Yuval Birnboim - Academia.edu (original) (raw)

Papers by Yuval Birnboim

Nature, 2009

The massive galaxies in the young Universe, ten billion years ago, formed stars at surprising int... more The massive galaxies in the young Universe, ten billion years ago, formed stars at surprising intensities. 1,2 Although this is commonly attributed to violent mergers, the properties of many of these galaxies are incompatible with such events, showing gas-rich, clumpy, extended rotating disks not dominated by spheroids. 1,3,4 Cosmological simulations 5 and clustering theory 6,7 are used to explore how these galaxies acquired their gas. Here we report that they are stream-fed galaxies, formed from steady, narrow, cold gas streams that penetrate the shock-heated media of massive dark matter haloes. 8,9 A comparison with the observed abundance of star-forming galaxies implies that most of the input gas must rapidly convert to stars. One-third of the stream mass is in gas clumps leading to mergers of mass ratio greater than 1:10, and the rest is in smoother flows. With a merger duy cycle of 0.1, three-quarters of the galaxies forming stars at a given rate are fed by smooth streams. The rarer, submillimetre galaxies that form stars even more intensely 2,10,11 are largely merger-induced starbursts. Unlike destructive mergers, the streams are likely to keep the rotating disk configuration intact, although turbulent and broken into giant starforming clumps that merge into a central spheroid. 4, This stream-driven scenario for the formation of disks and spheroids is an alternative to the merger picture.

Monthly Notices of the Royal Astronomical Society

Cold fronts (CFs) are found in most galaxy clusters, as well as in some galaxies and groups of ga... more Cold fronts (CFs) are found in most galaxy clusters, as well as in some galaxies and groups of galaxies. We propose that some CFs are relics of merging between two shocks propagating in the same direction. Such shock mergers typically result in a quasi-spherical, factor ~1.4-2.7 discontinuity in density and in temperature. These CFs may be found as far out as the virial shock, unlike what is expected in other CF formation models. As a demonstration of this effect, we use one dimensional simulations of clusters and show that shock induced cold fronts form when perturbations such as explosions or mergers occur near the cluster's centre. Perturbations at a cluster's core induce periodic merging between the virial shock and outgoing secondary shocks. These collisions yield a distinctive, concentric, geometric sequence of CFs which trace the expansion of the virial shock.

Monthly Notices of the Royal Astronomical Society, 2007

We simulate the buildup of galaxies by spherical gas accretion through dark-matter haloes, subjec... more We simulate the buildup of galaxies by spherical gas accretion through dark-matter haloes, subject to the development of virial shocks. We find that a uniform cosmological accretion rate turns into a rapidly varying disc buildup rate. The generic sequence of events (Shocked-Accretion Massive Burst & Shutdown: SAMBA) consists of four distinct phases: (a) continuous cold accretion while the halo is below a threshold mass M sh ∼ 10 12 M ⊙ , (b) tentative quenching of gas supply for ∼ 2 Gyr, starting abruptly once the halo is ∼ M sh and growing a rapidly expanding shock, (c) a massive burst due to the big crunch of ∼ 10 11 M ⊙ gas in ∼ 0.5 Gyr, when the accumulated heated gas cools and joins new infalling gas, and (d) a long-term shutdown, enhanced by a temporary shock instability in late SAMBAs, those that quench at z ∼ 2, burst at z ∼ 1 and end up quenched in 10 12−13 M ⊙ haloes today. The quenching and bursting occur at all redshifts in galaxies of baryonic mass ∼ 10 11 M ⊙ and involve a substantial fraction of this mass. They arise from rather smooth accretion, or minor mergers, which, unlike major mergers, may leave the disc intact while being built in a rapid pace. The early bursts match observed maximum starbursting discs at z > ∼ 2, predicted to reside in < ∼ 10 13 M ⊙ haloes. The late bursts resemble discy LIRGs at z < ∼ 1. On the other hand, the tentative quenching gives rise to a substantial population of ∼ 10 11 M ⊙ galaxies with a strongly suppressed star-formation rate at z ∼ 1-3. The predicted longterm shutdown leads to red & dead galaxies in groups. A complete shutdown in more massive clusters requires an additional quenching mechanism, as may be provided by clumpy accretion. Alternatively, the SAMBA bursts may trigger the AGN activity that couples to the hot gas above M sh and helps the required quenching. The SAMBA phenomenon is yet to be investigated using cosmological simulations.

Monthly Notices of the Royal Astronomical Society, 2011

Monthly Notices of the Royal Astronomical Society, 2007

We consider a simple gravitational-heating mechanism for the long-term quenching of cooling flows... more We consider a simple gravitational-heating mechanism for the long-term quenching of cooling flows and star formation in massive dark-matter haloes hosting elliptical galaxies and clusters. The virial shock heating in haloes 10 12 M ⊙ triggers natural quenching in 10 12−13 M ⊙ haloes . Analytic estimates and simple simulations argue that the long-term quenching in haloes M min ∼ 7 × 10 12 M ⊙ could be due to the gravitational energy of cosmological accretion delivered to the innerhalo hot gas by cold flows via ram-pressure drag and local shocks. M min is obtained by comparing the gravitational power of infall into the potential well with the overall radiative cooling rate. The heating wins if the gas inner density cusp is not steeper than r −0.5 and if the masses in the cold and hot phases are comparable. The effect is stronger at higher redshifts, making the maintenance easier also at later times. Particular energy carriers into the halo core are cold gas clumps of ∼ 10 5−8 M ⊙ . Clumps 10 5 M ⊙ penetrate to the inner halo with sufficient kinetic energy before they disintegrate, but they have to be 10 8 M ⊙ for the drag to do enough work in a Hubble time. Pressure confined ∼ 10 4 K clumps are stable against their own gravity and remain gaseous once below the Bonnor-Ebert mass ∼ 10 8 M ⊙ . Such clumps are also immune to tidal disruption. Clumps in the desired mass range could emerge by thermal instability in the outer halo or in the filaments that feed it if the conductivity is not too high. Alternatively, such clumps may be embedded in dark-matter subhaloes if the ionizing flux is ineffective, but they separate from their subhaloes by ram pressure before entering the inner halo. Heating by dynamical friction becomes dominant for massive satellites, which can contribute up to one third of the total gravitational heating. We conclude that gravitational heating by cosmological accretion is a viable alternative to AGN feedback as a long-term quenching mechanism.

Monthly Notices of the Royal Astronomical Society, 2003

We investigate the conditions for the existence of an expanding virial shock in the gas falling w... more We investigate the conditions for the existence of an expanding virial shock in the gas falling within a spherical dark-matter halo. The shock relies on pressure support by the shock-heated gas behind it. When the radiative cooling is efficient compared to the infall rate the post-shock gas becomes unstable; it collapses inwards and cannot support the shock. We find for a monoatomic gas that the shock is stable when the post-shock pressure and density obey γ eff ≡ (d ln P/dt)/(d ln ρ/dt) > 10/7. When expressed in terms of the pre-shock gas properties at radius r it reads ρrΛ(T )/u 3 < .0126, where ρ is the gas density, u is the infall velocity and Λ(T ) is the cooling function, with the post-shock temperature T ∝ u 2 . This result is confirmed by hydrodynamical simulations, using an accurate spheri-symmetric Lagrangian code. When the stability analysis is applied in cosmology, we find that a virial shock does not develop in most haloes that form before z ∼ 2, and it never forms in haloes less massive than a few 10 11 M ⊙ . In such haloes, the infalling gas is not heated to the virial temperature until it hits the disc, thus avoiding the cooling-dominated quasi-static contraction phase. The direct collapse of the cold gas into the disc should have nontrivial effects on the star-formation rate and on outflows. The soft X-ray produced by the shock-heated gas in the disc is expected to ionize the dense disc environment, and the subsequent recombination would result in a high flux of L α emission. This may explain both the puzzling low flux of soft X-ray background and the L α emitters observed at high redshift.

Monthly Notices of the Royal Astronomical Society, 2006

... 2001). With the new data from big surveys such as SDSS, 2MASS and 2dF, and the detailed semi-... more ... 2001). With the new data from big surveys such as SDSS, 2MASS and 2dF, and the detailed semi-analytic modelling (SAM) of galaxy formation, it is becoming clear that the observed scale is somewhat smaller and the drop is sharper than predicted by the original picture. ...

The Astrophysical Journal, 2010

Cold fronts (CFs) -density and temperature plasma discontinuities -are ubiquitous in cool cores o... more Cold fronts (CFs) -density and temperature plasma discontinuities -are ubiquitous in cool cores of galaxy clusters, where they appear as X-ray brightness edges in the intracluster medium, nearly concentric with the cluster center. We analyze the thermodynamic profiles deprojected across core CFs found in the literature. While the pressure appears continuous across these CFs, we find that all of them require significant centripetal acceleration beneath the front. This is naturally explained by a tangential, nearly sonic bulk flow just below the CF, and a tangential shear flow involving a fair fraction of the plasma beneath the front. Such shear should generate near-equipartition magnetic fields on scales 50 pc from the front, and could magnetize the entire core. Such fields would explain the apparent stability of cool-core CFs and the recently reported CF-radio minihalo association.

Cold fronts (CFs) are found in most galaxy clusters, as well as in some galaxies and groups of ga... more Cold fronts (CFs) are found in most galaxy clusters, as well as in some galaxies and groups of galaxies. We propose that some CFs are relics of collisions between trailing shocks. Such a collision typically results in a spherical, factor ~1.4-2.7 density/temperature discontinuity. These CFs may be found as far as the virial shock, unlike in other CF formation models. As a demonstration of this effect, we use one dimensional simulations where halo reverberations involving periodic collisions between the virial shock and outgoing secondary shocks exist. These collisions yield a distinctive, concentric geometric sequence of CFs which trace the expansion of the virial shock. Comment: 5 pages, 4 figures, this letter is superseded by a more detailed version in arXiv:1006.1892

Nature, 2009

The massive galaxies in the young Universe, ten billion years ago, formed stars at surprising int... more The massive galaxies in the young Universe, ten billion years ago, formed stars at surprising intensities. 1,2 Although this is commonly attributed to violent mergers, the properties of many of these galaxies are incompatible with such events, showing gas-rich, clumpy, extended rotating disks not dominated by spheroids. 1,3,4 Cosmological simulations 5 and clustering theory 6,7 are used to explore how these galaxies acquired their gas. Here we report that they are stream-fed galaxies, formed from steady, narrow, cold gas streams that penetrate the shock-heated media of massive dark matter haloes. 8,9 A comparison with the observed abundance of star-forming galaxies implies that most of the input gas must rapidly convert to stars. One-third of the stream mass is in gas clumps leading to mergers of mass ratio greater than 1:10, and the rest is in smoother flows. With a merger duy cycle of 0.1, three-quarters of the galaxies forming stars at a given rate are fed by smooth streams. The rarer, submillimetre galaxies that form stars even more intensely 2,10,11 are largely merger-induced starbursts. Unlike destructive mergers, the streams are likely to keep the rotating disk configuration intact, although turbulent and broken into giant starforming clumps that merge into a central spheroid. 4, This stream-driven scenario for the formation of disks and spheroids is an alternative to the merger picture.

Monthly Notices of the Royal Astronomical Society

Cold fronts (CFs) are found in most galaxy clusters, as well as in some galaxies and groups of ga... more Cold fronts (CFs) are found in most galaxy clusters, as well as in some galaxies and groups of galaxies. We propose that some CFs are relics of merging between two shocks propagating in the same direction. Such shock mergers typically result in a quasi-spherical, factor ~1.4-2.7 discontinuity in density and in temperature. These CFs may be found as far out as the virial shock, unlike what is expected in other CF formation models. As a demonstration of this effect, we use one dimensional simulations of clusters and show that shock induced cold fronts form when perturbations such as explosions or mergers occur near the cluster's centre. Perturbations at a cluster's core induce periodic merging between the virial shock and outgoing secondary shocks. These collisions yield a distinctive, concentric, geometric sequence of CFs which trace the expansion of the virial shock.

Monthly Notices of the Royal Astronomical Society, 2007

We simulate the buildup of galaxies by spherical gas accretion through dark-matter haloes, subjec... more We simulate the buildup of galaxies by spherical gas accretion through dark-matter haloes, subject to the development of virial shocks. We find that a uniform cosmological accretion rate turns into a rapidly varying disc buildup rate. The generic sequence of events (Shocked-Accretion Massive Burst & Shutdown: SAMBA) consists of four distinct phases: (a) continuous cold accretion while the halo is below a threshold mass M sh ∼ 10 12 M ⊙ , (b) tentative quenching of gas supply for ∼ 2 Gyr, starting abruptly once the halo is ∼ M sh and growing a rapidly expanding shock, (c) a massive burst due to the big crunch of ∼ 10 11 M ⊙ gas in ∼ 0.5 Gyr, when the accumulated heated gas cools and joins new infalling gas, and (d) a long-term shutdown, enhanced by a temporary shock instability in late SAMBAs, those that quench at z ∼ 2, burst at z ∼ 1 and end up quenched in 10 12−13 M ⊙ haloes today. The quenching and bursting occur at all redshifts in galaxies of baryonic mass ∼ 10 11 M ⊙ and involve a substantial fraction of this mass. They arise from rather smooth accretion, or minor mergers, which, unlike major mergers, may leave the disc intact while being built in a rapid pace. The early bursts match observed maximum starbursting discs at z > ∼ 2, predicted to reside in < ∼ 10 13 M ⊙ haloes. The late bursts resemble discy LIRGs at z < ∼ 1. On the other hand, the tentative quenching gives rise to a substantial population of ∼ 10 11 M ⊙ galaxies with a strongly suppressed star-formation rate at z ∼ 1-3. The predicted longterm shutdown leads to red & dead galaxies in groups. A complete shutdown in more massive clusters requires an additional quenching mechanism, as may be provided by clumpy accretion. Alternatively, the SAMBA bursts may trigger the AGN activity that couples to the hot gas above M sh and helps the required quenching. The SAMBA phenomenon is yet to be investigated using cosmological simulations.

Monthly Notices of the Royal Astronomical Society, 2011

Monthly Notices of the Royal Astronomical Society, 2007

We consider a simple gravitational-heating mechanism for the long-term quenching of cooling flows... more We consider a simple gravitational-heating mechanism for the long-term quenching of cooling flows and star formation in massive dark-matter haloes hosting elliptical galaxies and clusters. The virial shock heating in haloes 10 12 M ⊙ triggers natural quenching in 10 12−13 M ⊙ haloes . Analytic estimates and simple simulations argue that the long-term quenching in haloes M min ∼ 7 × 10 12 M ⊙ could be due to the gravitational energy of cosmological accretion delivered to the innerhalo hot gas by cold flows via ram-pressure drag and local shocks. M min is obtained by comparing the gravitational power of infall into the potential well with the overall radiative cooling rate. The heating wins if the gas inner density cusp is not steeper than r −0.5 and if the masses in the cold and hot phases are comparable. The effect is stronger at higher redshifts, making the maintenance easier also at later times. Particular energy carriers into the halo core are cold gas clumps of ∼ 10 5−8 M ⊙ . Clumps 10 5 M ⊙ penetrate to the inner halo with sufficient kinetic energy before they disintegrate, but they have to be 10 8 M ⊙ for the drag to do enough work in a Hubble time. Pressure confined ∼ 10 4 K clumps are stable against their own gravity and remain gaseous once below the Bonnor-Ebert mass ∼ 10 8 M ⊙ . Such clumps are also immune to tidal disruption. Clumps in the desired mass range could emerge by thermal instability in the outer halo or in the filaments that feed it if the conductivity is not too high. Alternatively, such clumps may be embedded in dark-matter subhaloes if the ionizing flux is ineffective, but they separate from their subhaloes by ram pressure before entering the inner halo. Heating by dynamical friction becomes dominant for massive satellites, which can contribute up to one third of the total gravitational heating. We conclude that gravitational heating by cosmological accretion is a viable alternative to AGN feedback as a long-term quenching mechanism.

Monthly Notices of the Royal Astronomical Society, 2003

We investigate the conditions for the existence of an expanding virial shock in the gas falling w... more We investigate the conditions for the existence of an expanding virial shock in the gas falling within a spherical dark-matter halo. The shock relies on pressure support by the shock-heated gas behind it. When the radiative cooling is efficient compared to the infall rate the post-shock gas becomes unstable; it collapses inwards and cannot support the shock. We find for a monoatomic gas that the shock is stable when the post-shock pressure and density obey γ eff ≡ (d ln P/dt)/(d ln ρ/dt) > 10/7. When expressed in terms of the pre-shock gas properties at radius r it reads ρrΛ(T )/u 3 < .0126, where ρ is the gas density, u is the infall velocity and Λ(T ) is the cooling function, with the post-shock temperature T ∝ u 2 . This result is confirmed by hydrodynamical simulations, using an accurate spheri-symmetric Lagrangian code. When the stability analysis is applied in cosmology, we find that a virial shock does not develop in most haloes that form before z ∼ 2, and it never forms in haloes less massive than a few 10 11 M ⊙ . In such haloes, the infalling gas is not heated to the virial temperature until it hits the disc, thus avoiding the cooling-dominated quasi-static contraction phase. The direct collapse of the cold gas into the disc should have nontrivial effects on the star-formation rate and on outflows. The soft X-ray produced by the shock-heated gas in the disc is expected to ionize the dense disc environment, and the subsequent recombination would result in a high flux of L α emission. This may explain both the puzzling low flux of soft X-ray background and the L α emitters observed at high redshift.

Monthly Notices of the Royal Astronomical Society, 2006

... 2001). With the new data from big surveys such as SDSS, 2MASS and 2dF, and the detailed semi-... more ... 2001). With the new data from big surveys such as SDSS, 2MASS and 2dF, and the detailed semi-analytic modelling (SAM) of galaxy formation, it is becoming clear that the observed scale is somewhat smaller and the drop is sharper than predicted by the original picture. ...

The Astrophysical Journal, 2010

Cold fronts (CFs) -density and temperature plasma discontinuities -are ubiquitous in cool cores o... more Cold fronts (CFs) -density and temperature plasma discontinuities -are ubiquitous in cool cores of galaxy clusters, where they appear as X-ray brightness edges in the intracluster medium, nearly concentric with the cluster center. We analyze the thermodynamic profiles deprojected across core CFs found in the literature. While the pressure appears continuous across these CFs, we find that all of them require significant centripetal acceleration beneath the front. This is naturally explained by a tangential, nearly sonic bulk flow just below the CF, and a tangential shear flow involving a fair fraction of the plasma beneath the front. Such shear should generate near-equipartition magnetic fields on scales 50 pc from the front, and could magnetize the entire core. Such fields would explain the apparent stability of cool-core CFs and the recently reported CF-radio minihalo association.

Cold fronts (CFs) are found in most galaxy clusters, as well as in some galaxies and groups of ga... more Cold fronts (CFs) are found in most galaxy clusters, as well as in some galaxies and groups of galaxies. We propose that some CFs are relics of collisions between trailing shocks. Such a collision typically results in a spherical, factor ~1.4-2.7 density/temperature discontinuity. These CFs may be found as far as the virial shock, unlike in other CF formation models. As a demonstration of this effect, we use one dimensional simulations where halo reverberations involving periodic collisions between the virial shock and outgoing secondary shocks exist. These collisions yield a distinctive, concentric geometric sequence of CFs which trace the expansion of the virial shock. Comment: 5 pages, 4 figures, this letter is superseded by a more detailed version in arXiv:1006.1892