Pub Date : 2021-04-23DOI: 10.1051/0004-6361/202140893
L. Haemmerl'e
Supermassive stars (SMSs) collapsing via the general-relativistic (GR) instability are invoked as the possible progenitors of supermassive black holes. Their mass and angular momentum at the onset of the instability are key in many respects, in particular regarding the possibility for observational signatures of direct collapse. Here, we study the stability of rotating, rapidly accreting SMSs against GR and derive the properties of these stars at death. On the basis of hylotropic structures, relevant for rapidly accreting SMSs, we define rotation profiles under the assumption of local angular momentum conservation in radiative regions, which allows for differential rotation. We find that rotation favours the stability of rapidly accreting SMSs as soon as the accreted angular momentum represents a fraction f > 0.1% of the Keplerian angular momentum. For f = 0.3%-0.5% the maximum masses consistent with GR stability are increased by an order of magnitude compared to the non-rotating case. For f = 1%, the GR instability cannot be reached if the stellar mass does not exceed 10^7-10^8 Msun. These results imply that, like in the non-rotating case, the final masses of the progenitors of direct collapse black holes range in distinct intervals depending on the scenario considered: 10^5 Msun < M < 10^6 Msun for primordial atomically cooled haloes; 10^6 Msun < M < 10^9 Msun for metal-rich galaxy mergers. The models suggest that the centrifugal barrier is inefficient to prevent the direct formation of a supermassive black hole at the collapse of a SMS. Moreover, the conditions of galaxy mergers appear as more favorable than those of atomically cooled haloes for detectable gravitational wave emission and ultra-long gamma-ray bursts at black hole formation.
{"title":"General-relativistic instability in rapidly accreting supermassive stars: The impact of rotation","authors":"L. Haemmerl'e","doi":"10.1051/0004-6361/202140893","DOIUrl":"https://doi.org/10.1051/0004-6361/202140893","url":null,"abstract":"Supermassive stars (SMSs) collapsing via the general-relativistic (GR) instability are invoked as the possible progenitors of supermassive black holes. Their mass and angular momentum at the onset of the instability are key in many respects, in particular regarding the possibility for observational signatures of direct collapse. Here, we study the stability of rotating, rapidly accreting SMSs against GR and derive the properties of these stars at death. On the basis of hylotropic structures, relevant for rapidly accreting SMSs, we define rotation profiles under the assumption of local angular momentum conservation in radiative regions, which allows for differential rotation. We find that rotation favours the stability of rapidly accreting SMSs as soon as the accreted angular momentum represents a fraction f > 0.1% of the Keplerian angular momentum. For f = 0.3%-0.5% the maximum masses consistent with GR stability are increased by an order of magnitude compared to the non-rotating case. For f = 1%, the GR instability cannot be reached if the stellar mass does not exceed 10^7-10^8 Msun. These results imply that, like in the non-rotating case, the final masses of the progenitors of direct collapse black holes range in distinct intervals depending on the scenario considered: 10^5 Msun < M < 10^6 Msun for primordial atomically cooled haloes; 10^6 Msun < M < 10^9 Msun for metal-rich galaxy mergers. The models suggest that the centrifugal barrier is inefficient to prevent the direct formation of a supermassive black hole at the collapse of a SMS. Moreover, the conditions of galaxy mergers appear as more favorable than those of atomically cooled haloes for detectable gravitational wave emission and ultra-long gamma-ray bursts at black hole formation.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"79 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91214044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-12DOI: 10.1051/0004-6361/202140784
I. Roberts, R. Weeren, S. McGee, A. Botteon, A. Drabent, A. Ignesti, H. Rottgering, T. Shimwell, C. Tasse
In this paper we present a large sample of jellyfish galaxies in low redshift clusters (z<0.05), identified through 120-168 MHz radio continuum from the LOFAR Two-metre Sky Survey (LoTSS). From a parent sample of 29 X-ray-detected SDSS galaxy clusters and their spectroscopic members, we visually identify 95 star-forming, LoTSS jellyfish galaxies with 144 MHz radio tails. Star formation rates (SFRs) and stellar masses are obtained for all galaxies from SED fits. For each jellyfish galaxy we determine the tail orientation with respect to the cluster centre and quantify the prominence of the radio tails with the 144 MHz shape asymmetry. After carefully accounting for redshift-dependent selection effects, we find that the frequency of jellyfish galaxies is relatively constant from cluster to cluster. LoTSS jellyfish galaxies are preferentially found at small clustercentric radius and large velocity offsets within their host clusters and have radio tails that are oriented away from the cluster centre. These galaxies also show enhanced star formation, relative to both 'normal' cluster galaxies and isolated field galaxies, but generally fall within the scatter of the L144MHz - SFR relation. The properties of the LoTSS jellyfish galaxies identified in this work are fully consistent with expectations from ram pressure stripping. This large sample of jellyfish galaxies will be valuable for further constraining ram pressure stripping and star formation quenching in nearby galaxy clusters. We show that LOFAR is a powerful instrument for identifying ram pressure stripped galaxies across extremely wide fields. Moving forward we will push the search for jellyfish galaxies beyond this initial cluster sample, including a comprehensive survey of the galaxy group regime.
{"title":"LoTSS jellyfish galaxies. I. Radio tails in low redshift clusters","authors":"I. Roberts, R. Weeren, S. McGee, A. Botteon, A. Drabent, A. Ignesti, H. Rottgering, T. Shimwell, C. Tasse","doi":"10.1051/0004-6361/202140784","DOIUrl":"https://doi.org/10.1051/0004-6361/202140784","url":null,"abstract":"In this paper we present a large sample of jellyfish galaxies in low redshift clusters (z<0.05), identified through 120-168 MHz radio continuum from the LOFAR Two-metre Sky Survey (LoTSS). From a parent sample of 29 X-ray-detected SDSS galaxy clusters and their spectroscopic members, we visually identify 95 star-forming, LoTSS jellyfish galaxies with 144 MHz radio tails. Star formation rates (SFRs) and stellar masses are obtained for all galaxies from SED fits. For each jellyfish galaxy we determine the tail orientation with respect to the cluster centre and quantify the prominence of the radio tails with the 144 MHz shape asymmetry. After carefully accounting for redshift-dependent selection effects, we find that the frequency of jellyfish galaxies is relatively constant from cluster to cluster. LoTSS jellyfish galaxies are preferentially found at small clustercentric radius and large velocity offsets within their host clusters and have radio tails that are oriented away from the cluster centre. These galaxies also show enhanced star formation, relative to both 'normal' cluster galaxies and isolated field galaxies, but generally fall within the scatter of the L144MHz - SFR relation. The properties of the LoTSS jellyfish galaxies identified in this work are fully consistent with expectations from ram pressure stripping. This large sample of jellyfish galaxies will be valuable for further constraining ram pressure stripping and star formation quenching in nearby galaxy clusters. We show that LOFAR is a powerful instrument for identifying ram pressure stripped galaxies across extremely wide fields. Moving forward we will push the search for jellyfish galaxies beyond this initial cluster sample, including a comprehensive survey of the galaxy group regime.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"130 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85264231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-12DOI: 10.1051/0004-6361/202039842
S. Goswami, A. Slemer, P. Marigo, A. Bressan, L. Silva, M. Spera, L. Boco, V. Grisoni, L. Pantoni, A. Lapi
Context. There is mounting evidence that the stellar initial mass function (IMF) could extend much beyond the canonical Mi ∼ 100M limit, but the impact of such hypothesis on the chemical enrichment of galaxies still remains to be clarified. Aims. We aim to address this question by analysing the observed abundances of thinand thick-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair instability supernovae. Methods. We built new sets of chemical yields from massive and very massive stars up to Mi ∼ 350M , by combining the wind ejecta extracted from our hydrostatic stellar evolution models with explosion ejecta from the literature. Using a simple chemical evolution code we analyse the effects of adopting different yield tables by comparing predictions against observations of stars in the solar vicinity. Results. After several tests, we focus on the [O/Fe] ratio which best separates the chemical patterns of the two Milky Way components. We find that with a standard IMF, truncated at Mi ∼ 100M , we can reproduce various observational constraints for thin-disc stars, but the same IMF fails to account for the [O/Fe] ratios of thick-disc stars. The best results are obtained by extending the IMF up to Mi = 350M and including the chemical ejecta of very massive stars, in the form of winds and pair instability supernova explosions. Conclusions. Our study indicates that PISN could have played a significant role in shaping the chemical evolution of the Milky Way thick disc. By including their chemical yields it is easier to reproduce not only the level of the α-enhancement but also the observed slope of thick-disc stars in the [O/Fe] vs. [Fe/H] diagram. The bottom line is that the contribution of very massive stars to the chemical enrichment of galaxies is potentially quite important and should not be neglected in chemical evolution models.
{"title":"The effects of the initial mass function on Galactic chemical enrichment","authors":"S. Goswami, A. Slemer, P. Marigo, A. Bressan, L. Silva, M. Spera, L. Boco, V. Grisoni, L. Pantoni, A. Lapi","doi":"10.1051/0004-6361/202039842","DOIUrl":"https://doi.org/10.1051/0004-6361/202039842","url":null,"abstract":"Context. There is mounting evidence that the stellar initial mass function (IMF) could extend much beyond the canonical Mi ∼ 100M limit, but the impact of such hypothesis on the chemical enrichment of galaxies still remains to be clarified. Aims. We aim to address this question by analysing the observed abundances of thinand thick-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair instability supernovae. Methods. We built new sets of chemical yields from massive and very massive stars up to Mi ∼ 350M , by combining the wind ejecta extracted from our hydrostatic stellar evolution models with explosion ejecta from the literature. Using a simple chemical evolution code we analyse the effects of adopting different yield tables by comparing predictions against observations of stars in the solar vicinity. Results. After several tests, we focus on the [O/Fe] ratio which best separates the chemical patterns of the two Milky Way components. We find that with a standard IMF, truncated at Mi ∼ 100M , we can reproduce various observational constraints for thin-disc stars, but the same IMF fails to account for the [O/Fe] ratios of thick-disc stars. The best results are obtained by extending the IMF up to Mi = 350M and including the chemical ejecta of very massive stars, in the form of winds and pair instability supernova explosions. Conclusions. Our study indicates that PISN could have played a significant role in shaping the chemical evolution of the Milky Way thick disc. By including their chemical yields it is easier to reproduce not only the level of the α-enhancement but also the observed slope of thick-disc stars in the [O/Fe] vs. [Fe/H] diagram. The bottom line is that the contribution of very massive stars to the chemical enrichment of galaxies is potentially quite important and should not be neglected in chemical evolution models.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"33 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79840212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-10DOI: 10.1051/0004-6361/202140624
A. Ershova, J. Schmidt
We present a model for the configuration of noninteracting material that is ejected in a continuous manner from an atmosphereless gravitating body for a given distribution of sources. The model is applicable to material on bound or unbound trajectories and to steady and nonsteady modes of ejection. For a jet that is inclined to the surface normal, we related the distributions of ejection direction, velocity, and size to the phase-space number density at the distance from the source body. Integrating over velocity space, we obtained an expression from which we inferred the density, flux, or optical depth of the ejected material. As examples for the application of the code, we calculate profiles of the dust density in the Enceladus plume, the pattern of mass deposition rates around a plume on Europa, and images of optical depth following the nonstationary emission of material from a volcano on Io. We make the source code of a Fortran-95 implementation of the model freely available.
{"title":"Two-body model for the spatial distribution of dust ejected from an atmosphereless body","authors":"A. Ershova, J. Schmidt","doi":"10.1051/0004-6361/202140624","DOIUrl":"https://doi.org/10.1051/0004-6361/202140624","url":null,"abstract":"We present a model for the configuration of noninteracting material that is ejected in a continuous manner from an atmosphereless gravitating body for a given distribution of sources. The model is applicable to material on bound or unbound trajectories and to steady and nonsteady modes of ejection. For a jet that is inclined to the surface normal, we related the distributions of ejection direction, velocity, and size to the phase-space number density at the distance from the source body. Integrating over velocity space, we obtained an expression from which we inferred the density, flux, or optical depth of the ejected material. As examples for the application of the code, we calculate profiles of the dust density in the Enceladus plume, the pattern of mass deposition rates around a plume on Europa, and images of optical depth following the nonstationary emission of material from a volcano on Io. We make the source code of a Fortran-95 implementation of the model freely available.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"15 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90519769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-09DOI: 10.1051/0004-6361/202141036
A. Upadhyay, K. Oman, S. Trager
We study the relation between star formation history of galaxies falling into a high-density cluster environment and their likely orbital histories using both observational and simulation data. We use high-resolution spectra of 12 galaxies of the Coma Cluster around NGC 4874 (the X-ray center of the Coma Cluster). The stellar and kinematic properties of the galaxies are modeled using STECKMAP. We extract the probability distribution of two orbital parameters - infall and pericenter times - of these galaxies from N-body dark matter only simulations extending up to z = -1/2 ( ~10 Gyr in the future). The probability distribution of orbital parameters is compensated for the interloper probabilities of the satellites. We carry out a probability-based study to compare the cumulative (probability) distribution of the two orbital parameters with the star formation rates and the fraction of stellar mass formed. We find that massive galaxies (M_* > 10^10 M_sun) are quenched even before falling into the cluster environment. This may be due to internal quenching mechanisms or group pre-processing, although it is hard to ascertain the individual contribution of various processes. Lower mass galaxies form stars between infall and first pericenter passage and all the galaxies in our sample are quenched by the time of their first pericentric passage. Ram pressure and tidal stripping are likely to be the dominant processes as they peak with proximity to the cluster center.
{"title":"Star formation histories of Coma cluster galaxies matched to simulated orbits hint at quenching around first pericenter","authors":"A. Upadhyay, K. Oman, S. Trager","doi":"10.1051/0004-6361/202141036","DOIUrl":"https://doi.org/10.1051/0004-6361/202141036","url":null,"abstract":"We study the relation between star formation history of galaxies falling into a high-density cluster environment and their likely orbital histories using both observational and simulation data. We use high-resolution spectra of 12 galaxies of the Coma Cluster around NGC 4874 (the X-ray center of the Coma Cluster). The stellar and kinematic properties of the galaxies are modeled using STECKMAP. We extract the probability distribution of two orbital parameters - infall and pericenter times - of these galaxies from N-body dark matter only simulations extending up to z = -1/2 ( ~10 Gyr in the future). The probability distribution of orbital parameters is compensated for the interloper probabilities of the satellites. We carry out a probability-based study to compare the cumulative (probability) distribution of the two orbital parameters with the star formation rates and the fraction of stellar mass formed. We find that massive galaxies (M_* > 10^10 M_sun) are quenched even before falling into the cluster environment. This may be due to internal quenching mechanisms or group pre-processing, although it is hard to ascertain the individual contribution of various processes. Lower mass galaxies form stars between infall and first pericenter passage and all the galaxies in our sample are quenched by the time of their first pericentric passage. Ram pressure and tidal stripping are likely to be the dominant processes as they peak with proximity to the cluster center.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"109 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90300781","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-09DOI: 10.1051/0004-6361/202140419
A. Jacob, K. Menten, H. Wiesemeyer, G. N. Ortiz-Le'on
Context. The intensities of the three widely observed radio-wavelength hyperfine structure (HFS) lines between the Λ-doublet components of the rotational ground state of CH are inconsistent with local thermodynamic equilibrium (LTE) and indicate ubiquitous population inversion. While this can be qualitatively understood assuming a pumping cycle that involves collisional excitation processes, the relative intensities of the lines and in particular the dominance of the lowest frequency satellite line has not been well understood. This has limited the use of CH radio emission as a tracer of the molecular interstellar medium. Aims. We aim to investigate the nature of the (generally) weak CH ground state masers by employing synergies between the ground state HFS transitions themselves and with the far-infrared lines, near 149 μm (2 THz), that connect these levels to an also HFS split rotationally excited level. Methods. We present the first interferometric observations, with the Karl G. Jansky Very Large Array, of the CH 9 cm ground state HFS transitions at 3.264 GHz, 3.335 GHz, and 3.349 GHz toward the four high mass star-forming regions (SFRs) Sgr B2 (M), G34.26+0.15, W49 (N), and W51. We combine this data set with our high spectral resolution observations of the N, J =2, 3/2→1, 1/2 transitions of CH near 149 μm observed toward the same sources made with the upGREAT receiver on SOFIA, which share a common lower energy levels with the HFS transitions within the rotational ground state. Results. Toward all four sources, we observe the 3.264 GHz lower satellite line in enhanced emission with its relative intensity higher than its expected value at LTE by a factor between 4 and 20. Employing recently calculated collisional rate coefficients, we perform statistical equilibrium calculations with the non-LTE radiative transfer code MOLPOP-CEP in order to model the excitation conditions traced by the ground state HFS lines of CH and to infer the physical conditions in the emitting regions. The models account for effects of far-infrared line overlap with additional constraints provided by reliable column densities of CH estimated from the 149 μm lines. Conclusions. The derived gas densities indicate that the CH radio emission lines (and the far-infrared absorption) arise from the diffuse and translucent outer regions of the SFRs’ envelopes as well as in such clouds located along the lines of sight. We infer temperatures ranging from 50 to 125 K. These elevated temperatures, together with astrochemical considerations, may indicate that CH is formed in material heated by the dissipation of interstellar turbulence, which has been invoked for other molecules. The excitation conditions we derive reproduce the observed level inversion in all three of the ground state HFS lines of CH over a wide range of gas densities with an excitation temperature of ∼−0.3 K, consistent with previous theoretical predictions.
{"title":"The CH radical at radio wavelengths: Revisiting emission in the 3.3 GHz ground-state lines","authors":"A. Jacob, K. Menten, H. Wiesemeyer, G. N. Ortiz-Le'on","doi":"10.1051/0004-6361/202140419","DOIUrl":"https://doi.org/10.1051/0004-6361/202140419","url":null,"abstract":"Context. The intensities of the three widely observed radio-wavelength hyperfine structure (HFS) lines between the Λ-doublet components of the rotational ground state of CH are inconsistent with local thermodynamic equilibrium (LTE) and indicate ubiquitous population inversion. While this can be qualitatively understood assuming a pumping cycle that involves collisional excitation processes, the relative intensities of the lines and in particular the dominance of the lowest frequency satellite line has not been well understood. This has limited the use of CH radio emission as a tracer of the molecular interstellar medium. Aims. We aim to investigate the nature of the (generally) weak CH ground state masers by employing synergies between the ground state HFS transitions themselves and with the far-infrared lines, near 149 μm (2 THz), that connect these levels to an also HFS split rotationally excited level. Methods. We present the first interferometric observations, with the Karl G. Jansky Very Large Array, of the CH 9 cm ground state HFS transitions at 3.264 GHz, 3.335 GHz, and 3.349 GHz toward the four high mass star-forming regions (SFRs) Sgr B2 (M), G34.26+0.15, W49 (N), and W51. We combine this data set with our high spectral resolution observations of the N, J =2, 3/2→1, 1/2 transitions of CH near 149 μm observed toward the same sources made with the upGREAT receiver on SOFIA, which share a common lower energy levels with the HFS transitions within the rotational ground state. Results. Toward all four sources, we observe the 3.264 GHz lower satellite line in enhanced emission with its relative intensity higher than its expected value at LTE by a factor between 4 and 20. Employing recently calculated collisional rate coefficients, we perform statistical equilibrium calculations with the non-LTE radiative transfer code MOLPOP-CEP in order to model the excitation conditions traced by the ground state HFS lines of CH and to infer the physical conditions in the emitting regions. The models account for effects of far-infrared line overlap with additional constraints provided by reliable column densities of CH estimated from the 149 μm lines. Conclusions. The derived gas densities indicate that the CH radio emission lines (and the far-infrared absorption) arise from the diffuse and translucent outer regions of the SFRs’ envelopes as well as in such clouds located along the lines of sight. We infer temperatures ranging from 50 to 125 K. These elevated temperatures, together with astrochemical considerations, may indicate that CH is formed in material heated by the dissipation of interstellar turbulence, which has been invoked for other molecules. The excitation conditions we derive reproduce the observed level inversion in all three of the ground state HFS lines of CH over a wide range of gas densities with an excitation temperature of ∼−0.3 K, consistent with previous theoretical predictions.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"36 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89595329","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-09DOI: 10.1051/0004-6361/202039210
S. Matsumura, R. Brasser, S. Ida
Aims. The connection between initial disc conditions and final orbital and physical properties of planets is not well-understood. In this paper, we numerically study the formation of planetary systems via pebble accretion and investigate the effects of disc properties such as masses, dissipation timescales, and metallicities on planet formation outcomes. Methods. We improved the N-body code SyMBA that was modified for our paper I by taking account of new planet-disc interaction models and type II migration. We adopted the ‘two-α’ disc model to mimic the effects of both the standard disc turbulence and the mass accretion driven by the magnetic disc wind. Results. We successfully reproduced the overall distribution trends of semi-major axes, eccentricities, and planetary masses of extrasolar giant planets. There are two types of giant planet formation trends, depending on whether or not the disc’s dissipation timescales are comparable to the planet formation timescales. When planet formation happens fast enough, giant planets are fully grown (Jupiter mass or higher) and are distributed widely across the disc. On the other hand, when planet formation is limited by the disc’s dissipation, discs generally form low-mass cold Jupiters (CJs). Our simulations also naturally explain why hot Jupiters (HJs) tend to be alone and how the observed eccentricity-metallicity trends arise. The low-metallicity discs tend to form nearly circular and coplanar HJs in situ, because planet formation is slower than high-metallicity discs, and thus protoplanetary cores migrate significantly before gas accretion. The high-metallicity discs, on the other hand, generate HJs in situ or via tidal circularisation of eccentric orbits. Both pathways usually involve dynamical instabilities, and thus HJs tend to have broader eccentricity and inclination distributions. When giant planets with very wide orbits (’super-cold Jupiters’) are formed via pebble accretion followed by scattering, we predict that they belong to metal-rich stars, have eccentric orbits, and tend to have (∼ 80%) companions interior to their orbits.
{"title":"N-body simulations of planet formation via pebble accretion. II. How to form various giant planets","authors":"S. Matsumura, R. Brasser, S. Ida","doi":"10.1051/0004-6361/202039210","DOIUrl":"https://doi.org/10.1051/0004-6361/202039210","url":null,"abstract":"Aims. The connection between initial disc conditions and final orbital and physical properties of planets is not well-understood. In this paper, we numerically study the formation of planetary systems via pebble accretion and investigate the effects of disc properties such as masses, dissipation timescales, and metallicities on planet formation outcomes. Methods. We improved the N-body code SyMBA that was modified for our paper I by taking account of new planet-disc interaction models and type II migration. We adopted the ‘two-α’ disc model to mimic the effects of both the standard disc turbulence and the mass accretion driven by the magnetic disc wind. Results. We successfully reproduced the overall distribution trends of semi-major axes, eccentricities, and planetary masses of extrasolar giant planets. There are two types of giant planet formation trends, depending on whether or not the disc’s dissipation timescales are comparable to the planet formation timescales. When planet formation happens fast enough, giant planets are fully grown (Jupiter mass or higher) and are distributed widely across the disc. On the other hand, when planet formation is limited by the disc’s dissipation, discs generally form low-mass cold Jupiters (CJs). Our simulations also naturally explain why hot Jupiters (HJs) tend to be alone and how the observed eccentricity-metallicity trends arise. The low-metallicity discs tend to form nearly circular and coplanar HJs in situ, because planet formation is slower than high-metallicity discs, and thus protoplanetary cores migrate significantly before gas accretion. The high-metallicity discs, on the other hand, generate HJs in situ or via tidal circularisation of eccentric orbits. Both pathways usually involve dynamical instabilities, and thus HJs tend to have broader eccentricity and inclination distributions. When giant planets with very wide orbits (’super-cold Jupiters’) are formed via pebble accretion followed by scattering, we predict that they belong to metal-rich stars, have eccentric orbits, and tend to have (∼ 80%) companions interior to their orbits.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"13 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85342498","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-08DOI: 10.1051/0004-6361/202140855
K. Steinvall, Y. Khotyaintsev, G. Cozzani, A. Vaivads, E. Yordanova, A. Eriksson, N. Edberg, M. Maksimović, S. Bale, T. Chust, V. Krasnoselskikh, M. Kretzschmar, E. Lorfèvre, D. Plettemeier, J. Souvcek, M. Steller, vS. vStver'ak, A. Vecchio, T. Horbury, H. O’Brien, V. Evans, A. Fedorov, P. Louarn, V. G'enot, N. Andr'e, B. Lavraud, A. Rouillard, C. Owen
Context. Solar Orbiter was launched on 10 February 2020 with the purpose of investigating solar and heliospheric physics using a payload of instruments designed for both remote and in situ studies. Similar to the recently launched Parker Solar Probe, and unlike earlier missions, Solar Orbiter carries instruments designed to measure low-frequency DC electric fields. Aims. In this paper, we assess the quality of the low-frequency DC electric field measured by the Radio and Plasma Waves instrument (RPW) on Solar Orbiter. In particular, we investigate the possibility of using Solar Orbiter’s DC electric and magnetic field data to estimate the solar wind speed. Methods. We used a deHo ff mann-Teller (HT) analysis, based on measurements of the electric and magnetic fields, to find the velocity of solar wind current sheets, which minimises a single component of the electric field. By comparing the HT velocity to the proton velocity measured by the Proton and Alpha particle Sensor (PAS), we have developed a simple model for the e ff ective antenna length, L e ff of the E-field probes. We then used the HT method to estimate the speed of the solar wind. Results. Using the HT method, we find that the observed variations in E y are often in excellent agreement with the variations in the magnetic field. The magnitude of E y , however, is uncertain due to the fact that the L e ff depends on the plasma environment. Here, we derive an empirical model relating L e ff to the Debye length, which we can use to improve the estimate of E y and, consequently, the estimated solar wind speed. Conclusions. The low-frequency electric field provided by RPW is of high quality. Using the deHo ff mann-Teller analysis, Solar Orbiter’s magnetic and electric field measurements can be used to estimate the solar wind speed when plasma data are unavailable.
上下文。太阳轨道器于2020年2月10日发射，目的是利用为远程和现场研究设计的有效载荷仪器研究太阳和日球层物理。与最近发射的帕克太阳探测器类似，与早期的任务不同，太阳轨道器携带了用于测量低频直流电场的仪器。目标本文对太阳轨道器上的射电和等离子体波仪(RPW)测量的低频直流电场质量进行了评价。特别地，我们探讨了利用太阳轨道飞行器的直流电场和磁场数据来估计太阳风速度的可能性。方法。基于对电场和磁场的测量，我们使用了deHo ff mann-Teller (HT)分析来找到太阳风电流片的速度，它使电场的单个成分最小化。通过比较质子和α粒子传感器(PAS)测量的质子速度，我们建立了一个简单的电场探头有效天线长度leff模型。然后我们用高温法估计太阳风的速度。结果。利用高温法，我们发现观测到的y的变化往往与磁场的变化非常吻合。然而，ey的大小是不确定的，因为eff取决于等离子体环境。在这里，我们推导出了一个关于e - ff和德拜长度的经验模型，我们可以用它来改进对e - y的估计，从而改进对太阳风速度的估计。结论。RPW提供的低频电场质量高。使用deHo off mann-Teller分析，太阳轨道器的磁场和电场测量可以用来估计当等离子体数据不可用时太阳风的速度。
{"title":"Solar wind current sheets and deHoffmann-Teller analysis. First results from Solar Orbiter's DC electric field measurements","authors":"K. Steinvall, Y. Khotyaintsev, G. Cozzani, A. Vaivads, E. Yordanova, A. Eriksson, N. Edberg, M. Maksimović, S. Bale, T. Chust, V. Krasnoselskikh, M. Kretzschmar, E. Lorfèvre, D. Plettemeier, J. Souvcek, M. Steller, vS. vStver'ak, A. Vecchio, T. Horbury, H. O’Brien, V. Evans, A. Fedorov, P. Louarn, V. G'enot, N. Andr'e, B. Lavraud, A. Rouillard, C. Owen","doi":"10.1051/0004-6361/202140855","DOIUrl":"https://doi.org/10.1051/0004-6361/202140855","url":null,"abstract":"Context. Solar Orbiter was launched on 10 February 2020 with the purpose of investigating solar and heliospheric physics using a payload of instruments designed for both remote and in situ studies. Similar to the recently launched Parker Solar Probe, and unlike earlier missions, Solar Orbiter carries instruments designed to measure low-frequency DC electric fields. Aims. In this paper, we assess the quality of the low-frequency DC electric field measured by the Radio and Plasma Waves instrument (RPW) on Solar Orbiter. In particular, we investigate the possibility of using Solar Orbiter’s DC electric and magnetic field data to estimate the solar wind speed. Methods. We used a deHo ff mann-Teller (HT) analysis, based on measurements of the electric and magnetic fields, to find the velocity of solar wind current sheets, which minimises a single component of the electric field. By comparing the HT velocity to the proton velocity measured by the Proton and Alpha particle Sensor (PAS), we have developed a simple model for the e ff ective antenna length, L e ff of the E-field probes. We then used the HT method to estimate the speed of the solar wind. Results. Using the HT method, we find that the observed variations in E y are often in excellent agreement with the variations in the magnetic field. The magnitude of E y , however, is uncertain due to the fact that the L e ff depends on the plasma environment. Here, we derive an empirical model relating L e ff to the Debye length, which we can use to improve the estimate of E y and, consequently, the estimated solar wind speed. Conclusions. The low-frequency electric field provided by RPW is of high quality. Using the deHo ff mann-Teller analysis, Solar Orbiter’s magnetic and electric field measurements can be used to estimate the solar wind speed when plasma data are unavailable.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"103 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77526530","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-08DOI: 10.1051/0004-6361/202038082
Q. M. Zhang, J. Cheng, Y. Dai, K. Tam, A. Xu
In this paper, we reanalyze the M1.2 confined flare with a large extreme-ultraviolet (EUV) late phase on 2011 September 9, focusing on its energy partition. The radiation ($sim$5.4$times$10$^{30}$ erg) in 1$-$70 {AA} is nearly eleven times larger than the radiation in 70$-$370 {AA}, and is nearly 180 times larger than the radiation in 1$-$8 {AA}. The peak thermal energy of the post-flare loops is estimated to be (1.7$-$1.8)$times$10$^{30}$ erg based on a simplified schematic cartoon. Based on previous results of Enthalpy-Based Thermal Evolution of Loops (EBTEL) simulation, the energy inputs in the main flaring loops and late-phase loops are (1.5$-$3.8)$times$10$^{29}$ erg and 7.7$times$10$^{29}$ erg, respectively. The nonthermal energy ((1.7$-$2.2)$times$10$^{30}$ erg) of the flare-accelerated electrons is comparable to the peak thermal energy and is sufficient to provide the energy input of the main flaring loops and late-phase loops. The magnetic free energy (9.1$times$10$^{31}$ erg) before flare is large enough to provide the heating requirement and radiation, indicating that the magnetic free energy is adequate to power the flare.
{"title":"Energy partition in a confined flare with an extreme-ultraviolet late phase","authors":"Q. M. Zhang, J. Cheng, Y. Dai, K. Tam, A. Xu","doi":"10.1051/0004-6361/202038082","DOIUrl":"https://doi.org/10.1051/0004-6361/202038082","url":null,"abstract":"In this paper, we reanalyze the M1.2 confined flare with a large extreme-ultraviolet (EUV) late phase on 2011 September 9, focusing on its energy partition. The radiation ($sim$5.4$times$10$^{30}$ erg) in 1$-$70 {AA} is nearly eleven times larger than the radiation in 70$-$370 {AA}, and is nearly 180 times larger than the radiation in 1$-$8 {AA}. The peak thermal energy of the post-flare loops is estimated to be (1.7$-$1.8)$times$10$^{30}$ erg based on a simplified schematic cartoon. Based on previous results of Enthalpy-Based Thermal Evolution of Loops (EBTEL) simulation, the energy inputs in the main flaring loops and late-phase loops are (1.5$-$3.8)$times$10$^{29}$ erg and 7.7$times$10$^{29}$ erg, respectively. The nonthermal energy ((1.7$-$2.2)$times$10$^{30}$ erg) of the flare-accelerated electrons is comparable to the peak thermal energy and is sufficient to provide the energy input of the main flaring loops and late-phase loops. The magnetic free energy (9.1$times$10$^{31}$ erg) before flare is large enough to provide the heating requirement and radiation, indicating that the magnetic free energy is adequate to power the flare.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"85 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89438841","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-03DOI: 10.1051/0004-6361/202140298
M. Vergara, D. Schleicher, T. Boekholt, B. Reinoso, M. Fellhauer, R. Klessen, N. Leigh
Fragmentation often occurs in disk-like structures, both in the early Universe and in the context of present-day star formation. Supermassive black holes (SMBHs) are astrophysical objects whose origin is not well understood; they weigh millions of solar masses and reside in the centers of galaxies. An important formation scenario for SMBHs is based on collisions and mergers of stars in a massive cluster with a high stellar density, in which the most massive star moves to the center of the cluster due to dynamical friction. This increases the rate of collisions and mergers since massive stars have larger collisional cross sections. This can lead to a runaway growth of a very massive star which may collapse to become an intermediate-mass black hole. Here we investigate the dynamical evolution of Miyamoto-Nagai models that allow us to describe dense stellar clusters, including flattening and different degrees of rotation. We find that the collisions in these clusters depend mostly on the number of stars and the initial stellar radii for a given radial size of the cluster. By comparison, rotation seems to affect the collision rate by at most 20%. For flatness, we compared spherical models with systems that have a scale height of about 10% of their radial extent, in this case finding a change in the collision rate of less than 25%. Overall, we conclude that the parameters only have a minor effect on the number of collisions. Our results also suggest that rotation helps to retain more stars in the system, reducing the number of escapers by a factor of 2− 3 depending on the model and the specific realization. After two million years, a typical lifetime of a very massive star, we find that about 630 collisions occur in a typical models with N = 104, R = 100 R and a half-mass radius of 0.1 pc, leading to a mass of about 6.3 × 103 M for the most massive object. We note that our simulations do not include mass loss during mergers or due to stellar winds. On the other hand, the growth of the most massive object may subsequently continue, depending on the lifetime of the most massive object.
{"title":"Stellar collisions in flattened and rotating Population III star clusters","authors":"M. Vergara, D. Schleicher, T. Boekholt, B. Reinoso, M. Fellhauer, R. Klessen, N. Leigh","doi":"10.1051/0004-6361/202140298","DOIUrl":"https://doi.org/10.1051/0004-6361/202140298","url":null,"abstract":"Fragmentation often occurs in disk-like structures, both in the early Universe and in the context of present-day star formation. Supermassive black holes (SMBHs) are astrophysical objects whose origin is not well understood; they weigh millions of solar masses and reside in the centers of galaxies. An important formation scenario for SMBHs is based on collisions and mergers of stars in a massive cluster with a high stellar density, in which the most massive star moves to the center of the cluster due to dynamical friction. This increases the rate of collisions and mergers since massive stars have larger collisional cross sections. This can lead to a runaway growth of a very massive star which may collapse to become an intermediate-mass black hole. Here we investigate the dynamical evolution of Miyamoto-Nagai models that allow us to describe dense stellar clusters, including flattening and different degrees of rotation. We find that the collisions in these clusters depend mostly on the number of stars and the initial stellar radii for a given radial size of the cluster. By comparison, rotation seems to affect the collision rate by at most 20%. For flatness, we compared spherical models with systems that have a scale height of about 10% of their radial extent, in this case finding a change in the collision rate of less than 25%. Overall, we conclude that the parameters only have a minor effect on the number of collisions. Our results also suggest that rotation helps to retain more stars in the system, reducing the number of escapers by a factor of 2− 3 depending on the model and the specific realization. After two million years, a typical lifetime of a very massive star, we find that about 630 collisions occur in a typical models with N = 104, R = 100 R and a half-mass radius of 0.1 pc, leading to a mass of about 6.3 × 103 M for the most massive object. We note that our simulations do not include mass loss during mergers or due to stellar winds. On the other hand, the growth of the most massive object may subsequently continue, depending on the lifetime of the most massive object.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"53 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85223957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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