The detection of gravitational waves (GWs) generated by merging black holes has recently opened up a new observational window into the Universe. The mass of the black holes in the first and third LIGO detections, ($36-29 \, \mathrm{M_{\odot}}$ and $32-19 \, \mathrm{M_{\odot}}$), suggests low-metallicity stars as their most likely progenitors. Based on high-resolution N-body simulations, coupled with state-of-the-art metal enrichment models, we find that the remnants of Pop III stars are preferentially located within the cores of galaxies. The probability of a GW signal to be generated by Pop III stars reaches $\sim 90\%$ at $\sim 0.5 \, \mathrm{kpc}$ from the galaxy center, compared to a benchmark value of $\sim 5\%$ outside the core. The predicted merger rates inside bulges is $\sim 60 \times β_{III} \, \mathrm{Gpc^{-3} \, yr^{-1}}$ ($β_{III}$ is the Pop III binarity fraction). To match the $90\%$ credible range of LIGO merger rates, we obtain: $0.03 < β_{III} < 0.88$. Future advances in GW observatories and the discovery of possible electromagnetic counterparts could allow the localization of such sources within their host galaxies. The preferential concentration of GW events within the bulge of galaxies would then provide an indirect proof for the existence of Pop III stars.
Negative feedback from active galactic nuclei (AGN) is the leading mechanism for the quenching of massive galaxies in the vast majority of modern galaxy evolution models. However, direct observational evidence that AGN feedback causes quenching on a population scale is lacking. Studies have shown that luminous AGN are preferentially located in gas-rich and star-forming galaxies, an observation that has sometimes been suggested to be in tension with a negative AGN feedback picture. We investigate three of the current cosmological simulations (IllustrisTNG, EAGLE and SIMBA) along with post-proce…
We investigate signatures of population III (PopIII) stars in the metal-enriched environment of GRBs originating from population II-I (PopII/I) stars by using abundance ratios derived from numerical simulations that follow stellar evolution and chemical enrichment. We find that at $z>10$ more than $10%$ of PopII/I GRBs explode in a medium previously enriched by PopIII stars (we refer to them as GRBII$\rightarrow$III). Although the formation of GRBII$\rightarrow$III is more frequent than that of pristine PopIII GRBs (GRBIIIs), we find that the expected GRBII$\rightarrow$III observed rate is com…
We complement a recent ApJ Letter by Luo et al. by comparing the fraction of starburst galaxies which are interacting with the overall fraction of interacting galaxies in the nearby galaxy population (within 40 Mpc). We confirm that in starburst galaxies the fraction of interacting galaxies is enhanced, by a factor of around 2, but crucially we do so by studying a sample of almost 1500 of the nearest galaxies, including many dwarfs and irregulars. We discuss how adjusting the starburst definition influences the final result and conclude that our result is stable. We find significantly lower fr…
We analyse the structure of galaxies with high specific star formation rate (SSFR) in cluster and field environments in the redshift range $0.5<z<1.0$. Recent studies have shown that these galaxies are strongly depleted in dense environments due to rapid environmental quenching, giving rise to post-starburst galaxies (PSBs). We use effective radii and Sérsic indices as tracers of galaxy structure, determined using imaging from the UKIDSS Ultra Deep Survey (UDS). We find that the high-SSFR galaxies that survive into the cluster environment have, on average, larger effective radii than those in …
Distant powerful radio-loud active galactic nuclei (RLAGN) tend to reside in dense environments and are commonly found in proto-clusters at z > 1.3. We examine whether this occurs because RLAGN are hosted by massive galaxies, which preferentially reside in rich environments. We compare the environments of powerful RLAGN at 1.3 < z < 3.2 from the CARLA survey to a sample of radio-quiet galaxies matched in mass and redshift. We find the environments of RLAGN are significantly denser than those of radio-quiet galaxies, implying that not more than 50% of massive galaxies in this epoch can host pow…
Luminous compact blue galaxies (LCBGs) have enhanced star formation rates and compact morphologies. We combine Sloan Digital Sky Survey data with HI data of 29 LCBGs at redshift z~0 to understand their nature. We find that local LCBGs have high atomic gas fractions (~50%) and star formation rates per stellar mass consistent with some high redshift star forming galaxies. Many local LCBGs also have clumpy morphologies, with clumps distributed across their disks. Although rare, these galaxies appear to be similar to the clumpy star forming galaxies commonly observed at z~1-3. Local LCBGs separate…
We investigate the spatial distribution of the satellites of bright, isolated host galaxies. In agreement with previous studies, we find that, on average, the satellites of red hosts are found preferentially close to their hosts' major axes, while the satellites of blue hosts are distributed isotropically. We compute the pairwise clustering of the satellites and find a strong tendency for pairs of satellites to be located on the same side of their host, resulting in lopsided distributions. The signal is most pronounced for the satellites of blue hosts, where the number of pairs on the same sid…
We use the stellar-mass-selected catalog from the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) in the COSMOS field to study the environments of galaxies via galaxy density and clustering analyses up to $z \sim 2.5$. The clustering strength of quiescent galaxies exceeds that of star-forming galaxies, implying that quiescent galaxies are preferentially located in more massive halos. When using local density measurement, we find a clear positive quiescent fraction--density relation at $z < 1$, consistent with earlier results. However, the quiescent fraction--density relation reverses…
For about 500 intermediate-redshift sources ($0.04<z<0.4$), whose radio flux densities at $1.4\,{\rm GHz}$ are larger than 10 mJy, we performed additional observations at 4.85 GHz and 10.45 GHz using 100-m Effelsberg telescope. Our radio-optical galaxies are located preferentially in the composite and AGN spectral classes in the narrow line optical diagnostic diagrams (ODD). In the analysis, we focused on the distribution of radio spectral indices of radio synchrotron power-law profiles, $S_ν\propto ν^{+α}$, in the ODDs. Using different analysis techniques, both observationally motivated and m…
We investigate the effects of Population III stars on the sky-averaged 21-cm background radiation, which traces the collective emission from all sources of ultraviolet and X-ray photons before reionization is complete. While UV photons from PopIII stars can in principle shift the onset of radiative coupling of the 21-cm transition -- and potentially reionization -- to early times, we find that the remnants of PopIII stars are likely to have a more discernible impact on the 21-cm signal than PopIII stars themselves. The X-rays from such sources preferentially heat the IGM at early times, which …
We investigate the host galaxies of compact objects merging in the local Universe, by combining the results of binary population-synthesis simulations with the Illustris cosmological box. Double neutron stars (DNSs) merging in the local Universe tend to form in massive galaxies (with stellar mass $>10^{9}$ M$_\odot$) and to merge in the same galaxy where they formed, with a short delay time between the formation of the progenitor stars and the DNS merger. In contrast, double black holes (DBHs) and black hole $-$ neutron star binaries (BHNSs) form preferentially in small galaxies (with stellar …
NGC 1980 is a young cluster that is located about 0.5 degrees south of the Orion Nebula Cluster (ONC). Recent studies by Bouy et al. and Pillitteri et al. have suggested that NGC 1980 contains an older population of stars compared to a much younger ONC, and that it belongs to a foreground population that may be located in front of the Orion A molecular gas by as much as 40 pc. In this work we present low-resolution spectra towards 148 young stars found towards the NGC 1980 region. We determine the spectral types of these stars, examine accretion signatures and measure the extinction towards th…
We present for the first time extended stellar density and/or surface brightness radial profiles for almost all the known Large Magellanic Cloud (LMC) old globular clusters (GCs). These were built from DECam images and reach out to ~ 4 times the GCs' tidal radii. The background subtracted radial profiles reveal that the GCs located closer than ~ 5 kpc from the LMC centre contain an excess of stars in their outermost regions with respect to the stellar density expected from a King profile. Such a residual amount of stars - not seen in GCs located farther than ~ 5 kpc from the LMC centre-, as we…
Extremely-Metal Poor Stars in the Milky Way: A Second Generation Formed after Reionization
第三星族恒星形成的宇宙学模拟显示，当冷却由氢分子驱动时，初始质量函数（IMF）偏向于在红移z>20的迷你晕中形成的超大质量恒星（M> 100 Msun）。然而，这一结果与银河系晕中的极贫金属（EMP）恒星的观测结果相冲突，其r过程元素丰度似乎与非常大的第三星族祖先的预期不相容。我们提出了一个新的解决方案的问题，其中的IMF的第二代恒星形成在z>10，再电离之前，是不足的亚太阳质量的恒星，由于高宇宙微波背景温度地板。观测到的EMP星优先在z <10 in pockets of gas enriched to metallicity Z>10^{-3.5} Zsun由星族II星的风形成。我们对像银河系这样的暗物质晕的宇宙学模拟表明，目前的EMP星样本只能限制晚期第三星族恒星的IMF，这些恒星形成于z<13的晕中，维里温度Tvir约为10^4 K。这表明对不稳定性超新星主要不是由这个群体产生的。要开始探测形成于高红移的第三星族恒星的IMF，需要进行一次大规模的巡天，至少要有500颗，可能是几千颗金属丰度为Z~10^{-3.5} Zsun的EMP星。
We study the link between gas flow events and key galaxy scaling relations: the relations between star formation rate (SFR) and stellar mass (the main sequence, MS), gas metallicity and stellar mass (the mass-metallicity relation, MZR) and gas metallicity, stellar mass and SFR (the fundamental metallicity relation, FMR). Using all star-forming galaxies (SFGs) in the 22 MUSE fields of the MusE GAs FLOw and Wind (MEGAFLOW) survey, we derive the MS, MZR and FMR scaling relations for 385 SFGs with $M = 10^8 - 10^{11.5}$ $M_\odot$ at redshifts 0.35 < z < 0.85. Using the MUSE data and complementary …
Star-forming galaxies (SFGs) harbour an abundant reservoir of cosmic rays (CRs). At GeV energies, these CRs undergo interactions with their environment to produce $γ$-rays, and the unresolved $γ$-ray emission from populations of SFGs forms a component of the isotropic extragalactic $γ$-ray background (EGB). In this work, we investigate the contribution to the 0.01 - 50 GeV EGB from SFG populations located up to redshift $z=3$. We find this is dominated by starbursts, while the contribution from main sequence SFGs is marginal at all energies. We also demonstrate that most of the $γ$-ray contrib…
We report a detection of the effect of the large-scale velocity shear on the spatial distributions of the galactic satellites around the isolated hosts. Identifying the isolated galactic systems each of which consists of a single host galaxy and its satellites from the Seventh Data Release of the Sloan Digital Sky Survey and reconstructing linearly the velocity shear field in the local universe, we measure the alignments between the relative positions of the satellites from their isolated hosts and the principal axes of the local velocity shear tensors projected on to the plane of sky. We find…
Context: Giant radio galaxies (with projected linear size of radio structure larger than 0.7 Mpc) are very rare and unusual objects. Only $\sim$5% of extended radio sources reach such sizes. Understanding of the processes responsible for their large sizes is crucial to further our knowledge about the radio source's evolution. Aims: We check the hypothesis that giants become extremely large due to the specific history of their host galaxy formation, as well as in the context of the cluster or group of galaxies where they evolve. Therefore we study the star formation histories in their host gala…
In galaxy clusters, efficiently accreting active galactic nuclei (AGN) are preferentially located in the infall regions of the cluster projected phase-space, and are rarely found in the cluster core. This has been attributed to both an increase in triggering opportunities for infalling galaxies, and a reduction of those mechanisms in the hot, virialised, cluster core. Exploiting the depth and completeness ($98\,$per cent at $r<19.8\,$mag) of the Galaxy And Mass Assembly survey (GAMA), we probe down the group halo mass function to assess whether AGN are found in the same regions in groups as th…
Dust grains in neutral gas behave as aerodynamic particles, so they can develop large density fluctuations independent of gas density fluctuations. Specifically, gas turbulence can drive order-of-magnitude 'resonant' fluctuations in the dust on scales where the gas stopping/drag timescale is comparable to the turbulent eddy turnover time. Here we show that for large grains (size >0.1 micron, containing most grain mass) in sufficiently large molecular clouds (radii >1-10 pc, masses >10^4 M_sun), this scale becomes larger than the characteristic sizes of pre-stellar cores (the sonic length), so …
