Stellar Populations in the Nuclei of Late-Type Spiral Galaxies

By C. Walcher, Torsten Boeker, S. Charlot, Luis C. Ho, Hans-Walter Rix, J. Rossa, Joseph C.Shields, R. P. van der Marel. 2006

171 citations recorded by the source corpus.

As part of an ongoing effort to study the stellar nuclei of very late type, bulge-less spirals, we present results from a high-resolution spectroscopic survey of nine such nuclear star clusters, undertaken with the VLT UVES. We fit the spectra with population synthesis models and measure Lick-type indices to determine mean luminosity-weighted ages, which range from 4.1 × 107 to 1.1 × 1010 yr and are insensitive to assumed metallicity or internal extinction. The average metallicity of nuclear clusters in late-type spirals is slightly subsolar (⟨Z⟩ = 0.015) but shows significant scatter. Most of the clusters have moderate extinctions of 0.1-0.3 mag in the I band. The nuclear cluster spectra are best described by age-composite stellar populations, as only such models yield mass-to-light ratios that match those obtained from dynamical measurements. For our nine sample clusters, the last star formation episode was on average 34 Myr ago, while all clusters experienced some star formation in the last 100 Myr. We thus conclude that the nuclear clusters undergo repeated episodes of star formation. Our results are robust to possible contamination from the underlying galaxy disk, as demonstrated by comparison to a similar analysis using smaller aperture spectra obtained with the HST STIS. Also considering the 2005 results from Walcher et al., we have thus shown that the stellar nuclei of bulge-less galaxies are massive and dense star clusters that form stars recurrently until the present day. This set of properties is unique among the various classes of star clusters. To elucidate whether and how these unique properties are related to the nuclear location of the cluster in its host galaxy remains a challenging question.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c3c366061fe8781052bd668962a1f62db15180d2

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Instrumentation

Citations in the corpus

THE NEXT GENERATION VIRGO CLUSTER SURVEY (NGVS). I. INTRODUCTION TO THE SURVEY (2012, background): “…distinct stellar components in their cores.44 This is true for galaxies across the Hubble sequence (Carollo et al. 1998; Böker et al. 2002, 2004; Walcher et al. 2005, 2006; Seth et al. 2008) and along the luminosity function (e.g., Côté et al. 2006; Turner et al. 2012), suggesting that a…”
The Coincidence of Nuclear Star Clusters and Active Galactic Nuclei (2008, background): “The in situ scenario is favored by observations that NCs in spiral galaxies have complicated star formation histories, suggesting frequent episodic star formation (Walcher et al. 2006; Rossa et al. 2006).”
THE NGC 404 NUCLEUS: STAR CLUSTER AND POSSIBLE INTERMEDIATE-MASS BLACK HOLE (2010, background): “All of these involved fitting a small subsample (∼10) of the SSPs with ages ranging from 1 Myr to 20 Gyr (see Walcher et al. 2006; Koleva et al. 2008, for a more complete discussion of stellar population synthesis).”
MERGING BLACK HOLE BINARIES IN GALACTIC NUCLEI: IMPLICATIONS FOR ADVANCED-LIGO DETECTIONS (2016, background): “…NSCs are characterized by complex star formation histories with a mixture of morphological components and different stellar populations spanning a wide range of characteristic ages (from 10 Myr to 10 Gyr) and metallicities (Figer et al. 2004; Rossa et al. 2006; Walcher et al. 2006; Do et al. 2015).”
EXTRAGALACTIC CHEMICAL ABUNDANCES: DO H ii REGIONS AND YOUNG STARS TELL THE SAME STORY? THE CASE OF THE SPIRAL GALAXY NGC 300 (2009, background): “…it the subject of a number of investigations during the past decade concerning the stellar populations in the central/nuclear regions (Davidge 1998; Walcher et al. 2006) and in the outskirts (Tikhonov et al. 2005; Bland-Hawthorn et al. 2005; Mouhcine 2006; Vlajić et al. 2009), the star formation…”
Fitting the integrated spectral energy distributions of galaxies (2010, methodology): “…analysis are now common and include MOPED (Heavens et al. 2000), PLATEFIT (Tremonti et al. 2004), VESPA (Tojeiro et al. 2007), STECKMAP (Ocvirk et al. 2006), STARLIGHT (Cid Fernandes et al. 2005), sedfit (Walcher et al. 2006), NBURSTS (Chilingarian et al. 2007), ULySS (Koleva et al. 2009).”
DISSIPATION AND EXTRA LIGHT IN GALACTIC NUCLEI. II. “CUSP” ELLIPTICALS (2008, background): “Stellar nuclei tend to be extremely young (ages 100 Myr) and have somewhat sub-solar metallicities (Walcher et al. 2006).”
Nuclear Activity in Nearby Galaxies (2008, background): “…compact, photometrically distinct nuclei (Böker et al. 2002), morphologically not dissimilar from that in NGC 4395, but, with few exceptions (Shields et al. 2008), these nuclei are compact star clusters with no compelling evidence for an accompanying accreting central BH (Walcher et al. 2006).”
The nuclear star cluster of the Milky Way: proper motions and mass (2009, background): “Most NSCs contain a mixed stellar population with signs of repeated episodes of star formation (Walcher et al. 2006).”
Surface brightness profile of the Milky Way’s nuclear star cluster (2014, background): “The majority of NSCs have mixed old and young stellar populations and show frequently signs of star formation within the past 100 Ma (e.g., Rossa et al. 2006; Seth et al. 2006; Walcher et al. 2006).”
OPTICAL DISCOVERY OF PROBABLE STELLAR TIDAL DISRUPTION FLARES (2010, background): “The nuclear star clusters reported by Walcher et al. (2005) in nine late-type spirals range from 8 × 105 − 6 × 107M⊙ with a median ≈ 10 6.5M⊙; the mean age of the last star formation burst is 34 Myr with the youngest stellar population having a mean mass of 105.5M⊙(Walcher et al. 2006).”
Masses and scaling relations for nuclear star clusters, and their co-existence with central black holes (2016, unknown): “As shown by spectroscopic studies of NSCs in late-type galaxies, the assumption of solar metallicity is a reasonable one for these objects (e.g. Rossa et al. 2006; Walcher et al. 2006; Seth et al. 2006).”
Multiple populations in globular clusters (2012, background): “…central black hole in galactic nuclei, and might explain the origin of the nuclear star clusters observed in almost all late type galaxies including the Milky Way (Böker 2010) where there seems to be repeated episodes of star formation (Krabbe et al. 1995; Rossa et al. 2006; Walcher et al. 2006).”
Nuclear star clusters (2009, background): “The mass of these young populations is of order 105M , sufficient to explain the total mass of the NSC if they had formed through similar formation episodes repeated every ∼100 Myr over a Hubble time (Walcher et al. 2006; Seth et al. 2006).”