Upper limits on the escape fraction of ionizing radiation from galaxies at 2 ≲ z < 6

In this work, we investigate upper limits on the global escape fraction of ionizing photons ($f_{\rm esc/global}^{\rm abs}$) from a sample of galaxies probed for Lyman-continuum (LyC) emission characterized as non-LyC and LyC leakers. We present a sample of 9 clean non-contaminated (by low redshift interlopers, CCD problems and internal reflections of the instrument) galaxies which do not show significant (&gt; 3σ) LyC flux between 880Å &lt;λrest &lt; 910Å. The 9 galaxy stacked spectrum reveals no significant LyC flux with an upper limit of $f_{\rm esc}^{\rm abs} \le 0.06$. In the next step of our analysis, we join all estimates of $f_{\rm esc}^{\rm abs}$ upper limits derived from different samples of 2 ≲ z &lt; 6 galaxies from the literature reported in last ∼20 years and include the sample presented in this work. We find the $f_{\rm esc}^{\rm abs}$ upper limit ≤ 0.084 for the galaxies recognized as non-LyC leakers. After including all known detections from literature $f_{\rm esc/global}^{\rm abs}$ upper limit ≤ 0.088 for all galaxies examined for LyC flux. Furthermore, $f_{\rm esc}^{\rm abs}$ upper limits for different groups of galaxies indicate that the strongest LyC emitters could be galaxies classified as Lyman alpha emitters. We also discuss the possible existence of a correlation among the observed flux density ratio $(F_{\nu }^{LyC}/F_{\nu }^{UV})_{\rm obs}$ and Lyman alpha equivalent width EW(Lyα), where we confirm the existence of moderately significant correlation among galaxies classified as non-LyC leakers.

The Origin of Intergalactic Light in Compact Groups of Galaxies

We investigate the origin of intergalactic light (IGL) in close groups of galaxies. IGL is hypothesized to be the byproduct of interaction and merger within compact groups. Comparing the X-ray point source population in our sample of compact groups that have intergalactic light with compact groups without IGL, we find marginal evidence for a small increase in ultra-luminous X-ray sources (ULXs). There is also a significant bias towards lower luminosity high mass X-ray binaries (HMXRBs). We interpret this as an indication that groups with visible IGL represent a later evolutionary phase than other compact groups. They have galaxies characterized by quenching of star formation (lower star formation rate (SFR) inferred from lower HMXRB luminosity) after stellar material has been removed from the galaxies into the intergalactic medium, which is the source of the IGL. We conclude that the presence of an increased fraction of ULXs is due to past interaction and mergers within groups that have IGL.

The Physical Properties of the Groups of Galaxies

Galaxy groups consist of a few tens of galaxies bound in a common gravitational potential [...]

Peculiar motions of galaxy clusters in the regions of super clusters of galaxies

We present results of the study of peculiar motions of 57 clusters and groups of galaxies in the regions of the Corona Borealis (CrB), Bootes (Boo), Z 5029/A 1424, A 1190, A 1750/A 1809 superclusters of galaxies and 20 galaxy clusters located beyond massive structures (0.05 z 0.10). Using the SDSS Data Release 8 data, a sample of early-type galaxies was compiled in the systems under study, their Fundamental Planes (FP) were built and relative distances and peculiar velocities were determined.

The Hercules cluster in X-rays with XMM-Newton and Chandra

ABSTRACT We present a detailed X-ray study of the central subcluster of the nearby ($z\, \sim$0.0368) Hercules cluster (Abell 2151) identified as A2151C that shows a bimodal structure. A bright clump of hot gas with X-ray emission extending to radius $r\, \sim$304 kpc and $L_X = 3.03_{-0.04}^{+0.02}\times 10^{43}$ erg s−1 in the 0.4–7.0 keV energy range is seen as a fairly regular subclump towards the west (A2151C(B)). An irregular, fainter and cooler subclump with radius $r\, \sim$364 kpc is seen towards the east (A2151C(F)) and has LX = 1.13 ± 0.02 × 1043 erg s−1 in the 0.4–7.0 keV energy band. The average temperature and elemental abundance of A2151C(B) are 2.01 ± 0.05 keV and 0.43 ± 0.05 Z⊙, respectively, while these values are 1.17 ± 0.04 keV and 0.13 ± 0.02 Z⊙ for A2151C(F). Low temperature (1.55 ± 0.07 keV) and a short cooling time (∼0.81 Gyr) within the central 15 arcsec region confirm the presence of a cool core in A2151C(B). We identify several compact groups of galaxies within A2151C(F). We find that A2151C(F) is a distinct galaxy group in the process of formation and likely not a ram-pressure stripped part of the eastern subcluster in Hercules (A2151E). X-ray emission from A2151C shows a region of overlap between A2151C(B) and A2151C(F) but without any enhancement of temperature or entropy in the two-dimensional (2D) projected thermodynamic maps that could have indicated an interaction due to a merger between the two subclumps.

A new way to constrain the densities of intragroup medium in groups of galaxies with convolutional neural networks

ABSTRACT Ram pressure (RP) can influence the evolution of cold gas content and star formation rates of galaxies. One of the key parameters for the strength of RP is the density of intragroup medium (ρigm), which is difficult to estimate if the X-ray emission from it is too weak to be observed. We propose a new way to constrain ρigm through an application of convolutional neural networks (CNNs) to simulated gas density and kinematic maps galaxies under strong RP. We train CNNs using 9 × 104 2D images of galaxies under various RP conditions, then validate performance with 104 new test images. This new method can be applied to real observational data from ongoing WALLABY and SKA surveys to quickly obtain estimates of ρigm. Simulated galaxy images have 1.0 kpc resolution, which is consistent with that expected from the future WALLABY survey. The trained CNN models predict the normalized IGM density, $\hat{\rho }_{\rm igm}$ where $0.0 \le \hat{\rho }_{\rm igm, n} \lt 10.0$, accurately with root mean squared error values of 0.72, 0.83, and 0.74 for the density, kinematic, and joined 2D maps, respectively. Trained models are unable to predict the relative velocity of galaxies with respect to the IGM (vrel) precisely, and struggle to generalize for different RP conditions. We apply our CNNs to the observed H i column density map of NGC 1566 in the Dorado group to estimate its IGM density.

H0LiCOW – XI. A weak lensing measurement of the external convergence in the field of the lensed quasar B1608+656 using HST and Subaru deep imaging

ABSTRACT We investigate the environment and line of sight (LoS) of the H0LiCOW (H0 Lenses in COSMOGRAIL’s Wellspring) lens B1608+656 using Subaru Suprime-Cam and the Hubble Space Telescope (HST) to perform a weak lensing analysis. We compare three different methods to reconstruct the mass map of the field, i.e. the standard Kaiser–Squires inversion coupled with inpainting and Gaussian or wavelet filtering, and ${\rm {\small {glimpse}}}$, a method based on sparse regularization of the shear field. We find no substantial difference between the 2D mass reconstructions, but we find that the ground-based data are less sensitive to small-scale structures than the space-based observations. Marginalizing over the results obtained with all the reconstruction techniques applied to the two available HST filters F606W and F814W, we estimate the external convergence, κext, at the position of B1608+656 is $\kappa _{\mathrm{ext}}= 0.11^{+0.06}_{-0.04}$, where the error bars correspond, respectively, to the 16th and 84th quartiles. This result is compatible with previous estimates using the number counts technique, suggesting that B1608+656 resides in an overdense LoS, but with a completely different technique. Using our mass reconstructions, we also compare the convergence at the position of several groups of galaxies in the field of B1608+656 with the mass measurements using various analytical mass profiles, and find that the weak lensing results favour truncated halo models.