Red variables in the OGLE-II data base -- III. Constraints on the three-dimensional structures of the LMC and SMC

We present an analysis of the 3-D structure of the Magellanic Clouds, using period-luminosity (P-L) relations of pulsating red giants in the OGLE-II sample. By interpreting deviations from the mean P-L relations as distance modulus variations, we examine the three-dimensional distributions of the sample. The results for the Large Magellanic Cloud, based solely on stars below the tip of the Red Giant Branch, confirm previous results on the inclined and possibly warped bar of the LMC. The depth variation across the OGLE-II field is about 2.4 kpc, interpreted as the distance range of a thin but inclined structure. The inclination angle is about 29 deg. A comparison with OGLE-II red clump distances revealed intriguing differences that seem to be connected to the red clump reddening correction. A spatially variable red clump population in the LMC can explain the deviations, which may have a broader impact on our understanding of the LMC formation history. For the Small Magellanic Cloud, we find a complex structure showing patchy distribution scattered within 3.2 kpc of the mean. However, the larger range of the overall depth on every line-of-sight is likely to smooth out significantly the real variations.Comment: 5 pages, 4 figures, accepted for publication in MNRAS (online Letters

Eclipsing binaries in the MACHO database: New periods and classifications for 3031 systems in the Large Magellanic Cloud

Eclipsing binaries offer a unique opportunity to determine fundamental physical parameters of stars using the constraints on the geometry of the systems. Here we present a reanalysis of publicly available two-color observations of about 6800 stars in the Large Magellanic Cloud, obtained by the MACHO project between 1992 and 2000 and classified as eclipsing variable stars. Of these, less than half are genuine eclipsing binaries. We determined new periods and classified the stars, 3031 in total, using the Fourier parameters of the phased light curves. The period distribution is clearly bimodal, reflecting refer to the separate groups of more massive blue main sequence objects and low mass red giants. The latter resemble contact binaries and obey a period-luminosity relation. Using evolutionary models, we identified foreground stars. The presented database has been cleaned of artifacts and misclassified variables, thus allowing searches for apsidal motion, tertiary components, pulsating stars in binary systems and secular variations with time-scales of several years.Comment: 11 figures, 9 pages, accepted for publication in Ap

Ultraluminous Quasars At High Redshift Show Evolution In Their Radio-Loudness Fraction In Both Redshift And Ultraviolet Luminosity

We take a sample of 94 ultraluminous, optical quasars from the search of over 14,486 deg^2 by Onken et al. 2022 in the range 4.4<redshift<5.2 and match them against the Rapid ASKAP Continuum Survey (RACS) observed on the Australian Square Kilometre Array Pathfinder (ASKAP). From this most complete sample of the bright end of the redshift ~5 quasar luminosity function, there are 10 radio continuum detections of which 8 are considered radio-loud quasars. The radio-loud fraction for this sample is 8.5 \pm 2.9 per cent. Jiang et al. 2007 found that there is a decrease in the radio-loud fraction of quasars with increasing redshift and an increase with increasing absolute magnitude at rest frame 2500 Angstroms. We show that the radio-loud fraction of our quasar sample is consistent with that predicted by Jiang et al. 2007, extending their result to higher redshifts.Comment: Accepted by MNRA

The HI gas content of galaxies around Abell 370, a galaxy cluster at z = 0.37

We used observations from the Giant Metrewave Radio Telescope to measure the atomic hydrogen gas content of 324 galaxies around the galaxy cluster Abell 370 at a redshift of z = 0.37 (a look-back time of ~4 billion years). The HI 21-cm emission from these galaxies was measured by coadding their signals using precise optical redshifts obtained with the Anglo-Australian Telescope. The average HI mass measured for all 324 galaxies is (6.6 +- 3.5)x10^9 solar masses, while the average HI mass measured for the 105 optically blue galaxies is (19.0 +- 6.5)x10^9 solar masses. The significant quantities of gas found around Abell 370, suggest that there has been substantial evolution in the gas content of galaxy clusters since redshift z = 0.37. The total amount of HI gas found around Abell 370 is up to ~8 times more than that seen around the Coma cluster, a nearby galaxy cluster of similar size. Despite this higher gas content, Abell 370 shows the same trend as nearby clusters, that galaxies close to the cluster core have lower HI gas content than galaxies further away. The Abell 370 galaxies have HI mass to optical light ratios similar to local galaxy samples and have the same correlation between their star formation rate and HI mass as found in nearby galaxies. The average star formation rate derived from [OII] emission and from de-redshifted 1.4 GHz radio continuum for the Abell 370 galaxies also follows the correlation found in the local universe. The large amounts of HI gas found around the cluster can easily be consumed by the observed star formation rate in the galaxies over the ~4 billion years (from z = 0.37) to the present day.Comment: accepted by MNRA

Trace element fractionation between PM10 and PM2.5 in coal mine dust: Implications for occupational respiratory health

This is the final version. Available on open access from Elsevier via the DOI in this recordInvestigations into the respiratory health impacts of coal mine particulate matter (PM) face the challenge of understanding its chemical complexity. This includes highly variable concentrations of trace metals and metalloids such as Fe, Ti, Mn, Zn, Ni, V, Cr, Cu, Pb, Cd, Sb, As and Sn, which may be capable of inducing cell damage. Analysis of PM10 and PM2.5 samples size-separated from deposited coal mine dusts collected on PVC flat surfaces at a height of 1.5-2 m inside the second level in the Velenje lignite mine, Slovenia, demonstrates that some of these metallic elements (in this case Cu, Sb, Sn, Pb, Zn, As, Ni) can be concentrated in PM2.5, the most deeply inhalable and therefore potentially most bioreactive size fraction. These elements are likely to be mainly present in silicates, oxides, and perhaps antimonides and arsenides, rather than in the calcareous, carbonaceous or sulphide components which show no obvious affinity for PM2.5. Whereas in the Velenje lignites concentrations of these metallic elements are low and so do not present any obvious extra health risk to the miners, this is unlikely to be the case in mines where unusually metal-enriched coals are being excavated. We therefore recommend that levels of potentially toxic elements in PM2.5 should be assessed where metal- and metalloid-rich coals are being mined worldwide, especially given uncertainties relating to the efficiency of current dust suppression and respiratory protective equipment for such fine particle sizes.European Commission Research Fund for Coal and Stee

Detecting neutral hydrogen in emission at redshift z ~ 1

We use a large N-body simulation to examine the detectability of HI in emission at redshift z ~ 1, and the constraints imposed by current observations on the neutral hydrogen mass function of galaxies at this epoch. We consider three different models for populating dark matter halos with HI, designed to encompass uncertainties at this redshift. These models are consistent with recent observations of the detection of HI in emission at z ~ 0.8. Whilst detection of 21 cm emission from individual halos requires extremely long integrations with existing radio interferometers, such as the Giant Meter Radio Telescope (GMRT), we show that the stacked 21 cm signal from a large number of halos can be easily detected. However, the stacking procedure requires accurate redshifts of galaxies. We show that radio observations of the field of the DEEP2 spectroscopic galaxy redshift survey should allow detection of the HI mass function at the 5-12 sigma level in the mass range 10^(11.4) M_sun/h < M_halo < 10^(12.5)M_sun/h, with a moderate amount of observation time. Assuming a larger noise level that corresponds to an upper bound for the expected noise for the GMRT, the detection significance for the HI mass function is still at the 1.7-3 sigma level. We find that optically undetected satellite galaxies enhance the HI emission profile of the parent halo, leading to broader wings as well as a higher peak signal in the stacked profile of a large number of halos. We show that it is in principle possible to discern the contribution of undetected satellites to the total HI signal, even though cosmic variance limitation make this challenging for some of our models.Comment: 14 pages, 9 figures, Submitted To MNRA

An Empirical Study of the I2P Anonymity Network and its Censorship Resistance

Tor and I2P are well-known anonymity networks used by many individuals to protect their online privacy and anonymity. Tor's centralized directory services facilitate the understanding of the Tor network, as well as the measurement and visualization of its structure through the Tor Metrics project. In contrast, I2P does not rely on centralized directory servers, and thus obtaining a complete view of the network is challenging. In this work, we conduct an empirical study of the I2P network, in which we measure properties including population, churn rate, router type, and the geographic distribution of I2P peers. We find that there are currently around 32K active I2P peers in the network on a daily basis. Of these peers, 14K are located behind NAT or firewalls. Using the collected network data, we examine the blocking resistance of I2P against a censor that wants to prevent access to I2P using address-based blocking techniques. Despite the decentralized characteristics of I2P, we discover that a censor can block more than 95% of peer IP addresses known by a stable I2P client by operating only 10 routers in the network. This amounts to severe network impairment: a blocking rate of more than 70% is enough to cause significant latency in web browsing activities, while blocking more than 90% of peer IP addresses can make the network unusable. Finally, we discuss the security consequences of the network being blocked, and directions for potential approaches to make I2P more resistant to blocking.Comment: 14 pages, To appear in the 2018 Internet Measurement Conference (IMC'18

ALFALFA HI Data Stacking I. Does the Bulge Quench Ongoing Star Formation in Early-Type Galaxies?

We have carried out an HI stacking analysis of a volume-limited sample of ~5000 galaxies with imaging and spectroscopic data from GALEX and the Sloan Digital Sky Survey, which lie within the current footprint of the Arecibo Legacy Fast ALFA (ALFALFA) Survey. Our galaxies are selected to have stellar masses greater than 10^10 Msun and redshifts in the range 0.025<z<0.05. We extract a sub-sample of 1833 "early-type" galaxies with inclinations less than 70deg, with concentration indices C>2.6 and with light profiles that are well fit by a De Vaucouleurs model. We then stack HI line spectra extracted from the ALFALFA data cubes at the 3-D positions of the galaxies from these two samples in bins of stellar mass, stellar mass surface density, central velocity dispersion, and NUV-r colour. We use the stacked spectra to estimate the average HI gas fractions M_HI/M_* of the galaxies in each bin. Our main result is that the HI content of a galaxy is not influenced by its bulge. The average HI gas fractions of galaxies in both our samples correlate most strongly with NUV-r colour and with stellar surface density. The relation between average HI fraction and these two parameters is independent of concentration index C. We have tested whether the average HI gas content of bulge-dominated galaxies on the red sequence, differs from that of late-type galaxies on the red sequence. We find no evidence that galaxies with a significant bulge component are less efficient at turning their available gas reservoirs into stars. This result is in contradiction with the "morphological quenching" scenario proposed by Martig et al. (2009).Comment: 21 pages, 15 figures. Accepted for publication in MNRAS. Version with high resolution figures available at http://www.mpa-garching.mpg.de/GASS/pubs.ph

A Radio and Optical Polarization Study of the Magnetic Field in the Small Magellanic Cloud

We present a study of the magnetic field of the Small Magellanic Cloud (SMC), carried out using radio Faraday rotation and optical starlight polarization data. Consistent negative rotation measures (RMs) across the SMC indicate that the line-of-sight magnetic field is directed uniformly away from us with a strength 0.19 +/- 0.06 microGauss. Applying the Chandrasekhar-Fermi method to starlight polarization data yields an ordered magnetic field in the plane of the sky of strength 1.6 +/- 0.4 microGauss oriented at a position angle 4 +/- 12 degs, measured counter-clockwise from the great circle on the sky joining the SMC to the Large Magellanic Cloud (LMC). We construct a three-dimensional magnetic field model of the SMC, under the assumption that the RMs and starlight polarization probe the same underlying large-scale field. The vector defining the overall orientation of the SMC magnetic field shows a potential alignment with the vector joining the center of the SMC to the center of the LMC, suggesting the possibility of a "pan-Magellanic'' magnetic field. A cosmic-ray driven dynamo is the most viable explanation of the observed field geometry, but has difficulties accounting for the observed uni-directional field lines. A study of Faraday rotation through the Magellanic Bridge is needed to further test the pan-Magellanic field hypothesis.Comment: 28 pages, 6 figures, accepted for publication in Ap