arXiv subjects

Anna Pancoast

Publications and source records attributed to Anna Pancoast.

21 records · Page 2Linked to original sources

arXiv2011

The Mass of the Black Hole in Arp 151 from Bayesian Modeling of Reverberation Mapping Data

Supermassive black holes are believed to be ubiquitous at the centers of galaxies. Measuring their masses is extremely challenging yet essential for understanding their role in the formation and evolution of cosmic structure. We present a direct measurement of the mass of a black hole in an active galactic nucleus (Arp 151) based on the motion of the gas responsible for the broad emission lines. By analyzing and modeling spectroscopic and photometric time series, we find that the gas is well described by a disk or torus with an average radius of 3.99 +- 1.25 light days and an opening angle of 68.9 (+21.4, -17.2) degrees, viewed at an inclination angle of 67.8 +- 7.8 degrees (that is, closer to face-on than edge-on). The black hole mass is inferred to be 10^(6.51 +- 0.28) solar masses. The method is fully general and can be used to determine the masses of black holes at arbitrary distances, enabling studies of their evolution over cosmic time.

astro-ph.CO↗

arXiv2011

Geometric and Dynamical Models of Reverberation Mapping Data

We present a general method to analyze reverberation mapping data that provides both estimates for the black hole mass and for the geometry and dynamics of the broad line region (BLR) in active galactic nuclei (AGN). Our method directly infers the spatial and velocity distribution of the BLR from the data, allowing us to easily derive a velocity-resolved transfer function and allowing for a self-consistent estimate of the black hole mass without a virial coefficient. We obtain estimates and reasonable uncertainties of the BLR model parameters by implementing a Markov Chain Monte Carlo algorithm using the formalism of Bayesian probability theory. We use Gaussian Processes to interpolate the the continuum light curve data and create mock light curves that can be fitted to the data. We test our method by creating simulated reverberation mapping data-sets with known true parameter values and by trying to recover these parameter values using our models. We are able to recover the parameters with realistic uncertainties that depend upon the variability of the AGN and the quality of the reverberation mapping campaign. With a geometry model we can recover the mean radius of the BLR to within ~0.1dex random uncertainty for simulated data with an integrated line flux uncertainty of 1.5%, while with a dynamical model we can recover the black hole mass and the mean radius to within ~0.05dex random uncertainty, for simulated data with a line profile average signal to noise ratio of 4 per spectral pixel. These uncertainties do not include modeling errors, which are likely to be present in the analysis of real data, and should therefore be considered as lower limits to the accuracy of the method.

astro-ph.CO↗

arXiv2010

Star formation and dust obscuration in the tidally distorted galaxy NGC 2442

Abridged: We present a detailed investigation of the morphological distribution and level of star formation and dust obscuration in the nearby tidally distorted galaxy NGC2442. Spitzer images in the IR at 3.6, 4.5, 5.8, 8.0um, and 24um and GALEX images at 1500Å and 2300Å allow us to resolve the galaxy on scales between 240-600pc. We supplement these with archival data in the B, J, H, and K bands. We use the 8um, 24um and FUV (1500Å) emission to study the star formation rate (SFR). We find that globally, these tracers of star formation give a range of results of ~6-11\msun/yr, with the dust-corrected FUV giving the highest value of SFR. We can reconcile the UV and IR-based estimates by adopting a steeper UV extinction curve that lies in between the starburst (Calzetti) and SMC extinction curves. However, the regions of highest SFR intensity along the spiral arms are consistent with a starburst-like extinction. Overall, the level of star-formation we find is higher than previously published for this galaxy, by about a factor of two, which, contrary to previous conclusions, implies that the interaction that caused the distorted morphology of NGC2442 likely also triggered increased levels of star-formation activity. Outside of the spiral arms, we discover what appears to be a superbubble, ~1.7kpc across in the IRAC images. Significant Hα, UV and IR emission in the area also suggest vigorous ongoing star-formation. A known, recent supernova (SN1999ga) is located at the edge of this superbubble. Although speculative at this stage, this area suggests a large star-forming region with a morphology shaped by generations of supernovae. Lastly, we discover an 8um (PAH) circumnuclear ring with an ~0.8kpc radius. The Hα emission is largely concentrated inside that ring and shows a vague spiral structure in the rest of the galaxy.

astro-ph.GA↗