ABSTRACT We study star formation histories (SFHs) of 500 dwarf galaxies (stellar mass $M_\ast =10^5\!-\!10^9\, \rm {M}_\odot$) from FIRE-2 cosmological zoom-in simulations. We compare dwarfs around individual Milky Way (MW)-mass galaxies, dwarfs in Local Group (LG)-like environments, and true field (i.e. isolated) dwarf galaxies. We reproduce observed trends wherein higher mass dwarfs quench later (if at all), regardless of environment. We also identify differences between the environments, both in terms of ‘satellite versus central’ and ‘LG versus individual MW versus isolated dwarf central.’ Around the individual MW-mass hosts, we recover the result expected from environmental quenching: central galaxies in the ‘near field’ have more extended SFHs than their satellite counterparts, with the former more closely resemble isolated (true field) dwarfs (though near-field centrals are still somewhat earlier forming). However, this difference is muted in the LG-like environments, where both near-field centrals and satellites have similar SFHs, which resemble satellites of single MW-mass hosts. This distinction is strongest for M* = 106–$10^7\, \rm {M}_\odot$ but exists at other masses. Our results suggest that the paired halo nature of the LG may regulate star formation in dwarf galaxies even beyond the virial radii of the MW and Andromeda. Caution is needed when comparing zoom-in simulations targeting isolated dwarf galaxies against observed dwarf galaxies in the LG.
more »
« less
Extinguishing the FIRE: environmental quenching of satellite galaxies around Milky Way-mass hosts in simulations
The star formation and gas content of satellite galaxies around the Milky Way (MW) and Andromeda (M31) are depleted relative to more isolated galaxies in the Local Group (LG) at fixed stellar mass. We explore the environmental regulation of gas content and quenching of star formation in z = 0 galaxies at $M_{*}=10^{5\!-\!10}\, \rm {M}_{\odot }$ around 14 MW-mass hosts from the Feedback In Realistic Environments 2 (FIRE-2) simulations. Lower mass satellites ($M_{*}\lesssim 10^7\, \rm {M}_{\odot }$) are mostly quiescent and higher mass satellites ($M_{*}\gtrsim 10^8\, \rm {M}_{\odot }$) are mostly star forming, with intermediate-mass satellites ($M_{*}\approx 10^{7\!-\!8}\, \rm {M}_{\odot }$) split roughly equally between quiescent and star forming. Hosts with more gas in their circumgalactic medium have a higher quiescent fraction of massive satellites ($M_{*}=10^{8\!-\!9}\, \rm {M}_{\odot }$). We find no significant dependence on isolated versus paired (LG-like) host environments, and the quiescent fractions of satellites around MW-mass and Large Magellanic Cloud (LMC)-mass hosts from the FIRE-2 simulations are remarkably similar. Environmental effects that lead to quenching can also occur as pre-processing in low-mass groups prior to MW infall. Lower mass satellites typically quenched before MW infall as central galaxies or rapidly during infall into a low-mass group or a MW-mass galaxy. Most intermediate- to high-mass quiescent satellites have experienced ≥1–2 pericentre passages (≈2.5–5 Gyr) within a MW-mass halo. Most galaxies with $M_{*}\gtrsim 10^{6.5}\, \rm {M}_{\odot }$ did not quench before falling into a host, indicating a possible upper mass limit for isolated quenching. The simulations reproduce the average trend in the LG quiescent fraction across the full range of satellite stellar masses. Though the simulations are consistent with the Satellites Around Galactic Analogs (SAGA) survey’s quiescent fraction at $M_{*}\gtrsim 10^8\, \rm {M}_{\odot }$, they do not generally reproduce SAGA’s turnover at lower masses.
more » « less- PAR ID:
- 10368611
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 514
- Issue:
- 4
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 5276-5295
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
ABSTRACT Low-mass galaxies are highly susceptible to environmental effects that can efficiently quench star formation. We explore the role of ram pressure in quenching low-mass galaxies ($M_{*}\sim 10^{5}{-}10^{9}\, \rm {M}_{\odot }$) within 2 Mpc of Milky Way (MW) hosts using the FIRE-2 simulations. Ram pressure is highly variable across different environments, within individual MW haloes, and for individual low-mass galaxies over time. The impulsiveness of ram pressure – the maximum ram pressure scaled to the integrated ram pressure prior to quenching – correlates with whether a galaxy is quiescent or star forming. The time-scale between maximum ram pressure and quenching is anticorrelated with impulsiveness, such that high impulsiveness corresponds to quenching time-scales <1 Gyr. Galaxies in low-mass groups ($M_\mathrm{*,host}10^{7}{-}10^{9}\, \rm {M}_{\odot }$) outside of MW haloes experience typical ram pressure only slightly lower than ram pressure on MW satellites, helping to explain effective quenching via group preprocessing. Ram pressure on MW satellites rises sharply with decreasing distance to the host, and, at a fixed physical distance, more recent pericentre passages are typically associated with higher ram pressure because of greater gas density in the inner host halo at late times. Furthermore, the ram pressure and gas density in the inner regions of Local Group-like paired host haloes are higher at small angles off the host galaxy disc compared to isolated hosts. The quiescent fraction of satellites within these low-latitude regions is also elevated in the simulations and observations, signaling possible anisotropic quenching via ram pressure around MW-mass hosts.
-
more » « less
ABSTRACT While many tensions between Local Group (LG) satellite galaxies and Λ cold dark matter cosmology have been alleviated through recent cosmological simulations, the spatial distribution of satellites remains an important test of physical models and physical versus numerical disruption in simulations. Using the FIRE-2 cosmological zoom-in baryonic simulations, we examine the radial distributions of satellites with $M_*\gt 10^5$ M⊙ around eight isolated Milky Way (MW) mass host galaxies and four hosts in LG-like pairs. We demonstrate that these simulations resolve the survival and physical destruction of satellites with $M_*\gtrsim 10^5$ M⊙. The simulations broadly agree with LG observations, spanning the radial profiles around the MW and M31. This agreement does not depend strongly on satellite mass, even at distances ≲100 kpc. Host-to-host variation dominates the scatter in satellite counts within 300 kpc of the hosts, while time variation dominates scatter within 50 kpc. More massive host galaxies within our sample have fewer satellites at small distances, likely because of enhanced tidal destruction of satellites via the baryonic discs of host galaxies. Furthermore, we quantify and provide fits to the tidal depletion of subhaloes in baryonic relative to dark matter-only simulations as a function of distance. Our simulated profiles imply observational incompleteness in the LG even at $M_*\gtrsim 10^5$ M⊙: we predict 2–10 such satellites to be discovered around the MW and possibly 6–9 around M31. To provide cosmological context, we compare our results with the radial profiles of satellites around MW analogues in the SAGA survey, finding that our simulations are broadly consistent with most SAGA systems.
-
more » « less
ABSTRACT Using the eagle (Evolution and Assembly of GaLaxies and their Environments) suite of simulations, we demonstrate that both cold gas stripping and starvation of gas inflow play an important role in quenching satellite galaxies across a range of stellar and halo masses, M⋆ and M200. Quantifying the balance between gas inflows, outflows, and star formation rates, we show that even at z = 2, only $\approx 30{{\ \rm per\ cent}}$ of satellite galaxies are able to maintain equilibrium or grow their reservoir of cool gas – compared to $\approx 50{{\ \rm per\ cent}}$ of central galaxies at this redshift. We find that the number of orbits completed by a satellite on first-infall to a group environment is a very good predictor of its quenching, even more so than the time since infall. On average, we show that intermediate-mass satellites with M⋆ between will be quenched at $10^{9}\, {\rm M}_{\odot }\, {\rm and}\, 10^{10}\, {\rm M}_{\odot }$ first pericenter in massive group environments, $M_{200}\gt 10^{13.5}\, {\rm M}_{\odot }$; and will be quenched at second pericenter in less massive group environments, $M_{200}\lt 10^{13.5}\, {\rm M}_{\odot }$. On average, more massive satellites ($M_{\star }\gt 10^{10}\, {\rm M}_{\odot }$) experience longer depletion time-scales, being quenched between first and second pericenters in massive groups, while in smaller group environments, just $\approx 30{{\ \rm per\ cent}}$ will be quenched even after two orbits. Our results suggest that while starvation alone may be enough to slowly quench satellite galaxies, direct gas stripping, particularly at pericenters, is required to produce the short quenching time-scales exhibited in the simulation.
-
ABSTRACT Surveys of the Milky Way (MW) and M31 enable detailed studies of stellar populations across ages and metallicities, with the goal of reconstructing formation histories across cosmic time. These surveys motivate key questions for galactic archaeology in a cosmological context: When did the main progenitor of an MW/M31-mass galaxy form, and what were the galactic building blocks that formed it? We investigate the formation times and progenitor galaxies of MW/M31-mass galaxies using the Feedback In Realistic Environments-2 cosmological simulations, including six isolated MW/M31-mass galaxies and six galaxies in Local Group (LG)-like pairs at z = 0. We examine main progenitor ‘formation’ based on two metrics: (1) transition from primarily ex-situ to in-situ stellar mass growth and (2) mass dominance compared to other progenitors. We find that the main progenitor of an MW/M31-mass galaxy emerged typically at z ∼ 3–4 ($11.6\!\!-\!\!12.2\, \rm {Gyr}$ ago), while stars in the bulge region (inner 2 kpc) at z = 0 formed primarily in a single main progenitor at z ≲ 5 (${\lesssim} \!12.6\, \rm {Gyr}$ ago). Compared with isolated hosts, the main progenitors of LG-like paired hosts emerged significantly earlier (Δz ∼ 2, $\Delta t\!\sim \!1.6\, \rm {Gyr}$), with ∼4× higher stellar mass at all z ≳ 4 (${\gtrsim} \!12.2\, \rm {Gyr}$ ago). This highlights the importance of environment in MW/M31-mass galaxy formation, especially at early times. On average, about 100 galaxies with $\rm {\it{ M}}_\rm {star}\!\gtrsim \!10^5\, \rm {M}_\odot$ went into building a typical MW/M31-mass system. Thus, surviving satellites represent a highly incomplete census (by ∼5×) of the progenitor population.more » « less
