Day 1559

Wednesday.

1904.12871
Unravelling the origin of the counter-rotating core in IC 1459 with KMOS and MUSE
Prichard, Vaughan, Davies

The massive early-type galaxy (ETG) IC 1459 is a slowly rotating galaxy that exhibits a rapidly counter-rotating kinematically decoupled core (KDC, $R_{\rm KDC}\approx 5^{\prime\prime}\approx 0.1 R_{\rm e}$). To investigate the origin of its KDC, we coupled large data mosaics from the near-infrared (NIR)/optical integral field unit (IFU) instruments K-band Multi-Object Spectrograph (KMOS) and Multi Unit Spectroscopic Explorer (MUSE). We studied IC 1459's stellar populations and, for the first time for a KDC, the spatially resolved initial mass function (IMF). We used full-spectral-fitting to fit the stellar populations and IMF simultaneously, and an alternative spectral-fitting method that does not assume a star-formation history (SFH; although does not constrain the IMF) for comparison. When no SFH is assumed, we derived a negative metallicity gradient for IC 1459 that could be driven by a distinct metal-poor population in the outer regions of the galaxy, and a radially constant old stellar age. We found a radially constant bottom-heavy IMF out to $\sim \frac{1}{3} R_{\rm e}$. The radially flat IMF and age extend beyond the counter-rotating core. We detected high velocity dispersion along the galaxy's major axis. Our results potentially add weight to findings from orbital modelling of other KDCs that the core is not a distinct population of stars but in fact two smooth co-spatial counter-rotating populations. No clear picture of formation explains the observational results of IC 1459, but we propose it could have included a gas-rich intense period of star formation at early times, perhaps with counter-rotating accreting cold streams, followed by dry and gas-rich mergers through to the present day.

1904.12890

Supermassive black holes in the early universe

Smith, Bromm

The emergence of the first black holes during the first billion years of cosmic history marks a key event in cosmology. Their formation is part of the overall process of ending the cosmic dark ages, when the first stars appeared in low-mass dark matter haloes about a few 100 million years after the Big Bang. The first stars, galaxies, and black holes transformed the Universe from its simple initial state into one of ever increasing complexity. We review recent progress on our emerging theoretical picture of how the first black holes appeared on the cosmic scene, and how they impacted the subsequent history of the Universe. Our focus is on supermassive black holes, in particular assessing possible pathways to the formation of the billion-solar-mass black holes inferred to power the luminous quasars at high redshifts. We conclude with a discussion of upcoming empirical probes, such as the James Webb Space Telescope (JWST), and the Laser Interferometer Space Antenna (LISA), further ahead in time.

1904.13155

'Scraggy' dark halos around bulge-less spiral galaxies

Karachentsev, Karachentseva

We use a sample of 220 face-on bulge-less galaxies situated in the low density environment to estimate their total mass via orbital motions of supposed rare satellites. Our inspection reveals 43 dwarf companions having the mean projected separation of 130 kpc and the mean-square velocity difference of 96 km/s. For them, we obtain the mean orbital-mass-to-K-band luminosity ratio of $20\pm3$. Seven bulge-less spirals in the Local Volume are also characterized by the low mean ratio, $M_{orb}/L_K = 22\pm5$. We conclude that bulge-less Sc-Scd-Sd galaxies have poor dark halos, about two times lower than that of bulgy spiral galaxies of the same stellar mass.

1904.13345

The impact of plasma instabilities on the spectra of TeV Blazars

Batista, et al

Relativistic jets from blazars are known to be sources of very-high-energy gamma rays (VHEGRs). During their propagation in the intergalactic space, VHEGRs interact with pervasive cosmological photon fields such as the extragalactic background light (EBL) and the cosmic microwave background (CMB), producing electron-positron pairs. These pairs can upscatter CMB/EBL photons to high energies via inverse Compton scattering, thereby continuing the cascade process. This is often used to set limits on intergalactic magnetic fields (IGMFs). However, the picture may change if plasma instabilities, arising due to the interaction of the pairs with the intergalactic medium (IGM), cool down the electrons/positrons faster than inverse Compton scattering. As a consequence, the kinetic energy lost by the pairs to the IGM could cause a hardening in the observed gamma-ray spectrum at energies below $\sim$100 GeV. Here we study several types and models of instabilities and assess their impact for interpreting observations of distant blazars. Our results suggest that plasma instabilities can describe the spectra of some blazars and mimic the effects of IGMFs, depending on parameters such as intrinsic spectrum of the object, the density and temperature of the IGM, and the luminosity of the beam.

1904.13348

Kinematics of CIV and [OIII] emission in luminous high-redshift quasars

Coatman, et al

We characterise ionised gas outflows using a large sample of ~330 high-luminosity (45.5 < log(L_bol/erg s^-1) < 49.0), high-redshift (1.5 < z < 4.0) quasars via their [OIII]4960,5008 emission. The median velocity width of the [OIII] emission line is 1540 kms^-1, increasing with increasing quasar luminosity. Broad, blue-shifted wings are seen in the [OIII] profiles of 42 per cent of the sample. Rest-frame ultraviolet spectra with well-characterised CIV 1550 emission line properties are available for more than 210 quasars, allowing an investigation of the relationship between the Broad Line Region (BLR) and Narrow Line Region (NLR) emission properties. The [OIII] blueshift is correlated with CIV blueshift, even when the dependence of both quantities on quasar luminosity has been taken into account. A strong anti-correlation between the [OIII] equivalent width (EW) and CIV blueshift also exists. Furthermore, [OIII] is very weak, with EW<1A, in ~10 per cent of the sample, a factor of 10 higher compared to quasars at lower luminosities and redshifts. If the [OIII] emission originates in an extended NLR, the observations suggest that quasar-driven winds are capable of influencing the host-galaxy environment out to kilo-parsec scales. The mean kinetic power of the ionised gas outflows is then 10^44.7 erg s^-1, which is ~0.15 per cent of the bolometric luminosity of the quasar. These outflow efficiencies are broadly consistent with those invoked in current active galactic nuclei feedback models.

1904.13378

Cosmology with dropout selection: straw-man surveys and CMB lensing

Wilson, White

We seek to prove the means, motive and opportunity of 2 < z < 5 dropout galaxies for large-scale structure. Together with low-z tracers, these samples would map practically every linear mode and facilitate a tomographic decomposition of the CMB lensing kernel over an unprecedented volume, thereby yielding a proxy for (the time evolution of) matter density fluctuations that provides compelling tests of horizon-scale General Relativity, neutrino masses and Inflation-- viz., curvature, running of the spectral index and a scale-dependent halo bias induced by (local) primordial non-Gaussianity. Focusing on color-color selection, we estimate the completeness, contamination, and spectroscopic survey speed of tailored Lyman-break galaxy (LBG) samples. We forecast the potential of CMB lensing cross-correlation, clustering redshifts and Redshift-Space Distortions (RSD) analyses. In particular, we estimate: the depth dependence of interlopers based on CFHTLS data and propagate this to biases in cosmology; new inferences of (non-linear) halo bias at these redshifts and depths using legacy data; detailed forecasts of LBG spectra as would be observed by DESI, PFS, and their successors. We further assess the relative competitiveness of potential spectroscopic facilities based on an intuitive figure-of-merit and define a modernisation of traditional selections to the photometric system of LSST where necessary. We confirm these science cases to be compelling for achievable facilities in the next decade by defining a LBG sample of increasing Lyman-alpha equivalent width with redshift, which delivers both percent-level RSD constraints on the growth rate at high-z and measurements of CMB lensing cross-correlation at z=3 and 4 with a significance measured in the hundreds. Finally, we discuss the limitations and avenues for improvement beyond this initial exploration (abridged).