Open accessJournal Article

# MusE GAs FLOw and Wind V. The dust/metallicity-anisotropy of the circum-galactic medium

02 Mar 2021-Monthly Notices of the Royal Astronomical Society (Oxford Academic)-Vol. 502, Iss: 3, pp 3733-3745
Abstract: Based on 13 galaxy-MgII absorber pairs (9 - 81 kpc distance) from the MusE GAs FLOw and Wind (MEGAFLOW) survey at 0.4 0.8 along the minor axis. Given that [Zn/Fe] is a good proxy for metallicity, these results suggest that the CGM along the minor axis is on average more metal enriched (by ~ 1dex) than the gas located along the major axis of galaxies - consistent with outflow and accretion models. Our results suggest a metallicity anisotropy of the CGM provided there is a constant dust-to-metal ratio.

Topics: Metallicity (52%)
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01 Jan 1985-
Abstract: A reexamination is conducted of the formation of dwarf, diffuse, metal-poor galaxies due to supernova-driven winds, in view of data on the systematic properties of dwarfs in the Local Group and Virgo Cluster. The critical condition for global gas loss as a result of the first burst of star formation is that the virial velocity lie below an approximately 100 km/sec critical value. This leads, as observed, to two distinct classes of galaxies, encompassing the diffuse dwarfs, which primarily originate from typical density perturbations, and the normal, brighter galaxies, including compact dwarfs, which can originate only from the highest density peaks. This furnishes a statistical biasing mechanism for the preferential formation of bright galaxies in denser regions, enhancing high surface brightness galaxies' clustering relative to the diffusive dwarfs.

Topics: Dwarf galaxy problem (74%), , Dwarf galaxy (73%) ... show more

1,227 Citations

Open accessJournal Article
Abstract: Galactic-scale outflows regulate the stellar mass growth and chemical enrichment of galaxies, yet key outflow properties such as the chemical composition and mass loss rate remain largely unknown. We address these properties with Keck/ESI echellete spectra of nine gravitationally lensed z=2-3 star forming galaxies, probing a range of absorption transitions. Interstellar absorption in our sample is dominated by outflowing material, with typical velocities -150 km/s. Approximately 80% of the total column density is associated with a net outflow. Mass loss rates in the low ionization phase are comparable to or in excess of the star formation rate, with total outflow rates likely higher when accounting for ionized gas. Of order half of the heavy element yield from star formation is ejected in the low ionization phase, confirming that outflows play a critical role in regulating galaxy chemical evolution. Covering fractions vary and are in general non-uniform, with most galaxies having incomplete covering by the low ions across all velocities. Low ion abundance patterns show remarkably little scatter, revealing a distinct "chemical fingerprint" of outflows. Gas phase Si/Fe abundances are significantly super-solar ([Si/Fe]$\gtrsim$0.4) indicating a combination of $\alpha$-enhancement and dust depletion. Derived properties are comparable to the most kinematically broad, metal-rich, and depleted intergalactic absorption systems at similar redshifts, suggesting that these extreme systems are associated with galactic outflows at impact parameters conservatively within a few tens of kpc. We discuss implications of the abundance patterns in z=2-3 galaxies and the role of outflows at this epoch.

Topics: Star formation (57%), Galaxy (56%), Stellar mass (56%) ... show more

15 Citations

Open accessJournal Article
Simon P. Goodwin1, Nate Bastian2Institutions (2)
Abstract: We examine the luminosity and dynamical mass estimates for young massive stellar clusters. For many young (<50 Myr) clusters, the luminosity and dynamical mass estimates differ by a significant amount. We explain this as being due to many young clusters being out of virial equilibrium (which is assumed in dynamical mass estimates) because the clusters are undergoing violent relaxation after expelling gas not used in star formation. We show that, if we assume that luminous mass estimates are correct (for a standard IMF), at least 50 per cent of young clusters for which dynamical masses are known are likely to be destroyed within a few 10s Myr of their formation. Even clusters which will retain a bound core may lose a large fraction of their stellar mass. We also show that the core radius and other structural parameters change significantly during the violent relaxation that follows gas expulsion and that they should be considered instantaneous values only, not necessarily reflecting the final state of the cluster. In particular we note that the increasing core radii observed in young LMC/SMC clusters can be well explained as an effect of rapid gas loss.

Topics: Stellar mass (54%), Star formation (53%)

12 Citations

Open accessJournal Article
Abstract: We present a pilot program using IRAM's NOrthern Extended Millimeter Array (NOEMA) to probe the molecular gas reservoirs of six $z=0.6-1.1$ star-forming galaxies whose circumgalactic medium has been observed in absorption along quasar lines-of-sight as part of the MusE GAs FLOw and Wind (MEGAFLOW) survey and for which we have estimates of either the accretion or the outflow rate. This program is motivated by testing the quasi equilibrium model and the compaction scenario describing the evolution of galaxies along the main sequence of star formation, which imply tight relations between the gas content, the star formation activity, and the amount of gas flowing in and out. We report individual carbon monoxide CO(4-3), CO(3-2) and dust continuum upper limits, as well as stacked CO detections over the whole sample and the three galaxies identified with outflows. The resulting molecular gas fractions and depletion times are compatible with published scaling relations established within a mass-selected sample, indicating that galaxies selected through their absorption follow similar relations on average. We further detect the dust continuum of three of the quasars and a strong emission line in one of them, which we identify as CO(4-3). Extending the sample to more galaxies and deeper observations will enable to quantify how the molecular gas fraction and depletion time depend on the inflow and ouflow rates.

7 Citations

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