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Title: THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. VI. THE ANCIENT STAR-FORMING DISK OF NGC 404

Abstract

We present HST/WFPC2 observations across the disk of the nearby isolated dwarf S0 galaxy NGC 404, which hosts an extended gas disk. The locations of our fields contain a roughly equal mixture of bulge and disk stars. All of our resolved stellar photometry reaches m {sub F814W} = 26 (M {sub F814W} = -1.4), which covers 2.5 mag of the red giant branch and main-sequence stars with ages <300 Myr. Our deepest field reaches m {sub F814W} = 27.2 (M {sub F814W} = -0.2), sufficient to resolve the red clump and main-sequence stars with ages <500 Myr. Although we detect trace amounts of star formation at times more recent than 10 Gyr ago for all fields, the proportion of red giant stars to asymptotic giants and main-sequence stars suggests that the disk is dominated by an ancient (>10 Gyr) population. Detailed modeling of the color-magnitude diagram suggests that {approx}70% of the stellar mass in the NGC 404 disk formed by z {approx} 2 (10 Gyr ago) and at least {approx}90% formed prior to z {approx} 1 (8 Gyr ago). These results indicate that the stellar populations of the NGC 404 disk are on average significantly older than those of othermore » nearby disk galaxies, suggesting that early- and late-type disks may have different long-term evolutionary histories, not simply differences in their recent star formation rates. Comparisons of the spatial distribution of the young stellar mass and FUV emission in Galaxy Evolution Explorer images show that the brightest FUV regions contain the youngest stars, but that some young stars (<160 Myr) lie outside of these regions. FUV luminosity appears to be strongly affected by both age and stellar mass within individual regions. Finally, we use our measurements to infer the relationship between the star formation rate and the gas density of the disk at previous epochs. We find that most of the history of the NGC 404 disk is consistent with star formation that has decreased with the gas density according to the Schmidt law. However, {approx} 0.5-1 Gyr ago, the star formation rate was unusually low for the inferred gas density, consistent with the possibility that there was a gas accretion event that reignited star formation {approx}0.5 Gyr ago. Such an event could explain why this S0 galaxy hosts an extended gas disk.« less

Authors:
; ; ;  [1];  [2];  [3]; ;  [4]
  1. Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States)
  2. Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States)
  3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  4. Department of Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States)
Publication Date:
OSTI Identifier:
21450888
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 716; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/716/1/71; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COLOR; EMISSION; GALACTIC EVOLUTION; GALAXIES; LUMINOSITY; MAIN SEQUENCE STARS; MASS; PHOTOMETRY; RED GIANT STARS; TRACE AMOUNTS; EVOLUTION; GIANT STARS; OPTICAL PROPERTIES; ORGANOLEPTIC PROPERTIES; PHYSICAL PROPERTIES; STARS

Citation Formats

Williams, Benjamin F, Dalcanton, Julianne J, Gilbert, Karoline M, Stilp, Adrienne, Dolphin, Andrew, Seth, Anil C, Weisz, Daniel, and Skillman, Evan. THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. VI. THE ANCIENT STAR-FORMING DISK OF NGC 404. United States: N. p., 2010. Web. doi:10.1088/0004-637X/716/1/71.
Williams, Benjamin F, Dalcanton, Julianne J, Gilbert, Karoline M, Stilp, Adrienne, Dolphin, Andrew, Seth, Anil C, Weisz, Daniel, & Skillman, Evan. THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. VI. THE ANCIENT STAR-FORMING DISK OF NGC 404. United States. doi:10.1088/0004-637X/716/1/71.
Williams, Benjamin F, Dalcanton, Julianne J, Gilbert, Karoline M, Stilp, Adrienne, Dolphin, Andrew, Seth, Anil C, Weisz, Daniel, and Skillman, Evan. Thu . "THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. VI. THE ANCIENT STAR-FORMING DISK OF NGC 404". United States. doi:10.1088/0004-637X/716/1/71.
@article{osti_21450888,
title = {THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. VI. THE ANCIENT STAR-FORMING DISK OF NGC 404},
author = {Williams, Benjamin F and Dalcanton, Julianne J and Gilbert, Karoline M and Stilp, Adrienne and Dolphin, Andrew and Seth, Anil C and Weisz, Daniel and Skillman, Evan},
abstractNote = {We present HST/WFPC2 observations across the disk of the nearby isolated dwarf S0 galaxy NGC 404, which hosts an extended gas disk. The locations of our fields contain a roughly equal mixture of bulge and disk stars. All of our resolved stellar photometry reaches m {sub F814W} = 26 (M {sub F814W} = -1.4), which covers 2.5 mag of the red giant branch and main-sequence stars with ages <300 Myr. Our deepest field reaches m {sub F814W} = 27.2 (M {sub F814W} = -0.2), sufficient to resolve the red clump and main-sequence stars with ages <500 Myr. Although we detect trace amounts of star formation at times more recent than 10 Gyr ago for all fields, the proportion of red giant stars to asymptotic giants and main-sequence stars suggests that the disk is dominated by an ancient (>10 Gyr) population. Detailed modeling of the color-magnitude diagram suggests that {approx}70% of the stellar mass in the NGC 404 disk formed by z {approx} 2 (10 Gyr ago) and at least {approx}90% formed prior to z {approx} 1 (8 Gyr ago). These results indicate that the stellar populations of the NGC 404 disk are on average significantly older than those of other nearby disk galaxies, suggesting that early- and late-type disks may have different long-term evolutionary histories, not simply differences in their recent star formation rates. Comparisons of the spatial distribution of the young stellar mass and FUV emission in Galaxy Evolution Explorer images show that the brightest FUV regions contain the youngest stars, but that some young stars (<160 Myr) lie outside of these regions. FUV luminosity appears to be strongly affected by both age and stellar mass within individual regions. Finally, we use our measurements to infer the relationship between the star formation rate and the gas density of the disk at previous epochs. We find that most of the history of the NGC 404 disk is consistent with star formation that has decreased with the gas density according to the Schmidt law. However, {approx} 0.5-1 Gyr ago, the star formation rate was unusually low for the inferred gas density, consistent with the possibility that there was a gas accretion event that reignited star formation {approx}0.5 Gyr ago. Such an event could explain why this S0 galaxy hosts an extended gas disk.},
doi = {10.1088/0004-637X/716/1/71},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 716,
place = {United States},
year = {2010},
month = {6}
}