The Herschel Virgo Cluster Survey

XX. Dust and gas in the foreground Galactic cirrus^⋆,⋆⋆

¹ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
e-mail: sbianchi@arcetri.astro.it
² School of Physics and Astronomy, Cardiff University, Queens Building, The Parade, Cardiff, CF24 3AA, UK
³ Instituto de Radioastronomía y Astrofísica, UNAM, Antigua Carretera a Pátzcuaro # 8701, Morelia, Michoacán, Mexico
⁴ Cornell Center for Astrophysics and Planetary Science, Space Sciences Bldg., Cornell University, Ithaca, NY 14853, USA
⁵ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281-S9, 9000 Gent, Belgium
⁶ Institut d’Astrophysique Spatiale (IAS), UMR 8617, CNRS/Université Paris-Sud, 91405 Orsay, France
⁷ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
⁸ Unidad de Astronomia, Facultad de Ciencias Basicas, Universidad de Antofagasta, Avenida Angamos 601, 1270300 Antofagasta, Chile
⁹ Dept. of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
¹⁰ Observatório do Valongo, Universidade Federal do Rio de Janeiro, Ladeira Pedro Antônio 43, Rio de Janeiro, Brazil
¹¹ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
¹² Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot, IRFU/Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France
¹³ Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
¹⁴ Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal

Received: 27 May 2016
Accepted: 19 September 2016

Abstract

We study the correlation between far-infrared/submm dust emission and atomic gas column density in order to derive the properties of the high Galactic latitude, low density, Milky Way cirrus in the foreground of the Virgo cluster of galaxies. Dust emission maps from 60 to 850 μm are obtained from observations with the Spectral and Photometric Imaging Receiver (SPIRE) and carried out within the Herschel Virgo Cluster Survey (HeViCS); these are complemented by IRAS and Planck maps. Data from the Arecibo legacy Fast ALFA Survey is used to derive atomic gas column densities for two broad velocity components: low and intermediate velocity clouds. Dust emissivities are derived for each gas component and each far-infrared/submm band. For the low velocity clouds, we measure an average emissivity ϵ^LVC_ν = (0.79 ± 0.08) × 10^-20 MJy sr^-1 cm² at 250 μm. After fitting a modified blackbody to the available bands, we estimated a dust absorption cross section of τ^LVC_ν/N_{H i} = (0.49 ± 0.13) × 10^-25 cm² H^-1 at 250 μm (with dust temperature T = 20.4 ± 1.5 K and spectral index β = 1.53 ± 0.17). The results are in excellent agreement with those obtained by Planck over a much larger coverage of the high Galactic latitude cirrus (50% of the sky versus 0.2% in our work). For dust associated with intermediate velocity gas, we confirm earlier Planck results and find a higher temperature and lower emissivity and cross section. After subtracting the modeled components, we find regions at scales smaller than 20′ in which the residuals deviate significantly from the average scatter, which is dominated by cosmic infrared background. These large residuals are most likely due to local variations in the cirrus dust properties or to high-latitude molecular clouds with average N_H2 ≲ 10²⁰ cm^-2. We find no conclusive evidence for intracluster dust emission in Virgo.