Day 795

Thursday.

1411.7029
On the recovery of galaxy properties from SED fitting solutions
Gladis, et al

Explore the ability of 4 different inverse population synthesis codes to recover the physical properties of galaxies from their spectra by SED fitting.  DynBaS, TGASPEX, and GASPEX have been implemented by the authors and are described in detail.  STARLIGHT is publicly available.  DynBaS selects dynamically a different spectral basis to expand the spectrum of each target galaxy; TGASPEX uses an unconstrained age basis, where as GASPEX and STARLIGHT use for all fits a fixed spectral basis selected a priori by the code developers.  Variable and unconstrained basis reflect the peculiarities of the fitted spectrum and allow for simple and robust solutions to the problem of extracting galaxy parameters from spectral fits.  Assemble a Synthetic Spectral Atlas of Galaxies (SSAG), comprising of 100k galaxy spectra corresponding to an equal number of SFHs based on the recipe of Chen+2012.  Select a subset of 120 galaxies from SSAG with a color distribution similar to that of local galaxies in SDSS DR7 and produce 30 random noise realizations for each of these spectra.  For each spectrum, recover the mass, mean age, metallicity, internal dust extinction, and velocity dispersion characterizing the dominant stellar population in the problem galaxy.  All methods produce almost perfect fits to the target spectrum, but the recovered physical parameters can differ significantly.  The tests provide a quantitative measure of the accuracy and precision with which these parameters are recovered by each method.  From a statistical point of view, all methods yield similar precisions, whereas DynBaS produces solutions with minimal systematic biases in the distributions of residuals for all of these parameters.

1411.7032
A dust-parallax distance of 19 megaparsecs to the supermassive black hole in NGC 4151
Hönig, Watson, Kishimoto, Hjorth

The active galaxy NGC 4151 has a crucial role as one of the only two active galactic nuclei for which BH mass measurements based on emission line reverberation mapping can be calibrated against other dynamical methods.  Unfortunately, effective calibration requires an accurate distance to NGC 4151, which is currently not available.  Recently reported distances range from 4 to 29 Mpc. Strong peculiar motions make a z-based distance very uncertain, and the geometry of the galaxy and its nucleus prohibit accurate measurements using other techniques.  Report a dust-parallax distance to NGC 4151 of D_A=19.0pm2.5 Mpc.  The measurement is based on an adaptation of a geometric method proposed previously using the emission line regions of active galaxies.  Since this region is too small for current imaging capabilities, use instead the ratio of the physical-to-angular sizes of the more extended hot dust emission as determined from time-delays and IR interferometry.  This new distance leads to an approximately 1.4x increase in the dynamical BH mass, implying a corresponding correction to emission line reverberation masses of BHs if they are calibrated against the two objects with additional dynamical masses.
1411.7371
Uncovering blue diffuse dwarf galaxies
James, et al

Extremely metal poor (XMP) galaxies are known to be very rare, despite the large numbers of low-mass galaxies predicted by the local galaxy LF.  Present a sub-sample of galaxies that were selected via a morphology-based search on SDSS images with the aim of finding the elusive XMP galaxies.  By using the recently discovered extremely metal-poor galaxy, Leo P, as a guide, obtain a collection of faint, blue systems, each with isolated HII regions embedded in a diffuse continuum, that have remained undetected until now.  Here show the first results from optical spectroscopic follow-up observations of 12 of ~100 of these blue, diffuse dwarf (BDD) galaxies yielded by the search algorithm.  Oxygen abundances were obtained via the direct method for eight galaxies, and found to be in the range 7.45<12+log(O/H)<8.0, with two galaxies being classified as XMPs.  All BDDs were found to currently have a young SF population (<10 Myr) and relatively high ionization parameters of their HII regions.  Despite their low luminosities (-11<M_B<-18) and low surface brightnesses (~23-25 mag arcsec^-2), the galaxies were found to be actively SF, with current SFRs between 0.0003 and 0.078 Msun/yr.  From the current subsample, BDD galaxies appear to be a population of non-quiescent dIrr galaxies, or the diffuse counterparts to blue compact galaxies (BCDs) and as such may bridge the gap between these two populations.  The search algorithm demonstrates that morphology-based searches are successful in uncovering more diffuse metal-poor SF galaxies, which traditional emission-line based searches overlook.