and feedback in small galaxies

Abstract

Context. Low-luminosity, active star-forming blue compact galaxies (BCGs) are excellent laboratories for investigating the process of star formation on galactic scales and to probe the interplay between massive stars and the surrounding interstellar (or intergalactic) medium. Aims. We investigate the morphology, structure, and stellar content of BCG Mrk 900, as well as the excitation, ionization conditions, and kinematics of its H ii regions and surrounding ionized gas. Methods. We obtained integral field observations of Mrk 900 working with the Visible Multi-Object Spectrograph at the Very Large Telescope. The observations were taken in the wavelength range 4150-7400 Å covering a field of view of 27 ′′ × 27 ′′ on the sky with a spatial sampling of 0. ′′ 67. From the integral field data we built continuum, emission, and diagnostic line ratio maps and produced velocity and velocity dispersion maps. We also generated the integrated spectrum of the major H ii regions and the nuclear area to determine reliable physical parameters and oxygen abundances. Integral field spectroscopy was complemented with deep broad-band photometry taken at the 2.5 m NOT telescope; the broad-band data, tracing the galaxy up to radius 4 kpc, allowed us to investigate the properties of the low surface brightness underlying stellar host. Results. We disentangle two different stellar components in Mrk 900: a young population, which resolves into individual stellar clusters with ages ∼5.5-6.6 Myr and extends about 1 kpc along the galaxy minor axis, is placed on top of a rather red and regular shaped underlying stellar host, several Gyr old. We find evidence of a substantial amount of dust and an inhomogeneous extinction pattern, with a dust lane crossing the central starburst. Mrk 900 displays overall rotation, although distorted in the central, starburst regions; the dispersion velocity map is highly inhomogeneous, with values increasing up to 60 km s −1 at the periphery of the SF regions, where we also find hints of the presence of shocks. Our observational results point to an interaction or merger with a lowmass object or infalling gas as plausible trigger mechanisms for the present starburst event.Conclusions.

Warm ionized gas in the blue compact galaxy Haro 14 viewed by MUSE

“…Similar spaxel distributions below the maximum starburst line have been found for NGC 4214 (Calzetti et al 2004), Mrk 900 (Cairós & González-Pérez 2020), and Tololo 1937-423 (Cairós & González-Pérez 2017b, objects that also present an extended area of ongoing SF made of multiple H ii-region complexes. In Haro 14 (as well as in NGC 4214), the galaxy inclination (we see the galaxy almost face on) allows us to resolve individual sources that in edge-on galaxies would appear integrated along the line of sight.…”

“…These features confer to the diagnostic diagrams the distinctive shape of a butterfly, a general arrangement that could already be seen, though much less clearly, in the diagrams of Haro 14 built from VIMOS data (Cairós & González-Pérez 2017a). Interestingly, this characteristic shape is also visible in the diagrams of the BCGs Mrk 900 (Cairós & González-Pérez 2020) and Tololo 1937-423 (Cairós & González-Pérez 2017b). It would be interesting to explore whether or not this butterfly shape also appears in the diagnostic diagrams of other BCGs and, if so, how often and for which conditions.…”

MUSE observations of the blue compact dwarf galaxy Haro 14

“…A lot of effort has been invested into finding out how the SF in BCGs is triggered and maintained, but no conclusive findings have been found so far (Brinks 1990;Taylor 1997;Hunter & Elmegreen 2004;Pustilnik et al 2001;Brosch et al 2004). However, recent observational results indicate that dwarf-dwarf mergers, interactions, or infalling gas may play a major role in the ignition of the burst in low-mass systems (López-Sánchez et al 2012;Nidever et al 2013;Stierwalt et al 2015;Privon et al 2017;Pearson et al 2018;Zhang et al 2020a,b;Cairós & González-Pérez 2020).…”

Splitting the lentils: Clues to galaxy/black hole coevolution from the discovery of offset relations for non-dusty versus dusty (wet-merger-built) lenticular galaxies in theMbh–M*,spheroid andMbh–M*,galaxy diagrams

“…Some dusty S0 galaxies are well known to be young mergers (e.g., NGC 5128), while others are old mergers which have since curtailed, if not ceased, their star formation (e.g., NGC 1316). It is expected that within the 'down-sizing' scenario, the lower-mass dusty S0 galaxies will, on average, have been built most recently (Cairós & González-Pérez 2020;Zhang et al 2020). What is of relevance here is that they all experienced a major wet merger in the past, evolving them to higher masses.…”