Origin of the unusually low nitrogen abundances in young populations of the Large Magellanic Cloud

Abstract

It is a longstanding problem that HII regions and very young stellar populations in the Large Magellanic Cloud (LMC) have the nitrogen abundances ([N/H]) by a factor of ~7 lower than the solar value. We here discuss a new scenario in which the observed unusually low nitrogen abundances can be closely associated with recent collision and subsequent accretion of HI high velocity clouds (HVCs) that surround the Galaxy and have low nitrogen abundances. We show that if the observed low [N/H] is limited to very young stars with ages less than ~10^7 yr, then the collision/accretion rate of the HVCs onto the LMC needs to be ~ 0.2 M_sun/yr (corresponding to the total HVC mass of 10^6-10^7 M_sun) to dilute the original interstellar medium (ISM) before star formation. The required accretion rate means that even if the typical mass of HVCs accreted onto the LMC is ~ 10^7 M_sun, the Galaxy needs to have ~2500 massive HVCs within the LMC's orbital radius with respect to the Galactic center. The required rather large number of massive HVCs drives us to suggest that the HVCs are not likely to efficiently dilute the ISM of the LMC and consequently lower the [N/H]. We thus suggest the transfer of gas with low [N/H] from the Small Magellanic Cloud (SMC) to the LMC as a promising scenario that can explain the observed low [N/H].

24pages, 6 figures, accepted in ApJ

References in corpus (9)

• The Star Formation History of the Large Magellanic Cloud
• Is the SMC Bound to the LMC? The HST Proper Motion of the SMC
• An Accurate Distance to High-Velocity Cloud Complex C
• The Chemical Enrichment History of the Small Magellanic Cloud and Its Gradients
• Metallicity and Ionization in High Velocity Cloud Complex C
• Ongoing Galactic Accretion: Simulations and Observations of Condensed Gas in Hot Halos
• A Spitzer Space Telescope far-infrared spectral atlas of compact sources in the Magellanic Clouds. I. The Large Magellanic Cloud
• The Carnegie Observatories Astrophysics Series
• Chemical Signature of a Major Merger in the Early Formation of Small Magellanic Cloud

Cited by in corpus (8)

• The Tidal Origin of the Magellanic Stream and the Possibility of a Stellar Counterpart
• The ESO UVES Advanced Data Products Quasar Sample - III. Evidence of Bimodality in the [N/alpha] Distribution
• Evolution of dust and molecular hydrogen in the Magellanic System
• Chemical evolution of the Large Magellanic Cloud
• ASTE observations in the 345 GHz window towards the HII region N113 of the Large Magellanic Cloud
• The origin of dust extinction curves with or without the 2175 A bump in galaxies: The case of the Magellanic Clouds
• Implications of a non-universal IMF from C, N, and O abundances in very metal-poor Galactic stars and damped Lyman-alpha absorbers
• Stripping of nitrogen-rich AGB ejecta from interacting dwarf irregular galaxies