Near-infrared reddening of extra-galactic giant molecular clouds in a face-on geometry

Author(s)

J. Kainulainen, M. Juvela, J. Alves

Abstract

Aims: We describe the near-infrared reddening signature of giant

molecular clouds (GMCs) in external galaxies. In particular, we examine

the EJ-H and EH-K color excesses and the effective

extinction law observed in discrete GMC regions. We also study the

effect of the relative scale height of the GMC distribution to the color

excesses, and to the observed mass function of GMCs when the masses are

derived using color excess as a linear estimator of mass. Methods: We performed Monte Carlo radiative transfer simulations with

3D models of stellar radiation and clumpy dust distributions, resembling

a face-on geometry. The scattered light is included in the models, and

near-infrared color maps were calculated from the simulated data. We

performed the simulations with different scale heights of GMCs and

compared the color excesses and attenuation of light in different

geometries. We extracted GMCs from the simulated color maps and compared

the mass functions to the input mass functions. Results: The

effective near-infrared reddening law, i.e. the ratio

EJ-H/EH-K, has a value close to unity in GMC

regions. The ratio depends significantly on the relative scale height of

GMCs, ξ, and for ξ values 0.1...0.75, we find the typical ratios

of 0.6...1.1. The effective extinction law turns out to be very flat in

GMC regions. We find the ratios of apparent extinctions of

AH^a/AKa = 1.35...1.55 and

AJ^a/AHa = 1.15. The effect of the

scattered flux on the effective reddening law, as well as on the

effective extinction law, is significant. Regarding the GMC mass

function, we find no correlation between the input and observed slopes

of the mass functions. Instead, the observed slope reflects the

parameter ξ and the dynamical range of the mass function. As the

observed slope depends on the geometric parameters, which are not known,

it is not possible to constrain the slope of the mass function using

this technique. We estimate that only a fraction of 10...20% of the

total mass of GMCs is recovered, if the observed color excess values are

transformed to masses using the Galactic reddening law. In the case of

individual clouds, the fraction can vary between ~0...50%.

Organisation(s)

Department of Astrophysics

External organisation(s)

University of Helsinki, European Southern Observatory (Germany)

Journal

Astronomy & Astrophysics

Volume

482

Pages

229-236

ISSN

0004-6361

DOI

https://doi.org/10.1051/0004-6361:20078896

Publication date

04-2008

Peer reviewed

Yes

Austrian Fields of Science 2012

103003 Astronomy, 103004 Astrophysics

Keywords

Portal url

https://ucrisportal.univie.ac.at/en/publications/ecfe330f-c8c3-4594-8574-2eef41fbd239