Large galaxies harbor massive central black holes and their feedback causes a substantial impact in their evolution. Recently, observations suggested that dwarf galaxies might host black holes in their centers, but with lower masses (intermediate-mass black holes - IMBH). The impact of such IMBHs on the evolution of the dwarf spheroidal galaxies (dSphs), however, has not been so far properly analysed. In this work, we investigate the effects of an outflow from an IMBH on the gas dynamics in dSph galaxies by means of non-cosmological, three-dimensional hydrodynamic simulations, letting the galactic gas distribution evolve over 3 Gyr under the influence of the IMBH's outflow and supernova feedback. All simulations have a numerical resolution of 20.0 pc cell$^{-1}$. Two scenarios are considered to infer the differences in the propagation of the outflow, one with a homogeneous ISM and another one with inhomogeneities caused by supernovae feedback. A minimal initial speed and a minimal initial density are required for the outflow to propagate, with the values depending on the conditions of the medium. In an unperturbed medium, the outflow propagates freely in both directions with the same velocity (lower than the initial one), removing a small fraction of the gas from the galaxy (the exact fraction depends on the initial physical conditions of the outflow). However, in an inhomogeneous ISM, the impact of the outflow is substantially reduced, and its contribution to the removal of gas from the galaxy is almost negligible.
We present a general phenomenological model for the metallicity distribution (MD) in terms of [Fe/H] for dwarf spheroidal galaxies (dSphs). These galaxies appear to have stopped accreting gas from the intergalactic medium and are fossilized systems with their stars undergoing slow internal evolution. For a wide variety of infall histories of unprocessed baryonic matter to feed star formation, most of the observed MDs can be well described by our model. The key requirement is that the fraction of the gas mass lost by supernova-driven outflows is close to unity. This model also predicts a relati…
The stars in the dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are significantly more metal-poor than would be expected from a closed box model of chemical evolution. Gas outflows likely carried away most of the metals produced by the dSphs. Based on previous Keck/DEIMOS observations and models, we calculate the mass in Mg, Si, Ca, and Fe expelled from each of eight dSphs. Essentially, these masses are the differences between the observed amount of metals present in the dSphs' stars today and the inferred amount of metals produced by supernovae. We conclude that the dSphs lost 9…
Fornax is the brightest Milky Way (MW) dwarf spheroidal galaxy and its star formation history (SFH) has been derived from observations. We estimate the time evolution of its gas mass and net inflow and outflow rates from the SFH using a simple star formation law that relates the star formation rate to the gas mass. We present a chemical evolution model on a 2D mass grid with supernovae (SNe) as sources of metal enrichment. We find that a key parameter controlling the enrichment is the mass M_x of the gas to mix with the ejecta from each SN. The choice of M_x depends on the evolution of SN remn…
We present a new chemical evolution model for dwarf spheroidal galaxies (dSphs) in the Local Universe. Our main aim is to explain both their observed star formation histories and metallicity distribution functions simultaneously. Applying our new model for the four local dSphs, that is, Fornax, Sculptor, Leo II, and Sextans, we find that our new model reproduces the observed chemical properties of the dSphs consistently. Our results show that the dSphs have evolved with both a low star formation efficiency and a large gas outflow efficiency compared with the Milky Way, as suggested by previous…
Several models have predicted that stars could form inside galactic outflows and that this would be a new major mode of galaxy evolution. Observations of galactic outflows have revealed that they host large amounts of dense and clumpy molecular gas, which provide conditions suitable for star formation. We have investigated the properties of the outflows in a large sample of galaxies by exploiting the integral field spectroscopic data of the large MaNGA-SDSS4 galaxy survey. We find that star formation occurs inside at least half of the galactic outflows in our sample. We also show that even if …
Dwarf spheroidal satellite galaxies have emerged a powerful probe of small-scale dark matter clustering and of cosmic reionization. They exhibit structural and chemical continuity with dwarf irregular galaxies in the field and with spheroidal galaxies in high-density environments. By combining empirical constraints derived for star formation at low gas column densities and metallicities in the local universe with a model for dark matter and baryonic mass assembly, we provide an analytical description of how the dwarf spheroidals acquired their stellar content. Their progenitors formed stars un…
It's a matter of time: Empirical Constraints on Supernova Yields and Delay Times from Dwarf Spheroidal Galaxies
University of Toronto（多伦多大学）；David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto（多伦多大学戴维·A·邓拉普天文学与天体物理系）；Dunlap Institute for Astronomy & Astrophysics, University of Toronto（多伦多大学邓拉普天文学与天体物理研究所）；Data Sciences Institute, University of Toronto（多伦多大学数据科学研究所）；Department of Astronomy & Astrophysics, University of Chicago（芝加哥大学天文学与天体物理系）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）
We propose that detailed data on the star formation history of a dwarf spheroidal galaxy (dSph) may be used to estimate the evolution of the total mass M_g(t) for cold gas in its star-forming disk. Using Fornax as an illustrative example, we estimate its M_g(t) and the corresponding net gas flow rate Delta F(t) assuming a global star formation rate psi(t) = lambda_*(t)[M_g(t)/M_sun]^alpha consistent with observations of nearby galaxies. We identify the onset of the transition in Delta F(t) from a net inflow to a net outflow as the time t_sat at which the Fornax halo became a Milky Way satellit…
Nuclear outflows driven by accreting massive black holes are one of the main feedback mechanisms invoked at high-z to reproduce the distinct separation between star-forming, disk galaxies and quiescent spheroidal systems. Yet, our knowledge of feedback at high-z remains limited by the lack of observations of the multiple gas phases in galaxy outflows. In this work we use new deep, high-spatial resolution ALMA CO(3-2) and archival VLT/SINFONI H$α$ observations to study the molecular and ionized components of the AGN-driven outflow in zC400528 ---a massive, main sequence galaxy at z=2.3 in the p…
We suggest a direct link between the two "missing" baryon problems of contemporary galaxy formation theory: (1) that large galaxies are known to contain too little gas and stars and (2) that too few dwarf satellite galaxies are observed around large galaxies compared with cosmological simulations. The former can be explained by invoking some energetic process -- most likely AGN or star formation feedback -- which expels to infinity a significant fraction of the gas initially present in the proto-galaxy, while the latter problem is usually explained by star formation feedback inside the dwarf o…
We investigate the prevalence of galactic-scale outflows in post-starburst (PSB) galaxies at high redshift ($1 < z < 1.4$), using the deep optical spectra available in the UKIDSS Ultra Deep Survey (UDS). We use a sample of $\sim40$ spectroscopically confirmed PSBs, recently identified in the UDS field, and perform a stacking analysis in order to analyse the structure of strong interstellar absorption features such as Mg ii ($\lambda2800$ Ang.). We find that for massive ($M_* > 10^{10}\rm\,M_{\odot}$) PSBs at $z > 1$, there is clear evidence for a strong blue-shifted component to the Mg ii abso…
The Fermi Bubbles are giant, gamma-ray emitting lobes emanating from the nucleus of the Milky Way discovered in ~1-100 GeV data collected by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope. Previous work has revealed substructure within the Fermi Bubbles that has been interpreted as a signature of collimated outflows from the Galaxy's super-massive black hole. Here we show via a spatial template analysis that much of the gamma-ray emission associated to the brightest region of substructure -- the so-called cocoon -- is likely due to the Sagittarius dwarf spheroidal (Sgr d…
From chemical abundance analysis of stars in the Sagittarius dwarf spheroidal galaxy (Sgr), we conclude that the alpha-element deficiencies cannot be due to the Type Ia supernova (SNIa) time-delay scenario of Tinsley (1979). Instead, the evidence points to low [alpha/Fe] ratios resulting from an initial mass function (IMF) deficient in the highest mass stars. The critical evidence is the 0.4 dex deficiency of [O/Fe], [Mg/Fe] and other hydrostatic elements, contrasting with the normal trend of r-process [Eu/Fe]r with [Fe/H]. Supporting evidence comes from the hydrostatic element (O, Mg, Na, Al,…
Active galactic nucleus (AGN) feedback provides the link between the central black hole and its host galaxy. We assume AGN feedback driven by radiation pressure on dust, which sweeps up the ambient dusty gas into an outflowing shell, and consider feedback-triggered star formation in the outflow. An upper limit to the characteristic size of galaxies may be defined by the critical radius beyond which radiation pressure on dust is no longer able to drive the shell. The corresponding enclosed mass may be compared with the host galaxy bulge mass. We show that the resulting relation between characte…
Recent inspections of local available data suggest that the almost linear relation between the stellar mass of spheroids ($M_{\rm sph}$) and the mass of the super massive Black Holes (BHs) residing at their centres, shows a break below $M_{\rm sph} \sim 10^{10}\ {\rm M}_\odot$, with a steeper, about quadratic relation at smaller masses. We investigate the physical mechanisms responsible for the change in slope of this relation, by comparing data with the results of the semi-analytic model of galaxy formation MORGANA, which already predicted such a break in its original formulation. We find tha…
We present more results from a fully cosmological LCDM simulation of a group of isolated dwarf galaxies that has been shown to reproduce the observed stellar mass and cold gas content, resolved star formation histories, and metallicities of dwarfs in the Local Volume. Here we investigate the energetics and timetable of the cusp-core transformation. As suggested by previous work, supernova-driven gas outflows remove dark matter (DM) cusps and create kpc-size cores in all systems having a stellar mass above 1e6 Msun. The "DM core mass removal efficiency" -- dark mass ejected per unit stellar mas…
We study the evolution of Eu and Ba abundances in local group dwarf spheroidal and ultra faint dwarf galaxies by means of detailed chemical evolution models and compare our results with new sets of homogeneous abundances. The adopted models include gas infall and outflow and have been previously tested. We investigate several production scenarios for r-process elements: merging neutron stars and magneto-rotational driven supernovae. Production of Ba through the main s-process acting in low- and intermediate- mass stars is considered as well. We also test different sets of nucleosynthesis yield…
Three-dimensional hydrodynamic simulations are commonly used to study the evolution of the gaseous content in isolated galaxies, besides its connection with galactic star formation histories. Stellar winds, supernova blasts, and black hole feedback are mechanisms usually invoked to drive galactic outflows and decrease the initial galactic gas reservoir. However, any simulation imposes the need of choosing the limits of the simulated volume, which depends, for instance, on the size of the galaxy and the required numerical resolution, besides the available computational capability to perform it.…
For almost two decades the properties of "dwarf" galaxies have challenged the Cold Dark Matter (CDM) paradigm of galaxy formation. Most observed dwarf galaxies consists of a rotating stellar disc embedded in a massive DM halo with a near constant-density core. Yet, models based on the CDM scenario invariably form galaxies with dense spheroidal stellar "bulges" and steep central DM profiles, as low angular momentum baryons and DM sink to the center of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet …
We study the impact of baryons on the distribution of dark matter in a Milky Way-size halo by comparing a high-resolution, moving-mesh cosmological simulation with its dark matter-only counterpart. We identify three main processes related to baryons -- adiabatic contraction, tidal disruption and reionization -- which jointly shape the dark matter distribution in both the main halo and its subhalos. The relative effect of each baryonic process depends strongly on the subhalo mass. For massive subhalos with maximum circular velocity $v_{\rm max} > 35 km/s$, adiabatic contraction increases the da…
