Contribution of galaxies and galaxy clusters to the diffuse gamma-ray background

Izučavanje kosmičkog zračenja, veoma je bitno za razumevanje fizičkih procesa na visokim energijama, a energije do kojih čestice mogu da se ubrzaju u svemiru mnogo su više od energija koje čovek trenutno može da postigne u akceleratorima na Zemlji. Procesi u kojima nastaje kosmičko zračenje su još uvek nedovoljno objašnjeni, a modeli koji se predlažu čekaju na eksperimentalnu potvrdu. Prisustvo kosmičkog zračenja može da se meri kroz detekciju različitih produkata interakcija ovih visokoenergijskih čestica sa međuzvezdanom materijom kroz koju se kreću. Ova doktorska disertacija bavi se akrecionim udarnim talasima kao izvorom kosmičkog zračenja u jatima galaksija, ali i kosmičkim zracima ubrzanim u ostacima supernovih u samim galaksijama. Bez obzira koji od ovih mehanizama se razmatra, kosmičko zračenje u sudaru sa atomima i jonima međuzvezdane materije, između ostalog, proizvodi gama zračenje, neutrine, kao i lake elemente, od kojih se posebno razmatra litijum. U disertaciji se pre svega razvijaju modeli koji opisuju gama zračenje proizvodeno od strane kosmičkog zračenja ubrzanog na udarnim talasim nastalih u različitim procesima. Prvo se razmatra akrecije gasa na već virijalizovane strukture na najvećim skalama (na primer u jatima galaksija). U modelima prvi put je implementirana vremenska promena proizvodnje gama zračenja u toku istorije svemira, koja nastaje zbog evolucije akrecionih udarnih talasa u toku formiranja velikih struktura. Zbog toga modeli razvijeni u ovoj disertaciji realnije opisuju gama zračenje na velikim skalama, u odnosu na modele koji su ranije razvijani i u kojima se pretpostavljalo da gama zračenje potiče sa jednog crvenog pomaka. Modeli se koriste za predviđanje ukupnog gama zračenja nerazlučenih jata galaksija. Ovo modelirano gama zračenje se zatim poredi sa posmatranim izotropnim difuznim pozadinskim gama zračenjem, koje je izmerio teleskop Fermi-LAT, iz čega se zaključuje da ovaj tip kosmičkog zračenja ima nezanemariv doprinos pozadinskom gama zračenju (u zavisnosti od normalizacije modela, moguće je objasniti i skoro celu gama pozadinu) i da bi trebalo da se uzima u razmatranje pored drugih komponenti za koje se pretpostavlja da imaju veliki doprinos, kao što su na primer normalne nerazlučene galaksije ili blazari. Modeli za gama zračenje akrecionih udarnih talasa se u okviru disertacije takođe porede i sa merenjima visokoenergijskih neutrina detektovanih od strane detektora IceCube. Neutrini se koriste za normiranje modela, iz čega se zaključilo da ako su akrecioni udarni talasi pretežno jaki, neutrinska pozadina jače ograničava moguću gama emisivnost ovakvih objekata, u odnosu na pozadinsko gama zračenje koje smo pre toga koristili. Izučavanje neutrina kao produkata interakcija kosmičkog zračenja je od posebne važnosti, zbog toga što neutrini slabo interaguju sa drugim česticama, pa zbog toga u sebi kriju nepromenjenu informaciju o trenutku kada su nastali, tj. o kosmičkim zracima koji ih proizvode. Jedan deo disertacije se bavi i proizvodnjom kosmičkog zračenja u ostacima supernovih, konkretno u slučaju Malog Magelanovog oblaka, koji je inače detektovan u gama oblasti. U ovoj galaksiji prvi put je izmerena zastupljenost litijuma u međuzvezdanom gasu, izvan Mlečnog puta. S obzirom na to da i gama zračenje i litijum nastaju kroz interakcije kosmičkog zračenja sa međuzvezdanom materijom, njihovo zajedničko poreklo se može iskoristiti za procenu moguće proizvodnje litijuma i gama zračenja od strane bilo koje populacije kosmičkog zračenja. Pokazano je da galaktičko kosmičko zračenje, za koje se smatra da je dominantno u okviru Malog Magelanovog oblaka, može da objasni tek delić posmatrane zastupljenosti litijuma, ako se pretpostavi da je ukupna gama emisivnost ove galaksije koja se danas meri takođe potekla od interakcija galaktičkog kosmičkog zračenja sa gasom unutar galaksije. Ovaj zaključak je zanimljiv, jer navodi na mogućnost postojanja drugog izvora litijuma u okviru Malog Magelanovog oblaka. Takođe, koristeći zajedničko poreklo litijuma i gama zračenja procenjeno je i koliko nepravilne patuljaste galaksije mogu da doprinesu difuznoj gama pozadini. Razmatranja nekoliko različitih produkata interakcija kosmičkog zračenja sa međuzvezdanom materijom (gama zračenja, neutrina i litijuma), na manjim skalama (u okviru galaksija) kao i na veoma velikim skalama (jata galaksija), pokazala su da pored galaktičkog kosmičkog zračenja nastalog u ostacima supernovih i drugo, još uvek hipotetičko, kosmičko zračenje (nastalo npr. prilikom akrecije gasa na velikim skalama ili plimskih interakcija galaksija), takođe može imati nezanemariv doprinos merenjima.Studying cosmic rays is very important for better understanding of high energy physical processes, since particles accelerated in space can reach energies far above what we can produce in accelerators on Earth, at the moment. Processes that produce cosmic rays are still unexplained to some extent, and models that have been proposed are awaiting cofirmation. Presence of cosmic rays can be measured by detecting dfferent products of interactions of these high energy particles with the interstellar medium through which they propagate. This thesis deals with the accretion shock as sources of cosmic rays in clusters of galaxies, as well as cosmic rays accelerated in supernova remnants inside galaxies. No matter which of these mechanisms is being considered, cosmic rays will collide with atoms and ions in the interstellar medium, and produce, among other things, gamma rays, neutrinos, as well as light elements, of which we will discuss lithium. In the thesis we primarily develop models that describe gamma rays produced by cosmic rays accelerated in shocks that can appear in dfferent processes. We first examine accretion of new gas onto already virialized structures (for example in galaxy clusters). For the first time, we include the change of gamma-ray production with time, through the history of the universe, that re ects the evolution of accretion shocks which appear during large scale structure formation. Therefore, the models developed in this thesis describe the gamma rays from large scale structures more realistically, compared to models which have previously been developed and which use single redshift approximation for the gamma-ray origin. Models are used to derive the gamma-ray ux of all unresolved galaxy clusters. These modeled gamma rays are then compared to the isotropic dffuse gamma-ray background, measured by telescope Fermi-LAT. This leads to the conclusion that these cosmic rays have non-negligible contribution to the isotropic diffuse gamma-ray background (depending on the normalization, they can even explain the whole isotropic diffuse gamma-ray background) and that this population of cosmic rays has to be taken into consideration in addition to other components that are thought to be major contributors, like for example, unresolved normal galaxies or blazars. In the thesis, models of gamma-ray production in accretion shocks are also compared to observations of high-energy neutrinos detected by IceCube detector. Neutrinos are used to normalize gamma-ray models, from which we conclude that if the accretion shocks are predominantly strong, neutrino background is more limiting to the possible gamma-ray emissivity of these objects, compared to the gamma-ray background we first used. Study of neutrinos as products of cosmic-ray interactions is very important, since neutrinos interact weakly with other particles, and therefore keep all of the information about the time they were produced and about cosmic rays that produced them. One part of the thesis deals with the production of cosmic rays in supernova remnants, in particular, the case of the Small Magellanic Cloud, which was detected in gamma rays. In this galaxy we also have the first measurements of the lithium abundances in the interstellar gas outside of the Milky Way. Since gamma rays and lithium are produced through interactions of cosmic rays with the interstellar medium, their same origin can be used to estimate the production of lithium and gamma rays by any cosmic-ray population. We show that galactic cosmic rays, which are considered to be dominant population of cosmic rays in the Small Magellanic Cloud, can only explain a very small part of the observed abundance of lithium, if we assume that the entire present gamma-ray emissivity that we observe also originates from the interaction of galactic cosmic rays with gas within the galaxy. This conclusion is interesting, because it leads to the possible existence of other sources of lithium in the Small Magellanic Cloud. Also, using the fact that gamma rays and lithium share the same origin, we estimate how much can irregular dwarf galaxies contribute to the diffuse gamma-ray background. Study of several different products of cosmic-ray interactions with the interstellar medium (gamma rays, neutrinos and lithium) on smaller scales (within the galaxy), as well as on the largest scales (galaxy clusters), showed that in addition to the galactic cosmic rays accelerated in supernova remnants, other still hypothetical cosmic rays (produced for example during accretion of gas on largest scales, or tidal interactions of galaxies) can have a non-negligible contribution to the measurements

Contribution of galaxies and galaxy clusters to the diffuse gamma-ray background

Izučavanje kosmičkog zračenja, veoma je bitno za razumevanje fizičkih procesa na visokim energijama, a energije do kojih čestice mogu da se ubrzaju u svemiru mnogo su više od energija koje čovek trenutno može da postigne u akceleratorima na Zemlji. Procesi u kojima nastaje kosmičko zračenje su još uvek nedovoljno objašnjeni, a modeli koji se predlažu čekaju na eksperimentalnu potvrdu. Prisustvo kosmičkog zračenja može da se meri kroz detekciju različitih produkata interakcija ovih visokoenergijskih čestica sa međuzvezdanom materijom kroz koju se kreću. Ova doktorska disertacija bavi se akrecionim udarnim talasima kao izvorom kosmičkog zračenja u jatima galaksija, ali i kosmičkim zracima ubrzanim u ostacima supernovih u samim galaksijama. Bez obzira koji od ovih mehanizama se razmatra, kosmičko zračenje u sudaru sa atomima i jonima međuzvezdane materije, između ostalog, proizvodi gama zračenje, neutrine, kao i lake elemente, od kojih se posebno razmatra litijum. U disertaciji se pre svega razvijaju modeli koji opisuju gama zračenje proizvodeno od strane kosmičkog zračenja ubrzanog na udarnim talasim nastalih u različitim procesima. Prvo se razmatra akrecije gasa na već virijalizovane strukture na najvećim skalama (na primer u jatima galaksija). U modelima prvi put je implementirana vremenska promena proizvodnje gama zračenja u toku istorije svemira, koja nastaje zbog evolucije akrecionih udarnih talasa u toku formiranja velikih struktura. Zbog toga modeli razvijeni u ovoj disertaciji realnije opisuju gama zračenje na velikim skalama, u odnosu na modele koji su ranije razvijani i u kojima se pretpostavljalo da gama zračenje potiče sa jednog crvenog pomaka. Modeli se koriste za predviđanje ukupnog gama zračenja nerazlučenih jata galaksija. Ovo modelirano gama zračenje se zatim poredi sa posmatranim izotropnim difuznim pozadinskim gama zračenjem, koje je izmerio teleskop Fermi-LAT, iz čega se zaključuje da ovaj tip kosmičkog zračenja ima nezanemariv doprinos pozadinskom gama zračenju (u zavisnosti od normalizacije modela, moguće je objasniti i skoro celu gama pozadinu) i da bi trebalo da se uzima u razmatranje pored drugih komponenti za koje se pretpostavlja da imaju veliki doprinos, kao što su na primer normalne nerazlučene galaksije ili blazari. Modeli za gama zračenje akrecionih udarnih talasa se u okviru disertacije takođe porede i sa merenjima visokoenergijskih neutrina detektovanih od strane detektora IceCube. Neutrini se koriste za normiranje modela, iz čega se zaključilo da ako su akrecioni udarni talasi pretežno jaki, neutrinska pozadina jače ograničava moguću gama emisivnost ovakvih objekata, u odnosu na pozadinsko gama zračenje koje smo pre toga koristili. Izučavanje neutrina kao produkata interakcija kosmičkog zračenja je od posebne važnosti, zbog toga što neutrini slabo interaguju sa drugim česticama, pa zbog toga u sebi kriju nepromenjenu informaciju o trenutku kada su nastali, tj. o kosmičkim zracima koji ih proizvode. Jedan deo disertacije se bavi i proizvodnjom kosmičkog zračenja u ostacima supernovih, konkretno u slučaju Malog Magelanovog oblaka, koji je inače detektovan u gama oblasti. U ovoj galaksiji prvi put je izmerena zastupljenost litijuma u međuzvezdanom gasu, izvan Mlečnog puta. S obzirom na to da i gama zračenje i litijum nastaju kroz interakcije kosmičkog zračenja sa međuzvezdanom materijom, njihovo zajedničko poreklo se može iskoristiti za procenu moguće proizvodnje litijuma i gama zračenja od strane bilo koje populacije kosmičkog zračenja. Pokazano je da galaktičko kosmičko zračenje, za koje se smatra da je dominantno u okviru Malog Magelanovog oblaka, može da objasni tek delić posmatrane zastupljenosti litijuma, ako se pretpostavi da je ukupna gama emisivnost ove galaksije koja se danas meri takođe potekla od interakcija galaktičkog kosmičkog zračenja sa gasom unutar galaksije. Ovaj zaključak je zanimljiv, jer navodi na mogućnost postojanja drugog izvora litijuma u okviru Malog Magelanovog oblaka. Takođe, koristeći zajedničko poreklo litijuma i gama zračenja procenjeno je i koliko nepravilne patuljaste galaksije mogu da doprinesu difuznoj gama pozadini. Razmatranja nekoliko različitih produkata interakcija kosmičkog zračenja sa međuzvezdanom materijom (gama zračenja, neutrina i litijuma), na manjim skalama (u okviru galaksija) kao i na veoma velikim skalama (jata galaksija), pokazala su da pored galaktičkog kosmičkog zračenja nastalog u ostacima supernovih i drugo, još uvek hipotetičko, kosmičko zračenje (nastalo npr. prilikom akrecije gasa na velikim skalama ili plimskih interakcija galaksija), takođe može imati nezanemariv doprinos merenjima.Studying cosmic rays is very important for better understanding of high energy physical processes, since particles accelerated in space can reach energies far above what we can produce in accelerators on Earth, at the moment. Processes that produce cosmic rays are still unexplained to some extent, and models that have been proposed are awaiting cofirmation. Presence of cosmic rays can be measured by detecting dfferent products of interactions of these high energy particles with the interstellar medium through which they propagate. This thesis deals with the accretion shock as sources of cosmic rays in clusters of galaxies, as well as cosmic rays accelerated in supernova remnants inside galaxies. No matter which of these mechanisms is being considered, cosmic rays will collide with atoms and ions in the interstellar medium, and produce, among other things, gamma rays, neutrinos, as well as light elements, of which we will discuss lithium. In the thesis we primarily develop models that describe gamma rays produced by cosmic rays accelerated in shocks that can appear in dfferent processes. We first examine accretion of new gas onto already virialized structures (for example in galaxy clusters). For the first time, we include the change of gamma-ray production with time, through the history of the universe, that re ects the evolution of accretion shocks which appear during large scale structure formation. Therefore, the models developed in this thesis describe the gamma rays from large scale structures more realistically, compared to models which have previously been developed and which use single redshift approximation for the gamma-ray origin. Models are used to derive the gamma-ray ux of all unresolved galaxy clusters. These modeled gamma rays are then compared to the isotropic dffuse gamma-ray background, measured by telescope Fermi-LAT. This leads to the conclusion that these cosmic rays have non-negligible contribution to the isotropic diffuse gamma-ray background (depending on the normalization, they can even explain the whole isotropic diffuse gamma-ray background) and that this population of cosmic rays has to be taken into consideration in addition to other components that are thought to be major contributors, like for example, unresolved normal galaxies or blazars. In the thesis, models of gamma-ray production in accretion shocks are also compared to observations of high-energy neutrinos detected by IceCube detector. Neutrinos are used to normalize gamma-ray models, from which we conclude that if the accretion shocks are predominantly strong, neutrino background is more limiting to the possible gamma-ray emissivity of these objects, compared to the gamma-ray background we first used. Study of neutrinos as products of cosmic-ray interactions is very important, since neutrinos interact weakly with other particles, and therefore keep all of the information about the time they were produced and about cosmic rays that produced them. One part of the thesis deals with the production of cosmic rays in supernova remnants, in particular, the case of the Small Magellanic Cloud, which was detected in gamma rays. In this galaxy we also have the first measurements of the lithium abundances in the interstellar gas outside of the Milky Way. Since gamma rays and lithium are produced through interactions of cosmic rays with the interstellar medium, their same origin can be used to estimate the production of lithium and gamma rays by any cosmic-ray population. We show that galactic cosmic rays, which are considered to be dominant population of cosmic rays in the Small Magellanic Cloud, can only explain a very small part of the observed abundance of lithium, if we assume that the entire present gamma-ray emissivity that we observe also originates from the interaction of galactic cosmic rays with gas within the galaxy. This conclusion is interesting, because it leads to the possible existence of other sources of lithium in the Small Magellanic Cloud. Also, using the fact that gamma rays and lithium share the same origin, we estimate how much can irregular dwarf galaxies contribute to the diffuse gamma-ray background. Study of several different products of cosmic-ray interactions with the interstellar medium (gamma rays, neutrinos and lithium) on smaller scales (within the galaxy), as well as on the largest scales (galaxy clusters), showed that in addition to the galactic cosmic rays accelerated in supernova remnants, other still hypothetical cosmic rays (produced for example during accretion of gas on largest scales, or tidal interactions of galaxies) can have a non-negligible contribution to the measurements

Contribution of galaxies and galaxy clusters to the diffuse gamma-ray background

Izučavanje kosmičkog zračenja, veoma je bitno za razumevanje fizičkih procesa na visokim energijama, a energije do kojih čestice mogu da se ubrzaju u svemiru mnogo su više od energija koje čovek trenutno može da postigne u akceleratorima na Zemlji. Procesi u kojima nastaje kosmičko zračenje su još uvek nedovoljno objašnjeni, a modeli koji se predlažu čekaju na eksperimentalnu potvrdu. Prisustvo kosmičkog zračenja može da se meri kroz detekciju različitih produkata interakcija ovih visokoenergijskih čestica sa međuzvezdanom materijom kroz koju se kreću. Ova doktorska disertacija bavi se akrecionim udarnim talasima kao izvorom kosmičkog zračenja u jatima galaksija, ali i kosmičkim zracima ubrzanim u ostacima supernovih u samim galaksijama. Bez obzira koji od ovih mehanizama se razmatra, kosmičko zračenje u sudaru sa atomima i jonima međuzvezdane materije, između ostalog, proizvodi gama zračenje, neutrine, kao i lake elemente, od kojih se posebno razmatra litijum. U disertaciji se pre svega razvijaju modeli koji opisuju gama zračenje proizvodeno od strane kosmičkog zračenja ubrzanog na udarnim talasim nastalih u različitim procesima. Prvo se razmatra akrecije gasa na već virijalizovane strukture na najvećim skalama (na primer u jatima galaksija). U modelima prvi put je implementirana vremenska promena proizvodnje gama zračenja u toku istorije svemira, koja nastaje zbog evolucije akrecionih udarnih talasa u toku formiranja velikih struktura. Zbog toga modeli razvijeni u ovoj disertaciji realnije opisuju gama zračenje na velikim skalama, u odnosu na modele koji su ranije razvijani i u kojima se pretpostavljalo da gama zračenje potiče sa jednog crvenog pomaka. Modeli se koriste za predviđanje ukupnog gama zračenja nerazlučenih jata galaksija. Ovo modelirano gama zračenje se zatim poredi sa posmatranim izotropnim difuznim pozadinskim gama zračenjem, koje je izmerio teleskop Fermi-LAT, iz čega se zaključuje da ovaj tip kosmičkog zračenja ima nezanemariv doprinos pozadinskom gama zračenju (u zavisnosti od normalizacije modela, moguće je objasniti i skoro celu gama pozadinu) i da bi trebalo da se uzima u razmatranje pored drugih komponenti za koje se pretpostavlja da imaju veliki doprinos, kao što su na primer normalne nerazlučene galaksije ili blazari. Modeli za gama zračenje akrecionih udarnih talasa se u okviru disertacije takođe porede i sa merenjima visokoenergijskih neutrina detektovanih od strane detektora IceCube. Neutrini se koriste za normiranje modela, iz čega se zaključilo da ako su akrecioni udarni talasi pretežno jaki, neutrinska pozadina jače ograničava moguću gama emisivnost ovakvih objekata, u odnosu na pozadinsko gama zračenje koje smo pre toga koristili. Izučavanje neutrina kao produkata interakcija kosmičkog zračenja je od posebne važnosti, zbog toga što neutrini slabo interaguju sa drugim česticama, pa zbog toga u sebi kriju nepromenjenu informaciju o trenutku kada su nastali, tj. o kosmičkim zracima koji ih proizvode. Jedan deo disertacije se bavi i proizvodnjom kosmičkog zračenja u ostacima supernovih, konkretno u slučaju Malog Magelanovog oblaka, koji je inače detektovan u gama oblasti. U ovoj galaksiji prvi put je izmerena zastupljenost litijuma u međuzvezdanom gasu, izvan Mlečnog puta. S obzirom na to da i gama zračenje i litijum nastaju kroz interakcije kosmičkog zračenja sa međuzvezdanom materijom, njihovo zajedničko poreklo se može iskoristiti za procenu moguće proizvodnje litijuma i gama zračenja od strane bilo koje populacije kosmičkog zračenja. Pokazano je da galaktičko kosmičko zračenje, za koje se smatra da je dominantno u okviru Malog Magelanovog oblaka, može da objasni tek delić posmatrane zastupljenosti litijuma, ako se pretpostavi da je ukupna gama emisivnost ove galaksije koja se danas meri takođe potekla od interakcija galaktičkog kosmičkog zračenja sa gasom unutar galaksije. Ovaj zaključak je zanimljiv, jer navodi na mogućnost postojanja drugog izvora litijuma u okviru Malog Magelanovog oblaka. Takođe, koristeći zajedničko poreklo litijuma i gama zračenja procenjeno je i koliko nepravilne patuljaste galaksije mogu da doprinesu difuznoj gama pozadini. Razmatranja nekoliko različitih produkata interakcija kosmičkog zračenja sa međuzvezdanom materijom (gama zračenja, neutrina i litijuma), na manjim skalama (u okviru galaksija) kao i na veoma velikim skalama (jata galaksija), pokazala su da pored galaktičkog kosmičkog zračenja nastalog u ostacima supernovih i drugo, još uvek hipotetičko, kosmičko zračenje (nastalo npr. prilikom akrecije gasa na velikim skalama ili plimskih interakcija galaksija), takođe može imati nezanemariv doprinos merenjima.Studying cosmic rays is very important for better understanding of high energy physical processes, since particles accelerated in space can reach energies far above what we can produce in accelerators on Earth, at the moment. Processes that produce cosmic rays are still unexplained to some extent, and models that have been proposed are awaiting cofirmation. Presence of cosmic rays can be measured by detecting dfferent products of interactions of these high energy particles with the interstellar medium through which they propagate. This thesis deals with the accretion shock as sources of cosmic rays in clusters of galaxies, as well as cosmic rays accelerated in supernova remnants inside galaxies. No matter which of these mechanisms is being considered, cosmic rays will collide with atoms and ions in the interstellar medium, and produce, among other things, gamma rays, neutrinos, as well as light elements, of which we will discuss lithium. In the thesis we primarily develop models that describe gamma rays produced by cosmic rays accelerated in shocks that can appear in dfferent processes. We first examine accretion of new gas onto already virialized structures (for example in galaxy clusters). For the first time, we include the change of gamma-ray production with time, through the history of the universe, that re ects the evolution of accretion shocks which appear during large scale structure formation. Therefore, the models developed in this thesis describe the gamma rays from large scale structures more realistically, compared to models which have previously been developed and which use single redshift approximation for the gamma-ray origin. Models are used to derive the gamma-ray ux of all unresolved galaxy clusters. These modeled gamma rays are then compared to the isotropic dffuse gamma-ray background, measured by telescope Fermi-LAT. This leads to the conclusion that these cosmic rays have non-negligible contribution to the isotropic diffuse gamma-ray background (depending on the normalization, they can even explain the whole isotropic diffuse gamma-ray background) and that this population of cosmic rays has to be taken into consideration in addition to other components that are thought to be major contributors, like for example, unresolved normal galaxies or blazars. In the thesis, models of gamma-ray production in accretion shocks are also compared to observations of high-energy neutrinos detected by IceCube detector. Neutrinos are used to normalize gamma-ray models, from which we conclude that if the accretion shocks are predominantly strong, neutrino background is more limiting to the possible gamma-ray emissivity of these objects, compared to the gamma-ray background we first used. Study of neutrinos as products of cosmic-ray interactions is very important, since neutrinos interact weakly with other particles, and therefore keep all of the information about the time they were produced and about cosmic rays that produced them. One part of the thesis deals with the production of cosmic rays in supernova remnants, in particular, the case of the Small Magellanic Cloud, which was detected in gamma rays. In this galaxy we also have the first measurements of the lithium abundances in the interstellar gas outside of the Milky Way. Since gamma rays and lithium are produced through interactions of cosmic rays with the interstellar medium, their same origin can be used to estimate the production of lithium and gamma rays by any cosmic-ray population. We show that galactic cosmic rays, which are considered to be dominant population of cosmic rays in the Small Magellanic Cloud, can only explain a very small part of the observed abundance of lithium, if we assume that the entire present gamma-ray emissivity that we observe also originates from the interaction of galactic cosmic rays with gas within the galaxy. This conclusion is interesting, because it leads to the possible existence of other sources of lithium in the Small Magellanic Cloud. Also, using the fact that gamma rays and lithium share the same origin, we estimate how much can irregular dwarf galaxies contribute to the diffuse gamma-ray background. Study of several different products of cosmic-ray interactions with the interstellar medium (gamma rays, neutrinos and lithium) on smaller scales (within the galaxy), as well as on the largest scales (galaxy clusters), showed that in addition to the galactic cosmic rays accelerated in supernova remnants, other still hypothetical cosmic rays (produced for example during accretion of gas on largest scales, or tidal interactions of galaxies) can have a non-negligible contribution to the measurements

DeepAdversaries: Examining the Robustness of Deep Learning Models for Galaxy Morphology Classification

With increased adoption of supervised deep learning methods for processing and analysis of cosmological survey data, the assessment of data perturbation effects (that can naturally occur in the data processing and analysis pipelines) and the development of methods that increase model robustness are increasingly important. In the context of morphological classification of galaxies, we study the effects of perturbations in imaging data. In particular, we examine the consequences of using neural networks when training on baseline data and testing on perturbed data. We consider perturbations associated with two primary sources: 1) increased observational noise as represented by higher levels of Poisson noise and 2) data processing noise incurred by steps such as image compression or telescope errors as represented by one-pixel adversarial attacks. We also test the efficacy of domain adaptation techniques in mitigating the perturbation-driven errors. We use classification accuracy, latent space visualizations, and latent space distance to assess model robustness. Without domain adaptation, we find that processing pixel-level errors easily flip the classification into an incorrect class and that higher observational noise makes the model trained on low-noise data unable to classify galaxy morphologies. On the other hand, we show that training with domain adaptation improves model robustness and mitigates the effects of these perturbations, improving the classification accuracy by 23% on data with higher observational noise. Domain adaptation also increases by a factor of ~2.3 the latent space distance between the baseline and the incorrectly classified one-pixel perturbed image, making the model more robust to inadvertent perturbations.Comment: 20 pages, 6 figures, 5 tables; accepted in MLS

Snowmass 2021 Computational Frontier CompF03 Topical Group Report: Machine Learning

The rapidly-developing intersection of machine learning (ML) with high-energy physics (HEP) presents both opportunities and challenges to our community. Far beyond applications of standard ML tools to HEP problems, genuinely new and potentially revolutionary approaches are being developed by a generation of talent literate in both fields. There is an urgent need to support the needs of the interdisciplinary community driving these developments, including funding dedicated research at the intersection of the two fields, investing in high-performance computing at universities and tailoring allocation policies to support this work, developing of community tools and standards, and providing education and career paths for young researchers attracted by the intellectual vitality of machine learning for high energy physics

Snowmass 2021 Computational Frontier CompF03 Topical Group Report: Machine Learning

The rapidly-developing intersection of machine learning (ML) with high-energy physics (HEP) presents both opportunities and challenges to our community. Far beyond applications of standard ML tools to HEP problems, genuinely new and potentially revolutionary approaches are being developed by a generation of talent literate in both fields. There is an urgent need to support the needs of the interdisciplinary community driving these developments, including funding dedicated research at the intersection of the two fields, investing in high-performance computing at universities and tailoring allocation policies to support this work, developing of community tools and standards, and providing education and career paths for young researchers attracted by the intellectual vitality of machine learning for high energy physics

Snowmass 2021 Computational Frontier CompF03 Topical Group Report: Machine Learning

The rapidly-developing intersection of machine learning (ML) with high-energy physics (HEP) presents both opportunities and challenges to our community. Far beyond applications of standard ML tools to HEP problems, genuinely new and potentially revolutionary approaches are being developed by a generation of talent literate in both fields. There is an urgent need to support the needs of the interdisciplinary community driving these developments, including funding dedicated research at the intersection of the two fields, investing in high-performance computing at universities and tailoring allocation policies to support this work, developing of community tools and standards, and providing education and career paths for young researchers attracted by the intellectual vitality of machine learning for high energy physics