P. Lustig, V. Strazzullo, C. D’Eugenio, E. Daddi, M. Pannella, A. Renzini, A. Cimatti, R. Gobat, S. Jin, J. Mohr, M. Onodera
We study structural properties of spectroscopically confirmed massive quiescent galaxies at $zapprox 3$ with one of the first sizeable samples of such sources, made of ten $10.8
我们研究了在$zapprox 3$的光谱确认的大质量静止星系的结构特性，其中一个是这样的源的第一个相当大的样本，由10个位于$2.4 < z < 3.2$的$10.8
{"title":"Compact, bulge-dominated structures of spectroscopically confirmed quiescent galaxies at z ≈ 3","authors":"P. Lustig, V. Strazzullo, C. D’Eugenio, E. Daddi, M. Pannella, A. Renzini, A. Cimatti, R. Gobat, S. Jin, J. Mohr, M. Onodera","doi":"10.1093/mnras/staa3766","DOIUrl":"https://doi.org/10.1093/mnras/staa3766","url":null,"abstract":"We study structural properties of spectroscopically confirmed massive quiescent galaxies at $zapprox 3$ with one of the first sizeable samples of such sources, made of ten $10.8<log(M_{star}/M_{odot})<11.3$ galaxies at $2.4 < z < 3.2$ in the COSMOS field whose redshifts and quiescence are confirmed by HST grism spectroscopy. Although affected by a weak bias toward younger stellar populations, this sample is deemed to be largely representative of the majority of the most massive and thus intrinsically rarest quiescent sources at this cosmic time. We rely on targeted HST/WFC3 observations and fit S'ersic profiles to the galaxy surface brightness distributions at $approx 4000$ angstrom restframe. We find typically high S'ersic indices and axis ratios (medians $approx 4.5$ and $0.73$, respectively) suggesting that, at odds with some previous results, the first massive quiescent galaxies may largely be already bulge-dominated systems. We measure compact galaxy sizes with an average of $approx 1.4$kpc at $log(M_{star}/M_{odot})approx 11.2$, in good agreement with the extrapolation at the highest masses of previous determinations of the stellar mass - size relation of quiescent galaxies, and of its redshift evolution, from photometrically selected samples at lower and similar redshifts. This work confirms the existence of a population of compact, bulge dominated, massive, quiescent sources at $zapprox 3$, providing one of the first statistical estimates of their structural properties, and further constraining the early formation and evolution of the first quiescent galaxies.","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87632368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Natsuko Izumi, Y. Fukui, K. Tachihara, S. Fujita, K. Torii, T. Kamazaki, H. Kaneko, Andrea Silva, D. Iono, M. Momose, K. Sugimoto, T. Nakazato, G. Kosugi, J. Maekawa, Shigeru Takahashi, A. Yoshino, S. Asayama
We present observations of the $^3P_1$-$^3P_0$ fine-structure line of atomic carbon using the ASTE 10 m sub-mm telescope towards RCW38, the youngest super star cluster in the Milky Way. The detected [CI] emission is compared with the CO $J$ = 1-0 image cube presented in Fukui et al. (2016) which has an angular resolution of 40$^{prime prime}$ ($sim$ 0.33 pc). The overall distribution of the [CI] emission in this cluster is similar to that of the $^{13}$CO emission. The optical depth of the [CI] emission was found to be $tau$ = 0.1-0.6, suggesting mostly optically thin emission. An empirical conversion factor from the [CI] integrated intensity to the H$_2$ column density was estimated as $X_{rm [CI]}$ = 6.3 $times$ 10$^{20}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s (for visual extinction: $A_V$ $le$ 10 mag) and 1.4 $times$ 10$^{21}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s (for $A_V$ of 10-100 mag). The column density ratio of the [CI] to CO ($N_{rm [CI]}/N_{rm CO}$) was derived as $sim$ 0.1 for $A_V$ of 10-100 mag, which is consistent with that of the Orion cloud presented in Ikeda et al. (2002). However, our results cover an $A_V$ regime of up to 100 mag, which is wider than the coverage found in Orion, which reach up to $sim$ 60 mag. Such a high [CI]/CO ratio in a high $A_V$ region is difficult to be explained by the plane-parallel photodissociation region (PDR) model, which predicts that this ratio is close to 0 due to the heavy shielding of the ultraviolet (UV) radiation. Our results suggest that the molecular gas in this cluster is highly clumpy, allowing deep penetration of UV radiation even at averaged $A_V$ values of 100 mag. Recent theoretical works have presented models consistent with such clumped gas distribution with a sub-pc clump size (e.g., Tachihara et al. 2018).
我们利用ASTE 10 m亚毫米望远镜对银河系中最年轻的超级星团RCW38进行了$^3P_1$ - $^3P_0$原子碳精细结构线的观测。将检测到的[CI]发射与Fukui等人(2016)提出的CO $J$ = 1-0图像立方体进行比较，后者的角分辨率为40 $^{prime prime}$ ($sim$ 0.33 pc)。该星团中[CI]排放的总体分布与$^{13}$ CO排放的分布相似。发现[CI]发射的光深为$tau$ = 0.1-0.6，表明主要是光薄发射。从[CI]综合强度到H $_2$柱密度的经验转换因子估计为$X_{rm [CI]}$ = 6.3 $times$ 10 $^{20}$ cm $^{-2}$ K $^{-1}$ km $^{-1}$ s(对于视觉消光:$A_V$$le$ 10 mag)和1.4 $times$ 10 $^{21}$ cm $^{-2}$ K $^{-1}$ km $^{-1}$ s(对于$A_V$ 10-100 mag)。[CI]与CO ($N_{rm [CI]}/N_{rm CO}$)的柱密度比在$A_V$为10-100等时为$sim$ 0.1，这与Ikeda et al.(2002)提出的猎户座云的柱密度比一致。然而，我们的结果覆盖了高达100等的$A_V$区域，这比猎户座的覆盖范围更广，猎户座的覆盖范围高达$sim$ 60等。在高$A_V$区域中如此高的[CI]/CO比率很难用平面平行光解区(PDR)模型来解释，该模型预测由于紫外线(UV)辐射的强烈屏蔽，该比率接近于0。我们的研究结果表明，该星团中的分子气体是高度块状的，即使在平均$A_V$值为100等的情况下，也允许紫外线辐射深入穿透。最近的理论工作提出了与亚pc大小的这种块状气体分布相一致的模型(例如，Tachihara et al. 2018)。
{"title":"Observations of the [C i] (3P1–3P0) emission toward the massive star-forming region RCW 38: Further evidence for highly-clumped density distribution of the molecular gas","authors":"Natsuko Izumi, Y. Fukui, K. Tachihara, S. Fujita, K. Torii, T. Kamazaki, H. Kaneko, Andrea Silva, D. Iono, M. Momose, K. Sugimoto, T. Nakazato, G. Kosugi, J. Maekawa, Shigeru Takahashi, A. Yoshino, S. Asayama","doi":"10.1093/PASJ/PSAA113","DOIUrl":"https://doi.org/10.1093/PASJ/PSAA113","url":null,"abstract":"We present observations of the $^3P_1$-$^3P_0$ fine-structure line of atomic carbon using the ASTE 10 m sub-mm telescope towards RCW38, the youngest super star cluster in the Milky Way. The detected [CI] emission is compared with the CO $J$ = 1-0 image cube presented in Fukui et al. (2016) which has an angular resolution of 40$^{prime prime}$ ($sim$ 0.33 pc). The overall distribution of the [CI] emission in this cluster is similar to that of the $^{13}$CO emission. The optical depth of the [CI] emission was found to be $tau$ = 0.1-0.6, suggesting mostly optically thin emission. An empirical conversion factor from the [CI] integrated intensity to the H$_2$ column density was estimated as $X_{rm [CI]}$ = 6.3 $times$ 10$^{20}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s (for visual extinction: $A_V$ $le$ 10 mag) and 1.4 $times$ 10$^{21}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s (for $A_V$ of 10-100 mag). The column density ratio of the [CI] to CO ($N_{rm [CI]}/N_{rm CO}$) was derived as $sim$ 0.1 for $A_V$ of 10-100 mag, which is consistent with that of the Orion cloud presented in Ikeda et al. (2002). However, our results cover an $A_V$ regime of up to 100 mag, which is wider than the coverage found in Orion, which reach up to $sim$ 60 mag. Such a high [CI]/CO ratio in a high $A_V$ region is difficult to be explained by the plane-parallel photodissociation region (PDR) model, which predicts that this ratio is close to 0 due to the heavy shielding of the ultraviolet (UV) radiation. Our results suggest that the molecular gas in this cluster is highly clumpy, allowing deep penetration of UV radiation even at averaged $A_V$ values of 100 mag. Recent theoretical works have presented models consistent with such clumped gas distribution with a sub-pc clump size (e.g., Tachihara et al. 2018).","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76358873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. McConnachie, C. Higgs, G. Thomas, K. Venn, P. Cot'e, G. Battaglia, G. Lewis
We measure systemic proper motions for distant dwarf galaxies in the Local Group and investigate if these isolated galaxies have ever had an interaction with the Milky Way or M31. We cross-match photometry of isolated, star forming, dwarf galaxies in the Local Group, taken as part of the {it Solo} survey, with astrometric measurements from Gaia Data Release 2. We find that NGC 6822, Leo A, IC 1613 and WLM have sufficient supergiants with reliable astrometry to derive proper motions. An additional three galaxies (Leo T, Eridanus 2 and Phoenix) are close enough that their proper motions have already been derived using red giant branch stars. Systematic errors in Gaia DR2 are significant for NGC 6822, IC 1613 and WLM. We explore the orbits for these galaxies, and conclude that Phoenix, Leo A and WLM are unlikely to have interacted with the Milky Way or M31, unless these large galaxies are very massive ($gtrsim 1.6 times 10^{12},M_odot$). We rule out a past interaction of NGC 6822 with M31 at $sim 99.99%$ confidence, and find there is a $<10$% chance that NGC 6822 has had an interaction with the Milky Way. We examine the likely origins of NGC 6822 in the periphery of the young Local Group, and note that a future interaction of NGC 6822 with the Milky Way or M31 in the next 4,Gyrs is essentially ruled out. Our measurements indicate that future Gaia data releases will provide good constraints on the interaction history for the majority of these galaxies.
{"title":"Solo dwarfs – III. Exploring the orbital origins of isolated Local Group galaxies with Gaia Data Release 2","authors":"A. McConnachie, C. Higgs, G. Thomas, K. Venn, P. Cot'e, G. Battaglia, G. Lewis","doi":"10.1093/mnras/staa3740","DOIUrl":"https://doi.org/10.1093/mnras/staa3740","url":null,"abstract":"We measure systemic proper motions for distant dwarf galaxies in the Local Group and investigate if these isolated galaxies have ever had an interaction with the Milky Way or M31. We cross-match photometry of isolated, star forming, dwarf galaxies in the Local Group, taken as part of the {it Solo} survey, with astrometric measurements from Gaia Data Release 2. We find that NGC 6822, Leo A, IC 1613 and WLM have sufficient supergiants with reliable astrometry to derive proper motions. An additional three galaxies (Leo T, Eridanus 2 and Phoenix) are close enough that their proper motions have already been derived using red giant branch stars. Systematic errors in Gaia DR2 are significant for NGC 6822, IC 1613 and WLM. We explore the orbits for these galaxies, and conclude that Phoenix, Leo A and WLM are unlikely to have interacted with the Milky Way or M31, unless these large galaxies are very massive ($gtrsim 1.6 times 10^{12},M_odot$). We rule out a past interaction of NGC 6822 with M31 at $sim 99.99%$ confidence, and find there is a $<10$% chance that NGC 6822 has had an interaction with the Milky Way. We examine the likely origins of NGC 6822 in the periphery of the young Local Group, and note that a future interaction of NGC 6822 with the Milky Way or M31 in the next 4,Gyrs is essentially ruled out. Our measurements indicate that future Gaia data releases will provide good constraints on the interaction history for the majority of these galaxies.","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81792190","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Cameron, T. Yuan, M. Trenti, D. Nicholls, L. Kewley
We investigate how HII region temperature structure assumptions affect "direct-method" spatially-resolved metallicity observations using multispecies auroral lines in a galaxy from the SAMI Galaxy Survey. SAMI609396B, at redshift $z=0.018$, is a low-mass galaxy in a minor merger with intense star formation, analogous to conditions at high redshifts. We use three methods to derive direct metallicities and compare with strong-line diagnostics. The spatial metallicity trends show significant differences among the three direct methods. Our first method is based on the commonly used electron temperature $T_e$([OIII]) from the [OIII]$lambda$4363 auroral line and a traditional $T_e$([OII]) -- $T_e$([OIII]) calibration. The second method applies a recent empirical correction to the O$^+$ abundance from the [OIII]/[OII] strong-line ratio. The third method infers the $T_e$([OII]) from the [SII]$lambdalambda$4069,76 auroral lines. The first method favours a positive metallicity gradient along SAMI609396B, whereas the second and third methods yield flattened gradients. Strong-line diagnostics produce mostly flat gradients, albeit with unquantified contamination from shocked regions. We conclude that overlooked assumptions about the internal temperature structure of HII regions in the direct method can lead to large discrepancies in metallicity gradient studies. Our detailed analysis of SAMI609396B underlines that high-accuracy metallicity gradient measurements require a wide array of emission lines and improved spatial resolutions in order to properly constrain excitation sources, physical conditions, and temperature structures of the emitting gas. Integral-field spectroscopic studies with future facilities such as JWST/NIRSpec and ground-based ELTs will be crucial in minimising systematic effects on measured gradients in distant galaxies.
{"title":"Spatially resolved direct method metallicity in a high-redshift analogue local galaxy: temperature structure impact on metallicity gradients","authors":"A. Cameron, T. Yuan, M. Trenti, D. Nicholls, L. Kewley","doi":"10.1093/mnras/staa3757","DOIUrl":"https://doi.org/10.1093/mnras/staa3757","url":null,"abstract":"We investigate how HII region temperature structure assumptions affect \"direct-method\" spatially-resolved metallicity observations using multispecies auroral lines in a galaxy from the SAMI Galaxy Survey. SAMI609396B, at redshift $z=0.018$, is a low-mass galaxy in a minor merger with intense star formation, analogous to conditions at high redshifts. We use three methods to derive direct metallicities and compare with strong-line diagnostics. The spatial metallicity trends show significant differences among the three direct methods. Our first method is based on the commonly used electron temperature $T_e$([OIII]) from the [OIII]$lambda$4363 auroral line and a traditional $T_e$([OII]) -- $T_e$([OIII]) calibration. The second method applies a recent empirical correction to the O$^+$ abundance from the [OIII]/[OII] strong-line ratio. The third method infers the $T_e$([OII]) from the [SII]$lambdalambda$4069,76 auroral lines. The first method favours a positive metallicity gradient along SAMI609396B, whereas the second and third methods yield flattened gradients. Strong-line diagnostics produce mostly flat gradients, albeit with unquantified contamination from shocked regions. We conclude that overlooked assumptions about the internal temperature structure of HII regions in the direct method can lead to large discrepancies in metallicity gradient studies. Our detailed analysis of SAMI609396B underlines that high-accuracy metallicity gradient measurements require a wide array of emission lines and improved spatial resolutions in order to properly constrain excitation sources, physical conditions, and temperature structures of the emitting gas. Integral-field spectroscopic studies with future facilities such as JWST/NIRSpec and ground-based ELTs will be crucial in minimising systematic effects on measured gradients in distant galaxies.","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89893722","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-01DOI: 10.1051/0004-6361/202039395
Phillip A. B. Galli, Hervé Bouy, J. Olivares, N. Miret-Roig, L. Sarro, D. Barrado, A. Berihuete, Emmanuel Bertin, Jean-Charles Cuillandre
Context: Chamaeleon is the southernmost low-mass star-forming complex within 200 pc from the Sun. Its stellar population has been extensively studied in the past, but the current census of the stellar content is not complete yet and deserves further investigation. Aims: We take advantage of the second data release of the textit{Gaia} space mission to expand the census of stars in Chamaeleon and to revisit the properties of the stellar populations associated to the Chamaeleon I (Cha I) and Chamaeleon II (Cha II) dark clouds. Methods: We perform a membership analysis of the sources in the textit{Gaia} catalogue over a field of 100 deg$^{2}$ encompassing the Chamaeleon clouds, and use this new census of cluster members to investigate the 6D structure of the complex. Results: We identify 188 and 41 high-probability members of the stellar populations in Cha I and Cha II, respectively, including 19 and 7 new members. Our sample covers the magnitude range from $G=6$ to $G=20$ mag in Cha I, and from $G=12$ to $G=18$ mag in Cha II. We confirm that the northern and southern subgroups of Cha I are located at different distances ($191.4^{+0.8}_{-0.8}$ pc and $186.7^{+1.0}_{-1.0}$ pc), but they exhibit the same space motion within the reported uncertainties. Cha II is located at a distance of $197.5^{+1.0}_{-0.9}$ pc and exhibits a space motion that is consistent with Cha I within the admittedly large uncertainties on the spatial velocities of the stars that come from radial velocity data. The median age of the stars derived from the Hertzsprung-Russell diagram (HRD) and stellar models is about 1-2 Myr, suggesting that they are somewhat younger than previously thought. We do not detect significant age differences between the Chamaeleon subgroups, but we show that Cha II exhibits a higher fraction of disc-bearing stars compared to Cha I.
{"title":"Chamaeleon DANCe","authors":"Phillip A. B. Galli, Hervé Bouy, J. Olivares, N. Miret-Roig, L. Sarro, D. Barrado, A. Berihuete, Emmanuel Bertin, Jean-Charles Cuillandre","doi":"10.1051/0004-6361/202039395","DOIUrl":"https://doi.org/10.1051/0004-6361/202039395","url":null,"abstract":"Context: Chamaeleon is the southernmost low-mass star-forming complex within 200 pc from the Sun. Its stellar population has been extensively studied in the past, but the current census of the stellar content is not complete yet and deserves further investigation. \u0000Aims: We take advantage of the second data release of the textit{Gaia} space mission to expand the census of stars in Chamaeleon and to revisit the properties of the stellar populations associated to the Chamaeleon I (Cha I) and Chamaeleon II (Cha II) dark clouds. \u0000Methods: We perform a membership analysis of the sources in the textit{Gaia} catalogue over a field of 100 deg$^{2}$ encompassing the Chamaeleon clouds, and use this new census of cluster members to investigate the 6D structure of the complex. \u0000Results: We identify 188 and 41 high-probability members of the stellar populations in Cha I and Cha II, respectively, including 19 and 7 new members. Our sample covers the magnitude range from $G=6$ to $G=20$ mag in Cha I, and from $G=12$ to $G=18$ mag in Cha II. We confirm that the northern and southern subgroups of Cha I are located at different distances ($191.4^{+0.8}_{-0.8}$ pc and $186.7^{+1.0}_{-1.0}$ pc), but they exhibit the same space motion within the reported uncertainties. Cha II is located at a distance of $197.5^{+1.0}_{-0.9}$ pc and exhibits a space motion that is consistent with Cha I within the admittedly large uncertainties on the spatial velocities of the stars that come from radial velocity data. The median age of the stars derived from the Hertzsprung-Russell diagram (HRD) and stellar models is about 1-2 Myr, suggesting that they are somewhat younger than previously thought. We do not detect significant age differences between the Chamaeleon subgroups, but we show that Cha II exhibits a higher fraction of disc-bearing stars compared to Cha I.","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88791183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Ballone, S. Torniamenti, M. Mapelli, Ugo N Di Carlo, M. Spera, S. Rastello, N. Gaspari, G. Iorio
We present a new method to obtain more realistic initial conditions for N-body simulations of young star clusters. We start from the outputs of hydrodynamical simulations of molecular cloud collapse, in which star formation is modelled with sink particles. In our approach, we instantaneously remove gas from these hydrodynamical simulation outputs to mock the end of the gas-embedded phase, induced by stellar feedback. We then enforce a realistic initial mass function by splitting or joining the sink particles based on their mass and position. Such initial conditions contain more consistent information on the spatial distribution and the kinematical and dynamical states of young star clusters, which are fundamental to properly study these systems. For example, by applying our method to a set of previously run hydrodynamical simulations, we found that the early evolution of young star clusters is affected by gas removal and by the early dry merging of sub-structures. This early evolution can either quickly erase the rotation acquired by our (sub-)clusters in their embedded phase or "fuel" it by feeding of angular momentum by sub-structure mergers, before two-body relaxation acts on longer timescales.
{"title":"From hydrodynamics to N-body simulations of star clusters: mergers and rotation","authors":"A. Ballone, S. Torniamenti, M. Mapelli, Ugo N Di Carlo, M. Spera, S. Rastello, N. Gaspari, G. Iorio","doi":"10.1093/mnras/staa3763","DOIUrl":"https://doi.org/10.1093/mnras/staa3763","url":null,"abstract":"We present a new method to obtain more realistic initial conditions for N-body simulations of young star clusters. We start from the outputs of hydrodynamical simulations of molecular cloud collapse, in which star formation is modelled with sink particles. In our approach, we instantaneously remove gas from these hydrodynamical simulation outputs to mock the end of the gas-embedded phase, induced by stellar feedback. We then enforce a realistic initial mass function by splitting or joining the sink particles based on their mass and position. Such initial conditions contain more consistent information on the spatial distribution and the kinematical and dynamical states of young star clusters, which are fundamental to properly study these systems. For example, by applying our method to a set of previously run hydrodynamical simulations, we found that the early evolution of young star clusters is affected by gas removal and by the early dry merging of sub-structures. This early evolution can either quickly erase the rotation acquired by our (sub-)clusters in their embedded phase or \"fuel\" it by feeding of angular momentum by sub-structure mergers, before two-body relaxation acts on longer timescales.","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84207974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Secular evolution of binaries driven by an external (tidal) potential is a classic astrophysical problem. Tidal perturbations can arise due to an external point mass, as in the Lidov-Kozai (LK) theory of hierarchical triples, or due to an extended stellar system (e.g. galaxy or globular cluster) in which the binary resides. For many applications, general-relativistic (GR) apsidal precession is important, and has been accounted for in some LK calculations. Here we generalise and extend these studies by exploring in detail the effect of GR precession on (quadrupole-level) tidal evolution of binaries orbiting in arbitrary axisymmetric potentials (which includes LK theory as a special case). We study the (doubly-averaged) orbital dynamics for arbitrary strengths of GR and binary initial conditions and uncover entirely new phase space morphologies with important implications for the binary orbital evolution. We also explore how GR precession affects secular evolution of binary orbital elements when the binary reaches high eccentricity ($eto 1$) and delineate several different dynamical regimes. Our results are applicable to a variety of astrophysical systems. In particular, they can be used to understand the high-eccentricity behaviour of (cluster) tide-driven compact object mergers -- i.e. LIGO/Virgo gravitational wave sources -- for which GR effects are crucial.
{"title":"Secular dynamics of binaries in stellar clusters – III. Doubly averaged dynamics in the presence of general-relativistic precession","authors":"C. Hamilton, R. Rafikov","doi":"10.1093/mnras/stab1284","DOIUrl":"https://doi.org/10.1093/mnras/stab1284","url":null,"abstract":"Secular evolution of binaries driven by an external (tidal) potential is a classic astrophysical problem. Tidal perturbations can arise due to an external point mass, as in the Lidov-Kozai (LK) theory of hierarchical triples, or due to an extended stellar system (e.g. galaxy or globular cluster) in which the binary resides. For many applications, general-relativistic (GR) apsidal precession is important, and has been accounted for in some LK calculations. Here we generalise and extend these studies by exploring in detail the effect of GR precession on (quadrupole-level) tidal evolution of binaries orbiting in arbitrary axisymmetric potentials (which includes LK theory as a special case). We study the (doubly-averaged) orbital dynamics for arbitrary strengths of GR and binary initial conditions and uncover entirely new phase space morphologies with important implications for the binary orbital evolution. We also explore how GR precession affects secular evolution of binary orbital elements when the binary reaches high eccentricity ($eto 1$) and delineate several different dynamical regimes. Our results are applicable to a variety of astrophysical systems. In particular, they can be used to understand the high-eccentricity behaviour of (cluster) tide-driven compact object mergers -- i.e. LIGO/Virgo gravitational wave sources -- for which GR effects are crucial.","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82197484","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Stephanie O’Neil, D. Barnes, M. Vogelsberger, B. Diemer
The splashback radius, $R_{rm sp}$, is a physically motivated halo boundary that separates infalling and collapsed matter of haloes. We study $R_{rm sp}$ in the hydrodynamic and dark matter only IllustrisTNG simulations. The most commonly adopted signature of $R_{rm sp}$ is the radius at which the radial density profiles are steepest. Therefore, we explicitly optimise our density profile fit to the profile slope and find that this leads to a $sim5%$ larger radius compared to other optimisations. We calculate $R_{rm sp}$ for haloes with masses between $10^{13-15}{rm M}_{odot}$ as a function of halo mass, accretion rate and redshift. $R_{rm sp}$ decreases with mass and with redshift for haloes of similar $M_{rm200m}$ in agreement with previous work. We also find that $R_{rm sp}/R_{rm200m}$ decreases with halo accretion rate. We apply our analysis to dark matter, gas and satellite galaxies associated with haloes to investigate the observational potential of $R_{rm sp}$. The radius of steepest slope in gas profiles is consistently smaller than the value calculated from dark matter profiles. The steepest slope in galaxy profiles, which are often used in observations, tends to agree with dark matter profiles but is lower for less massive haloes. We compare $R_{rm sp}$ in hydrodynamic and N-body dark matter only simulations and do not find a significant difference caused by the addition of baryonic physics. Thus, results from dark matter only simulations should be applicable to realistic haloes.
{"title":"The splashback boundary of haloes in hydrodynamic simulations","authors":"Stephanie O’Neil, D. Barnes, M. Vogelsberger, B. Diemer","doi":"10.1093/mnras/stab1221","DOIUrl":"https://doi.org/10.1093/mnras/stab1221","url":null,"abstract":"The splashback radius, $R_{rm sp}$, is a physically motivated halo boundary that separates infalling and collapsed matter of haloes. We study $R_{rm sp}$ in the hydrodynamic and dark matter only IllustrisTNG simulations. The most commonly adopted signature of $R_{rm sp}$ is the radius at which the radial density profiles are steepest. Therefore, we explicitly optimise our density profile fit to the profile slope and find that this leads to a $sim5%$ larger radius compared to other optimisations. We calculate $R_{rm sp}$ for haloes with masses between $10^{13-15}{rm M}_{odot}$ as a function of halo mass, accretion rate and redshift. $R_{rm sp}$ decreases with mass and with redshift for haloes of similar $M_{rm200m}$ in agreement with previous work. We also find that $R_{rm sp}/R_{rm200m}$ decreases with halo accretion rate. We apply our analysis to dark matter, gas and satellite galaxies associated with haloes to investigate the observational potential of $R_{rm sp}$. The radius of steepest slope in gas profiles is consistently smaller than the value calculated from dark matter profiles. The steepest slope in galaxy profiles, which are often used in observations, tends to agree with dark matter profiles but is lower for less massive haloes. We compare $R_{rm sp}$ in hydrodynamic and N-body dark matter only simulations and do not find a significant difference caused by the addition of baryonic physics. Thus, results from dark matter only simulations should be applicable to realistic haloes.","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76104575","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Hayden, Sanjib Sharma, J. Bland-Hawthorn, L. Spina, S. Buder, M. Asplund, A. Casey, G. D. Silva, V. D’Orazi, K. Freeman, J. Kos, G. Lewis, Jane Lin, K. Lind, S. Martell, K. Schlesinger, J. Simpson, D. Zucker, T. Zwitter, Boquan Chen, K. Čotar, D. Feuillet, J. Horner, M. Joyce, T. Nordlander, D. Stello, T. Tepper-García, Y. Ting, Purmortal Wang, R. Wittenmyer
Previous studies have found that the elemental abundances of a star correlate directly with its age and metallicity. Using this knowledge, we derive ages for a sample of 250,000 stars taken from GALAH DR3 using only their overall metallicity and chemical abundances. Stellar ages are estimated via the machine learning algorithm $XGBoost$, using main sequence turnoff stars with precise ages as our input training set. We find that the stellar ages for the bulk of the GALAH DR3 sample are accurate to 1-2 Gyr using this method. With these ages, we replicate many recent results on the age-kinematic trends of the nearby disk, including the age-velocity dispersion relationship of the solar neighborhood and the larger global velocity dispersion relations of the disk found using $Gaia$ and GALAH. The fact that chemical abundances alone can be used to determine a reliable age for a star have profound implications for the future study of the Galaxy as well as upcoming spectroscopic surveys. These results show that the chemical abundance variation at a given birth radius is quite small, and imply that strong chemical tagging of stars directly to birth clusters may prove difficult with our current elemental abundance precision. Our results highlight the need of spectroscopic surveys to deliver precision abundances for as many nucleosynthetic production sites as possible in order to estimate reliable ages for stars directly from their chemical abundances. Applying the methods outlined in this paper opens a new door into studies of the kinematic structure and evolution of the disk, as ages may potentially be estimated for a large fraction of stars in existing spectroscopic surveys. This would yield a sample of millions of stars with reliable age determinations, and allow precise constraints to be put on various kinematic processes in the disk, such as the efficiency and timescales of radial migration.
{"title":"The GALAH Survey: Chemical Clocks.","authors":"M. Hayden, Sanjib Sharma, J. Bland-Hawthorn, L. Spina, S. Buder, M. Asplund, A. Casey, G. D. Silva, V. D’Orazi, K. Freeman, J. Kos, G. Lewis, Jane Lin, K. Lind, S. Martell, K. Schlesinger, J. Simpson, D. Zucker, T. Zwitter, Boquan Chen, K. Čotar, D. Feuillet, J. Horner, M. Joyce, T. Nordlander, D. Stello, T. Tepper-García, Y. Ting, Purmortal Wang, R. Wittenmyer","doi":"10.1093/mnras/stac2787","DOIUrl":"https://doi.org/10.1093/mnras/stac2787","url":null,"abstract":"Previous studies have found that the elemental abundances of a star correlate directly with its age and metallicity. Using this knowledge, we derive ages for a sample of 250,000 stars taken from GALAH DR3 using only their overall metallicity and chemical abundances. Stellar ages are estimated via the machine learning algorithm $XGBoost$, using main sequence turnoff stars with precise ages as our input training set. We find that the stellar ages for the bulk of the GALAH DR3 sample are accurate to 1-2 Gyr using this method. With these ages, we replicate many recent results on the age-kinematic trends of the nearby disk, including the age-velocity dispersion relationship of the solar neighborhood and the larger global velocity dispersion relations of the disk found using $Gaia$ and GALAH. The fact that chemical abundances alone can be used to determine a reliable age for a star have profound implications for the future study of the Galaxy as well as upcoming spectroscopic surveys. These results show that the chemical abundance variation at a given birth radius is quite small, and imply that strong chemical tagging of stars directly to birth clusters may prove difficult with our current elemental abundance precision. Our results highlight the need of spectroscopic surveys to deliver precision abundances for as many nucleosynthetic production sites as possible in order to estimate reliable ages for stars directly from their chemical abundances. Applying the methods outlined in this paper opens a new door into studies of the kinematic structure and evolution of the disk, as ages may potentially be estimated for a large fraction of stars in existing spectroscopic surveys. This would yield a sample of millions of stars with reliable age determinations, and allow precise constraints to be put on various kinematic processes in the disk, such as the efficiency and timescales of radial migration.","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84399580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Furtak, H. Atek, M. Lehnert, J. Chevallard, S. Charlot
We present new measurements of the very low-mass end of the galaxy stellar mass function (GSMF) at $zsim6-7$ computed from a rest-frame ultraviolet selected sample of dropout galaxies. These galaxies lie behind the six Hubble Frontier Fields clusters and are all gravitationally magnified. Using deep Spitzer/IRAC and Hubble Space Telescope imaging, we derive stellar masses by fitting galaxy spectral energy distributions and explore the impact of different model assumptions and parameter degeneracies on the resulting GSMF. Our sample probes stellar masses down to $M_{star}>10^{6},text{M}_{odot}$ and we find the $zsim6-7$ GSMF to be best parametrized by a modified Schechter function which allows for a turnover at very low masses. Using a Monte-Carlo Markov Chain analysis of the GSMF, including accurate treatment of lensing uncertainties, we obtain a relatively steep low-mass end slope $alphasimeq-1.96_{-0.08}^{+0.09}$ and a turnover at $log(M_T/text{M}_{odot})simeq7.10_{-0.56}^{+0.17}$ with a curvature of $betasimeq1.00_{-0.73}^{+0.87}$ for our minimum assumption model with constant star-formation history (SFH) and low dust attenuation, $A_Vleq0.2$. We find that the $zsim6-7$ GSMF, in particular its very low-mass end, is significantly affected by the assumed functional form of the star formation history and the degeneracy between stellar mass and dust attenuation. For example, the low-mass end slope ranges from $alphasimeq-1.82_{-0.07}^{+0.08}$ for an exponentially rising SFH to $alphasimeq-2.34_{-0.10}^{+0.11}$ when allowing $A_V$ of up to 3.25. Future observations at longer wavelengths and higher angular resolution with the James Webb Space Telescope are required to break these degeneracies and to robustly constrain the stellar mass of galaxies on the extreme low-mass end of the GSMF.
{"title":"How robustly can we constrain the low-mass end of the z ∼ 6−7 stellar mass function? The limits of lensing models and stellar population assumptions in the Hubble Frontier Fields","authors":"L. Furtak, H. Atek, M. Lehnert, J. Chevallard, S. Charlot","doi":"10.1093/mnras/staa3760","DOIUrl":"https://doi.org/10.1093/mnras/staa3760","url":null,"abstract":"We present new measurements of the very low-mass end of the galaxy stellar mass function (GSMF) at $zsim6-7$ computed from a rest-frame ultraviolet selected sample of dropout galaxies. These galaxies lie behind the six Hubble Frontier Fields clusters and are all gravitationally magnified. Using deep Spitzer/IRAC and Hubble Space Telescope imaging, we derive stellar masses by fitting galaxy spectral energy distributions and explore the impact of different model assumptions and parameter degeneracies on the resulting GSMF. Our sample probes stellar masses down to $M_{star}>10^{6},text{M}_{odot}$ and we find the $zsim6-7$ GSMF to be best parametrized by a modified Schechter function which allows for a turnover at very low masses. Using a Monte-Carlo Markov Chain analysis of the GSMF, including accurate treatment of lensing uncertainties, we obtain a relatively steep low-mass end slope $alphasimeq-1.96_{-0.08}^{+0.09}$ and a turnover at $log(M_T/text{M}_{odot})simeq7.10_{-0.56}^{+0.17}$ with a curvature of $betasimeq1.00_{-0.73}^{+0.87}$ for our minimum assumption model with constant star-formation history (SFH) and low dust attenuation, $A_Vleq0.2$. We find that the $zsim6-7$ GSMF, in particular its very low-mass end, is significantly affected by the assumed functional form of the star formation history and the degeneracy between stellar mass and dust attenuation. For example, the low-mass end slope ranges from $alphasimeq-1.82_{-0.07}^{+0.08}$ for an exponentially rising SFH to $alphasimeq-2.34_{-0.10}^{+0.11}$ when allowing $A_V$ of up to 3.25. Future observations at longer wavelengths and higher angular resolution with the James Webb Space Telescope are required to break these degeneracies and to robustly constrain the stellar mass of galaxies on the extreme low-mass end of the GSMF.","PeriodicalId":8452,"journal":{"name":"arXiv: Astrophysics of Galaxies","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85546290","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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