CaltechAUTHORS
Published February 1, 2020 | Version Published + Accepted Version
Journal Article Open

LEGUS and H_α-LEGUS Observations of Star Clusters in NGC 4449: Improved Ages and the Fraction of Light in Clusters as a Function of Age

Creators

  • 1. ROR icon Space Telescope Science Institute
  • 2. ROR icon University of Toledo
  • 3. ROR icon Infrared Processing and Analysis Center
  • 4. ROR icon Stockholm University
  • 5. ROR icon University of Massachusetts Amherst
  • 6. ROR icon University of Wyoming
  • 7. ROR icon IBM Research - Thomas J. Watson Research Center
  • 8. ROR icon Heidelberg University
  • 9. ROR icon Max Planck Institute for Astronomy
  • 10. ROR icon Australian National University
  • 11. ROR icon University of Virginia
  • 12. ROR icon National Autonomous University of Mexico

Abstract

We present a new catalog and results for the cluster system of the starburst galaxy NGC 4449, based on multiband imaging observations taken as part of the LEGUS and H_α-LEGUS surveys. We improve the spectral energy fitting method used to estimate cluster ages, and find that the results, particularly for older clusters, are in better agreement with those from spectroscopy. The inclusion of H_α measurements, the role of stochasticity for low-mass clusters, the assumptions about reddening, and the choices of SSP model and metallicity all have important impacts on the age dating of clusters. A comparison with ages derived from stellar color–magnitude diagrams for partially resolved clusters shows reasonable agreement, but large scatter in some cases. The fraction of light found in clusters relative to the total light (i.e., T_L) in the U, B, and V filters in 25 different ≈ kiloparsec-size regions throughout NGC 4449 correlates with both the specific region luminosity, R_L , and the dominant age of the underlying stellar population in each region. The observed cluster age distribution is found to decline over time as dN/dτ ∝ τ^γ , with γ = −0.85 ± 0.15, independent of cluster mass, and is consistent with strong, early cluster disruption. The mass functions of the clusters can be described by a power law with dN/dM ∝ M^β and β = −1.86 ± 0.2, independent of cluster age. The mass and age distributions are quite resilient to differences in age-dating methods. There is tentative evidence for a factor of 2–3 enhancement in both the star and cluster formation rate ≈100–300 Myr ago, indicating that cluster formation tracks star formation generally. The enhancement is probably associated with an earlier interaction event.

Additional Information

© 2020. The American Astronomical Society. Received 2019 June 10; revised 2019 October 14; accepted 2019 October 24; published 2020 February 3. This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 526555. These observations are associated with program #13364. R.C. acknowledges support from NSF grant 1517819. M.C. and M.T. acknowledge support from the INAF PRIN-SKA 2017 program 1.05.01.88.04. We thank Francesca Annibali for useful discussions. We also thank the referee for many useful comments that improved the paper. Facility: HST. -

Attached Files

Published - Whitmore_2020_ApJ_889_154.pdf

Accepted Version - 2005.02840.pdf

Files

2005.02840.pdf

Files (14.3 MB)

Name Size
md5:08b9dd42e5083e050817b01931d7a72b
8.3 MB Preview Download
md5:5fa872f2d73fbaa27725fa5f8d06a036
6.0 MB Preview Download

Additional details

Additional titles

Alternative title
LEGUS and Hα-LEGUS Observations of Star Clusters in NGC 4449: Improved Ages and the Fraction of Light in Clusters as a Function of Age
Alternative title
LEGUS and Halpha-LEGUS Observations of Star Clusters in NGC 4449: Improved Ages and the Fraction of Light in Clusters as a Function of Ageb

Identifiers

Eprint ID
103994
Resolver ID
CaltechAUTHORS:20200624-104211145

Related works

Describes
https://arxiv.org/abs/2005.02840 (URL)

Funding

NASA
NAS-526555
NSF
1517819
Istituto Nazionale di Astrofisica (INAF)
1.05.01.88.04

Dates

Created
2020-06-24
Created from EPrint's datestamp field
Updated
2021-11-16
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
Infrared Processing and Analysis Center (IPAC)