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Unlocking the secrets of stellar haloes using combined star counts and surface photometry
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
2012 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 421, no 1, 190-201 p.Article in journal (Refereed) Published
Abstract [en]

The stellar haloes of galaxies can currently be studied either throughobservations of resolved halo stars or through surface photometry.Curiously, the two methods appear to give conflicting results, asa number of surface photometry measurements have revealed integratedcolours that are too red to be reconciled with the halo propertiesinferred from the study of resolved stars. Several explanations forthis anomaly have been proposed - including dust photoluminescence,extinction of extragalactic background light and a bottom-heavy stellarinitial mass function. A decisive test is, however, still lacking.Here, we explain how observations of the halo of a nearby galaxy,involving a combination of both surface photometry and bright starcounts, can be used to distinguish between the proposed explanations.We derive the observational requirements for this endeavour and findthat star counts in filters VI and surface photometry in filtersVIJ appear to be the optimal strategy. Since the required halo starcounts are already available for many nearby galaxies, the most challengingpart of this test is likely to be the optical surface photometry,which requires several nights of exposure time on a 4-8 m telescope,and the near-infrared surface photometry, which is most readily carriedout using the upcoming James Webb Space Telescope.

Place, publisher, year, edition, pages
2012. Vol. 421, no 1, 190-201 p.
Keyword [en]
dust, extinction, galaxies: haloes, galaxies: photometry, diffuse radiation
National Category
Astronomy, Astrophysics and Cosmology
Research subject
URN: urn:nbn:se:su:diva-75815DOI: 10.1111/j.1365-2966.2011.20290.xISI: 000302693600046OAI: diva2:524113
Available from: 2012-05-09 Created: 2012-04-27 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Unveiling the nature of blue compact galaxies
Open this publication in new window or tab >>Unveiling the nature of blue compact galaxies
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Blue compact galaxies (BCGs) are gas-rich star-forming low redshift galaxies with low metallicities. In some cases the relative strength of the starburst can be so high that it completely dominates the light output of the galaxy, an obstacle which has been countered by deeper optical imaging data and observations in the near infra-red (NIR) regime. This has revealed an older population referred to as the "host". In an effort to study the hosts of BCGs we have analyzed new and extremely deep UBVRIHKs imaging data for 46 high and low luminosity BCGs. For several BCGs the data reveal previously undetected extended low surface brightness components beyond the μB~26 mag arcsec-2 isophote. These are predominantly the luminous BCGs in the sample, and they show tails, plumes, optical bridges between companion galaxies, and other signs of merging or strong tidal interactions. The low luminosity BCGs, on the other hand, are well represented by an exponential disk profile down to the reliability limit of the data at a surface brightness level of μB~28 mag arcsec-2.

The burst and host populations are examined separately. The integrated colors of both are compared to predictions from spectral evolutionary models, giving an indication of their respective ages and metallicities. Our analysis suggests that for the luminous BCGs a strong contribution by nebular emission is present almost down to the Holmberg radius, invalidating the host structural parameters obtained from brighter isophotes. Possible evolutionary links to quiescent galaxies like dEs, dIs, and LSBGs are explored by examining the structural parameters derived from two radial ranges typically assumed to be dominated by the underlying host galaxy. In this parameter space the luminous BCGs in our sample deviate from their low luminosity counterparts and from BCG data in the literature. They are instead consistent with the structural properties of giant low surface brightness galaxies with central surface brightnesses μB≥23 mag arcsec-2. We further examine the asymmetry and concentration parameters for the sample and study the correlation between the minimum asymmetry distribution in the optical and NIR vs morphological class, concentration and integrated colors to identify mergers/tidally interacting galaxies. A shift in the asymmetry distribution occurs for low luminosity BCGs from the optical to the NIR. In contrast, we find that the flocculent asymmetry component (due to star formation) completely dominates the composite asymmetry of high luminosity BCGs. We introduce an alternative asymmetry measure which successfully traces the dynamical asymmetry component (due to merging/tidal interaction) of the host.  

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2012. 45 p.
blue compact galaxies, starbursts, host galaxy, stellar populations, surface photometry, optical and NIR broadband
National Category
Astronomy, Astrophysics and Cosmology
Research subject
urn:nbn:se:su:diva-75765 (URN)978-91-7447-525-8 (ISBN)
Public defence
2012-06-01, sal FB 55, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2012-05-11 Created: 2012-04-26 Last updated: 2013-11-19Bibliographically approved

Open Access in DiVA

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