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Title: HST/ACS PHOTOMETRY OF OLD STARS IN NGC 1569: THE STAR FORMATION HISTORY OF A NEARBY STARBURST

Abstract

We used Hubble Space Telescope/Advanced Camera for Surveys to obtain deep V- and I-band images of NGC 1569, one of the closest and strongest starburst galaxies in the universe. These data allowed us to study the underlying old stellar population, aimed at understanding NGC 1569's evolution over a full Hubble time. We focus on the less-crowded outer region of the galaxy, for which the color-magnitude diagram (CMD) shows predominantly a red giant branch (RGB) that reaches down to the red clump/horizontal branch feature (RC/HB). A simple stellar population analysis gives clear evidence for a more complicated star formation history (SFH) in the outer region. We derive the full SFH using a newly developed code, SFHMATRIX, which fits the CMD Hess diagram by solving a non-negative least-squares problem. Our analysis shows that the relative brightnesses of the RGB tip and RC/HB, along with the curvature and color of the RGB, provide enough information to ameliorate the age-metallicity-extinction degeneracy. The distance/reddening combination that best fits the data is E(B - V) = 0.58 {+-} 0.03 and D = 3.06 {+-} 0.18 Mpc. Star formation began {approx}13 Gyr ago, and this accounts for the majority of the mass in the outer region. However,more » the initial burst was followed by a relatively low, but constant, rate of star formation until {approx}0.5-0.7 Gyr ago when there may have been a short, low intensity burst of star formation. Stellar metallicity increases over time, consistent with chemical evolution expectations. The dominant old population shows a considerable spread in metallicity, similar to the Milky Way halo. However, the star formation in NGC 1569's outer region lasted much longer than in the Milky Way. The distance and line-of-sight velocity of NGC 1569 indicate that it has moved through the IC 342 group of galaxies, which may have caused this extended star formation. Comparison with other recent work provides no evidence for radial population gradients in the old population of NGC 1569, suggesting that our results are representative of the old stellar population throughout the galaxy.« less

Authors:
; ;  [1];
  1. Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States)
Publication Date:
OSTI Identifier:
22034630
Resource Type:
Journal Article
Journal Name:
Astronomical Journal (New York, N.Y. Online)
Additional Journal Information:
Journal Volume: 143; Journal Issue: 5; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1538-3881
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; BRIGHTNESS; CAMERAS; COLOR; COMPARATIVE EVALUATIONS; DIAGRAMS; DISTANCE; GALACTIC EVOLUTION; GIANT STARS; IMAGES; LEAST SQUARE FIT; MILKY WAY; PHOTOMETRY; S CODES; STAR EVOLUTION; TELESCOPES; UNIVERSE

Citation Formats

Grocholski, Aaron J, Van der Marel, Roeland P, Aloisi, Alessandra, and others, and. HST/ACS PHOTOMETRY OF OLD STARS IN NGC 1569: THE STAR FORMATION HISTORY OF A NEARBY STARBURST. United States: N. p., 2012. Web. doi:10.1088/0004-6256/143/5/117.
Grocholski, Aaron J, Van der Marel, Roeland P, Aloisi, Alessandra, & others, and. HST/ACS PHOTOMETRY OF OLD STARS IN NGC 1569: THE STAR FORMATION HISTORY OF A NEARBY STARBURST. United States. https://doi.org/10.1088/0004-6256/143/5/117
Grocholski, Aaron J, Van der Marel, Roeland P, Aloisi, Alessandra, and others, and. 2012. "HST/ACS PHOTOMETRY OF OLD STARS IN NGC 1569: THE STAR FORMATION HISTORY OF A NEARBY STARBURST". United States. https://doi.org/10.1088/0004-6256/143/5/117.
@article{osti_22034630,
title = {HST/ACS PHOTOMETRY OF OLD STARS IN NGC 1569: THE STAR FORMATION HISTORY OF A NEARBY STARBURST},
author = {Grocholski, Aaron J and Van der Marel, Roeland P and Aloisi, Alessandra and others, and},
abstractNote = {We used Hubble Space Telescope/Advanced Camera for Surveys to obtain deep V- and I-band images of NGC 1569, one of the closest and strongest starburst galaxies in the universe. These data allowed us to study the underlying old stellar population, aimed at understanding NGC 1569's evolution over a full Hubble time. We focus on the less-crowded outer region of the galaxy, for which the color-magnitude diagram (CMD) shows predominantly a red giant branch (RGB) that reaches down to the red clump/horizontal branch feature (RC/HB). A simple stellar population analysis gives clear evidence for a more complicated star formation history (SFH) in the outer region. We derive the full SFH using a newly developed code, SFHMATRIX, which fits the CMD Hess diagram by solving a non-negative least-squares problem. Our analysis shows that the relative brightnesses of the RGB tip and RC/HB, along with the curvature and color of the RGB, provide enough information to ameliorate the age-metallicity-extinction degeneracy. The distance/reddening combination that best fits the data is E(B - V) = 0.58 {+-} 0.03 and D = 3.06 {+-} 0.18 Mpc. Star formation began {approx}13 Gyr ago, and this accounts for the majority of the mass in the outer region. However, the initial burst was followed by a relatively low, but constant, rate of star formation until {approx}0.5-0.7 Gyr ago when there may have been a short, low intensity burst of star formation. Stellar metallicity increases over time, consistent with chemical evolution expectations. The dominant old population shows a considerable spread in metallicity, similar to the Milky Way halo. However, the star formation in NGC 1569's outer region lasted much longer than in the Milky Way. The distance and line-of-sight velocity of NGC 1569 indicate that it has moved through the IC 342 group of galaxies, which may have caused this extended star formation. Comparison with other recent work provides no evidence for radial population gradients in the old population of NGC 1569, suggesting that our results are representative of the old stellar population throughout the galaxy.},
doi = {10.1088/0004-6256/143/5/117},
url = {https://www.osti.gov/biblio/22034630}, journal = {Astronomical Journal (New York, N.Y. Online)},
issn = {1538-3881},
number = 5,
volume = 143,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2012},
month = {Tue May 15 00:00:00 EDT 2012}
}