From voids to filaments: environmental transformations of galaxies in the SDSS

We investigate the impact of filament and void environments on galaxies, looking for residual effects beyond the known relations with environment density. We quantified the host environment of galaxies as the distance to the spine of the nearest filament, and compared various galaxy properties within 12 bins of this distance. We considered galaxies up to 10 $h^{-1}$Mpc from filaments, i.e. deep inside voids. The filaments were defined by a point process (the Bisous model) from the Sloan Digital Sky Survey data release 10. In order to remove the dependence of galaxy properties on the environment density and redshift, we applied weighting to normalise the corresponding distributions of galaxy populations in each bin. After the normalisation with respect to environment density and redshift, several residual dependencies of galaxy properties still remain. Most notable is the trend of morphology transformations, resulting in a higher elliptical-to-spiral ratio while moving from voids towards filament spines, bringing along a corresponding increase in the $g-i$ colour index and a decrease in star formation rate. After separating elliptical and spiral subsamples, some of the colour index and star formation rate evolution still remains. The mentioned trends are characteristic only for galaxies brighter than about $M_{r} = -20$ mag. Unlike some other recent studies, we do not witness an increase in the galaxy stellar mass while approaching filaments. The detected transformations can be explained by an increase in the galaxy-galaxy merger rate and/or the cut-off of extragalactic gas supplies (starvation) near and inside filaments. Unlike voids, large-scale galaxy filaments are not a mere density enhancement, but have their own specific impact on the constituent galaxies, reducing the star formation rate and raising the chances of elliptical morphology also at a fixed environment density level.Comment: 4 pages, 3 figures, Astronomy & Astrophysics letters accepte

Properties of brightest group galaxies in cosmic web filaments

Context. The cosmic web, a complex network of galaxy groups and clusters connected by filaments, is a dynamical environment in which galaxies form and evolve. However, the impact of cosmic filaments on the properties of galaxies is difficult to study because of the much more influential local (galaxy-group scale) environment. Aims. The aim of this paper is to investigate the dependence of intrinsic galaxy properties on distance to the nearest cosmic web filament, using a sample of galaxies for which the local environment is easily assessable.} Methods. Our study is based on a volume-limited galaxy sample with $M_\mathrm{r}$ $\leq -19$ mag, drawn from the SDSS DR12. We chose brightest group galaxies (BGGs) in groups with two to six members as our probes of the impact of filamentary environment because their local environment can be determined more accurately. We use the Bisous marked point process method to detect cosmic-web filaments with radii of $0.5-1.0$ Mpc and measure the perpendicular filament spine distance ($D_{\mathrm{fil}}$) for the BGGs. We limit our study to $D_{\mathrm{fil}}$ values up to 4 Mpc. We use the luminosity density field as a tracer of the local environment. To achieve uniformity of the sample and to reduce potential biases we only consider filaments longer than 5 Mpc. Our final sample contains 1427 BGGs. Results. We note slight deviations between the galaxy populations inside and outside the filament radius in terms of stellar mass, colour, the 4000AA break, specific star formation rates, and morphologies. However, all these differences remain below 95% confidence and are negligible compared to the effects arising from local environment density. Conclusions. Within a 4 Mpc radius of the filament axes, the effect of filaments on BGGs is marginal. The local environment is the main factor in determining BGG properties.Comment: 11 pages, 9 figures, Accepted for publication in A&

The scaling relation between galaxy luminosity and WHIM density from EAGLE simulations with application to SDSS data

This paper presents an updated scaling relation between the optical luminosity density (LD) of galaxies in the r band and the density of the warm-hot intergalactic medium (WHIM) in cosmic filaments, using the high-resolution EAGLE simulations. We find a strong degree of correlation between the WHIM density and the galaxy luminosity density, resulting in a scaling relation between the two quantities that permits us to predict the WHIM density of filaments with a scatter of less than 1/2 dex in a broad range of smoothed filament luminosity densities. In order to estimate the performance of the simulation-based calibration of the LD-WHIM density relation, we applied it to a sample of low-redshift filaments detected with the Bisous method in the Legacy Survey SDSS DR12 data. In the volume covered by the SDSS data, our relation predicts a WHIM density amounting to 31 +/- 7 +/- 12 per cent (statistical errors followed by systematic) of cosmic baryon density. This agrees, albeit within the large uncertainties, with the current estimates of the cosmological missing baryon fraction, implying that our LD-WHIM density relation may be a useful tool in the search for the missing baryons. This method of analysis provides a new promising avenue to study the physical properties of the missing baryons, using an observable that is available for large volumes of the sky, complementary and independent from WHIM searches with absorption-line systems in the FUV or X-rays.</p

Properties of brightest group galaxies in cosmic web filaments

Context. The cosmic web, a complex network of galaxy groups and clusters connected by filaments, is a dynamical environment in which galaxies form and evolve. However, the impact of cosmic filaments on the properties of galaxies is difficult to study because of the much more influential local (galaxy-group scale) environment.Aims. The aim of this paper is to investigate the dependence of intrinsic galaxy properties on distance to the nearest cosmic web filament, using a sample of galaxies for which the local environment is easily assessable.Methods. Our study is based on a volume-limited galaxy sample with M-r <= -19 mag, drawn from the SDSS DR12. We chose brightest group galaxies (BGGs) in groups with two to six members as our probes of the impact of filamentary environment because their local environment can be determined more accurately. We use the Bisous marked point process method to detect cosmic-web filaments with radii of 0.5-1.0 Mpc and measure the perpendicular filament spine distance (D-fil) for the BGGs. We limit our study to D-fil values up to 4 Mpc. We use the luminosity density field as a tracer of the local environment. To achieve uniformity of the sample and to reduce potential biases we only consider filaments longer than 5 Mpc. Our final sample contains 1427 BGGs.Results. We note slight deviations between the galaxy populations inside and outside the filament radius in terms of stellar mass, colour, the 4000 angstrom break, specific star formation rates, and morphologies. However, all these differences remain below 95% confidence and are negligible compared to the effects arising from local environment density.Conclusions. Within a 4 Mpc radius of the filament axes, the effect of filaments on BGGs is marginal. The local environment is the main factor in determining BGG properties

The Astropy Problem

The Astropy Project (http://astropy.org) is, in its own words, "a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages." For five years this project has been managed, written, and operated as a grassroots, self-organized, almost entirely volunteer effort while the software is used by the majority of the astronomical community. Despite this, the project has always been and remains to this day effectively unfunded. Further, contributors receive little or no formal recognition for creating and supporting what is now critical software. This paper explores the problem in detail, outlines possible solutions to correct this, and presents a few suggestions on how to address the sustainability of general purpose astronomical software

Galaktikad ja muu barüonaine kosmilistes filamentides

Väitekirja elektrooniline versioon ei sisalda publikatsiooneGalaktikad on ühed huvitavamad taevas vaadeldavad objektid. Need on erineva kujuga, vankriratta või CD-plaadi kettakujulistest spiraalsetest kuni ilmetute kanamuna kujuga el- liptilisteni. Sada aastat tagasi mõõdeti esimest korda galaktikate kaugusi ja sai ilmsiks, et need on meist tohutult kaugel asuvad tähtede kogumikud. Ka meie Päike asub ühes galakti- kas, Linnutee, mis on ainult üks miljarditest teistest galaktikatest meie universumis. Tänu teleskoopidega tehtud taevaülevaadetele, mille eesmärk on galaktikate täpsete asu- kohtade määramine, on saanud selgeks, et galaktikad ei asu üksteise suhtes juhuslikult, vaid eelistatud paigutuses. Mõned neist on tihedas koosluses üksteise lähedal, parvedes. Parvede vahel on pikad galaktikate ahelad, filamendid. On ka piirkondasid, kus on väga vähe või po- le üldse galaktikaid, tühikud. Seda jaotust võib ette kujutada kui inimeste jaotust Maa peal, kus parved on suurlinnad, filamendid suuremad teed, mille lähedal on väiksemad linnad ja tühikud väheasustatud alad. Samuti on leitud, et galaktikad erinevad sõltuvalt nende keskkondade tihedusest. Par- vedes on hilisemas arengujärgus galaktikad: suuremad ja vanemad. Tühikud on vastandina väiksemate ja noorte galaktikate ala. Filamendid on vahepealsed, kus leidub palju erine- vaid galaktikaid. Nad esinevad ka väga erinevates keskkondades asudes nii tühikutes kui ka parvede kogumite vahel. Selle teesi eesmärgiks on iseloomustada just filamentides asuvaid galaktikaid. Prae- guseni pole veel selge kuidas filamendi keskkond mõjutab galaktikate arengut. Probleemi lahendamiseks kasutasime kaasautoritega nii avalikult kättesaadavaid vaaltusandmeid kui ka Tartu Ülikooli Tartu Observatooriumi teadlaste kogemust galaktikate konfiguratsioonide iseloomustamises. Selle töö tulemusena leidsime, et filamentides on galaktikad väiksema tähetekke aktiivsusega ja üldiselt hilisemas arengufaasis kui eeldaks ainuüksi keskkonna tiheduse põhjal. Edaspidi on vaja veel uurida galaktikaid, et nende olemusest aru saada.Galaxies are some of the most interesting objects visible in the sky. They have different shapes, from cartwheel or CD-like disky spirals to featureless egg-shaped ellipticals. One hundred years ago the distances of galaxies were first measured and it became apparent that they are collections of stars at vast distances from us. Even the Sun is located within a galaxy, the Milky Way, which is just one of billions of other galaxies in our universe. Sky surveys with telescopes have measured exact positions of galaxies. From these we know that galaxies are not situated randomly, but in preferred configurations. Some are in dense associations, clusters. Clusters are connected by long chains of galaxies, filaments. There are regions where there are very few or no galaxies at all, voids. This configuration can be imagined as similar to human populations on Earth, where the clusters are big cities, filaments highways with nearby towns and the voids regions of sparse inhabitation. It has also been determined that galaxies differ based on the density of their environ- ment. In clusters galaxies are more likely in a later stage of evolution: larger and older. Voids in contrast are territories of small young galaxies. Filaments are intermediate, where many different types of galaxies are found. Filaments also inhabit a variety of environments, inside voids and between dense clusters. The goal of this thesis is to characterise galaxies in filaments. It is still not well unders- tood how the filament environment affects the evolution of galaxies. In order to gain insight into this problem we utilised publicly available observational data and the expertise of the scientists at the Tartu University Tartu Observatory in identifying galaxy configurations. As the result of this work we found that galaxies in filaments are less star forming and general- ly more evolved than would be expected based on density alone. However more research is needed to fully understand the nature of galaxies.https://www.ester.ee/record=b546202

K2 Campaign 5 observations of pulsating subdwarf B stars: Binaries and super-Nyquist frequencies

We report the discovery of three pulsating subdwarf B stars in binary systems observed with the Kepler space telescope during Campaign 5 of K2. EPIC 211696659 (SDSS J083603.98+155216.4) is a g-mode pulsator with a white dwarf companion and a binary period of 3.16 d. EPICs 211823779 (SDSS J082003.35+173914.2) and 211938328 (LB 378) are both p-mode pulsators with main-sequence F companions. The orbit of EPIC 211938328 is long (635 ± 146 d) while we cannot constrain that of EPIC 211823779. The p modes are near the Nyquist frequency and so we investigate ways to discriminate super- from sub-Nyquist frequencies. We search for rotationally induced frequency multiplets and all three stars appear to be slow rotators with EPIC 211696659 subsynchronous to its orbit