A close look at the Centaurus A group of galaxies

Crnojević, Denija; Grebel, Eva K.; Koch, Andreas

doi:10.1051/0004-6361/200913429

Cited by 40 publications

(77 citation statements)

References 98 publications

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“…Unfortunately, it is difficult to compare these results to those previously obtained for the sample of early-type dwarf companions of CenA (Crnojević et al 2010). This is because the estimate of the metallicity for the late-type dwarfs is an average that includes both old and young stars (SFH recovery method), while the metallicity values for early-type dwarfs come primarily from their old A131, page 10 of 16 Karachentsev et al 2007).…”

Section: Discussionmentioning

confidence: 97%

“…In particular, dwarf galaxies in nearby groups have been predominantly found to have similar properties to those of our close neighbors (e.g. Karachentsev et al 2002aKarachentsev et al ,b, 2003aKarachentsev et al ,b, 2004Karachentsev et al , 2007Trentham & Tully 2002;Karachentsev 2005;Sharina et al 2008;Bouchard et al 2009;Weisz et al 2008;Côté et al 2009;Dalcanton et al 2009;Koleva et al 2009;McQuinn et al 2009;McQuinn et al 2010;Crnojević et al 2010Crnojević et al , 2011bLianou et al 2010;Makarova et al 2010). A recent Hubble Space Telescope (HST) survey of dwarf galaxies (ANGST, Weisz et al 2011), comprising about 60 objects located within ∼4 Mpc, has led to a large compilation of color-magnitude diagrams (CMDs) of their resolved stellar populations.…”

Section: Introductionmentioning

confidence: 99%

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A close look at the Centaurus A group of galaxies

Crnojević

Grebel

Cole

2012

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Aims. We study a sample of five dwarf irregular galaxies in the CenA/M 83 group, which are companions to the giant elliptical CenA. We aim at deriving their physical properties over their lifetime and compare them to those of dwarfs located in different environments. Methods. We use archival HST/ACS data and apply synthetic color-magnitude diagram fitting in order to reconstruct the past star formation activity of the target galaxies. Results. The average star formation rate for the studied galaxies ranges from 10 −3 M yr −1 up to ∼7 × 10 −2 M yr −1 , and their mean metallicities correlate with their luminosities (from [Fe/H] ∼ −1.4 up to ∼−1.0). The form of the star formation histories varies across the sample, with quiescent periods alternating with intermittent enhancements in the star formation (from a few up to several times the average lifetime value). The dwarfs in this sample formed ∼35% to 60% of their stellar content prior to ∼5 Gyr ago. Conclusions. The resulting star formation histories for the CenA companions are similar to those found for comparable Local Group and M 81 group dwarfs. We consider this sample of dwarfs together with five previously studied M 83 dwarf irregular companions. We find no trend of the average star formation rate with tidal index or distance from the main galaxy of the group. However, dwarfs with higher baryonic masses do show higher average star formation rates, underlining the importance of intrinsic properties in governing the evolution of these galaxies. On the other hand, there is also a clear trend when looking at the recent (∼0.5−1 Gyr) level of activity. Namely, dwarfs within a denser region of the group appear to have had their star formation quenched while dwarfs located in the group outskirts show a wide range of possible star formation rates, thus indicating that external processes play a fundamental role, complementary to mass, in shaping the star formation histories of dwarf galaxies.

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Section: Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

A close look at the Centaurus A group of galaxies

Crnojević

Grebel

Cole

2012

A&A

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“…How do the stellar populations in the new Centaurus dwarfs compare to Local Group look-alikes? Crnojević et al (2010Crnojević et al ( , 2011aCrnojević et al ( ,b, 2012 conducted an extensive study of the resolved stellar content of dwarf galaxies in the Centaurus group. They investigated their star formation histories and metallicity content, and what effect the denser environment has on shaping these properties.…”

Section: Discussionmentioning

confidence: 99%

New low surface brightness dwarf galaxies in the Centaurus group

Müller

Jerjen

Binggeli

2016

A&A

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Context. The distribution of satellite galaxies around the Milky Way and Andromeda and their correlation in phase space pose a major challenge to the standard ΛCDM model of structure formation. Other nearby groups of galaxies are now being scrutinized to test for the ubiquity of the phenomenon. Aims. We conducted an extensive CCD imaging survey for faint, unresolved dwarf galaxies of very low surface brightness in the whole Centaurus group region, encompassing the Cen A and M 83 subgroups lying at a distance of roughly 4 and 5 Mpc, respectively. The aim is to significantly increase the sample of known Centaurus group members down to a fainter level of completeness, serving as a basis for future studies of the 3D structure of the group. Methods. Following our previous survey of 60 square degrees covering the M 83 subgroup, we extended and completed our survey of the Centaurus group region by imaging another 500 square degrees area in the g and r bands with the wide-field Dark Energy Survey camera at the 4 m Blanco telescope at CTIO. The surface brightness limit reached for unresolved dwarf galaxies is µ r ≈ 29 mag arcsec −2 . The faintest suspected Centaurus members found have m r ≈ 19.5 mag or M r ≈ −8.8 mag at the mean distance of the group. The images were enhanced using different filtering techniques. Results. We found 41 new dwarf galaxy candidates, which together with the previously discovered 16 dwarf candidates in the M 83 subgroup amounts to almost a doubling of the number of known galaxies in the Centaurus complex, if the candidates are confirmed. We carried out surface photometry in g and r, and report the photometric parameters derived therefrom, for all new candidates as well as previously known members in the surveyed area. The photometric properties of the candidates, when compared to those of Local Group dwarfs and previously known Centaurus dwarfs, suggest membership in the Centaurus group. The sky distribution of the new objects is generally following a common envelope around the Cen A and M 83 subgroups. How the new dwarfs are connected to the intriguing double-planar feature recently reported must await distance information for the candidates.

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“…The latter two techniques serve to either bracket the range of the metal abundances or to interpolate between them in order to derive the metallicity distribution function. Examples using the mean color of the RGB can be found in Mould et al (1983), Caldwell et al (1998), Grebel & Guhathakurta (1999), Caldwell (2006); using GC fiducials or analytic fits of GC fiducial loci in Harris et al (1999), Sarajedini et al (2002); using interpolation between theoretical tracks or isochrones in Harris & Harris (2000), Mouhcine et al (2005), Crnojevic et al (2010), Bird et al (2010), Lianou et al (2010). In the case of GCs, dwarf spheroidals (dSphs), and the stellar haloes of galaxies, the assumption under which these techniques are used is that the red giants represent populations of an old age (≥10 Gyr).…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic versus photometric metallicities: Milky Way dwarf spheroidal companions as a test case

Lianou

Grebel

Koch

2011

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Aims. The method of deriving photometric metallicities using red giant branch stars is applied to resolved stellar populations under the common assumption that they mainly consist of single-age old stellar populations. We explore the effect of the presence of mixed-age stellar populations on deriving photometric metallicities. Methods. We use photometric data sets for the five Galactic dwarf spheroidals Sculptor, Sextans, Carina, Fornax, and Leo II in order to derive their photometric metallicity distribution functions from their resolved red giant branches using isochrones of the Dartmouth Stellar Evolutionary Database. We compare the photometric metallicities with published spectroscopic metallicities based on the analysis of the near-infrared Ca triplet (Ca T), both on the metallicity scale of Carretta & Gratton and on the scale defined by the Dartmouth isochrones. In addition, we compare the photometric metallicities with published spectroscopic metallicities based on spectral synthesis and medium-resolution spectroscopy, and on high resolution spectra where available. Results. The mean properties of the spectroscopic and photometric metallicity samples are comparable within the intrinsic scatter of each method although the mean metallicities of dSphs with pronounced intermediate-age population fractions may be underestimated by the photometric method by up to a few tenths of dex in [Fe/H]. The star-by-star differences of the spectroscopic minus the photometric metallicities show a wide range of values along the fiducial spectroscopic metallicity range, with the tendency to have systematically lower photometric metallicities for those dwarf spheroidals with a higher fraction of intermediate-age populations. Such discrepancies persist even in the case of the purely old Sculptor dSph, where one would naïvely expect a very good match when comparing with medium or low resolution metallicity measurements. Overall, the agreement between Ca T metallicities and photometric metallicities is very good in the metallicity range from ∼−2 dex to ∼−1.5 dex. We find that the photometric method is reliable in galaxies that contain small (less than 15%) intermediate-age stellar fractions. Therefore, in the presence of mixed-age stellar populations, one needs to quantify the fraction of the intermediate-age stars in order to assess their effect on determining metallicities from photometry alone. Finally, we note that the comparison of spectroscopic metallicities of the same stars obtained with different methods reveals similarly large discrepancies as the comparison with photometric metallicities.

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A close look at the Centaurus A group of galaxies

Cited by 40 publications

References 98 publications

A close look at the Centaurus A group of galaxies

A close look at the Centaurus A group of galaxies

New low surface brightness dwarf galaxies in the Centaurus group

Spectroscopic versus photometric metallicities: Milky Way dwarf spheroidal companions as a test case

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