Global Extinction in Spiral Galaxies

A spiral galaxy partially ovelapping a more distant elliptical offers an unique opportunity to measure the dust extinction in the foreground spiral. From the Sloan Digital Sky Survey DR4 spectroscopic sample, we selected 83 occulting galaxy pairs and measured disk opacity over the redshift range z = 0.0-0.2 with the goal to determine the recent evolution of disk dust opacity. The enrichment of the ISM changes over the lifetime of a disk and it is reasonable to expect the du...

A large luminosity--linewidth template sample is now available, improved absorption corrections have been derived, and there are a statistically significant number of galaxies with well determined distances to supply the zero point. A revised estimate of the Hubble Constant is H_0=77 +-4 km/s/Mpc where the error is the 95% probability statistical error. Systematic uncertainties are potentially twice as large.

The correlation between the luminosities and rotation velocities of galaxies can be used to estimate distances to late-type galaxies. It is an appropriate moment to re-evaluate this method given the great deal of new information available. The major improvements described here include: (a) the template relations can now be defined by large, complete samples, (b) the samples are drawn from a wide range of environments, (c) the relations are defined by photometric information a...

Based on the data obtained from the Spitzer/GLIPMSE Legacy Program and the 2MASS project, we derive the extinction in the four IRAC bands, [3.6], [4.5], [5.8] and [8.0] micron, relative to the 2MASS Ks band (at 2.16 micron) for 131 GLIPMSE fields along the Galactic plane within |l|<65 deg, using red giants and red clump giants as tracers. As a whole, the mean extinction in the IRAC bands (normalized to the 2MASS Ks band), A_[3.6]/A_Ks=0.63, A_[4.5]/A_Ks=0.57, A_[5.8]/A_Ks=0.4...

We have determined K-band luminosity functions for 13,325 local Universe galaxies as a function of morphology and color (for K_tot <= 10.75). Our sample is drawn from the 2MASS Extended Source Catalog, with all sample galaxies having measured morphologies and distances (including 4,219 archival redshift-independent distances). The luminosity function for our total sample is in good agreement with previous works, but is relatively smooth at faint magnitudes (due to bulk flow d...

We describe the use of partially overlapping galaxies to provide direct measurements of the effective absorption in galaxy disks, independent of assumptions about internal disk structure. The non-overlapping parts of the galaxies and symmetry considerations are used to reconstruct, via differential photometry, how much background galaxy light is lost in passing through the foreground disks. Extensive catalog searches yield ~15-25 nearby galaxy pairs suitable for varying degre...

Extinction is the elephant in the room that almost everyone tries to avoid when analyzing optical/IR data: astronomers tend to find a quick fix for it that the referee will accept, but that does not mean such a solution is correct or even optimal. In this contribution I address three important issues related to extinction that are commonly ignored and present current and future solutions for them: [1] Extinction produces non-linear photometric effects, [2] the extinction law ...

The Lyon-Meudon Extragalactic database (LEDA) gives a free access to the main astrophysical parameters for more than 100,000 galaxies. The most common names are compiled allowing users to recover quickly any galaxy. All these measured astrophysical parameters are first reduced to a common system according to well defined reduction formulae leading to mean homogeneized parameters. Further, these parameters are also transformed into corrected parameters from widely accepted mod...

We study the effects of dusty spiral arms on the photometric properties of disk galaxies using a series of 2D radiative transfer models, approximating the arms with axially symmetrical rings. We find that dusty arms, as well as dusty disks, have a significant influence on the aperture photometry and surface brightness profiles altering colors of model galaxies. We suggest that, in addition to the conventionally modeled diffuse absorbing layers or disks, the dusty arms should ...

We present a new method to classify galaxies from large surveys like the Sloan Digital Sky Survey using inclination-corrected concentration, inclination-corrected location on the color-magnitude diagram, and apparent axis ratio. Explicitly accounting for inclination tightens the distribution of each of these parameters and enables simple boundaries to be drawn that delineate three different galaxy populations: Early-type galaxies, which are red, highly concentrated, and round...