A galaxisok kialakulásának asztrofizikája és kozmológiája = Astrophysics and Cosmology of galaxy Formation

Az ELTE Atomfizika Tanszékén dolgozó kutatók elméleti asztrofizikai kutatásaiból egységes kutatási programot hoztunk létre, hosszú évekre meghatározva a Fizikai Intézeten belül az asztrofizikai alapkutatás irányát. Többek között megalkottunk egy ún. "merger tree" programot, amellyel a nagyskálás szerkezet időbeli fejlődése az eddigieknél jobban modellezhető. Elvégeztük a Sunyaev-Zel'dovich effektuson alapuló, a galaxishalmazokban várt lökéshullámok kimutathatóságának vizsgálatát (a galaxishamazok megfigyelésére adtunk új módszert). Megbecsültük, hogy az összeolvadó galaxismagok (fekete lyukak) optikai megfelelője is megtalálható a gravitációs hullámok detektálása nyomán. Mindezek jelentős eredmények a galaxisok feljődésének területén. Kimutattuk, hogy a 12C atommag energiaszintjeinek helye időben változik. Ez izotóparány-eltolódáshoz vezet, és ennek eredményeként módosulhattak a korai, fémben szegény csillagok által létrehozott gázfelhők izotóparányai, illetve a kozmológiai távolságmérésben használt Ia-típusú szupernovák szén-oxigén törzse, és így fényessége. Ezzel pontosítottuk a távoli (azaz korai) galaxisok megfigyelésére szolgáló legfontosabb módszert. Elkészült egy szemirelativisztikus magnetohidrodinamikai program, amley a kialakulás körülményeit szimulálja. Fotometrikus vöröseltolódás segítségével választottuk szét az alacsony és magas vöröseltolódású galaxis mintákat az SDSS adathalmazában, és ezzel hozzájárultunk a nagy minták elemzésének technikájához. | We have created a uniform research activity out of the previous work of the researchers at the Departmant of Atomic Physics, Eötvös University. At the same time we have defined the long term research direction in Astrophysics within the Physics Institute. Among the many results: we have created a merger-tree code to symulate the evolution of large scale structure in the Universe. We have shown that based on the Sunyaev-Zel'dovich effect we can observe the shock waves within large galaxy clusters (we effectively gave a new method to observe clusters). We also estimated that the optical counterparts of merging black hole (in galaxy centers) gravity wave events can be identified and observed. All of these are important contributions to the science of galaxy evolution. We have also shown that positions of energy levels in 12C atoms change with time. This results in a shift in isotope-ratios, and isotope-ratios in gas clouds created by early metal-poor stars can also change as a result. Similarly, this can change the ratios in type Ia supernovae, resulting in a magnitude change. We have enhanced the method of measuring galaxy distances on cosmological scales. We have written a semi-relativistic magnetohydrodynamics code that can help in understanding galaxy formation. We have separated high- and low-redshift galaxies in the SDSS sample, contributing to the development of data reduction techniques

Testing a prediction of the merger origin of early-type galaxies: a correlation between stellar populations and asymmetry

One of the key predictions of the merger hypothesis for the origin of early-type (elliptical and lenticular) galaxies is that tidally-induced asymmetric structure should correlate with signatures of a relatively young stellar population. Such a signature was found by Schweizer and Seitzer (1992; AJ, 104, 1039) at roughly 4sigma confidence. In this paper, we revisit this issue with a nearly ten-fold larger sample of 0.01<z<0.03 galaxies selected from the Two Micron All-Sky Survey and the Sloan Digital Sky Survey. We parameterize tidal structure using a repeatable algorithmic measure of asymmetry, and correlate this with color offset from the early-type galaxy color-magnitude relation. We recover the color offset-asymmetry correlation; furthermore, we demonstrate observationally for the first time that this effect is driven by a highly-significant trend towards younger ages at higher asymmetry values. We present a simple model for the evolution of early-type galaxies through gas-rich major and minor mergers that reproduces their observed build-up from z=1 to the present day and the distribution of present-day colors and ages. We show using this model that if both stellar populations and asymmetry were ideal `clocks' measuring the time since last major or minor gas-rich interaction, then we would expect a rather tight correlation between age and asymmetry. We suggest that the source of extra scatter is natural diversity in progenitor star formation history, gas content, and merger mass ratio, but quantitative confirmation of this conjecture will require sophisticated modeling. We conclude that the asymmetry-age correlation is in basic accord with the merger hypothesis, and indicates that an important fraction of the early-type galaxy population is affected by major or minor mergers at cosmologically-recent times.Comment: Astrophysical Journal, in press. 20 pages, 18 figure

Correlations between Nebular Emission and the Continuum Spectral Shape in SDSS Galaxies

We present a statistical study of the correlations and dimensionality of emission lines carried out on a sample of over 40,000 Sloan Digital Sky Survey (SDSS) galaxies. Using principal component analysis, we found that the equivalent widths of the 11 strongest lines can be well represented using three parameters. We also explore correlations of the emission pattern with the eigenspace representation of the continuum spectrum. The observed relations are used to provide an empirical prescription for expectation values and variances of emission-line strengths as a function of spectral shape. We show that this estimation of emission lines has a sufficient accuracy to make it suitable for photometric applications. The method has already proved useful in SDSS photometric redshift estimation.Comment: 38 pages, 20 figure

HUNCHEST-II contributes to a shift to earlier-stage lung cancer detection: final results of a nationwide screening program

The introduction of low-dose CT (LDCT) altered the landscape of lung cancer (LC) screening and contributed to the reduction of mortality rates worldwide. Here we report the final results of HUNCHEST-II, the largest population-based LDCT screening program in Hungary, including the screening and diagnostic outcomes, and the characteristics of the LC cases.A total of 4215 high-risk individuals aged between 50 and 75 years with a smoking history of at least 25 pack-years were assigned to undergo LDCT screening. Screening outcomes were determined based on the volume, growth, and volume doubling time of pulmonary nodules or masses. The clinical stage distribution of screen-detected cancers was compared with two independent practice-based databases consisting of unscreened LC patients.The percentage of negative and indeterminate tests at baseline were 74.2% and 21.7%, respectively, whereas the prevalence of positive LDCT results was 4.1%. Overall, 76 LC patients were diagnosed throughout the screening rounds (1.8% of total participants), out of which 62 (1.5%) patients were already identified in the first screening round. The overall positive predictive value of a positive test was 58%. Most screen-detected malignancies were stage I LCs (60.7%), and only 16.4% of all cases could be classified as stage IV disease. The percentage of early-stage malignancies was significantly higher among HUNCHEST-II screen-detected individuals than among the LC patients in the National Koranyi Institute of Pulmonology's archive or the Hungarian Cancer Registry (p < 0.001).HUNCHEST-II demonstrates that LDCT screening for LC facilitates early diagnosis, thus arguing in favor of introducing systematic LC screening in Hungary.HUNCHEST-II is the so-far largest population-based low-dose CT screening program in Hungary. A positive test's overall positive predictive value was 58%, and most screen-detected malignancies were early-stage lesions. These results pave the way for expansive systematic screening in the region.• Conducted in 18 medical facilities, HUNCHEST-II is the so far largest population-based low-dose CT screening program in Hungary. • The vast majority of screen-detected malignancies were early-stage lung cancers, and the overall positive predictive value of a positive test was 58%. • HUNCHEST-II facilitates early diagnosis, thus arguing in favor of introducing systematic lung cancer screening in Hungary