arXiv subjects

Sadegh Khochfar

Publications and source records attributed to Sadegh Khochfar.

At least 91 records · Page 5Linked to original sources

arXiv2013

The Atlas3D project - XV. Benchmark for early-type galaxies scaling relations from 260 dynamical models: mass-to-light ratio, dark matter, Fundamental Plane and Mass Plane

We study the volume-limited and nearly mass selected (stellar mass M>6*10^9 Msun) Atlas3D sample of 260 early-type galaxies. We construct detailed axisymmetric dynamical models (JAM), which allow for orbital anisotropy, include a dark matter halo, and reproduce in detail both the galaxy images and the high-quality integral-field stellar kinematics. We derive accurate total M/L and dark matter fractions f_DM, within a sphere of radius r=Re. We also measure the stellar M/L and derive a median dark matter fraction f_DM=13%. We find that the thin two-dimensional subset spanned by galaxies in the (M_JAM,sigma_e,R_e) coordinates system, which we call the Mass Plane (MP) has an observed rms scatter of 19% and an intrinsic one of 11%. The MP satisfies the scalar virial relation M_JAM sigma_e^2 R_e within our tight errors. However, the details of how both Re and sigma_e are determined are critical in defining the precise deviation from the virial exponents. We revisit the (M/L)-sigma_e relation, which describes most of the deviations between the MP and the FP. The best-fitting relation is (M/L) sigma_e^0.72 (r-band). It provides an upper limit to any systematic increase of the IMF mass normalization with sigma_e. We study of the link between sigma_e and the galaxies circular velocity V_circ within 1Re (where stars dominate) and find the relation max(V_circ)~1.76*sigma_e, which has an observed scatter of 7%. The accurate parameters described in this paper are used in the companion Paper XX of this series to explore the variation of global galaxy properties, including the IMF, on the projections of the MP. [Abridged]

astro-ph.CO↗

arXiv2013

The Atlas3D project - XIX. The hot-gas content of early-type galaxies: fast versus slow rotators

For early-type galaxies, the ability to sustain a corona of hot, X-ray emitting gas could have played a key role in quenching their star-formation history. Yet, it is still unclear what drives the precise amount of hot gas around these galaxies. By combining photometric and spectroscopic measurements for the early-type galaxies observed during the Atlas3D integral-field survey with measurements of their X-ray luminosity based on X-ray data of both low and high spatial resolution we conclude that the hot-gas content of early-type galaxies can depend on their dynamical structure. Specifically, whereas slow rotators generally have X-ray halos with luminosity L_X,gas and temperature T values that are in line with what is expected if the hot-gas emission is sustained by the thermalisaton of the kinetic energy carried by the stellar-mass loss material, fast rotators tend to display L_X,gas values that fall consistently below the prediction of this model, with similar T values that do not scale with the stellar kinetic energy as observed in the case of slow rotators. Considering that fast rotators are likely to be intrinsically flatter than slow rotators, and that the few L_X,gas-deficient slow rotators also happen to be relatively flat, the observed L_X,gas deficiency in these objects would support the hypothesis whereby flatter galaxies have a harder time in retaining their hot gas. We discuss the implications that a different hot-gas content could have on the fate of both acquired and internally-produced gaseous material, considering in particular how the L_X,gas deficiency of fast rotators would make them more capable to recycle the stellar-mass loss material into new stars than slow rotators. This is consistent with the finding that molecular gas and young stars are detected only in fast rotators in the Atlas3D sample, and that fast rotators tend to dustier than slow rotators. [Abridged]

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arXiv2012

The ATLAS3D project - XXII. Low-efficiency star formation in early-type galaxies: hydrodynamic models and observations

We study the global efficiency of star formation in high resolution hydrodynamical simulations of gas discs embedded in isolated early-type and spiral galaxies. Despite using a universal local law to form stars in the simulations, we find that the early-type galaxies are offset from the spirals on the large-scale Kennicutt relation, and form stars 2 to 5 times less efficiently. This offset is in agreement with previous results on morphological quenching: gas discs are more stable against star formation when embedded in early-type galaxies due to the lower disc self-gravity and increased shear. As a result, these gas discs do not fragment into dense clumps and do not reach as high densities as in the spiral galaxies. Even if some molecular gas is present, the fraction of very dense gas (above 10^4 cm-3) is significantly reduced, which explains the overall lower star formation efficiency. We also analyse a sample of local early-type and spiral galaxies, measuring their CO and HI surface densities and their star formation rates as determined by their non-stellar 8um emission. As predicted by the simulations, we find that the early-type galaxies are offset from the Kennicutt relation compared to the spirals, with a twice lower efficiency. Finally, we validate our approach by performing a direct comparison between models and observations. We run a simulation designed to mimic the stellar and gaseous properties of NGC524, a lenticular galaxy, and find a gas disc structure and global star formation rate in good agreement with the observations. Morphological quenching thus seems to be a robust mechanism, and is also consistent with other observations of a reduced star formation efficiency in early-type galaxies in the COLD GASS survey. This lower efficiency of star formation is not enough to explain the formation of the whole Red Sequence, but can contribute to the reddening of some galaxies.

astro-ph.CO↗

arXiv2012

The ATLAS 3D project - XVI. Physical parameters and spectral line energy distributions of the molecular gas in gas-rich early-type galaxies

[Abridged] We present a detailed study of the physical properties of the molecular gas in a sample of 18 molecular gas-rich early-type galaxies (ETGs) from the ATLAS$ 3D sample. Our goal is to better understand the star formation processes occurring in those galaxies, starting here with the dense star-forming gas. We use existing integrated $^{12}$CO(1-0, 2-1), $^{13}$CO(1-0, 2-1), HCN(1-0) and HCO$^{+}$(1-0) observations and present new $^{12}$CO(3-2) single-dish data. From these, we derive for the first time the average kinetic temperature, H$_{2}$ volume density and column density of the emitting gas, this using a non-LTE theoretical model. Since the CO lines trace different physical conditions than of those the HCN and HCO$^{+}$ lines, the two sets of lines are treated separately. We also compare for the first time the predicted CO spectral line energy distributions (SLEDs) and gas properties of our molecular gas-rich ETGs with those of a sample of nearby well-studied disc galaxies. The gas excitation conditions in 13 of our 18 ETGs appear analogous to those in the centre of the Milky Way. Such results have never been obtained before for ETGs and open a new window to explore further star-formation processes in the Universe. The conclusions drawn should nevertheless be considered carefully, as they are based on a limited number of observations and on a simple model. In the near future, with higher CO transition observations, it should be possible to better identify the various gas components present in ETGs, as well as more precisely determine their associated physical conditions. To achieve these goals, we show here from our theoretical study, that mid-J CO lines (such as the $^{12}$CO(6-5) line) are particularly useful.

astro-ph.CO↗

arXiv2012

The ATLAS3D Project - XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

We explore the connection between the local escape velocity, V_esc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of our galaxies. We are able to fit the full range of surface brightness profiles found in our sample, and in addition we reproduce the results of state-of-the-art photometry in the literature with residuals of 0.04 mags. We utilise these photometric models and SAURON integral-field spectroscopy, combined with Jeans dynamical modelling, to determine the local V_esc derived from the surface brightness. We find that the local V_esc is tightly correlated with the Mgb and Fe5015 linestrengths and optical colours, and anti-correlated with the Hbeta linestrength. In the case of the Mgb and Colour - V_esc relations we find that the relation within individual galaxies follows the global relation between different galaxies. We intentionally ignored any uncertain contribution due to dark matter since we are seeking an empirical description of stellar population gradients in early-type galaxies that is ideal for quantitative comparison with model predictions. We identify a population of galaxies that occur only at low V_esc that exhibit negative gradients in the Mgb - and Colour -V_esc relations. These galaxies typically have young central stellar populations and contain significant amounts of molecular gas and dust. Combining these results with N-body simulations of binary mergers we use the Mgb-V_esc relation to constrain the possible number of dry mergers experienced by the local early-type galaxy population - a typical massive ETG can have experienced only ~1.5 major mergers before becoming a significant outlier in the Mgb-V_esc relation. [Abridged]

astro-ph.CO↗

arXiv2012

The ATLAS3D project - XVII. Linking photometric and kinematic signatures of stellar discs in early-type galaxies

[Abridged] We analyse the morphological structures in galaxies of the ATLAS3D sample by fitting a single Sersic profile and decomposing all non-barred objects (180 of 260 objects) in two components parameterised by an exponential and a general Sersic function. The aim of this analysis is to look for signatures of discs in light distributions of nearby early-type galaxies and compare them to kinematic properties. Using Sersic index from single component fits for a distinction between slow and fast rotators, or even late- and early-type galaxies, is not recommended. Assuming that objects with n>3 are slow rotators (or ellipticals), there is only a 22 per cent probability to correctly classify objects as slow rotators (or 37 per cent of previously classified as ellipticals). We show that exponential sub-components, as well as light profiles fitted with only a single component of a low Sersic index, can be linked with the kinematic evidence for discs in early-type galaxies. The median disk-to-total light ratio for fast and slow rotators is 0.41 and 0.0, respectively. Similarly, the median Sersic indices of the bulge (general Sersic component) are 1.7 and 4.8 for fast and slow rotators, respectively. Overall, discs or disc-like structures, are present in 83 per cent of early-type galaxies which do not have bars, and they show a full range of disk-to-total light ratios. Discs in early-type galaxies contribute with about 40 per cent to the total mass of the analysed (non-barred) objects. The decomposition into discs and bulges can be used as a rough approximation for the separation between fast and slow rotators, but it is not a substitute, as there is only a 59 per cent probability to correctly recognise slow rotators. Kinematics (i.e. projected angular momentum) remains the best approach to mitigate the influence of the inclination effects.

astro-ph.CO↗

arXiv2012

The First Billion Years project - IV: Proto-galaxies reionising the Universe

The contribution of stars in galaxies to cosmic reionisation depends on the star formation history in the Universe, the abundance of galaxies during reionisation, the escape fraction of ionising photons and the clumping factor of the inter-galactic medium (IGM). We compute the star formation rate and clumping factor during reionisation in a cosmological volume using a high-resolution hydrodynamical simulation. We post-process the output with detailed radiative transfer simulations to compute the escape fraction of ionising photons. Together, this gives us the opportunity to assess the contribution of galaxies to reionisation self-consistently. The strong mass and redshift dependence of the escape fraction indicates that reionisation occurred between z=15 and z=10 and was mainly driven by proto-galaxies forming in dark-matter haloes with masses between 1e7 and 1e8 solar mass. More massive galaxies that are rare at these redshifts and have significantly lower escape fractions contribute less photons to the reionisation process than the more-abundant low-mass galaxies. Star formation in the low-mass haloes is suppressed by radiative feedback from reionisation, therefore these proto-galaxies only contribute when the part of the Universe they live in is still neutral. After z~10, massive galaxies become more abundant and provide most of the ionising photons. In addition, we find that Population (Pop) III stars are too short-lived and not frequent enough to have a major contribution to reionisation. Although the stellar component of the proto-galaxies that produce the bulk of ionising photons during reionisation is too faint to be detected by the James Webb Space Telescope (JWST), these sources are brightest in the H-alpha and Ly-alpha recombination lines, which will likely be detected by JWST in deep surveys.

astro-ph.CO↗

arXiv2012

The Atlas3D project - XIV. The extent and kinematics of molecular gas in early-type galaxies

We use interferometric CO observations to compare the extent, surface brightness profiles and kinematics of the molecular gas in CO-rich Atlas3D early-type galaxies (ETGs) and spiral galaxies. We find that the molecular gas extent is smaller in absolute terms in ETGs than in late-type galaxies, but that the size distributions are similar once scaled by the galaxies optical/stellar characteristic scale-lengths. Virgo cluster ETGs have less extended molecular gas reservoirs than field counterparts. Approximately half of ETGs have molecular gas surface brightness profiles that follow the stellar light profile. These systems often have relaxed gas out to large radii, suggesting they are unlikely to have had recent merger/accretion events. A third of the sample galaxies show molecular gas surface brightness profiles that fall off slower than the light, and sometimes show a truncation. We suggest that ram pressure stripping and/or the presence of hot gas has compressed/truncated the gas in these systems. The remaining galaxies have rings, or composite profiles, that we argue can be caused by the effects of bars. We investigated the kinematics of the molecular gas using position-velocity diagrams, and compared the observed kinematics with dynamical model predictions, and the observed stellar and ionised gas velocities. We confirm that the molecular gas reaches beyond the turnover of the circular velocity curve in ~70% of our CO-rich Atlas3D ETGs. In general we find that in most galaxies the molecular gas is relaxed and dynamically cold. Molecular gas is a better direct tracer of the circular velocity than the ionised gas, justifying its use as a kinematic tracer for Tully-Fisher and similar analyses. (abridged)

astro-ph.CO↗

arXiv2012

The ATLAS3D project - XVIII. CARMA CO imaging survey of early-type galaxies

We present the Combined Array for Research in Millimeter Astronomy (CARMA) ATLAS3D molecular gas imaging survey, a systematic study of the distribution and kinematics of molecular gas in CO-rich early-type galaxies. Our full sample of 40 galaxies (30 newly mapped and 10 taken from the literature) is complete to a 12CO(1-0) integrated flux of 18.5 Jy km/s, and it represents the largest, best-studied sample of its type to date. A comparison of the CO distribution of each galaxy to the g-r color image (representing dust) shows that the molecular gas and dust distributions are in good agreement and trace the same underlying interstellar medium. The galaxies exhibit a variety of CO morphologies, including discs (50%), rings (15%), bars+rings (10%), spiral arms (5%), and mildly (12.5%) and strongly (7.5%) disrupted morphologies. There appear to be weak trends between galaxy mass and CO morphology, whereby the most massive galaxies in the sample tend to have molecular gas in a disc morphology. We derive a lower limit to the total accreted molecular gas mass across the sample of 2.48x10^10 Msuns, or approximately 8.3x10^8 Msuns per minor merger within the sample, consistent with minor merger stellar mass ratios.

astro-ph.CO↗

arXiv2012

Discovery of a giant HI tail in the galaxy group HCG 44

We report the discovery of a giant HI tail in the intra-group medium of HCG 44 as part of the Atlas3D survey. The tail is ~300 kpc long in projection and contains ~5x10^8 M_sun of HI. We detect no diffuse stellar light at the location of the tail down to ~28.5 mag/arcsec^2 in g band. We speculate that the tail might have formed as gas was stripped from the outer regions of NGC 3187 (a member of HCG 44) by the group tidal field. In this case, a simple model indicates that about 1/3 of the galaxy's HI was stripped during a time interval of <1 Gyr. Alternatively, the tail may be the remnant of an interaction between HCG 44 and NGC 3162, a spiral galaxy now ~650 kpc away from the group. Regardless of the precise formation mechanism, the detected HI tail shows for the first time direct evidence of gas stripping in HCG 44. It also highlights that deep HI observations over a large field are needed to gather a complete census of this kind of events in the local Universe.

astro-ph.CO↗

arXiv2012

Jet interactions with a giant molecular cloud in the Galactic centre and ejection of hypervelocity stars

The hypervelocity OB stars in the Milky Way Galaxy were ejected from the central regions some 10-100 million years ago. We argue that these stars, {as well as many more abundant bound OB stars in the innermost few parsecs,} were generated by the interactions of an AGN jet from the central black hole with a dense molecular cloud. Considerations of the associated energy and momentum injection have broader implications for the possible origin of the Fermi bubbles and for the enrichment of the intergalactic medium.

astro-ph.CO↗

arXiv2012

Looking at the relation between haloes and galaxies under the lens

We use an empirical approach to model the stellar mass of galaxies according to their host dark-matter haloes and subhaloes ('HASH'), where each galaxy resides in a subhalo taken from a large N-body cosmological simulation. This approach allows us to study the mass relation between subhaloes and galaxies (MR) using: the weak lensing signal (WL), the two point auto-correlation function (CF), and the stellar mass function of galaxies (SMF). Our method is based on modeling the lensing signal directly from the cosmological simulation, and should thus be more accurate than other methods based on analytic halo models. We find that the WL does not provide a strong constraint on the MR, allowing for more than a factor of 10 freedom in the subhalo mass of central galaxies, for a given stellar mass. The freedom for satellite galaxies is much larger, providing a very poor constraint on the fraction of satellite galaxies (0.05-0.8). These results are not significantly modified when using both the SMF and WL as constraints. We show that for the most massive galaxies, observational constraints based on the CF with 0.1 dex errors, are equivalent to 0.05 dex error in the WL. For intermediate and low mass galaxies the WL and CF constrain the MR in a different way. Although the WL is currently not adding much information at these masses, it has the potential of being important using future, more accurate measurements. The models found here do not match simultaneously the observed CF and WL signals, and show a limited ability to match the WL & SMF. We suspect that this is partially due to the cosmological model assumed here and we therefore adopt a mock WL signal through most of this work. In comparison to previous models in the literature, the method presented here is probably more general, as it reveals a larger range of solutions for a given set of observational constraints [abridged].

astro-ph.CO↗

arXiv2012

Ubiquitous seeding of supermassive black holes by direct collapse

We study for the first time the environment of massive black hole (BH) seeds (~10^4-5 Msun) formed via the direct collapse of pristine gas clouds in massive haloes (>10^7 Msun) at z>6. Our model is based on the evolution of dark matter haloes within a cosmological N-body simulation, combined with prescriptions for the formation of BH along with both Pop III and Pop II stars. We calculate the spatially-varying intensity of Lyman Werner (LW) radiation from stars and identify the massive pristine haloes in which it is high enough to shut down molecular hydrogen cooling. In contrast to previous BH seeding models with a spatially constant LW background, we find that the intensity of LW radiation due to local sources, J_local, can be up to 10^6 times the spatially averaged background in the simulated volume and exceeds the critical value, J_crit, for the complete suppression of molecular cooling, in some cases by 4 orders of magnitude. Even after accounting for possible metal pollution in a halo from previous episodes of star formation, we find a steady rise in the formation rate of direct collapse (DC) BHs with decreasing redshift from 10^{-3}/Mpc^3/z at z=12 to 10^{-2}/Mpc^3/z at z=6. The onset of Pop II star formation at z~16 simultaneously marks the onset of the epoch of DCBH formation, as the increased level of LW radiation from Pop II stars is able to elevate the local levels of the LW intensity to J_local > J_crit while Pop III stars fail to do so at any time. The number density of DCBHs is sensitive to the number of LW photons and can vary by an order of magnitude at z=6 after accounting for reionisation feedback. Haloes hosting DCBHs are more clustered than similar massive counterparts that do not host DCBHs, especially at redshifts z>10. We also show that planned surveys with JWST should be able to detect the supermassive stellar precursors of DCBHs.

astro-ph.CO↗

arXiv2012

Gemini GMOS and WHT SAURON integral-field spectrograph observations of the AGN driven outflow in NGC 1266

We use the SAURON and GMOS integral field spectrographs to observe the active galactic nucleus (AGN) powered outflow in NGC 1266. This unusual galaxy is relatively nearby (D=30 Mpc), allowing us to investigate the process of AGN feedback in action. We present maps of the kinematics and line strengths of the ionised gas emission lines Halpha, Hbeta, [OIII], [OI], [NII] and [SII], and report on the detection of Sodium D absorption. We use these tracers to explore the structure of the source, derive the ionised and atomic gas kinematics and investigate the gas excitation and physical conditions. NGC 1266 contains two ionised gas components along most lines of sight, tracing the ongoing outflow and a component closer to the galaxy systemic, the origin of which is unclear. This gas appears to be disturbed by a nascent AGN jet. We confirm that the outflow in NGC 1266 is truly multiphase, containing radio plasma, atomic, molecular and ionised gas and X-ray emitting plasma. The outflow has velocities up to \pm900 km/s away from the systemic velocity, and is very likely to be removing significant amounts of cold gas from the galaxy. The LINER-like line-emission in NGC 1266 is extended, and likely arises from fast shocks caused by the interaction of the radio jet with the ISM. These shocks have velocities of up to 800 km/s, which match well with the observed velocity of the outflow. Sodium D equivalent width profiles are used to set constraints on the size and orientation of the outflow. The ionised gas morphology correlates with the nascent radio jets observed in 1.4 GHz and 5 GHz continuum emission, supporting the suggestion that an AGN jet is providing the energy required to drive the outflow.

astro-ph.CO↗

arXiv2012

The Growth of the Stellar Seeds of Supermassive Black Holes

One of the most promising explanations for the origin of the billion solar mass black holes (BHs) inferred to power quasars at redshifts z > 6 is that supermassive stars (SMSs) with masses > 10,000 solar masses collapse to form the seed BHs from which they grow. Here we review recent theoretical advances which provide support for this scenario. Firstly, given sufficiently high accretion rates of gas into the cores of primordial protogalaxies, it appears that neither the high energy radiation emitted from the stellar surface nor the limited lifetime of SMSs can prevent their growth to masses of up to > 100,000 solar masses. Secondly, recent cosmological simulations suggest that the high fluxes of molecule-dissociating radiation which may be required in order to achieve such high accretion rates may be more common in the early universe than previously thought. We conclude that the majority of supermassive BHs may originate from SMSs at high redshifts.

astro-ph.CO↗

arXiv2012

The First Billion Years project - III: The impact of stellar radiation on the coevolution of Populations II and III

With the first metal enrichment by Population (Pop) III supernovae (SNe), the formation of the first metal-enriched, Pop II stars becomes possible. In turn, Pop III star formation and early metal enrichment are slowed by the high energy radiation emitted by Pop II stars. Thus, through the SNe and radiation they produce, Populations II and III coevolve in the early Universe, one regulated by the other. We present large (4 Mpc)^3, high resolution cosmological simulations in which we self-consistently model early metal enrichment and the stellar radiation responsible for the destruction of the coolants (H2 and HD) required for Pop III star formation. We find that the molecule-dissociating stellar radiation produced both locally and over cosmological distances reduces the Pop III star formation rate at z > 10 by up to an order of magnitude compared to the case in which this radiation is not included. However, we find that the effect of LW feedback is to enhance the amount of Pop II star formation. We attribute this to the reduced rate at which gas is blown out of dark matter haloes by SNe in the simulation with LW feedback, which results in larger reservoirs for metal-enriched star formation. Even accounting for metal enrichment, molecule-dissociating radiation and the strong suppression of low-mass galaxy formation due to reionization at z < 10, we find that Pop III stars are still formed at a rate of ~ 10^-5 M_sun yr^-1 Mpc^-3 down to z ~ 6. This suggests that the majority of primordial pair-instability SNe that may be uncovered in future surveys will be found at z < 10. We also find that the molecule-dissociating radiation emitted from Pop II stars may destroy H2 molecules at a high enough rate to suppress gas cooling and allow for the formation of supermassive primordial stars which collapse to form ~ 100,000 solar mass black holes.

astro-ph.CO↗

arXiv2012

The road to the red sequence: A detailed view of the formation of a massive galaxy at z~2

(Abridged) We present here a detailed analysis of the star formation history (SFH) of FW4871, a massive galaxy at z=1.893+-0.002. We compare rest-frame optical and NUV slitless grism spectra from the Hubble Space Telescope with a large set of composite stellar populations to constrain the underlying star formation history. Even though the morphology features prominent tidal tails, indicative of a recent merger, there is no sign of on-going star formation within an aperture encircling one effective radius, which corresponds to a physical extent of 2.6 kpc. A model assuming truncation of an otherwise constant SFH gives a formation epoch zF~10, with a truncation after 2.7 Gyr, giving a mass-weighted age of 1.5 Gyr and a stellar mass of 0.8-3E11Msun, implying star formation rates of 30-110 Msun/yr. A more complex model including a recent burst of star formation places the age of the youngest component at 145 Myr, with a mass contribution lower than 20%, and a maximum amount of dust reddening of E(B-V)<0.4 mag (95% confidence levels). This low level of dust reddening is consistent with the low emission observed at 24 micron, corresponding to rest-frame 8 micron, where PAH emission should contribute significantly if a strong formation episode were present. The colour profile of FW4871 does not suggest a significant radial trend in the properties of the stellar populations out to 3Re. We suggest that the recent merger that formed FW4871 is responsible for the quenching of its star formation.

astro-ph.CO↗

arXiv2012

Jet-induced star formation in gas-rich galaxies

Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of quenching cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the quenching of star formation. To shed more light on the actual physics of the "radio mode" part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc (10^11 solar masses) of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 10^7 years, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to 10^10 solar masses for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.

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