TY - JOUR A1 - Hani, Maan H. A1 - Sparre, Martin A1 - Ellison, Sara L. A1 - Torrey, Paul A1 - Vogelsberger, Mark T1 - Galaxy mergers moulding the circum-galactic medium BT - I. The impact of a major merger JF - Monthly notices of the Royal Astronomical Society N2 - Galaxies are surrounded by sizeable gas reservoirs which host a significant amount of metals: the circum-galactic medium (CGM). The CGM acts as a mediator between the galaxy and the extragalactic medium. However, our understanding of how galaxy mergers, a major evolutionary transformation, impact the CGM remains deficient. We present a theoretical study of the effect of galaxy mergers on the CGM. We use hydrodynamical cosmological zoom-in simulations of a major merger selected from the Illustris project such that the z = 0 descendant has a halo mass and stellar mass comparable to the Milky Way. To study the CGM we then re-simulated this system at a 40 times better mass resolution, and included detailed post-processing ionization modelling. Our work demonstrates the effect the merger has on the characteristic size of the CGM, its metallicity, and the predicted covering fraction of various commonly observed gas-phase species, such as H I, C IV, and O VI. We show that merger-induced outflows can increase the CGM metallicity by 0.2-0.3 dex within 0.5 Gyr post-merger. These effects last up to 6 Gyr post-merger. While the merger increases the total metal covering fractions by factors of 2-3, the covering fractions of commonly observed UV ions decrease due to the hard ionizing radiation from the active galactic nucleus, which we model explicitly. Our study of the single simulated major merger presented in this work demonstrates the significant impact that a galaxy interaction can have on the size, metallicity, and observed column densities of the CGM. KW - methods: numerical KW - galaxies: evolution KW - galaxies: haloes KW - galaxies: interactions Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx3252 SN - 0035-8711 SN - 1365-2966 VL - 475 IS - 1 SP - 1160 EP - 1176 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Weilbacher, Peter Michael A1 - Monreal-Ibero, Ana A1 - Verhamme, Anne A1 - Sandin, Christer A1 - Steinmetz, Matthias A1 - Kollatschny, Wolfram A1 - Krajnovic, Davor A1 - Kamann, Sebastian A1 - Roth, Martin M. A1 - Erroz-Ferrer, Santiago A1 - Marino, Raffaella Anna A1 - Maseda, Michael V. A1 - Wendt, Martin A1 - Bacon, Roland A1 - Dreizler, Stefan A1 - Richard, Johan A1 - Wisotzki, Lutz T1 - Lyman-continuum leakage as dominant source of diffuse ionized gas in the Antennae galaxy JF - Astronomy and astrophysics : an international weekly journal N2 - The Antennae galaxy (NGC 4038/39) is the closest major interacting galaxy system and is therefore often studied as a merger prototype. We present the first comprehensive integral field spectroscopic dataset of this system, observed with the MUSE instrument at the ESO VLT. We cover the two regions in this system which exhibit recent star formation: the central galaxy interaction and a region near the tip of the southern tidal tail. In these fields, we detect H II regions and diffuse ionized gas to unprecedented depth. About 15% of the ionized gas was undetected by previous observing campaigns. This newly detected faint ionized gas is visible everywhere around the central merger, and shows filamentary structure. We estimate diffuse gas fractions of about 60% in the central field and 10% in the southern region. We are able to show that the southern region contains a significantly different population of H II regions, showing fainter luminosities. By comparing H II region luminosities with the HST catalog of young star clusters in the central field, we estimate that there is enough Lyman-continuum leakage in the merger to explain the amount of diffuse ionized gas that we detect. We compare the Lyman-continuum escape fraction of each H II region against emission line ratios that are sensitive to the ionization parameter. While we find no systematic trend between these properties, the most extreme line ratios seem to be strong indicators of density bounded ionization. Extrapolating the Lyman-continuum escape fractions to the southern region, we conclude that simply from the comparison of the young stellar populations to the ionized gas there is no need to invoke other ionization mechanisms than Lyman-continuum leaking H II regions for the diffuse ionized gas in the Antennae. KW - galaxies: interactions KW - galaxies: individual: NGC 4038, NGC 4039 KW - galaxies: ISM KW - ISM: structure KW - H II regions Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201731669 SN - 1432-0746 VL - 611 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Bustamante, Sebastian A1 - Sparre, Martin A1 - Springel, Volker A1 - Grand, Robert J. J. T1 - Merger-induced metallicity dilution in cosmological galaxy formation simulations JF - Monthly notices of the Royal Astronomical Society N2 - Observational studies have revealed that galaxy pairs tend to have lower gas-phase metallicity than isolated galaxies. This metallicity deficiency can be caused by inflows of low-metallicity gas due to the tidal forces and gravitational torques associated with galaxy mergers, diluting the metal content of the central region. In this work we demonstrate that such metallicity dilution occurs in state-of-the-art cosmological simulations of galaxy formation. We find that the dilution is typically 0.1 dex for major mergers, and is noticeable at projected separations smaller than 40 kpc. For minor mergers the metallicity dilution is still present, even though the amplitude is significantly smaller. Consistent with previous analysis of observed galaxies we find that mergers are outliers from the fundamental metallicity relation, with deviations being larger than expected for a Gaussian distribution of residuals. Our large sample of mergers within full cosmological simulations also makes it possible to estimate how the star formation rate enhancement and gas consumption timescale behave as a function of the merger mass ratio. We confirm that strong starbursts are likely to occur in major mergers, but they can also arise in minor mergers if more than two galaxies are participating in the interaction, a scenario that has largely been ignored in previous work based on idealised isolated merger simulations. KW - methods: numerical KW - galaxies: interactions KW - galaxies: star formation KW - galaxies: evolution Y1 - 2018 U6 - https://doi.org/10.1093/mnras/sty1692 SN - 0035-8711 SN - 1365-2966 VL - 479 IS - 3 SP - 3381 EP - 3392 PB - Oxford Univ. Press CY - Oxford ER -