The nature of damped HI absorbers probed by cosmological simulations: satellite accretion and outflows

We use state-of-the-art cosmological zoom simulations to explore the distribution of neutral gas in and around galaxies that gives rise to high column density \ion{H}{i} \mbox{Ly-$\alpha$} absorption (formally, sub-DLAs and DLAs) in the spectra of background quasars. Previous cosmological hydrodynamic simulations under-predict the mean projected separations $(b)$ of these absorbers relative to the host, and invoke selection effects to bridge the gap with observations. On the other hand, single lines of sight (LOS) in absorption cannot uniquely constrain the galactic origin. Our simulations match all observational data, with DLA and sub-DLA LOS existing over the entire probed parameter space ($-4\lesssim$[M/H]$\lesssim 0.5$, $b<50$ kpc) at all redshifts ($z\sim 0.4 - 3.0$). We demonstrate how the existence of DLA LOS at $b\gtrsim 20-30$ kpc from a massive host galaxy require high numerical resolution, and that these LOS are associated with dwarf satellites in the main halo, stripped metal-rich gas and outflows. Separating the galaxy into interstellar ("\ion{H}{i} disc") and circumgalactic ("halo") components, we find that both components significantly contribute to damped \ion{H}{i} absorption LOS. Above the sub-DLA (DLA) limits, the disc and halo contribute with $\sim 60 (80)$ and $\sim 40 (20)$ per cent, respectively. Our simulations confirm analytical model-predictions of the DLA-distribution at $z\lesssim 1$. At high redshift ($z\sim 2-3$) sub-DLA and DLAs occupy similar spatial scales, but on average separate by a factor of two by $z\sim 0.5$. On whether sub-DLA and DLA LOS sample different stellar-mass galaxies, such a correlation can be driven by a differential covering-fraction of sub-DLA to DLA LOS with stellar mass. This preferentially selects sub-DLA LOS in more massive galaxies in the low-$z$ universe.Comment: 12 pages, 5 figures, submitted to MNRAS 29/01/201

All-Sky Near Infrared Space Astrometry

Gaia is currently revolutionizing modern astronomy. However, much of the Galactic plane, center and the spiral arm regions are obscured by interstellar extinction, rendering them inaccessible because Gaia is an optical instrument. An all-sky near infrared (NIR) space observatory operating in the optical NIR, separated in time from the original Gaia would provide microarcsecond NIR astrometry and millimag photometry to penetrate obscured regions unraveling the internal dynamics of the Galaxy.Comment: 7 page

Mammographic density and structural features can individually and jointly contribute to breast cancer risk assessment in mammography screening:a case-control study

BACKGROUND: Mammographic density is a well-established risk factor for breast cancer. We investigated the association between three different methods of measuring density or parenchymal pattern/texture on digitized film-based mammograms, and examined to what extent textural features independently and jointly with density can improve the ability to identify screening women at increased risk of breast cancer. METHODS: The study included 121 cases and 259 age- and time matched controls based on a cohort of 14,736 women with negative screening mammograms from a population-based screening programme in Denmark in 2007 (followed until 31 December 2010). Mammograms were assessed using the Breast Imaging-Reporting and Data System (BI-RADS) density classification, Tabár’s classification on parenchymal patterns and a fully automated texture quantification technique. The individual and combined association with breast cancer was estimated using binary logistic regression to calculate Odds Ratios (ORs) and the area under the receiver operating characteristic (ROC) curves (AUCs). RESULTS: Cases showed significantly higher BI-RADS and texture scores on average than controls (p < 0.001). All three methods were individually able to segregate women into different risk groups showing significant ORs for BI-RADS D3 and D4 (OR: 2.37; 1.32–4.25 and 3.93; 1.88–8.20), Tabár’s PIII and PIV (OR: 3.23; 1.20–8.75 and 4.40; 2.31–8.38), and the highest quartile of the texture score (3.04; 1.63–5.67). AUCs for BI-RADS, Tabár and the texture scores (continuous) were 0.63 (0.57–0–69), 0.65 (0.59–0–71) and 0.63 (0.57–0–69), respectively. Combining two or more methods increased model fit in all combinations, demonstrating the highest AUC of 0.69 (0.63-0.74) when all three methods were combined (a significant increase from standard BI-RADS alone). CONCLUSION: Our findings suggest that the (relative) amount of fibroglandular tissue (density) and mammographic structural features (texture/parenchymal pattern) jointly can improve risk segregation of screening women, using information already available from normal screening routine, in respect to future personalized screening strategies. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12885-016-2450-7) contains supplementary material, which is available to authorized users

The Lyman-alpha glow of gas falling into the dark matter halo of a z=3 galaxy

Quasars are the visible signatures of super-massive black holes in the centres of distant galaxies. It has been suggested that quasars are formed during ``major merger events'' when two massive galaxies collide and merge, leading to the prediction that quasars should be found in the centres of the regions of largest overdensity in the early Universe. In dark matter (DM)-dominated models of the early Universe, massive DM halos are predicted to attract the surrounding gas, which falls towards its centre. The neutral gas is not detectable in emission by itself, but gas falling into the ionizing cone of such a quasar will glow in the Lyman-alpha line of hydrogen, effectively imaging the DM halo. Here we present a Lyman-alpha image of a DM halo at redshift 3, along with a two-dimensional spectrum of the gaseous halo. Our observations are best understood in the context of the standard model for DM halos; we infer a mass of (2-7) x 10^12 solar masses (Msun) for the halo.Comment: 4 pages, 4 figures. Published as a Letter to Nature in the August 26, 2004 issue; see accompanying News and Views article by Z. Haiman in the same issu

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

We report on the HST detection of the Lyman-continuum (LyC) radiation emitted by a galaxy at redshift z=3.794, dubbed Ion1 (Vanzella et al. 2012). The LyC from Ion1 is detected at rest-frame wavelength 820$\sim$890 \AA with HST WFC3/UVIS in the F410M band ($m_{410}=27.60\pm0.36$ magnitude (AB), peak SNR = 4.17 in a circular aperture with radius r = 0.12'') and at 700$\sim$830 \AA with the VLT/VIMOS in the U-band ($m_U = 27.84\pm0.19$ magnitude (AB), peak SNR = 6.7 with a r = 0.6'' aperture). A 20-hr VLT/VIMOS spectrum shows low- and high-ionization interstellar metal absorption lines, the P-Cygni profile of CIV and Ly$\alpha$ in absorption. The latter spectral feature differs from what observed in known LyC emitters, which show strong Ly$\alpha$ emission. An HST far-UV color map reveals that the LyC emission escapes from a region of the galaxy that is bluer than the rest, presumably because of lower dust obscuration. The F410M image shows that the centroid of the LyC emission is offset from the centroid of the non-ionizing UV emission by 0.12''$\pm$0.03'', corresponding to 0.85$\pm$0.21 kpc (physical), and that its morphology is likely moderately resolved. These morphological characteristics favor a scenario where the LyC photons produced by massive stars escape from low HI column-density "cavities" in the ISM, possibly carved by stellar winds and/or supernova. We also collect the VIMOS U-band images of a sample of 107 Lyman-break galaxies with spectroscopic redshifts at $3.40<z<3.95$, i.e. sampling the LyC, and stack them with inverse-variance weights. No LyC emission is detected in the stacked image, resulting in a 32.5 magnitude (AB) flux limit (1$\sigma$) and an upper limit of absolute LyC escape fraction $f_{esc}^{abs} < 0.63\%$. LyC emitters like Ion1 are very likely at the bright-end of the LyC luminosity function.Comment: 24 pages, 13 figures, accepted for publication in Ap