@article{c041e1ee464b466f81d4ddbd3eccf200,
title = "ALMA detection of the dusty object silhouetted against the S0 galaxy NGC 3269 in the Antlia cluster",
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 12CO(2- 1) TMB 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, Vr, 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 ∼4″ angular size of the patch corresponds to a linear size of ∼1 kpc at the galaxy's Hubble distance of 50.7 Mpc. The mass estimated from the 12CO(2- 1) emission is ∼1.4 × 106(d/50.7 Mpc)2 M⊙, while the attenuation derived from the optical spectrum implies a dust mass of ∼2.6 × 104(d/50.7 Mpc)2 M⊙. 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. ",
keywords = "Dust, Extinction, Galaxies: individual: 3269, Galaxies: ISM",
author = "Haikala, {L. K.} and R. Salinas and T. Richtler and M. G{\'o}mez and Gahm, {G. F.} and K. Mattila",
note = "Funding Information: Acknowledgements. T.R. acknowledges support from the BASAL Centro de Astrof{\'i}sica y Tecnologias Afines (CATA) PFB-06/2007. Based partly on observations obtained at the international Gemini Observatory, a program of NSF{\textquoteright}s NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agen-cia Nacional de Investigaci{\'o}n y Desarrollo (Chile), Ministerio de Ciencia, Tec-nolog{\'i}a e Innovaci{\'o}n (Argentina), Minist{\'e}rio da Ci{\^e}ncia, Tecnologia, Inova{\c c}{\~o}es e Comunica{\c c}{\~o}es (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea) and partly on data acquired with the Atacama Pathfinder EXperiment (APEX) (project O-079F-9321A). APEX is a collaboration between the Max–Planck–Institut f{\"u}r Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile obtained via CNTAC program CN2018A-83 This paper makes use of the following ALMA data: ADS/JAO.ALMA#2017.1.00066.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. Publisher Copyright: {\textcopyright} ESO 2021. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.",
year = "2021",
month = jan,
day = "1",
doi = "10.1051/0004-6361/202038994",
language = "English",
volume = "645",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
}