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Issue A&A
Volume 408, Number 1, September II 2003
Page(s) 287 - 295
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20030980



A&A 408, 287-295 (2003)
DOI: 10.1051/0004-6361:20030980

On the calibration of the COBE/IRAS dust emission reddening maps

C. M. Dutra1, 2, A. V. Ahumada3, J. J. Clariá3, E. Bica4 and B. Barbuy1

1  Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Rua do Matão 1226, Cid. Universitária, São Paulo, 05508-900 SP, Brazil
2  Universidade Estadual do Rio Grande do Sul, Rua Bompland 512, São Borja 97670-000, RS, Brazil
3  Observatorio Astronómico de Córdoba, Laprida 854, 5000 Córdoba, Argentina
4  Universidade Federal do Rio Grande do Sul, Instituto de Fisica, CP 15051, Porto Alegre 91501-970, RS, Brazil

(Received 10 January 2003 / Accepted 19 June 2003)

Abstract
In this work we study the spectral properties (3600-6800 Å) of the nuclear region of early-type galaxies at low ( $\vert b\vert<25^{\circ}$), intermediate (including surroundings of the Magellanic Clouds) and high (South Polar Cap) Galactic latitudes. We determine the E(B-V) reddening values of the galaxies by matching their continuum distribution with respect to those of reddening-free spectral galaxy templates with similar stellar populations. We also compare the spectroscopic reddening value of each galaxy with that derived from 100  $\mu$m dust emission ( $E(B-V)_{\rm FIR}$) in its line of sight, and we find that there is agreement up to  E(B-V)=0.25. Beyond this limit  $E(B-V)_{\rm FIR}$ values are higher. Taking into account the data up to  $E(B-V) \approx 0.7$, we derive a calibration factor of 0.016 between the spectroscopic E(B-V) values and Schlegel et al.'s (1998) opacities. By combining this result with an AK extinction map built within ten degrees of the Galactic centre using Bulge giants as probes (Dutra et al. 2003), we extended the calibration of dust emission reddening maps to low Galactic latitudes down to $\vert b\vert=4^{\circ}$ and E(B-V)= 1.6 ( $A_V \approx 5$). According to this new calibration, a multiplicative factor of  $\approx$0.75 must be applied to the COBE/IRAS dust emission reddening maps.


Key words: ISM: dust, extinction -- Galaxy: general -- galaxies: ISM

Offprint request: C. M. Dutra, dutra@astro.iag.usp.br

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