Pub Date : 2025-01-16DOI: 10.3847/1538-4357/ada02f
Megan R. Sturm, Bayli Hayes and Amy E. Reines
Effectively finding and identifying active galactic nuclei (AGNs) in dwarf galaxies is an important step in studying black hole formation and evolution. In this work, we examine four mid-infrared (IR)-selected AGN candidates in dwarf galaxies with stellar masses between M⋆ ~ 108 and 109 M⊙ and find that the galaxies are host to nuclear star clusters (NSCs) that are notably rare in how young and massive they are. We perform photometric measurements on the central star clusters in our target galaxies using Hubble Space Telescope optical and near-IR imaging and compare their observed properties to models of stellar population evolution. We find that these galaxies are host to very massive (~107 M⊙), extremely young (≲8 Myr), and dusty (0.6 ≲ Av ≲ 1.8) NSCs. Our results indicate that these galactic nuclei have ongoing star formation, are still at least partially obscured by clouds of gas and dust, and are most likely producing the extremely red AGN-like mid-IR colors. Moreover, prior work has shown that these galaxies do not exhibit X-ray or optical AGN signatures. Therefore, we recommend caution when using mid-IR color–color diagnostics for AGN selection in dwarf galaxies, since, as directly exemplified in this sample, they can be contaminated by massive star clusters with ongoing star formation.
{"title":"Star-forming Nuclear Clusters in Dwarf Galaxies Mimicking Active Galactic Nucleus Signatures in the Mid-infrared","authors":"Megan R. Sturm, Bayli Hayes and Amy E. Reines","doi":"10.3847/1538-4357/ada02f","DOIUrl":"https://doi.org/10.3847/1538-4357/ada02f","url":null,"abstract":"Effectively finding and identifying active galactic nuclei (AGNs) in dwarf galaxies is an important step in studying black hole formation and evolution. In this work, we examine four mid-infrared (IR)-selected AGN candidates in dwarf galaxies with stellar masses between M⋆ ~ 108 and 109 M⊙ and find that the galaxies are host to nuclear star clusters (NSCs) that are notably rare in how young and massive they are. We perform photometric measurements on the central star clusters in our target galaxies using Hubble Space Telescope optical and near-IR imaging and compare their observed properties to models of stellar population evolution. We find that these galaxies are host to very massive (~107 M⊙), extremely young (≲8 Myr), and dusty (0.6 ≲ Av ≲ 1.8) NSCs. Our results indicate that these galactic nuclei have ongoing star formation, are still at least partially obscured by clouds of gas and dust, and are most likely producing the extremely red AGN-like mid-IR colors. Moreover, prior work has shown that these galaxies do not exhibit X-ray or optical AGN signatures. Therefore, we recommend caution when using mid-IR color–color diagnostics for AGN selection in dwarf galaxies, since, as directly exemplified in this sample, they can be contaminated by massive star clusters with ongoing star formation.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"37 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142986104","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 : 2025-01-16DOI: 10.3847/1538-4357/ad9b0b
Chang Liu, 畅 刘, Ricardo Yarza and Enrico Ramirez-Ruiz
Stars grazing supermassive black holes on bound orbits may produce periodic flares over many passages, known as repeating partial tidal disruption events (TDEs). Here, we present 3D hydrodynamic simulations of Sun-like stars over multiple tidal encounters. The star is significantly restructured and becomes less concentrated as a result of mass loss and tidal heating. The vulnerability to mass loss depends sensitively on the stellar density structure, and the strong correlation between the fractional mass loss ΔM/M* and the ratio of the central and average density , which was initially derived in disruption simulations of main-sequence stars, also applies for stars strongly reshaped by tides. Over multiple orbits, the star loses progressively more mass in each encounter and is doomed to a complete disruption. Throughout its lifetime, the star may produce numerous weak flares (depending on the initial impact parameter), followed by a couple of luminous flares whose brightness increases exponentially. Flux-limited surveys are heavily biased toward the brightest flares, which may appear similar to the flare produced by the same star undergoing a full disruption on its first tidal encounter. This places new challenges on constraining the intrinsic TDE rates, which need to take repeating TDEs into account. Other types of stars with different initial density structures (e.g., evolved stars with massive cores) follow distinct evolution tracks, which might explain the diversity of the long-term luminosity evolution seen in recently uncovered repeaters.
{"title":"Repeating Partial Tidal Encounters of Sun-like Stars Leading to Their Complete Disruption","authors":"Chang Liu, 畅 刘, Ricardo Yarza and Enrico Ramirez-Ruiz","doi":"10.3847/1538-4357/ad9b0b","DOIUrl":"https://doi.org/10.3847/1538-4357/ad9b0b","url":null,"abstract":"Stars grazing supermassive black holes on bound orbits may produce periodic flares over many passages, known as repeating partial tidal disruption events (TDEs). Here, we present 3D hydrodynamic simulations of Sun-like stars over multiple tidal encounters. The star is significantly restructured and becomes less concentrated as a result of mass loss and tidal heating. The vulnerability to mass loss depends sensitively on the stellar density structure, and the strong correlation between the fractional mass loss ΔM/M* and the ratio of the central and average density , which was initially derived in disruption simulations of main-sequence stars, also applies for stars strongly reshaped by tides. Over multiple orbits, the star loses progressively more mass in each encounter and is doomed to a complete disruption. Throughout its lifetime, the star may produce numerous weak flares (depending on the initial impact parameter), followed by a couple of luminous flares whose brightness increases exponentially. Flux-limited surveys are heavily biased toward the brightest flares, which may appear similar to the flare produced by the same star undergoing a full disruption on its first tidal encounter. This places new challenges on constraining the intrinsic TDE rates, which need to take repeating TDEs into account. Other types of stars with different initial density structures (e.g., evolved stars with massive cores) follow distinct evolution tracks, which might explain the diversity of the long-term luminosity evolution seen in recently uncovered repeaters.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"93 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142986100","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 : 2025-01-16DOI: 10.3847/1538-4357/ad9b12
Divjyot Singh, Omar French, Fan Guo and Xiaocan Li
Relativistic magnetic turbulence has been proposed as a process for producing nonthermal particles in high-energy astrophysics. The particle energization may be contributed by both magnetic reconnection and turbulent fluctuations, but their interplay is poorly understood. It has been suggested that during magnetic reconnection the parallel electric field dominates the particle acceleration up to the lower bound of the power-law particle spectrum, but recent studies show that electric fields perpendicular to the magnetic field can play an important, if not dominant role. In this study, we carry out two-dimensional fully kinetic particle-in-cell simulations of magnetically dominated decaying turbulence in a relativistic pair plasma. For a fixed magnetization parameter σ0 = 20, we find that the injection energy εinj converges with increasing domain size to εinj ≃ 10 mec2. In contrast, the power-law index, the cut-off energy, and the power-law extent increase steadily with domain size. We trace a large number of particles and evaluate the contributions of the work done by the parallel (W∥) and perpendicular (W⊥) electric fields during both the injection phase and the postinjection phase. We find that during the injection phase, the W⊥ contribution increases with domain size, suggesting that it may eventually dominate injection for a sufficiently large domain. In contrast, on average, both components contribute equally during the postinjection phase, insensitive to the domain size. For high energy (ε ≫ εinj) particles, W⊥ dominates the subsequent energization. These findings may improve our understanding of nonthermal particles and their emissions in astrophysical plasmas.
{"title":"Low-energy Injection and Nonthermal Particle Acceleration in Relativistic Magnetic Turbulence","authors":"Divjyot Singh, Omar French, Fan Guo and Xiaocan Li","doi":"10.3847/1538-4357/ad9b12","DOIUrl":"https://doi.org/10.3847/1538-4357/ad9b12","url":null,"abstract":"Relativistic magnetic turbulence has been proposed as a process for producing nonthermal particles in high-energy astrophysics. The particle energization may be contributed by both magnetic reconnection and turbulent fluctuations, but their interplay is poorly understood. It has been suggested that during magnetic reconnection the parallel electric field dominates the particle acceleration up to the lower bound of the power-law particle spectrum, but recent studies show that electric fields perpendicular to the magnetic field can play an important, if not dominant role. In this study, we carry out two-dimensional fully kinetic particle-in-cell simulations of magnetically dominated decaying turbulence in a relativistic pair plasma. For a fixed magnetization parameter σ0 = 20, we find that the injection energy εinj converges with increasing domain size to εinj ≃ 10 mec2. In contrast, the power-law index, the cut-off energy, and the power-law extent increase steadily with domain size. We trace a large number of particles and evaluate the contributions of the work done by the parallel (W∥) and perpendicular (W⊥) electric fields during both the injection phase and the postinjection phase. We find that during the injection phase, the W⊥ contribution increases with domain size, suggesting that it may eventually dominate injection for a sufficiently large domain. In contrast, on average, both components contribute equally during the postinjection phase, insensitive to the domain size. For high energy (ε ≫ εinj) particles, W⊥ dominates the subsequent energization. These findings may improve our understanding of nonthermal particles and their emissions in astrophysical plasmas.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142986101","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 : 2025-01-16DOI: 10.3847/1538-4357/ad98f2
J. A. le Roux and R. K. Shikha
A theory for steady-state tempered superdiffusive shock acceleration of energetic particles at a plane perpendicular shock is presented that involves solving analytically a tempered fractional Parker transport equation for perpendicular transport in quasi-2D turbulence. The main predictions of the theory are as follows: (i) Tempered perpendicular superdiffusion (tempered Lévy flights) upstream reduces the effectiveness of classical perpendicular superdiffusion (standard Lévy flights) through a transition toward normal perpendicular diffusion when the particle transport distance upstream surpasses a critical spatial scale. Consequently, the accelerated particle distribution upstream decays spatially as a stretched exponential close to the shock that becomes a power law farther upstream under some conditions (superdiffusion), followed by an exponential rollover (transition to normal diffusion); (ii) Downstream, the accelerated particle distribution for tempered superdiffusion converges to a uniform distribution closer to the shock because of a stronger decay close to the shock compared to classical superdiffusion, and a shift of the peak in the distribution at the shock to just downstream of the shock occurs under some conditions; (iii) The accelerated power-law momentum spectrum at the shock is modulated upstream by the incoming solar wind flow to be a hardened power law instead of featuring an exponential rollover at lower particle momenta as for classical diffusive shock acceleration; and (iv) Tempered superdiffusive shock acceleration tends to be more efficient compared to standard superdiffusive shock acceleration.
{"title":"Tempered Superdiffusive Shock Acceleration at a Perpendicular Shock","authors":"J. A. le Roux and R. K. Shikha","doi":"10.3847/1538-4357/ad98f2","DOIUrl":"https://doi.org/10.3847/1538-4357/ad98f2","url":null,"abstract":"A theory for steady-state tempered superdiffusive shock acceleration of energetic particles at a plane perpendicular shock is presented that involves solving analytically a tempered fractional Parker transport equation for perpendicular transport in quasi-2D turbulence. The main predictions of the theory are as follows: (i) Tempered perpendicular superdiffusion (tempered Lévy flights) upstream reduces the effectiveness of classical perpendicular superdiffusion (standard Lévy flights) through a transition toward normal perpendicular diffusion when the particle transport distance upstream surpasses a critical spatial scale. Consequently, the accelerated particle distribution upstream decays spatially as a stretched exponential close to the shock that becomes a power law farther upstream under some conditions (superdiffusion), followed by an exponential rollover (transition to normal diffusion); (ii) Downstream, the accelerated particle distribution for tempered superdiffusion converges to a uniform distribution closer to the shock because of a stronger decay close to the shock compared to classical superdiffusion, and a shift of the peak in the distribution at the shock to just downstream of the shock occurs under some conditions; (iii) The accelerated power-law momentum spectrum at the shock is modulated upstream by the incoming solar wind flow to be a hardened power law instead of featuring an exponential rollover at lower particle momenta as for classical diffusive shock acceleration; and (iv) Tempered superdiffusive shock acceleration tends to be more efficient compared to standard superdiffusive shock acceleration.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"31 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142986097","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 : 2025-01-16DOI: 10.3847/1538-4357/ad7e2b
Zhuo Chen, Benjamin Williams, Dustin Lang, Andrew Dolphin, Meredith Durbin, Julianne J. Dalcanton, Adam Smercina, Léo Girardi, Claire E. Murray, Eric F. Bell, Martha L. Boyer, Richard D’Souza, Karoline Gilbert, Karl Gordon, Puragra Guhathakurta, Francois Hammer, L. Clifton Johnson, Tod R. Lauer, Margaret Lazzarini, Jeremiah W. Murphy, Ekta Patel, Amanda Quirk, Mariangelly Díaz Rodríguez, Julia Christine Roman-Duval, Robyn E. Sanderson, Anil Seth, Tobin M. Wainer and Daniel R. Weisz
The Panchromatic Hubble Andromeda Southern Treasury (PHAST) is a large 195-orbit Hubble Space Telescope program imaging ∼0.45 deg2 of the southern half of M31's star-forming disk at optical and near-ultraviolet (NUV) wavelengths. The PHAST survey area extends the northern coverage of the Panchromatic Hubble Andromeda Treasury (PHAT) down to the southern half of M31, covering out to a radius of ∼13 kpc along the southern major axis and in total ∼two-thirds of M31's star-forming disk. This new legacy imaging yields stellar photometry of over 90 million resolved stars using the Advanced Camera for Surveys in the optical (F475W and F814W), and the Wide Field Camera 3 (WFC3) in the NUV (F275W and F336W). The photometry is derived using all overlapping exposures across all bands, and achieves a 50% completeness-limited depth of F475W ∼ 27.7 in the lowest surface density regions of the outer disk and F475W ∼ 26.0 in the most crowded, high surface brightness regions near M31's bulge. We provide extensive analysis of the data quality, including artificial star tests to quantify completeness, photometric uncertainties, and flux biases, all of which vary due to the background source density and the number of overlapping exposures. We also present seamless population maps of the entire M31 disk, which show relatively well-mixed distributions for stellar populations older than 1–2 Gyr, and highly structured distributions for younger populations. The combined PHAST + PHAT photometry catalog of ∼0.2 billion stars is the largest ever produced for equidistant sources and is available for public download by the community.
{"title":"PHAST. The Panchromatic Hubble Andromeda Southern Treasury. I. Ultraviolet and Optical Photometry of over 90 Million Stars in M31","authors":"Zhuo Chen, Benjamin Williams, Dustin Lang, Andrew Dolphin, Meredith Durbin, Julianne J. Dalcanton, Adam Smercina, Léo Girardi, Claire E. Murray, Eric F. Bell, Martha L. Boyer, Richard D’Souza, Karoline Gilbert, Karl Gordon, Puragra Guhathakurta, Francois Hammer, L. Clifton Johnson, Tod R. Lauer, Margaret Lazzarini, Jeremiah W. Murphy, Ekta Patel, Amanda Quirk, Mariangelly Díaz Rodríguez, Julia Christine Roman-Duval, Robyn E. Sanderson, Anil Seth, Tobin M. Wainer and Daniel R. Weisz","doi":"10.3847/1538-4357/ad7e2b","DOIUrl":"https://doi.org/10.3847/1538-4357/ad7e2b","url":null,"abstract":"The Panchromatic Hubble Andromeda Southern Treasury (PHAST) is a large 195-orbit Hubble Space Telescope program imaging ∼0.45 deg2 of the southern half of M31's star-forming disk at optical and near-ultraviolet (NUV) wavelengths. The PHAST survey area extends the northern coverage of the Panchromatic Hubble Andromeda Treasury (PHAT) down to the southern half of M31, covering out to a radius of ∼13 kpc along the southern major axis and in total ∼two-thirds of M31's star-forming disk. This new legacy imaging yields stellar photometry of over 90 million resolved stars using the Advanced Camera for Surveys in the optical (F475W and F814W), and the Wide Field Camera 3 (WFC3) in the NUV (F275W and F336W). The photometry is derived using all overlapping exposures across all bands, and achieves a 50% completeness-limited depth of F475W ∼ 27.7 in the lowest surface density regions of the outer disk and F475W ∼ 26.0 in the most crowded, high surface brightness regions near M31's bulge. We provide extensive analysis of the data quality, including artificial star tests to quantify completeness, photometric uncertainties, and flux biases, all of which vary due to the background source density and the number of overlapping exposures. We also present seamless population maps of the entire M31 disk, which show relatively well-mixed distributions for stellar populations older than 1–2 Gyr, and highly structured distributions for younger populations. The combined PHAST + PHAT photometry catalog of ∼0.2 billion stars is the largest ever produced for equidistant sources and is available for public download by the community.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142987391","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 : 2025-01-15DOI: 10.3847/1538-4357/ad8eb3
Rouven Lemmerz, Mohamad Shalaby, Christoph Pfrommer and Timon Thomas
Cosmic-ray (CR) feedback is critical for galaxy formation as CRs drive galactic winds, regularize star formation in galaxies, and escape from active galactic nuclei to heat the cooling cores of galaxy clusters. The feedback strength of CRs depends on their coupling to the background plasma and, as such, on the effective CR transport speed. Traditionally, this has been hypothesized to depend on the balance between the wave growth of CR-driven instabilities and their damping. Here, we study the physics of CR-driven instabilities from first principles, starting from a gyrotropic distribution of CR ions that stream along a background magnetic field. We develop a theory of the underlying processes that organize the particles’ orbits and in particular their gyrophases, which provides an intuitive physical picture of (i) wave growth as the CR gyrophases start to bunch up lopsidedly toward the local wave magnetic field, (ii) instability saturation as a result of CRs overtaking the wave and damping its amplitude without isotropizing CRs in the wave frame, and (iii) CR backreaction onto the unstable plasma waves as the CR gyrophases follow a pendulum motion around the wave magnetic field. Using our new fluid-particle-in-cell code fluid-SHARP, we validate our theory on the evolution and excitation of individual unstable modes, such as forward- and backward-propagating Alfvén and whistler waves. We show that these kinetic simulations support our theoretical considerations, thus potentially foreshadowing a revision of the theory of CR transport in galaxies and galaxy clusters.
{"title":"The Theory of Resonant Cosmic Ray–driven Instabilities—Growth and Saturation of Single Modes","authors":"Rouven Lemmerz, Mohamad Shalaby, Christoph Pfrommer and Timon Thomas","doi":"10.3847/1538-4357/ad8eb3","DOIUrl":"https://doi.org/10.3847/1538-4357/ad8eb3","url":null,"abstract":"Cosmic-ray (CR) feedback is critical for galaxy formation as CRs drive galactic winds, regularize star formation in galaxies, and escape from active galactic nuclei to heat the cooling cores of galaxy clusters. The feedback strength of CRs depends on their coupling to the background plasma and, as such, on the effective CR transport speed. Traditionally, this has been hypothesized to depend on the balance between the wave growth of CR-driven instabilities and their damping. Here, we study the physics of CR-driven instabilities from first principles, starting from a gyrotropic distribution of CR ions that stream along a background magnetic field. We develop a theory of the underlying processes that organize the particles’ orbits and in particular their gyrophases, which provides an intuitive physical picture of (i) wave growth as the CR gyrophases start to bunch up lopsidedly toward the local wave magnetic field, (ii) instability saturation as a result of CRs overtaking the wave and damping its amplitude without isotropizing CRs in the wave frame, and (iii) CR backreaction onto the unstable plasma waves as the CR gyrophases follow a pendulum motion around the wave magnetic field. Using our new fluid-particle-in-cell code fluid-SHARP, we validate our theory on the evolution and excitation of individual unstable modes, such as forward- and backward-propagating Alfvén and whistler waves. We show that these kinetic simulations support our theoretical considerations, thus potentially foreshadowing a revision of the theory of CR transport in galaxies and galaxy clusters.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"93 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142981235","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 : 2025-01-15DOI: 10.3847/1538-4357/ad9901
Ikechukwu A. Obi, Pius N. Okeke and Bonaventure I. Okere
In this paper, we compute, by means of the recently and thoroughly updated PARSE v1.2 s database of stellar nonrotating evolutionary tracks, the integrated stellar spectra, the ionizing photon budget, and the supernovae rates of young simple stellar populations (SSPs), for five metallicities between 0.0001 and 0.02 and four choices of stellar initial mass function (IMF) upper mass limits between 40 M⊙ and 350 M⊙. Using the photo-ionization code CLOUDY, we compute, at this same range of metallicities and limits, the intensities of some selected recombination and collisionally excited lines as a function of the age of the SSP. We account for the electron temperature dependence on IMF upper mass limit and metallicity while computing the thermal radio emission component, and also accounted for recent advances in core-collapse supernova explosion models while computing the nonthermal radio emission component. We self-consistently add the emission lines, nebular continuum, and nonthermal radio emission to the original SSP integrated photospheric spectra. Finally, from the resulting new suite of SSPs, we provide a consistent set of analytical relations between star formation rate (SFR) and ultraviolet, optical, and thermal radio luminosities that can be used to convert attenuation-corrected and dust-unaffected luminosities to SFR estimates. In a forthcoming paper, we will use our new SSP libraries as input to the state-of-the-art radiative transfer model GRAphites and SILicates to test the overall performance of these SSPs in reproducing the observed spectral energy distribution of young star-forming galaxies.
{"title":"Nebular and Nonthermal Radio Emissions for Young Stellar Populations with PARSEC v1.2s","authors":"Ikechukwu A. Obi, Pius N. Okeke and Bonaventure I. Okere","doi":"10.3847/1538-4357/ad9901","DOIUrl":"https://doi.org/10.3847/1538-4357/ad9901","url":null,"abstract":"In this paper, we compute, by means of the recently and thoroughly updated PARSE v1.2 s database of stellar nonrotating evolutionary tracks, the integrated stellar spectra, the ionizing photon budget, and the supernovae rates of young simple stellar populations (SSPs), for five metallicities between 0.0001 and 0.02 and four choices of stellar initial mass function (IMF) upper mass limits between 40 M⊙ and 350 M⊙. Using the photo-ionization code CLOUDY, we compute, at this same range of metallicities and limits, the intensities of some selected recombination and collisionally excited lines as a function of the age of the SSP. We account for the electron temperature dependence on IMF upper mass limit and metallicity while computing the thermal radio emission component, and also accounted for recent advances in core-collapse supernova explosion models while computing the nonthermal radio emission component. We self-consistently add the emission lines, nebular continuum, and nonthermal radio emission to the original SSP integrated photospheric spectra. Finally, from the resulting new suite of SSPs, we provide a consistent set of analytical relations between star formation rate (SFR) and ultraviolet, optical, and thermal radio luminosities that can be used to convert attenuation-corrected and dust-unaffected luminosities to SFR estimates. In a forthcoming paper, we will use our new SSP libraries as input to the state-of-the-art radiative transfer model GRAphites and SILicates to test the overall performance of these SSPs in reproducing the observed spectral energy distribution of young star-forming galaxies.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142981239","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 : 2025-01-15DOI: 10.3847/1538-4357/ad9b8b
J. Michael Shull, Rachel M. Curran and Michael W. Topping
The B2 star Epsilon Canis Majoris (ϵ CMa), at parallax distance d = 124 ± 2 pc, dominates the H i photoionization of the Local Interstellar Cloud. At its closer parallax distance compared to previous estimates, ϵ CMa has a 0.9 mag fainter absolute magnitude MV = −3.97 ± 0.04. We combine measurements of distance with the integrated flux f = (41.5 ± 3.3) × 10−6 erg cm−2 s−1 and angular diameter θd = 0.80 ± 0.05 mas to produce a consistent set of stellar parameters: radius R = 10.7 ± 0.7 R⊙, mass M = 13.1 ± 2.3 M⊙, gravity , effective temperature Teff ≈ 21,000 K, and luminosity L ≈ 20,000 L⊙. These parameters place ϵ CMa outside the β Cephei instability strip, consistent with its observed lack of pulsations. The observed extreme-ultraviolet spectrum yields a hydrogen photoionization rate ΓHI ≈ 10−15 s−1 (at Earth). The total flux decrement factor at the Lyman limit (ΔLL = 5000 ± 500) is a combination of attenuation in the stellar atmosphere (Δstar = 110 ± 10) and interstellar medium (ΔISM = 45 ± 5) with optical depth τLL = 3.8 ± 0.1. After correcting for interstellar H i column density NHI = (6 ± 1) × 1017cm−2, we find a stellar LyC photon flux ΦLyC ≈ 3000 cm−2 s−1 and ionizing luminosity QLyC = 1045.7±0.3 photons s−1. The photoionization rate ΓH ≈ (1–2) × 10−14 s−1 at the cloud surface produces an ionization fraction (30%–40%) for total hydrogen density nH = 0.2 cm−3. With its 27.3 ± 0.4 km s−1 heliocentric radial velocity and small proper motion, ϵ CMa passed within 9.3 ± 0.5 pc of the Sun 4.4 Myr ago, with a 180 times higher photoionization rate.
{"title":"Epsilon Canis Majoris: The Brightest Extreme-ultraviolet Source with Surprisingly Low Interstellar Absorption","authors":"J. Michael Shull, Rachel M. Curran and Michael W. Topping","doi":"10.3847/1538-4357/ad9b8b","DOIUrl":"https://doi.org/10.3847/1538-4357/ad9b8b","url":null,"abstract":"The B2 star Epsilon Canis Majoris (ϵ CMa), at parallax distance d = 124 ± 2 pc, dominates the H i photoionization of the Local Interstellar Cloud. At its closer parallax distance compared to previous estimates, ϵ CMa has a 0.9 mag fainter absolute magnitude MV = −3.97 ± 0.04. We combine measurements of distance with the integrated flux f = (41.5 ± 3.3) × 10−6 erg cm−2 s−1 and angular diameter θd = 0.80 ± 0.05 mas to produce a consistent set of stellar parameters: radius R = 10.7 ± 0.7 R⊙, mass M = 13.1 ± 2.3 M⊙, gravity , effective temperature Teff ≈ 21,000 K, and luminosity L ≈ 20,000 L⊙. These parameters place ϵ CMa outside the β Cephei instability strip, consistent with its observed lack of pulsations. The observed extreme-ultraviolet spectrum yields a hydrogen photoionization rate ΓHI ≈ 10−15 s−1 (at Earth). The total flux decrement factor at the Lyman limit (ΔLL = 5000 ± 500) is a combination of attenuation in the stellar atmosphere (Δstar = 110 ± 10) and interstellar medium (ΔISM = 45 ± 5) with optical depth τLL = 3.8 ± 0.1. After correcting for interstellar H i column density NHI = (6 ± 1) × 1017cm−2, we find a stellar LyC photon flux ΦLyC ≈ 3000 cm−2 s−1 and ionizing luminosity QLyC = 1045.7±0.3 photons s−1. The photoionization rate ΓH ≈ (1–2) × 10−14 s−1 at the cloud surface produces an ionization fraction (30%–40%) for total hydrogen density nH = 0.2 cm−3. With its 27.3 ± 0.4 km s−1 heliocentric radial velocity and small proper motion, ϵ CMa passed within 9.3 ± 0.5 pc of the Sun 4.4 Myr ago, with a 180 times higher photoionization rate.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"22 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142981285","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 : 2025-01-15DOI: 10.3847/1538-4357/ad9bad
Daichi Tsuna, Xiaoshan Huang, Jim Fuller and Anthony L. Piro
Failed supernovae (SNe), which are likely the main channel for forming stellar-mass black holes, are predicted to accompany mass ejections much weaker than typical core-collapse SNe. We conduct a grid of one-dimensional radiation hydrodynamical simulations to explore the emission of failed SNe from red supergiant progenitors, leveraging recent understanding of the weak explosion and the dense circumstellar matter (CSM) surrounding these stars. We find from these simulations and semianalytical modeling that diffusion in the CSM prolongs the early emission powered by shock breakout/cooling. The early emission has peak luminosities of ~107–108 L⊙ in optical and UV and durations of days to weeks. The presence of dense CSM aids in the detection of the early bright peak from these events via near-future wide-field surveys such as Rubin Observatory, ULTRASAT, and UVEX.
{"title":"Transients by Black Hole Formation from Red Supergiants: Impact of Dense Circumstellar Matter","authors":"Daichi Tsuna, Xiaoshan Huang, Jim Fuller and Anthony L. Piro","doi":"10.3847/1538-4357/ad9bad","DOIUrl":"https://doi.org/10.3847/1538-4357/ad9bad","url":null,"abstract":"Failed supernovae (SNe), which are likely the main channel for forming stellar-mass black holes, are predicted to accompany mass ejections much weaker than typical core-collapse SNe. We conduct a grid of one-dimensional radiation hydrodynamical simulations to explore the emission of failed SNe from red supergiant progenitors, leveraging recent understanding of the weak explosion and the dense circumstellar matter (CSM) surrounding these stars. We find from these simulations and semianalytical modeling that diffusion in the CSM prolongs the early emission powered by shock breakout/cooling. The early emission has peak luminosities of ~107–108 L⊙ in optical and UV and durations of days to weeks. The presence of dense CSM aids in the detection of the early bright peak from these events via near-future wide-field surveys such as Rubin Observatory, ULTRASAT, and UVEX.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"24 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142981286","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 : 2025-01-15DOI: 10.3847/1538-4357/ad98ee
E. P. Lagioia, A. P. Milone, M. V. Legnardi, G. Cordoni, E. Dondoglio, A. Renzini, M. Tailo, T. Ziliotto, M. Carlos, S. Jang, A. F. Marino, A. Mohandasan, J. Qi, G. Rangwal, E. Bortolan and F. Muratore
The pseudo two-color diagram, known as chromosome map (ChM), is a valuable tool for identifying globular clusters (GCs), which consist of single or multiple stellar populations (MPs). Recent surveys of Galactic GCs using ChMs have provided stringent observational constraints on the formation of GCs and their stellar populations. However, these surveys have primarily focused on GCs at moderate distances from the Galactic center and composed of MPs. In this paper, we present the first detailed study of the stellar composition of four GCs in the outer halo of the Milky Way: Arp 2, Ruprecht 106, Terzan 7, and Terzan 8. Our analysis is based on high-precision photometry obtained from images collected with the Hubble Space Telescope in the F275W, F336W, F438W, F606W, and F814W bands. We find that Ruprecht 106 and Terzan 7 are composed solely of a single stellar population, whereas Arp 2 and Terzan 8 host both first- and second-population stars. In these clusters, the second population comprises about half and one-third of the total number of GC stars, respectively. The results from this paper and the literature suggest that the threshold in the initial GC mass, if present, should be smaller than approximately 105M⊙. The first-population stars of Arp 2 and Terzan 8, along with the stars of the simple-population GCs Ruprecht 106 and Terzan 7, exhibit intrinsic F275W – F814W color spreads, likely indicative of [Fe/H] variations of approximately 0.05–0.30 dex. This suggests that star-to-star metallicity variations are a common feature of star clusters, regardless of the presence of MPs.
{"title":"Exploring Simple-population and Multiple-population Globular Clusters in the Outer Galactic Halo Using the Hubble Space Telescope","authors":"E. P. Lagioia, A. P. Milone, M. V. Legnardi, G. Cordoni, E. Dondoglio, A. Renzini, M. Tailo, T. Ziliotto, M. Carlos, S. Jang, A. F. Marino, A. Mohandasan, J. Qi, G. Rangwal, E. Bortolan and F. Muratore","doi":"10.3847/1538-4357/ad98ee","DOIUrl":"https://doi.org/10.3847/1538-4357/ad98ee","url":null,"abstract":"The pseudo two-color diagram, known as chromosome map (ChM), is a valuable tool for identifying globular clusters (GCs), which consist of single or multiple stellar populations (MPs). Recent surveys of Galactic GCs using ChMs have provided stringent observational constraints on the formation of GCs and their stellar populations. However, these surveys have primarily focused on GCs at moderate distances from the Galactic center and composed of MPs. In this paper, we present the first detailed study of the stellar composition of four GCs in the outer halo of the Milky Way: Arp 2, Ruprecht 106, Terzan 7, and Terzan 8. Our analysis is based on high-precision photometry obtained from images collected with the Hubble Space Telescope in the F275W, F336W, F438W, F606W, and F814W bands. We find that Ruprecht 106 and Terzan 7 are composed solely of a single stellar population, whereas Arp 2 and Terzan 8 host both first- and second-population stars. In these clusters, the second population comprises about half and one-third of the total number of GC stars, respectively. The results from this paper and the literature suggest that the threshold in the initial GC mass, if present, should be smaller than approximately 105M⊙. The first-population stars of Arp 2 and Terzan 8, along with the stars of the simple-population GCs Ruprecht 106 and Terzan 7, exhibit intrinsic F275W – F814W color spreads, likely indicative of [Fe/H] variations of approximately 0.05–0.30 dex. This suggests that star-to-star metallicity variations are a common feature of star clusters, regardless of the presence of MPs.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142981238","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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