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Black holes are usually observed to be of stellar-mass or supermassive. By natural extension, there should be a population of Intermediate-Mass Black Holes (IMBHs: with mass between $100$ to $10^6 M_{\odot}$) in the Universe; which has started to been observed. An exciting claim has been made recently by Silk (2017): that early feedback by IMBHs in gas-rich dwarf galaxies at $z=5-8$, can potentially solve multiple dwarf galaxy problems within the $\Lambda$-cold-dark-matter cosmology. We are performing Cosmological Hydrodynamical Simulations of $(2 Mpc)^3$ volumes, starting from $z=100$, to test the case for IMBHs in Dwarf Galaxies. Black holes of mass $1000 M_{\odot}$ are seeded inside halos when they reach a mass of $10^7 M_{\odot}$. The black holes grow by accretion of gas from their surroundings and by merger with other black holes, and consequently eject feedback energy. We analyze the simulation output in post-processing to study the growth of the first IMBHs, and their impact on star-formation. Our conclusions, based on numerical simulation results, support the phenomenological ideas made by Silk (2017). IMBHs at the centers of dwarf galaxies can be a strong source of feedback to quench star-formation and generate outflows. At the same time, these IMBHs form the missing link between stellar-mass and supermassive BHs., Comment: 4 pages, Proceedings of Talk presented at the IAU Symposium 342 - "Perseus in Sicily: from black hole to cluster outskirts", held at Noto (Sicily, Italy), 2018 May 13-18

Magnetic fields of the order of $\mu$-Gauss are observationally detected in galaxies and galaxy clusters, which can be (at least) in part originated by the amplification of much weaker primordial seed fields. These fields should be carried out by strong galactic outflows, magnetically enriching the InterGalactic Medium (IGM). However direct observation of magnetic fields in the IGM is scarce. This talk will give a review of how Intergalactic Magnetic Field (IGMF) can be constrained using gamma-ray observations. High-energy TeV photons emitted by distant blazars can interact with the cosmic extragalactic optical/infrared/microwave background light, producing electron-positron pairs, and initiating electromagnetic cascades in the IGM. The charged component of these cascades is deflected by IGMFs, thereby reducing the observed point-like TeV flux, and creating an extended image in the GeV energy range, which can potentially be detected with $\gamma$-ray telescopes (Fermi-LAT, HESS, CTA). Studies (e.g., Neronov & Vovk 2010, Dolag et al. 2011) have put lower limits on the IGMF strength of the order of $10^{-16} - 10^{-15} G$, and filling factors of $60\%$. This talk will describe the constraints which the Cherenkov Telescope Array sensitivity is expected to give (CTA Consortium 2018)., Comment: 4 pages, Proceedings of Talk presented at the IAU Focus Meeting FM8: "New Insights in Extragalactic Magnetic Fields", held at the IAU General Assembly - Vienna, 2018 August 29-31

Intermediate-mass black holes (IMBHs: masses between $100 - 10^{6} M_{\odot}$) historically comprise of an elusive population compared to stellar-mass and supermassive BHs. Recently IMBHs have started to be observed at the centers of low-mass galaxies. We perform cosmological hydrodynamical simulations of $(2 h^{-1} ~ {\rm Mpc})^3$ comoving boxes and investigate the growth and feedback of central IMBHs in dwarf galaxies (DGs). The earliest BHs appear at $z \sim 18 - 25$, and grow thereafter by accreting gas and by merger with other BHs. We find that, starting from $10^{2} M_{\odot}$, it is possible to build up IMBHs of a few$\times 10^{5} - 10^{6} M_{\odot}$ by $z = 5$, when the BHs are seeded in halos less massive than $4 \times 10^{7} M_{\odot}$. The BH accretion rates increase with time, and reaches $\dot{M}_{\rm BH} = (0.2 - 0.8) \dot{M}_{\rm Edd}$ for the massive IMBHs by $z = 4$. The star formation rate density (SFRD) evolution of the DGs (stellar mass $10^{5} - 10^{8} M_{\odot}$) has a peak plateau between $z = 4 - 6$. Star formation is quenched between $z = 9 - 4$. The SFRD is reduced by factors up to $3$, when the BHs have grown to a few times $10^5 M_{\odot}$. Even in the presence of stronger SN-driven mass ejection, the BHs continue to grow up to $z \sim 6$, sustained by gas inflows driven by galaxy mergers and interactions in a cosmological environment. Our conclusions, based on numerical simulation results, support the scenario that early feedback from IMBHs in gas-rich DGs at $z = 5 - 8$ can potentially solve several anomalies in the DG mass range within the concordance $\Lambda$CDM cosmological scenario (Silk 2017). Our results suggest that IMBHs at DG centers grow faster than their host galaxies in the early Universe, and the resulting BH feedback turns the DGs and the BHs dormant., Comment: 18 pages, 9 figures, 2 tables. Version accepted for publication in the MNRAS

We present ALMA observations of the CO(6-5) and [CII] emission lines and the sub-millimeter continuum of the $z\sim6$ quasi-stellar object (QSO) SDSS J231038.88+185519.7. Compared to previous studies, we have analyzed a synthetic beam that is ten times smaller in angular size, we have achieved ten times better sensitivity in the CO(6-5) line, and two and half times better sensitivity in the [CII] line, enabling us to resolve the molecular gas emission. We obtain a size of the dense molecular gas of $2.9\pm0.5$ kpc, and of $1.4\pm0.2$ kpc for the 91.5 GHz dust continuum. By assuming that CO(6-5) is thermalized, and by adopting a CO--to--$H_2$ conversion factor $\rm \alpha_{CO} = 0.8~ M_{\odot}~K^{-1}~ (km/s)^{-1} ~pc^{2}$, we infer a molecular gas mass of $\rm M(H_2)=(3.2 \pm0.2) \times 10^{10}\rm M_{\odot}$. Assuming that the observed CO velocity gradient is due to an inclined rotating disk, we derive a dynamical mass of $\rm M_{dyn}~sin^2(i) = (2.4\pm0.5) \times 10^{10}~ M_{\odot}$, which is a factor of approximately two smaller than the previously reported estimate based on [CII]. Regarding the central black hole, we provide a new estimate of the black hole mass based on the C~IV emission line detected in the X-SHOOTER/VLT spectrum: $\rm M_{BH}=(1.8\pm 0.5) \times 10^{9}~ M_{\odot}$. We find a molecular gas fraction of $\rm \mu=M(H_2)/M^*\sim4.4$, where $\rm M^*\approx M_{dyn} - M(H_2)-M(BH)$. We derive a ratio $v_{rot}/\sigma \approx 1-2$ suggesting high gas turbulence, outflows/inflows and/or complex kinematics due to a merger event. We estimate a global Toomre parameter $Q\sim 0.2-0.5$, indicating likely cloud fragmentation. We compare, at the same angular resolution, the CO(6-5) and [CII] distributions, finding that dense molecular gas is more centrally concentrated with respect to [CII]. We find that the current BH growth rate is similar to that of its host galaxy., Comment: A&A in press

List of contributions from the Cherenkov Telescope Array Consortium presented at the 35th International Cosmic Ray Conference, July 12-20 2017, Busan, Korea., Comment: Index of Cherenkov Telescope Array conference proceedings at the ICRC2017, Busan, Korea

We investigate quasar outflows at $z \geq 6$ by performing zoom-in cosmological hydrodynamical simulations. By employing the SPH code GADGET-3, we zoom in the $2 R_{200}$ region around a $2 \times 10^{12} M_{\odot}$ halo at $z = 6$, inside a $(500 ~ {\rm Mpc})^3$ comoving volume. We compare the results of our AGN runs with a control simulation in which only stellar/SN feedback is considered. Seeding $10^5 M_{\odot}$ BHs at the centers of $10^{9} M_{\odot}$ halos, we find the following results. BHs accrete gas at the Eddington rate over $z = 9 - 6$. At $z = 6$, our most-massive BH has grown to $M_{\rm BH} = 4 \times 10^9 M_{\odot}$. Fast ($v_{r} > 1000$ km/s), powerful ($\dot{M}_{\rm out} \sim 2000 M_{\odot}$/yr) outflows of shock-heated low-density gas form at $z \sim 7$, and propagate up to hundreds kpc. Star-formation is quenched over $z = 8 - 6$, and the total SFR (SFR surface density near the galaxy center) is reduced by a factor of $5$ ($1000$). We analyse the relative contribution of multiple physical process: (i) disrupting cosmic filamentary cold gas inflows, (ii) reducing central gas density, (iii) ejecting gas outside the galaxy; and find that AGN feedback has the following effects at $z = 6$. The inflowing gas mass fraction is reduced by $\sim 12 \%$, the high-density gas fraction is lowered by $\sim 13 \%$, and $\sim 20 \%$ of the gas outflows at a speed larger than the escape velocity ($500$ km/s). We conclude that quasar-host galaxies at $z \geq 6$ are accreting non-negligible amount of cosmic gas, nevertheless AGN feedback quenches their star formation dominantly by powerful outflows ejecting gas out of the host galaxy halo., Comment: 17 pages (excluding references and appendix), 11 figures, Submitted

We characterize the properties of the intergalactic medium (IGM) around a sample of galaxies extracted from state-of-the-art hydrodynamical simulations of structure formation in a cosmological volume of 25 Mpc comoving at $z\sim 2$. The simulations are based on two different subresolution schemes for star formation and supernova feedback: the MUlti-Phase Particle Integrator (MUPPI) scheme and the Effective Model. We develop a quantitative and probabilistic analysis based on the apparent optical depth method of the properties of the absorbers as a function of impact parameter from their nearby galaxies: in such a way we probe different environments from circumgalactic medium to low-density filaments. Absorbers' properties are then compared with a spectroscopic observational data set obtained from high-resolution quasar spectra. Our main focus is on the N$_{\rm{ CIV}}$-N$_{\rm { HI}}$ relation around simulated galaxies: the results obtained with MUPPI and the Effective model are remarkably similar, with small differences only confined to regions at impact parameters $b = [1-3] \times r_{\rm {vir}}$. Using $\mbox{C IV}$ as a tracer of the metallicity, we obtain evidence that the observed metal absorption systems have the highest probability to be confined in a region of 150-400 kpc around galaxies. Near-filament environments have instead metallicities too low to be probed by present-day telescopes, but could be probed by future spectroscopical studies. Finally we compute $\mbox{C IV}$ covering fractions which are in agreement with observational data., Comment: 25 pages, 20 figures

At low densities the standard ionisation history of the intergalactic medium (IGM) predicts a decreasing temperature of the IGM with decreasing density once hydrogen (and helium) reionisation is complete. Heating the high-redshift, low-density IGM above the temperature expected from photo-heating is difficult, and previous claims of high/rising temperatures in low density regions of the Universe based on the probability density function (PDF) of the opacity in Lyman-$\alpha$ forest data at $2

In this work, we investigate the abundance and distribution of metals in the intergalactic medium (IGM) at $\langle z \rangle \simeq 2.8$ through the analysis of an ultra-high signal-to-noise ratio UVES spectrum of the quasar HE0940-1050. In the CIV forest, our deep spectrum is sensitive at $3\,\sigma$ to lines with column density down to $\log N_{\rm CIV} \simeq 11.4$ and in 60 per cent of the considered redshift range down to $\simeq11.1$. In our sample, all HI lines with $\log N_{\rm HI} \ge 14.8$ show an associated CIV absorption. In the range $14.0 \le \log N_{\rm HI} <14.8$, 43 per cent of HI lines has an associated CIV absorption. At $\log N_{\rm HI} < 14.0$, the detection rates drop to $<10$ per cent, possibly due to our sensitivity limits and not to an actual variation of the gas abundance properties. In the range $\log N_{\rm HI} \ge 14$, we observe a fraction of HI lines with detected CIV a factor of 2 larger than the fraction of HI lines lying in the circum-galactic medium (CGM) of relatively bright Lyman-break galaxies hosted by dark matter haloes with $\langle M\rangle \sim10^{12}$ M$_{\odot}$. The comparison of our results with the output of a grid of photoionization models and of two cosmological simulations implies that the volume filling factor of the IGM gas enriched to a metallicity $\log Z/Z_{\odot} \ge -3$ should be of the order of $\sim 10-13$ percent. In conclusion, our results favour a scenario in which metals are found also outside the CGM of bright star-forming galaxies, possibly due to pollution by lower mass objects and/or to an early enrichment by the first sources., Comment: 23 pages, 28 figures. Accepted by MNRAS on 2016 August 24. Received 2016 August 10; in original form 2016 April 15

We implement novel numerical models of AGN feedback in the SPH code GADGET-3, where the energy from a supermassive black hole (BH) is coupled to the surrounding gas in the kinetic form. Gas particles lying inside a bi-conical volume around the BH are imparted a one-time velocity (10,000 km/s) increment. We perform hydrodynamical simulations of isolated cluster (total mass 10^14 /h M_sun), which is initially evolved to form a dense cool core, having central T<10^6 K. A BH resides at the cluster center, and ejects energy. The feedback-driven fast wind undergoes shock with the slower-moving gas, which causes the imparted kinetic energy to be thermalized. Bipolar bubble-like outflows form propagating radially outward to a distance of a few 100 kpc. The radial profiles of median gas properties are influenced by BH feedback in the inner regions (r<20-50 kpc). BH kinetic feedback, with a large value of the feedback efficiency, depletes the inner cool gas and reduces the hot gas content, such that the initial cool core of the cluster is heated up within a time 1.9 Gyr, whereby the core median temperature rises to above 10^7 K, and the central entropy flattens. Our implementation of BH thermal feedback (using the same efficiency as kinetic), within the star-formation model, cannot do this heating, where the cool core remains. The inclusion of cold gas accretion in the simulations produces naturally a duty cycle of the AGN with a periodicity of 100 Myr., Comment: 22 pages, 11 figures, version accepted for publication in MNRAS, references and minor revisions added

From the Voigt profile fitting analysis of 183 intervening CIV systems at 1.7 < z < 3.3 in 23 high-quality UVES/VLT and HIRES/Keck QSO spectra, we find that a majority of CIV systems (~75%) display a well-characterised scaling relation between integrated column densities of HI and CIV with a negligible redshift evolution, when column densities of all the HI and CIV components are integrated within a given (-150, +150) km/sec range centred at the CIV flux minimum. The integrated CIV column density N(CIV, sys) increases with N(HI, sys) at log N(HI, sys) = 14.0--15.5 and log N(CIV, sys) = 11.8--14.0, then becomes almost independent of N(HI, sys) at log N(HI, sys) > 16, with a large scatter: at log N(HI, sys) = 14--22, log N(CIV, sys) = C1 / (log(NHI, sys) + C2) + C3, with C1 = -1.90+0.55, C2 = -14.11+0.19 and C3 = 14.76+0.17, respectively. The steep (flat) part is dominated by SiIV-free (SiIV-enriched) CIV systems. Extrapolating the N(HI, sys)-N(CIV, sys) relation implies that most absorbers with log N(HI) < 14 are virtually CIV-free. The N(HI, sys)-N(CIV, sys) relation does not hold for individual components, clumps or the integration velocity range less than +-100 km/sec. It is expected if the line-of-sight extent of CIV is smaller than HI and N(CIV, sys) decreases more rapidly than N(HI, sys) at the larger impact parameter, regardless of the location of the HI+CIV gas in the IGM filaments or in the intervening galactic halos., Comment: Accepted for publication on MNRAS, 26 pages, 20 figures, 4 tables. On-line materials are found in the submitted civ.tar.gz file: complete Table 2, complete Table 3, complete Table 4, velocity plots civ1.pdf, civ2.pdf, civ3.pdf, civ4.pdf and civ5.pdf

Formation of bacterial colonies as biofilm on the surface/interface of various objects has the potential to impact not only human health and disease but also energy and environmental considerations. Biofilms can be regarded as soft materials, and comprehension of their shear response to external forces is a key element to the fundamental understanding. A mesoscale model has been presented in this article based on digitization of a biofilm microstructure. Its response under externally applied shear load is analyzed. Strain stiffening type behavior is readily observed under high strain loads due to the unfolding of chains within soft polymeric substrate. Sustained shear loading of the biofilm network results in strain localization along the diagonal direction. Rupture of the soft polymeric matrix can potentially reduce the intercellular interaction between the bacterial cells. Evolution of stiffness within the biofilm network under shear reveals two regions: a) initial increase in stiffness due to strain stiffening of polymer matrix, and b) eventual reduction in stiffness because of tear in polymeric substrate.

We measure and quantify properties of galactic outflows and diffuse gas at $z \geq 1$ in cosmological hydrodynamical simulations. Our novel sub-resolution model, MUPPI, implements supernova feedback using fully local gas properties, where the wind velocity and mass loading are not given as input. We find the following trends at $z = 2$ by analysing central galaxies having a stellar mass higher than $10^{9} M_{\odot}$. The outflow velocity and mass outflow rate ($\dot{M}_{\rm out}$) exhibit positive correlations with galaxy mass and with the star formation rate (SFR). However, most of the relations present a large scatter. The outflow mass loading factor ($\eta$) is between $0.2 - 10$. The comparison Effective model generates a constant outflow velocity, and a negative correlation of $\eta$ with halo mass. The number fraction of galaxies where outflow is detected decreases at lower redshifts, but remains more than $80 \%$ over $z = 1 - 5$. High SF activity at $z \sim 2 - 4$ drives strong outflows, causing the positive and steep correlations of velocity and $\dot{M}_{\rm out}$ with SFR. The outflow velocity correlation with SFR becomes flatter at $z = 1$, and $\eta$ displays a negative correlation with halo mass in massive galaxies. Our study demonstrates that both the MUPPI and Effective models produce significant outflows at $\sim 1 / 10$ of the virial radius; at the same time shows that the properties of outflows generated can be different from the input speed and mass loading in the Effective model. Our MUPPI model, using local properties of gas in the sub-resolution recipe, is able to develop galactic outflows whose properties correlate with global galaxy properties, and consistent with observations., Comment: 23 pages, 16 figures, accepted for publication in MNRAS

Using a large N-body cosmological simulation combined with a subgrid treatment of galaxy formation, we study the formation and evolution of the galaxy and cluster population in a comoving volume (100 Mpc)^3 in a LCDM universe. At z = 0, our computational volume contains 1788 clusters with mass M_cl > 1.1x10^12 Msun, including 18 massive clusters with M_cl > 10^14 Msun. It also contains 1 088 797 galaxies with mass M_gal > 2x10^9 Msun and luminosity L > 9.5x10^5 Lsun. For each cluster, we identified the brightest cluster galaxy (BCG). We then computed the fraction f_BNC of clusters in which the BCG is not the closest galaxy to the center of the cluster in projection, and the ratio Dv/s, where Dv is the difference in radial velocity between the BCG and the whole cluster, and s is the radial velocity dispersion of the cluster. f_BNC increases from 0.05 for low-mass clusters (M_cl ~ 10^12 Msun) to 0.5 for high-mass ones (M_cl > 10^14 Msun), with no dependence on cluster redshift. The values of Dv/s vary from 0 to 1.8. These results are consistent with previous observational studies, and indicate that the central galaxy paradigm, which states that the BCG should be at rest at the center of the cluster, is usually valid, but exceptions are too common to be ignored. Analysis of the merger trees for the 18 most massive clusters in the simulation reveals that 16 of these clusters have experienced major mergers in the past. These mergers leave each cluster in a non-equilibrium state, but eventually the cluster settles into an equilibrium configuration, unless it is disturbed by another major merger. We found evidence that these mergers are responsible for the off-center positions and peculiar velocities of some BCGs. Our results thus support the merging-group scenario, in which some clusters form by the merger of smaller groups in which the galaxies have already formed., Comment: 32 pages, 11 figures (one in color). Accepted for publication in The Astrophysical Journal

We study the role of feedback from supernovae and black holes in the evolution of the star formation rate function (SFRF) of z~4-7 galaxies. We use a new set of cosmological hydrodynamic simulations, ANGUS (AustraliaN GADGET-3 early Universe Simulations), run with a modified and improved version of the parallel TreePM-smoothed particle hydrodynamics code GADGET-3 called P-GADGET3(XXL), that includes a self-consistent implementation of stellar evolution and metal enrichment. In our simulations both Supernova (SN) driven galactic winds and Active Galactic Nuclei (AGN) act simultaneously in a complex interplay. The SFRF is insensitive to feedback prescription at z>5, meaning that it cannot be used to discriminate between feedback models during reionisation. However, the SFRF is sensitive to the details of feedback prescription at lower redshift. By exploring different SN driven wind velocities and regimes for the AGN feedback, we find that the key factor for reproducing the observed SFRFs is a combination of "strong" SN winds and early AGN feedback in low mass galaxies. Conversely, we show that the choice of initial mass function and inclusion of metal cooling have less impact on the evolution of the SFRF. When variable winds are considered, we find that a non-aggressive wind scaling is needed to reproduce the SFRFs at z>4. Otherwise, the amount of objects with low SFRs is greatly suppressed and at the same time winds are not effective enough in the most massive systems., Comment: 18 pages, 3 tables, 8 figures, accepted for publication in MNRAS

(Abridged) We investigate two modes of coupling the feedback energy from a central AGN to the neighboring gas in galaxy simulations: kinetic - velocity boost, and thermal - heating. We formulate kinetic feedback models for energy-driven wind (EDW) and momentum-driven wind (MDW), using two free parameters: feedback efficiency epsilon_f, and AGN wind velocity v_w. A novel numerical algorithm is implemented in the SPH code GADGET-3, to prevent the expansion of a hole in the gas distribution around the BH. We perform simulations of isolated evolution and merger of disk galaxies, of Milky-Way mass as well as lower and higher masses. We find that in the isolated galaxy BH kinetic feedback generates intermittent bipolar jet-like gas outflows. We infer that current prescriptions for BH subgrid physics in galaxy simulations can grow the BH to observed values even in an isolated disk galaxy. The BH growth is enhanced in a galaxy merger. Comparing the [M_BH - sigma_star] relation obtained in our simulations with observational data, we conclude that it is possible to find parameter sets for a fit in all the models, except for the case with MDW feedback in a galaxy merger, in which the BH is always too massive. The BH thermal feedback implementation of Springel, Di Matteo & Hernquist (2005) within the multiphase star-formation model is found to have negligible impact on gas properties; and the effect claimed in all previous studies is attributed to gas depletion around the BH by the creation of an artificial hole. The BH mass accretion rate in our simulations exhibit heavy fluctuations. The star formation rate is quenched with feedback by removal of gas. The CGM gas at galactocentric distances (20 - 100)/h kpc are found to give the best metallicity observational diagnostic to distinguish between BH models., Comment: 22 pages, 9 figures, 2 tables. Version accepted for publication in MNRAS. Title changed (to clarify focus of the paper) and more discussion added during revision

We study the effect of the sample thickness in planar crack front propagation in a disordered elastic medium using the random fuse model. We employ different loading conditions and we test their stability with respect to crack growth. We show that the thickness induces characteristic lengths in the stress enhancement factor in front of the crack and in the stress transfer function parallel to the crack. This is reflected by a thickness-dependent crossover scale in the crack front morphology that goes from from multi-scaling to self-affine with exponents in agreement with line depinning models and experiments. Finally, we compute the distribution of crack avalanches which is shown to depend on the thickness and the loading mode., Comment: 8 pages, 11 figures

We present a new integrated, portable device to provide a convenient solution for remote monitoring heart rate at the fingertip and body temperature using Ethernet technology and widely spreading internet. Now a days, heart related disease is rising. Most of the times in these cases, patients may not realize their actual conditions and even it is a common fact that there are no doctors by their side, especially in rural areas, but now a days most of the diseases are curable if detected in time. We have tried to make a system which may give information about one's physical condition and help him or her to detect these deadly but curable diseases. The system gives information of heart rate and body temperature simultaneously acquired on the portable side in real time and transmits results to web. In this system, the condition of heart and body temperature can be monitored from remote places. Eventually, this device provides a low cost, easily accessible human health monitor solution bridging the gaps between patients and doctors.

We introduce a novel formalism to investigate the role of the spin angular momentum of astrophysical black holes in influencing the behaviour of low angular momentum general relativistic accretion. We propose a metric independent analysis of axisymmetric general relativistic flow, and consequently formulate the space and time dependent equations describing the general relativistic hydrodynamic accretion flow in the Kerr metric. The associated stationary critical solutions for such flow equations are provided and the stability of the stationary transonic configuration is examined using an elegant linear perturbation technique. We examine the properties of infalling material for both prograde and retrograde accretion as a function of the Kerr parameter at extremely close proximity to the event horizon. Our formalism can be used to identify a new spectral signature of black hole spin, and has the potential of performing the black hole shadow imaging corresponding to the low angular momentum accretion flow., Comment: To appear in New Astronomy. 46 pages. 14 figures

(Abridged) We explore new observationally-constrained sub-resolution models of galactic outflows and investigate their impact on the circumgalactic medium (CGM) over redshifts z = 2 - 4. We perform cosmological hydrodynamic simulations, including star formation, chemical enrichment, and four cases of SNe-driven outflows: no wind (NW), an energy-driven constant velocity wind (CW), a radially varying wind (RVWa) where the outflow velocity has a positive correlation with galactocentric distance (r), and a RVW with additional dependence on halo mass (RVWb). Overall, we find that the outflows expel metal-enriched gas away from galaxies, significantly quench star formation, and enrich the CGM. At z = 2, the radial profiles of gas properties around galaxy centers are most sensitive to the choice of the wind model for halo masses (10^9 - 10^11) M_sun. We infer that the RVWb model is similar to the NW case, except that it substantially enriches the CGM: the carbon metallicity (Z_C) is 10 times higher in RVWb than in NW at r > R_200; and the warm gas of 10^4 - 10^5 K and delta < 100 is enriched to 50 times higher than in NW. We also find that the impact of models CW and RVWa are similar, with the following differences. RVWa causes a greater suppression of star formation rate at z < 5, and has a higher fraction of low-density (delta < 10), warm-hot (10^4 - 10^6 K) gas than in CW. Outflows in CW produce a higher and earlier enrichment of some IGM phases than RVWa. By visual inspection, we note that the RVWa model shows more pronounced bipolar outflows and galactic disks. We present fitting formulae for [Z_C-delta] and [Z_C-r], also for the abundance of CIV as a function of r. We predict observational diagnostics to distinguish between different outflow scenarios: Z_C of the CGM gas at r = (30 - 300) kpc/h comoving, and CIV fraction of the inner gas at r < (4 - 5) kpc/h comoving., Comment: Version accepted for publication in MNRAS. Manuscript file with higher resolution Fig. 2 can be found here: http://adlibitum.oats.inaf.it/barai/AllPages/Images-Movies/RadialVarWind.pdf

We combine a N-body simulation algorithm with a subgrid treatment of galaxy formation, mergers, and tidal destruction, and an observed conditional luminosity function Phi(L|M), to study the origin and evolution of galactic and extragalactic light inside a cosmological volume of size (100 Mpc)^3, in a concordance LCDM model. This algorithm simulates the growth of large-scale structures and the formation of clusters, the evolution of the galaxy population in clusters, the destruction of galaxies by mergers and tides, and the evolution of the intracluster light. We find that destruction of galaxies by mergers dominates over destruction by tides by about an order of magnitude at all redshifts. However, tidal destruction is sufficient to produce intracluster light fractions f_ICL that are sufficiently high to match observations. The bulk of the intracluster light (60%) is provided by intermediate galaxies of total masses 10^11 Msun-10^12 Msun and stellar masses 6x10^8 Msun-3x10^10 Msun that were tidally destroyed by even more massive galaxies. The contribution of low-mass galaxies to the intracluster light is small and the contribution of dwarf galaxies is negligible, even though, by numbers, most galaxies that are tidally destroyed are dwarfs. Tracking clusters back in time, we find that their values of f_ICL tend to increase over time, but can experience sudden changes that are sometimes non-monotonic. These changes occur during major mergers involving clusters of comparable masses but very different intracluster luminosities. Most of the tidal destruction events take place in the central regions of clusters. As a result, the intracluster light is more centrally concentrated than the galactic light. Our results support tidal destruction of intermediate-mass galaxies as a plausible scenario for the origin of the intracluster light., Comment: 13 figures, one in color. Accepted for publication in ApJ

(Abridged) We investigate non-spherical behavior of gas accreting onto a central supermassive black hole performing simulations using the SPH code GADGET-3 including radiative cooling and heating by the central X-ray source. As found in earlier 1D studies, our 3D simulations show that the accretion mode depends on the X-ray luminosity (L_X) for a fixed density at infinity and accretion efficiency. In the low L_X limit, gas accretes in a stable, spherically symmetric fashion. In the high L_X limit, the inner gas is significantly heated up and expands, reducing the central mass inflow rate. The expanding gas can turn into a strong enough outflow capable of expelling most of the gas at larger radii. For some intermediate L_X, the accretion flow becomes unstable developing prominent non-spherical features, the key reason for which is thermal instability (TI) as shown by our analyses. Small perturbations of the initially spherically symmetric accretion flow that is heated by the intermediate L_X quickly grow to form cold and dense clumps surrounded by overheated low density regions. The cold clumps continue their inward motion forming filamentary structures; while the hot infalling gas slows down because of buoyancy and can even start outflowing through the channels in between the filaments. We found that the ratio between the mass inflow rates of the cold and hot gas is a dynamical quantity depending on several factors: time, spatial location, and L_X; and ranges between 0 and 4. We briefly discuss astrophysical implications of such TI-driven fragmentation of accreting gas on the formation of clouds in narrow and broad line regions of AGN, the formation of stars, and the observed variability of the AGN luminiosity., Comment: 25 pages, 13 figures. Version accepted for publication in MNRAS. Uploaded version contains low-resolution color figures. Complete paper with high-resolution figures can be found at: http://adlibitum.oats.inaf.it/barai/AllPages/Images-Movies/BHaccr_MultiPhase.pdf

We study the gas accretion onto a supermassive black hole (SMBH) using the 3D SPH code GADGET-3 on scales of 0.1-200 pc. First we test our code with spherically symmetric, adiabatic Bondi accretion problem. We find that our simulation can reproduce the expected Bondi accretion flow very well for a limited amount of time until the effect of outer boundary starts to be visible. We also find artificial heating of gas near the inner accretion boundary due to the artificial viscosity of SPH. Second, we implement radiative cooling and heating due to X-rays, and examine the impact of thermal feedback by the central X-ray source. The accretion flow roughly follows the Bondi solution for low central X-ray luminosities, however, the flow starts to exhibit non-spherical fragmentation due to thermal instability for a certain range of central L_X, and a strong overall outflow develops for greater L_X. The cold gas develops filamentary structures that fall into the central SMBH, whereas the hot gas tries to escape through the channels in-between the cold filaments. Such fragmentation of accreting gas can assist in the formation of clouds around AGN, induce star-formation, and contribute to the observed variability of narrow-line regions., Comment: 5 pages, 3 figures. Conference proceedings of "AGN Winds in Charleston", Charleston, SC, Oct 15-18, 2011. Ed. by G. Chartas, et al. To be published by ASP. Updated one reference

(Abridged) We test how accurately the smoothed particle hydrodynamics (SPH) numerical technique can follow spherically-symmetric Bondi accretion. Using the 3D SPH code GADGET-3, we perform simulations of gas accretion onto a central supermassive black hole (SMBH) of mass 10^8 M_sun within the radial range of 0.1 - 200 pc. We carry out simulations without and with radiative heating by a central X-ray corona and radiative cooling. For an adiabatic case, the radial profiles of hydrodynamical properties match the Bondi solution, except near the inner and outer radius of the computational domain. We find that adiabatic Bondi accretion can be reproduced for durations of a few dynamical times at the Bondi radius, and for longer times if the outer radius is increased. With radiative heating and cooling included, the spherically accreting gas takes a longer time to reach a steady-state than the adiabatic Bondi accretion runs, and in some cases does not reach a steady-state even within several hundred dynamical times. We find that artificial viscosity in the GADGET code causes excessive heating near the inner radius, making the thermal properties of the gas inconsistent with a physical solution. This overheating occurs typically only in the supersonic part of the flow, so that it does not affect the mass accretion rate. We see that increasing the X-ray luminosity produces a lower central mass inflow rate, implying that feedback due to radiative heating is operational in our simulations. With a sufficiently high X-ray luminosity, the inflowing gas is radiatively heated up, and an outflow develops. We conclude that the SPH simulations can capture the gas dynamics needed to study radiative feedback provided artificial viscosity alters only highly supersonic part of the inflow., Comment: 25 pages, 3 tables, and 16 figures. Version accepted for publication in MNRAS. Sec. 3.1.5 extensively revised, results from new runs added

We investigate the large-scale influence of outflows from AGNs in enriching the IGM with metals in a cosmological context. We combine cosmological simulations of large scale structure formation with a detailed model of metal enrichment, in which outflows expand anisotropically along the direction of least resistance, distributing metals into the IGM. The metals carried by the outflows are generated by two separate stellar populations: stars located near the central AGN, and stars located in the greater galaxy. Using this algorithm, we performed a series of 5 simulations of the propagation of AGN-driven outflows in a cosmological volume of size (128/h Mpc)^3 in a Lambda-CDM universe, and analyze the resulting metal enrichment of the IGM. We found that the metallicity induced in the IGM is greatly dominated by AGNs having bolometric luminosity L > 10^9 L_sun, sources with 10^8 < L / L_sun < 10^9 having a negligible contribution. Our simulations produced an average IGM metallicity of [O/H] = -5 at z = 5.5, which then rises gradually, and remains relatively flat at a value [O/H] = -2.8 between z = 2 and z = 0. The ejection of metals from AGN host galaxies by AGN-driven outflows is found to enrich the IGM to > 10 - 20% of the observed values, the number dependent on redshift. The enriched IGM volume fractions are small at z > 3, then rise rapidly to the following values at z = 0: 6 - 10% of the volume enriched to [O/H] > -2.5, 14 - 24% volume to [O/H] > -3, and 34 - 45% volume to [O/H] > -4. At z > 2, there is a gradient of the induced enrichment, the metallicity decreasing with increasing IGM density, enriching the underdense IGM to higher metallicities, a trend more prominent with increasing anisotropy of the outflows. This can explain observations of metal-enriched low-density IGM at z = 3 - 4., Comment: 18 pages, 12 figures, submitted