Browsing by Author "Cresci, Giovanni"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Gaseous nebulae and massive stars in the giant HI ring in Leo
    (2021) Corbelli, Edvige; Mannucci, Filippo; Thilker, David; Cresci, Giovanni; Venturi, Giacomo
    Context. Chemical abundances in the Leo ring, the largest HI cloud in the local Universe, have recently been determined to be close to or above Solar values. This is a finding that is incompatible with prior claims that the ring was primordial in origin. The gas, pre-enriched in a galactic disk and tidally stripped, did not manage to efficiently form stars in the intergalactic space.Aims. Using H alpha emission and a multi-wavelengths analysis of its extremely faint optical counterpart, we investigate the process of star formation and the slow build-up of a stellar population that could form diffuse and metal-rich dwarf galaxies in the Leo ring.Methods. We mapped nebular lines in three dense HI clumps and complemented the data with archival stellar continuum observations from the Galaxy Evolution Explorer and the Hubble Space Telescope, as well as with population synthesis models.Results. We detect a sparse population of stars in the main body of the ring, with individual young stars as massive as O7-types powering some HII regions. The average star-formation rate density in the ring is on order of 10(-5)M(circle dot) yr(-1) kpc(-2) and proceeds with local bursts a few hundred parsecs in size, where loose stellar associations of 500-1000 M-circle dot occasionally host massive outliers. The far ultraviolet-to-H alpha emission ratio in nebular regions implies recent stellar bursts, from 2 to 7 Myr ago. The relation between the local HI gas density and the star-formation rate in the ring is similar to what is found in dwarfs and outer disks with gas depletion times as long as 100 Gyr. We find a candidate planetary nebula in a compact and faint H alpha region with [OIII]/H alpha line enhancement, which is consistent with the estimated mean stellar surface brightness of the ring. The presence of a 1 kpc partial ring that is emitting weak H alpha lines around the brightest and youngest HII region suggests that local shocks might triggers future star-forming sites.
  • No Thumbnail Available
    Item
    Heavy Elements Unveil the Non-primordial Origin of the Giant H I Ring in Leo
    (2021) Corbelli, Edvige; Cresci, Giovanni; Mannucci, Filippo; Thilker, David; Venturi, Giacomo
    The origin and fate of the most extended extragalactic neutral cloud known in the local universe, the Leo ring, is still debated 38 yr after its discovery. Its existence is alternatively attributed to leftover primordial gas with some low level of metal pollution versus enriched gas stripped during a galaxy-galaxy encounter. Taking advantage of Multi Unit Spectroscopic Explorer operating at the Very Large Telescope, we performed optical integral field spectroscopy of three H I clumps in the Leo ring where ultraviolet continuum emission has been found. We detected, for the first time, ionized hydrogen in the ring and identify four nebular regions powered by massive stars. These nebulae show several metal lines ([O III], [N II], [S II]) that allowed reliable measures of metallicities, found to be close to or above the solar value (0.8 <= Z/Z <= 1.4). Given the faintness of the diffuse stellar counterparts, less than 3% of the observed heavy elements could have been produced locally in the main body of the ring and not much more than 15% in the H I clump toward M96. This inference, and the chemical homogeneity among the regions, convincingly demonstrates that the gas in the ring is not primordial, but has been pre-enriched in a galaxy disk, then later removed and shaped by tidal forces and it is forming a sparse population of stars.
  • Thumbnail Image
    Item
    Pre-supernova stellar feedback in nearby starburst dwarf galaxies
    (2024) Rowland, Lucie E.; Mcleod, Anna F.; Fattahi, Azadeh; Belfiore, Francesco; Cresci, Giovanni; Hunt, Leslie; Krumholz, Mark; Kumari, Nimisha; Marasco, Antonino; Venturi, Giacomo
    Context. Stellar feedback in dwarf galaxies remains, to date, poorly explored, yet is crucial to understanding galaxy evolution in the early Universe. In particular, pre-supernova feedback has recently been found to play a significant role in regulating and disrupting star formation in larger spiral galaxies, but it remains uncertain if it also plays this role in dwarfs. Aims. We study the ionised gas properties and stellar content of individual star-forming regions across three nearby, low-metallicity (12 + log(O/H)similar to 7.5), dwarf (M* similar to 40 x 106 M circle dot), starburst (log(SFR)similar to - 2.8) galaxies (J0921, KKH046, and Leo P) to investigate how massive stars influence their surroundings and how this influence changes as a function of environment. Methods. We extracted integrated spectra of 30 HII regions from archival VLT/MUSE integral field spectroscopic observations of these three dwarf starburst galaxies. We fitted the HII regions' main emission lines with Gaussian profiles to derive their oxygen abundances, electron densities, and luminosities, and we used the Stochastically Ligthing Up Galaxies (SLUG) code to derive the stellar mass, age, and bolometric luminosity of the stellar populations driving the HII regions. We quantified two pre-supernova stellar feedback mechanisms, namely the direct radiation pressure and photoionisation feedback, and explored how feedback strength varies with HII region properties. Results. Our findings suggest that stellar feedback has less of an impact on evolved regions, with both the pressure of the ionised gas and the direct radiation pressure decreasing as a function of HII region size (i.e. the evolutionary stage). We find that these stellar feedback mechanisms are also dependent on the metallicity of the HII regions. These findings extend results from stellar feedback studies of more massive star-forming galaxies to the low-mass, low-metallicity regime. In addition, we conclude that the use of stochastic stellar population models significantly affects the relationships found between feedback-related pressure terms and HII region properties, and in particular that non-stochastic models can severely underestimate the bolometric luminosity of low-mass stellar populations.