Galactic fountains and outflows in star forming dwarf galaxies: ISM expulsion and chemical enrichment

We investigated the impact of supernova feedback in gas-rich dwarf galaxies experiencing a low-to-moderate star formation rate, typical of relatively quiescent phases between starbursts. We calculated the long term evolution of the ISM and the metal-rich SN ejecta using 3D hydrodynamic simulations, in which the feedback energy is deposited by SNeII exploding in distinct OB associations. We found that a circulation flow similar to galactic fountains is generally established, with some ISM lifted at heights of one to few kpc above the galactic plane. This gas forms an extra-planar layer, which falls back to the plane in about $10^8$ yr, once the star formation stops. Very little or no ISM is expelled outside the galaxy system for the considered SFRs, even though in the most powerful model the SN energy is comparable to the gas binding energy. The metal-rich SN ejecta is instead more vulnerable to the feedback and we found that a significant fraction (25-80\%) is vented in the intergalactic medium, even for low SN rate ($7\times 10^{-5}$ - $7\times 10^{-4}$ yr$^{-1}$). About half of the metals retained by the galaxy are located far ($z >$ 500 pc) from the galactic plane. Moreover, our models indicate that the circulation of the metal-rich gas out from and back to the galactic disk is not able to erase the chemical gradients imprinted by the (centrally concentrated) SN explosions.Comment: 19 pages, MNRAS accepte

Evolution of the ISM of Starburst galaxies: the SN heating efficiency

The interstellar medium heated by SN explosions may acquire an expansion velocity larger than the escape velocity and leave the galaxy through a supersonic wind. SN ejecta are transported out of the galaxies by such winds which thus affect the chemical evolution of the galaxies. The effectiveness of the processes mentioned above depends on the heating efficiency (HE) of the SNe, that is a matter of debate. We have constructed a simple semi-analytic model, considering the essential ingredients of a SB environment which is able to qualitatively trace the thermalisation history of the ISM in a SB region and determine the HE evolution. We find that, as long as the mass-loss rate of the clouds remains larger than the rate at which the SNRs interact one with each other, the SN heating efficiency remains very small, as radiative cooling of the gas dominates. We conclude that the HE value has a time-dependent trend that is sensitive to the initial conditions of the system.Comment: 17 pages, 18 figures, A&A accepte

Multidimensional Hydrodynamical Simulations of radiative cooling SNRs-clouds interactions: an application to Starburst Environments

In this work we are interested to study the by-products of SNR-clouds in a starburst (SB) system. These interactions can have an important role in the recycling of matter from the clouds to the ISM and vice-versa. In the present work, we have focused our attention on the global effects of the interactions between clouds and SN shock waves in the ISM of SB environments, and performed 3-D radiative cooling hydrodynamical simulations with the adaptive YGUAZU grid code. We have also considered the effects of the photo-evaporation due to the presence of a high number of UV photons from hot stars and supernovae (SNe). The results have shown that, in the presence of radiative cooling, instead of an efficient gas mixing with the diffuse ISM, the interactions cause the fragmentation of the clouds into smaller ones. The results have also revealed that the SNR-clouds interactions are less efficient at producing substantial mass loss from the clouds to the diffuse ISM than mechanisms such as the photo-evaporation caused by the UV flux from the hot stars.Comment: 15 pages, 25 figures. Figures with higher resolution at the page: http://www.astro.iag.usp.br/~dalpino/ Astronomy & Astrophysics accepte

Star formation triggered by SN explosions: an application to the stellar association of β\beta Pictoris

In the present study, considering the physical conditions that are relevant in interactions between supernova remnants (SNRs) and dense molecular clouds for triggering star formation we have built a diagram of SNR radius versus cloud density in which the constraints above delineate a shaded zone where star formation is allowed. We have also performed fully 3-D radiatively cooling numerical simulations of the impact between SNRs and clouds under different initial conditions in order to follow the initial steps of these interactions. We determine the conditions that may lead either to cloud collapse and star formation or to complete cloud destruction and find that the numerical results are consistent with those of the SNR-cloud density diagram. Finally, we have applied the results above to the $\beta-$Pictoris stellar association which is composed of low mass Post-T Tauri stars with an age of 11 Myr. It has been recently suggested that its formation could have been triggered by the shock wave produced by a SN explosion localized at a distance of about 62 pc that may have occurred either in the Lower Centaurus Crux (LCC) or in the Upper Centaurus Lupus (UCL) which are both nearby older subgroups of that association (Ortega and co-workers). Using the results of the analysis above we have shown that the suggested origin for the young association at the proposed distance is plausible only for a very restricted range of initial conditions for the parent molecular cloud, i.e., a cloud with a radius of the order of 10 pc and density of the order of 20 cm$^{-3}$ and a temperature of the order of 50$-$100 K.Comment: 9 pages, 10 figures, to appear in MNRA

Galactic Outflows and the pollution of the Galactic Environment by Supernovae

We here explore the effects of the SN explosions into the environment of star-forming galaxies like the Milky Way. Successive randomly distributed and clustered SNe explosions cause the formation of hot superbubbles that drive either fountains or galactic winds above the galactic disk, depending on the amount and concentration of energy that is injected by the SNe. In a galactic fountain, the ejected gas is re-captured by the gravitational potential and falls back onto the disk. From 3D nonequilibrium radiative cooling hydrodynamical simulations of these fountains, we find that they may reach altitudes up to about 5 kpc in the halo and thus allow for the formation of the so called intermediate-velocity-clouds (IVCs) which are often observed in the halos of disk galaxies. The high-velocity-clouds that are also observed but at higher altitudes (of up to 12 kpc) require another mechanism to explain their production. We argue that they could be formed either by the capture of gas from the intergalactic medium and/or by the action of magnetic fields that are carried to the halo with the gas in the fountains. Due to angular momentum losses to the halo, we find that the fountain material falls back to smaller radii and is not largely spread over the galactic disk. Instead, the SNe ejecta fall nearby the region where the fountain was produced, a result which is consistent with recent chemical models of the galaxy. The fall back material leads to the formation of new generations of molecular clouds and to supersonic turbulence feedback in the disk.Comment: 10 pages, 5 figures; paper of invited talk for the Procs. of the 2007 WISER Workshop (World Space Environment Forum), Alexandria, Egypt, October 2007, Spa. Sci. Rev

3D Numerical Simulations of AGN Outflows in Clusters and Groups

We compute 3D gasdynamical models of jet outflows from the central AGN, that carry mass as well as energy to the hot gas in galaxy clusters and groups. These flows have many attractive attributes for solving the cooling flow problem: why the hot gas temperature and density profiles resemble cooling flows but show no spectral evidence of cooling to low temperatures. Subrelativistic jets, described by a few parameters, are assumed to be activated when gas flows toward or cools near a central SMBH. Using approximate models for a rich cluster (A1795), a poor cluster (2A 0336+096) and a group (NGC 5044), we show that mass-carrying jets with intermediate mechanical efficiencies ($\sim10^{-3}$) can reduce for many Gyr the global cooling rate to or below the low values implied by X-spectra, while maintaining $T$ and $\rho$ profiles similar to those observed, at least in clusters. Groups are much more sensitive to AGN heating and present extreme time variability in both profiles. Finally, the intermittency of the feedback generates multiple generations of X-ray cavities similar to those observed in Perseus cluster and elsewhere. Thus we also study the formation of buoyant bubbles and weak shocks in the ICM, along with the injection of metals by SNIa and stellar winds.Comment: 4 pages, 2 figures, to appear in proceedings of the conference "The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", June 2009, Madison Wisconsi