23 research outputs found
Effects of Inclination on Measuring Velocity Dispersion and Implications for Black Holes
The relation of central black hole mass and stellar spheroid velocity
dispersion (the M- relation) is one of the best-known and tightest
correlations linking black holes and their host galaxies. There has been much
scrutiny concerning the difficulty of obtaining accurate black hole
measurements, and rightly so; however, it has been taken for granted that
measurements of velocity dispersion are essentially straightforward. We examine
five disk galaxies from cosmological SPH simulations and find that
line-of-sight effects due to galaxy orientation can affect the measured
by 30%, and consequently black hole mass predictions by up to 1.0 dex.
Face-on orientations correspond to systematically lower velocity dispersion
measurements, while more edge-on orientations give higher velocity dispersions,
due to contamination by disk stars when measuring line of sight quantities. We
caution observers that the uncertainty of velocity dispersion measurements is
at least 20 km/s, and can be much larger for moderate inclinations. This effect
may account for some of the scatter in the locally measured M-
relation, particularly at the low-mass end. We provide a method for correcting
observed values for inclination effects based on observable
quantities.Comment: 11 pages, 7 figures, replaced with accepted versio
The Intrinsic Shapes of Low Surface Brightness Galaxies (LSBGs):A Discriminant of LSBG Galaxy Formation Mechanisms
We use the low surface brightness galaxy (LSBG) samples created from the Hyper Suprime-Cam Subaru Strategic Program (781 galaxies), the Dark Energy Survey (20977 galaxies), and the Legacy Survey (selected via H I detection in the Arecibo Legacy Fast ALFA Survey, 188 galaxies) to infer the intrinsic shape distribution of the LSBG population. To take into account the effect of the surface brightness cuts employed when constructing LSBG samples, we simultaneously model both the projected ellipticity and the apparent surface brightness in our shape inference. We find that the LSBG samples are well characterized by oblate spheroids, with no significant difference between red and blue LSBGs. This inferred shape distribution is in good agreement with similar inferences made for ultra-diffuse cluster galaxy samples, indicating that environment does not play a key role in determining the intrinsic shape of LSBGs. We also find some evidence that LSBGs are more thickened than similarly massive high surface brightness dwarfs. We compare our results to intrinsic shape measures from contemporary cosmological simulations, and find that the observed LSBG intrinsic shapes place considerable constraints on the formation path of such galaxies. In particular, LSBG production via the migration of star formation to large radii produces intrinsic shapes in good agreement with our observational findings