Clusters in the inner spiral arms of M 51: The cluster IMF and the formation history

By A. Bik, H. Lamers, N. Bastian, N. Panagia, M. Romaniello. 2002

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We present the results of an analysis of the HST-WFPC2 observations of the interacting galaxy M51. From the observations in 5 broadband filters (UBVRI) and two narrowband filters (Hα and (OIII)) we study the cluster population in a region of 3.2 ×3.2 kpc 2 in the inner spiral arms of M51, at a distance of about 1 to 3 kpc from the nucleus. We found 877 cluster candidates and we derived their ages, initial masses and extinctions by means of a comparison between the observed spectral energy distribution and the predictions from cluster synthesis models for instantaneous star formation and solar metallicity. The lack of (OIII) emission in even the youngest clusters with strong Hα emission, indicates the absence of the most massive stars and suggests a mass upper limit of about 25 to 30 M� . The mass versus age distribution of the clusters shows a drastic decrease in the number of clusters with age, much more severe than can be expected on the basis of evolutionary fading of the clusters. This indicates that cluster dispersion is occurring on a timescale of 10 Myr or longer. The cluster initial mass function has been derived from clusters younger than 10 Myr by a linear regression fit of the cumulative mass distribution. This results in an exponent α = −dlogN(M)/dlog (M) = 2.1 ± 0.3 in the range of 2.5 × 10 3 2 × 10 4 M� . In the restricted range of 2.5 × 10 3 < M < 2 × 10 4 Mwe find α = 2.0 ± 0.05. This exponent is very similar to the value derived for clusters in the interacting Antennae galaxies, and to the exponent of the mass distribution of the giant molecular clouds in our Galaxy. To study the possible effects of the interaction of M51 with its companion NGC 5195 about 400 Myr ago, which triggered a huge starburst in the nucleus, we determined the cluster formation rate as a function of time for clusters with an initial mass larger than 10 4 M� . There is no evidence for a peak in the cluster formation rate at around 200 to 400 Myr ago within 2 σ accuracy, i.e. within a factor two. The formation rate of the detected clusters decreases strongly with age by about a factor 10 2 between 10 Myr and 1 Gyr. For clusters older than about 150 Myr this is due to the evolutionary fading of the clusters below the detection limit. For clusters younger than 100 Myr this is due to the dispersion of the clusters, unless one assumes that the cluster formation rate has been steadily increasing with time from 1 Gyr ago to the present time.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/6bb36400630b4d07c80f4d8a15b3fc776b4d04d7

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Citations in the corpus

TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS (2012, background): “The mass function of young star clusters can also be approximated by the Schechter form (Zhang & Fall 1999; de Grijs et al. 2003; Bik et al. 2003; Cresci et al. 2005; McCrady & Graham 2007b, see Portegies Zwart et al. 2010 for a review).”
Stellar-mass black holes in star clusters: implications for gravitational-wave radiation (2009, background): “Such distributions are far from being well determined, except for the mass distribution for young clusters in spiral and starburst galaxies (Bastian & Lamers 2003; Bik et al. 2003; Gieles, Bastian & Lamers 2004).”
THE ANTENNAE GALAXIES (NGC 4038/4039) REVISITED: ADVANCED CAMERA FOR SURVEYS AND NICMOS OBSERVATIONS OF A PROTOTYPICAL MERGER (2010, background): “Several studies have also found that the young cluster mass function (MF) in a variety of galaxies is a power law of the form φ(M)dM ∝ MβdM with a value of β ≈ −2 (e.g., Zhang & Fall 1999 in the Antennae; Hunter et al. 2003 in the Magellanic Clouds; Bik et al. 2003 in M51; and Chandar et al. 2010 in”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “…is welldescribed by a power law dN/dM ∝ M−β with β ≈ 2 over most of its range; the uncertainty on the value of β is roughly 0.1−0.2 (Williams & McKee 1997; Zhang & Fall 1999; Larsen 2002; Bik et al. 2003; de Grijs et al. 2003a; Goddard et al. 2010; Bastian et al. 2011; Fall & Chandar 2012).”
The mass function of young star clusters in spiral galaxies (2008, background): “In the small number of cases where MFs have been determined, they are generally found to be consistent with power-laws dN/dM ∝ Mα with a slope α ≈ −2 (Bik et al. 2003; de Grijs et al. 2003; McCrady & Graham 2007; Zhang & Fall 1999; Dowell et al. 2008).”
An analytical description of the disruption of star clusters in tidal fields with an application to Galactic open clusters (2005, background): “Suppose that the CIMF is a power law with a slope −α = −2 (Zhang & Fall 1999; Larsen 2002; Bik et al. 2003; de Grijs et al. 2003) in the range of Mmin < Mcl < Mmax, Mmin ≈ 10 2M⊙ and Mmax ≈ 10 7M⊙, then the number of clusters with initial mass Mi formed at time t will be N(Mi, t) = S(t) ( Mi…”
Star cluster formation and evolution in nearby starburst galaxies – II. Initial conditions (2003, background): “…in excess of the median age of the cluster system, so that at least the high-luminosity (high-mass) end of the CLF (and cluster mass function) probably remains unaffected by significant alterations caused by disruption (e.g. Buta, Crocker & Byrd 1999; Zhang & Fall 1999; Bik et al. 2003; Paper I).”
Young Massive Star Clusters (2010, background): “Several CIMF determinations have also found power-law functions with indices close to −2 (Zhang & Fall 1999, McCrady & Graham 2007, Bik et al. 2003), and other studies have found evidence for a truncation of this power-law at the high-mass end (Gieles et al. 2006b, Bastian 2008, Larsen 2009a,…”
The formation of very wide binaries during the star cluster dissolution phase (2010, background): “The initial cluster mass distribution may be approximated byf (M) ∝ M−γ with γ ≈ 2 (see, e.g., Zhang & Fall 1999; Ashman & Zepf 2001; Bik et al. 2003; Hunter et al. 2003).”