Rubin-LSST

Abstract:

We measure the harmonic-space auto-power spectrum of the galaxy overdensity in the LOFAR Two-metre Sky Survey (LoTSS) First Data Release and its cross correlation with the map of the lensing convergence of the cosmic microwave background (CMB) from the Planck collaboration. We report a ∼5σ detection of the cross-correlation. We show that the combination of the clustering power spectrum and CMB lensing cross-correlation allows us to place constraints on the high-redshift tail of the redshift distribution, one of the largest sources of uncertainty in the use of continuum surveys for cosmology. Our analysis shows a preference for a broader redshift tail than that predicted by the photometric redshifts contained in the LoTSS value added catalog, as expected, and more compatible with predictions from simulations and spectroscopic data. Although the ability of CMB lensing to constrain the width and tail of the redshift distribution could also be valuable for the analysis of current and future photometric weak lensing surveys, we show that its performance relies strongly on the redshift evolution of the galaxy bias. Assuming the redshift distribution predicted by the Square Kilometre Array Design simulations, we use our measurements to place constraints on the linear bias of radio galaxies and the amplitude of matter inhomogeneities σ8, finding σ8=0.69+0.14−0.21 assuming the galaxy bias scales with the inverse of the linear growth factor, and σ8=0.79+0.17−0.32 assuming a constant bias.

Abstract:

With the advent of deep optical-to-near-infrared extragalactic imaging on the degree scale, samples of high-redshift sources are being selected that contain both bright star-forming (SF) galaxies and faint active galactic nuclei (AGN). In this study, we investigate the transition between SF- and AGN-dominated systems at z ≃ 4 in the rest-frame ultraviolet (UV). We find a rapid transition to AGN-dominated sources brightward of MUV ≃ −23.2. The effect is observed in the rest-frame UV morphology and size–luminosity relation, where extended clumpy systems become point-source-dominated, and also in the available spectra for the sample. These results allow us to derive the rest-frame UV luminosity function (LF) for the SF- and AGN-dominated subsamples. We find the SF-dominated LF is best fit with a double power law, with a lensed Schechter function being unable to explain the existence of extremely luminous SF galaxies at MUV ≃ −23.5. If we identify AGN-dominated sources according to a point-source morphology criterion, we recover the relatively flat faint-end slope of the AGN LF determined in previous studies. If we instead separate the LF according to the current spectroscopic AGN fraction, we find a steeper faint-end slope of α = −1.83 ± 0.11. Using a simple model to predict the rest-frame AGN LF from the z = 4 galaxy LF, we find that the increasing impact of host galaxy light on the measured morphology of faint AGN can explain our observations.

Abstract:

Context. The stellar initial mass function (IMF) seems to be variable and not universal, contrary to what has been argued in the literature over the last three decades. Several relations of the low-mass end of the IMF slope with other stellar population, photometrical, and kinematical parameters of massive early-type galaxies (ETGs) have been proposed, but consensus on the factual cause of the observed variations has not yet been reached.

Aims. We investigate the relationship between the IMF and other stellar population parameters in NGC 3311, the central galaxy of the Hydra I cluster. NGC 3311 is a unique laboratory, characterized by old and metal-rich stars, that is similar to other massive ETGs for which the IMF slope has been measured to be bottom-heavy (i.e., dwarf-rich); however, it has unusual stellar velocity dispersion and [α/Fe] profiles, both of which increase with radius.

Methods. We use the spatially resolved stellar population parameters (age, total metallicity, and [α/Fe]) that were derived in a forthcoming paper (Barbosa et al. 2020) – via the full-spectrum fitting of high signal-to-noise MUSE observations – to compare the IMF slope in the central part of NGC 3311 (R ≲ 16 kpc) against other stellar parameters, with the goal of assessing their relations and dependencies.

Results. For NGC 3311, we unambiguously invalidate the previously observed direct correlation between the IMF slope and the local stellar velocity dispersion, confirming some doubts that had been raised in the literature. This relation may simply arise as a spatial coincidence between the region with the largest stellar velocity dispersion and the region where the oldest in situ population is found and dominates the light. We also show robust evidence that the proposed IMF−metallicity relation is contaminated by the degeneracy between these two parameters. We do confirm that the stellar content in the innermost region of NGC 3311 follows a bottom-heavy IMF, in line with other literature results. The tightest correlations we found are those between stellar age and the IMF and between the galactocentric radius and the IMF.

Conclusions. The variation of the IMF at its low-mass end is not due to kinematical, dynamical, or global properties in NGC 3311. We speculate instead that the IMF might be dwarf-dominated in the “red nuggets” that formed through a very short and intense star formation episode at high redshifts (z >  2) when the Universe was denser and richer in gas, and which then ended up being the central cores of today’s giant ellipticals.

Abstract:

V341 Ara was recently recognized as one of the closest (d ≃ 150 pc) and brightest (V ≃ 10) nova-like cataclysmic variables. This unique system is surrounded by a bright emission nebula, likely to be the remnant of a recent nova eruption. Embedded within this nebula is a prominent bow shock, where the system’s accretion disc wind runs into its own nova shell. In order to establish its fundamental properties, we present the first comprehensive multiwavelength study of the system. Long-term photometry reveals quasi-periodic, super-orbital variations with a characteristic time-scale of 10–16 d and typical amplitude of ≃1 mag. High-cadence photometry from theTransiting Exoplanet Survey Satellite (TESS) reveals for the first time both the orbital period and a ‘negative superhump’ period. The latter is usually interpreted as the signature of a tilted accretion disc. We propose a recently developed disc instability model as a plausible explanation for the photometric behaviour. In our spectroscopic data, we clearly detect antiphased absorption and emission-line components. Their radial velocities suggest a high mass ratio, which in turn implies an unusually low white-dwarf mass. We also constrain the wind mass-loss rate of the system from the spatially resolved [O III] emission produced in the bow shock; this can be used to test and calibrate accretion disc wind models. We suggest a possible association between V341 Ara and a ‘guest star’ mentioned in Chinese historical records in AD 1240. If this marks the date of the system’s nova eruption, V341 Ara would be the oldest recovered nova of its class and an excellent laboratory for testing nova theory.