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Jet-clump interactions in quasars
NUCLEAR PHYSICS A ELSEVIER
Nuclear Physics A621 (1997) 584c-588c
Jet-Clump Interactions in Quasars J. D. VandegritP, R. N. Boyd ~'b, G. Raimann ~, P. Osmer b ~Department of Physics, The Ohio State University 174 W. 18th Ave., Columbus, OH 43210 bDepartment of Astronomy, The Ohio State University 174 W. 18th Ave., Columbus, OH 43210 Some high redshift quasars (z,,4) show strong emission lines for C, N, and O, indicating high abundances of these elements. In this context, we have explored the nucleosynthesis that would occur between a high energy particle jet emanating from an Active Galactic Nucleus (AGN) and nearby gas. CNO production proceeds through nuclides which result from collisions between the jet and the gas. Final abundances of the CNO nuclides vary widely over the densities studied, but reach and even exceed solar levels for some combinations of temperature, density, and jet intensity and duration. 1. M e t a l s at H i g h R e d s h i f t Spectra of high redshift quasars exhibit metal lines of surprising strength. Emission lines from carbon, nitrogen, and oxygen are easily visible in nearly all of the 31 high resolution spectra from the APM survey of z,,~4 quasars [1]. Analysis of similar spectra [2] seems to indicate N abundances at or above solar values. The generation of large metallicities in the environment of very high redshift quasars presents an interesting puzzle: how do C, N, and O evolve to solar levels in less than 1 Gyr? Starburst production models [2] require very rapid mass infall and star formation times (,~0.5 Gyr for 85% of the gas to be consumed by stars) as well as an initial mass function which greatly favors high mass stars. Both requirements push the parameters to their plausible limits. Consequently we have explored another possible means of producing C, N, and O. 2. D e s c r i p t i o n of J e t - C l u m p
Nucleosynthesis
Principal components of our nucleosynthesis model include a jet and a dense clump of gas. Observations of many AGNs, thought to provide a model of quasars, show jets and clouds, although these clouds are much cooler and presumably further away from the central black hole than the clumps which we utilize in our model. However, we study the nucleosynthesis that would occur in any jet-clump interaction, and so the model could as well apply to the accretion disk around the black hole. The disk is much denser and hotter than the AGN clouds, and could be lumpy. We assume a particle jet with an energy of at least 100 MeV/nucleon, and gas densities on the order of 101° particles/era 3. Because of the accretion disk possibility, though, we have investigated initial densities as high as 0375-9474/97/$17.00 © 1997 ElsevierScience B.V. All rights reserved. PII: S0375-9474(97)00308-4
JD. Vandegriff et al./Nuclear Physics A621 (1997) 584c-588c
585c
10 is particles/cm a. Typical jet lifespans in AGNs are assumed to be on the order of 10s yr [3], although this is much longer than necessary to produce large effects. Both the jet and the gas clump are assumed to have primordial composition. The jet is eventually stopped within the clump, thereby adding to its density. Some high energy particles in the jet will produce nuclear reactions with gas nuclei, e. g., 4He(a,n)TBe, 4He(p,d)3He, and 4He(rBe,p)l°B. The last reaction occurs occasionally as the 7Be created in the jet recoils through the clump and undergoes further collisions. Production of 7Be and l°B can occur both through the (highly nonthermal) jet-clump interactions, which we describe by their measured cross sections [4], and through thermonuclear reactions in the hot clump environment. If the gas temperatures reach T9--~0.2-1, thermonuclear reactions can proceed on all nuclei present in the clump. The long capture lifetime of 7Be in this environment allows rBe to be an effective stepping stone to the higher masses. We do not propose a heating mechanism, but note that similar temperatures have been suggested by others in the context of AGN accretion disks [5]. We have considered two extreme situations: either the density builds up as mass from the jet enters the clump, or it may remain constant if the interaction region is not strongly confined. A simple one zone model is used for both cases. 3. I m p l e m e n t a t i o n A network code has been developed to simulate the thermonuclear reactions in the clump. Special features of the code couple the non-thermal generation of jet-clump reaction products and mass addition from the jet to the (thermonuclear) network calculation. Many reaction rate formulas were taken from a Big Bang code[6]. Rates typical of the hot CNO cycle were taken from compilations [7-9]. The code was designed to allow direct comparison with previous hot CNO calculations. Using the same reaction rates and initial abundances, good agreement was found with the results of Wiescher [10]. 4. A b u n d a n c e O u t p u t The abundance evolution for 8 key nuclides is shown in Fig. 1 for two widely differing combinations of temperature and density. The "clump density" parameter represents the initial[ density in particles/cm 3. The "jet intensity" is the mass input rate of the jet in units of solar masses per year. In both cases, the shape of the jet-clump interaction region used was a cylinder with diameter and length equal to 1013 cm (0.01 light days). The final density depends on how the density evolves, either constant or increasing with the mass deposition from the jet. For the results shown in Fig. la, the density was kept constant at 10 l s particles/cm 3, while in Fig lb, the density started at 1018 particles/cm 3 and climbed to 10~4 particles/cm 3 after 105 yr as a result of the input from the jet. While this buildup probably represents an unrealizable extreme, significant spatial constraint of the (fully ionized) ions in the high temperature environment would result from the strong magnetic fields thought to be associated with AGNs and quasars. In the constant density cases, the mole fractions were renormalized at each time step to simulate the outflow of equal numbers of each species. Beam intensities ranged from 0.1 solar masses per year, which is quite low, up to 10 solar masses per year, a more typical value [3]. The mean jet particle energy was 100 MeV, and we assumed a gaussian
586c
,I.D. Vandegriff et al./Nuclear Physics A621 (1997) 584c-588c
,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I
10 2°
E
o
(~)
'H 4He
10,4 SHe
El. "--"
10 5
6~ E
10=
7Be
Clump density = 1016 Jet intensity 0.1 T 9 = 1.0
10 25
E o
i0,9
o_ ~-"
_o
,v
/ I .'_I 'I 'I "I 'I 'I !I 'I 'I !I 'I ' ' 'I ' ' ' 10 - = 10 -7 I 0 - * 10 -I i~ 2 1 i~ 5 11,
time in yeers
1
~
10 ~
10'
E
,-~ -t//
3He
10 ~
c"(2
-~ 104
,I ,I ,I KI ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I hl
E
~
=
1
0
m
.~14~, /
10 -s ~
/ / Jet i n t e n = l O '7 / T9=0"25 '1 '1 '1 .'1 '1 '1_'1 '1 '1.'1 LIO-' I 0 - r I() ~ "I()''I
time in yeors
Figure 1. Abundance evolution in the jet-clump model for two cases of temperature and density: a) constant density, and b) density increasing with jet deposition. See the text for an explanation of the parameters. The number abundance ratios in a and b for 12C to 1H are 10 -15 after 10 yr and 10 -2 after 104 yr, respectively. distribution with a +10% standard deviation. For the higher temperature, lower density case in Fig. la, the l°B abundance is the bottleneck for CNO productions. All nuclides with mass > 10 are siphoned up from l°B via the (a,p) and (a,n) thermal reactions. 7Be in the clump is easily destroyed at T9 = 1 and cannot serve as an intermediary for l°B production. Thus l°B can only be made by the small amount of rBe in the jet which participates in the non-thermal jet-clump reaction 4He(rBe,p)l°B. CNO abundances rise far above primordial levels in just a fraction of a year, but nevertheless fall far short of solar levels for this combination of temperature, density, and jet intensity. The abundance evolution for lower temperatures and higher densities is shown in Fig. lb. T9 is low enough that rBe does not photodissociate and high enough that the ZBe lifetime against electron capture is still long. 7Be production is now dominated by the thermal 3He(a,7)rBe reaction, which is sustained by 3He produced non-thermally by the jet. The main destruction reaction, rBe(p,o,)SB, has such a small Q-value (0.137 MeV) that at T9 = 0.25 the photodissociation of SB is much faster than its fl-decay. With a large rBe abundance, 7Be(a,7)nc jumps the mass 8 gap, and CNO nuclides can easily be produced from n c . Towards the end of the simulation, the rising density increases the destruction rate for 7Be, but the protons are eventually used up. Then the 7Be abundance rises sharply, driving a surge in the n c abundance which subsequently leads to the huge increase observed in CNO production. Abundance ratios for C, N, and 0 to hydrogen after 104 yr are 10 -2, 10 -2, and 10 -1, respectively, which are 10 times solar for C, and 100 times solar for N and O. The abundances continue to increase until the hydrogen is exhausted. At 104 yr, the rBe abundance is just 100 times less than 1H. Such a high mass 7 abundance could present a problem for the model unless, as is likely, the 7Be decays to 7Li, and is then destroyed by 7Li(p,a) by a small remaining hydrogen admixture. Maximum CNO production occurs for parameters similar to those in Fig. lb. As T9 increases to 0.5, the ratios of CNO to hydrogen drop roughly an order of magnitude per
J.D. Vandegriff et al./Nuclear Physics A621 (1997) 584c-588c
587c
0.1 change in Tg. Below T9 = 0.2, CNO to hydrogen ratios drop very sharply, and by T9 = 0.1 they are at 10-18. Thus, although CNO production can be large for specific parameter choices, the range over which large production occurs is relatively small. Since CNO production in this scenario can rise far above primordial values in times the order of a year, and above even solar values in just 104 yr, the earliest generation of stars might be expected to include some material processed by jet-clump interactions. A massive star with zero metallicity may not produce as high abundances output as a star with at least a small metallicity [11], since the ejecta mass of a supernova depends on the opacity, which in turn is largely determined by the metal content. Thus jet-clump interactions may assist starburst nucleosynthesis in quasars. If the conditions that produce large CNO abundances in jet-clump nucleosynthesis were frequently realized, jet clump interactions themselves might even produce a large fraction of the observed CNO abundances. 5. Conclusions Jet-clump interactions in quasars may provide an alternate mechanism to stellar nucleosynthesis either as seeds for first generation stars or by direct production of the CNO nuclides which are observed in spectra of high redshift quasars. Nuclei produced by the jet in non-thermal reactions with the ambient gas serve as essential stepping stones in the normal thermal nucleosynthesis in the hot gas. For certain choices of temperature, density, and beam intensity, solar levels of CNO nuclides are obtainable. However, these latter results are possible only over a fairly restricted part of parameter space. This work was supported in part by NSF grant PHY-9513893. REFERENCES
1. L.J. Storrie-Lombardi, R. G. McMahon, M. J. Irwin, and C. Hazard, LANL preprint astro-ph/9604021, to appear in Astrophys. J. Suppl. 2. F. Hamman, and G. Ferland, Astrophys. J. 418 (1993) 11. 3. C. Norman, and N. Scoville, Astrophys. J. 332 (1988) 124. 4. S. Bunch, et al., Nucl. Phys. 53 (1964) 241; S. Harbison, et al., Nucl. Phys. A152 (1970) 503; D. Cairns, et al., Nucl. Phys. 60 (1964) 369; L. Votta, et al., Phys. Rev. C 10 (1974) 520; W. Selove, and J. Teem, Phys. Ray. 112 (1958) 1658; M. Bernas, et al., Nucl. Phys. A156 (1970) 289; J. Jenkin, et al., Nucl. Phys. 50 (1964) 516; H. llauser, et al., Nucl. Phys. A456 (1986) 253; c. King, et al., Phys. Rev. C 16 (1977) 1712; B. Glagola, et al., Phys. Rev. C 25 (1982) 34; L. Woo, et al., Phys. Rev. C 32 (11985) 706; A. SpasskiY, et al., Sov. J. Nucl Phys. 3 (1966) 477. 5. M. Kusunose, and S. Mineshige, Astrophys. J. 423 (1994) 600. 6. L. Kawano, FERMILAB-PUB-88/34-A. 7. G. Caughlan, and W. Fowler, Atomic Data and Nuclear Data Tables 40 (1988) 284. 8. R.V. Wagoner, Astrophys. J. 162 (1969) 247. 9. R.V. Wagoner, W. A. Fowler, and F. Hoyle, Astrophys. J. 148 (1967) 3. 10. M. Wiescher, and K. Kettner, Astrophys. J. 263 (1982) 891. 11. T. A. Weaver, and S. E. Woosley, these proceedings.
Nuclear Physics A621 (1997) 584c-588c
Jet-Clump Interactions in Quasars J. D. VandegritP, R. N. Boyd ~'b, G. Raimann ~, P. Osmer b ~Department of Physics, The Ohio State University 174 W. 18th Ave., Columbus, OH 43210 bDepartment of Astronomy, The Ohio State University 174 W. 18th Ave., Columbus, OH 43210 Some high redshift quasars (z,,4) show strong emission lines for C, N, and O, indicating high abundances of these elements. In this context, we have explored the nucleosynthesis that would occur between a high energy particle jet emanating from an Active Galactic Nucleus (AGN) and nearby gas. CNO production proceeds through nuclides which result from collisions between the jet and the gas. Final abundances of the CNO nuclides vary widely over the densities studied, but reach and even exceed solar levels for some combinations of temperature, density, and jet intensity and duration. 1. M e t a l s at H i g h R e d s h i f t Spectra of high redshift quasars exhibit metal lines of surprising strength. Emission lines from carbon, nitrogen, and oxygen are easily visible in nearly all of the 31 high resolution spectra from the APM survey of z,,~4 quasars [1]. Analysis of similar spectra [2] seems to indicate N abundances at or above solar values. The generation of large metallicities in the environment of very high redshift quasars presents an interesting puzzle: how do C, N, and O evolve to solar levels in less than 1 Gyr? Starburst production models [2] require very rapid mass infall and star formation times (,~0.5 Gyr for 85% of the gas to be consumed by stars) as well as an initial mass function which greatly favors high mass stars. Both requirements push the parameters to their plausible limits. Consequently we have explored another possible means of producing C, N, and O. 2. D e s c r i p t i o n of J e t - C l u m p
Nucleosynthesis
Principal components of our nucleosynthesis model include a jet and a dense clump of gas. Observations of many AGNs, thought to provide a model of quasars, show jets and clouds, although these clouds are much cooler and presumably further away from the central black hole than the clumps which we utilize in our model. However, we study the nucleosynthesis that would occur in any jet-clump interaction, and so the model could as well apply to the accretion disk around the black hole. The disk is much denser and hotter than the AGN clouds, and could be lumpy. We assume a particle jet with an energy of at least 100 MeV/nucleon, and gas densities on the order of 101° particles/era 3. Because of the accretion disk possibility, though, we have investigated initial densities as high as 0375-9474/97/$17.00 © 1997 ElsevierScience B.V. All rights reserved. PII: S0375-9474(97)00308-4
JD. Vandegriff et al./Nuclear Physics A621 (1997) 584c-588c
585c
10 is particles/cm a. Typical jet lifespans in AGNs are assumed to be on the order of 10s yr [3], although this is much longer than necessary to produce large effects. Both the jet and the gas clump are assumed to have primordial composition. The jet is eventually stopped within the clump, thereby adding to its density. Some high energy particles in the jet will produce nuclear reactions with gas nuclei, e. g., 4He(a,n)TBe, 4He(p,d)3He, and 4He(rBe,p)l°B. The last reaction occurs occasionally as the 7Be created in the jet recoils through the clump and undergoes further collisions. Production of 7Be and l°B can occur both through the (highly nonthermal) jet-clump interactions, which we describe by their measured cross sections [4], and through thermonuclear reactions in the hot clump environment. If the gas temperatures reach T9--~0.2-1, thermonuclear reactions can proceed on all nuclei present in the clump. The long capture lifetime of 7Be in this environment allows rBe to be an effective stepping stone to the higher masses. We do not propose a heating mechanism, but note that similar temperatures have been suggested by others in the context of AGN accretion disks [5]. We have considered two extreme situations: either the density builds up as mass from the jet enters the clump, or it may remain constant if the interaction region is not strongly confined. A simple one zone model is used for both cases. 3. I m p l e m e n t a t i o n A network code has been developed to simulate the thermonuclear reactions in the clump. Special features of the code couple the non-thermal generation of jet-clump reaction products and mass addition from the jet to the (thermonuclear) network calculation. Many reaction rate formulas were taken from a Big Bang code[6]. Rates typical of the hot CNO cycle were taken from compilations [7-9]. The code was designed to allow direct comparison with previous hot CNO calculations. Using the same reaction rates and initial abundances, good agreement was found with the results of Wiescher [10]. 4. A b u n d a n c e O u t p u t The abundance evolution for 8 key nuclides is shown in Fig. 1 for two widely differing combinations of temperature and density. The "clump density" parameter represents the initial[ density in particles/cm 3. The "jet intensity" is the mass input rate of the jet in units of solar masses per year. In both cases, the shape of the jet-clump interaction region used was a cylinder with diameter and length equal to 1013 cm (0.01 light days). The final density depends on how the density evolves, either constant or increasing with the mass deposition from the jet. For the results shown in Fig. la, the density was kept constant at 10 l s particles/cm 3, while in Fig lb, the density started at 1018 particles/cm 3 and climbed to 10~4 particles/cm 3 after 105 yr as a result of the input from the jet. While this buildup probably represents an unrealizable extreme, significant spatial constraint of the (fully ionized) ions in the high temperature environment would result from the strong magnetic fields thought to be associated with AGNs and quasars. In the constant density cases, the mole fractions were renormalized at each time step to simulate the outflow of equal numbers of each species. Beam intensities ranged from 0.1 solar masses per year, which is quite low, up to 10 solar masses per year, a more typical value [3]. The mean jet particle energy was 100 MeV, and we assumed a gaussian
586c
,I.D. Vandegriff et al./Nuclear Physics A621 (1997) 584c-588c
,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I
10 2°
E
o
(~)
'H 4He
10,4 SHe
El. "--"
10 5
6~ E
10=
7Be
Clump density = 1016 Jet intensity 0.1 T 9 = 1.0
10 25
E o
i0,9
o_ ~-"
_o
,v
/ I .'_I 'I 'I "I 'I 'I !I 'I 'I !I 'I ' ' 'I ' ' ' 10 - = 10 -7 I 0 - * 10 -I i~ 2 1 i~ 5 11,
time in yeers
1
~
10 ~
10'
E
,-~ -t//
3He
10 ~
c"(2
-~ 104
,I ,I ,I KI ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I ,I hl
E
~
=
1
0
m
.~14~, /
10 -s ~
/ / Jet i n t e n = l O '7 / T9=0"25 '1 '1 '1 .'1 '1 '1_'1 '1 '1.'1 LIO-' I 0 - r I() ~ "I()''I
time in yeors
Figure 1. Abundance evolution in the jet-clump model for two cases of temperature and density: a) constant density, and b) density increasing with jet deposition. See the text for an explanation of the parameters. The number abundance ratios in a and b for 12C to 1H are 10 -15 after 10 yr and 10 -2 after 104 yr, respectively. distribution with a +10% standard deviation. For the higher temperature, lower density case in Fig. la, the l°B abundance is the bottleneck for CNO productions. All nuclides with mass > 10 are siphoned up from l°B via the (a,p) and (a,n) thermal reactions. 7Be in the clump is easily destroyed at T9 = 1 and cannot serve as an intermediary for l°B production. Thus l°B can only be made by the small amount of rBe in the jet which participates in the non-thermal jet-clump reaction 4He(rBe,p)l°B. CNO abundances rise far above primordial levels in just a fraction of a year, but nevertheless fall far short of solar levels for this combination of temperature, density, and jet intensity. The abundance evolution for lower temperatures and higher densities is shown in Fig. lb. T9 is low enough that rBe does not photodissociate and high enough that the ZBe lifetime against electron capture is still long. 7Be production is now dominated by the thermal 3He(a,7)rBe reaction, which is sustained by 3He produced non-thermally by the jet. The main destruction reaction, rBe(p,o,)SB, has such a small Q-value (0.137 MeV) that at T9 = 0.25 the photodissociation of SB is much faster than its fl-decay. With a large rBe abundance, 7Be(a,7)nc jumps the mass 8 gap, and CNO nuclides can easily be produced from n c . Towards the end of the simulation, the rising density increases the destruction rate for 7Be, but the protons are eventually used up. Then the 7Be abundance rises sharply, driving a surge in the n c abundance which subsequently leads to the huge increase observed in CNO production. Abundance ratios for C, N, and 0 to hydrogen after 104 yr are 10 -2, 10 -2, and 10 -1, respectively, which are 10 times solar for C, and 100 times solar for N and O. The abundances continue to increase until the hydrogen is exhausted. At 104 yr, the rBe abundance is just 100 times less than 1H. Such a high mass 7 abundance could present a problem for the model unless, as is likely, the 7Be decays to 7Li, and is then destroyed by 7Li(p,a) by a small remaining hydrogen admixture. Maximum CNO production occurs for parameters similar to those in Fig. lb. As T9 increases to 0.5, the ratios of CNO to hydrogen drop roughly an order of magnitude per
J.D. Vandegriff et al./Nuclear Physics A621 (1997) 584c-588c
587c
0.1 change in Tg. Below T9 = 0.2, CNO to hydrogen ratios drop very sharply, and by T9 = 0.1 they are at 10-18. Thus, although CNO production can be large for specific parameter choices, the range over which large production occurs is relatively small. Since CNO production in this scenario can rise far above primordial values in times the order of a year, and above even solar values in just 104 yr, the earliest generation of stars might be expected to include some material processed by jet-clump interactions. A massive star with zero metallicity may not produce as high abundances output as a star with at least a small metallicity [11], since the ejecta mass of a supernova depends on the opacity, which in turn is largely determined by the metal content. Thus jet-clump interactions may assist starburst nucleosynthesis in quasars. If the conditions that produce large CNO abundances in jet-clump nucleosynthesis were frequently realized, jet clump interactions themselves might even produce a large fraction of the observed CNO abundances. 5. Conclusions Jet-clump interactions in quasars may provide an alternate mechanism to stellar nucleosynthesis either as seeds for first generation stars or by direct production of the CNO nuclides which are observed in spectra of high redshift quasars. Nuclei produced by the jet in non-thermal reactions with the ambient gas serve as essential stepping stones in the normal thermal nucleosynthesis in the hot gas. For certain choices of temperature, density, and beam intensity, solar levels of CNO nuclides are obtainable. However, these latter results are possible only over a fairly restricted part of parameter space. This work was supported in part by NSF grant PHY-9513893. REFERENCES
1. L.J. Storrie-Lombardi, R. G. McMahon, M. J. Irwin, and C. Hazard, LANL preprint astro-ph/9604021, to appear in Astrophys. J. Suppl. 2. F. Hamman, and G. Ferland, Astrophys. J. 418 (1993) 11. 3. C. Norman, and N. Scoville, Astrophys. J. 332 (1988) 124. 4. S. Bunch, et al., Nucl. Phys. 53 (1964) 241; S. Harbison, et al., Nucl. Phys. A152 (1970) 503; D. Cairns, et al., Nucl. Phys. 60 (1964) 369; L. Votta, et al., Phys. Rev. C 10 (1974) 520; W. Selove, and J. Teem, Phys. Ray. 112 (1958) 1658; M. Bernas, et al., Nucl. Phys. A156 (1970) 289; J. Jenkin, et al., Nucl. Phys. 50 (1964) 516; H. llauser, et al., Nucl. Phys. A456 (1986) 253; c. King, et al., Phys. Rev. C 16 (1977) 1712; B. Glagola, et al., Phys. Rev. C 25 (1982) 34; L. Woo, et al., Phys. Rev. C 32 (11985) 706; A. SpasskiY, et al., Sov. J. Nucl Phys. 3 (1966) 477. 5. M. Kusunose, and S. Mineshige, Astrophys. J. 423 (1994) 600. 6. L. Kawano, FERMILAB-PUB-88/34-A. 7. G. Caughlan, and W. Fowler, Atomic Data and Nuclear Data Tables 40 (1988) 284. 8. R.V. Wagoner, Astrophys. J. 162 (1969) 247. 9. R.V. Wagoner, W. A. Fowler, and F. Hoyle, Astrophys. J. 148 (1967) 3. 10. M. Wiescher, and K. Kettner, Astrophys. J. 263 (1982) 891. 11. T. A. Weaver, and S. E. Woosley, these proceedings.