1909.04663
The ultra-diffuse dwarf galaxies NGC 1052-DR2 and 1052-DF4 are in conflict with standard cosmology
Haslbauer, et al
Recently van Dokkum et al. (2018b) reported that the galaxy NGC 1052-DF2 (DF2) lacks dark matter if located at $20$ Mpc from Earth. In contrast, DF2 is a dark-matter-dominated dwarf galaxy with a normal globular cluster population if it has a much shorter distance near $10$ Mpc. However, DF2 then has a high peculiar velocity wrt. the cosmic microwave background of $886$ $\rm{km\,s^{-1}}$, which differs from that of the Local Group (LG) velocity vector by $1298$ $\rm{km\,s^{-1}}$ with an angle of $117 \, ^{\circ}$. Taking into account the dynamical $M/L$ ratio, the stellar mass, half-light radius, peculiar velocity, motion relative to the LG, and the luminosities of the globular clusters, we show that the probability of finding DF2-like galaxies in the lambda cold dark matter ($\Lambda$CDM) TNG100-1 simulation is at most $1.0\times10^{-4}$ at $11.5$ Mpc and is $4.8\times10^{-7}$ at $20.0$ Mpc. At $11.5$ Mpc, the peculiar velocity is in significant tension with the TNG100-1, TNG300-1, and Millennium simulations, but occurs naturally in a Milgromian cosmology. At $20.0$ Mpc, the unusual globular cluster population would challenge any cosmological model. Estimating that precise measurements of the internal velocity dispersion, stellar mass, and distance exist for $100$ galaxies, DF2 is in $2.6\sigma$ ($11.5$ Mpc) and $4.1\sigma$ ($20.0$ Mpc) tension with standard cosmology. Adopting the former distance for DF2 and assuming that NGC 1052-DF4 is at $20.0$ Mpc, the existence of both is in tension at $\geq4.8\sigma$ with the $\Lambda$CDM model. If both galaxies are at $20.0$ Mpc the $\Lambda$CDM cosmology has to be rejected by $\geq5.8\sigma$.
The ultra-diffuse dwarf galaxies NGC 1052-DR2 and 1052-DF4 are in conflict with standard cosmology
Haslbauer, et al
Recently van Dokkum et al. (2018b) reported that the galaxy NGC 1052-DF2 (DF2) lacks dark matter if located at $20$ Mpc from Earth. In contrast, DF2 is a dark-matter-dominated dwarf galaxy with a normal globular cluster population if it has a much shorter distance near $10$ Mpc. However, DF2 then has a high peculiar velocity wrt. the cosmic microwave background of $886$ $\rm{km\,s^{-1}}$, which differs from that of the Local Group (LG) velocity vector by $1298$ $\rm{km\,s^{-1}}$ with an angle of $117 \, ^{\circ}$. Taking into account the dynamical $M/L$ ratio, the stellar mass, half-light radius, peculiar velocity, motion relative to the LG, and the luminosities of the globular clusters, we show that the probability of finding DF2-like galaxies in the lambda cold dark matter ($\Lambda$CDM) TNG100-1 simulation is at most $1.0\times10^{-4}$ at $11.5$ Mpc and is $4.8\times10^{-7}$ at $20.0$ Mpc. At $11.5$ Mpc, the peculiar velocity is in significant tension with the TNG100-1, TNG300-1, and Millennium simulations, but occurs naturally in a Milgromian cosmology. At $20.0$ Mpc, the unusual globular cluster population would challenge any cosmological model. Estimating that precise measurements of the internal velocity dispersion, stellar mass, and distance exist for $100$ galaxies, DF2 is in $2.6\sigma$ ($11.5$ Mpc) and $4.1\sigma$ ($20.0$ Mpc) tension with standard cosmology. Adopting the former distance for DF2 and assuming that NGC 1052-DF4 is at $20.0$ Mpc, the existence of both is in tension at $\geq4.8\sigma$ with the $\Lambda$CDM model. If both galaxies are at $20.0$ Mpc the $\Lambda$CDM cosmology has to be rejected by $\geq5.8\sigma$.
1909.04664
EDGE: the origin of scatter in ultra-faint dwarf stellar masses and surface brightnesses
Rey, et al
We demonstrate how the least luminous galaxies in the Universe, ultra-faint dwarf galaxies, are sensitive to their dynamical mass at the time of cosmic reionization. We select a low-mass ($\sim \text{1.5} \times 10^{9} \, \text{M}_{\odot}$) dark matter halo from a cosmological volume, and perform zoom hydrodynamical simulations with multiple alternative histories using "genetically modified" initial conditions. Earlier forming ultra-faints have higher stellar mass today, due to a longer period of star formation before their quenching by reionization. Our histories all converge to the same final dynamical mass, demonstrating the existence of extended scatter ($\geq$ 1 dex) in stellar masses at fixed halo mass due to the diversity of possible histories. One of our variants builds less than 2 \% of its final dynamical mass before reionization, rapidly quenching in-situ star formation. The bulk of its final stellar mass is later grown by dry mergers, depositing stars in the galaxy's outskirts and hence expanding its effective radius. This mechanism constitutes a new formation scenario for highly diffuse ($\text{r}_{1 /2} \sim 820 \, \text{pc}$, $\sim 32 \, \text{mag arcsec}^2$), metal-poor ($\big[ \mathrm{Fe}\, / \mathrm{H} \big]= -2.9$), ultra-faint ($\mathcal{M}_V= -5.7$) dwarf galaxies within the reach of next-generation low surface brightness surveys.
1909.04670
A new sample of (wandering) massive black holes in dwarf galaxies from high-resolution radio observations
Reines, et al
We present a sample of nearby dwarf galaxies with radio-selected accreting massive black holes (BHs), the majority of which are non-nuclear. We observed 111 galaxies using sensitive, high-resolution observations from the Karl G. Jansky Very Large Array (VLA) in its most extended A-configuration at X-band (~8-12 GHz), yielding a typical angular resolution of ~0.25" and rms noise of ~15 uJy. Our targets were selected by cross matching galaxies with stellar masses M_stellar < 3 x 10^9 M_sun and redshifts z<0.055 in the NASA-Sloan Atlas with the VLA Faint Images of the Radio Sky at Twenty centimeters (FIRST) Survey. With our new high-resolution VLA observations, we detect compact radio sources towards 39 galaxies and carefully evaluate possible origins for the radio emission including thermal HII regions, supernova remnants, younger radio supernovae, background interlopers, and AGNs in the target galaxies. We find that 13 dwarf galaxies almost certainly host active massive BHs despite the fact that only one object was previously identified as having optical signatures of an AGN. We also identify a candidate dual radio AGN in a more massive galaxy system. The majority of the radio-detected BHs are offset from the center of the host galaxies with some systems showing signs of interactions/mergers. Our results indicate that massive BHs need not always live in the nuclei of dwarf galaxies, confirming predictions from simulations. Moreover, searches attempting to constrain BH seed formation using observations of dwarf galaxies need to account for such a population of "wandering" BHs.
1909.04672
The MUSE Ultra Deep Field (MUDF). II. Survey design and the gaseous properties of galaxy groups at 0.5<z<1.5
Fossati, et al
We present the goals, design, and first results of the MUSE Ultra Deep Field (MUDF) survey, a large programme using the Multi Unit Spectroscopic Explorer (MUSE) instrument at the ESO Very Large Telescope. The MUDF survey is collecting ~ 150 hours on-source of integral field optical spectroscopy in a 1.5 x 1.2 square arcmin region which hosts several astrophysical structures along the line of sight, including two bright z ~ 3.2 quasars with close separation (~ 500 kpc). Following the description of the data reduction procedures, we present the analysis of the galaxy environment and gaseous properties of seven groups detected at redshifts 0.5 < z < 1.5, spanning a large dynamic range in halo mass, log(Mh/Msun) ~ 11 - 13.5. For four of the groups, we find associated MgII absorbers tracing cool gas in high-resolution spectroscopy of the two quasars, including one case of correlated absorption in both sightlines at distance ~ 480 kpc. The absorption strength associated with the groups is higher than what has been reported for more isolated galaxies of comparable mass and impact parameters. We do not find evidence for widespread cool gas giving rise to strong absorption within these groups. Combining these results with the distribution of neutral and ionised gas seen in emission in lower-redshift groups, we conclude that gravitational interactions in the group environment strip gas from the galaxy haloes into the intragroup medium, boosting the cross section of cool gas and leading to the high fraction of strong MgII absorbers that we detect.
1909.04679
The biggest splash
Belokurov, et al
1909.04765
The separation distribution of ultra-wide binaries across galactic populations
Tian, et al
We present an extensive sample of ultra-wide binary stars in the solar neighborhood, focusing on separations of $0.01<s/{pc}<1$. Using data from Gaia DR2, we define kinematic sub-populations via the systems' tangential velocities, i.e., disk-like ($v_{\perp, tot}<40$km/s), intermediate ($v_{\perp,tot}=(40-85)$km/s), and halo-like ($v_{\perp,tot}>85$km/s) samples, presuming that these velocity cuts represent a rough ordering in the binaries' age and metallicity. Through stringent cuts on astrometric precision, we can obtain pure binary samples with thousands of binaries in each sample. For all three populations, the distribution of binary separations extends smoothly to 1pc, displaying neither strong truncation nor bimodality. Fitting a smoothly-broken power law for the separation distribution, we find that its slope at separations $s=10^{2.5-4}$AU is the same for all sub-populations, $p(s)\propto s^{\gamma}$, with $\gamma\sim-1.54$. However, the logarithmic slope of $p(s)$ steepens at $s \gtrsim 10^4$AU. We find some evidences that the degree of steepening increases with the binaries' age, with a slope-change of only $\Delta\gamma\sim0.5$ for disk-like stars, but $\Delta\gamma>1$ for halo-like stars. This trend is contrary to what might be expected if steepening at wide separations were due to gravitational perturbations by molecular clouds or stars, which would preferentially disrupt disk binaries. If we were to interpret steepening at $s\gtrsim 10^4$AU as a consequence of disruption by massive halo objects, we would have to invoke a MACHO population inconsistent with other constraints. As a more plausible alternative, we propose a simple model to predict the separation distribution of wide binaries formed in dissolving star clusters. This model generically predicts $\gamma\sim-1.5$ as observed, with steepening at larger separations due to the finite size of binaries' birth clusters.
1909.05277
Cosmological parameters from the BOSS galaxy power spectrum
Ivanov, et al
We present cosmological parameter measurements from the publicly available Baryon Oscillation Spectroscopic Survey (BOSS) data on anisotropic galaxy clustering in Fourier space. Compared to previous studies, our analysis has two main novel features. First, we use a complete perturbation theory model that properly takes into account the non-linear effects of dark matter clustering, short-scale physics, galaxy bias, redshift-space distortions, and large-scale bulk flows. Second, we employ a Markov-Chain Monte-Carlo technique and consistently reevaluate the full power spectrum likelihood as we scan over different cosmologies. Assuming a minimal $\Lambda$CDM cosmology with massive neutrinos, fixing the primordial power spectrum tilt, and imposing the big bang nucleosynthesis (BBN) prior on the physical baryon density $\omega_b$, we find the following late-Universe parameters: Hubble constant $H_0=(67.89\pm 1.06)$ km$\,$s$^{-1}$Mpc$^{-1}$, matter density fraction $\Omega_m=0.295\pm 0.010$, and the mass fluctuation amplitude $\sigma_8=0.721\pm 0.043$. These parameters were measured directly from the BOSS data and independently of the Planck cosmic microwave background observations. Our constraints remain unchanged if we replace the BBN prior on $\omega_b$ by a tighter Planck constraint. Finally, we discuss the information content of the BOSS power spectrum and show that it is dominated by the location of the baryon acoustic oscillations and the power spectrum shape. We argue that the contribution of the Alcock-Paczynski effect is marginal in $\Lambda$CDM, but becomes important for non-minimal cosmological models.
1909.05852
A gravitational lensing detection of filamentary structures connecting luminous red galaxies
Xia, et al
We present a weak lensing detection of filamentary structures in the cosmic web, combining data from the Kilo-Degree Survey, the Red Cluster Sequence Lensing Survey and the Canada-France-Hawaii Telescope Lensing Survey. The line connecting luminous red galaxies with a separation of $3 - 5\, h^{-1}\text{Mpc}$ is chosen as a proxy for the location of filaments. We measure the average weak lensing shear around $\sim$11,000 candidate filaments selected in this way from the Sloan Digital Sky Survey. After nulling the shear induced by the dark matter haloes around each galaxy, we report a $3.3\,\sigma$ detection of an anisotropic shear signal from the matter that connects them. Adopting a filament density profile, motivated from $N$-body simulations, the average density at the centre of these filamentary structures is found to be $15 \pm 4$ times the critical density.
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