ALMA detection of the dusty object silhouetted against the S0 galaxy NGC 3269 in the Antlia cluster

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Haikala , L K , Salinas , R , Richtler , T , Gomez , M , Gahm , G F & Mattila , K 2021 , ' ALMA detection of the dusty object silhouetted against the S0 galaxy NGC 3269 in the Antlia cluster ' , Astronomy & Astrophysics , vol. 645 , 36 . https://doi.org/10.1051/0004-6361/202038994

Title: ALMA detection of the dusty object silhouetted against the S0 galaxy NGC 3269 in the Antlia cluster
Author: Haikala, L. K.; Salinas, R.; Richtler, T.; Gomez, M.; Gahm, G. F.; Mattila, K.
Contributor: University of Helsinki, Department of Physics
Date: 2021-01-05
Language: eng
Number of pages: 6
Belongs to series: Astronomy & Astrophysics
ISSN: 0004-6361
URI: http://hdl.handle.net/10138/325864
Abstract: Context. An intriguing silhouette of a small dust patch can be seen against the disk of the S0 galaxy NGC 3269 in the Antlia cluster in optical images. The images do not provide any clue as to whether the patch is a local Jupiter mass-scale cloudlet or a large extragalactic dust complex.Aims. We aim to resolve the nature of this object: is it a small Galactic cloudlet or an extragalactic dust complex?Methods. ALMA and APEX spectroscopy and Gemini GMOS long-slit spectroscopy were used to measure the velocity of the patch and the NGC 3269 disk radial velocity curve.Results. A weak 16 2.5 km s(-1) wide (CO)-C-12(2-1) T-MB 19 +/- 2.5. mK line in a 2 .('') . '' 2 by 2 .('') .'' 12 beam associated with the object was detected with ALMA. The observed heliocentric velocity, V-r,V- hel=3878 +/- 5.0 km s(-1), immediately establishes the extragalactic nature of the object. The patch velocity is consistent with the velocity of the nucleus of NGC 3269, but not with the radial velocity of the NGC 3269 disk of the galaxy at its position. The similar to 4 '' angular size of the patch corresponds to a linear size of similar to 1 kpc at the galaxy's Hubble distance of 50.7 Mpc. The mass estimated from the (CO)-C-12(2-1) emission is similar to 1.4x10(6)(d/50.7 Mpc)M-2(circle dot), while the attenuation derived from the optical spectrum implies a dust mass of similar to 2.6x10(4)(d/50.7 Mpc)M-2(circle dot). The derived attenuation ratio A ' (B)/(A ' (B)-A ' (R)) of 1.6 +/- 0.11 is substantially lower than the corresponding value for the mean Milky Way extinction curve for point sources (2.3).Conclusions. We established the extragalactic nature of the patch, but its origin remains elusive. One possibility is that the dust patch is left over from the removal of interstellar matter in NGC 3269 through the interaction with its neighbour, NGC 3268.
Subject: galaxies: individual: 3269
galaxies: ISM
dust
extinction
HII-REGIONS
SPACE
FRAGMENTATION
MASS
115 Astronomy, Space science
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