Constraints on Quasar Lifetimes from Proximity Zone Measurements
The lifetime of quasars is one of the most fundamental quantities for understanding black hole formation and quasar evolution, but yet it remains uncertain by several orders of magnitude. Quasar lifetimes can be constrained by measuring the sizes of their proximity zones, which is the region of enhanced transmitted flux around the quasar due to its own ionizing radiation. By analyzing a new data set of 34 medium resolution spectra at redshift 5.8 ≤ z ≤ 6.5 we identified a new population of quasars with very small proximity zones, indicating quasar lifetimes of less than 100,000 years. These objects pose a significant challenge to current black hole formation models, which require lifetimes of the order of the Hubble time to grow the observed supermassive black holes in the center of these quasars. For more information please have a look at our paper and at the press release.
First Spectroscopic Study of a Young Quasar
The presence of young quasars in the early Universe poses an interesting challenge for current models of the growth and formation of supermassive black holes, and puts stringent constraints on quasar and galaxy evolution theories. We conduct the first comprehensive spectroscopic study of the youngest quasar known, SDSS J1335+3533 at z=5.9012, whose lifetime we estimate to be less than 10,000 years. Deep optical and near-infrared spectra allow us to measure the mass of the central black hole, the Eddington ratio, and its bolometric luminosity, which are consistent with properties of other co-eval quasar of similar luminosity. The only possible anomaly associated with youth are its weak emission lines, but larger samples are needed to shed light on a potential causal connection. We discuss the implications of short quasar lifetimes for various black hole growth scenarios, and argue that future observations of young quasars with JWST could distinguish between them. For details please have a look at our paper.
The Opacity of the Intergalactic Medium and its Implications for the Epoch of Reionization
Determining when and how the epoch of reionization proceeded is one of the major goals of observational cosmology today. During this early evolutionary phase of our universe, the cosmic “dark ages” following recombination ended, and the intergalactic medium (IGM) transitioned from a neutral state into the ionized medium that we observe today due to the ultraviolet radiation of the first stars, galaxies and quasars. The details of the reionization process not only reflect the nature of these primordial objects, but also the formation of large scale structure and are therefore a subject of major interest. We presented new measurements of the evolution of the mean opacity of the IGM within the Lyman-alpha forest between 4.8 ≲ z ≲ 6.3, which provides constraints about the timing of the reionization process as well as its morphology. We compare our measurements to hydrodynamical simulations with a fluctuating ultraviolett background and a fluctuating temperature field and find good agreement between the observations and the simulations. More information can be found in our paper. The data set used for this project is publicly available.
Spectrophotometric Distances to Luminous Red Giant Stars
With contemporary infrared spectroscopic surveys like APOGEE, red-giant stars can be observed to distances and extinctions at which Gaia parallaxes are not highly informative. Here we employ a linear combination of APOGEE spectral pixel intensities and multi-band photometry from Gaia, 2MASS, and WISE to predict parallaxes spectrophotometrically, using a data-driven model for 45,000 red-giant branch stars that are more luminous than the red clump. We obtain distance estimates with 10% uncertainties out to heliocentric distances of 20 kpc, which enables us to make global maps of the Milky Way’s disk. For more information, please check out our paper. Our predicted spectrophotometric parallaxes are available here.
The Circular Velocity Curve of the Milky Way out to 25 kpc
The circular velocity of the Milky Way and in particular its value at the sun's Galactocentric radius, provide important constraints on the mass distribution of our Galaxy and the local dark matter density. The latter is crucial for interpreting and analyzing any direct as well as indirect detection experiments of dark matter. The local circular velocity at the sun's location plays an important role when placing the Milky Way in a cosmological context and asking for instance, whether it falls onto the Tully-Fisher relation. Assuming an axisymmetric gravitational potential of the Milky Way we measure its circular velocity by means of Jeans modeling out to a Galactocentric distance of 25 kpc with more than 23,000 luminous red giant stars as a tracer population. We find that the circular velocity curve is gently declining with a very shallow derivative. For more information, please have a look at our paper.