Spatially resolved star formation relation in two HI-rich galaxies with central post-starburst signature
arXiv:1611.07672 · doi:10.1051/0004-6361/201527922
Abstract
E+A galaxies are post-starburst systems that are identified from their optical spectra. These galaxies contain a substantial young A-type stellar component, but have only little ongoing star formation (SF). HI 21-cm line emission is found in approximately half of the nearby E+A galaxies, indicating that they contain a reservoir of gas that could fuel active SF. Here, we study two HI-rich galaxies, which show a typical E+A spectrum at the centre and SF at larger radii. We present new high spatial resolution radio interferometric observations of the HI 21-cm emission line using the VLA and of the CO(1-0) emission line using ALMA. We combine these data sets to predict the SFR and show that it does not correlate well with the SFR derived from H alpha on sub-kpc scales. We apply a recently developed statistical model for the small scale behaviour of the SF relation to predict and interpret the observed scatter. We find smoothly distributed, regularly rotating HI gas. The CO(1-0) emission line is not detected for both galaxies. The derived upper limit on the CO mass implies a molecular gas depletion time shorter than 20 Myr. However, due to the low metallicity, the CO-to-H2 conversion factor is highly uncertain. In the relations between the H alpha-based SFR and the HI mass, we observe a substantial scatter we demonstrate results from small-number statistics of independent star-forming regions on sub-kpc scales. This finding adds to the existing literature reporting a scale dependence of the molecular SF relation, showing that the atomic and molecular phases are both susceptible to the evolutionary 'cycling' of individual regions. This suggests that the atomic gas reservoirs host substantial substructure, which should be observable with future high-resolution observations. (abridged)
14 pages, 7 figures, accepted for publication in Astronomy & Astrophysics
References in corpus (13)
- Detection of quiescent galaxies in a bicolor sequence from z=0-2
- The Role of Pressure in GMC Formation II: The H_2 - Pressure Relation
- An uncertainty principle for star formation. I. Why galactic star formation relations break down below a certain spatial scale
- The rotation curves shapes of late-type dwarf galaxies
- The mass distribution in early-type disk galaxies: declining rotation curves and correlations with optical properties
- Discovery of Large Molecular Gas Reservoirs in Post-Starburst Galaxies
- Molecular depletion times and the CO-to-H2 conversion factor in metal-poor galaxies
- HI and CO Velocity Dispersions in Nearby Galaxies
- The spatially resolved Kennicutt-Schmidt relation in the HI dominated regions of spiral and dwarf irregular galaxies
- Radio Continuum Observations of the Galactic Center: Photoevaporative Proplyd-like Objects near Sgr A*
- The Variation in Molecular Gas Depletion Time among Nearby Galaxies: What are the Main Parameter Dependencies?
- The HI content of E+A galaxies
- Integral Field spectroscopy of two HI rich E+A galaxies