We study the effects of time-dependent mass injection and heating on the
evolution of the interstellar medium (ISM) in elliptical galaxies. As the large
and luminous ellipticals have supermassive black holes at their cores, which
were probably much less massive in the young universe, feeding these black
holes is essential. We examine steady state solutions and describe the impact
of the initial starburst on the evolution of the ISM and consequences for
galactic activity, based on results from Starburst99.Comment: 6 pages, 5 figures, poster contribution for the 1st
  Arizona/Heidelberg Symposium "The High Redshift Frontier", November 30 -
  December 3, 2004, Tucson, AZ, USA. Proceedings available at
  http://highz.ita.uni-heidelberg.de/Proceedings.pd

Camenzind, Max

Gaibler, Volker

Krause, Martin

English

arXiv

Volker Gaibler, Max Camenzind, and Martin Krause, 'Evolution of the ISM and Galactic Activity', paper presented at the 1st Arizona/Heidelberg Symposium "The High Redshift Frontier", 30 November 2004 - 3 December 2004, Tucson, AZ, USA.We study the effects of time-dependent mass injection and heating on the evolution of the interstellar medium (ISM) in elliptical galaxies. As the large and luminous ellipticals have supermassive black holes at their cores, which were probably much less massive in the young universe, feeding these black holes is essential. We examine steady state solutions and describe the impact of the initial starburst on the evolution of the ISM and consequences for galactic activity, based on results from Starburst99.Non peer reviewe

Gaibler, V.

Camenzind, M.

Krause, M.

University of Hertfordshire Research Archive

Volker Gaibler, Max Camenzind, and Martin Krause, 'Evolution of the ISM and Galactic Activity', paper presented at the1st Arizona/Heidelberg Symposium "The High Redshift Frontier", 30 November 2004 - 3 December 2004, Tucson, AZ, USA. arXiv:astro-ph/0502403v1  21 Feb 2005Evolution of the ISM and Galactic ActivityVolker Gaibler∗, Max Camenzind, Martin KrauseLandessternwarte Heidelberg–Ko¨nigstuhl1 IntroductionWe examine the impact of time-dependent mass injection and heating on the evolu-tion of the interstellar medium (ISM) in elliptical galaxies. As the large and luminousellipticals have supermassive black holes at their cores, which were probably much lessmassive in the young universe, feeding these black holes is essential. The evolution of theISM, controlled by supernova and/or AGN heating as well as cooling by bremsstrahlung(Mathews & Brighenti 2003), could provide an abundant matter supply for this if a suf-ficient fraction of the ISM flows towards the center.The hot phase of the ISM has typical temperatures around 107 K at the galacticcores. While stellar winds and planetary nebulae are widely seen as the sources of theinterstellar gas, there is no generally established model to explain the heating of the ISM(supernovae, AGN heating, collisions). We concentrate on supernovae as a source of theheating.2 Model and Basic EquationsWe use simple Plummer models as well as combined Hernquist/NFW models for themass distribution of our galaxies, with ρ⋆(r) being the stellar mass density. In addition,we have a black hole with mass MH at the center. Most calculations are performed inone spatial dimension, some in 2D including random disturbances, with the magneto-hydrodynamic code NIRVANA by Udo Ziegler (Ziegler & Yorke 1997).∂ρ∂t+∇ · (ρv) = αρ⋆ (1)∂(ρv)∂t+∇ · (ρv ⊗ v) = −∇p− ρ∇Φ (2)∂e∂t+∇ · (ev) = −p∇ · v+ αρ∗cvT0 − ρ2Λ (3)∗Contact: V.Gaibler@lsw.uni-heidelberg.de1Figure 1. Typical temperature profiles of steady state outflow and inflow solutions. The two typesof solutions can be easily distinguished in this figure: While inflows generally have low temper-atures and positive gradients, galactic winds show high temperatures and negative gradients,which might be very difficult to observe directly as the densities are much lower. α = 10−19 s−1,inflows: T0 = 5 · 105K . . . 107 K, outflows: T0 = 1 · 108K . . . 9 · 108K.Here ρ, u, T , p and e (energy density) are the state variables of the gas, ρ2Λ is thecooling rate, and cvT0 is the supplied energy relative to the injected matter αρ⋆, so theheating is controlled by the value of T0. The mass injection by stellar mass loss as wellas the supernova heating are assumed to be proportional to the stellar density becauseof their physical origins.3 ISM SimulationsFor constant mass injection and heating we find steady state solutions, which can becharacterized as inflow and outflow types (Figure 1). Inflow solutions show temperaturesnear the virial temperature and subsonic gas flows towards the center (cooling flows)independent of the heating rate. Outflows on the other hand generally are supersonic,of high temperature and low gas density. Their velocity and temperature profile isindependent of the mass injection rate.Although there is a transition region between inflow and outflow in the (α, T0) para-meter space where we have spatially bimodal flows, this region seems to be narrow. Ifthere exists at least a partial inflow, then a significant fraction of the globally injectedmass flows towards the center.Figure 2 shows the distribution of the two solution types in the parameter space.There obviously exists a critical heating parameter T0,crit which separates these types.This can be explained easily by checking the energy balance. The ISM evolution inour simulations with time-dependent mass injection and heating can be understood byexamining the evolution of the model in the (α, T0) parameter space.The time-dependence of mass injection follows from the initial mass function of the210410510610710810910−20 10−19 10−18 10−17 10−16 10−150.1 1 10 100 1000T0[K]α [s−1]mass injection rate [M⊙ yr−1]0.01 SNu 0.1 SNu 1 SNu10 SNu100 SNu1 000 SNuFigure 2. Distribution of inflow (filled symbols) and outflow (open symbols) solutions in the(α, T0) parameter space for our model galaxy (dark matter contribution is not included). Themass injection parameter α directly corresponds to the overall mass injection rate in the galaxy,while the heating parameter T0 depends on the supernova rate (in SNu) and the mass injection.1 SNu corresponds to 1 supernova per 100 yr and 1010 L⊙. The diagonal lines represent constantsupernova rates.10410510610710810910−20 10−19 10−18 10−17 10−16 10−15T0[K]α [s−1]0.01 SNu 0.1 SNu 1 SNu10 SNu100 SNu1 000 SNu13 5 2 1 0.5 0.2 0.1 Gyrs = 0.9s = 1.3s = 1.7Figure 3. Evolution of SN Ia heating in the (α, T0) parameter space for a powerlaw behaviorat late times in the galaxy: supernova rate ∝ t−s and mass injection α ∝ t−1.3. The arrowsindicate the α-position of the galaxy at a given time.3stellar population generated by a monolithic starburst. The amount of mass injectionseems to be in good agreement with observations (Bregman & Athey 2004).The time-dependence of the supernova rate is rather unknown. During the initialstarburst there is much contribution from SNe II, but soon after SNe Ia are the only onesoccurring. At late times, in passively evolving galaxies, the evolution of the SN Ia heatingrate is often assumed to be a powerlaw (∝ t−s), but observational confirmation for thisis still missing so that the powerlaw exponent could vary over a large range. Figure 3shows the evolutionary tracks of the model for three different powerlaw exponents.The critical heating parameter is governed by the virial mass of the galaxy, and su-pernova rates in local ellipticals (Cappellaro et al. 1999) suggest that our model galaxyof 1011M⊙ virial mass should be near the turnover region between inflow and outflow.For early times, we find a galactic wind for s = 1.7 and inflow for s = 0.9. This showsthat higher supernova rates in the past (s > 0) are not sufficient to drive galactic winds— they have to increase stronger (s > 1.3) than the mass injection (Ciotti et al. 1991).For a galaxy with much higher or much lower mass, the position of the turnoverregion is much more important than the evolution of the supernova rate so that high-mass galaxies would generate inflows with high X-ray luminosities while low-mass dwarfgalaxies would have strong galactic winds and unobservable X-ray luminosities.4 Impact of the Initial StarburstAt very early times in the galaxy, during its formation, the abovementioned powerlawbehavior of course breaks down. Figure 4 shows the evolution of the parameters α and T0during galaxy formation based on two very simple scenarios with data from Starburst99(Leitherer et al. 1999): The galaxy is instantaneously formed from a gas cloud or thegalaxy is formed during 500 Myr by a constant star formation rate. The mass injectionα decreases with increasing formation timescale, but the heating parameter T0 remainsthe same because T0 is proportional to the heating rate per injected mass.The extremely high supernova rates during the starburst lead to high heating rates,but this does not necessarily lead to galactic winds. Figure 4 shows that T0 ∼ 108 Kduring the starburst. This would drive a galactic wind for the model galaxy, but couldn’tdo so for a galaxy with a virial mass of & 1012 M⊙ as the threshold-T0 for winds increasesproportional to the galaxy mass. The reason is that a huge amount of injected matterwould have to be lifted out of the galaxy’s gravitational potential.5 Effects on Black Hole GrowthThe evolution of the ISM might be a crucial factor for fuelling central black holes. Ifa galactic wind arises and stays for a long time, this could effectively avoid black holegrowth because of low gas densities and high temperatures. A big galaxy in inflow state,on the other hand, could easily accrete some 1010 M⊙ because the total injected gas massis of the order of the stellar mass of the galaxy.41e-201e-191e-181e-171e-161e-151e-14 1e+06  1e+07  1e+08alpha  [1/s]t  [yr]continuous formation(500 Myr)instantaneous formationZ=0.040Z=0.020Z=0.008Z=0.004Z=0.0011e+061e+071e+081e+09 1e+06  1e+07  1e+08T 0  [K]t  [yr]continuous formation(500 Myr)instantaneous formationZ=0.040Z=0.020Z=0.008Z=0.004Z=0.001Figure 4. Evolution of the mass injection and heating parameters α and T0 during galaxy for-mation for different metallicities Z, derived from Starburst99. The time-dependence of massinjection (top) and heating parameter (bottom) are shown for instantaneous formation of thegalaxy and continuous formation during 500Myr. Heating by SNe Ia is not included.Depending on the galaxy mass and the evolution of the heating rate, there is a richvariety of possible scenarios for the interstellar gas. Inflow at early times can producesupermassive black holes very quickly and possibly resulting activity could provide afeedback through additional heating which could turn the inflow into an outflow. Theimpact of further star formation in cooling flows could be a similar feedback mechanismand induce a cyclic behavior.5References[Bregman & Athey 2004] J. N. Bregman & A. E. Athey. Elliptical Galaxy CoolingFlows. In Proceedings of The Riddle of Cooling Flows in Galaxies and Clusters ofGalaxies, 2004.[Cappellaro et al. 1999] E. Cappellaro, R. Evans, & M. Turatto. A new determinationof supernova rates and a comparison with indicators for galactic star formation. A&A,351:459–466, 1999.[Ciotti et al. 1991] L. Ciotti, S. Pellegrini, A. Renzini, and A. D’Ercole. Winds, outflows,and inflows in X-ray elliptical galaxies. ApJ, 376:380–403, 1991.[Leitherer et al. 1999] C. Leitherer, D. Schaerer, J. D. Goldader, R. M. G. Delgado, C.Robert, D. F. Kune, D. F. de Mello, D. Devost, & T. M. Heckman. Starburst99:Synthesis Models for Galaxies with Active Star Formation. ApJS, 123:3–40, 1999.[Mathews & Brighenti 2003] W. G. Mathews & F. Brighenti. Hot Gas in and aroundElliptical Galaxies. ARA&A, 41:191–239, 2003.[Ziegler & Yorke 1997] U. Ziegler & H. W. Yorke. A nested grid refinement technique formagnetohydrodynamical flows. Computer Physics Communications, 101:54–74, 1997.6

Evolution of the ISM and Galactic Activity

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Evolution of the ISM and Galactic Activity

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